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Course Title Multiband GSM Network Radio Optimization / B8
Course Reference 3FL 12034 AAAA - AUE
Audience
Radio Network Engineers (operator or Alcatel staff) in charge of optimizing a multi-band network.
Objectives
During the course, the trainee will be able to describe the specific radio algorithms in multi-band networks in order to enhance the offered QoS.
By the end of the course, the participant will be able to:
- Describe the concepts and strategy of multi-band networks.
- Describe the specific type of cells implemented in multi-band networks.
- Describe the specific radio algorithms used in the Alcatel BSS in a multi-band network.
- Propose default parameter values for the cells of a multi-band network using these algorithms.
- Propose a list of specific indicators to monitor QoS and traffic in a multi-band network.
Note: Radio Network Planning issues like micro site detection, site planning, frequency planning are not included.
Prerequisites
Training module “Introduction to GSM QoS and Traffic Load Monitoring” (3FL 10491 ABAA–AUE) and “Introduction to Radio Fine Tuning” (3FL 10493 ABAA–AUE) or equivalent level.
Training Methods
Theory / Practice.
Language
English, French
Duration
3 Days
Location
Alcatel University or Customer Premises.
Number of participants
Maximum 8
Course content
1 Multi-band Network Architecture
1.1 Concepts and strategies
1.2 Cellular network architecture
1.3 Choosing a relevant architecture
1.4 Requirements
2 Algorithms and Associated Parameters
2.1 Introduction
2.2 Neighboring cells list
2.3 Idle mode selection and reselection
2.4 Call setup
2.5 Handover strategies
2.6 Main standard handover algorithms
2.7 HO algorithms for multi-band networks
2.8 HO algorithms for concentric cells
2.9 Candidate cell evaluation
3 Creating a Multi-band Network
3.1 Introduction
3.2 Adding a 1800 band in an existing 900 network
3.3 Adding a 900 band in an existing 1800 network
3.4 Adding a 1800 band in an existing 900 (macro+micro) network
> In a mono-layer network, a new band may be introduced:
• In the same layer
– Macro 900 (single)
– Macro 1800 (single)
– 900-1800 interworking managed by priority set by the operator
• In a separate layer
– Macro 900 (umbrella)
– Macro 1800 = mini
– 900-1800 interworking driven by a dual layer architecture (easier to introduce but less flexible)
1.3 Choosing a relevant architectureMono-layer architecture
900 900 1800 1800
900 900
mini1800 mini1800
> All examples in this document will be using 900 as an “historical” band and 1800 as a “new” band (thus preferred band).
> All other network configurations are anyway possible.
> The dual layer configuration is interesting in case the dual band implementation strategy is traffic driven due to a low penetration rate of multi-band MSs.
> A dual layer allows for example, for a multi-band MS located in a 900 cell, to discriminate its behavior between a Forced Directed Retry and an emergency HO. 1800 neighboring cells can be favored for a FDR whereas 900 neighboring cells will be preferred on an emergency HO.
> A dual layer also allows to decide the MS transfer from 900 to 1800 band on speed criterion instead of on traffic criterion if needed (macro 1800 hot spot for instance).
> In a multi-layer network, a new band may be introduced:
• In the upper layer
– Macro 900 (umbrella)
– Macro 1800 (umbrella)
– Micro 900
• In the lower layer
– Macro 900 (umbrella)
– Macro 1800 = mini
– Micro 900
1.3 Choosing a relevant architectureMulti-layer architecture (1/3)
900 900 1800 1800
900 900
mini1800
µ900 µ900
µ900 µ900
> In the first configuration, the major difficulty is to manage 900-1800 interworking in the upper layer.
> In the second configuration, the operator has to deal with priority between the preferred cells: mini or micro? For both selections in idle mode and capture from the upper layer.
> MULTIBAND_REPORTING has to be tuned carefully in multi-band 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: 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
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. Thus, MULTIBAND_REPORTING = 3
2.2 Neighboring cells list Parameters optimization
> At startup (IMSI Attach), the MS is selecting cell with
• Define 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 on another one if:
• C1 criterion is too low
• The MS cannot decode downlink messages
• The current cell is becoming forbidden (e.g. barred)
• The MS cannot access the cell
• there is a better cell, regarding C2 criterion
2.3 Idle mode selection and reselection Selection and reselection principles
> 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. (done after 5 s, etc.)).
– CELL_RESELECT_OFFSET used to favor a cell among others (e.g. microcell vs. umbrella, once T > PENALTY_TIME)
– Or C2 = C1 - CELL_RESELECT_OFFSET(if PENALTY_TIME = 31)
– CELL_RESELECT_OFFSET used to handicap some cells among others
• One reselection criterion is comparison with C2– C2neighboring cell > C2current if cells belong to the same LA
– C2neighboring cell > C2current+CELL_RESELECT_HYSTERESIS if cells from different LAs
2.3 Idle mode selection and reselection C2 criterion
> The use of a second formula (Penalty_time = 31) is restricted to very special cases, as we do not like to penalize a cell. If a cell is set with PT=31, it will be penalized compared to ALL its neighboring cells. To penalize a cell compared to one neighboring cell, one should better boost the neighboring cell (using first formula).
