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EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
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Module Objectives
Upon completion of this module, you should be able to:
� Describe algorithms dedicated to multilayer and multiband networks management
EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
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Table of Contents
Switch to notes view! Page
1 Introduction 72 Neighboring cells list 103 Idle Mode Selection and Reselection 194 Call Setup 375 Handover Strategies 516 Main Standard Handover Algorithms 597 Emergency Handover Algorithms for MBML Networks 988 Better Conditions Handover Algorithms for MBML Networks 1109 Multiband Cells 13610 Candidate Cell Evaluation 161
EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
EVOLIUM Base Station Subsystem · Multiband and Multilayer GSM network radio optimization - B10Multiband & Multilayer Optimisation · Algorithms and Associated Parameters
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1 Introduction
Justification
� Multiband/Multilayer brings new features and algorithms :
� Designing, managing and monitoring complex networks is more difficult
� A relevant choice of architecture and parameters settings will precede the introduction of a new layer in the existing network
� To be sure to implement correctly the best strategy for your network, knowledge of all algorithms and parameters is mandatory.
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1 Introduction
Typing Conventions
� In all this document
� SYSTEM PARAMETERS (can be set at the OMC-R level) will always be written in BLUE BOLD FONT
� VARIABLES (averages, internal system variables, etc.) will be typed in NORMAL FONT
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2 Neighboring cells list
Purpose
� Neighboring cells list is sent to the MS regularly and contains all BCCH frequencies of neighbor cells to be monitored by the MS
� The MS measures them regularly in order to :
� Perform cell selection & reselection (in idle mode)
� Report 6 BCCH RxLev to the BSS for handovers (in dedicated mode)
798798 2020
4545
800800
805805
22
MS shall measure the BCCH of neighbor cells and decode their BSIC at least once every 10 seconds.
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2 Neighboring cells list
Idle Mode
� 2 possibilities, the MS camps on either :
� A cell with a BCCH on a DCS 1800 frequency
� Or a cell with a BCCH on a GSM 900 frequency
805805BCCH 1800
SI 2 and 2bis : 1800 neighboring cells
SI 2ter : 900 neighboring cells
2020BCCH 900
SI 2: 900 neighboring cells
SI 2ter (& 2bis): 1800 neighboring cells
SI : Sytem Information Messages
Description of all SI messages : 3GPP TS 44.018 Mobile radio interface layer 3 specification; Radio Resource Control (RRC) protocol, several chapters starting from §9.1.31
It takes up more space to broadcast 1800 frequencies, therefore 2 SI are necessary.
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2 Neighboring cells list
Dedicated Mode
� 2 possibilities, the call is performed on either :
� A cell with a BCCH on a DCS 1800 frequency
� Or a cell with a BCCH on a GSM 900 frequency
805805SACCH
SI 5 and 5bis: 1800 neighboring cells
SI 5ter: 900 neighboring cells
2020SACCH
SI 5: 900 neighboring cells
SI 5ter (& 5bis): 1800 neighboring cells
SACCH can be either on a 1800 MHz TRX or a 900 MHz TRX.
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2 Neighboring cells list
Multiband configuration
� Which ever is the band of the current cell, the MS can receive BCCH list that belongs to the other band only with :
� SI-2ter
� SI-5ter
� To enable/disable this SI messages on BCCH and SACCH
� EN_INTERBAND_NEIGH = enable (1)
� EN_INTERBAND_NEIGH = disable (0)
� Description : BSC parameter that enables / disables the multiband operation by filtering the sending of SYSTEM INFORMATION TYPE 2ter/5ter.
Note : on the OMC-R "cell edit" screen, this parameter is named "EN_INTERBAND_HO".
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2 Neighboring cells list
Cell Monitoring
� In dedicated mode, a MS can only report 6 measurements :
� Standard behavior in a mono-band network : MS reports the 6 strongest cells
� Problem : in a multiband network, 1800 cells provides less signal strength and might not be included in the 6 strongest neighbors !
805805
MEAS REPORT…
N1 : (BSIC, RXLEV)
N2 : (BSIC, RXLEV)
N3 : (BSIC, RXLEV)
N4 : (BSIC, RXLEV)
N5 : (BSIC, RXLEV)
N6 : (BSIC, RXLEV)
MEASUREMENT REPORT is sent on the UL SACCH of the dedicated TCH, every 480ms.
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2 Neighboring cells list
Cell Monitoring [cont.]
� Reported neighbors from each band can be forced thanks to the cell parameter :
� MULTIBAND_REPORTING
� 4 possible values
� 0: 6 strongest cells irrespective of the frequency band
� 1: 1 strongest cell (non-serving cell frequency band) + 5 strongest cells(serving cell frequency band)
� 2: 2 strongest cells (non-serving cell frequency band) + 4 strongest cells(serving cell frequency band)
� 3: 3 strongest cells (non-serving cell frequency band) + 3 strongest cells(serving cell frequency band)
� Default value:
� 0 for mono-band network
� 3 for multiband network
For a multi band MS, the number of cells per freq band which shall be included in the measurement report is
indicated by the parameter MULTIBAND_REPORTING, broadcast on BCCH.
An MS attached to GPRS shall use the parameter broadcast on BCCH. The parameter may also be sent to the MS
on SACCH.
The meaning of different values of the parameter is specified as follows:
Value Meaning
00 Normal reporting of the six strongest cells, with known and allowed NCC part of BSIC, irrespective
of the band used.
01 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.
10 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.
11 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
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2 Neighboring cells list
Cell Monitoring Optimization
� MULTIBAND_REPORTING has to be tuned carefully in multiband network, since no handover can be done to a cell which is not reported
� The parameter value is depending on network strategy and may be tuned differently in each band
Example: give priority to 1800 cells
� In 900 layer cells
MULTIBAND_REPORTING = 1 is most of the time sufficient to make a handover towards the preferred band
� In 1800 layer cells
MULTIBAND_REPORTING = 3 : 1800 neighboring cells have to be reported to keep the MS in the same band when possible, but 900 cells should be reliably reported as they are rescue cells.
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2 Neighboring cells list
Number of neighboring cells
� Neighboring cells list limited to 32 BCCH's in OMC-R :
� Limit easily reached in a network with 3 or 4 layers, and 2 bands
� A special care must be taken when defining the list of neighboring cells
� The multiband cells solution dramatically reduces this problem when introducing new frequency band
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3 Idle Mode Selection and Reselection
Strategy
� Adding a new band/layer is a powerful way of increasing network capacity if the MS can be sent to the preferred cell
� In dedicated mode: see next sections
� But also in idle mode, so that the call is established directly in the preferred cell
� Really increase capacity
� Maintain high QoS level, without creating extra HO
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3 Idle Mode Selection and Reselection
Selection and Reselection Principle
� At startup (IMSI Attach), the MS is selecting cell with
� Defined priorities with CELL_BAR_QUALIFY
� Best C1 amongst highest priority cells (using CBQ)
� Once “camped on” one cell (in idle mode)…
� … The MS can decide to reselect another one if:
� C1 criterion < 0
� The MS cannot decode downlink signalling blocks of Paging Channel
� The current cell is becoming forbidden (e.g. barred)
� A random access attempt is still unsuccessful after "Max retrans" repetitions
� MS detects the network has failed authentication check
� There is a better cell, regarding C2 criterion
MAX_RETRANS is a cell parameter, transmitted in SI-2.
Authentication check : during SDCCH phase (call setup, location update)
Note:
Cell selection (first selection) is performed using C1 criterion only (the chosen cell is the one with the best C1)
Reselection is done using the mechanisms referenced above.
e.g., the MS cannot access the cell.
It can be linked to SDCCH congestion, filtering of CHARQD due to TA greater than RACH_TA_FILTER, radio access
problem during the Radio Link Establishment phase.
� If SDCCH is to be seized for LU purpose, the MS will reselect on another cell.
� If SDCCH is seized for something else (e.g., MOC), the MS « may » reselect (this is up to the MS vendor
choice!!!). Some MSs do nothing. Call will never be possible. Some others do reselect. In that case, the user has
to reattempt his call (after the reselection, but before the MS is back to the original cell due to better C2, etc.
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3 Idle Mode Selection and Reselection
Cell Selection with CBQ
� Cell selection, use of CELL_BAR_QUALIFY:
� Set on a per cell basis
� Broadcast on the BCCH
� 2 possible values:
� 0 = normal priority (default value)
� 1 = lower priority
� The MS selects the suitable (C1 > 0) cell with the highest C1 belonging to the list of highest priority
The CELL_BAR_QUALIFY parameter is not understood by phase 1 MS.
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3 Idle Mode Selection and Reselection
Cell Selection with CBQ [cont.]
� Example: highest priority set on microcell
� The MS will select the microcell (if available, C1>0), whatever the level of the macrocell
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3 Idle Mode Selection and Reselection
Cell Selection with CBQ [cont.]
�WARNING: usage of CELL_BAR_QUALIFY:
� interacts with CELL_BAR_ACCESS
� A cell with low priority (CELL_BAR_QUALIFY = 1) cannot be barred
� Some MSs will be able to access it, whatever the value of CELL_BAR_ACCESS
normal (see note 1)low11
normal (see note 1)low01
barredbarred10
normalnormal00
Status for cell reselectionCell selection priorityCELL_BAR
ACCESS
CELL_BAR
QUALIFY
NOTE 1: Two identical semantics are used for cross phase compatibility reasons. This allows an operator to
declare a cell always as a low priority one for a phase 2 MS, but keeps the opportunity for an operator to
decide whether a phase 1 MS is permitted to camp on such a cell or not.
Because phase-1 MS do not support this feature, it is recommended to keep cell bar qualify = 0.
Also, some early phase-2 MS do not handle this parameter properly.
This is only useful during selection (switching the MS, before C1 computation). Afterwards, only reselection will
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3 Idle Mode Selection and Reselection
C1 Criterion
� C1
� ensures that, if a call was attempted, it would be done with a sufficient downlink and uplink received level
� based on 2 parameters, broadcast on the BCCH
� RXLEV_ACCESS_MIN [dBm]� Minimum level to access the cell
� Default value (for Evolium): -103 dBm
� MS_TXPWR_MAX_CCH [dBm]� Maximum level for MS emitting
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3 Idle Mode Selection and Reselection
C1 Criterion [cont.]
� C1
� evaluated every 5 s (minimum)
� C1 = A - MAX(0,B) > 0
� A = RxLev - RXLEV_ACCESS_MIN
� assess that the MS received level is sufficient
� B = MS_TXPWR_MAX_CCH - P
� P maximum power of MS
� assess that the BTS received level will be sufficient
� if MS_TXPWR_MAX_CCH < P
C1 is computed for each neighbor, using the parameters broadcasted in each neighbor !
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3 Idle Mode Selection and Reselection
C2 Criterion [cont.]
� C2
� If CELL_RESELECT_PARAM_IND= present
� And if PENALTY_TIME = Infinity (= 640s)
C2 = C1 - CELL_RESELECT_OFFSET
CELL_RESELECT_OFFSET used to handicap some cells among others
Step size = 20s. 0: 20s, 1: 40s, ..., 30: 620s, 31: TEMPORARY OFFSET ignored and cell_RESELECT_OFFSET has a
negative value
This formula is very useful to favor an indoor cell or a microcell.
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3 Idle Mode Selection and Reselection
C2 Criterion [cont.]
� Case of "better cell" reselection
� The MS will select the neighbor cell if :
� Cells in same Location Area
C2neighbor > C2current
� Cells in different Location Area
C2neighbor > C2current + CELL_RESELECT_HYSTERESIS
CELL RESELECT HYSTERESIS is a parameter defined in the current cell.
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3 Idle Mode Selection and Reselection
C2 Parameters
� CELL_RESELECT_PARAM_IND
� C2 parameters are broadcast if = ENABLE (default)
� otherwise C2 = C1
� PENALTY_TIME
� From 20s to 620s, in "20s" increment step
� Default value = 20s
� 640s : infinite penalty
� CELL_RESELECT_OFFSET
� From 0 dB to 126 dB, in "2dB" increment step
� Default value = 0dB
� TEMPORARY_OFFSET
� From 0 dB to 60 dB, in "10dB" increment step (+ Infinity)
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3 Idle Mode Selection and Reselection
CRO Tuning
In a multiband network :
� Differences in TRX output power
� TRX 1800 MP (TRADE) = 45.4 dBm
� TRX 900 MP (TRAGE) = 46.5 dBm
� Differences in path loss
� On a same path :
Average propagation loss = difference in path loss + difference in TRX output power = 10dB approx.
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3 Idle Mode Selection and Reselection
CRO Tuning [cont.]
� Therefore, a 1800 cell will provide less coverage than a 900 cell
� Delta = 8~10dB
� Less traffic is carried by 1800 cells (more capacity available)
� Additionally, the 1800 frequency planning is usually cleaner than the 900 one.
Even at low RxLev, a 1800 cell might provide a coverage with good quality and good capacity
For this reason, CRO is used to advantage 1800 cells over 900 cells.
� Within a same layer : CRO(1800) = CRO(900) + 2~8dB
� Among different layers : CRO(1800) = CRO(900) + 4~12dB
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3 Idle Mode Selection and Reselection
Exercise
� Is there a way to keep fast-moving mobiles in the upper layer ?
