Dual Band Networks - Parameters and Optimization

Alcatel File Reference Date Edition Page Dual Band Networks - Parameters and Optimization Jarreau 3DF 00973 0002 ASZZA 17/03/05 2.0 1

Site Vélizy

Radio Communication Division / Mobile Radio

Originator F. Jarreau

Dual band networks : parameters and optimization

Domain : Alcatel 900/1800 BSS

Division :

Rubric :

Type : Guide lines

Distribution codes :

Predistribution :

Abstract : This document presents the parameters and the optimization of dual band networks using

the dual BCCH solution or the single BCCH solution.

Approval

Name

Signature

C. Blachier P. Godet

Name

Signature


Table of contents

1 INTRODUCTION....................................................................................... 6

2 PRESENTATION OF THE ALGORITHMS AND PARAMETERS ... 7

2.1 NEIGHBOURING CELLS LIST AND REPORTING................................................................. 7

2.1.1 Neighbouring cells list ........................................................................................... 7

2.1.2 Neighbouring cells reporting ................................................................................. 7

2.2 IDLE MODE .................................................................................................................... 9

2.2.1 Cell selection .......................................................................................................... 9

2.2.2 Cell re-selection ..................................................................................................... 9

2.3 B5 HANDOVER ALGORITHMS....................................................................................... 11

2.3.1 Call set-up (SDCCH-TCH handover) .................................................................. 11

2.3.2 Handovers ............................................................................................................ 13

2.3.3 Candidate cell evaluation process ....................................................................... 17

2.4 B6 HANDOVER ALGORITHMS....................................................................................... 20

2.4.1 Call set-up (SDCCH-TCH handover) .................................................................. 20

2.4.2 Handovers ............................................................................................................ 21

2.4.3 Candidate cell evaluation process ....................................................................... 26

2.4.4 Load and traffic evaluation .................................................................................. 28

2.5 B6 MULTIBAND CELL SOLUTION ................................................................................. 30

2.5.1 Normal assignment............................................................................................... 30

2.5.2 Incoming handover............................................................................................... 31

2.5.3 Outgoing better conditions handovers ................................................................. 31

2.5.4 Inter zone handovers ............................................................................................ 33

2.5.5 Emergency handovers .......................................................................................... 34

2.6 CLASSMARK HANDLING .............................................................................................. 35

2.6.1 Principles ............................................................................................................. 35

2.6.2 Behaviour of B5 release ....................................................................................... 36

3 PARAMETERS AND CONFIGURATIONS......................................... 37

3.1 DESCRIPTION OF THE PARAMETERS ............................................................................. 37

3.1.1 B5 parameters ...................................................................................................... 37


3.1.2 B6 parameters ...................................................................................................... 40 3.2 DEFAULT VALUES OF CONFIGURATION INDEPENDENT PARAMETERS ........................... 42

3.2.1 B5 parameters ...................................................................................................... 42

3.2.2 B6 parameters ...................................................................................................... 43

3.3 MULTIBAND BSC CONFIGURATIONS ........................................................................... 45

3.3.1 Introduction.......................................................................................................... 45

3.3.2 Existing 900 MHz network and addition of 1800 MHz macro cells .................... 47

3.3.3 Existing 900 MHz network with micro cells and addition of 1800 macro cells... 56

3.3.4 Existing 900 MHz network and addition of 1800 macro and micro cells............ 65

3.3.5 Existing 900 MHz network with micro cells and addition of 1800 macro and micro cells....................................................................................................................... 73

3.3.6 Complements ........................................................................................................ 80

3.4 MULTIBAND CELL CONFIGURATIONS........................................................................... 81

3.4.1 900 macro cells with addition of 1800 TRX......................................................... 82

3.4.2 900 macro cells with addition of 1800 TRX + micro cells (900, 1800)............... 86

3.5 OTHER ASPECTS .......................................................................................................... 91

3.5.1 Multi vendor environment .................................................................................... 91

3.5.2 Existing 1800 MHz network ................................................................................. 91

4 SPECIAL SETS OF PARAMETERS..................................................... 94

4.1 ZONE EXIT................................................................................................................... 94

4.1.1 Description of the problem................................................................................... 94

4.1.2 Solutions with B5 release ..................................................................................... 94

4.1.3 Solutions with B6 release ..................................................................................... 98

4.1.4 Solutions for the multiband cell configuration..................................................... 98

4.2 CAPTURE THRESHOLD SET ON A PER CELL BASIS ......................................................... 99

4.2.1 Description of the problem................................................................................... 99

4.2.2 Example................................................................................................................ 99

4.2.3 Solution of the problem ...................................................................................... 100

5 TUNING AND MONITORING ............................................................ 101

5.1 TUNING ..................................................................................................................... 101

5.1.1 Idle mode ............................................................................................................ 101

5.1.2 Connected mode ................................................................................................. 101

5.1.3 Other aspects...................................................................................................... 103


5.2 MONITORING............................................................................................................. 104

5.2.1 Key issues ........................................................................................................... 104

5.2.2 Tools ................................................................................................................... 104

5.2.3 Multiband BSC : QoS follow-up with OMC-R indicators.................................. 104

5.2.4 Multiband cell : QoS follow-up with OMC-R indicators ................................... 106

6 WEAKNESSES OF THE ALGORITHMS .......................................... 107

6.1 DETECTION OF BETTER CONDITION HANDOVER CAUSES............................................ 107

6.1.1 Description of the problem................................................................................. 107

6.1.2 Examples ............................................................................................................ 107


6.2 CAUSE 21 AND MICRO 1800 CELLS............................................................................ 110

6.2.1 Description of the problem................................................................................. 110

6.2.2 Example.............................................................................................................. 110



History : Edition Date Originator Comments

1 22/12/98 F. Jarreau Creation of the document 2 28/12/99 F. Jarreau New version of the document including :

- B6 algorithms : improvement of the dual BCCH solution and introduction of the single BCCH solution,

- experience gained on dual BCCH networks since edition 1.

Edition changes : Following parts have been modified compared to the previous edition :

- 2.3.1 : B5 handover algorithms/Call set-up,

- 3.3.2.1, 3.3.3.1, 3.3.4.1, 3.3.5.1 : Parameters and configurations/Multiband BSC configurations : modification of the tuning of the CELL_RESELECT_OFFSET parameter,

- 3.5.2 : Parameters and configurations/Other aspects/Existing 1800 MHz network : new solutions for the 900 <-> 1800 handovers when the two frequency bands are used in different areas,

- 4.1 : Special sets of parameters/Zone exit : new solutions,

- 5.2.3 : Tuning and Monitoring/Monitoring : guide lines for the QoS follow-up with OMC-R indicators,

Following parts have been added :

- 2.4 : B6 HO algorithms,

- 2.5 : description of the B6 Multiband cell solution,

- 3.1.2 : description of B6 parameters,

- 3.2.2 : default value of B6 parameters,

- 3.3.2.2, 3.3.3.2, 3.3.4.2, 3.3.5.2 : B6 Multiband BSC configurations,

- 3.4 : Multiband cell configurations,

- 3.5.2 : Parameters and configurations/Other aspects/Existing 1800 MHz network : multiband cell solution,

- 5.2.4 : Tuning and Monitoring/Monitoring : guide lines for the QoS follow-up with OMC-R indicators (multiband cell)

References : [1] Handover preparation, release B5, Ed. 03, 3BK 11202 0111 DSZZA

[2] Classmark handling, B5, Ed. 02, 3BK 11202 0106 DSZZA

[3] Activation strategy for micro cellular networks, 3DF 00968 0001 TQZZA

[4] France Telecom Mobiles, Dual band field trial, Test report, 3DF 00973 0015 QTZZA

[5] Handover preparation, release B6.2, Ed. 01, 3BK 11202 0276 DSZZA

Introduction


1 Introduction The aim of this document is to present the parameters and the optimization of dual band

networks. It deals with the Multiband BSC solution available since BSS release 5 and also with the Mutiband cell solution introduced in BSS release 6.

We will present in part 2 the algorithms and parameters used to manage a dual band network in idle and dedicated modes. The aim of part 3 is to show the possible configurations. Part 4 gives special sets of parameters. Part 5 is dedicated to tuning and monitoring of dual band networks. Finally, part 6 shows some weaknesses of handover algorithms.

Finally, it will be necessary to update this document after the first single BCCH field trials.

Presentation of the algorithms and parameters


2 Presentation of the algorithms and parameters

2.1 Neighbouring cells list and reporting

2.1.1 Neighbouring cells list

Sending of neighbouring cells list in each frequency band is necessary in order to allow monitoring and then re-selection and handovers.

In idle mode, a mobile finds the list of neighbouring cells on the BCCH, reading SYSTEM INFORMATION 2, 2ter and possibly 2bis :

Neighbouring cells

Serving cell

900 MHz 1800 MHz

900 MHz SI 2 SI 2ter (and 2bis)

1800 MHz SI 2ter SI 2 (and 2bis)

Remark : SI 2bis must be avoided because it may cause some misbehaviour of phase 1 MS. If it is needed (too many neighbouring cells) a warning is issued at the OMC-R.

In dedicated mode, a mobile finds the list of neighbouring cells on the SACCH, reading SYSTEM INFORMATION 5, 5bis and 5ter :

Neighbouring cells

Serving cell

900 MHz 1800 MHz

900 MHz SI 5 SI 5ter and 5bis

1800 MHz SI 5ter SI 5 and 5bis

Remark : SI 5ter is sent according to the MS revision level (1 or 2).

The BSS parameter EN_INTERBAND_NEIGH enables sending of SI 2bis/2ter and SI 5bis/5ter. If this parameter is set to disable a dual band MS is unable to make inter-band handovers or re-selection.

2.1.2 Neighbouring cells reporting

In a single band network, a mobile reports the 6 strongest neighbouring cells. In order to allow inter-band handovers, it is necessary to inform a dual band MS how to report neighbouring cells in each frequency band. This is the aim of the parameter MULTIBAND_REPORTING which is set on a per cell basis.



This parameter has 4 values (GSM 05.08) :

- 0 = normal reporting of the six strongest cells, with known and allowed NCC part of BSIC, irrespective of the band used,

- 1 = the MS shall report the strongest cell, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used,

- 2 = the MS shall report the two strongest cells, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used,

- 3 = the MS shall report the three strongest cells, with known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used.



2.2 Idle mode It is important to direct the mobiles to the desired layer not only in dedicated mode but also

in idle mode in order to take full advantage of the different layers and to reduce the number of handovers. With phase 2 mobiles (dual band mobiles are phase 2 mobiles) it is possible to use the parameter CELL_BAR_QUALIFY for cell selection and the C2 criterion for cell re-selection.

2.2.1 Cell selection

A phase 2 mobile selects the cell with the highest C1 (suitable cell : C1 > 0) belonging to the list of highest priority. The priority is given by the parameter CELL_BAR_QUALIFY which is broadcasted on the BCCH. This parameter is set on a per cell basis and takes two values : 0 = normal priority and 1 = low priority. It interacts with the parameter CELL_BAR_ACCESS. Consequently, it is not possible to use the CELL_BAR_QUALIFY parameter when the cell is barred.

Remark : it seems that some mobiles are not able to handle properly the selection process when the parameter CELL_BAR_QUALIFY is set to 1.

2.2.2 Cell re-selection

A phase 2 mobile uses the C2 criterion for cell re-selection.

Cell re-selection parameters are broadcasted on the BCCH (re-selection parameters of neighbouring cells are not found on the BCCH of the serving cell) if CELL_RESELECT_PARAM_IND = 1, otherwise C2 = C1.

There are two formulas according to the value of the parameter PENALTY_TIME.

If PENALTY_TIME ≠ 31 (binary coding ≠ 11111) : - C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET * H(PENALTY_TIME - T)

with H(x) = 0 for the serving cell and if x < 0 and H(x) = 1 otherwise

If PENALTY_TIME = 31 (binary coding = 11111) : - C2 = C1 - CELL_RESELECT_OFFSET

T is a timer incremented from 0 when the neighbouring cell enters in the list of the 6 strongest neighbouring cells. T is put back to 0 when the neighbouring cell does not belong to this list any longer.

The range for the cell re-selection parameters is : - CELL_RESELECT_OFFSET : 0 to 126 dB, 2 dB step,

- TEMPORARY_OFFSET : 0, 10, 20, 30, 40, 50, 60, infinite dB,

- PENALTY_TIME : 20 to 620 s, 20 s step.

Remarks :

- the infinite value of the TEMPORARY_OFFSET parameter is not supported by some mobiles. That is why this value is not used in this document,

- the parameter MULTIBAND_REPORTING is not used in idle mode. Consequently, a dual band MS only takes into account the 6 strongest neighbouring cells irrespective of the frequency band. A problem occurs when for example 1800 neighbouring cells



are not seen by a dual band mobile (6 strongest cells = 900 cells). In this case, it is not possible to re-select 1800 neighbouring cells.



2.3 B5 handover algorithms The aim of this part is to describe parameters and algorithms used in B5 release for call

set-up, handover detection and candidate cell evaluation process.

2.3.1 Call set-up (SDCCH-TCH handover)

In B5 release, a handover from a SDCCH of the serving cell to a TCH of a neighbouring cell (= Directed Retry) is only possible in case of complete congestion of the serving cell (it is possible to imagine Directed Retry without congestion and according to a load threshold).

Directed Retry and Forced Directed Retry algorithms are enabled when the Assignment Request message is put in the queue. If queuing is not allowed by the MSC in the Assignment Request message, there is a solution in B5 release which is the Directed Retry without queuing. If queuing is not allowed and the parameter QUEUE_ANYWAY is set to enable then the Assignment Request message is put in the queue without indication sent to the MSC. Whatever the case, the duration of the queuing phase is given by the timer T11.

Only internal Directed Retry is fully available. There is a solution for external Directed Retry with Alcatel and Ericsson MSC. In order to activate external Directed Retry, it is necessary to set the flag EN_EXT_DR (DLS parameter only) to enable.

The SDCCH-TCH handover may be performed :

- either on classical handover causes : if a classical handover cause is verified during queuing then the BSS will perform Directed Retry,

- or on Forced Directed Retry cause (= cause 20) : if during queuing, a neighbouring cell is reported with a sufficient level (cause 20) then the BSS will perform Forced Directed Retry.

Directed Retry may be enabled on a per cell basis with the parameter EN_DR. Forced Directed Retry may be enabled on a per cell basis with the parameter EN_FORCED_DR, which is relevant only if EN_DR = ENABLE.

2.3.1.1 Directed Retry

All classical handover causes are available, except causes 10, 11 and 13 (concentric cells) and causes 15 and 16 (intracell HO). For instance, a Directed Retry on cause 4 is possible in case of bad downlink quality.

The candidate cell evaluation process is the one described hereafter for TCH TCH handovers.

Remark : because of the size of averaging windows for normal HO (A_PBGT_HO, A_QUAL_HO, A_LEV_HO) it is difficult to trigger Directed Retry before the end of the queuing phase (T11 around 5-6 seconds).

2.3.1.2 Forced Directed Retry

If during queuing, a neighbouring cell is reported with a sufficient level, cause 20 is triggered :



- AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)

and

- EN_FORCED_DR = ENABLE

Remarks :

- cause 20 has the lowest priority of all handover causes but is triggered before other better condition handover causes as it uses a shorter averaging window size (A_PBGT_DR) than other better condition handover causes,

- if less than A_PBGT_DR samples are available, AV_RXLEV_NCELL_DR(n) is calculated with the available samples and the averaging window is filled in with 0 (-110 dBm). Thus, if a neighbouring cell is received with a very good level, cause 20 could be triggered before the availability of A_PBGT_DR samples.

The beginning of the candidate cell evaluation process is identical to the one described hereafter for TCH TCH handovers : PREF_LAYER, PRIORITY(0,n) and frequency band. The end is different because the PBGT filtering process does not take place and neighbouring cells are sorted according to their PBGT_DR(n) :

- AV_RXLEV_NCELL_DR(n) > RXLEVmin(n) + max(0, MS_TXPWR_MAX(n) - P)

- t(n) > FREElevel_DR(n) with t(n) the absolute number of free TCH in neighbouring cell n

- PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR

- (BS_TXPWR_MAX - BS_TXPWR)

- (MS_TXPWR_MAX(n) - MS_TXPWR_MAX)

The condition t(n) > FREElevel_DR(n) guarantees a certain number of free TCH in the target cell for Forced Directed Retry. This condition is effective for internal cells where the number of free TCH is known but also for external cells where a fixed value of t(n) (t(n) = 255) allows the inhibition of Forced Directed Retry (if FREElevel_DR(n) = 255).



2.3.2 Handovers

2.3.2.1 Better condition handover causes

There are five better condition handover causes : cause 21, cause 14, cause 12, cause 13 and cause 20.

Cause 13 is used in a concentric cell and is not described hereafter. Cause 20 (Forced Directed Retry) is described above.

Each time a measurement result is received, better condition handover causes are checked with the following priority order : cause 21, cause 14, cause 12.

If a handover cause is triggered, handover causes with lower priority are not checked. For example, if cause 21 is triggered, cause 14 is not checked.

2.3.2.1.1 Cause 21

This cause is used for handovers from cells not working in the preferred band to cells working in the preferred band.

The preferred band is indicated on a per BSS basis by the parameter PREFERRED_BAND.

There is a handover alarm when :

- the load of the serving cell exceeds a threshold : AV_LOAD(0) > MULTIBAND_LOAD_LEVEL

with AV_LOAD(0) the average percentage of busy TCH (over a period of one minute)

- a neighbouring cell working in the preferred band is received with a level higher than a threshold :

AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(n) + max(0, MS_TXPWR_MAX(n) - P)

with MS_TXPWR_MAX(n) and P powers in the preferred band

- cause 21 is enabled : EN_PREFERRED_BAND_HO = ENABLE

Remarks :

- AV_RXLEV_NCELL(n) is calculated with the averaging window A_PBGT_HO,

- if less than A_PBGT_HO samples are available, AV_RXLEV_NCELL(n) is calculated with the available samples and the averaging window is filled in with 0 (-110 dBm). Thus, if a neighbouring cell working in the preferred band is received with a very good level, the condition AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(n) + max(0, MS_TXPWR_MAX(n) - P) could be verified before the availability of A_PBGT_HO samples,

- the load of the serving cell is calculated independently. AV_LOAD(0) is calculated every D_BRO_TIM*LOAD_EV_PERIOD seconds. Imagine the case where AV_LOAD(0) = 0% at the beginning of the call on the non-preferred band cell and MULTIBAND_LOAD_LEVEL = 0%. It could be necessary to wait up to D_BRO_TIM*LOAD_EV_PERIOD seconds in order to have a new value of AV_LOAD(0) and to fulfil the condition AV_LOAD(0) > MULTIBAND_LOAD_LEVEL.



2.3.2.1.2 Cause 14

This cause is used in a hierarchical network to go from a cell of the upper layer to a cell of a lower layer.

It is thus possible to go from an umbrella cell (CELL_LAYER_TYPE = upper) to a micro cell (CELL_LAYER_TYPE = lower) or a mini cell (CELL_LAYER_TYPE = lower).


- a neighbouring cell of a lower layer is received with a level higher than a threshold : AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(n)

- the mobile is a slow mobile : MS_SPEED = slow

- cause 14 is enabled : EN_MCHO_NCELL = ENABLE

Remarks :

- AV_RXLEV_NCELL(n) is calculated with the averaging window A_PBGT_HO,

- if less than A_PBGT_HO samples are available, AV_RXLEV_NCELL(n) is calculated with the available samples and the averaging window is filled in with 0 (-110 dBm). Thus, if a lower layer neighbouring cell is received with a very good level, the condition AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(n) could be verified before the availability of A_PBGT_HO samples,

- the speed of a mobile is determined independently by the MS speed discrimination process (see below).