> The first formula is very useful to favor an indoor cell or a microcell.
• EN_FORCED_DR value is only relevant if EN_DR = true
• AV_RXLEV_NCELL_DR(n) is calculated with the A_PBGT_DR window
• if less than A_PBGT_DR samples are available, the average value is calculated with the available samples and the average window is filled in with -110 dBm
> This algorithm and the related parameters are detailed in session 2.8
> Compared to HO CAUSE 13 equation, parameter EN_BETTER_ZONE_HO is not used at call setup
> If less than A_LEV_HO (A_PBGT_HO for neighboring cells measurements) have been received, averages are calculated on theavailable number of measurements
2.4 Call setupSpecific case of concentric cells (3/3)
Assignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSSAssignment of HO functions in the ALCATEL BSS
• 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 band
cause 14 : high level in neighboring cell of a lower or an indoor layer cell for slow mobile
cause 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
2.6 Main standard handover algorithmsHandover Cause 2: UL Quality
QUAL
LEV
> Quality and Level causes (2, 3, 4, 5, 15, 16)
> 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.
2.6 Main standard handover algorithms Handover Cause 6: Distance
> 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 for the power control to react.
2.6 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 HOP
• 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 an HO CAUSE 15 (or 16) fails, it can be modified as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).
2.6 Main standard handover algorithms Handover Cause 12: Power Budget (2/7)
Single 900
Upper 900
µ900
900 1800
indoor900
Upper 1800
µ900
mini1800
Upper 900
Single 1800
900 1800
indoor900
mini900
fastfast
fastfast
fast
Upper
Upper
> This scheme highlights well the difficulty of introducing multi-band cells if EN_MULTIBAND_PBGT_HO is disabled (this was the only configuration in the first B6.2 networks): Multi-band cells interoperate only with, etc. multi-band cells.
DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the serving cell and the neighboring cell cell n (Traffic_load(n)) in the following way:
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
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.
2.6 Main standard handover algorithms Handover Cause 12: Power Budget (6/7)
> The MS is in the INNER zone of a concentric cell, the PBGT equation is:
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)
> For example, in a multi-band cells network
2.6 Main standard handover algorithms Cause 12: parameters for concentric cells (1/2)
9001800 900 1800Cell 1Serving
Cell 2Target
RxLev on TCH = -80dBm RxLev of BCCH = -72dBm
PBGT = +5 dB
> If RxLev(n) = -72 dBm, PBGT(n) = +5 dB > HO_MARGIN = 4 dB
> If cause 12 was triggered at this moment, the MS will be for example in the outer zone of cell 2. Its received level will be about -71 dBm.
> It will then check possible cause 12 HO towards cell 1. The received level of cell 1 is NOT -80 dBm (this was the level of the 1800 TCH).
> Field results show that a 900 BCCH will be received roughly at -80+10=-70 dBm. The risk of ping pong handover is then very high! In fact, cause 12 HO should NOT have been triggered.
> A solution is to be found in tuning OFFSET_HO_MARGIN_INNER used in cause 12 equation. See next slide.
2.6 Main standard handover algorithms Handover Cause 23: Traffic (1/2)
> CAUSE 23: Traffic Handover
• The aim of this cause is to speed HO detection when
– The serving cell is loaded
– The target cell is unloaded
• When traffic distribution is taken into account for handover detection,
this cause reacts in the opposite way of cause 12, to maintain an
equivalent ping-pong static hysteresis
> Checked between– Cells of the same layer only
– If EN_MULTIBAND_PBGT_HO = disabled
– Cells of the same cell_band_type only
– if the MS is located in the inner zone of a multi-band cell, it can only go to another multi-band cell
– Else any other cells whatever their cell_band_type
HIGH LOW
Modified B8
B8
> In some multi-band 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 multi-band 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 neighboring cellhood.
> The solution consists in allowing intra-layer traffic handovers (Cause 23) based on a power budget evaluation between cells of different bands.
2.6 Main standard handover algorithms Handover Cause 23: Traffic (2/2)
> CAUSE 23: Traffic Handover
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
� Size of window for level average: A_PBGT_HO
B8(See comments)
> 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 multi-band cell:
• a) The MS is not in the inner zone of a multi-band cell
– If the flag EN_MULTIBAND_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_MULTIBAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.
• b) The MS is in the inner zone of a multi-band cell
– If the flag EN_MULTIBAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all theneighboring cell multi-band cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the same BSC as the serving cell.
– If the flag EN_MULTIBAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all theneighboring cells without any cell frequency band restriction.
2.6 Main standard handover algorithms Handover Cause 28: Fast Traffic HO (3/3)
> CAUSE 28: Fast Traffic Handover equation
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
� Size of window for average 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
> 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.