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4 Call Setup
Principles
� Call setup is made on the cell (re)selected in idle mode
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4 Call Setup
Congestion in the Preferred Cell
� The risk is to have congestion in the preferred cell!
� Classical band / upper cells are unloaded…
� … as all MSs are sent to new cells in idle mode
� This phenomenon is further amplified by handovers behavior
� Multiband/multilayer algorithms are based on CAPTURE mechanisms
� Send the MS in the preferred cell as soon as it is OK…
� … Without comparing serving and preferred cells…
� … to reach the maximum capacity increase
(See handover parts for details)
When a MS camps on a cell in Idle mode, it will perform call setup on this cell (and all other procedures : location
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4 Call Setup
Algorithms Principles (cont.)
New capacity
Trafficincrease
Old capacity
Water Valve with filter:
Dual layer algorithms
As seen earlier :
Cell Selection & Reselection can favor new cells
Handovers can capture traffic from old cells and push it to new cells
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4 Call Setup
Algorithms Principles (cont.)
New capacity
Trafficincrease
Old capacity
Water Pump:
Forced
Directed Retry and
Fast Traffic
handover
By sending too much traffic on new cells, there is a risk of congestion. It can be avoided by Forced Directed Retry
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4 Call Setup
Directed Retry Principles
� A Directed Retry:
� SDCCH to TCH intercell handover
� Triggered during a call setup procedure
MSServingCell BSC MSC
Assignment Request
SDCCH Assignment PhaseSDCCH Assignment Phase
SDCCH PhaseSDCCH Phase(SDCCH)
T11
ChannelActivation
HandoverHandover
(TCH)
TargetCell
HO Command
ack
HO Access
HO CompleteAssignment Complete
Serving cell is congested, waiting to find a neighbor cell
� After channel request, a SDCCH is allocated to the MS
� If no TCH is available, the MS is queued in the TCH QUEUE
� If a HO is detected & the target cell has a TCH availble
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4 Call Setup
Directed Retry Principles [cont.]
� Internal and External Directed Retries are possible
Handover detection based on standard intercell HO algorithms:
- Too low level- Too bad quality- Power Budget / Traffic HO- Capture (14, 21, 24)- etc. (except Fast Traffic HO)
Handover detection based on a specific algorithm (Cause 20).
Candidate cell evaluation based on specific criteria.
Normal Directed RetryNormal Directed Retry Forced Directed RetryForced Directed Retry
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4 Call Setup
Normal Directed Retry
� Set on a per cell basis with parameter EN_DR
� EN_DR = enable (DR execution is enabled in the cell)
� EN_DR = disable (DR execution is disabled in the cell)
� Executed only if no TCH available in serving cell and standard intercell HO detected
� Except Intracell HO causes 10, 11 and 13 (concentric cells) and causes 15 and 16 (interference HO)
� Except Cause 28 (Fast Traffic HO)
� The target cell is chosen by the BSC based on the HO detected
If the target cell is congested, the counter MC555 is incremented :
Definition : Number of incoming internal directed retry (forced or normal) -preparation failures due to
congestion (on Air or A-bis interface). The target TCH channel can be in HR or FR usage.
Trigger condition
1) Whenever there are no free TCH in the target cell during a forced or normal internal directed retry.
2) Whenever no TCH resource is available on A-bis interface for a forced or normal internal directed retry.
(not valid in B7)
EN_EXT_DR : enables/disables the Outgoing External Directed Retry procedure (on a per BSC basis)
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4 Call Setup
Forced Directed Retry (Cause 20)
� CAUSE 20: Forced Directed Retry
� To activate FDR : EN_FORCED_DR = Enable AND EN_DR = Enable
� AV_RXLEV_NCELL_DR(n) is calculated with the A_PBGT_DR window
� If less than A_PBGT_DR samples are available
� AV_RXLEV_NCELL_DR(n) is calculated with the available "n" samples and remaining "A_PBGT_DR – n" are filled with -110 dBm
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)
And EN_FORCED_DR = ENABLED
AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)
And EN_FORCED_DR = ENABLED
AV_RXLEV_NCELL_DR(n) is calculated for each neighbor (neighbor's BCCH), and compared to the
L_RXLEV_NCELL_DR(n) of this neighbor, within the BSC.
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4 Call Setup
FDR Parameters
� L_RXLEV_NCELL_DR(n): level required in the neighboring cell n
� The parameter considered is the one set in the neighboring cell
� The default value depends on the network architecture
� See the next slide
� Freelevel_DR(n): number of free TCH channels required in the neighboring cell n
� The parameter considered is the one set in the neighboring cell
� Default value = 0 to 4 TCHs (linked to the nb of TRXs)
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4 Call Setup
Managing DR Parameters
� Normal DR
� Pro's: no radio problem as MS's remain within the service area of the new serving cell
� Con's: poor probability of happening, as MS is already camping on the best server cell
� Forced DR
� Pro's: Probability of detecting a FDR depends on parameter settings.
� Con's: Interference problems because MS is perhaps outside the cell normal service area
Umbrella cell
Micro cell
FDRcapture
Forced Directed Retry strategy:
� Between one micro cell and its umbrella macro cell
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4 Call Setup
Access Strategy
� Prevention of congestion in the “old” cells
� MSs are sent in idle mode to the “preferred cell”
� HO strategy favoring the “preferred cell” in dedicated mode
� Prevention of congestion in the “preferred cell”
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� A dual layer network is considered
� Umbrella cells 900
� Micro cells 900
� Set FDR parameters to avoid interference and allow a powerful TCH resource usage
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5 Handover Strategies
Objectives
1. Maximize capacity of the network, with:
� Intelligent MS sharing between available resources
� Avoid congestion of historical band (for old MS)
� Consider traffic conditions of all layers
� Use full capacity of new resources (1800 band is offering more channels)
� Consider MS speed for layer discrimination
� Avoid too many handovers
� Degradation of voice quality
� In order to ease traffic analysis, it is recommended to avoid too many handovers between layers.
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5 Handover Strategies
Objectives [cont.]
2. Insuring good quality communications and avoiding call drops
� Send MS towards the layer that will provide the best QoS
� Minimize the number of HO between cells for good speech Quality
� Fast moving mobiles are handled by the macrocell layer
� Identify a best target for emergency handovers cases
� The tuning of the parameters will result in trade-offs
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5 Handover Strategies
Handover Algorithms
� Next parts will detail available HO causes for multilayer network management
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5 Handover Strategies
HO Causes
� Standard HO causes
� cause 2 : too low quality on the uplink
� cause 3 : too low level on the uplink
� cause 4 : too low quality on the downlink
� cause 5 : too low level on the downlink
� cause 6 : too large distance between the MS and the BTS
� cause 15 : high interference on the uplink (intra-cell HO)
� cause 16 : high interference on the downlink (intra-cell HO)
� cause 26 : AMR channel adaptation HO (HR to FR)
� cause 12 : power budget evaluation
� cause 23 : traffic
� cause 27 : AMR channel adaptation HO (FR to HR)
� cause 28 : Fast traffic HO
� cause 29 : TFO HO
� cause 20 : FDR
EM
BC
These causes will always work, whether the network is monoband monolayer, or multiband multilayer.
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5 Handover Strategies
HO Causes [cont.]
� HO causes for multilayer and multiband networks
� cause 10 : too low level on the uplink in the inner zone
� cause 11 : too low level on the downlink in the inner zone
� cause 7 : consecutive bad SACCH frames received in a microcell
� cause 17 : too low level on the uplink in a microcell compared to a high threshold
� cause 18 : too low level on the downlink in a microcell compared to a high threshold
� cause 13 : too high level on the uplink and the downlink in the outer zone
� cause 14 : high level in the neighboring cell of a lower or indoor layer for slow mobile
� cause 21 : high level in the neighboring cell in the preferred band
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5 Handover Strategies
HO Causes Priority
� cause 7 : consecutive bad SACCH frames received in a microcell� cause 17 : too low level on the uplink in a µcell compared to a high threshold� cause 18 : too low level on the downlink in a µcell compared to a high threshold� cause 2 : too low quality on the uplink � cause 3 : too low level on the uplink � cause 4 : too low quality on the downlink � cause 5 : too low level on the downlink � cause 6 : too large distance between the MS and the BTS� cause 10 : too low level on the uplink in the inner zone� cause 11 : too low level on the downlink the in inner zone� cause 26 : AMR channel adaptation HO (HR to FR)� cause 15 : high interference on the uplink (intra-cell HO)� cause 16 : high interference on the downlink (intra-cell HO)
� cause 21 : high level in the neighboring cell in the preferred bandcause 14 : high level in neighboring cell of a lower or an indoor layer cell for slow mobilecause 24 : general capturecause 12 : power budget evaluationcause 23 : traffic
� cause 13 : too high level on the uplink and downlink in the outer zone� cause 27 : AMR channel adaptation HO (FR to HR)� cause 20 : Forced Directed Retry DR� cause 28 : Fast traffic HO
EM
BC
The handover causes are checked with the priority order defined here.
The better condition causes 21, 14, 24, 12 and 23 have the same priority. For each cell in the list of possible
candidate cells is associated a cause.
If a cell is in the candidate cells list because of 2 different causes, only the one with the highest priority in the
ordered list (cause 21, cause 14, cause 24, cause 12 and cause 23) in which cause 21 has the highest priority is
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6 Main Standard Handover Algorithms
Emergency Intercell Algorithms
� Emergency intercell handovers
� cause 2 : too low quality on the uplink
� cause 3 : too low level on the uplink
� cause 4 : too low quality on the downlink
� cause 5 : too low level on the downlink
� cause 6 : too large distance between the MS and the BTS
� May be triggered
� From any serving cell (any band, any zone, any layer)
� Towards any neighbour, except the serving cell
� Note : EM HO detected while in the inner zone of a cell
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The aim of these causes is to keep the call going when the radio link is degrading otherwise the radio link failure might be detected and the call released. These causes wait generally for the power control process to increase the BTS and MS power to their maximum values, except for the causes specific to microcellular environment.
Handover on "too low level" is used to avoid situations where the interference level is low, while the attenuation is quite high. These conditions may appear for example in big city streets which ENABLED a line of sight propagation from the BTS antenna. There is in this case a risk of abrupt quality degradation, if the MS moves away from the line of sight street.
In case of simultaneous low-level and low-quality signals, an intercell handover is requested.
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6 Main Standard Handover Algorithms
Handover Cause 6: Distance
� CAUSE 6 : Too long distance
� Size of window for averaging distance : A_RANGE_HO
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
AV_RANGE_HO > U_TIME_ADVANCE
and EN_DIST_HO = ENABLED
This cause is used when a dominant cell provides a lot of scattered coverages inside other cells, due to
propagation conditions of the operational network. These spurious coverages is the probable production of a high
level of co-channel interference.
This cause is different from the others as it is more preventive. It does not make use of the propagation
conditions of a call. It just does not allow an MS to talk to a BTS if it is too far away.
It may happen for example that some peculiar propagation conditions exist at one point in time that provide
exceptional quality and level although the serving BTS is far and another is closer and should be the one the
mobile should be connected to if the conditions were normal.
It may then happen that these exceptional conditions suddenly drop and the link is lost, which would not have
happened if the mobile had been connected to the closest cell. For these reasons also, this cause does not wait
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6 Main Standard Handover Algorithms
Emergency Intracell Handovers
� Emergency intracell handovers
� cause 15 : high interference on the uplink (intra-cell HO)
� cause 16 : high interference on the downlink (intra-cell HO)
� May be triggered
� From any serving cell (any band, any zone, any layer)
� Towards only the serving cel
� Note : If the MS is on a non-hopping TRX, the BSC will tend to allocate a TCH on another TRX.
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6 Main Standard Handover Algorithms
New Parameters for Causes 15 & 16
� CAUSE 15 and CAUSE 16:
� THR_RXQUAL_CAUSE_15 (or 16) and EN_CAUSE_15 (or 16) are specific to variable computed by the BSC :
� THR_RXQUAL_CAUSE_15 (or 16) =
� L_RXQUAL_XX_H for a non AMR call (same threshold as CAUSE 2 or CAUSE 4)
� L_RXQUAL_XX_H_AMR for an AMR call
� EN_ CAUSE _15 (or 16) =
� EN_INTRA_XX for a non-AMR call
� EN_INTRA_XX_AMR for an AMR call
XX = UL or DL
For a non AMR call, the thresholds used are identical to the ones used for CAUSE 2 and CAUSE 4.
In this case and if EN_INTRACELL_REPEATED = DISABLED, when a HO CAUSE 15 (or 16) fails, it can be modified as
UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
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Causes 15 & 16: specific case of concentric cells
� For an MS in the INNER zone, if cause 15 or 16 is triggered:
� TCH may be allocated in the outer zone or in the inner zone
� For an MS in the OUTER zone, if cause 15 or 16 is triggered:
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget
�Definition of PBGT HO :
� “Comfort” handover type, no matter of emergency
� Possible targets depend on the cells layer type :
Single or UpperSingle or UpperSingle
MS Speed = FASTMS Speed ≠ FAST
Indoor
Lower
Single or Upper
Target Layer Type
Upper or Indoor
Upper or Lower
Single or Upper
Serving Layer Type
Indoor
Lower
Upper
If the MS is measured as fast, HO preferably towards upper cells with
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
�Definition of PBGT HO :
� Possible targets depend also on the cells band type :
GSMAnyGSM
EN_MULTIBAND_PBGT_HO= Disable
EN_MULTIBAND_PBGT_HO= Enable
Any
Target Band Type
DCS
Serving Band Type
(MS not in inner zone of a MB cell)
DCS
A multiband cell is "GSM" if the outer zone is in GSM (cf. note)
The cell band type is an internal variable in the BSC, it depends on the BCCH frequency only. Therefore a
multiband cell has a cell band type = GSM if the outer zone is in GSM900.