MS speed discrimination :

For each call on the upper layer and for each neighbouring lower layer cell n, a counter C_DWELL(n) measures the number of SACCH periods of monitoring the neighbouring cell n over the threshold L_RXLEV_CPT_HO(n). Each time cell n is monitored C_DWELL(n) is compared to the threshold (variable according to the load of the serving umbrella cell) 2*MIN_DWELL_TIME in order to determine the MS speed. If for one neighbouring lower layer cell n, C_DWELL(n) >= 2*MIN_DWELL_TIME, then MS_SPEED is set to slow.

If EN_SPEED_DISC = DISABLE, C_DWELL(n) is initialized with the value 2*(MIN_DWELL_TIME - L_MIN_DWELL_TIME). In this case, there is no regulation according to the load of the serving umbrella cell (if DWELL_TIME_STEP = 0 s). Thus if 2*L_MIN_DWELL_TIME consecutive samples of the received level from a lower layer neighbouring cell n are higher than L_RXLEV_CPT_HO(n), MS_SPEED is set to slow.

2.3.2.1.3 Cause 12

It is the classical Power Budget cause only possible between cells belonging to the same layer and working in the same band.




- the power budget between the serving cell and a neighbouring cell exceeds a threshold :

PBGT(n) > HO_MARGIN(0,n)

- cause 12 is enabled : EN_PBGT_HO = ENABLE

PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO

- (BS_TXPWR_MAX - BS_TXPWR)


- PING_PONG_MARGIN(n, call_ref)

Remarks :

- AV_RXLEV_NCELL(n) and AV_RXLEV_PBGT_HO are calculated with the averaging window A_PBGT_HO,

- cause 12 is not triggered before the availability of A_PBGT_HO samples.

Anti ping-pong mechanism :

PING_PONG_MARGIN(n, call_ref) is a penalty put on the neighbouring cell n if :

- it is the immediately precedent cell on which the call has been,

- this cell belongs to the same BSC than the serving cell,

- the call has not performed a Forced Directed Retry towards the serving cell,

- less than T_HCP seconds have elapsed since the last handover.

In this case PING_PONG_MARGIN(n, call_ref) = PING_PONG_HCP

otherwise PING_PONG_MARGIN(n, call_ref) = 0 dB

Remark : this penalty is also used in the formula of PBGT(n) in the PBGT filtering process and the ORDER or GRADE evaluation processes.

2.3.2.2 Emergency handover causes

There are 12 emergency handover causes :

- cause 7 : consecutive bad SACCH frames (micro cells only),

- causes 17 and 18 : level UL/DL high threshold (micro cells only),

- causes 2 and 4 : quality UL/DL,

- causes 3 and 5 : level UL/DL,

- cause 6 : distance,

- causes 10 and 11 : inner zone level UL/DL (concentric cells only),

- causes 15 and 16 : intracell UL/DL.



Emergency handover causes are checked before better condition handover causes and with the following priority order : 7, 17, 18, 2, 4, 3, 5, 6, 10, 11, 15 and 16.

Following averaging windows are used :

- causes 2, 3, 4, 5, 10, 11, 15 and 16 : A_LEV_HO and A_QUAL_HO,

- cause 6 : A_RANGE_HO,

- causes 17 and 18 : A_LEV_MCHO.

An emergency handover cause is not triggered before the averaging window is not filled in.



2.3.3 Candidate cell evaluation process

2.3.3.1 Indications sent to the HO candidate cell evaluation process

The handover detection process gives to the handover candidate cell evaluation process the following information :

- the handover cause value (for cause dependent offsets),

- the preferred layer for the target cell indicated by the variable PREF_LAYER,

- the list of candidates.

2.3.3.1.1 List of candidate cells

Non hierarchical network (= only one layer) :

- all neighbouring cells in case of emergency alarm,

- the neighbouring cells which verify the cause in case of better condition alarm.

Hierarchical network (= at least 2 layers) :

- all neighbouring cells in case of emergency alarm,

- the neighbouring cells which verify the cause in case of better condition alarm. If the serving CELL_LAYER_TYPE = lower, the handover cause = 12 and MS_SPEED = fast, the list must also contain the whole set of internal neighbouring umbrella cells which averaged load AV_LOAD(n) < L_LOAD_OBJ(n).

2.3.3.1.2 Preferred layer

Non hierarchical network : PREF_LAYER = upper+single.

Hierarchical network :

- in case of emergency alarm, PREF_LAYER = - upper if CELL_LAYER_TYPE = lower and EN_RESCUE_UM = ENABLE (used generally for

micro cells),

- lower if CELL_LAYER_TYPE = lower and EN_RESCUE_UM = DISABLE (used generally for mini cells),

- none if CELL_LAYER_TYPE = lower and EN_RESCUE_UM = INDEFINITE,

- upper + single if CELL_LAYER_TYPE = upper.

- in case of better condition alarm, PREF_LAYER = - none,

- upper if the serving CELL_LAYER_TYPE = lower, the handover cause = 12 and MS_SPEED = fast.



2.3.3.2 Candidate cell evaluation process

The ordering of candidate cells (from the highest priority to the lowest one) is performed according to the following scheme :

First, candidate cells are sorted according to the variable PREF_LAYER : a higher priority is given to candidate cells which CELL_LAYER_TYPE is equal to PREF_LAYER.

Then candidate cells are sorted according to the parameter PRIORITY(0,n). This parameter has four values : 0 = highest priority, 3 = lowest priority. Candidate cells are sorted from the lowest value (= highest priority) to the highest value (= lowest priority). Thanks to this parameter, it is possible to modify the standard priority order which takes into account the frequency band of the serving cell.

Finally, candidate cells are sorted according to their frequency band : a higher priority is given to candidate cells working in the same frequency band than the serving cell.

Then a filtering process is possible before the ORDER or GRADE evaluation process. This filtering process is enabled or disabled on a per cell basis by the flag EN_PBGT_FILTERING.

If EN_PBGT_FILTERING is set to Enable, all neighbouring cells n which do not fulfil the following condition are rejected from the list sent to the ORDER or GRADE evaluation process :

PBGT(n) > HO_MARGIN_XX(0,n) + Cause_Margin_P_X

with HO_MARGIN_XX(0,n) =

Cell_layer_type = Pref_layer

Cell_layer_type ≠ Pref_layer

List of candidate cells n

Frequency band = serving cell

Frequency band ≠ serving cell

Priority(0,n) = 0

Priority(0,n) = 1

Priority(0,n) = 2

Priority(0,n) = 3

Priority(0,n) = 0

Priority(0,n) = 1

Priority(0,n) = 2

Priority(0,n) = 3

Frequency band = serving cell

Frequency band ≠ serving cell

Highest priority

Lowest priority



- HO_MARGIN_QUAL(0,n) if cause = 2, 4 or 7,

- HO_MARGIN_LEV(0,n) if cause = 3, 5, 6, 17 or 18,

- HO_MARGIN(0,n) if cause = 12, 14 or 21.

Remark : the PBGT filtering is effective even if the corresponding averaging window (A_PBGT_HO) is not full. In this case, AV_RXLEV_NCELL(n) and AV_RXLEV_PBGT_HO are calculated with the available samples and the averaging window is filled in with 0 (-110 dBm).

Finally, the ORDER or the GRADE process is used (according to the parameter CELL_EV) to classify the remaining (after the PBGT filtering) candidate cells in each group built by the ordering process (PREF_LAYER, PRIORITY(0,n), frequency band).



2.4 B6 handover algorithms The aim of this part is to describe parameters and algorithms used in B6 release for call

set-up, handover detection and candidate cell evaluation process.

Compared to B5 release, there are a lot of modifications and improvements leading to a new management of dual band networks.

This part is not dedicated to the Multiband cell or single BCCH solution which is presented in part 2.5.

2.4.1 Call set-up (SDCCH-TCH handover)

There are some improvements compared to B5 release :

Directed Retry without queuing

If queuing is not allowed by the MSC in the Assignment Request message and if the parameter QUEUE_ANYWAY is set to enable then the Assignment Request message is put in the queue. The duration of the queuing phase is given by the timer T11_forced.

Forced Directed Retry

The formula PBGT_DR(n), used in the candidate cell evaluation process when the Forced Directed Retry cause is triggered, is modified (AV_BS_TXPWR_DR) :

PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR

- (BS_TXPWR_MAX - AV_BS_TXPWR_DR)




2.4.2 Handovers

2.4.2.1 Better condition handover causes

Causes 21, 14 and 12 which exist in B5 release are modified in B6 release. On the other hand new causes are added : causes 23 and 24.

Level of priority of better condition HO causes

This is a major change between B5 and B6 releases ! In B5 the level of priority of better condition HO causes is : 21 > 14 > 12 > 13 > 20. On the

other hand, when the better condition HO cause of priority n is verified, the better condition HO cause of priority n-1 is not checked leading to an unsatisfactory behaviour.

In B6, causes 21, 14, 24, 12 and 23 have the same level of priority at the detection level. If for example cause 21 is verified causes 14, 24, 12 and 23 are checked. Furthermore the level of priority of better condition HO causes is : 21 = 14 = 24 = 12 = 23 > 13 > 20.

2.4.2.1.1 Cause 21

Compared to the B5 release, cause 21 is modified :

- the way to take into account the load of the serving cell is different,

- the load of the neighbouring cell working in the preferred band is taken into account,

- the capture threshold is now set on a per couple of cells basis.

Therefore cause 21 is triggered when : - Traffic_load(0) = MULTIBAND_TRAFFIC_CONDITION,

- Traffic_load(n) ≠ high,

- AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) + max(0, MS_TXPWR_MAX(n) - P).

The parameter MULTIBAND_TRAFFIC_CONDITION can have three values :

- ANY_LOAD : the condition is always fulfilled,

- NOT_LOW : the condition is fulfilled if Traffic_load(0) ≠ low,

- HIGH : the condition is fulfilled if Traffic_load(0) = high.

2.4.2.1.2 Cause 14

Cause 14 is also modified. This cause is used to go from cells with CELL_LAYER_TYPE = upper to cells with CELL_LAYER_TYPE = lower except in the following cases described in the picture below :



In the above picture, the left case corresponds to a dual band mobile located in the inner zone of a multiband cell. Then if the lower layer neighbouring cell uses the same frequency band than the outer zone of the multiband cell and if the parameter EN_BI-BAND_MS is set to disable then cause 14 is not checked towards this neighbouring cell. The underlying idea is that the dual band MS must stay in the inner zone of the multiband cell.

In the right case we don’t want to make a handover from the preferred frequency band to the non-preferred frequency band.

Therefore, the parameter EN_BI-BAND_MS (new in B6) is useful to define the possible target cells for cause 14.

On the other hand, the capture threshold (L_RXLEV_CPT_HO(0,n)) is now set on a per couple of cells basis.

2.4.2.1.3 Cause 12

Cause 12 (power budget) is deeply modified :

- an offset is used in the inner zone of a concentric or multiband cell,

- an offset is used to take into account the load of serving and neighbouring cells,

- there is a condition on the level of the serving cell,

- the formula of PBGT is modified,

- according to the value of the new parameter EN_MULTIBAND_PBGT_HO, cause 12 may be checked over all the neighbouring cells without any cell frequency band restriction. Remark : this modification is only available with the SMG29-2 version of the B6.2 release because it was introduced after a change request and it is not applied on cause 23.

For a TCH -> TCH handover and a SDCCH -> TCH handover (Directed Retry) cause 12 is verified when :

If EN_TRAFFIC_HO(0,n) = enable - then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER

+ max(0, DELTA_HO_MARGIN(0,n))

CELL_BAND_TYPE = Preferred_band

CELL_LAYER_TYPE = upper

CELL_LAYER_TYPE = lower

EN_BI-BAND_MS = disableCELL_BAND_TYPE = CELL_BAND_TYPE(0)

Cause 14

EN_BI-BAND_MS = disableCELL_BAND_TYPE ≠ Preferred_band

Cause 14



- else PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER

and AV_RXLEV_PBGT_HO <= RXLEV_LIMIT_PBGT_HO

with PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO

- (BS_TXPWR_MAX - AV_BS_TXPWR_HO)


- PING_PONG_MARGIN(n,call_ref)

For a SDCCH -> SDCCH handover cause 12 is verified when (SDCCH channels are always in the outer zone) :

- PBGT(n) > HO_MARGIN(0,n)

- and AV_RXLEV_PBGT_HO <= RXLEV_LIMIT_PBGT_HO

Explanations :

- OFFSET_HO_MARGIN_INNER is only used in the inner zone of a concentric or multiband cell. This offset is useful to take into account the difference of propagation losses between 900 and 1800 MHz bands,

- DELTA_HO_MARGIN(0,n) is determined according to the load of the serving cell and the neighbouring cell n :

- if Traffic_load(0) = high and Traffic_load(n) = low then DELTA_HO_MARGIN(0,n) = -DELTA_DEC_HO_margin,

- if Traffic_load(0) = low and Traffic_load(n) = high then DELTA_HO_MARGIN(0,n) = DELTA_INC_HO_margin,

- otherwise DELTA_HO_MARGIN(0,n) = 0,

- because of the condition max(0, DELTA_HO_MARGIN(0,n)) an offset (positive) is only added to HO_MARGIN(0,n) when the load of the serving cell is low and the load of the neighbouring cell n is high in order to delay the PBGT HO.

- RXLEV_LIMIT_PBGT_HO is used to prevent a handover when the level of the serving cell is high. This condition will be mainly useful in a micro layer where the overlap between micro cells occurs at high level,

- AV_BS_TXPWR_HO is the average of BS_POWER over A_PBGT_HO measurements. This average value will be useful in case of activation of the DL power control,

- the possibility to make inter-band PBGT HO (EN_MULTIBAND_PBGT_HO = enable) could be useful in case of a dual band mono layer network (1800 cells in the city and 900 cells in the suburbs for example) and in case of a dual band dual layer network (exit of the new frequency band layer).



2.4.2.1.4 Cause 23

This cause is new in B6. It is called the traffic HO cause and is the complementary cause of cause 12.

It is used to make handovers between cells of the same layer (same CELL_LAYER_TYPE) and with BCCH in the same frequency band (same CELL_BAND_TYPE).

In the inner zone, cause 23 is checked only towards other multiband neighbouring cells (FREQUENCY_RANGE = GSM-DCS) belonging to the same BSC than the serving cell in order to keep dual band MS in the new frequency band.

Cause 23 is fulfilled when : - DELTA_HO_MARGIN(0,n) < 0 dB,

- PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER + DELTA_HO_MARGIN(0,n),

- EN_TRAFFIC_HO(0,n) = enable.

DELTA_HO_MARGIN(0,n) is calculated like for cause 12 (see above).

Cause 23 is the complementary cause of cause 12 because an offset (this time negative) is added to HO_MARGIN(0,n) when the load of the serving cell is high and the load of the neighbouring cell n is low in order to accelerate the PBGT HO (reduction of the serving area of the congested serving cell).

2.4.2.1.5 Cause 24

This cause is new in B6. It is called the general capture HO cause. It is a capture HO (like causes 14 and 21) but without conditions (general capture) on the type of the serving and neighbouring cells. Nevertheless, some rules are used (like with cause 14) in order to keep dual band MS in the preferred band. Cause 24 is always checked except in the following cases described in the picture below :



Cause24


Cause 24



Cause 24 is fulfilled when : - Traffic_load(0) = CAPTURE_TRAFFIC_CONDITION,

- Traffic_load(n) ≠ high,

- AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) + max(0, MS_TXPWR_MAX(n) - P),

- EN_GENERAL_CAPTURE_HO = enable.

The parameter CAPTURE_TRAFFIC_CONDITION can have three values :

- ANY_LOAD : the condition is always fulfilled,

- NOT_LOW : the condition is fulfilled if Traffic_load(0) ≠ low,

- HIGH : the condition is fulfilled if Traffic_load(0) = high.

2.4.2.2 Emergency handover causes

There is one modification : quality thresholds (L_RXQUAL_UL/DL_H) have a step size of 0.1 instead of 1.



2.4.3 Candidate cell evaluation process

2.4.3.1 Indications sent to the HO candidate cell evaluation process

2.4.3.1.1 Number of the HO cause

A HO cause number is associated to each candidate cell. If a candidate cell is present because of two HO causes the number of the HO cause with highest priority is used (in this case, 21 > 14 > 24 > 12 > 23).

2.4.3.1.2 List of candidate cells

There are some modifications :

- in case of emergency HO cause in a 1800 inner zone of a multiband cell, the serving multiband cell is added to the list of candidate cells (= all the neighbouring cells) with the MS zone indication Outer. The serving cell is put at the end of the list,

- the way to take into account the load is different : if cause 12 is verified in a lower layer cell and MS_SPEED = fast, it is necessary to add to the list of candidate cells all the internal umbrella neighbouring cells not loaded (Traffic_load(n) = low),

- in case of emergency HO cause in a lower layer cell, the neighbouring umbrella cells not verifying the condition AV_RXLEV_NCELL(n) > OUTDOOR_UMB_LEV(0,n) are discarded.


This process is deeply modified.

Remark : the serving cell (if present) is always put at the end of the list.

After the triggering of cause 20 or the triggering of an emergency handover cause, candidate cells are sorted according to :

- the variable PREF_LAYER,

- the parameter PRIORITY(0,n) if EN_PRIORITY_ORDERING = enable,

- the cell band type.

After the triggering of a better condition handover cause (except cause 20), candidate cells are sorted according to :

- the variable PREF_LAYER,

- the parameter PRIORITY(0,n) if EN_PRIORITY_ORDERING = enable.

This behaviour is new in B6 : in B5, the candidate cells were also sorted according to the cell band type.

The PBGT filtering process which takes place before the ORDER and GRADE processes is also modified :



- it is only applied in case of emergency HO cause (it is not applied on the serving cell or after the triggering of causes 12, 14, 20, 21, 23, 24),

- the condition is now : PBGT(n) > HO_MARGIN_XX(0,n) + OFFSET_HO_MARGIN_INNER, with HO_MARGIN_XX(0,n) = HO_MARGIN_QUAL(0,n) if cause = 2, 4 or 7, HO_MARGIN_XX(0,n) = HO_MARGIN_LEV(0,n) if cause = 3, 5, 17 or 18, HO_MARGIN_XX(0,n) = HO_MARGIN_DIST(0,n) if cause = 6 or 22, OFFSET_HO_MARGIN_INNER is only used in the inner zone of a concentric or multiband cell.

Finally the GRADE process is also modified :

- the GRADE formula is modified : FREEfactor is removed,

- the condition GRADE(n) > DISTmargin + Cause_Margin_G_X is removed.



2.4.4 Load and traffic evaluation

There are three different evaluations made on a per cell basis :

- total number of free TCH with associated FREEfactor and LOADfactor provided every TCH_INFO_PERIOD seconds,

- load evaluation,

- traffic evaluation.

Remark : for all these evaluations, the number of TCH is based on TS and not on channels (HR is not taken into account).

Load evaluation (medium term)

The load of cell n is calculated according to the following formula :

AV_LOAD(n) = (1 / Nsamples) ∑i=1, Nsamples 100 * (1 - Nb free TCH(i) / Nb tot TCH(n)), where Nsamples is the number of load samples (= LOAD_EV_PERIOD), Nb tot TCH(n) the total number of TCH of cell n, Nb free TCH(i) the number of free TCH reported every TCH_INFO_PERIOD seconds.

AV_LOAD(n) is a non sliding average.