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
�Definition of PBGT HO :
� … And if the MS is in the inner zone of a multiband concentric cell :
GSM-DCSAnyGSM
EN_MULTIBAND_PBGT_HO= Disable
EN_MULTIBAND_PBGT_HO= Enable
Any
Target Frequency Band
GSM-DCS
Serving Band Type
(MS in inner zone of a MB cell)
DCS
When in the MB inner zone, it is possible to force PBGT HO only towards other
MB cell.
Serving cell is a multiband cell : Band type depends on the BCCH frequency.
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Handover Cause 12: Power Budget [cont.]
� If EN_MULTIBAND_PBGT_HO = disable
Single 900
Upper 900
µ900
900 1800
indoor900
Upper 1800
µ900
mini1800
Upper 900
Single 1800
900 1800
indoor900
mini900
fast
fast
fast
fastfast
Upper
Upper
This scheme highlights well the difficulty of introducing multiband cells if EN_MULTIBAND_PBGT_HO is disabled
(this was the only configuration in the first B6.2 networks): Multiband cells interoperate only with, etc.
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
� Based on Power budget equation
� Size of window for level averaging: A_PBGT_HO
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)
- PING_PONG_MARGIN(n, call_ref)
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)
- PING_PONG_MARGIN(n, call_ref)
(A)
(B)
(C)
(D)
The value of PBGT(n) is calculated every SACCH period for each neighboring cell n whose measures are kept in
the book-keeping list
A : favor cell with highest difference between RXLEV(n) and RXLEV(s)
B : compensate for effect of the power control in DL (if PC DL attenuates BS TXPWR by 4dB, the RXLEV(s) is also
attenuated by 4dB)
C : favor the cell where the MS is the most limited in TX power (to limit UL interference and extend battery life)
� automatic bonus of +3dB from 900-serving to 1800-neighbours.
� automatic handicap of -3dB from 1800-serving to 900-neighbours.
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
� A Handover cause 12 is detected only if the following conditions are met :
� Size of window for level averaging: A_PBGT_HO
if EN_TRAFFIC_HO(0,n) = DISABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
if EN_TRAFFIC_HO(0,n) = DISABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
(*) OFFSET_HO_MARGIN_INNER is applied only if the MS is currently located in the inner zone of a concentric
cell (multiband or monoband). This parameter will be explained in chapter 7.
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
� In case the feature "Traffic HO" is enabled, the previous condition is modified :
� Size of window for level averaging: A_PBGT_HO
if EN_TRAFFIC_HO(0,n) = ENABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)+ max(0, DELTA_HO_MARGIN(0,n))
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
if EN_TRAFFIC_HO(0,n) = ENABLED
then PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER (*)+ max(0, DELTA_HO_MARGIN(0,n))
and AV_RXLEV_PBGT_HO ≤ RXLEV_LIMIT_PBGT_HO
and EN_PBGT_HO = ENABLED
max(0, DELTA_HO_MARGIN(0,n)) is always positive � it increases the HO_MARGIN(O,n)max(0, DELTA_HO_MARGIN(0,n)) is always positive � it increases the HO_MARGIN(O,n)
Cause 12 HO is correlated with cause 23 HO. This is why there is a difference according to the activation of cause
23 HO (EN_TRAFFIC_HO).
(*) OFFSET_HO_MARGIN_INNER is applied only if the MS is currently located in the inner zone of a concentric
cell (multiband or monoband). This parameter will be explained in chapter 7.
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
� DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the serving cell and the neighboring cell n (Traffic_load(n)) in the following way:
� Philosophy:
This mechanism aims at penalizing cause 12 detection when the traffic in the serving cell is low and is high in the cell n
If Traffic_load(0) = high and Traffic_load(n) = low,
� DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0) = low and Traffic_load(n) = high,� DELTA_HO_MARGIN(0,n) = + DELTA_INC_HO_MARGIN
Else DELTA_HO_MARGIN(0,n) = 0
If Traffic_load(0) = high and Traffic_load(n) = low,
� DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0) = low and Traffic_load(n) = high,� DELTA_HO_MARGIN(0,n) = + DELTA_INC_HO_MARGIN
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6 Main Standard Handover Algorithms
Handover Cause 12: Power Budget [cont.]
� What is the traffic_load() ?
� Computed for every cell by the BSC
� Not available for neighbour cells that are external (different BSC's)
� Can have three values:
� HIGH: cell is loaded
� LOW: cell is unloaded
� INDEFINITE: cell load is neither loaded nor unloaded, or unknown
� Modified according to the long term traffic evaluation algorithm using the following parameters:
� A_TRAFFIC_LOAD, N_TRAFFIC_LOAD : averaging windows
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6 Main Standard Handover Algorithms
Handover Cause 12: Inter-band situation
Separated 900 – 1800 coverages
� Allow the flow of PBGT HO between the 2 bands
� EN_MULTIBAND_PBGT_HO = enable
1800 cells 900 cells
EN_MULTIBAND_PBGT_HO = enable or disable
HO_MARGIN(0,n) =5 dB HO_MARGIN(0,n) = 5 dB
HO_MARGIN(0,n) = 8 dB
EN_MULTIBAND_PBGT_HO = enable
HO_MARGIN(0,n) = 2 dB
EN_MULTIBAND_PBGT_HO = enable
Typical example: dense urban area covered in 1800, and surrounding cells, outside the city area, are in 900.
For cells which are not in the vicinity of cells from other band, the parameter " EN_MULTIBAND_PBGT_HO" has no
impact on HO detection (except for multiband cells)
Note : to ease design of parameters, one can use the following syntax (i.e. for the case above) :
HO_MARGIN(900,900) = 5dB
HO_MARGIN(900,1800) = 8dB
HO_MARGIN(1800,1800) = 5dB
HO_MARGIN(1800,900) = 2dB
EN_MULTIBAND_PBGT_HO(900) = enable
EN_MULTIBAND_PBGT_HO(1800) = enable
Why 8dB ? Because there is a automatic bonus of 3dB from 900 � 1800 (cf p.77). In order keep a difference of
5dB of RXLEV, it is necessary to increase the HO_MARGIN by 3dB.
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Handover Cause 12: Inter-band situation [cont.]
Common 900 – 1800 coverages
� Solution 1 : Allow the exit from "border 1800", but use other HO causes to manage "core 1800"
macro 900
macro 1800
HO_MARGIN(0,n) = 5 dB
HO_M(1800,900)
= 2 dB
"Border" strategy
Smooth exit of the 1800 area
EN_MULTIBAND_PBGT_HO = Enable"Core" strategy
Prevent PBGT HO, to keep MS in 1800
EN_MULTIBAND_PBGT_HO = Disable
HO_MARGIN(900,1800)
= 8 dB
HO_MARGIN(0,n) = 5 dB
Dual coverage of an area : full coverage in 1800 and full coverage in 900. However, to compensate for line (C) in
slide 77, we must compensate by 3 dB.
This way, there is no priority given to the 1800 band nor the 900 band.
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6 Main Standard Handover Algorithms
Handover Cause 12: Inter-band situation [cont.]
Common 900 – 1800 coverages
� Solution 2 : Manage all intra-layer HO with HO cause 12.
macro 900
macro 1800
HO_M = 2 dB
"Border" strategy
Smooth exit of the 1800 area
EN_MULTIBAND_PBGT_HO = Enable"Core" strategy
Allow PBGT HO, favour MS in 1800
EN_MULTIBAND_PBGT_HO = Enable
HO_M = 8 dB
HO_M(900,900) = 5 dB
HO_M(1800,900)
= 8dB
HO_M(900,1800)
= 2dB
HO_M(1800,1800) = 5 dB
Same management of HO at the "border" zone, but "core" zone is managed with PBGT HO also. Except the
HO_MARGIN are different :
HO_MARGIN(1800,900) = 8dB (6dB harder than default "2dB")
HO_MARGIN(900,1800) = 2dB (6dB easier than default "8dB")
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6 Main Standard Handover Algorithms
HO Cause 12: Tuning of Microcells Parameters
� HO_MARGIN(0,n) optimization
� Not triggering too many HOs(ping-pong)
� Not triggering HO to a transient cell (for example, the perpendicular cell at a crossroads)
� Avoid emergency HO to the umbrella if there is an available microcell (after a street corner).
Micro 1Micro 2
Micro 3
PBGT HO between micro cells 1, 2
-110
-100
-90
-80
-70
-60
-50
1 3 5 7 9
11
13
15
17
19
rxlev(cell 1)
rxlev(cell 2)
rxlev(cell 3)
Too many handovers can be perceived as a degradation of the voice quality (i.e. in QVoice)
Transient cell : the Rxlev of this cell is good only for a short duration (= passing cell)
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HO Cause 12: Tuning of Microcells Parameters [cont.]
� HO_MARGIN(0,n)
� Avoid ping-pong HO in urban environment
� Avoid emergency HO after street corners
� Avoid transcient PBGT HO
� Default value: up to 10 dB in dense urban microcellular area, with short A_PBGT_HO.
� Optimized: can be reduced to 5dB or 0dB when applying an anti ping-pong mechanism and long A_PBGT_HO.
� A_PBGT_HO
� To find a compromise with HO_MARGIN(0,n)
� Default value: 8 SACCHs for urban microcells, 6 for dense urban
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6 Main Standard Handover Algorithms
HO Cause 12: Tuning of Microcells Parameters [cont.]
� HO_MARGIN optimization
� if HO_MARGIN(0,n) > 5dB
�PBGT HO delayed
�C/I might drop below -9dB
�in case of adjacent frequencies between 2 neighbouring microcells, degradation of voice quality
� if HO_MARGIN(0,n) ≤ 5dB (0dB)
�adjacent frequencies between neighbouring microcells can be used
�BUT A_PBGT_HO should be increased
�AND the anti ping-pong mechanism should be applied (PING_PONG_HCP & T_HCP)
BTS1
BTS2
Building
Interferer
fn
fn+1
Area of potential interferences: (C/I)adj < -6dB
C/I = -9dB, means that the RXLEV(serving) is 9dB lower than the RXLEV(neighbour)
Alcatel recommends C/I > -6dB [BCCH] and > -9dB [TCH] in case of adjacent channels, to avoid call quality
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6 Main Standard Handover Algorithms
Cause 12: Speed Discrimination in Lower/Indoor
� Transfer of fast MSs from lower or indoor layers to upper layer
� If EN_SPEED_DISC = ENABLED
Traffic Load = low Traffic Load ≠≠≠≠ low
HO
HO (12) HO (12) HO (12)
HO (12)
MIN_CONNECT_TIME
At call setup: C_DWELL = 0 and is incremented by 1 every MEASUREMENT REPORTMS_SPEED is set to indefinite
After 1st HO: MS_SPEED is kept at indefinite, and C_DWELL reinits to 0Next HO: MS_SPEED is set to fast if
C_DWELL < 2 x MIN_CONNECT_TIMEHO is a Power Budget HO (cause 12)EN_SPEED_DISC = ENABLED in serving cell
Otherwise MS_SPEED is kept at indefinite and C_DWELL reinits to 0
At call setup: C_DWELL = 0 and is incremented by 1 every MEASUREMENT REPORTMS_SPEED is set to indefinite
After 1st HO: MS_SPEED is kept at indefinite, and C_DWELL reinits to 0Next HO: MS_SPEED is set to fast if
C_DWELL < 2 x MIN_CONNECT_TIMEHO is a Power Budget HO (cause 12)EN_SPEED_DISC = ENABLED in serving cell
Otherwise MS_SPEED is kept at indefinite and C_DWELL reinits to 0
If the handover is an intracell HO, nothing happens : C_DWELL continues to be incremented.
If the handover is an external HO (different BSC), then there is a reinitialisation of the variables C_DWELL and
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6 Main Standard Handover Algorithms
Exercise
� Draw arrows to indicate among which cells the HO cause 12 can be detected
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Handover Cause 23: Traffic
� The aim of this cause is to speed-up HO detection when
� The serving cell is loaded
� The target cell is unloaded
� Counter-reaction of cause 12
� Checked between :
� LAYER :
� Cells with the same CELL_LAYER_TYPE
� BAND :
� If EN_MULTIBAND_PBGT_HO = disable � Cells with the same CELL_BAND_TYPE
� if MS in inner zone of a multiband cell, it can only go to another multiband cell
� If EN_MULTIBAND_PBGT_HO = enable � Any CELL_BAND_TYPE
CAUSE 23
CAUSE 12
In some multiband networks, the radio coverage is ensured by DCS cells in one geographical area and by GSM cells
in another geographical area. As these cells form a multiband and mono-layer network, the capture handovers
between cells of different bands will be inefficient to regulate the CS traffic load in the serving cell
neighboringhood.