Traffic evaluation (long term)

This process is new in B6. It is divided into two steps :

- calculation of averages,

- decision process.

Using load samples (100 * (1 - Nb free TCH(i) / Nb tot TCH)) provided every TCH_INFO_PERIOD seconds the first step corresponds to the calculation of a non sliding average (AV_TRAFFIC_LOAD) using A_TRAFFIC_LOAD samples.

The second step corresponds to the calculation of the variable Traffic_load and Traffic_load_GPRS (for cells supporting GPRS) using several (N_TRAFFIC_LOAD) consecutive averages (AV_TRAFFIC_LOAD) compared to different thresholds (HIGH_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD, IND_TRAFFIC_LOAD).

The decision process is :

If Traffic_load = indefinite and : - the last N_TRAFFIC_LOAD averages AV_TRAFFIC_LOAD (including the new one) verify

AV_TRAFFIC_LOAD > HIGH_TRAFFIC_LOAD then Traffic_load = high

- the last N_TRAFFIC_LOAD averages AV_TRAFFIC_LOAD (including the new one) verify AV_TRAFFIC_LOAD < LOW_TRAFFIC_LOAD then Traffic_load = low

If Traffic_load = low and the new average AV_TRAFFIC_LOAD verifies : - IND_TRAFFIC_LOAD ≠ 0 and AV_TRAFFIC_LOAD > IND_TRAFFIC_LOAD or

AV_TRAFFIC_LOAD > HIGH_TRAFFIC_LOAD then Traffic_load = indefinite

If Traffic_load = high and the new average AV_TRAFFIC_LOAD verifies :



- IND_TRAFFIC_LOAD ≠ 0 and AV_TRAFFIC_LOAD < IND_TRAFFIC_LOAD or AV_TRAFFIC_LOAD < LOW_TRAFFIC_LOAD then Traffic_load = indefinite

Remarks :

- A_TRAFFIC_LOAD and N_TRAFFIC_LOAD are set on a per cell basis,

- Traffic_load(n) = indefinite if n is an external cell.



2.5 B6 Multiband cell solution The aim of this part is to describe the Multiband cell solution which is new in B6.

The picture below presents the Multiband cell solution (example of an existing 900 MHz network). With this solution, there is a mix of frequency bands within a cell, the BCCH frequency always belonging to the same frequency band.

An adapted version of the concentric cells algorithms is used in the Multiband cell solution.

A cell is a multiband cell if its FREQUENCY_RANGE is equal to GSM-DCS. On the other hand the parameter CELL_PARTITION_TYPE is equal to Concentric. Finally, following profiles are available for a multiband cell : single, umbrella, mini and micro. Nevertheless a multiband cell cannot be a concentric cell (i.e. 900+1800 outer zone and 900+1800 inner zone).

2.5.1 Normal assignment

All SDCCH channels are in the outer zone. Then, according to the MS location, the BSC can allocate a TCH in the inner zone or in the outer zone. In order to determine the MS location, cause 13 is checked.

Remarks concerning cause 13 in the context of normal assignment :

900 MHz BCCH, SDCCH and TCH

BS

Single bandDual band

Dual band

1800 MHz TCH



- the flag EN_BETTER_ZONE_HO is not taken into account,

- average level :

- if more than A_LEV_HO measurements have been received, AV_RXLEV_UL/DL is used,

- if less than A_LEV_HO measurements have been received, the average of these measurements is used.

2.5.2 Incoming handover

In case of incoming intra-BSC handover a TCH is allocated in the outer zone or in the inner zone according to the MS location. In order to determine the MS location the following condition is checked :

- AV_RXLEV_NCELL(n) > RXLEV_DL_ZONE + ZONE_HO_HYST_DL + BS_TXPWR_MAX - BS_TXPWR_MAX_INNER

Remarks :

- here, the value of the flag EN_BETTER_ZONE_HO is taken into account. If EN_BETTER_ZONE_HO = disable, the TCH is allocated in the outer zone,

- the parameters RXLEV_DL_ZONE, ZONE_HO_HYST_DL, BS_TXPWR_MAX and BS_TXPWR_MAX_INNER are parameters of the target cell which are known only if the target cell belongs to the same BSC than the serving cell,

- average level :

- if more than A_LEV_HO measurements have been received, AV_RXLEV_NCELL(n) is used,

- if less than A_LEV_HO measurements have been received, the average of these measurements is used.

In case of incoming inter-BSC handover a TCH is always allocated in the outer zone whatever the MS location.

2.5.3 Outgoing better conditions handovers

Cause 12

In the outer zone, cause 12 (power budget) is checked towards all neighbouring cells belonging to the same layer (CELL_LAYER_TYPE) and working in the same frequency band (CELL_BAND_TYPE) than the serving cell. Nevertheless (SMG29-2 B6.2 only), if EN_MULTIBAND_PBGT_HO = enable, cause 12 is checked over all the neighbouring cells without any cell frequency band restriction.

In the inner zone, cause 12 is checked only towards other multiband neighbouring cells (FREQUENCY_RANGE = GSM-DCS) belonging to the same BSC than the serving cell in order to keep dual band MS in the inner zone frequency band. Nevertheless (SMG29-2 B6.2 only), if EN_MULTIBAND_PBGT_HO = enable, cause 12 is checked over all the neighbouring cells without any cell frequency band restriction.



For a MS in the inner zone, cause 12 is modified : an offset is added to HO_MARGIN(0,n) in order to take into account the difference of propagation losses between 900 and 1800 bands.

Cause 14

In order to keep dual band MS in the preferred band, cause 14 is not checked in the following cases :

The left case corresponds to a dual band MS located in the inner zone of an umbrella multiband cell. The micro cell under this umbrella cell does not work in the same frequency band than the inner zone. Using the parameter EN_BI-BAND_MS the operator decides if the micro cell is a possible target cell or not. For example, EN_BI-BAND_MS = disable for an outdoor micro cell and EN_BI-BAND_MS = enable for an indoor micro cell.

The second case corresponds to a dual band MS located in the outer zone of an umbrella multiband cell. The micro cell under this umbrella cell does not work in the same frequency band than the outer zone.

Cause 23

In the inner zone, cause 23 is checked only towards other multiband neighbouring cells (FREQUENCY_RANGE = GSM-DCS) belonging to the same BSC than the serving cell in order to keep dual band MS in the inner zone frequency band.

Cause 24

In order to keep dual band MS in the preferred band, cause 24 is not checked in the following cases :


CELL_LAYER_TYPE = lower


Cause 14


Cause 14

CELL_LAYER_TYPE = upper



2.5.4 Inter zone handovers

Outer to inner

Cause 13 is used to make handovers from the outer zone to the inner zone :

- AV_RXLEV_UL_HO > RXLEV_UL_ZONE + ZONE_HO_HYST_UL + (MS_TXPWR –

MS_TXPWR_MAX_INNER) + PING_PONG_MARGIN(0,call_ref),

- AV_RXLEV_DL_HO > RXLEV_DL_ZONE + ZONE_HO_HYST_DL + (BS_TXPWR – BS_TXPWR_MAX_INNER) + PING_PONG_MARGIN(0, call_ref),

- AV_RXLEV_NCELL_BIS(n) <= NEIGHBOUR_RXLEV(0,n),

- EN_BETTER_ZONE_HO = Enable.

The condition AV_RXLEV_NCELL_BIS(n) <= NEIGHBOUR_RXLEV(0,n) is new in B6. It is checked towards all neighbouring cells belonging to the same layer and working in the same frequency band than the serving cell.

PING_PONG_MARGIN(0, call_ref) is a penalty used only if :

- the call was just before in the inner zone of the serving cell,

- less the T_HCP seconds have elapsed since the last HO,

- the last HO was not an external intracell HO.

Inner to outer

Causes 10 and 11 are used to make handovers from the inner zone to the outer zone.



Cause24


Cause 24



Cause 10 : - AV_RXLEV_UL_HO < RXLEV_UL_ZONE,

- MS_TXPWR = min(P, MS_TXPWR_MAX_INNER).

Cause 11 : - AV_RXLEV_DL_HO < RXLEV_DL_ZONE,

- BS_TXPWR = BS_TXPWR_MAX_INNER.

2.5.5 Emergency handovers

In case of emergency HO cause in a 1800 inner zone of a multiband cell, the serving multiband cell is added to the list of candidate cells (= all the neighbouring cells) with the MS zone indication Outer. The serving cell is put at the end of the list.

For a mobile connected to the inner zone, if cause 15 or 16 is triggered (interference problem : bad quality and high level) a TCH may be allocated in the outer zone. Using the parameter TRX_PREF_MARK it is possible to send the MS preferably to the outer zone.

For a mobile connected to the outer zone, if cause 15 or 16 is triggered a TCH is always allocated in the outer zone.



2.6 Classmark handling

2.6.1 Principles

Classmark 1 mainly contains the revision level, the RF power capability and the A5/1 ciphering capability.

Classmark 2 mainly contains the revision level, the RF power capability and the A5/1 and A5/2 ciphering capabilities.

Classmark 3 gives the frequency bands supported with associated RF power capabilities.

At call establishment, a mobile sends a Classmark 1 (CM1) or Classmark 2 (CM2) information in the first message sent to the network :

- CM1 is sent in LOCATION UPDATING REQUEST and IMSI DETACH INDICATION,

- CM2 is sent in CM SERVICE REQUEST, PAGING RESPONSE or CM RE_ESTABLISHMENT REQUEST.

This Classmark information is built by the MS according to the frequency band used at call set-up.

The difference between a CM1 or CM2 built on GSM900 and a CM1 or CM2 built on GSM1800 is the power capability of the mobile. This power is coded on 3 bits and the meaning depends on the frequency band. The following table gives encoding of RF power capability :

Coding of the power capability (CM1 or CM2) GSM900 GSM1800

0 0 0 20 W 1 W

0 0 1 8 W 0.25 W

0 1 0 5 W 4 W

0 1 1 2 W Not used

1 0 0 0.8 W Not used

Others Not used Not used

There is no indication, in the Classmark information, of the band used to build it. The only way to know the power capability of a multiband mobile in each band is to use the CM3.

As long as the call is handled by a single BSS, there should be no problem because the BSS is aware of the band used to establish the call.

Problem occurs during external handovers if the BSS or the MSC do not support CM3 information. Indeed, the target BSS receives the HANDOVER REQUEST message (provided by the MSC), which should contain the CM1 or CM2 information, and optionally the CM3 information. If the target BSS does not get (case where MSC does not support CM3) or does not support CM3, the target BSS can not know on which band the CM1 or CM2 was built. There is a risk of misunderstanding of the power capability.



Case of interworking problem :

For example, a GSM900 target BSC receives a HANDOVER REQUEST with CM2 indicating a power capability coded "001". The target BSC thinks it is a 8 W mobile.

In fact, the mobile is a multiband mobile, 0.25 W on GSM1800 (coded "001") and 2 W on GSM900 (coded "011"). The call was initiated on a GSM1800 cell, that is why CM2 indicates "001".

Once the call established on the GSM900 cell, the quality of the radio link can decrease because the mobile is moving away from the BTS. The BSS will trigger power control, but the mobile will not answer to requests to transmit higher than 2W. Indeed the mobile is physically limited to 2 W on GSM900.

The BSS will never trigger a handover as long as the MS does not transmit at its maximum output power, which is supposed to be 8W. After a while, if the MS is still moving away, the call will be lost.

There is no mechanism in the BSS to prevent from such a situation. A strategy is to bar GSM1800 cells in a dual band network (to avoid sending of 1800 CM1 and CM2), as long as single band 900 BSS (not supporting Classmark 3) will remain in the network (dual band BSS and single band BSS within the same network).

2.6.2 Behaviour of B5 release

B5 release supports the Classmark Enquiry procedure. Therefore, in case of incoming external handover, the interworking problem is solved :

- as soon as the CM3 is present, it is processed to get all relevant information,

- if CM3 is not present but the mobile may be a multiband mobile (HANDOVER REQUEST message with CM2 present and bit ES_IND = 1), then a Classmark Enquiry procedure is autonomously triggered by the BSS as soon as the mobile is on the new channel. The BSS will get all reliable Classmark information (CM2 and optionally CM3) from the mobile.

In case of outgoing external handover towards a non-B5 BSS, it is necessary to verify the behaviour of the target BSS (support of CM3, ability to trigger a Classmark Enquiry procedure).

Parameters and configurations


3 Parameters and configurations

3.1 Description of the parameters

3.1.1 B5 parameters

First and according to field experience, it is possible to reuse 900 MHz and 1800 MHz default radio parameters for a dual band network.

The second idea is that few parameters are used to manage a dual band network in idle and dedicated modes. These parameters are listed in bold type in the table below :

Parameter Type Use

Neighbouring cells reporting and description EN_INTERBAND_NEIGH BSS Sending of the list of neighbouring cells in

each frequency band MULTIBAND_REPORTING Cell Reporting of neighbouring cells in each

frequency band NCC_PERMITTED Cell NCC that the MS is allowed to report

Classmark handling BSS_SEND_CM_ENQUIRY BSS Management of the Classmark Enquiry

procedure in case of Location Updating EN_SEND_CM3 BSS Control of MS CM2 and MS CM3 sent to the

MSC STRIP_O5_CM2 BSS Control of MS CM2 and MS CM3 sent to the

MSC

Cell selection CELL_BAR_ACCESS Cell Bar the cell CELL_BAR_QUALIFY Cell Give a normal or low priority to the cell RXLEV_ACCESS_MIN Cell Minimum received level to select the cell.

Used in C1 criterion

Cell re-selection CELL_RESELECT_HYSTERESIS Cell Hysteresis for cell re-selection in case of

Location Updating CELL_RESELECT_OFFSET Cell Used in C2 criterion CELL_RESELECT_PARAM_IND Cell Sending of C2 parameters PENALTY_TIME Cell Used in C2 criterion TEMPORARY_OFFSET Cell Used in C2 criterion

Cell administration CELL_DIMENSION_TYPE Cell Used to define the cell profile and then the

allowed outgoing and incoming handover causes. Macro, micro.

CELL_LAYER_TYPE Cell Used to define the cell profile and then the allowed outgoing and incoming handover causes. Upper, lower, single.

CELL_PARTITION_TYPE Cell Used to define the cell profile and then the allowed outgoing and incoming handover causes. Concentric cells.

CELL_RANGE Cell Used to define the cell profile and then the allowed outgoing and incoming handover causes. Extended cells.



Call set-up A_PBGT_DR Cell Averaging window for the calculation of the

average level of serving and neighbouring cells used for Forced Directed Retry (cause 20)

EN_DR Cell Enable Directed Retry EN_FORCED_DR Cell Enable Forced Directed Retry FREElevel_DR(n) Cell Load threshold for the evaluation of a

candidate cell when cause 20 is triggered L_RXLEV_NCELL_DR(n) Cell Level threshold for the detection of cause 20

Better condition handovers A_PBGT_HO Cell Averaging window for the calculation of the

average level of serving and neighbouring cells. Average values used by causes 21, 14 and 12.

D_BRO_TIM BSS (internal)

Time between 2 raw samples of the load of a cell. These raw samples are used for the calculation of the average load of a cell.

DWELL_TIME_STEP BSS Decrease or increase step of the variable MIN_DWELL_TIME.

EN_MCHO_NCELL Cell Enable cause 14 EN_PBGT_HO Cell Enable cause 12 EN_PREFERRED_BAND_HO Cell Enable cause 21 EN_SPEED_DISC Cell Enable speed discrimination H_LOAD_OBJ Cell Used by the traffic load control process H_MIN_DWELL_TIME BSS Maximum value of the variable

MIN_DWELL_TIME. L_LOAD_OBJ Cell Used by the traffic load control process L_MIN_DWELL_TIME BSS Minimum value of the variable

MIN_DWELL_TIME. Time threshold for cause 14 if the speed discrimination is disabled.

L_RXLEV_CPT_HO(n) Cell Level threshold used by causes 21 and 14 LOAD_EV_PERIOD BSS

(internal) Number of raw samples used for the calculation of the average load of a cell. The average load is used by cause 21.

MULTIBAND_LOAD_LEVEL Cell Load threshold (serving cell) used by cause 21 PREFERRED_BAND BSS Define the preferred band and then the target

frequency band for cause 21

Candidate cell evaluation process Cause_Margin_G_X Cell Grade : filtering condition Cause_Margin_P_X Cell PBGT filtering CELL_EV Cell Selection of Order or Grade evaluation

processes DISTmargin_1-5 Cell Take into account the BS-MS distance in

Grade EN_LOAD_ORDER Cell Order and Grade processes : take into account

the load of serving and neighbouring cells EN_PBGT_FILTERING Cell Enable PBGT filtering EN_RESCUE_UM Cell Define the preferred layer in case of

emergency cause when the serving cell is a lower layer cell

FREEfactor_1-5 Cell Take into account the absolute number of free TCH in Order and Grade

FREElevel_1-4 Cell Boundaries for FREEfactor_1-5 HO_MARGIN(0,n) Neighborhood Threshold for cause 12.



relationship Used by PBGT filtering and Order processes. HO_MARGIN_LEV(0,n) Neighborhood

relationship Used by PBGT filtering and Order processes.

HO_MARGIN_QUAL(0,n) Neighborhood relationship

Used by PBGT filtering and Order processes.

LINKfactor(0,n) Neighborhood relationship

Order and Grade : used to give a fixed advantage to a neighbouring cell

LOADfactor_1-5 Cell Take into account the percentage of busy TCH in Grade

LOADlevel_1-4 Cell Boundaries for LOADfactor_1-5 PRIORITY(0,n) Neighborhood

relationship Used to give a level of priority to a cell or a layer.

RXLEVmin(n) Cell Minimum received level to make a handover TA_level_1-4 Cell Boundaries for DISTmargin_1-5



3.1.2 B6 parameters

The table below gives the new parameters in B6. Parameters listed in bold type are directly useful for the management of dual band mobiles.

Parameter Type Use

A_TRAFFIC_LOAD Cell Number of load samples used by the traffic evaluation process

CAPTURE_TRAFFIC_CONDITION Cell Load condition on the serving cell for the triggering of cause 24

DELTA_DEC_HO_margin Cell Value of -DELTA_HO_MARGIN(0,n) when Traffic_load(0) = high and Traffic_load(n) = low

DELTA_INC_HO_margin Cell Value of DELTA_HO_MARGIN(0,n) when Traffic_load(0) = low and Traffic_load(n) = high

EN_BETTER_ZONE_HO Cell Enable cause13 EN_BI-BAND_MS(n) Cell Used for the triggering of causes 14 and 24 :

enable / disable the incoming HO of dual band MS in a non-preferred band cell

EN_EXT_DR BSC Enable external DR EN_GENERAL_CAPTURE_HO Cell Enable / disable cause 24 EN_MULTIBAND_PBGT_HO Cell Enable / disable inter band PBGT HO (cause

12) EN_PRIORITY_ORDERING Cell Enable / disable the use of PRIORITY(0,n) EN_TRAFFIC_HO(0,n) Neighborhood

relationship Enable / disable cause 23 and the use of DELTA_HO_MARGIN(0,n) in cause 12

HIGH_TRAFFIC_LOAD Cell Threshold used by the traffic evaluation process

HO_MARGIN_DIST(0,n) Neighborhood relationship

Used in the PBGT filtering for distance causes 6 and 22

IND_TRAFFIC_LOAD Cell Threshold used by the traffic evaluation process

L_RXLEV_CPT_HO(0,n) Neighborhood relationship

Level threshold used for the triggering of capture HO causes 14, 21 and 24

L_TIME_ADVANCE Cell Distance threshold for cause 22 LOAD_EV_PERIOD Cell Number of samples used by the load

evaluation process LOW_TRAFFIC_LOAD Cell Threshold used by the traffic evaluation

process MULTIBAND_TRAFFIC_CONDITION Cell Load condition on the serving cell for the

triggering of cause 21 N_TRAFFIC_LOAD Cell Number of averages used by the traffic

evaluation process NEIGHBOUR_RXLEV(0,n) Neighborhood

relationship Triggering of cause 13

OFFSET_HO_MARGIN_INNER Cell Used in the inner zone of a concentric or multiband cell for the triggering of causes 12 and 23 and in the PBGT filtering

OUTDOOR_UMB_LEV(0,n) Neighborhood relationship

In case of emergency HO cause in a lower layer cell, the neighbouring umbrella cells received with a level lower than OUTDOOR_UMB_LEV(0,n) are discarded

RXLEV_LIMIT_PBGT_HO Cell Triggering of cause 12



TCH_INFO_PERIOD OMC read only Periodicity of the sending of the message « TCH usage information » to the TCU

ZONE_HO_HYST_DL Cell DL offset used for the triggering of cause 13 in a concentric or multiband cell

ZONE_HO_HYST_UL Cell UL offset used for the triggering of cause 13 in a concentric or multiband cell

The table below gives the removed parameters in B6 :

Parameter Type

CAUSE_MARGIN_P_X Cell CAUSE_MARGIN_G_X Cell TA_level_1-4 Cell DISTmargin_1-5 Cell



3.2 Default values of configuration independent parameters The tables below give the values of the parameters which are configuration independent.

The values of the parameters which are configuration dependent are given in part 3.3.

3.2.1 B5 parameters

Parameter Value Explanation

Neighbouring cells reporting and description MULTIBAND_REPORTING 3 MS shall report the 3 strongest cells, with

known and allowed NCC part of BSIC, in each of the frequency bands in the BA list, excluding the frequency band of the serving cell. Remaining positions in the measurement report shall be used for reporting of cells in the band of the serving cell. If there are still remaining positions, these shall be used to report the next strongest identified cells in the other bands irrespective of the band used

EN_INTERBAND_NEIGH Enable Enable sending of the list of neighbouring cells in each frequency band

Classmark handling BSS_SEND_CM_ENQUIRY 1 Classmark Enquiry in case of reception of a

Location Updating Request message with ES IND = 0

EN_SEND_CM3 1 Assumption : the MSC fully supports MAP version 2. MS CM3 is sent by the BSC.

STRIP_O5_CM2 0 Assumption : the MSC fully supports MAP version 2. No stripping of byte 5 of MS CM2.

Cell selection CELL_BAR_ACCESS 0 Normally, cells are not barred

Cell re-selection CELL_RESELECT_HYSTERESIS 3 = 6 dB C2 neighbouring cell > C2 serving cell + 6 dB

for cell re-selection in case of new location area

CELL_RESELECT_PARAM_IND 1 Sending of C2 parameters

Better condition handovers D_BRO_TIM 5 s LOAD_EV_PERIOD 12 samples

A new value of the average load of a cell is calculated every one minute

EN_SPEED_DISC Disable The speed discrimination process is too much complicated

H_MIN_DWELL_TIME L_MIN_DWELL_TIME

Use of a fixed MIN_DWELL_TIME

DWELL_TIME_STEP 0 s Use of a fixed MIN_DWELL_TIME L_LOAD_OBJ 0 % Use of a fixed MIN_DWELL_TIME H_LOAD_OBJ 100 % Use of a fixed MIN_DWELL_TIME

Candidate cell evaluation process EN_LOAD_ORDER Enable Use of FREEfactor and LOADfactor in the

formulas FREElevel_1-4 ? FREEfactor_1-5 0 dB Load is not taken into account LOADlevel_1-4 ?



LOADfactor_1-5 0 dB Load is not taken into account TA_level_1-4 ? DISTmargin_1-5 0 dB Distance is not taken into account

3.2.2 B6 parameters

Remark : the parameters listed in the table below are new in B6.

Parameter Value Explanation

A_TRAFFIC_LOAD 1-2 TRX : 4 3-4 TRX : 8 > 4 TRX : 12

The idea is that A_TRAFFIC_LOAD * N_TRAFFIC_LOAD is constant whatever the number of TRX. The values were determined by the technical department.

CAPTURE_TRAFFIC_CONDITION ANY_LOAD Tuning is obviously possible DELTA_DEC_HO_margin 5 dB Fine tuning required on the field DELTA_INC_HO_margin 5 dB Fine tuning required on the field EN_BETTER_ZONE_HO Enable EN_EXT_DR ? The value is MSC dependent EN_PRIORITY_ORDERING Enable Use of PRIORITY(0,n) like in B5 EN_TRAFFIC_HO(0,n) Disable No variation of HO_MARGIN(0,n)

according to the load of serving and neighbouring cells by default because fine tuning is necessary

HIGH_TRAFFIC_LOAD 1-2 TRX : 70 %> 2 TRX : 80 %

The values were determined by the technical department.

IND_TRAFFIC_LOAD 1-2 TRX : 45 %> 2 TRX : 60 %

The values were determined by the technical department.

L_RXLEV_CPT_HO(0,n) -85 dBm Tuning is obviously possible LOAD_EV_PERIOD 12 samples The value was determined by the technical

department. LOW_TRAFFIC_LOAD 1-2 TRX : 20 %

> 2 TRX : 50 %The values were determined by the technical department.

MULTIBAND_TRAFFIC_CONDITION ANY_LOAD Tuning is obviously possible N_TRAFFIC_LOAD 1-2 TRX : 6

3-4 TRX : 3 > 4 TRX : 2

The idea is that A_TRAFFIC_LOAD * N_TRAFFIC_LOAD is constant whatever the number of TRX. The values were determined by the technical department.

NEIGHBOUR_RXLEV(0,n) -47 dBm The level of the neighbouring cell is not taken into account for the triggering of cause 13

OFFSET_HO_MARGIN_INNER 0 dB +/- 10 dB

0 dB for a concentric cell +10 dB if 900 outer zone and 1800 inner zone -10 dB if 1800 outer zone and 900 inner zone Assumption : difference in propagation losses between 900 and 1800 is 10 dB

OUTDOOR_UMB_LEV(0,n) -88 dBm Tuning is obviously possible RXLEV_LIMIT_PBGT_HO -47 dBm This parameter is used for fine tuning only

(triggering of cause 12) TCH_INFO_PERIOD 5 s OMC-R read only



ZONE_HO_HYST_DL 6 dB +16 / -4 dB


ZONE_HO_HYST_UL 6 dB +16 / -4 dB




3.3 Multiband BSC configurations

3.3.1 Introduction

The amount of imaginable configurations is very elevated. The aim of this part is not to deal with all these possible configurations but only to give guide lines. Then the reader should be able to properly define the parameters for his special case.

Before starting with the main configurations, let us list all the possibilities.

First, the dual band network may be a new network or an old one. Then, in the second case, the existing network may be a 900 MHz or a 1800 MHz one.

Now, let us take the case of an existing 900 MHz network. We can first imagine a dual layer network with addition of 1800 MHz macro cells. These 1800 MHz macro cells may be co-located with the 900 MHz one but it is possible to have two independent layers. The first case (co-location) seems to be more sensible to reduce expenditures. For each case (co-location or not), 1800 MHz macro cells may be added as hot spots (in order to catch traffic in a well defined area) or provide a continuous coverage. Finally, for the last case, it seems sensible to distinguish (like for micro cells) cells which are located at the center of the 1800 MHz area from cells located at the border.

In the case of an existing 900 MHz network, the second step is to imagine a network with 3 or 4 layers and with different level of priorities (for example micro 900 > macro 1800 or macro 1800 > micro 900) for the traffic distribution :

- macro 900 + macro 1800 + micro 900,


- macro 900 + macro 1800 + micro 900 + micro 1800.

Again, it is necessary to distinguish two cases : continuous coverage provided by the 1800 MHz macro cells or not (in order to define the preferred layer in case of emergency handover on a micro cell).

The picture below summarizes all the possibilities :

New dual band network

Existing network

900 MHz

1800 MHz

Macro 1800 co-located

Macro 1800 not co-locatedHot spot

Continuous coverage

+ micro 900+ micro 1800+ micro 900 and 1800



We will study hereafter following configurations :

- macro 900 + macro 1800,

- macro 900 + micro 900 + macro 1800,


- macro 900 + micro 900 + macro 1800 + micro 1800.

In each case, we make the assumption that the network is an existing 900 MHz network and that 1800 macro cells are co-located with 900 macro cells.

Each configuration is described in the same way :

- idle mode,

- call set-up,

- cell administration,

- better condition handovers,

- candidate cell evaluation process.



3.3.2 Existing 900 MHz network and addition of 1800 MHz macro cells

3.3.2.1 Use of the B5 release

3.3.2.1.1 Idle mode

It is important to direct dual band MS to the desired layer not only in dedicated mode but also in idle mode.

For cell selection it is possible to give a higher priority to the macro 1800 layer using the parameter CELL_BAR_QUALIFY :

- CELL_BAR_QUALIFY = 0 for macro 1800 cells,

- CELL_BAR_QUALIFY = 1 for macro 900 cells.

Important remarks :

- this parameter interacts with the parameter CELL_BAR_ACCESS. Consequently, it is not possible to use CELL_BAR_QUALIFY = 1 when CELL_BAR_ACCESS = 1 (otherwise the cell is no more barred),

- it seems that some mobiles are not able to handle properly the selection process when the parameter CELL_BAR_QUALIFY is set to 1. Therefore, the solution described above is not used on the field.

For cell re-selection, using the C2 criterion it is possible to give a higher priority to the macro 1800 layer :

Cell RXLEV_ACCESS_MIN CELL_RESELECT

_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 - 100 dBm 0 dB 0 dB 20 s

Macro 1800 - 100 dBm 14 dB 0 dB 20 s

With these values, C2 =

- C1 for macro 900 cells,

- C1 + 14 dB for macro 1800 cells.

Remarks :

- it is not a good idea to use high values (126 dB for example) for the parameter CELL_RESELECT_OFFSET. Indeed, if such values are used, we can imagine a situation where the MS re-selects a 1800 cell (C2(1800) >> C2(900)) received with a level just higher than RXLEV_ACCESS_MIN. Then the risk is to trigger an emergency alarm on the 1800 cell just after the beginning of the call. Here the idea is to compensate for the difference in propagation losses between the two band (assumption : 10 dB) and to add a little offset (4 dB).



- do not forget to take into account the difference between the values of RXLEV_ACCESS_MIN for macro 900 and 1800 cells in order to obtain the desired offset between the two layers,

- an absolute priority of the 1800 layer can also be obtained by only providing 1800 neighbouring cells to monitor when MS camp on 1800 cells. In this case MS leave the 1800 layer only if they lose the 1800 coverage.

3.3.2.1.2 Call set-up

The picture below gives the parameters for Directed and Forced Directed Retry.

Here it is possible to make a SDCCH -> TCH handover on Forced Directed Retry between two 900 cells or two 1800 cells. Normally, this situation only occurs when the mobile is located at the border of the cell. Then there is a risk of interferences because the TCH is not necessarily allocated in the best cell from the radio point of view. Indeed, if the neighbouring cell is received with a level higher than L_RXLEV_NCELL_DR(n) (default value = -85 dBm) Forced Directed Retry is triggered. If interference problems occur then the solution is to disable Forced Directed Retry on the macro 900 layer and to set L_RXLEV_NCELL_DR(n) to -47 dBm on the macro 1800 layer. Then Forced DR is only possible from a 1800 cell towards a 900 cell.

In order to define the priority of each layer (if cause 20 is triggered by a macro 900 cell and a macro 1800 cell at the same time) it could be necessary to use the parameter PRIORITY(0,n). Be careful because the parameter PRIORITY(0,n) has also an impact on the traffic flow in case of emergency handover. We will discuss this topic below. Nevertheless, the default behaviour (PRIORITY(0,n) = 1 for all the neighborhood relationships) is to give a higher priority to neighbouring cells working in the same frequency band than the serving cell. It is only in the case where the operator wants to modify this default behaviour that it is necessary to use the parameter PRIORITY(0,n).

3.3.2.1.3 Cell administration

macro 900

EN_DR = EnableEN_FORCED_DR = EnableL_RXLEV_NCELL_DR(n) = -85 dBmFREElevel_DR(n) = 2 if 1 TRX, 4 otherwise

macro 1800

EN_DR = EnableEN_FORCED_DR = EnableL_RXLEV_NCELL_DR(n) = -85 dBmFREElevel_DR(n) = 2 if 1 TRX, 4 otherwiseCause 20

Cause 20

Cause 20



There are 3 possibilities :

- macro 900 = umbrella cell and macro 1800 = umbrella cell,

- macro 900 = single cell and macro 1800 = single cell,

- macro 900 = umbrella cell and macro 1800 = mini cell.

The first two solutions offer the same possibilities : use of cause 21 for inter-band handovers and same behaviour in case of emergency handover and Forced Directed Retry. The third solution offers more flexibility : use of cause 21 or 14 for inter-band handovers, distinct behaviour in case of Forced Directed Retry and emergency handover.

3.3.2.1.4 Better condition handovers

The pictures below give the parameters for better condition handovers :

Remark : MULTIBAND_LOAD_LEVEL = 0% in order to send dual band MS to the macro 1800 layer whatever the load of the macro 900 serving cell.

macro 900umbrella or single

MULTIBAND_LOAD_LEVEL = 0%A_PBGT_HO = 8 (urban)


L_RXLEV_CPT_HO(n) = -85 dBmA_PBGT_HO = 8 (urban)

Cause 12

Cause 12

Cause 21

BSS parameters :

PREFERRED_BAND = 1800

HO_MARGIN(0,n) = 5dB




Remark : it is necessary to choose between causes 21 and 14. Cause 14 is interesting only in the case of a hot spot macro 1800 if there is a problem with fast mobiles.

3.3.2.1.5 Candidate cell evaluation process

The picture below gives the parameters for the candidate cell evaluation process.

At call set-up, if a macro 900 serving cell is congested, it is necessary to send dual band MS to the macro 1800 layer. For a macro 1800 serving cell, it is better to send dual band MS to the macro 900 layer in order to avoid interferences (with Forced Directed Retry, the target cell is not the best one from the radio point of view). That is why PRIORITY(0,n) =

- 1 between a macro 900 cell and a macro 900 cell,



- 0 between a macro 1800 cell and a macro 900 cell.

In case of emergency alarm on a macro 900 cell it is sensible to try first to find a solution in the macro 900 layer then in the macro 1800 layer. In case of emergency alarm on a macro 1800 cell it is sensible (mandatory for a hot spot) to send dual band MS to the macro 900 layer.

If macro 900 and 1800 cells are umbrella cells or single cells, in case of emergency alarm, the preferred layer is upper + single. Then using the values of PRIORITY(0,n) defined above, in case of emergency alarm on a macro 900 cell dual band MS are sent preferably to the macro 1800 layer. That is why the configuration with macro 900 umbrella cells and macro 1800 mini cells is better (it is possible to have a distinct behaviour in case of emergency alarm and in case of Forced DR).

macro 900umbrella

MULTIBAND_LOAD_LEVEL = 0%EN_SPEED_DISC = DisableA_PBGT_HO = 8 (urban)

macro 1800mini

L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 8 (urban)

Cause 12

Cause 12

Cause 21

BSS parameters :

PREFERRED_BAND = 1800L_MIN_DWELL_TIME = ? s


Cause 14




Remarks :

- HO_MARGIN_XX(0,n) = -127 dB between a macro 1800 cell and a macro 900 cell in order to disable the PBGT filtering (the macro 900 layer is seen as a rescue layer),

- it is interesting to enable the PBGT filtering which offers a great flexibility. It is always possible to disable it on a per neighborhood relationship basis using HO_MARGIN_XX(0,n) = -127 dB,

- with EN_RESCUE_UM = Indefinite, the preferred layer in case of emergency alarm is none. In order to stay on the macro 1800 layer in case of emergency handover, it is necessary to use EN_RESCUE_UM = Disable (then the preferred layer is lower).

macro 900umbrella

EN_PBGT_FILTERING = EnableCELL_EV = GRADERXLEVmin(n) = -100 dBm

macro 1800mini

EN_RESCUE_UM = Indefinite or EnableEN_PBGT_FILTERING = EnableCELL_EV = GRADERXLEVmin(n) = -100 dBm

PRIORITY(0,n) = 1HO_MARGIN(0,n) = 5dBHO_MARGIN_LEV(0,n) = 5dBHO_MARGIN_QUAL(0,n) = 5dB

PRIORITY(0,n) = 0HO_MARGIN(0,n) = -127 dBHO_MARGIN_LEV(0,n) = -127 dBHO_MARGIN_QUAL(0,n) = -127 dB






The idea is to show the new possibilities offered by the B6 release.

3.3.2.2.1 Idle mode

There is no modification compared to B5 release in the way to set the parameters.


The SDCCH -> TCH handover between two cells connected to two different BSC is fully available in B6 release provided that the MSC is able to handle inter-BSC Directed Retry.

On the other hand, there is no modification compared to B5 release in the way to set the parameters.


There is no modification compared to B5 release in the way to set the parameters. Moreover, the configuration with 900 umbrella cells and 1800 mini cells is strongly advisable.


As for better condition handovers, B6 release brings a lot of new possibilities.

For the handovers between 900 cells and the handovers between 1800 cells, it is possible to take into account the load of the serving and the neighbouring cells :

- if the serving cell is not loaded and the neighbouring cell is loaded, it is possible to add a positive offset to the parameter HO_MARGIN(0,n) used by cause 12 in order to delay the PBGT handover,

- if the serving cell is loaded and the neighbouring cell is not loaded, it is possible to add a negative offset to the parameter HO_MARGIN(0,n) used by cause 23 in order to accelerate the PBGT handover.

It seems interesting to use this new possibility. The problem is that it is difficult to give default sensible values for the parameters DELTA_DEC_HO_margin and DELTA_INC_HO_margin and also for the parameters related to the traffic and load evaluation processes.

For the handovers from 900 cells towards 1800 cells (use of cause 21 or cause 14), the capture threshold (L_RXLEV_CPT_HO(0,n)) is now set on a per couple of cells basis.

If cause 21 is used, an interesting feature is that this cause is not triggered if the load of the preferred band neighbouring cell is high. On the other hand, the way to take into account the load of the serving cell is different.

The pictures below give the parameters for better condition handovers.



Use of 1800 umbrella or single cells :

Use of 1800 mini cells :

Remark : it is necessary to choose between causes 21 and 14. Cause 14 is interesting only in the case of a hot spot macro 1800 if there is a problem with fast mobiles.


MULTIBAND_TRAFFIC_CONDITION = ANY_LOADDELTA_DEC_HO_margin = 5 dBDELTA_INC_HO_margin = 5 dB


DELTA_DEC_HO_margin = 5 dBDELTA_INC_HO_margin = 5 dB

Causes 12 and possibly 23


Cause 21L_RXLEV_CPT_HO(0,n) = -85 dBm

BSS parameters :

PREFERRED_BAND = 1800

HO_MARGIN(0,n) = 5dBEN_TRAFFIC_HO(0,n) = disable


macro 900umbrella

MULTIBAND_TRAFFIC_CONDITION = ANY_LOADEN_SPEED_DISC = DisableDELTA_DEC_HO_margin = 5 dBDELTA_INC_HO_margin = 5 dB

macro 1800mini

EN_SPEED_DISC = DisableDELTA_DEC_HO_margin = 5 dBDELTA_INC_HO_margin = 5 dB




BSS parameters :

PREFERRED_BAND = 1800L_MIN_DWELL_TIME = ? s







It is necessary to rethink the way to set the parameters related to the candidate cell evaluation process. The first reason is that the handover detection process has not the same behaviour. For example, if cause 21 is verified, cause 12 is also checked and it is possible to have in the candidate cells list a macro 1800 cell (cause 21) and a macro 900 cell (cause 12 or 23) if the serving cell is a macro 900 cell. The second reason is that after the triggering of a better condition handover cause (except cause 20) candidate cells are no more sorted according to their frequency band. Therefore, it is important to rethink the way to define the level of priority of each layer.