The solution consists in allowing intra-layer traffic handovers (Cause 23) based on a power budget evaluation
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Handover Cause 23: Traffic [cont.]
� CAUSE 23: Traffic Handover
� Size of window for level average: A_PBGT_HO
� DELTA_HO_MARGIN(0,n) uses the same algorithm as in p.77.
DELTA_HO_MARGIN(0,n) < 0 dB
AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
+ DELTA_HO_MARGIN(0,n)
AND EN_TRAFFIC_HO(0,n) = ENABLED
DELTA_HO_MARGIN(0,n) < 0 dB
AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
+ DELTA_HO_MARGIN(0,n)
AND EN_TRAFFIC_HO(0,n) = ENABLED
The principle of this handover is to reduce the size of the serving cell when it is high loaded relatively to a low loaded cell.
When the mobile moves away from the BTS, the power budget will increase and a better cell handover will be triggered earlier.
It is recommended to inhibit Traffic handover towards 1 TRX cells. These cells do not have enough resources to receive incoming handovers due to congestion of neighboring cells. Moreover because of the great variation of traffic in the 1 TRX cells, traffic load is never considered as low.
This cause is inhibited for handover from SDCCH to SDCCH.
Cause 23 is checked over all the neighboring cells belonging to the same layer. It means that it is checked between cells whose CELL_LAYER_TYPE is single or upper, between cells whose CELL_LAYER_TYPE is lower, and between cells whose CELL_LAYER_TYPE is indoor.
In addition to the condition on the cell layer type, the cell frequency band condition for checking Cause 23 is as follows whether or not the MS is in the inner zone of a multiband cell:
� The MS is not in the inner zone of a multiband cell
� If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 must not be checked between cells which use different frequency bands (i.e cells having different CELL_BAND_TYPE).
� If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all theneighboring cells without any cell frequency band restriction.
� The MS is in the inner zone of a multiband cell
� If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all the neighboring cell multiband cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the same BSC as the serving cell.
� If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all theneighboring cells without any cell frequency band restriction.
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6 Main Standard Handover Algorithms
Handover Cause 28: Fast Traffic HO
� CAUSE 28: Fast Traffic Handover
� Push out of a cell a mobile in dedicated mode to allow a queued request to be served in the serving cell
� May be triggered
� From any non-concentric cell OR concentric outer zone
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6 Main Standard Handover Algorithms
Handover Cause 28: Fast Traffic HO [cont.]
� CAUSE 28: Fast Traffic Handover
� Cause 28 is only checked if the channel of the candidate MS can support the channel rate (HR or FR) required by the queued request:
� HO is triggered when a request is queued at the top of the queue
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6 Main Standard Handover Algorithms
Handover Cause 28: Fast Traffic HO [cont.]
� CAUSE 28: Fast Traffic Handover
� Size of window for averaging level: A_PBGT_DR
� Same thresholds and window as Cause 20 (FDR)
� EN_CAUSE_28 is an internal HOP process variable, ENABLED when a request is queued
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max (0, [MS_TXPWR_MAX(n) - P])
and t(n) > FREELEVEL_DR(n)
and EN_CAUSE_28 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max (0, [MS_TXPWR_MAX(n) - P])
and t(n) > FREELEVEL_DR(n)
and EN_CAUSE_28 = ENABLED
and EN_FAST_TRAFFIC_HO = ENABLED
HO cause 28 process:
� If EN_FAST_TRAFFIC_HO = enabled, when an assignment request (or external emergency HO request) is queued,
the RAM process sends to the HOP process a Fast Traffic HO request which contains the queued request reference
and its channel rate.
� Then, HO cause 28 becomes checkable (EN_CAUSE_28=enabled).
� Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to “disabled” so as not to perform
more than one handover. In the same time, the HOP process gets back to the RAM process a Fast Traffic HO
Acknowledge which contains the queued request reference and the reference of the MS that can perform HO.
� If several answers are sent to the RAM process, only the first one corresponding to the queued request is taken
into account.
� The RAM process checks if the request is still queued. If it is so, RAM asks HOP to start HO for this mobile;
otherwise the process is stopped.
� Once the HOP process receives this message, the first two conditions of Cause 28 (good enough level, enough
free resources in the target cell) are checked one more time. If the conditions are fulfilled, the HOP process
sends an alarm to the HOM entity and the timer T_FILTER is started; otherwise the process is stopped.
Note: the first two conditions of cause 28 are tested twice in order to be sure that the candidate cells are still
valid when the « cause 28 start HO » message is received from the RAM process.
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� Detection of cause 12
� Parameters settings
� No Power Control DL, no anti ping-pong
� EN_PBGT_HO = enable
� EN_TRAFFIC_HO(0,n) = disable
� HO_MARGIN(0,n) = 5 dB
� RXLEV_LIMIT_PBGT_HO = -47 dBm
� BS_TXPWR_MAX_INNER = 0 dB
� OFFSET_HO_MARGIN_INNER = 0 dB
� In each case, determine if cause 12 is detected or not
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7 Emergency Handover Algorithms for MBML Networks
Emergency Handovers: Introduction
� In a hierarchical network, the MS can camp in any layer. Each layer is characterized by a certain cell type.
� Depending on the dimension type, the BSC is able to trigger some specific "microcell" emergency handovers in order to save the call.
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Emergency Handovers: Introduction [cont.]
� Recommended strategies :
� An MS is located in a micro or an indoor cell
� During an emergency HO, the MS is directed preferably towards an upper or a single cell
� An MS is located in a mini cell
� During an emergency HO, the MS is directed preferably towards neighboring mini cells
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Emergency Handovers Specific to Microcells
� Emergency handovers specific to microcells
� cause 7 : consecutive bad SACCH frames received in a microcell
� cause 17 : too low level on the uplink in a microcell compared to a high threshold
� cause 18 : too low level on the downlink in a microcell compared to a high threshold
� May be triggered
� From microcells only (cell_dimension_type = micro)
� Outdoor microcell (micro layer)
� Indoor microcell (indoor layer)
� Towards any cell except the serving one
� Note : If the MS in inner zone of a multiband cell, the serving cell is a candidate
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Microcell Emergency Handovers
� CAUSE 7: consecutive bad SACCH frames received in a microcell
� N_BAD_SACCH
� Rule : "Radio Link Recovery shall be triggered before the handover"
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Microcell Emergency Handovers [cont.]
� CAUSE 17: too low level on the UL in a microcell compared to a high threshold
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Microcell Emergency Handovers [cont.]
� CAUSE 18: too low level on the DL in a microcell compared to a high threshold
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Cause 17 & 18: Comparison to High Threshold
� High threshold (U_RXLEV_XX_MCHO)
� the HO is triggered when the signal drops under the threshold
� the corresponding HO causes consist in comparing, at 2 successive SACCH periods, the DL and UL levels in the serving microcell with a high threshold
� Beginning a call under the threshold does not trigger an HO
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Cause 17 & 18: Comparison to High Threshold [cont.]
� High threshold (U_RXLEV_XX_MCHO)
� With high value, mobiles will be sent too early to the macro layer
� With low value, mobiles turning at a street corner will be maintained in the microcell layer during a longer period
� Problems for MS's with a signal strength level close to the high threshold : due to fading, multiple handovers can be triggered during a call:
MS in Indoor cell : decrease in RXLEV leads to emergency HO � Umbrella
MS in Umbrella : RXLEV of indoor cell becomes good again, capture HO � Indoor
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Cause 17 & 18: Comparison to High Threshold [cont.]
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Cause 17 & 18: Alternative Strategy
� Alternative strategy : U_RXLEV_XX_MCHO < L_RXLEV_XX_H
ii-1
t
AV_RXLEV_XX_MCHO
High Threshold
µHO alarm
t
Standard Threshold
High Threshold
Standard Threshold
Std HO alarm
Based on 4-SACCH sliding averagesGoal : detect corner street effects
Based on 10-SACCH sliding averagesGoal : detect MS slowly exiting the cell
AV_RXLEV_XX_HO
Alternative strategy offers a different approach :
The "high" treshold U_RXLEV_XX_MCHO is not "high" anymore. Use this threshold as "emergency" exit from a
microcell, when the MS turns around a street corner.
The standard threshold should be used as a standard exit from microcell : don't forget that HO cause 12 towards
another cell in the same layer might not always be possible. In this case, the only way to exit a micro cell or an
indoor cell is to perform an emergency HO !
Therefore it is necessary to use one dedicated emergency HO as a "safe exit" HO, to keep a good RXLEV while
performing a HO towards another layer.
Example :
U_RXLEV_DL_MCHO =-92dBm
L_RXLEV_DL_H = -83dBm
A_LEV_MCHO : 4 SACCH
A_LEV_HO : 10 SACCHEN_MCHO_H_DL = ENABLE
In Uplink, default values can be kept for the standard emergency HO, and EN_MCHO_H_UL = DISABLE (exit performed with DL is enough)
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Cause 14: Lower/Indoor Capture for Slow MS
� Capture handover
� Improved in B7 (indoor & anti ping-pong)
� Send traffic in lower layers, even though the call is fine in upper layers
� May be triggered
� From upper layer cells
� Towards lower or indoor layer cells
� From lower layer cells
� Towards indoor layer cells
� Note : It can be triggered between different frequency bands or not
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Cause 14: Lower/Indoor Capture for Slow MS [cont.]
� In order to keep dual band MSs in the preferred band
� Cause 14 is not checked if
� serving cell or zone is "preferred band" AND target cell is "non preferred"
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Cause 14: Lower/Indoor Capture for Slow MS [cont.]
� If cell_layer_type (0) = upper
� Averaging window: A_PBGT_HO
� Anti ping-pong: not checked if T_INHIBIT_CPT is running
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Cause 14: Lower/Indoor Capture for Slow MS [cont.]
� If cell_layer_type (0) = lower
� Averaging window: A_PBGT_HO
� Anti ping-pong: not checked if T_INHIBIT_CPT is running
mini micro
indoor
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED ≠ FAST
and EN_MCHO_NCELL = ENABLED
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
and MS_SPEED ≠ FAST
and EN_MCHO_NCELL = ENABLED
MS_SPEED different than fast, because at call setup, the MS SPEED is set to indefinite. It cannot be set to "SLOW".
A "SLOW" MS might be a MS that came from an umbrella previously.
Therefore, in a mini cell, a MS with MS SPEED = indefinite should be able to be sent to an indoor cell.
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Cause 14: Speed Discrimination
� Only available for UPPER layers (umbrella cells)
� Speed discrimination objectives :
� Maximize capacity (maximum traffic in lower/indoor cells)
� While optimizing quality (minimize the number of handovers)
� Smart speed discrimination :
1. If the load of umbrella is too high � reduce the time a MS can stay in the umbrella
2. If the load of umbrella is low � increase the time a MS can stay in the umbrella
3. If the MS speed is fast in lower/indoor cells � it is sent to the umbrella cell
Benefits of the smart speed discrimination :
Case 1 : The umbrella cell is kept "less loaded" in order to accept incoming handovers and call setups (most of
call setups will be done on the umbrella cells, because of the better coverage). The extra-capacity of
lower/indoor cells is fully used.
Case 2 : No HO is performed in this case, because the umbrella has room to keep the calls. It is interesting to
avoid handovers, because less HO during a call � better voice quality.
Case 3 : a fast moving user should stay in upper layers, in order to avoid performing too many HO (increase the
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Cause 14: Speed Discrimination [cont.]
� MS speed in umbrella cells :
� Speed estimation based on the consecutive time the same lower/indoor cell is received as a neigbour by the MS
� If for one neighboring cell n, C_DWELL(n) ≥ 2 x MIN_DWELL_TIME
� MS_SPEED is set to SLOW
Upper layer
Lower layerCell 1 Lower layer
Cell 2
C_DWELL(1) �
C_DWELL(2)
To dwell : to reside
� If this dwell time exceeds MIN_DWELL_TIME, the MS is slow and is sent to the lower/indoor cell
� C_DWELL(n) is a counter measuring the number of SACCH periods of monitoring neighbour cell n over the
threshold L_RXLEV_CPT_HO(0,n)
� There is one C_DWELL() per neighbour cell
� MIN_DWELL_TIME is a variable linked to the load of the serving umbrella cell
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Cause 14: Speed Discrimination [cont.]
� Initialization of C_DWELL(n) in serving umbrella cell :
� if EN_SPEED_DISC = ENABLE
� C_DWELL(n) = 0
� MSs will handover to the lower/indoor layer after MIN_DWELL_TIME seconds
� if EN_SPEED_DISC = DISABLE
� C_DWELL(n) = 2 x (MIN_DWELL_TIME - L_MIN_DWELL_TIME)
� MSs will handover to the lower/indoor layer after L_MIN_DWELL_TIME seconds
MIN_DWELL_TIME is not a parameter ! It is a variable computed by BSC : it varies, depending on the umbrella
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Cause 14: Speed Discrimination [cont.]