The pictures below give the parameters for the candidate cell evaluation process.

Remarks :

- we propose to use the value 1 as default value for the parameter PRIORITY(0,n) in order to give easily a higher level of priority to a cell,

- the parameters Cause_Margin_P_X are removed in B6 release. Therefore, it is necessary to modify the parameters HO_MARGIN_XX(0,n) to have the same behaviour than in B5 release.

Use of 1800 umbrella or single cells :

The first idea is to set PRIORITY(0,n) = 0 between a macro 900 cell and a macro 1800 cell and PRIORITY(0,n) = 1 between two macro 900 cells in order to give a higher priority to the macro 1800 layer if causes 21 and 12 are triggered at the same time (this situation is only possible at the border of the 900 cell). The problem with these values is that in case of emergency handover, a higher priority is also given to the macro 1800 layer which is not


EN_PRIORITY_ORDERING = EnableEN_PBGT_FILTERING = EnableCELL_EV = GRADE



PRIORITY(0,n) = 1HO_MARGIN(0,n) = 5 dBHO_MARGIN_LEV(0,n) = 2 dBHO_MARGIN_QUAL(0,n) = 1 dBHO_MARGIN_DIST(0,n) = 2 dB

PRIORITY(0,n) = 0HO_MARGIN(0,n) = -127 dBHO_MARGIN_LEV(0,n) = -127 dBHO_MARGIN_QUAL(0,n) = -127 dBHO_MARGIN_DIST(0,n) = -127 dB





satisfactory. Therefore, the parameter PRIORITY(0,n) is set to 1 towards all the neighbouring cells of a macro 900 cell. In case of emergency cause, a higher priority is given to the 900 layer because of the use of the frequency band in the candidate cell evaluation process. On the other hand, if causes 21 and 12 are verified at the same time, no fixed or pre-defined priority is given to each layer (same PRIORITY(0,n) and the frequency band of the serving cell is not taken into account). Therefore, the target cell (macro 1800 or macro 900) will be the cell with the highest GRADE(n). In order to give a fixed priority to each layer (higher priority to the 1800 layer) it is possible to use the parameter LINKfactor(0,n). It is obvious that this behaviour is a little bit unsatisfactory.

Use of 1800 mini cells :

In case of emergency cause in a macro 900 cell, a higher priority is given to the 900 layer because Pref layer = upper + single (macro 1800 cells are lower layer cells). On the other hand, if causes 21 and 12 are verified at the same time, a higher priority is given to the 1800 layer thanks to the use of the parameter PRIORITY(0,n).

The problem encountered with macro 1800 umbrella or single cells is solved. It is therefore recommended to use this configuration for a dual layer dual band network.

macro 900umbrella


macro 1800mini

EN_RESCUE_UM = Indefinite or EnableEN_PRIORITY_ORDERING = EnableEN_PBGT_FILTERING = EnableCELL_EV = GRADE


PRIORITY(0,n) = 0HO_MARGIN(0,n) = -127 dBHO_MARGIN_LEV(0,n) = -127 dBHO_MARGIN_QUAL(0,n) = -127 dBHO_MARGIN_DIST(0,n) = -127 dB





3.3.3 Existing 900 MHz network with micro cells and addition of 1800 macro cells


This configuration was tested in Toulouse (May 1998) during the dual band field trial with France Telecom Mobiles.

3.3.3.1.1 Idle mode




- CELL_BAR_QUALIFY = 1 for macro and micro 900 cells.

Important remarks :

- this parameter interacts with the parameter CELL_BAR_ACCESS. Consequently, it is not possible to use CELL_BAR_QUALIFY = 1 when CELL_BAR_ACCESS = 1 (otherwise the cell is no more barred),


For cell re-selection, using the C2 criterion it is possible to give a higher priority to the macro 1800 layer or the micro 900 layer.

The table below gives a set of parameters (it is only an example) in order to give a higher priority to the micro 900 layer for slow mobiles only. This set of parameters is intended for corporate micro cells (indoor coverage).


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 - 100 dBm 0 dB 0 dB 20 s

Macro 1800 - 100 dBm 14 dB 0 dB 20 s

Micro 900 - 100 dBm 18 dB 60 dB 20 s

With these values C2 =


- C1 + 14 dB for macro 1800 cells,

- C1 + 18 dB for a micro 900 serving cell or a micro 900 neighbouring cell after 20 s of monitoring ; C1 - 42 dB otherwise.



The table below gives a set of parameters (it is only an example) in order to give a higher priority to the macro 1800 layer. This set of parameters is intended for public micro cells (outdoor coverage).


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 - 100 dBm 0 dB 0 dB 20 s

Macro 1800 - 100 dBm 18 dB 0 dB 20 s

Micro 900 - 100 dBm 14 dB 60 dB 20 s




- C1 + 14 dB for a micro 900 serving cell or a micro 900 neighbouring cell after 20 s of monitoring ; C1 – 46 dB otherwise.


For this kind of network the macro 900 cells must be umbrella cells (cause 14 is used between macro and micro 900 cells). It is not recommended to define macro 1800 cells as mini cells because then, there is no better condition handover cause between macro 1800 and micro 900 cells. Consequently, following profiles are used :

- macro 900 and 1800 cells : umbrella cells,

- micro 900 cells : micro cells.


The picture below gives the parameters for Directed and Forced Directed Retry :



The main idea is here to avoid to send fast mobiles towards the micro 900 layer on cause 20 (no speed discrimination). That is why L_RXLEV_NCELL_DR(n) = -47 dBm for micro 900 cells. Different levels of priority are obtained using the parameter PRIORITY(0,n) (see below) if the operator wants to modify the default behaviour (higher priority for neighbouring cells working in the same frequency band than the serving cell).

Here it is possible to make a SDCCH -> TCH handover on Forced Directed Retry between two 900 cells or two 1800 cells. Normally, this situation only occurs when the mobile is located at the border of the cell. Then there is a risk of interferences because the TCH is not necessarily allocated in the best cell from the radio point of view. Indeed, if the neighbouring cell is received with a level higher than L_RXLEV_NCELL_DR(n) (default value = -85 dBm) Forced Directed Retry is triggered.


The pictures below give the parameters for better condition causes.

With the first picture, the idea is to give a higher priority to the macro 1800 layer. This solution is intended for a network with public micro cells (outdoor coverage). It is necessary to send dual band mobiles to the new macro 1800 layer.

Macro 900


Macro 1800


Micro 900


Cause 20

Cause 20

Cause 20



It is also possible to give a higher priority to the micro 900 layer (see picture below). This solution is normally intended for corporate (indoor coverage) micro cells (these cells work in the old frequency band but have a higher priority because they are dedicated to the coverage of a building with special agreement between the operator and the owner of the building). Because a real network is made up of public and corporate micro cells it is necessary to use a special set of parameters for macro 1800 cells (see part 4 : Capture threshold set on a per cell basis).

Macro 900Cell_dimension_type = macroCell_layer_type = upper




Micro 900Cell_dimension_type = microCell_layer_type = lower

MULTIBAND_LOAD_LEVEL = 0%L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 6

Cause 21

Cause 14

Cause 12

Cause 12

Cause 12

Cause 21

BSS parameters :

PREFERRED_BAND = 1800L_MIN_DWELL_TIME = 8 s






Remark : the value for the capture threshold of the micro cells is only an example. It is necessary to tune this parameter according to the type of the micro cell : hot spot, micro cell located at the center or the border of a continuous micro area. Please refer to [3].



We propose to use the value 1 as default value for the parameter PRIORITY(0,n) in order to give easily a higher level of priority to a cell.

In case of emergency alarm a higher priority is given to the macro 900 layer : handover from a micro 900 cell or a macro 1800 cell towards the macro 900 layer. It is obviously possible (with the parameter PRIORITY(0,n)) to decide to give a higher priority to the macro 1800 layer (if the coverage provided by this layer is good enough) : handover from a micro 900 cell or a macro 1800 cell towards a macro 1800 cell.

The behaviour is unfortunately the same for call set-up. For example, if a micro 900 cell is congested and cause 20 is triggered at the same time by a macro 900 cell and a macro 1800 cell, a higher priority is given to the macro 900 cell.

Remarks :

- HO_MARGIN_XX(0,n) = -127 dB between a macro 1800 cell and a macro 900 cell in order to disable the PBGT filtering because the macro 900 layer is a rescue layer,




L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 8 (urban


L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 6

Cause 21

Cause 14

Cause 12

Cause 12

Cause 12

BSS parameters :







- EN_PBGT_FILTERING = Disable and CELL_EV = Order for micro cells because no filtering is generally used on micro cells,

- with EN_RESCUE_UM = Enable, the preferred layer is upper in case of emergency alarm on a micro cell.

PRIORITY(0,n) = 1HO_MARGIN_XX(0,n) = 5 dB

Macro 900


Macro 1800


Micro 900

EN_RESCUE_UM = EnableEN_PBGT_FILTERING = DisableCELL_EV = ORDERRXLEVmin(n) = -100 dBm






PRIORITY(0,n) = 0HO_MARGIN_XX(0,n) = -127 dB






The idea is to show the new possibilities offered by the B6 release.

3.3.3.2.1 Idle mode








The picture below gives the parameters for better condition handovers.

We propose to activate cause 14 in the 1800 layer and cause 21 in the micro layer. Cause 14 is used to make handovers towards a high priority micro cell (micro cell dedicated to the indoor coverage of a company for example). In order to inhibit cause 14 towards low priority micro cells (outdoor coverage) we propose to use the capture threshold (-47 dBm) which is set on a per couple of cells basis. Moreover, cause 21 will be used to make handovers from a

Macro 900Umbrella


Macro 1800Umbrella


Micro 900Micro







BSS parameters :








low priority micro cell towards the 1800 layer. In order to inhibit cause 21 from a high priority micro cell we propose again the use of the capture threshold (-47 dBm).



Remarks :



If the serving cell is a 900 micro cell we have the following levels of priority :

- in case of emergency : macro 900 > macro 1800 > micro 900,

- in case of Forced Directed Retry : macro 900 > macro 1800,

- in case of better condition HO cause (theoretical case where causes 21 and 12 are triggered at the same time) : macro 1800 > micro 900.

Macro 900Umbrella


Macro 1800Umbrella


Micro 900Micro

EN_RESCUE_UM = EnableEN_PRIORITY_ORDERING = EnableEN_PBGT_FILTERING = DisableCELL_EV = ORDER








PRIORITY(0,n) = 2 or 0HO_MARGIN(0,n) = 5 dBHO_MARGIN_LEV(0,n) = 2 dBHO_MARGIN_QUAL(0,n) = 1 dBHO_MARGIN_DIST(0,n) = 2 dB



If the serving cell is a 900 macro cell we have the following levels of priority :



- in case of better condition HO cause (theoretical case where causes 21, 14 and 12 are triggered at the same time) : micro 900 > macro 900 = macro 1800 (PRIORITY(0,n) = 0) or macro 900 = macro 1800 > micro 900 (PRIORITY(0,n) = 2).




- in case of better condition HO cause (theoretical case where causes 14 and 12 are triggered at the same time) : micro 900 > macro 1800.



3.3.4 Existing 900 MHz network and addition of 1800 macro and micro cells


This configuration was tested in Johannesburg (October 1998) during the dual band field trial with Vodacom.

3.3.4.1.1 Idle mode




- CELL_BAR_QUALIFY = 1 for macro 900 and micro 1800 cells.

CELL_BAR_QUALIFY = 1 for micro 1800 cells (low priority for cell selection) because there is no speed discrimination with the C1 criterion.

Important remarks :

- CELL_BAR_QUALIFY interacts with CELL_BAR_ACCESS. Consequently, it is not possible to use CELL_BAR_QUALIFY = 1 when CELL_BAR_ACCESS = 1 (otherwise the cell is no more barred),


For cell re-selection, using the C2 criterion it is possible to give a higher priority to the macro 1800 layer or the micro 1800 layer.

The table below gives a set of parameters (it is only an example) in order to give a higher priority to the micro 1800 layer for slow mobiles only.


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 -100 dBm 0 dB 0 dB 20 s

Macro 1800 -100 dBm 14 dB 0 dB 20 s

Micro 1800 -100 dBm 18 dB 60 dB 20 s






- C1 + 18 dB for a micro 1800 serving cell or a micro 1800 neighbouring cell after 20 s of monitoring; C1 - 42 dB otherwise.

The table below gives a set of parameters (it is only an example) in order to give a higher priority to the macro 1800 layer.


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 - 100 dBm 0 dB 0 dB 20 s

Macro 1800 - 100 dBm 18 dB 0 dB 20 s

Micro 1800 - 100 dBm 14 dB 60 dB 20 s




- C1 + 14 dB for a micro 1800 serving cell or a micro 1800 neighbouring cell after 20 s of monitoring; C1 – 46 dB otherwise.


It is not recommended to define macro 1800 cells as mini cells because then, there is only cause 12 (no speed discrimination) between macro 1800 and micro 1800 cells as better condition cause. Consequently, following profiles are used :


- micro 1800 cells : micro cells.


The picture below gives the parameters for Directed Retry and Forced Directed Retry. The main idea is to avoid to send fast mobiles to the micro 1800 layer on cause 20 (no speed discrimination). That is why the level threshold used by cause 20 is equal to -47 dBm. Different levels of priority are obtained using the parameter PRIORITY(0,n) if the operator wants to modify the default behaviour (higher priority for neighbouring cells working in the same frequency band than the serving cell).




The figure below gives the parameters used for better condition handovers.

In order to avoid a handover on cause 21 (no speed discrimination) towards a micro 1800 cell when the serving cell is a macro 900 cell, it is necessary to modify following parameters :

- Cause_Margin_P_21 = 60 dB for macro 900 cells,

- HO_MARGIN(0,n) = -127 dB between a macro 900 cell and a macro 1800 cell (no filtering),

- HO_MARGIN(0,n) = 5 dB between a macro 900 cell and a micro 1800 cell (filtering).

The problem with this solution is the case where cause 21 is only triggered by a micro 1800 cell. This cell is filtered but it is not possible to make a handover towards the micro cell using cause 14 (cause 14 is not checked).

Macro 900


Macro 1800


Micro 1800


Cause 20

Cause 20

Cause 20




The figure below gives the parameters for the candidate cell evaluation process. In case of emergency alarm a higher priority is given to the macro 900 layer. It is obviously possible (using the parameter PRIORITY(0,n)) to make the choice to give a higher priority to the macro 1800 layer if its coverage is good enough.

The behaviour is unfortunately the same for Forced Directed Retry :

- if a micro 1800 cell is congested and cause 20 is triggered by a macro 900 cell and a macro 1800 cell at the same time, a higher priority is given to the macro 900 layer,

- if a macro 1800 cell is congested and cause 20 is triggered by a macro 900 cell and a macro 1800 cell at the same time, a higher priority is given to the macro 900 layer,

- if a macro 900 cell is congested and cause 20 is triggered by a macro 900 cell and a macro 1800 cell at the same time, a higher priority is given to the macro 900 layer.






L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 6

Cause 21

Cause 14

Cause 12

Cause 12

Cause 12

BSS parameters :







Macro 900


Macro 1800


Micro 1800

EN_RESCUE_UM = EnableEN_PBGT_FILTERING = DisableCELL_EV = ORDERRXLEVmin(n) = -100 dBm













3.3.4.2.1 Idle mode








The picture below shows the parameters for better condition handover causes :

Remark : when the serving cell is a 900 macro cell, cause 21 is checked towards 1800 micro cells (no speed discrimination !). Unlike B5 release, cause 14 is also checked. If causes 21 and 14 are triggered at the same time by a 1800 micro cell, cause 14 is masked by cause 21 because only one cause number (here 21) is sent to the candidate cell evaluation process. On the other hand, it is not possible to filter the 1800 micro cell using the PBGT filtering because the PBGT filtering is no more used after the triggering of a better condition cause. Therefore it is still not possible to manage properly a network with 1800 macro and micro cells in B6 release.

Macro 900Umbrella


Macro 1800Umbrella


Micro 1800Micro







BSS parameters :









Remarks :





- in case of Forced Directed Retry : macro 900 > macro 1800.




- in case of better condition HO cause (theoretical case where causes 21, 14 and 12 are triggered at the same time) : micro 1800 > macro 900 = macro 1800 (PRIORITY(0,n) = 0) or macro 900 = macro 1800 > micro 1800 (PRIORITY(0,n) = 2).

Macro 900Umbrella


Macro 1800Umbrella


Micro 1800Micro

EN_RESCUE_UM = EnableEN_PRIORITY_ORDERING = EnableEN_PBGT_FILTERING = DisableCELL_EV = ORDER








PRIORITY(0,n) = 0 or 2HO_MARGIN(0,n) = 5 dBHO_MARGIN_LEV(0,n) = 2 dBHO_MARGIN_QUAL(0,n) = 1 dBHO_MARGIN_DIST(0,n) = 2 dB







- in case of better condition HO cause (theoretical case where causes 14 and 12 are triggered at the same time) : micro 1800 > macro 1800.



3.3.5 Existing 900 MHz network with micro cells and addition of 1800 macro and micro cells


3.3.5.1.1 Idle mode




- CELL_BAR_QUALIFY = 1 for macro 900, micro 900 and micro 1800 cells.

CELL_BAR_QUALIFY = 1 for micro cells (low priority for cell selection) because there is no speed discrimination with the C1 criterion.

Important remarks :

- CELL_BAR_QUALIFY interacts with CELL_BAR_ACCESS. Consequently, it is not possible to use CELL_BAR_QUALIFY = 1 when CELL_BAR_ACCESS = 1 (otherwise the cell is no more barred),


For cell re-selection, using the C2 criterion it is possible to give a higher priority to the macro 1800 layer or the micro layers.

The table below gives a set of parameters (it is only an example) in order to give a higher priority to the micro 900/1800 layers for slow mobiles only.


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 - 100 dBm 0 dB 0 dB 20 s

Macro 1800 - 100 dBm 14 dB 0 dB 20 s

Micro 900 - 100 dBm 18 dB 60 dB 20 s

Micro 1800 - 100 dBm 18 dB 60 dB 20 s






- C1 + 18 dB for a micro 900/1800 serving cell or a micro 900/1800 neighbouring cell after 20 s of monitoring; C1 - 42 dB otherwise.

The table below gives a set of parameters (it is only an example) in order to give a higher priority to the macro 1800 layer.


_OFFSET

TEMPORARY

_OFFSET

PENALTY

_TIME

Macro 900 -100 dBm 0 dB 0 dB 20 s

Macro 1800 -100 dBm 18 dB 0 dB 20 s

Micro 900 -100 dBm 14 dB 60 dB 20 s

Micro 1800 -100 dBm 14 dB 60 dB 20 s




- C1 + 14 dB for a micro 900/1800 serving cell or a micro 900/1800 neighbouring cell after 20 s of monitoring; C1 - 46 dB otherwise.