� Example with default values (EN_SPEED_DISC = disable)
� Initialization values
H_MIN_DWELL_TIME = 20s (= MIN_DWELL_TIME at initialization)
L_MIN_DWELL_TIME = 8s
C_DWELL(n) = 2 x (MIN_DWELL_TIME - L_MIN_DWELL_TIME)
= 2 x (20 - 8) = 24 SACCH (= 12 seconds)
� Algorithm
MS is deemed as slow if C_DWELL(n) > 2 x MIN_DWELL_TIME
C_DWELL(n) starts at 24, and is increased by 1 when RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n)
0 4 8 12 16 20 24 28 32 36 40 44
: EN_SPEED_DISC = Disable
: EN_SPEED_DISC = Enable
INDEFINITE or FAST SLOW
Maximum time to reach
MIN_DWELL_TIME
=
L_MIN_DWELL_TIME
C_DWELL MIN_DWELL_TIMEC_DWELL
MIN_DWELL_TIME is in seconds, whereas C_DWELL is in SACCH. This is the reason why MIN_DWELL_TIME is
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Cause 14: Speed Discrimination [cont.]
� Traffic regulation through the variation of MIN_DWELL_TIME
Default valuesdependent onthe number of TRXs
H_LOAD_OBJ
L_LOAD_OBJ
Traffic load umbrella
H_MIN_DWELL_TIME20 s
DWELL_TIME_STEP2 s
L_MIN_DWELL_TIME8 s
Start of day
low traffic
End of day
low traffic
End of BH
decreasing traffic
What are the values of MIN_DWELL_TIME during the day ?
Summary of parameters that controls the speed discrimination in the umbrella cells:
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Cause 24: General Capture
� capture handover
� Improved in B7 (anti ping-pong)
� Can be used to capture traffic by any cell, whatever its type, band, etc.
YES
NO
MS in inner zone of a multiband cell
EN_BI-BAND_MS(n) = ENABLE
Or CELL_BAND_TYPE(n) ≠ CELL_BAND_TYPE(0)Preferred band
EN_BI-BAND_MS(n) = ENABLE
Or CELL_BAND_TYPE(n) = PREFERRED_BANDPreferred band
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Cause 24: General Capture [cont.]
� In order to keep dual band MS in the preferred band, cause 24 is not checked when EN_BI-BAND_MS(n) = DISABLED, from preferred cell to classical cell.
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Cause 24: General Capture [cont.]
� CAUSE 24: general capture
� Size of window for averaging level: A_PBGT_HO
� CAPTURE_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOW
� Anti ping-pong: not checked when T_INHIBIT_CPT is running
AV_RXLEV_NCELL(n) >
L_RXLEV_CPT_HO(0,n) + max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) = CAPTURE_TRAFFIC_CONDITION
and Traffic_load(n) ≠≠≠≠ HIGH
and EN_GENERAL_CAPTURE_HO = ENABLED
AV_RXLEV_NCELL(n) >
L_RXLEV_CPT_HO(0,n) + max (0, [MS_TXPWR_MAX(n) - P])
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� Use of cause 21 or 14?
� Considering the following network
� Which cause has to be used for capture? 14 or 21?
� Highlight one complexity linked to causes 14 and 21 interworking when using traffic discrimination
Time allowed: 5 minutes
8 Better Conditions Handover Algorithms for MBML Networks
Exercise
Umbrella 900
Mini 1800
CAUSE 21: high level in the neighboring cell in the preferred band
AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) + max (0, [MS_TXPWR_MAX(n) - P])
and Traffic_load(0) = MULTI-BAND_TRAFFIC_CONDITION
and Traffic_load(n) ≠≠≠≠ HIGH
and EN_PREFERRED_BAND_HO = ENABLED
� Size of window for average level: A_PBGT_HO
� MULTI-BAND_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOW
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� Input settings for the next slide
� EN_MCHO_NCELL(source) = ENABLED
� L_RXLEV_CPT_HO(source, target) = -85 dBm
� Is cause 14 triggered in each of the following cases ?
� See next slide
Time allowed: 5 minutes
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� Speed discrimination
� What is the role of parameter EN_SPEED_DISC?
� If EN_SPEED_DISC is disabled, can fast MSs be directed toward microcells?
� What is the difference between EN_SPEED_DISC = DISABLED and EN_SPEED_DISC = ENABLED when L_LOAD_OBJ = 0% and H_LOAD_OBJ = 100%?
Time allowed: 5 minutes
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Cause 21: Preferred Band
� Capture handover
� Improved in B7 (anti ping-pong)
� Send traffic in preferred cells, even though the call is fine in classical cells
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Cause 21: Preferred Band [cont.]
� Cause 21: high level in the neighboring cell in the preferred band
� Averaging window: A_PBGT_HO
� MULTIBAND_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default), HIGH, NOT_LOW
� Anti ping-pong: not checked when T_INHIBIT_CPT is running
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Capture handovers
� Tuning of L_RXLEV_CPT_HO(0,n)
� Recommended range of investigation: from -65dBm to -85dBm
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Capture handovers [cont.]
� Tuning of MULTIBAND_TRAFFIC_CONDITION andCAPTURE_TRAFFIC_CONDITION
� Recommended setting: ANY_LOAD
� If HIGH or NOT_LOW:
� Capture to the preferred cell is limited to the loaded hours
� This choice is sensible: during unloaded hours, the non-preferred cells provide a good coverage, with little interference.
� The following parameters will impact the computation of traffic_load :
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Capture handovers [cont.]
� Inhibition of capture handovers
Cell B
Cell A
Cell C
1
3 1
2
3
During T_INHIBIT_CPT_HO, a capture HO towards cell B is inhibited for this call.
The MS experiences a poor RXQUAL, and a HO due to quality is triggered (causes 2, 4 or 7)
A capture HO to another cell is still possible
2
QUAL HO
T_INHIBIT_CPT_HOCPT HO
CPT HO
Refer to comments for further details
In this example, T_INHIBIT_CPT_HO is started only if either:
Cell A is UPPER or SINGLE and Cell B is LOWER or INDOOR,
or Cell A is LOWER and Cell B is INDOOR,
or Cell A is in a different frequency band than Cell B
Note : The cause 24 between two cells with same frequency band and same layer cannot be inhibited !!
A "handover due to quality" can be :
� Cause 2, 4 or 7: ULQ, DLQ or Bad SACCH
� OR external HO with A interface cause Uplink Quality or Downlink Quality
Generally the T_INHIBIT_CPT is set to a high value, such as 60s.
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Exercise
� Input settings for the next slide
� EN_PREFERRED_BAND_HO(0) = ENABLED
� L_RXLEV_CPT_HO(0,n) = -85 dBm
� MULTIBAND_TRAFFIC_CONDITION = NOT_LOW
� Is cause 21 triggered in each of the following cases ?
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8 Better Conditions Handover Algorithms for MBML Networks
Exercise [cont.]
� In a multiband network,
� How can you ensure capture will be performed from 900 cell towards 1800 cell, until 80% traffic load is achieved in the 1800 cell ?
� Parameters ?
� Settings ?
� Once this load is exceeded,
� What happens ?
� Will the 1800 cell accept more traffic ?
� What are the other possibilities of incoming traffic ?
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9 Multiband Cells
Introduction
� When changing a cell from "normal" to "concentric", 3 more handovers are available !
� Those are only INTRA-CELL handovers
� Cause 13 : entry in inner zone, from outer zone
� Causes 10 & 11 : exit to outer zone, from inner zone
Cell A
inner
outer
cause 13
cause 10/11
The activation of causes 10 and 11 is automatic, as soon as a cell type is defined as "CONCENTRIC"
The activation of cause 13 is controlled by EN_BETTER_ZONE_HO.
The parameters HO_INTRACELL_ALLOWED and EN_INTRACELL_REPEATED have no impact on those handovers, they
are used only for causes 15 & 16 (interference) and 25 & 26 (AMR).
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9 Multiband Cells
Introduction [cont.]
� Setting these 3 handover causes is simple
1. Work with downlink thresholds first
2. Propose an entry threshold, i.e. -75dBm
� MS enters in the inner zone only if the expected received level in the inner zone is above -75dBm
3. Propose an exit threshold, i.e. -83dBm
� MS exits the inner zone if the received level is less than -83dBm
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Introduction [cont.]
4. Compute the entry threshold as measured from the outer zone
� Due to 10dB propagation loss, it should be -65dBm
5. Compute the difference between
� the entry threshold from outer zone (-65dBm)
� the exit threshold (-83dBm)
Cell A
inner
outer
-75dBm
-83dBm
-65dBm
18dB
Only these two values are needed in order to tune a concentric cell
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Cause 10: Low uplink level in inner zone
� CAUSE 10: too low level on the uplink in inner zone
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9 Multiband Cells
Cause 11: Low downlink level in inner zone
� CAUSE 11: too low level on the downlink in inner zone
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9 Multiband Cells
Cause 13: High UL & DL level in outer zone
� CAUSE 13: too high level on the UL and the DL in the outer zone
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Cause 13: High UL & DL level in outer zone [cont.]
� ZONE_HO_HYS_DL and ZONE_HO_HYS_UL
� Differences between "entry threshold" and "exit threshold"
� They must be greater than the propagation loss, by at least a certain hysteresis
� There are 3dB difference between UL and DL, due to the value
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Cause 13: High UL & DL level in outer zone [cont.]
� PING_PONG_MARGIN(0,call_ref) = penalty of PING_PONG_HCP during T_HCP only if
� MS is coming from the inner zone to the outer zone with an interzonehandover
� In all other cases, PING_PONG_MARGIN(0,call_ref) = 0
MS in the 1800 inner zone of a cell can perform an emergency "intercell" HO towards the outer zone. In this case, the penaltyis not applied.
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Cause 13: High UL & DL level in outer zone [cont.]
� NEIGHBOUR_RXLEV(0,n)
� Avoid sending a MS in the inner zone if a neighbour cell is too strong
� Tuning depends on frequency planning
� By default, NEIGHBOUR_RXLEV(0,n) = 47dBm
� When inner zone frequency planning is very tight (i.e. reuse cluster = 3)
In this example, the inner zone of cell C_3 can be interfered locally by the inner zone of cell B_2C_2 by E_3…
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Cause 13: High UL & DL level in outer zone [cont.]
� EN_CAUSE_13: Traffic Load balancing
� MS will not be sent in the inner zone if the inner zone is more loaded than the outer zone
� Depends on EN_LOAD_BALANCE & current load in each zone
� EN_LOAD_BALANCE = ENABLE
� Outer zone more loaded (Load_sample_inner ≤ Load_sample_outer)
� EN_CAUSE_13 = ENABLE
� Inner zone more loaded (Load_sample_inner > Load_sample_outer)
� EN_CAUSE_13 = DISABLE
� EN_LOAD_BALANCE = DISABLE
� EN_CAUSE_13 = DISABLE
LOAD_SAMPLE_INNER: Ratio of TCH occupancy in the inner zone:
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Cause 13: High UL & DL level in outer zone [cont.]
� RXLEV_UL_ZONE : Uplink level threshold for inner to outer zone handover. From -110dBm to -47dBm. [-86 dBm]
� RXLEV_DL_ZONE : Downlink level threshold for inner to outer zone handover. From -110dBm to -47dBm. [-78 dBm]
� ZONE_HO_HYST_UL: Hysteresis applied to RXLEV_DL_ZONE for outer to inner zone handover. From -40dB to +40dB. [13 dB]
� ZONE_HO_HYS_DL: Hysteresis applied to RXLEV_UL_ZONE for outer to inner zone handover. From -40dB to +40dB. [16 dB]
� MS_TXPWR_MAX_INNER: MS maximum allowed transmission power in the inner zone of a concentric or multiband cell. From 5dBm to 43dBm. [30 or 33 dB]
� BS_TXPWR_MAX_INNER) : This parameter defines the power reduction relative to the maximum GMSK output power of the TRX of the inner zone in a concentric or multiband cell. From -30dB to 0dB. [0dB]
� NEIGHBOUR_RXLEV(0,n) : Threshold of maximum received level from the neighbour cells for cause 13. From -110dBm to -47dBm. [-47dBm]
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Call Setup
1. Radio Link Establishment Phase
2. SDCCH Phase
3. TCH Assignment Phase
In which zone will the TCH be allocated?
� The TCH is allocated in the inner zone if :
� UL and DL RxLev in outer zone are satisfying
� BSC can allocate a TCH in inner zone
� MS is multiband
� Otherwise, TCH is allocated in the outer zone
INNEROUTE
R
??
The cell's RXLEV is the one being measured by the MS while performing SDCCH phase and TCH Assignment phase.
Therefore, it is measuring only the outer zone RXLEV !!
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Outgoing intercell HO
� What are the possible outgoing handovers from the inner zone ?
� Emergency ?
� Better conditions ?
� Only 2 parameters have an influence
� EN_BI-BAND_MS(n)
� EN_MULTIBAND_PBGT_HO(0)
innerouter
GSM900
DCS1800
serving cell innerouter
YES
YES
EN_MULTIBAND_PBGT_HO : Enable/disable the power budget handovers Cause 12 and the traffic handovers
Cause 23 between cells belonging to different frequency bands
Recommended value: Enable
EN_BI-BAND_MS(n) : Enables/disables the incoming handovers of bi-band MSs from the preferred-band into a
classical band cell, in cause 14 and cause 24
Recommended value: Enable
From inner zone of a multiband cell, if both parameters are set to enable, all outgoing HO's are possible
If EN_MULTIBAND_PBGT_HO = Disable, cause 12 only possible to other multiband concentric cells (very
restrictive !)