For this kind of network the macro 900 cells must be umbrella cells (cause 14 is used between macro and micro 900 cells). It is not recommended to define macro 1800 cells as mini cells because then, there is no better condition handover cause between macro 1800 and micro 900 cells. Consequently, following profiles are used :


- micro 900 and 1800 cells : micro cells.


The picture below gives the parameters for Directed Retry and Forced Directed Retry :



The main idea is to avoid a handover on cause 20 towards a micro cell (speed is not taken into account). The solution is to use L_RXLEV_NCELL_DR(n) = -47 dBm for micro cells.


The picture below gives the parameters for better condition causes.

According to the type of micro 900 cell (public or corporate) it is necessary to enable (public = outdoor coverage) or not (corporate = indoor coverage) cause 21 on micro 900 cells. In order to avoid handovers on cause 14 between a macro 1800 cell and a public micro 900 cell, it is necessary to modify the parameter Cause_Margin_P_14 on macro 1800 cells and to play with the parameter HO_MARGIN(0,n) (see 4.2).

In order to avoid handovers on cause 21 towards a micro 1800 cell, it is necessary to modify the parameter Cause_Margin_P_21 on macro and micro 900 cells and to play with the parameter HO_MARGIN(0,n) (see 6.2).

Macro 900


Macro 1800


Micro 900 and 1800


Cause 20

Cause 20

Cause 20 Cause 20




The table below gives the parameters for the candidate cell evaluation process (PRIORITY(0,n), HO_MARGIN(0,n), HO_MARGIN_LEV(0,n), HO_MARGIN_QUAL(0,n)) :

Neighbouring cell

Serving cell

Macro 900 Macro 1800 Micro 900 Micro 1800

Macro 900 1, 5, 5, 5 1, -127, 5, 5 1, 5, 5, 5 0, 5, 5, 5

Macro 1800 0, -127, -127, -127 1, 5, 5, 5 1, 5, 5, 5 1, 5, 5, 5

Micro 900 1, 5, 5, 5 1, 5, 5, 5 1, 5, 5, 5 1, 5, 5, 5

Micro 1800 0, 5, 5, 5 1, 5, 5, 5 1, 5, 5, 5 1, 5, 5, 5

Remarks :


- if cause 14 is triggered by a micro 900 cell and a micro 1800 cell, a higher priority is given to the micro 1800 cell,

- HO_MARGIN(0,n) = -127 dB between a macro 900 cell and a macro 1800 cell in order to avoid filtering when cause 21 is triggered (if Cause_Margin_P_21 = 60 dB).





Micro 900 and 1800Cell_dimension_type = microCell_layer_type = lower

MULTIBAND_LOAD_LEVEL = 0%L_RXLEV_CPT_HO(n) = -85 dBmEN_SPEED_DISC = DisableA_PBGT_HO = 6

Cause 21

Cause 14

Cause 12

Cause 12

Cause 12

BSS parameters :






Cause 12

Cause 14Cause 21




3.3.5.2.1 Idle mode








The picture below gives the parameters for better condition causes.

Remark : when the serving cell is a 900 macro cell, cause 21 is checked towards 1800 micro cells (no speed discrimination !). Unlike B5 release, cause 14 is also checked. If causes 21 and 14 are triggered at the same time by a 1800 micro cell, cause 14 is masked by cause 21 because only one cause number (here 21) is sent to the candidate cell evaluation process. On the other hand, it is not possible to filter the 1800 micro cell using the PBGT filtering because the PBGT filtering is no more used after the triggering of a better condition cause. Therefore

Macro 900Umbrella


Macro 1800Umbrella


Micro 900 and 1800Micro

MULTIBAND_TRAFFIC_CONDITION = ANY_LOADEN_SPEED_DISC = DisableDELTA_DEC_HO_margin =5 dBDELTA_INC_HO_margin = 5 dB

Cause 21L_RXLEV_CPT_HO(0,n) = -85 dBm Cause 14

L_RXLEV_CPT_HO(0,n) = -85 dBm




BSS parameters :











it is still not possible to manage properly a network with 1800 macro and micro cells in B6 release.

In order to avoid a handover on cause 21 from a 900 micro cell towards a 1800 micro cell, it is necessary to use L_RXLEV_CPT_HO(0,n) = -47 dBm.


The table below gives the parameters for the candidate cell evaluation process (PRIORITY(0,n), HO_MARGIN(0,n), HO_MARGIN_LEV(0,n), HO_MARGIN_QUAL(0,n), HO_MARGIN_DIST(0,n)) :

Neighbouring cell

Serving cell

Macro 900 Macro 1800 Micro 900 Micro 1800

Macro 900 1, 5, 2, 1, 2 1, 5, 2, 1, 2 0 or 2, 5, 2, 1, 2 0 or 2, 5, 2, 1, 2

Macro 1800 0,- 127,- 127,- 127, -127 1, 5, 2, 1, 2 0, 5, 2, 1, 2 0, 5, 2, 1, 2

Micro 900 1, 5, 2, 1, 2 1, 5, 2, 1, 2 2, 5, 2, 1, 2 2, 5, 2, 1, 2

Micro 1800 0, 5, 2, 1, 2 1, 5, 2, 1, 2 1, 5, 2, 1, 2 1, 5, 2, 1, 2

Remarks :




- in case of emergency : macro 900 > macro 1800 > micro 1800 > micro 900,

- in case of Forced Directed Retry : macro 900 > macro 1800.




- in case of better condition HO cause (theoretical case where causes 21 and 12 are triggered at the same time) : macro 1800 > micro 900.






- in case of better condition HO cause (theoretical case where causes 21, 14 and 12 are triggered at the same time) : macro 900 = macro 1800 > micro 900 = micro 1800 (PRIORITY(0,n) = 2) or micro 900 = micro 1800 > macro 900 = macro 1800 (PRIORITY(0,n) = 0).




- in case of better condition HO cause (theoretical case where causes 14 and 12 are triggered at the same time) : micro 900 = micro 1800 > macro 1800.



3.3.6 Complements

3.3.6.1 Hot spot and continuous coverage

There are 2 differences between the case with hot spot macro 1800 cells and the case with a continuous macro 1800 coverage :

- the behaviour in case of emergency alarm,

- the way to exit a macro 1800 cell.

In case of emergency alarm on a hot spot macro 1800 cell, the target cell is obviously a macro 900 cell. If the coverage provided by the macro 1800 layer is good enough, it is possible to try to stay on this layer (emergency alarm on a macro 1800 cell) or to give a higher priority to this layer (emergency alarm on a micro cell). In order to obtain this behaviour, it is necessary to change :

- the parameter EN_RESCUE_UM (EN_RESCUE_UM = Disable) on macro 1800 cells (case of an existing macro 900 MHz network and addition of 1800 MHz macro cells, see 3.3.2),

- the parameter PRIORITY(0,n) between a macro 1800/micro cell and macro 900 and 1800 neighbouring cells (other configurations).

In case of a continuous macro 1800 coverage, dual band MS exit a macro 1800 cell located at the center of the macro 1800 area using cause 12 (PBGT handover). On the contrary, dual band MS exit a hot spot on emergency alarm. The risk is then to stay a long time connected to the hot stop and to be unable to find a macro 900 neighbouring cell. A special set of parameters is then proposed in part 4.1 (Zone exit).

3.3.6.2 Continuous coverage : inner cell and outer cell

In case of a continuous coverage provided by the macro 1800 layer, it is necessary to distinguish inner cells (located at the center of the area) from outer cells located at the border. A first difference is the way to exit the cell. In case of an outer macro 1800 cell it is interesting to use the same set of parameters than for a hot spot. Another idea is to use a higher capture threshold (L_RXLEV_CPT_HO) for outer cells.

3.3.6.3 1800 cells co-located or not with 900 cells

When 1800 cells are co-located with 900 cells it is sensible to consider in the default parameters (C2 parameters for example) a fixed offset (10-12 dB) in order to take into account the difference in propagation losses between the two frequency bands.

In the case of two independent layers (example of an operator managing a 900 MHz network and a 1800 MHz network who decides to merge the two networks), received levels from 900 and 1800 cells are not correlated. Consequently, it is not sensible to include an offset corresponding to the assumed difference in propagation losses.



3.4 Multiband cell configurations The aim of this part is to describe the possible configurations with the Multiband cell

solution. Again, we will take the example of an existing 900 MHz network and we will study the following configurations :

- 900 macro cells with addition of 1800 TRX,

- 900 macro cells with addition of 1800 TRX + micro cells (900, 1800).

Each configuration is described in the same way :

- idle mode,

- call set-up,

- cell administration,

- better condition handovers,

- candidate cell evaluation process.



3.4.1 900 macro cells with addition of 1800 TRX

The picture below shows the configuration. The network is made up of one 900 macro layer and 1800 TRX are added in the 900 macro cells. The BCCH frequency is always a 900 frequency.

3.4.1.1 Idle mode

Unlike the equivalent Multiband BSC configuration, there are only 900 MHz BCCH to monitor. Therefore, all the MS (single band and dual band) camp on 900 cells (900 BCCH) in idle mode. Here the CELL_BAR_QUALIFY parameter and the C2 criterion are not used.

3.4.1.2 Call set-up

At call set-up, a 900 SDCCH is always allocated to the MS (SDCCH channels are on the 900 TRX). Then according to the MS location (outer zone or inner zone), a TCH is allocated in the 900 band (outer zone) or in the 1800 band (inner zone). In order to determine the location of the mobile, cause 13 (outer zone to inner zone HO) is checked.

If the cell is completely congested, it is possible to allocate the TCH in a neighbouring cell (Directed Retry or Forced Directed Retry). Then, according to the location of the mobile, the value of the parameter EN_BETTER_ZONE_HO, the serving BSC of the serving and the neighbouring cells the TCH is allocated in :

- the 900 band if the two cells belong to two different BSC,

- the 900 band if the two cells belong to the same BSC and EN_BETTER_ZONE_HO = disable for the neighbouring cell,

- the 900 band if the two cells belong to the same BSC, EN_BETTER_ZONE_HO = enable for the neighbouring cell and the MS is located in the outer zone of the neighbouring cell,

- the 1800 band if the two cells belong to the same BSC, EN_BETTER_ZONE_HO = enable for the neighbouring cell and the MS is located in the inner zone of the neighbouring cell.

In order to determine the location of the MS, the downlink part of cause 13 (outer zone to inner zone HO) is checked.

Nevertheless, we don’t recommend to activate the Directed Retry and the Forced Directed Retry (EN_DR = disable and EN_FORCED_DR = disable). Indeed, unlike the equivalent Multiband

Macro 900 + 1800Single

1800 TCH900 BCCH, SDCCH, TCH



BSC configuration, 1800 TCH belong to the serving cell and are directly accessible during the Normal Assignment procedure. Therefore, the risk of congestion of the serving cell is reduced and the possibility to allocate the TCH in a neighbouring cell is less necessary (we make the assumption that MS are mainly dual band MS).

3.4.1.3 Cell administration

The network is made up of single cells which FREQUENCY_RANGE parameter is equal to GSM-DCS. On the other hand the parameter CELL_PARTITION_TYPE is equal to Concentric.

Remember that following profiles are available for a multiband cell : single, umbrella, mini and micro. Nevertheless a multiband cell cannot be a concentric cell (i.e. 900+1800 outer zone and 900+1800 inner zone).

3.4.1.4 Better condition handovers

The picture below shows the different better condition causes used. Remember that a mobile only monitors 900 BCCH.

Cause 13 is used for handovers from the outer zone (900 TRX) to the inner zone (1800 TRX).

In the outer zone, cause 12 (power budget) is checked towards all neighbouring cells (single band and multiband cells).

In the inner zone, cause 12 is checked only towards other multiband neighbouring cells (FREQUENCY_RANGE = GSM-DCS) belonging to the same BSC than the serving cell in order to keep dual band MS in the inner zone frequency band.

Remember that in case of incoming intra-BSC handover a TCH can be allocated in the inner zone. Therefore, it is possible to stay on the 1800 layer using cause 12.

Following parameters are used for cause 13 :

- RXLEV_DL_ZONE : -85 dBm,

- ZONE_HO_HYST_DL : 16 dB (10 dB to take into account the difference in propagation losses between 900 MHz and 1800 MHz),

- RXLEV_UL_ZONE : -93 dBm in order to take into account UL levels (-93 dBm = -85 dBm - 8dB : we make the assumption that -85 dBm in DL corresponds to -93 dBm in UL) or -110 dBm in order to disable the uplink condition of cause 13,

- ZONE_HO_HYST_UL : 16 dB (10 dB to take into account the difference in propagation losses between 900 MHz and 1800 MHz),

- BS_TXPWR_MAX_INNER : BS_TXPWR_MAX,


Cause 13

Cause 12 Cause 12



- MS_TXPWR_MAX_INNER : 30 dBm,

- NEIGHBOUR_RXLEV(0,n) : -47 dBm. We don’t take into account the level of the neighbouring cells,

- EN_BETTER_ZONE_HO : enable,

- T_HCP : 0 s,

- PING_PONG_HCP : 15 dB.

With these values, the DL condition of cause 13 is verified when the 900 DL level is higher than -69 dBm (if no DL PC). The difficulty is that the 1800 level is not known and therefore it is necessary to make an assumption for the difference of propagation losses between the 900 and the 1800 bands.


- HO_MARGIN(0,n) : 5 dB,

- OFFSET_HO_MARGIN_INNER : 10 dB.

With these values, cause 12 is triggered when :

- PBGT(n) > 5 dB for a MS in the outer zone (900 TRX),

- PBGT(n) > 15 dB for a MS in the inner zone (1800 TRX, comparison of a 1800 TCH and a 900 BCCH).


Unlike the equivalent Multiband BSC configuration, the contribution of the candidate cell evaluation process is less important. It is indeed not necessary to define the level of priority of the 900 and the 1800 layers (with the parameter PRIORITY(0,n) for example) because the network is made up of one layer. Therefore, the aim of the candidate cell evaluation process is here to filter the candidate cells (RXLEVmin(n), PBGT filtering) and to select the best one according to the ORDER or the GRADE criterion.

The picture below shows the parameters for the candidate cell evaluation process.

Remarks :

Macro 900 + 1800SingleEN_PRIORITY_ORDERING = enableEN_PBGT_FILTERING = enableCELL_EV = GRADE









3.4.2 900 macro cells with addition of 1800 TRX + micro cells (900, 1800)

The picture below shows the configuration. The network is made up of one 900 macro layer and one micro layer (900 micro cells and 1800 micro cells). 1800 TRX are added in the 900 macro cells. There are 900 BCCH (multiband macro cells, 900 micro cells) and 1800 BCCH (1800 micro cells).

3.4.2.1 Idle mode

It is possible to use the C2 criterion in order to give a higher priority to the micro layer for cell-reselection (slow mobiles only). The table below gives a set of parameters (it is only an example) in order to give a higher priority to the micro cells.


_OFFSET

TEMPORARY

_OFFSET

PENALTY_TIME

Macro multiband -100 dBm 0 dB 0 dB 20 s

Micro 900 -100 dBm 14 dB 60 dB 20 s

Micro 1800 -100 dBm 14 dB 60 dB 20 s


- C1 for the multiband macro cells,

- C1 + 14 dB for the micro cells.

3.4.2.2 Call set-up

It is interesting to enable Directed Retry and Forced Directed Retry in the micro layer. Then, if a micro cell is congested, it is possible to allocate a TCH in a neighbouring multiband cell.

The picture below gives the parameters for Directed Retry and Forced Directed Retry.

Macro 900 + 1800Umbrella

Micro 900 and 1800Micro



The level threshold for Forced Directed Retry (cause 20) is set to -47 dBm on the micro layer in order to avoid to send fast moving mobiles towards this layer on cause 20 (no speed discrimination).

On the other hand, it is not really necessary to activate Directed Retry and Forced Directed Retry on the macro layer because 1800 TCH belong to the serving cell and are directly accessible during the Normal Assignment procedure.

3.4.2.3 Cell administration

Following profiles are used :

- macro cells : umbrella cells,

- micro 900 and 1800 cells : micro cells.

Some umbrella cells are mutiband cells. Their FREQUENCY_RANGE parameter is equal to GSM-DCS. On the other hand the parameter CELL_PARTITION_TYPE is equal to Concentric.

Remember that following profiles are available for a multiband cell : single, umbrella, mini and micro. Nevertheless a multiband cell cannot be a concentric cell (i.e. 900+1800 outer zone and 900+1800 inner zone).

3.4.2.4 Better condition handovers

The picture below shows the better condition handovers and associated parameters.

Micro 900 and 1800EN_DR = EnableEN_FORCED_DR = EnableL_RXLEV_NCELL_DR(n) = -47 dBmFREElevel_DR(n) = 2 if 1 TRX, 4 otherwise

Macro 900 + 1800EN_DR = DisableEN_FORCED_DR = DisableL_RXLEV_NCELL_DR(n) = -85 dBmFREElevel_DR(n) = 2 if 1 TRX, 4 otherwise Cause 20



Cause 13 is used to make handovers from the outer zone (900 TRX) to the inner zone (1800 TRX) of a multiband cell.


- RXLEV_DL_ZONE : -85 dBm,

- ZONE_HO_HYST_DL : 16 dB (10 dB to take into account the difference in propagation losses between 900 MHz and 1800 MHz),

- RXLEV_UL_ZONE : -93 dBm in order to take into account UL levels (-93 dBm = -85 dBm - 8dB : we make the assumption that -85 dBm in DL corresponds to -93 dBm in UL) or -110 dBm in order to disable the uplink condition of cause 13,

- ZONE_HO_HYST_UL : 16 dB (10 dB to take into account the difference in propagation losses between 900 MHz and 1800 MHz),

- BS_TXPWR_MAX_INNER : BS_TXPWR_MAX,

- MS_TXPWR_MAX_INNER : 30 dBm,

- NEIGHBOUR_RXLEV(0,n) : -47 dBm. We don’t take into account the level of the neighbouring cells,

- EN_BETTER_ZONE_HO : enable,

- T_HCP : 0 s,

- PING_PONG_HCP : 15 dB.

With these values, the DL condition of cause 13 is verified when the 900 DL level is higher than -69 dBm (if no DL PC). The difficulty is that the 1800 level is not known and therefore it is necessary to make an assumption for the difference of propagation losses between the 900 and the 1800 bands.

Cause 12 is used to make handovers between cells belonging to the same layer and working in the same frequency band (same CELL_BAND_TYPE).

Micro 900 and 1800MicroEN_SPEED_DISC = disable

Macro 900 + 1800UmbrellaEN_SPEED_DISC = disable Cause 12

Cause 12

Cause 13

Cause 12

BSS parameters :L_MIN_DWELL_TIME = 8 s


Cause 14

EN_BI-BAND_MS = disable



In the outer zone of a multiband cell, cause 12 (power budget) is checked towards all neighbouring cells (single band and multiband cells).

In the inner zone of a multiband cell, cause 12 is checked only towards other multiband neighbouring cells (FREQUENCY_RANGE = GSM-DCS) belonging to the same BSC than the serving cell in order to keep dual band MS in the inner zone frequency band.


- HO_MARGIN(0,n) : 5 dB,

- OFFSET_HO_MARGIN_INNER : 10 dB.

With these values, cause 12 is triggered when :

- PBGT(n) > 5 dB for a MS in the outer zone (900 TRX),

- PBGT(n) > 15 dB for a MS in the inner zone (1800 TRX, comparison of a 1800 TCH and a 900 BCCH).

Cause 14 is used to make handovers from the umbrella cells towards the micro cells.

When the MS is in the inner zone (1800 TRX) of a multiband cell it is possible to inhibit cause 14 towards 900 micro cells using the parameter EN_BI-BAND_MS. If this parameter is set to disable for the micro cell, cause 14 is not checked and dual band MS stay in the 1800 layer.