If EN_BI-BAND_MS(n) = Disable, cause 14 and cause 24 only possible towards cells with the same frequency bandas the inner zone (i.e. DCS1800 cells)
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HO Cause 12
� If the MS in inner zone of a concentric cell, the PBGT equation is modified :
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX_INNER – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX_INNER)
- PING_PONG_MARGIN(n, call_ref)
PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO
- (BS_TXPWR_MAX_INNER – AV_BS_TXPWR_HO)
- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX_INNER)
- PING_PONG_MARGIN(n, call_ref)
9001800 900 1800Cell 1 Cell 2
RxLev on TCH = -79dBm RxLev of BCCH = -70dBm
The parameter HO_MARGIN(cell 1, cell 2) is set to 5 dB
If RxLev(cell 2) = -70 dBm, PBGT(cell 2) = +6 dB
� Cause 12 is triggered, the MS is sent in the outer zone of cell 2, with RxLev(cell 2) = -70 dBm.Let's assume that
the "outer�inner" HO is triggered: the MS enters the inner zone of cell 2.
The received level of cell 1 is NOT -79 dBm (this was the level of the inner TCH).
Field results show that a 900 BCCH will be received roughly at -79+10=-69 dBm.
The received level of cell 2 is NOT -70dBm (that was the RXLEV of the outer zone). In the inner zone, the RXLEV =
-70dBm – 10dBm = -80dBm.
PBGT(cell 1) = (-69+80)-3 = +8dB � PBGT HO is triggered from cell 2 to cell 1!!
In fact, cause 12 HO cell 1 � cell 2 should NOT have been triggered in the first place.
A solution is to be found in tuning OFFSET_HO_MARGIN_INNER used in cause 12 equation. See next slide.
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9 Multiband Cells
HO Cause 12 [cont.]
� What is happening in this situation ?
� How to fix the problem ?
� HO_MARGIN(1,2) = 5dB and HO_MARGIN(2,1) = 5dB
� OFFSET_HO_MARGIN_INNER= 0dB
� Inner zone entry threshold DL = -70dBm
9001800 900 1800Cell 1Serving
Cell 2Target
RxLev on TCH = -75 dBm RxLev of BCCH = -66 dBm
10 minutes
Inner zone entry threshold DL is a combination of 2 parameters :
RXLEV_DL_ZONE + ZONE_HO_HYST_DL
(cf. § HO cause 13)
To fix the problem : find the OFFSET_HO_MARGIN_INNER that would lead to leave the inner zone only for a
neighbour that is 5dB greater than the outer zone. This tends to reproduce a standard behaviour.
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HO Cause 12 [cont.]
� If the MS in inner zone of a concentric cell :
� HO cause 12 is detected if :
� OFFSET_HO_MARGIN_INNER is used to compensate the difference of propagation between inner and outer zones (carrying BCCH)
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9 Multiband Cells
Incoming intercell HO
� Is an incoming handover directly to the inner zone possible ?
� Emergency ?
� Better conditions ?
innerouter
GSM900
DCS1800
target cellinner
outer
YES
YES
EN_MULTIBAND_PBGT_HO : Enable/disable the power budget handovers Cause 12 and the traffic handovers
Cause 23 between cells belonging to different frequency bands
EN_BI-BAND_MS(n) : Enables/disables the incoming handovers of bi-band MSs from the preferred-band into a
classical band cell, in cause 14 and cause 24
Towards inner zone of a multiband cell, if both parameters are set to enable, all incoming HO's are possible
If EN_MULTIBAND_PBGT_HO = Disable, cause 12 only possible from other multiband concentric cells and cells
from preferred band (i.e. GSM900)
If EN_BI-BAND_MS(n) = Disable, cause 14 and cause 24 only possible from cells from preferred band (i.e. GSM900)
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9 Multiband Cells
Intracell Handovers
� Interference: Causes 15 & 16
� MS in the inner zone, all TRX's are candidate
� MS in the outer zone, only outer TRX's are candidate
� Note: the serving TRX can never be a candidate
� For other intracell handovers, the MS will stay in the same zone as before (TFO, AMR, return to CS zone)
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9 Multiband Cells
Limitations
� Power Control
� Same target levels are used for the inner zone and the outer zone, based on:
� L_RXLEV_DL_P & U_RXLEV_DL_P (resp. UL)
� L_RXQUAL_DL_P & U_RXQUAL_DL_P (resp. UL)
� A_LEV_PC, A_QUAL_PC
� Rule : ensure 10dB separation between
RXLEV_DL_ZONE and L_RXLEV_DL_P
RXLEV_UL_ZONE and L_RXLEV_UL_P
� Packet Switched service and Voice Group Call service
� PDCH or VGCH timeslots can be allocated only in the outer zone
� Preemption of a MS in the inner zone is not possible
� External handovers are always sent in the outer zone of the target cell
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Additional Features
� Multiband cell secured TCH assignment
� Subsequent TCH allocation in outer zone, if previous attempt in the inner zone failed
� Improved CSSR (TCH assignment failure due to radio is reduced)
� EN_LOAD_OUTER
� ENABLE: all load computations (short, medium and long terms) are based on the outer zone load
� DISABLE [default]: all load computations are based on the overall amount of timeslots (inner + outer)
� Enable only if ratio of dualband MS is very small
Subsequent allocation of outer TCH is failure during assignment of an inner zone TCH :
RTCH_assign_fail_radio = MC746b 1/ incremented when a failure in inner zone isfollowed by subsequent failure in outer zone2/ not incremented when failure in inner zone is followed by success in outer zone
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9 Multiband Cells
Exercise [cont.]
� Multiband cells parameters tuning
� An important parameter to be tuned in a multiband cell is OFFSET_HO_MARGIN_INNER
� Takes into account the propagation difference between 900 and 1800
� Proposed values between 7dB to 12dB
� Using all available optimization tools (RNO, drive-tests, traces, …), propose a method for tuning accurately this parameter
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� As soon as an intercell HO alarm has been detected
� HO Detection sends to Candidate Cell Evaluation
� the list of potential candidates (it depends on type of handover cause)
� the HO cause value
� the preferred layer for the target cell indicated by the variable PREF_LAYER (it depends on the cell network architecture and on the operator strategy)
10 Candidate Cell Evaluation
From HO Detection to Candidate Cell Evaluation
CandidateCell
Evaluation
Handover
Detection
Raw cell list
cell 1: cause C1
cell 2: cause C2
cell 3: cause C3
…
Max 32 cells
PREF_LAYER
BSCBSC
For intracell handovers, the only target cell is the serving cell � the raw cell list and the candidate cell
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Raw Cell List and PREF_LAYER
� Standard cell environment
� CELL_LAYER_TYPE = SINGLE
� Better condition HO cause
� Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multiband cell then it includes the serving cell
upper + singlePREF_LAYER
subset of cells verifying the HO causesRaw cell list
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10 Candidate Cell Evaluation
Raw Cell List and PREF_LAYER [cont.]
� Hierarchical cell environment
� CELL_LAYER_TYPE = UPPER
� Better condition HO cause
� Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multiband cell then it includes the serving cell
nonePREF_LAYER
subset of cells verifying the HO causesRaw cell list
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10 Candidate Cell Evaluation
Raw Cell List and PREF_LAYER [cont.]
� CELL_LAYER_TYPE = LOWER or INDOOR
� Better condition HO cause
� Emergency HO cause
* if the MS is in the DCS 1800 inner zone of a multiband cell then it includes the serving cell
noneUpperPREF_LAYER
Subset of cells verifying the HO causes
Subset of cells verifying the HO causes plus all neighboring umbrella cells with Traffic_Load(n) = LOW
Raw cell list
MS_SPEED <> FAST or
HO Cause <> 12
MS_SPEED = FAST and
There is a cell in the list because of cause 12
noneLower + indoorUpper + SinglePREF_LAYER
All neighboring cells except umbrella cells which do not verify AV_Rxlev_Ncell(n) > OUTDOOR_UMB_LEV(0,n)
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10 Candidate Cell Evaluation
Raw Cell List and PREF_LAYER [cont.]
� Emergency handovers from lower or indoor layers
� Standard parameter settings for minicells
� EN_RESCUE_UM = DISABLED
� Because a LOWER/INDOOR layer composed of MINI cells should offer good coverage
� Standard parameter settings for microcells
� EN_RESCUE_UM = ENABLED
� Because a LOWER/INDOOR layer composed of MICRO cells might not offer continuous coverage
� Risk of choosing a neighbor cell from LOWER/INDOOR layer with poor coverage
Depending on your network planning, these standard parameters can be further optimized.
EN_RESCUE_UM shall be set in the mini, micro or indoor cells. It cannot be set in umbrellas or single cells,
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HO Candidate Cells Evaluation
10 Candidate Cell Evaluation
Evaluation Process
HO Detection
Cause 2: uplink quality
Cause 3: uplink level
Cause 4: downlink quality
Cause 5: downlink level
Cause 6: distance
Cause 12: power budget
Performed every SACCH
MeasurementPreprocessing
A_LEV_HO
A_QUAL_HO
A_PBGT_HO
A_RANGE_HO
Performed every SACCH
Max
every SACCH
Preprocessmeasurement
Measurementresult
Grade
Priority (0, n) = 0
Cell 4: cause C2
Cell 2: cause C2
Cell 3: cause C2
Priority (0, n) = 1
Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Order
Priority (0, n) = 0
Cell 4: cause C2
Cell 3: cause C2
Cell 2: cause C2
Priority (0, n) = 1
Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Cell evaluation process (Order or Grade)
Priority (0, n) = 0
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2
Priority (0, n) = 1
Priority (0, n) = 2
Priority (0, n) = 3
Cell 6: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
PBGT filteringHO_MARGIN_XX(0,n)
Pre-ranking
Priority (0, n) = 0
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2
Priority (0, n) = 1
Cell 1: cause C2
Priority (0, n) = 2
Priority (0, n) = 3
Cell 5: cause C2
Cell 6: cause C2
Cell 7: cause C2
Cell 8: cause C2
Priority (0, n) = 4
Priority (0, n) = 5
Raw cell list
Cell 1: cause C2
Cell 2: cause C2
Cell 3: cause C2
Cell 4: cause C2
Cell 5: cause C2
Cell 6: cause C2
Cell 7: cause C2
Cell 8: cause C2
... max 32 cells
The HO candidate evaluation process is run after all intercell handover alarms.
In case of intra-cell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process is
skipped: the target cell is the serving cell.
The handover detection gives as indication the raw cell list (built from the book-keeping list) and the preferred
layer for the handover.In case of emergency handover alarms or cause 20 alarm, the cell evaluation will order the
cells given in the raw list, putting in the first position the cells belonging to the preferred layer, having the
highest priority (if EN_PRIORITY_ORDERING=ENABLED) and/or having the same frequency band type as the serving
cell. In case of an intercell handover alarm, if the serving cell belongs to the raw cell list (emergency handover
from the DCS 1800 inner zone of a multiband cell), this cell is put at the end of the candidate cell list with the
MS zone indication OUTER.
In case of better condition handover alarms (except cause 20), the cell evaluation will order the cells given in the
raw list, putting in the first position the cells belonging to the preferred layer and having the highest priority (if
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10 Candidate Cell Evaluation
Evaluation Process [cont.]
Raw cell list
Cell 1
Cell 2
Cell 3
Cell 4
Cell 5
Cell 6
Cell 7
Cell 8
� Case of MS in "MINI" cell, HO cause 2 detected :
Layer Type Priority Band Type Power Budget Filtering Cell Evaluation Process
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10 Candidate Cell Evaluation
Pre-Ranking in Complex Networks [cont.]
� Pre-ranking in case of emergency HO, plus cause 20 and 28 :
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10 Candidate Cell Evaluation
Pre-Ranking in Standard Networks
� With PRIORITY(0,n) settings
� One target cell can be favourized or penalized.
� From 0 (max) to 5 (min).
� It cannot supersede PREF_LAYER.
� Two main purposes:
� Favour 1800 cells, when exiting 900 cells.
� Direct traffic flow towards a certain neighbour.
� Safety belt:
� Favourite target would still be filtered out if its level is not good enough.
Serving cell
Candidate cell 1: RxLev: - 70 dBm, pbgt: + 10 dB
Candidate cell 2: Rxlev: - 90 dBm, PBGT: + 5dB
P0
P1
PRIORITY(0,n) can take 6 different values since B7, to take into account new indoor layers.
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10 Candidate Cell Evaluation
PBGT Filtering
� PBGT filtering
� Enabled with EN_PBGT_FILTERING
� For Emergency HO and Fast Traffic HO only
� Filter out cells from the target list that do not fulfill:
� OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of a concentric or multi band cell
� The average window is A_PBGT_HO
PBGT(n) > HO_MARGIN_QUAL (0,n) for causes 2, 4, 7or PBGT(n) > HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28or PBGT(n) > HO_MARGIN_DIST (0,n) for cause 6
PBGT(n) > HO_MARGIN_QUAL (0,n) for causes 2, 4, 7or PBGT(n) > HO_MARGIN_LEV (0,n) for causes 3, 5, 17, 18, 28or PBGT(n) > HO_MARGIN_DIST (0,n) for cause 6
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10 Candidate Cell Evaluation
PBGT Filtering [cont.]
� Recommended values
A neighbor cell with a lower RxLevcan be a good candidate, but there is a risk of PBGT HO back to the serving
cell.
A neighbor cell with a lower RxLevwill also trigger an emergency HO
A neighbor cell with a lower RxLevcan be a good candidate, but there is a risk of PBGT HO back to the serving
cell.
Strategy
� -127dB if mandatory HO, with anti ping-pong mechanism (*)
� +2dB if optional HO (*)
+2dB … +5dB
� MICRO/INDOOR : -127dB, with anti ping-pong mechanism
� Other cells : -5dB … +2dB
Proposed values
HO_MARGIN_DIST
HO_MARGIN_QUAL
HO_MARGIN_LEV
Parameter
Mandatory Distance HO : i.e. if the MS goes beyond the U_TIME_ADVANCE = 64, the call will drop.
Optional Distance HO : i.e. if the MS goes beyond the U_TIME_ADVANCE, the call can still be kept until a better
neighbour is found.
Anti ping-pong mechanism : can be based on HO_MARGIN and/or T_INHIBIT_CPT.
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10 Candidate Cell Evaluation
Order Evaluation
� CELL_EV = ORDER
� For all HO causes, candidate "n" is ranked among others according to the best ORDER:
� If EN_LOAD_ORDER = ENABLED and cell n is internal to the BSC
� LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
� FREEfactor(0) and FREEfactor(n) are a bonus/penalty based on the absolute load of the cell
� If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
Two types of cell evaluation algorithms can be used: ORDER and GRADE.
ORDER and GRADE are two different methods of cell ranking. They both consist in giving a mark or ’figure of merit’ to each candidate cell.
The basic differences between ORDER and GRADE are that:
� with ORDER:
� The candidate cell evaluation process interacts with the handover detection by use of cause dependent handover margins.
� The candidate cell evaluation process takes into account the number of free TCH in the candidate cells.
� with GRADE,:
� The candidate cell evaluation process does not interact with the handover detection.
� The candidate cell evaluation process takes into account the relative load of traffic channels in the candidate cells.
The type of cell evaluation is chosen by the operator on a (serving) cell basis and is provided to the BSC with the parameter CELL_EV
HO_MARGIN_XX = HO_MARGIN in case of better cell HO causes, otherwise HO_MARGIN_xx, with xx = LEV, DIST or QUAL accordingly to the HO Cause.
For any handover cause, the first cell in the list is taken as the target cell, i.e. the cell with the highest value of ORDER(n). The cells do not need to fulfil any other condition.
If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.
Note: the A_PBGT_HO average window is used for this process.
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10 Candidate Cell Evaluation
Grade Evaluation
� CELL_EV = GRADE [Recommended]
� For all HO causes, candidate "n" is ranked among others according to the best GRADE:
� If EN_LOAD_ORDER = ENABLED and cell n is internal to the BSC
� LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
� LOADfactor(n) is a bonus/penalty based on the relative load of the cell
� If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
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� In a hierarchical network (umbrella + micro cells)
� EN_SPEED_DISC is ENABLED
� A slow moving MS starts a call in lower layer
� After a while, this MS becomes a fast moving MS (for example, a car starting at traffic light)
� Explain the exact process that will send the MS towards the umbrella layer
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Self-Assessment on the Objectives
� Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this module
� The form can be found in the first partof this course documentation
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Module Objectives
Upon completion of this module, you should be able to:
� Define relevant parameters settings to introduce a new layer in an existing network
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Table of Contents
Switch to notes view! Page
1 Adding a Microcellular Layer 72 Adding Hot Spot Microcell for Traffic 293 Monitoring QoS in a Multilayer Network 33
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1 Adding a Microcellular Layer
Introduction
� The principle is to implement antennas below roof level
�confined propagation and low Tx power
�interferences avoided
�easier frequency planning
� Benefits :
� Higher network capacity per sq. km
� The right capacity at the right place (Airport, shopping malls, etc.)
� Improve the outdoor coverage and the indoor coverage (at street level)
� Improve the voice quality, thanks to cleaner frequencies
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1 Adding a Microcellular Layer
Introduction [cont.]
� Field Example: Busy Hour Traffic
� 20% of new traffic generation
� 50% of old macro traffic is handled by microcells
70.5
31.4
19.2
71
71.6 72.5
76.8
72.3
29.1
17.9
71.1 78
95.9 95.1 98.4 94.6
100.7
41.736.4
94.398.4
117.9114
116.9
54.7
42.9
116.1112.5
118.5
121.6
121.6
60
45.9
115.1
124.5
70.6
68.6
0
20
40
60
80
100
120
140
8/9
9/9
10/9
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12/9
13/9
14/9
15/9
16/9
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30/9
Macrocells Microcells
Microlayer commercial opening
This example corresponds to the following network design:
� Lower layer: 16 micro cells (37 TRXs)
� 11 outdoor micro cells with 2 TRXs
� 1 outdoor micro cell with 3 TRXs
� 2 indoor micro cells (pico cells) with 2 TRXs
� 2 indoor micro cells (pico cells) with 4 TRXs
� Upper layer: 12 macro cells
� umbrella macro cells are concentric (but not multiband)
� 4 belong to the same BSS as the micro cells
� 8 belong to another BSS
All micro cells were declared as micro and not as indoor.
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1 Adding a Microcellular Layer
Introduction [cont.]
� Keep a good QoS
� Avoid call drops on microcells
� Specific emergency HO towards umbrella rescue cells
� Avoid unnecessary handovers
� To ensure good QoS and speech quality
� Force idle mode in microcells to avoid subsequent capture
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1 Adding a Microcellular Layer
Architecture
� Capture towards microcells, emergency towards umbrella
� Capture HO is used to send slow MSs to the overlaid layer
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1 Adding a Microcellular Layer
Strategy
� Choose a handover to push traffic from these cells to the microlayer
� Cause 24 if all collocated cells and micro cells are all "Single"
� Cause 14 if collocated cells are Umbrella and micro cells are Micro
� The exercise next slide will show the best solution
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1 Adding a Microcellular Layer
Call Setup [cont.]
� DR and FDR are ENABLED
� An FDR (cause 20) is triggered when the average level of a neighboring cell is higher than L_RXLEV_NCELL_DR(n)
UmbrellaEN_DR = ENABLED
EN_FORCED_DR = DISABLED
L_RXLEV_NCELL_DR(n) = -88 dBm
FREElevel_DR(n) = 0
MicroEN_RESCUE_UM = ENABLED
EN_DR = ENABLED
EN_FORCED_DR = ENABLED
L_RXLEV_NCELL_DR(n) = -47 dBm
FREElevel_DR(n) = 0
DR & FDR
PRIORITY(micro, umb) = 1
DR only
PRIORITY(umb, umb) = 1
DR only
PRIORITY(umb, micro) = 0
DR & FDR
PRIORITY(micro, micro) = 1
The Setting of PRIORITY(0,n) is very important as network behavior will not be driven by Pref_layer which is
equal to "none" in this case.
But setting L_RXLEV_NCELL_DR(n) to -47 dBm in the micro cells inhibits the incoming FDR to them. Therefore
Priority(0,n) can be kept to the same value everywhere.
Priority(umb,micro) is set to 0 for Better Cell purpose (see the next pages).
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1 Adding a Microcellular Layer
Microcell Classes
� Parameter settings will depend on the microcells position in the lower layer
� Microcell “classes” are introduced to deal with typical parameters settings in each of these cases
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1 Adding a Microcellular Layer
Inner Microcell Class
� Definition
� A microcell surrounded by other microcells in a dense environment
� Rule
� The MS is comfortably installed in the microcell area. Calls have to be handled by a micro layer, which is a “traffic-catcher”
� Fast capture HO from the umbrella to micro cell
� If the MS is already on call in the micro-layer, it must stay on it
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1 Adding a Microcellular Layer
Inner Microcell: Better Condition Handovers
� Causes 12 and 14
UmbrellaEN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = DISABLED
L_MIN_DWELL_TIME = 6s
Inner MicrocellEN_PBGT_HO = ENABLED
EN_SPEED_DISC = ENABLED
A_PBGT_HO = 6
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -80 dBm
Cause 12 / 23
PRIORITY(umb, umb) = 1
HO_MARGIN(umb, umb) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12
PRIORITY(micro, micro) = 1
HO_MARGIN(micro, micro) = ?dB
Only fast mobiles can perform a PBGT
HO to an umbrella cell (with low load)
HO_MARGIN(micro, umb) = 5dB
A capture towards a microcell is triggered after L_MIN_DWELL_TIME. A low value is chosen, as we consider an
inner microcell.
In an umbrella 900 cell, a capture to a micro cell is preferred to a PBGT HO to a neighboring 900 cell using
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1 Adding a Microcellular Layer
Inner Microcell: Tuning of Cause 12 Parameters
� HO_MARGIN(micro,micro) and A_PBGT_HO(micro) tuning
� Case 1 : Avoid PBGT HO to a transcient cell (i.e. micro 3)
� Case 2 : Avoid an EM HO to an umbrella
�Reduce A_PBGT_HO & increase HO_MARGIN
or …
�Increase A_PBGT_HO & decrease HO_MARGIN
Micro 1Micro 2
Micro 3
HO_MARGIN tuning will be detailed in section 4: case studies.
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1 Adding a Microcellular Layer
Inner Microcell: Emergency Handovers
� Use Level, Quality causes
UmbrellaPref_layer = upper + single
Inner MicrocellEN_RESCUE_UM = ENABLED
Pref_layer = upper + single
A_QUAL_HO = 4
A_LEV_HO = 4
L_RXLEV_DL_H = -90 dBm
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 1
PRIORITY(micro,micro) = 1
PRIORITY(micro,umb) = 1
EN_RESCUE_UM is set to ENABLED for an emergency handovers behavior (send MSs towards the upper layer).
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1 Adding a Microcellular Layer
Inner Microcell: Candidate Cells Evaluation Process
UmbrellaEN_PRIORITY_ORDERING = ENABLED
EN_PBGT_FILTERING = ENABLED
CELL_EV = GRADE
Inner MicrocellEN_PRIORITY_ORDERING = ENABLED
EN_PBGT_FILTERING = ENABLED
CELL_EV = GRADE
EN_RESCUE_UM = ENABLED
HO_MARGIN_LEV(umb,umb)= 2 dB
HO_MARGIN_QUAL(umb,umb)= -2 dB
HO_MARGIN_DIST(umb,umb)= 2 dB
HO_MARGIN_LEV(micro,umb)= -127 dB
HO_MARGIN_QUAL(micro,umb)= -127 dB
HO_MARGIN_DIST(micro,umb)= -127 dB
OUTDOOR_UMB_LEV(micro,umb)=
-100 dBm
HO_MARGIN_LEV(umb,micro)= 2 dB
HO_MARGIN_QUAL(umb,micro)= -2 dB
HO_MARGIN_DIST(umb,micro)= 2 dB
HO_MARGIN_LEV(micro,micro)= 2 dB
HO_MARGIN_QUAL(micro,micro)= -2 dB
HO_MARGIN_DIST(micro,micro)= 2 dB
The upper layer is a rescue layer for microcells: thus, all HO_MARGIN_XX(micro,umb) are set to -127 dB.
OUTDOOR_UMB_LEV is set to -100 dBm: all umbrella cells with a received level lower than -100 dBm will be
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1 Adding a Microcellular Layer
Border Microcell Class
� Definition
� A microcell bordering the microcell area
� Hybrid situation between the inner microcell and the hotspot microcell
� Rule
� Ensure the MS is slow & well covered before a capture in microlayer
� Ensure a MS will exit this cell safely
� PBGT HO are of no use here
Border Microcell
The upper layer is a rescue layer for microcells: thus, all HO_MARGIN_XX(micro,umb) are set to -127 dB.
OUTDOOR_UMB_LEV is set to -100 dBm: all umbrella cells with a received level lower than -100 dBm will be
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1 Adding a Microcellular Layer
Border Microcell: Better Condition Handovers
� Causes 12 and 14
UmbrellaEN_SPEED_DISC = ENABLED
L_MIN_DWELL_TIME = 8s
H_MIN_DWELL_TIME = 16s
Border Microcell
Cause 14
L_RXLEV_CPT_HO(umb, micro)
= -75 dBm
Cause 12 / 23
Cause 12
Only fast mobiles can perform a PBGT
HO to an umbrella cell (with low load)
HO_MARGIN(micro, umb) = 5dB
All other parameters not shown here are identical to inner microcells.
A capture towards a microcell is triggered after MIN_DWELL_TIME which will vary from H_MIN_DWELL_TIME down
to L_MIN_DWELL_TIME if the umbrella 900 cell is loaded. MIN_DWELL_TIME is increased to prevent tangential MSs
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1 Adding a Microcellular Layer
Border Microcell: Emergency Handovers
� Use Level, Quality causes
UmbrellaPref_layer = upper + single
Border MicrocellEN_RESCUE_UM = ENABLED
EN_MCHO_H_DL = ENABLED
Pref_layer = upper + single
L_RXLEV_DL_H = -82 dBm
A_LEV_HO = 6
U_RXLEV_DL_MCHO = -90 dBm
A_LEV_MCHO = 4
Emergency HO considered as a "safe exit" HO, based on cause 5.