The table below shows the parameters for the candidate cell evaluation process (PRIORITY(0,n), HO_MARGIN(0,n), HO_MARGIN_LEV(0,n), HO_MARGIN_QUAL(0,n), HO_MARGIN_DIST(0,n)).

Remarks :



Neighbouring cell

Serving cell

Macro multiband Micro 900 Micro 1800

Macro multiband 2*, 5, 2, 1, 2 1, 5, 2, 1, 2 1, 5, 2, 1, 2

Micro 900 1, 5, 2, 1, 2 1, 5, 2, 1, 2 1, 5, 2, 1, 2

Micro 1800 1, 5, 2, 1, 2 1, 5, 2, 1, 2 1, 5, 2, 1, 2

* in order to give a higher priority to the micro layer if causes 14 and 12 are triggered at the same time (theoretical case)

Furthermore, we propose to use following cell parameters :



- macro multiband cells : EN_PRIORITY_ORDERING = enable, EN_PBGT_FILTERING = enable, CELL_EV = GRADE,

- micro cells : EN_RESCUE_UM = enable, EN_PRIORITY_ORDERING = enable, EN_PBGT_FILTERING = disable, CELL_EV = ORDER.



3.5 Other aspects

3.5.1 Multi vendor environment

Although it is not the best technical solution, it is possible to imagine a dual band network with 2 vendors : one for the macro 900 layer and one for the macro 1800 layer for example. In this case, one vendor makes capture handovers while the other one makes emergency handovers.

The values of radio parameters (capture threshold, emergency thresholds, C2 parameters, …) are identical.

Because inter-band handovers are inter-BSC handovers the operator has less possibilities to manage its network. For example, it is not possible to know the traffic load of the neighbouring cells in the other frequency band.

Finally, external Directed Retry is available in B5 release but not with all the MSC (only with Ericsson and Alcatel MSC). In B6 release, external Directed Retry is fully available.

3.5.2 Existing 1800 MHz network

In parts 3.3 and 3.4 we have seen the case of an existing 900 MHz network where 1800 frequencies are added. It is now interesting to study the case of an existing 1800 MHz network.

It is sensible to consider that this case is identical to the case of an existing 900 MHz network. There are only 3 differences :

- because propagation losses are lower in the 900 band, it is a good idea to give a higher priority to this band in case of emergency alarm,

- the 1800 operator may use the new frequency band to cover rural areas,

- the tuning of the hysteresis is different for a multiband cell.

3.5.2.1 Use of 900 and 1800 frequencies in different areas

The 900 band may be used to improve the coverage of rural areas. In such a case, the dual band network is made up of 900 MHz cells in rural areas and 1800 MHz cells in urban areas. It is a new configuration with the two bands belonging to the same layer.

The problem with this kind of configuration is that it is not possible to use the same better condition cause for the 1800 -> 900 handovers and the 900 -> 1800 handovers. Indeed :

- cause 12 is not possible between cells working in different frequency bands,

- cause 21 is used to go from cells working in the non-preferred band to cells working in the preferred band which is defined on a per BSC basis. Therefore, if 900 and 1800 cells are connected to the same BSC, it is not possible to use cause 21 for 900 <-> 1800 handovers. Then one solution (not really satisfactory) is to connect the 900 cells to one BSC and the 1800 cells to another BSC,

- cause 14 is used to go from upper layer cells to lower layer cells.



Therefore, we recommend to manage 900 <-> 1800 handovers with emergency handovers : level causes and distance cause. The drawback of level causes is that the same handover cause is used for interband handovers and in case of real level problem (MS entering in a building for example). Consequently, there is no specific OMC-R counter to monitor interband handovers. On the contrary, with the distance cause it is possible to monitor interband handovers with a specific counter.

If the operator absolutely wants to use the same better condition cause for the 1800 -> 900 handovers and the 900 -> 1800 handovers the only solution with B5 release is to simulate a PBGT handover using the PBGT filtering. In B6 release, it is possible to use the general capture cause (cause 24) as better condition cause for 900 <-> 1800 handovers.

The idea is to transform the emergency handover on distance or level into a power budget HO using the PBGT filtering of the candidate cell evaluation process. Let us take the example of the use of the distance cause.

The early triggering of the emergency alarm on distance is possible by tuning the threshold U_TIME_ADVANCE to a low value (0 for example).

The execution of such anticipated handover is controlled by the PBGT filtering applied to the candidate cells for handover. This filtering consists of (in case of emergency alarm on distance) :

- PBGT(n) > HO_MARGIN_LEV(0,n) + Cause_Margin_P_6 = HO_MARGIN_LEV(0,n).

The filtering must ensure the same handover limit than the handover limit defined by the power budget handover (cause 12). Then it is necessary to tune the parameter HO_MARGIN_LEV(0,n) between a serving cell on the zone frontier and its neighbouring cells in the following way :

- HO_MARGIN_LEV(0,n) = HO_MARGIN(0,n) = 5 dB between cells of the same frequency band,

- HO_MARGIN_LEV(0,n) = 2 dB between a 1800 cell and a 900 cell (5 - 3 = 2 dB to take into account the difference in MS_TXPWR_MAX in the two bands in the PBGT formula),

- HO_MARGIN_LEV(0,n) = 8 dB between a 900 cell and a 1800 cell (5 + 3 = 8 dB to take into account the difference in MS_TXPWR_MAX in the two bands in the PBGT formula).

Macro 900Macro 1800

Urban area = 1800 area Rural area = 900 area

HO_MARGIN_LEV(0,n) = 5dBHO_MARGIN_LEV(0,n) = 5dB

HO_MARGIN_LEV(0,n) = 2dB

HO_MARGIN_LEV(0,n) = 8dB



Remark : in B6 release, if the distance cause is used, the parameter HO_MARGIN_LEV(0,n) is replaced by the parameter HO_MARGIN_DIST(0,n).

The drawbacks of this solution are :

- capture handovers (towards micro cells or preferred band cells) are not available in most of the parts of the serving area of a cell located at the border of the 900 and the 1800 areas. Indeed, when an emergency handover is detected, capture handovers are not checked by the handover detection process,

- it is necessary to set the parameter HO_MARGIN_LEV(0,n) for each neighbouring cell of a cell located at the border of the 900 and the 1800 areas. With the previous solution, it is only necessary to play with cell parameters (U_TIME_ADVANCE or L_RXLEV_XX_H),

- it is no more possible to use the distribution of handover causes for the optimization of the cells located at the border of the 900 and the 1800 areas because a lot of emergency causes are triggered artificially.

3.5.2.2 Multiband cell

In case of an existing 1800 network, the tuning of the hysteresis is different if the operator uses the multiband cell solution and adds 900 TRX.

For outer zone (1800 TRX) to inner zone (900 TRX) handovers the hysteresis ZONE_HO_HYST_DL and ZONE_HO_HYST_UL are set to 6 – 10 = - 4 dB in order to take into account the difference in propagation losses between the two bands (10 dB).

For a MS located in the inner zone (900 TRX) of a multiband cell an hysteresis is added to HO_MARGIN(0,n). This hysteresis is set to OFFSET_HO_MARGIN_INNER = - 10 dB. This hysteresis is used for the triggering of cause 12 and in the PBGT filtering : comparison of a 900 TCH and a 1800 BCCH.


Cause 13

Cause 12 Cause 12

Special sets of parameters


4 Special sets of parameters

4.1 Zone exit

4.1.1 Description of the problem

For a 1800 hot spot cell or a 1800 cell located at the border of a continuous 1800 area, it is necessary to define the way to leave the cell (the same problem occurs with micro cells). Indeed the serving area of such cells may be very extended as there is no 1800 cell which limits the serving area because of power budget considerations. If the serving area is only limited by the level and quality thresholds of emergency handover causes, the serving area of the 1800 cell may be very extended. In this case it is necessary to define a lot of 900 neighbouring cells for the 1800 cell. This is a problem, because the efficiency of the monitoring is reduced when a mobile has to monitor a lot of neighbouring cells. On the other hand, on the operational point of view, it is an heavy task to define a lot of neighbouring cells and it is easy to forget some neighbouring cells leading to a risk of call drop.

The aim of this part is to describe the different possible strategies : - zone exit on level or quality emergency alarm,

- zone exit on distance emergency alarm (recommended solution),

- zone exit on anticipated level emergency alarm with use of the PBGT filtering,

- zone exit on anticipated distance emergency alarm with use of the PBGT filtering.

The idea is to find a zone exit strategy which guarantees a safe zone exit and allows to define a minimum number of 900 neighbouring cells.

4.1.2 Solutions with B5 release

4.1.2.1 Level or quality emergency alarm

This solution consists in using the same parameters (i.e. usual thresholds of level, quality and distance emergency causes) for the 1800 cells involved in the zone exit than for other 1800 cells. With this solution it is necesssary to define a high number of 900 neighbouring cells. Therefore this solution is not suitable.

4.1.2.2 Distance emergency alarm

This solution was tested in Strasbourg (June 1999) during the dual band field trial with Cegetel.

The idea is to activate the distance emergency cause (cause 6) for a 1800 cell involved in the zone exit and to tune the distance threshold U_TIME_ADVANCE.

This solution is very easy to implement.

The problem is to tune the parameter U_TIME_ADVANCE in order to reduce the number of 900 neighbouring cells (low value) but also to avoid ping-pong handovers between the 900 and the 1800 layers (high value). Indeed, the received level from the 1800 cell may be higher than the capture threshold (used for the capture handover from the 900 layer towards the 1800 layer) when the distance emergency cause is triggered on the 1800 cell. Then the risk is to have the following situation :



In fact the tuning of the parameter U_TIME_ADVANCE is determined by the coverage of the 1800 cell. It is useless and even dangerous (if the operator only defines as neighbouring cells the 900 cells corresponding to the 1800 coverage defined by the parameter U_TIME_ADVANCE) to reduce the value of the parameter U_TIME_ADVANCE if the received level from the 1800 cell is higher than the capture threshold when the emergency cause on distance is triggered.

In order to evaluate the ping-pong phenomenon we recommend to follow the indicator TCH MEAN HOLDING TIME on the macro 1800 cell involved in the zone exit.

Finally, it is not necessary to apply a PBGT filtering on 900 neighbouring cells (HO_MARGIN_LEV(0,n) = -127 dB between 1800 and 900 cells). The idea is to select the best 900 neighbouring cell according to the GRADE or the ORDER criteria.

4.1.2.3 Anticipated level emergency alarm with use of the PBGT filtering

This solution was tested in Toulouse (May 1998) during the dual band field trial with France Telecom Mobiles and also in Strasbourg (June 1999) during the dual band field trial with Cegetel.

The principle is to anticipate the 1800 zone exit by triggering earlier an emergency alarm on level and executing the handover only towards specific 900 neighbouring cells.

The early triggering of the emergency alarm on level is possible by tuning the threshold L_RXLEV_DL_H (or L_RXLEV_UL_H) to a stronger value (10 dB above the normal value of this threshold should be sufficient to provide a good anticipation).

The execution of such anticipated handover towards specific 900 neighbouring cells is controlled by the PBGT filtering applied to the candidate cells for handover. This filtering consists of (in case of emergency alarm on level) :

- PBGT(n) > HO_MARGIN_LEV(0,n) + Cause_Margin_P_X,

- where X is the cause number (X = 3 or 5 for emergency handover on level).

This condition is useful to avoid the anticipated handover towards some neighbouring cells. As the handover is detected earlier, the filtering must be more restrictive than usual to

1800 layer

900 layer

Distance emergency handoverTA > distance threshold

Capture handoverLevel(1800) > capture threshold



ensure the same handover limit for a MS located at the center of the 1800 cell or moving towards the center of the 1800 area.

With 1800 neighbouring cells it is proposed to consider the handover limit related to power budget handover (cause 12). Therefore it is necessary to tune the parameter HO_MARGIN_LEV(0,n) between the 1800 serving cell on the zone frontier and its 1800 neighbouring cells in the following way :

- HO_MARGIN_LEV(0,n) + Cause_Margin_P_X = HO_MARGIN(0,n) = 5 dB (default value),

- considering Cause_Margin_P_X = -3 dB, this gives HO_MARGIN_LEV(0,n) = 8 dB.

On the contrary, tuning HO_MARGIN_LEV(0,n) with a less restrictive value towards specific 900 neighbouring cells, allows to make earlier handover towards these cells and thus to ensure a safe zone exit.

This requires to modify the default value of HO_MARGIN_LEV(0,n) between 1800 cells and 900 cells (the default value is -127 dB to inhibit the filtering). In the context of zone exit, the following values could be used :

- HO_MARGIN_LEV(0,n) = 15 dB (considering Cause_Margin_P_X = - 3 dB),

- towards 900 cells which are not involved in the zone exit.

This value of 15 dB takes into account the difference of propagation losses (10 dB) between 900 and 1800 bands. With this value the 900 cell is not filtered when LEV(900) > LEV(1800) + 15 dB (10 dB of difference in propagation losses plus 5 dB of handover margin).

- HO_MARGIN_LEV(0,n) = X dB (considering Cause_Margin_P_X = - 3 dB),

- towards macro 900 cells which are involved in the zone exit.

X should be tuned to set the border of the 1800 zone. X = -127 dB is the default value and means that the border is fixed by the triggering of the handover alarm and so by the threshold L_RXLEV_DL_H (or L_RXLEV_UL_H).

The picture below summarizes the parameters :

macro 900

macro 1800

HO_MARGIN_LEV(0,n) = 8 dB

HO_MARGIN_LEV(0,n) = 15 dBHO_MARGIN_LEV(0,n) = X dB

Exit of the macro 1800 area

Use of a high L_RXLEV_DL_H



One drawback of this solution is that it requires a difficult tuning :

- L_RXLEV_DL_H on the 1800 cell,

- HO_MARGIN_LEV(0,n) between the 1800 cell and the 900 co-located cell.

The tuning must be done in order to :

- avoid ping-pong handovers between the 900 and the 1800 layers. It is easier to avoid ping-pong HO than in the case of the use of the distance cause because here the received level from the 1800 cell is known when the emergency cause is triggered,

- allow a MS located at the center of the 1800 cell and having a real level problem (for example a MS entering in a building) to make a handover towards the 900 co-located cell.

The difficulty is that it is necessary to make an assumption for the difference in propagation losses between the 900 and the 1800 bands.

The other drawbacks are :

- modification of the HO causes distribution (a lot of emergency causes on level are triggered),

- capture handovers are not checked because an emergency cause on level is often triggered. Therefore, it is not possible to use this solution when the 1800 cell is an umbrella cell with micro neighbouring cells.

4.1.2.4 Anticipated distance emergency alarm with use of the PBGT filtering

The principle is to anticipate the 1800 zone exit by triggering earlier an emergency alarm on distance and executing the handover only towards specific 900 neighbouring cells.

The early triggering of the emergency alarm on distance is possible by tuning the threshold U_TIME_ADVANCE to a low value (0 for example).

The execution of such anticipated handover towards specific 900 neighbouring cells is controlled by the PBGT filtering applied to the candidate cells for handover. This filtering consists of (in case of emergency alarm on distance) :

- PBGT(0,n) > HO_MARGIN_LEV(0,n) + Cause_Margin_P_6 = HO_MARGIN_LEV(0,n).

We propose the following tuning of the parameter HO_MARGIN_LEV(0,n) :

- HO_MARGIN_LEV(0,n) = 5 dB towards the 1800 neighbouring cells,

- HO_MARGIN_LEV(0,n) = X dB (-127 dB is the default value) towards the 900 neighbouring cells involved in the zone exit,

- HO_MARGIN_LEV(0,n) = 15 dB towards the 900 neighbouring cells not involved in the zone exit.

This solution has less impact than the previous one on the handovers inside the cell (i.e. distance < U_TIME_ADVANCE) because the emergency cause on distance is not triggered. The only impact is the possible filtering of the 900 co-located cell in case of emergency cause on level because of the use of HO_MARGIN_LEV(0,n) = 15 dB.



For a distance > U_TIME_ADVANCE, the emergency HO on distance is triggered and therefore capture HO are not checked. This is a drawback if the radius of the 1800 cells is higher than U_TIME_ADVANCE.

Compared to the previous solution, one drawback is that the received level from the 1800 cell may be higher than the capture threshold when the emergency HO on distance is triggered leading to a ping-pong situation.

4.1.3 Solutions with B6 release

4.1.3.1 Anticipated level emergency alarm with use of the PBGT filtering

Compared to the B5 release, the parameters Cause_Margin_P_3/5 are removed leading to new values for the parameter HO_MARGIN_LEV(0,n).

4.1.3.2 Anticipated distance emergency alarm with use of the PBGT filtering

Compared to the B5 release, the parameter Cause_Margin_P_6 is removed. On the other hand the parameter HO_MARGIN_LEV(0,n) is replaced by the parameter HO_MARGIN_DIST(0,n) in the PBGT filtering.

4.1.4 Solutions for the multiband cell configuration

Causes 10 (uplink) and 11 (downlink) are used to make handovers from the inner zone TRX to the outer zone TRX.

When the level is lower than RXLEV_UL_ZONE (cause 10, default value = -85 dBm) or RXLEV_DL_ZONE (cause 11, default value = -85 dBm) cause 10 or 11 is triggered and the dual band MS is sent to the outer zone.


Causes 10 and 11Cause 12 Cause 12



4.2 Capture threshold set on a per cell basis


This problem is not directly linked to the dual band concept but is often encountered in a dual band network which is normally a mature network made up of different layers and different types of cells. The problem is that the capture threshold used by causes 14 and 21 is set on a per cell basis (B5 release) instead of on a per couple of cells basis. A typical case is the difference between a corporate micro cell (indoor coverage) and a public (outdoor coverage) one.

4.2.2 Example

Imagine a network with 3 layers : macro 900, macro 1800 and micro 900. Among the micro 900 cells, some are public and some are corporate.

The operator may want to have the following behaviour for a dual band MS :

- handover from the macro 900 cell to the public micro 900 cell (if the macro 1800 layer is not available),

- no handover from the macro 1800 cell to the public micro 900 cell (dual band MS must stay on the macro 1800 layer in order to reduce congestion on the 900 layers),

- handover from the macro 1800 cell to the corporate micro 900 cell (special agreement between the operator and the owner of the building : the corporate cell has the highest priority).




Cause 21Cause 14Cause 14

public corporate

Cause 14



4.2.3 Solution of the problem

In B5 release, it is necessary to use the filtering process and to modify the parameter Cause_Margin_P_14 on the macro 1800 cell. The problem is that this parameter is not accessible at the OMC-R. It is necessary to use a BSC terminal to modify the DLS.

The idea is to filter the public micro 900 neighbouring cell which has triggered cause 14 using the following set of parameters :

- EN_PBGT_FILTERING = Enable on the macro 1800 cell,

- Cause_Margin_P_14 = 60 dB on the macro 1800 cell,

- HO_MARGIN(0,n) = 5 dB between the macro 1800 cell and the public micro 900 cell,

- HO_MARGIN(0,n) = -127 dB between the macro 1800 cell and the corporate micro 900 cell.

With these parameters, the filtering condition (PBGT filtering) is :

- PBGT(n) > HO_MARGIN(0,n) + Cause_Margin_P_14 = -127 + 60 = -67 dB for the corporate micro 900 cell when the serving cell is the macro 1800 cell (no filtering),

- PBGT(n) > HO_MARGIN(0,n) + Cause_Margin_P_14 = 5 + 60 = 65 dB for the public micro 900 cell when the serving cell is the macro 1800 cell (filtering).