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
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1 Adding a Microcellular Layer
Indoor Microcell Class
� Definition
� An indoor area located within the micro cell area
� This indoor cell aims at absorbing traffic in a strategic building
� Rules
� Absorb indoor traffic, and only indoor traffic
� Do not catch outdoor MS (Idle or Dedicated)
� An MS nearby the building door but still outside should camp on the outdoor cell
� Beware of "indoor" exit strategy
� Beware of jamming at higher floor
Indoor Microcell
Another type of indoor microcell can be defined:
Indoor microcell for coverage, when the indoor cell is a hotspot and the indoor coverage from the macro layer is
not good. This chapter does not deal with this case. See the next slides for detailed parameter settings of indoor
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1 Adding a Microcellular Layer
Indoor Microcell: Better Condition Handovers
� Causes 12 and 14
UmbrellaEN_PBGT_HO = ENABLED
EN_MCHO_NCELL = ENABLED
EN_SPEED_DISC = ENABLED
L_MIN_DWELL_TIME = 8s
H_MIN_DWELL_TIME = 16s
Indoor MicrocellEN_PBGT_HO = ENABLED
EN_SPEED_DISC = DISABLED
Cause 14
PRIORITY(umb, micro) = 0
L_RXLEV_CPT_HO(umb, micro)
= -75 dBm
Cause 12 / 23
Cause 12
Only fast mobiles can perform a PBGT
HO to an umbrella cell (with low load)
HO_MARGIN(micro, umb) = 5dB
L_RXLEV_CPT_HO tuning is closely linked to real radio propagation and cell coverage. Values given on this slide
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1 Adding a Microcellular Layer
Indoor Microcell: Emergency Handovers
� Use Level, Quality causes
UmbrellaPref_layer = upper + single
PRIORITY(umb,micro) = 0
PRIORITY(umb,umb) = 1
PRIORITY(micro,micro) = 1
PRIORITY(micro,umb) = 1
Indoor MicrocellEN_RESCUE_UM = ENABLED
EN_MCHO_H_DL = ENABLED
Pref_layer = upper + single
L_RXLEV_DL_H = -82 dBm
A_LEV_HO = 6
U_RXLEV_DL_MCHO = -90 dBm
A_LEV_MCHO = 4
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
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1 Adding a Microcellular Layer
Indoor Microcell: High Floors Case
� In high floors, the level from surrounding umbrella cells is very high
� More than 6 cells might be measured at -47dBm (maximum measured value)
� How can we ensure the indoor cell is included in the chosen 6 ?
� One solution
� Dedicate one cell to cover these floors
� Set a high CRO (8dB … 12dB) : the C2 is not limited
� Define many incoming adjacencies but just few selected outgoing adjacencies
� Use SFH with broad band to avoid interferences
A high threshold HO is used to trigger HO towards the umbrella cell for the microlayer zone exit.
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2 Adding Hot Spot Microcell for Traffic
Hotspot Microcell Class
� Definition
� A microcell totally isolated from any other microcell
� Rules
� Capture shall occur only if the MS is not moving
� There are no neighbour from the same layer
�No better cell handover can be triggered
�An emergency HO shall be used as an exit strategy
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3 Monitoring QoS in a Multilayer Network
Indicators Monitoring
� QoS indicators in each layer� Create a cell zone for each cell type : Umbrella, Mini, Micro, Indoor, Single
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3 Monitoring QoS in a Multilayer Network
Indicators Monitoring [cont.]
� Goal 3: Simplicity of parameter settings
� Apply the same settings within each cell type
� Find the best "overall" settings in order to obtain the best results (regarding goal 1, goal 2 or both)
� Once this is achieved, fine tune problematic cells only
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Self-Assessment on the Objectives
� Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this module
� The form can be found in the first partof this course documentation
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Module Objectives
Upon completion of this module, you should be able to:
� Define relevant parameters settings to introduce a new band in an existing network
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Table of Contents
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1 Introduction 72 Collocate the new band in a monolayer network 103 Collocate the new cells in upper layer of a multilayer network 184 Collocate the new cells in lower layer of a multilayer network 265 QoS Monitoring 34
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1 Adding a Microcellular Layer for Traffic and Coverage Increase
Strategies
� Several cases should be considered in order to cover all the possibilities
� What is the current architecture prior to the introduction of the new band ?
1. Monolayer
2. Multilayer
� What is the planned architecture after the introduction of the new band ?
1. Monolayer : the new band is located in the current layer
2. Multilayer : the new band is located within an existing layer
3. Multilayer : the new band is located within a dedicated layer
� In order to save cost, the new cells will be collocated with the existing cells
1. Dual-BCCH ? (two different cells)
2. Single-BCCH ? (multiband concentric cells)
� For each architecture, which settings to choose ?
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1 Introduction
Examples
� The main situations will be studied :
� Collocate the new band with :
1. Existing single cells (monolayer)
2. Existing umbrella cells� Existing micro cells in classical band
3. Existing mini cells� Existing umbrella cells in classical band
� Implement the new band in a new layer
1. New micro layer (for hotspot coverage)� refer to previous chapter "Adding a Microcellular Layer"
2. New mini layer (for continuous coverage)� this solution is not practical: macro cells in the new band are always Collocated with
existing cells
3. New umbrella layer (for extension of coverage)� this solution is not realistic: umbrella cells are always deployed first in a network
�
�
�
In this course, we focus only on realistic solutions which are chosen by all operators : the new band is never
deployed in a country without colocation with existing cells.
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2 Collocate the new band in a monolayer network
Single vs. Umbrella
� If the network is monolayer, there is no difference between Singles and Umbrellas.
� The only difference will appear if introduction of microcells in the future :
1. For Umbrellas, the cause 14 is available to push traffic to microlayer
2. For Single, the cause 24 (General Capture Handover) must be enabled
� In a case study, we will see the differences between the two solutions.
� Future proof solution: set all your cells as "Umbrella"
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2 Collocate the new band in a monolayer network
Collocated cells [cont.]
� For single-BCCH cells, refer to algorithms of causes 10, 11 and 13.
Cell A
inner
outer
cause 13
cause 10/11
CRO(A)
CELL_RESELECT_OFFSET must be set accordingly to the other cells
CAUSE 13: Entry HO, based on DL and UL RxLevof the outer zone
RXLEV_UL_ZONE & DL_ZONEZONE_HO_HYST_UL & DLMS and BS_TXPWR_MAX_INNERNEIGHBOUR_RXLEV(0,n)EN_BETTER_ZONE_HOEN_LOAD_BALANCEPING_PONG_HCP, T_HCP
CAUSE 10/11: Exit HO, based on DL or UL RxLevof the inner zone
RXLEV_UL_ZONE & DL_ZONE
INTERCELL HO: no changesOFFSET_HO_MARGIN_INNER
Rule : OFFSET_HO_MARGIN_INNER ≥ ∆ Propagation - ∆ MS TxPwrRule : OFFSET_HO_MARGIN_INNER ≥ ∆ Propagation - ∆ MS TxPwr
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2 Collocate the new band in a monolayer network
Collocated cells [cont.]
� For dual-BCCH cells, use "Preferred band HO" (cause 21)
CELL_RESELECT_OFFSET(A) > CELL_RESELECT_OFFSET(B)
Cell B
Cell A
cause 21
cause 5
CRO(B)
CRO(A)
CAUSE 21: Entry HO, based on DL RxLev of cell BL_RXLEV_CPT_HO(A,B)MS_TXPWR_MAX(B)MULTIBAND_TRAFFIC_CONDITION(B)HIGH_TRAFFIC_LOAD(A)EN_PREFERRED_BAND_HO(B)T_INHIBIT_CPT(A)
CAUSE 5: Exit HO, based on DL RxLev of cell BL_RXQUAL_DL_H(B)L_RXLEV_DL_H(B)EN_RXLEV_DL(B)
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2 Collocate the new band in a monolayer network
Collocated cells [cont.]
� Regarding Radio Parameters :
� Single-BCCH:
1. Less parameters
2. Much simpler settings, especially adjacency parameters
3. PBGT HO towards all neighbours are possible
� Dual-BCCH:
1. Cause 21 is using load conditions in serving and target cells
2. Cause 21 can push a MS from one 900 cell to its collocated cell and to other 1800 cells as well
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3 Collocate the new cells in upper layer of a multilayer network
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3 Collocate the new cells in upper layer of a multilayer network
Single-BCCH strategy
� As seen earlier, it is simpler to use single-BCCH
� In the OMC-R, create your collocated cells as "Concentric"
� Choose a handover to push traffic from these cells to the microlayer
� Cause 24 if collocated cells and micro cells are all "Single"
� Cause 14 if collocated cells are "Umbrella" and micro cells are "Micro"
� The choice has been done previously:
� The best solution is "cause 14" in order to take into account fast moving mobiles.
This strategy was fully studied in "Adding a Microcellular Layer""
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3 Collocate the new cells in upper layer of a multilayer network
Dual-BCCH strategy
� In case this solution is preferred, some settings to manage Umbrella 1800 / Umbrella 900 were given in the previous chapter.
� In this chapter, we introduce a Microcell layer.
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3 Collocate the new cells in upper layer of a multilayer network
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Umbrella
3 Collocate the new cells in upper layer of a multilayer network
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Umbrella
3 Collocate the new cells in upper layer of a multilayer network
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Umbrella
3 Collocate the new cells in upper layer of a multilayer network
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Umbrella
3 Collocate the new cells in upper layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
Single-BCCH vs. Dual-BCCH
� Assumptions:
� New cells are Collocated with classical Mini cells
� Umbrella cells are in the classical band
� The easiest solution is to create Concentric Multiband Mini cells
� Refer to "Create a multilayer network"
� The new band is "transparent", it does not impact algorithms other than intra-zone handovers (causes 10, 11, 13)
� In this chapter, the dual-BCCH solution is studied
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
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4 Collocate the new cells in lower layer of a multilayer network
Candidate Cell Evaluation
Umbrella
Mini
Use 1800 band for quality HO : special settings: default settings
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5 QoS Monitoring
Indicators Monitoring
� QoS indicators in each layer
� Create a cell zone for each cell type & band
� Umbrella 900
� Mini 900
� Micro 900
� Indoor 900
� Perform your QoS Monitoring per cell zone
� Goal 1: Intelligent traffic split
� Goal 2: Balanced QoS between different layers and bands
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5 QoS Monitoring
Investigation
� Special attention to:
� HO/Call and RTCH Duration Avg in intermediate layer
Too many incoming HO from top layer (probably due to capture)
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Self-Assessment on the Objectives
� Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this module
� The form can be found in the first partof this course documentation
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Table of Contents
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1 Radar Cell 72 Symmetric Microcells at a Street Corner 93 Asymmetric Microcells at a Street Corner 114 Indoor Microcell within a Monolayer Network 135 Trilayer Network: Indoor Cell within a Multi-Layer Network 156 Indoor Cell Congestion 177 Transforming a Microcell into an Indoor Cell 198 Picocells in Skyscrapers 21
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1 Load and Traffic Evaluation
Long Term Evaluation
� Long term measurement of the load of a cell
� corresponds to function Traffic_load(cell)
� Traffic_load() value is determined from a number N_TRAFFIC_LOAD of consecutive non-sliding window load averages AV_TRAFFIC_LOAD calculated from Nb free TCH samples updated every A_TRAFFIC_LOAD x TCH_INFO_PERIOD s
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2 Extended Cell Overview
Radio Link Establishment - MS Located in the Inner Cell Area
The TCU sends the IMMEDIATE ASSIGNMENT COMMAND (which provides the description of the allocated SDCCH ) to the BCCH TRE of the inner cell.
The TCU controlling the inner cell BCCH sends a copy of the message to the TCU handling the BCCH of the outer cell. This is done if and only if the timing advance IE included in the CHANNEL REQUIRED is smaller than 60, thus indicating that the MS is strictly in the inner cell (in order to avoid that the MS receives two Immediate Assignment messages when located in the overlap zone).
The TCU controlling the outer cell BCCH forwards the IMMEDIATE ASSIGNMENT COMMAND to the outer cell BCCH TRE.
(1) The MS in the outer cell sends an access burst on the RACH of the outer cell. This burst is successfully received by the outer cell BCCH TRE. In the inner cell, the access burst arrives too late to be successfully decoded.
(2) The outer cell BCCH TRE sends a CHANNEL REQUIRED message to the BSC containing the random reference sent by the mobile, the TDMA frame number when the message was sent over the air and the measured TOA.
(3) The TCU controlling this TRE allocates an SDCCH subchannel in the outer cell to the transaction and asks the BTS to activate this subchannel.
(4) The BTS activates the requested channel and sends back an acknowledgement, once this is done.
(5) The TCU then sends the description of the channel in the IMMEDIATE ASSIGNMENT COMMAND to the outer cell BCCH TRE.
(6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
(7) The mobile switches its transceiver to the required channel and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS.
(8) The BTS acknowledges the establishment of the LAPDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.