In B6 release the problem is solved by the use of a level threshold set on a per couple of cells basis : L_RXLEV_CPT_HO(0,n) instead of L_RXLEV_CPT_HO(n).

Tuning and monitoring


5 Tuning and monitoring

5.1 Tuning This section provides first inputs for dual band network tuning. It contains :

- parameters that may be tuned in a dual band network,

- impact of such a tuning on network behaviour.

5.1.1 Idle mode

For cell re-selection, CELL_RESELECT_OFFSET and TEMPORARY_OFFSET (in dB) must be tuned according to the received signal level from the cells of the different layers (macro 900, macro 1800, micro 900, ...).

Remarks:

- if 900 cells and 1800 cells are co-located, it is necessary to take into account the difference of propagation losses between 900 MHz and 1800 MHz (10-12 dB),

- it is necessary to take into account the value of RXLEV_ACCESS_MIN if this parameter is not the same for all the cells,

- the parameter MULTIBAND_REPORTING is not used in idle mode. Consequently, a dual band MS only takes into account the 6 strongest neighbouring cells irrespective of the frequency band. A problem occurs with a situation where 1800 neighbouring cells are not seen by a dual band mobile.

Moreover, proper balance must be ensured between re-selection and handover parameters, in order to avoid unexpected emergency handovers, once call is initiated. Take care of the :

- difference between the value of RXLEV_ACCESS_MIN and L_RXLEV_DL_H. A mobile connected to a cell in idle mode in extreme conditions (very low RXLEV_ACCESS_MIN) will trigger an emergency alarm at the beginning of the call,

- difference between the value of CELL_RESELECT_OFFSET for the different cells (macro 900 and macro 1800 for example). Imagine the case where RXLEV = -80 dBm for a macro 900 cell and -95 dBm for a macro 1800 cell. Imagine that with such values, C1 > 0 for both cells and C2(macro 1800) > C2(macro 900). A mobile will re-select the macro 1800 cell and an emergency alarm will certainly be triggered quickly, while it would have been better to re-select the macro 900 cell. Thus, it is necessary to take care of the values of C2 parameters in order to reduce emergency alarms on level.

5.1.2 Connected mode

5.1.2.1 Call set-up

If Forced Directed Retry is used, it is necessary to tune the parameter L_RXLEV_NCELL_DR(n) which is a capture threshold. If this threshold is too low, cause 20 is triggered more easily but a problem of quality is possible in the target cell.

In order to give a higher priority to a given layer, it is possible to tune this parameter but it is better to use the parameter PRIORITY(0,n).



5.1.2.2 Capture handovers

MULTIBAND_LOAD_LEVEL (B5), MULTIBAND_TRAFFIC_CONDITION (B6)

It may be useful to use this parameter (traffic load threshold used by cause 21 and corresponding to the average percentage of busy TCH in the cell) in order to trigger cause 21 only when the 900 MHz (we assume that PREFERRED_BAND = 1800) cell has a high traffic load. Using a value different from 0% leads to a decreased number of handovers and thus to an improved voice quality.

Remark : obviously, if a value different from 0% is used, the path for dual band mobiles is completely modified. For example, with a scenario (see 3.3.3) micro 900 > macro 1800 > macro 900, a dual band mobile connected to a macro 900 cell will go directly to the micro 900 cell whereas two handovers are necessary to reach the micro 900 cell with MULTIBAND_LOAD_LEVEL = 0 %.

In B6 release, the parameter MULTIBAND_LOAD_LEVEL is replaced by the parameter MULTIBAND_TRAFFIC_CONDITION which can take the following values : ANY_LOAD, NOT_LOW and HIGH. Using a value different from ANY_LOAD, cause 21 is only triggered when the serving cell is loaded.

L_RXLEV_CPT_HO(n) (B5), L_RXLEV_CPT_HO(0,n) (B6)

It is also necessary to tune the capture threshold L_RXLEV_CPT_HO(n) used by causes 14 and 21 in order to avoid ping-pong handovers because of quality problems in the target cell (macro 1800 cell or micro 900 cell for example). Indeed, there is no real anti ping-pong mechanism in case of inter-layer or inter-band handover (anti ping-pong mechanism only for the triggering of cause 12).

In B6 release the capture threshold gives more flexibility as it is set on a per couple of cells basis.


Two parameters are very useful in a dual band network : PRIORITY(0,n) and HO_MARGIN_LEV(0,n).

PRIORITY(0,n)

This parameter is useful in case of Forced Directed Retry alarm and in case of emergency alarm in order to direct a mobile to the desired layer. This parameter is very easy to use (only four values: 0, 1, 2 and 3) and is set on a per couple of cells basis.

Remark : PRIORITY(0,n) is less useful in case of better condition cause (causes 21, 14 and 12) because the list of candidate cells is limited to the neighbouring cells which are specific to the handover cause (preferred band cells, lower layer cells, …).

In B6 release, the parameter PRIORITY(0,n) is also useful in case of better condition cause because all better condition causes are checked. Therefore, it is possible to have different types of neighbouring cells in the candidate cells list.



HO_MARGIN_LEV(0,n)

See part 4.1 : Zone exit.

5.1.2.4 Multiband cell

For a mobile in the outer zone of a multiband cell (900 TRX for example) only 900 measurements are available (900 neighbouring BCCH and 900 serving TCH). No 1800 level is available. Therefore, it is necessary to assume a default difference in propagation losses between the two bands for the handover from the outer zone to the inner zone. This difference is included in the parameters ZONE_HO_HYST_DL and ZONE_HO_HYST_UL. It will be necessary to tune carefully these parameters.

For a mobile in the inner zone of a multiband cell (1800 TRX for example) it is necessary to add an hysteresis (OFFSET_HO_MARGIN_INNER) to the classical HO_MARGIN parameter in order to compare a 1800 TCH level to a 900 BCCH level (cause 12 = power budget). Again, it is necessary to assume a default difference in propagation losses between the two bands. It will be necessary to tune carefully this hysteresis.

Finally, the parameter EN_BI-BAND_MS will be very useful to control outgoing handovers on causes 14 and 24 especially fo dual band MS located in the inner zone of a multiband cell.

5.1.3 Other aspects

5.1.3.1 Neighbouring cells

There are two limitations : 32 neighbouring BCCH (BA list) and 64 neighbouring cells (BCCH, BSIC).

These numbers are reached very easily in a network with 3 or 4 layers. On the other hand the efficiency of the monitoring of neighbouring cells is reduced when the number of neighbouring cells is elevated. Consequently, special care must be taken when defining the list of neighbouring cells.

5.1.3.2 Neighbouring cells reporting

In case of a continuous coverage provided by the 2 frequency bands, it is necessary to use MULTIBAND_REPORTING = 3 in order to balance the reporting of neighbouring cells in each frequency band.

In case of hot spot macro 1800 cells, it is not problematic to use MULTIBAND_REPORTING = 3. Indeed, if for a 900 serving cell there is only one 1800 neighbouring cell, remaining positions in the Measurement Report are used to report 900 neighbouring cells.



5.2 Monitoring

5.2.1 Key issues

The aim of the new frequency band is most often to solve congestion problems. It is therefore important to study the efficiency of the new frequency band to increase the capacity of the network. The idea is to obtain the percentage of time spent in dedicated mode on each frequency band by dual band MS in order to validate the parameters. It is also interesting to obtain the traffic distribution (time spent on each layer (macro 900, macro 1800, micro 900, micro 1800)) per mobile type (single band, dual band).

It is interesting to study the efficiency of selection (CELL_BAR_QUALIFY) and re-selection (C2 criterion). The idea is to obtain the distribution of call attempts (percentage of call attempts per layer) per mobile type.

It is also important to verify that the introduction of a new frequency band is transparent for single band mobiles. The idea is to compare the traffic distribution (macro and micro layers) before and after the introduction of the new frequency band.

It is particularly important to verify that there are no ping-pong handovers (as in all multi-layer networks). It is also important to verify that dual-band mobiles leave safely the new frequency band hot spot cells and the new frequency band cells located at the border of a new frequency band area.

It is obviously necessary to follow per mobile type usual quality of service indicators.

5.2.2 Tools

With B5 and B6 releases, it is not possible to distinguish single band mobiles from dual band mobiles using OMC-R counters except for the Erlang traffic (in B6 release, the MC381 counter gives the Erlang traffic due to dual band mobiles).

With the last release of AGLAE (A interface traces post-processing), it is possible to distinguish the two types of mobiles. Moreover Excel macros are available for the post-processing of Aglae files.

Refer to [4], chapter 5 (A interface and OMC-R counters) for a detailed presentation.

5.2.3 Multiband BSC : QoS follow-up with OMC-R indicators

The aim of this part is to give some guide lines for the QoS follow-up of new frequency band cells with OMC-R indicators through the study of some typical problems. The idea is to give possible explanations specific to new frequency band cells.

5.2.3.1 Few RTCH seized by mobiles for normal assignment on a new frequency band cell

The cell re-selection parameters are set in order to send dual band mobiles to the new frequency band cells in idle mode. Therefore if the number of RTCH seized by mobiles for normal assignment is low there may be a problem. In this case it is necessary to verify following points :



- is the new frequency band cell barred ?

- what about the area covered by the new frequency band cell ? It is perhaps logical that MS access to this cell mainly by handover,

- EIRP(new frequency band cell) << EIRP(old frequency band co-located cell) ? The parameter BS_TXPWR_MAX is perhaps wrong for the new frequency band cell,

- is the new frequency band cell declared as a neighbour of the old frequency band cells in idle mode ?

- does the new frequency band cell belong to the six strongest neighbouring cells of the co-located old frequency band cell in idle mode ? If not, the C2 criterion is useless to send dual band MS to the new frequency band cell in idle mode,

- what about the dual band MS penetration rate ?

5.2.3.2 High call drop rate on a new frequency band cell

If the call drop rate is elevated, it is necessary to verify following points :

- are some neighbouring cells missing, especially in case of zone exit ?

- do the mobiles mainly access to the new frequency band cell by handover (coverage of a road for example) ? In this case the call drop rate is not appropriate (because denominator = number of normal assignments + number of incoming HO - number of outgoing HO ≈ number of normal assignments = low value). Therefore it is recommended to monitor the TCH drop rate (denominator = number of normal assignments + number of incoming HO).

5.2.3.3 Low efficiency of outgoing handovers on a new frequency band cell

If the efficiency of outgoing handovers is low, it is necessary to verify the following point :

- are some neighbouring cells missing, especially in case of zone exit ?

5.2.3.4 High number of outgoing HO on distance cause on a new frequency band cell

There are possible explanations :

- use of a low value of the threshold U_TIME_ADVANCE (= 0 for the anticipated zone exit on distance). In this case the % of outgoing HO on distance cause is not relevant,

- use of a normal value of the threshold U_TIME_ADVANCE but the received level from the new frequency band cell when the distance cause is triggered is higher than the capture threshold leading to a ping-pong situation between the new frequency band cell and the old frequency band layer. It is necessary to avoid this kind of situation.

- use of a normal value of the threshold U_TIME_ADVANCE and the distance cause is triggered before the level and quality causes. If the received level from the new frequency band cell is lower than the capture threshold, there is no risk of ping-pong. In this case, the high value of the indicator is not problematic.



5.2.3.5 Low RTCH mean holding time on a new frequency band cell

If the new frequency band cell covers an area with fast moving mobiles, the low value of the indicator is not problematic.Otherwise, there is perhaps a ping-pong situation between the new frequency band cell and the old frequency band layer :

- the new frequency band cell may be interfered even at a level higher than the capture threshold,

- the new frequency band cell is a hot spot cell or is located at the border of the new frequency band area and the zone exit is not made properly.

5.2.4 Multiband cell : QoS follow-up with OMC-R indicators

The aim of this part is to present the available counters and indicators for the monitoring of multiband cells. The way to monitor the dual band network is really different because 900 and 1800 frequencies belong to the same cell. Therefore, the difficulty is to provide QoS statistics per frequency band.

It is possible to obtain :

- Erlang traffic for 900 TRX and 1800 TRX. It is interesting to calculate the ratio Traffic inner zone / Traffic cell,

- Erlang traffic for 900 TRX and 1800 TRX due to dual band mobiles (MC381 counter),

- TCH mean holding time for 900 TRX and 1800 TRX,

- number of HO attempts (assignment command sent to the MS) on cause 13 (outer zone to inner zone HO) : C586c counter,

- number of HO attempts (assignment command sent to the MS) on causes 10 and 11 (inner zone to outer zone HO) : C586a and C586b counters,

- classical intracell HO statistics : efficiency, failure with drop cause radio, failure with drop cause BSS, failure with reversion to old channel, failure cause congestion. Nevertheless it is not possible to distinguish outer zone to inner zone HO from inner zone to outer zone HO. Moreover remember that inter zone handovers (inner to outer) are also possible on causes 15 and 16,

- rate of inter zone handovers per call (number of inter zone HO attempts on causes 13, 10 and 11 / (number of TCH successfully seized by MS - number of successful outgoing HO) : this indicator is interesting to detect a ping-pong situation between the two zones.

Therefore we are not able to provide the same statistics per frequency band (call drop, efficiency of incoming HO, …) than in the case of a multiband BSC network where there are 900 and 1800 cells. Some operators will perhaps complain about this situation.

Problems of B5 release


6 Weaknesses of the algorithms

6.1 Detection of better condition handover causes This weakness is linked to the B5.1 release. It is solved by the B5.2 release and obviously

by the B6 release.


One weakness of B5.1 release is the behaviour of the handover detection process. Indeed, handover causes are tested according to their level of priority. Then, when a handover cause is verified, the handover candidate cell evaluation process is started and handover causes with a lower level of priority are not checked.

This behaviour is problematic in a multi-layer, multi-band network. Indeed, a problem occurs with better condition handover causes. We saw that up to 4 better condition causes are available for TCH-TCH handovers in B5 release :

- cause 21 for handovers from a non-preferred band cell to a preferred band cell,

- cause 14 for handovers from a upper layer cell to a lower layer cell,

- cause 12 for handovers between cells working in the same frequency band and belonging to the same layer,

- cause 13 for handovers from the outer zone to the inner zone of a concentric cell.

These causes are checked with the following priority order : cause 21, cause 14, cause 12 and cause 13. If one of these 4 causes is verified, causes with a lower level of priority are not checked. This is a problem because :

- if the neighbouring cell which has triggered the handover cause with the level of priority n is not accessible (congestion for example) it is not possible to make a handover towards a neighbouring cell using a handover cause of priority n-1 or n-2,

- it is much more complicated to manage the priority between the different layers. Indeed, the use of the parameter PRIORITY(0,n) is limited to a group of neighbouring cells (lower layer cells, preferred band cells, …).

6.1.2 Examples

In order to illustrate the problem linked to the unavailability of a neighbouring cell accessible using a high level of priority handover cause, let us consider the example of a classical dual band network with 3 layers : macro 900, macro 1800, micro 900. This network was previously a 900 MHz network with 2 layers : macro 900 and micro 900. Then the operator added a third layer (macro 1800) in order to solve congestion problems. The idea is here to give the highest priority to the macro 1800 layer for dual band MS. If this layer is not available (congestion, bad coverage) the operator wants to send a dual band MS to the micro 900 layer.



Now, imagine the case of a dual band MS in a macro 900 cell whith at least a macro 1800 cell and a micro 900 cell available (good received level). Then, cause 21 is verified but the dual band MS is unable to make the handover towards the macro 1800 cell (congestion). In B5.1 release the dual band MS is also unable to go to the micro 900 cell because cause 14 is not checked (cause 21 is verified).

In order to illustrate the difficulty to manage the priority between the different layers, let us consider a second example. We take again the case of a classical dual band network with 3 layers : macro 900, macro 1800, micro 900. The idea is here to give the highest priority to the micro 900 layer for dual band MS (corporate micro cell dedicated to indoor coverage). If a macro 1800 cell and a micro 900 cell are available (good received level), two handovers are necessary to go to the micro 900 cell.




Cause 21

Cause 14

Cause 12

Cause 12

Cause 12

Cause 21




Cause 21

Cause 14

Cause 12

Cause 12

Cause 12




There is no solution in B5.1 release.

In B5.2 and B6 releases, the problem is solved because all better condition handover causes are checked before the beginning of the candidate cell evaluation process.

In the first case above, the micro 900 cell will belong to the list of candidate cells. Then, in case of congestion of the macro 1800 cell, it will be possible to attempt a handover towards the micro 900 cell.

In the second case, using the parameter PRIORITY(0,n) (PRIORITY(0,n) = 0 between a macro 900 cell and a micro 900 cell, = 1 between a macro 900 cell and a macro 1800 cell) and the general capture HO cause (B6 release; causes 21 and 14 are not synchronized), it will be possible to send a dual band MS directly to the micro 900 cell.



6.2 Cause 21 and micro 1800 cells This weakness exists in B5.1 release and is not solved by the B5.2 and B6 releases.


A problem occurs in the case of a network with 2 layers (macro and micro) in the preferred band. The idea is to use cause 21 to go to the macro preferred band layer and cause 14 (speed discrimination) to go to the micro preferred band layer.

The problem is that it is difficult to avoid a handover on cause 21 towards a micro preferred band cell. Indeed cause 21 is checked towards micro preferred band cells.

In B5.1 release, it is possible to filter a micro preferred band cell which triggers cause 21 but cause 14 is not checked. In B5.2 release, causes 21 and 14 are checked, the PBGT filtering is available but only one cause number (21) is sent to the candidate cell evaluation process (if causes 21 and 14 are verified at the same time). In B6 release, causes 21 and 14 are checked but it is no more possible to filter a micro preferred band cell which triggers cause 21.

6.2.2 Example

For the sake of simplicity, let us take the example of a dual band network with 3 layers : macro 900, macro and micro 1800.

It is necessary to avoid handovers on cause 21 between the macro 900 and the micro 1800 cells (no speed discrimination). The problem is that :

- it is necessary to enable cause 21 on the macro 900 cells in order to go to the macro 1800 layer,



Cause 21

Cause 14

Cause 12

Cause 12

Cause 12Micro 1800Cell_dimension_type = microCell_layer_type = lower



- it is not possible to play with the load threshold used by cause 21 because this threshold is also used for the handovers towards the macro 1800 layer,

- it is not possible to play with the level threshold used by cause 21 because this threshold is also used by cause 14.


This solution was tested in Johannesburg (October 1998) during the dual band field trial with Vodacom.

In B5.1 release, in order to avoid a handover on cause 21 towards the micro 1800 layer, it is necessary to use the PBGT filtering process and to modify the parameter Cause_Margin_P_21 on the macro 900 layer. The problem is that this parameter is not accessible at the OMC-R (DLS parameter).

The idea is to filter the micro 1800 neighbouring cell which has triggered cause 21 using the following set of parameters :

- EN_PBGT_FILTERING = Enable on the macro 900 layer,

- Cause_Margin_P_21 = 60 dB on the macro 900 layer,

- HO_MARGIN(0,n) = 5 dB between a macro 900 cell and a micro 1800 cell,

- HO_MARGIN(0,n) = -127 dB between a macro 900 cell and a macro 1800 cell.

With these parameters, the filtering condition (PBGT filtering) is :

- PBGT(n) > HO_MARGIN(0,n) + Cause_Margin_P_21 = -127 + 60 = -67 dB for a macro 1800 cell (no filtering),

- PBGT(n) > HO_MARGIN(0,n) + Cause_Margin_P_21 = 5 + 60 = 65 dB for a micro 1800 cell (filtering).

In B6 release, the PBGT filtering is no more available after the triggering of a better condition cause. Therefore the above solution is no more usable.

END OF DOCUMENT

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