• By forbidding capture for a while (T_INHIBIT_CPT) when an emergency quality handover has just been triggered
– Cause 2, 4 or 7: ULQ, DLQ or Bad SACCH
– OR external HO with A interface cause ULQ or DLQ
• In B8, the feature has been extended to the SINGLE cells
2.7 Handover algorithms for multi-band networksCapture alarms filtering (1/2)
Cell(0)
Cell(n-1) Cell(n)
1. Emergencyquality HO
2. Inhibit cause 21during T_INHIBIT_CPT
B8
> The role of the timer T_INHIBIT_CPT is to inhibit the capture handover Causes 14, 21, and 24 for a while so as to reduce the ping-pong effect. The immediately preceding cell on which the MS has been is here denoted n-1.
• If the serving cell is in the upper or single layercell_layer_type(0) = upper or single
– IF [ Cell_layer_type(n-1) = lower OR indoor ]
OR [ cell_band_type(n-1) ≠≠≠≠ cell_band_type(0) ]
– AND an emergency quality HO has just been performed
– THEN, T_INHIBIT_CPT is started
• If the serving cell is in a lower layer cell_layer_type(0) = lower
– IF [ Cell_layer_type(n-1) = indoor ]
OR [ cell_band_type(n-1) ≠≠≠≠ cell_band_type(0) ]
– AND an emergency quality HO has just been performed
– THEN, T_INHIBIT_CPT is started
2.7 Handover algorithms for multi-band networksCapture alarms filtering (2/2)
Modified B8
B8
> According to the layer of the serving cell the following conditions must be checked for starting the timer T_INHIBIT_CPT:
• Case of a serving cell in the upper or single layer (CELL_LAYER_TYPE(n0) = upper or single)
– Condition 1: The immediately preceding cell n-1 is in the indoor or lower layer, i.e. CELL_LAYER_TYPE(n–1) = lower or indoor, or the frequency band of the immediately preceding cell n-1 is different from the frequency band of the serving cell n0, i.e. CELL_BAND_TYPE(n–1) <> CELL_BAND_TYPE(n0).
– Condition 2: The call has previously performed i) an emergency internal handover on quality (Cause 2, 4, and 7) towards the serving cell or ii) an external handover with the A interface GSM cause “uplink quality or downlink quality” and there is a bi-directional adjacency link between the preceding external cell n-1 and the serving cell n0.
– If Conditions 1 and 2 are fulfilled, the timer T_INHIBIT_CPT is started.
• Case of a serving cell in the lower layer (CELL_LAYER_TYPE(n0) = lower)
– Condition 3: The immediately preceding cell is in the indoor layer, i.e. CELL_LAYER_TYPE(n–1) = indoor, or the frequency band of the immediately preceding cell n-1 is different from the frequency band of the serving cell n0, i.e. CELL_BAND_TYPE(n–1) <> CELL_BAND_TYPE(n0).
– Condition 4: The call has previously performed i) an emergency internal handover on quality (Cause 2, 4, and 7) towards the serving cell or ii) an external handover with the A interface GSM cause “uplink quality or down link quality” and there is a bi-directional adjacency link between the precedent external cell n-1and the serving cell n0.
– If Conditions 3 and 4 are fulfilled, the timer T_INHIBIT_CPT is started.
> If these conditions are not fulfilled, the timer T_INHIBIT_CPT is not started.
• UL static hysteresis for interzone HO from the outer to the inner
– In case of multi-band cells, it should take into account the difference of propagation between GSM and DCS
• Added to cause 10 threshold RXLEV_UL_ZONE
> ZONE_HO_HYST_DL
• DL static hysteresis for interzone HO from the outer to the inner
– In case of multi-band cells, it should take into account the difference of propagation between GSM and DCS and the difference of BTS transmission power in the two bands
• Added to cause 11 threshold RXLEV_DL_ZONE
2.8 Handover algorithms for concentric cellsCause 13: too high level on the UL and the DL in the outer zone (3/6)
> Outgoing intercell handovers from concentric cells
• As explained before, an MS located in a concentric cell can make intercell, emergency or better condition HO regardless their current zone
– For example, an MS located in the INNER zone of a concentric cell can make directly a cause 12 HO towards another cell, WITHOUT having to trigger any cause 10 or 11 to the OUTER zone before
– The only restrictions have been already presented: they are linked to EN_MULTIBAND_PBGT_HO and EN_BI-BAND_MS parameters
2.8 Handover algorithms for concentric cellsOutgoing intercell handovers from Concentric Cells
> As soon as an intercell HO alarm has been detected
> HO Detection sends to Candidate Cell Evaluation
– 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)
– the list of potential candidates (it depends on type of handover cause)
2.9 Candidate cell evaluationFrom HO Detection to Candidate Cell Evaluation
> The HO candidate cell 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 multi-band 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 EN_PRIORITY_ORDERING=ENABLED).
– HO_MARGIN_XX (0,n) = HO_MARGIN_DIST (0,n) for cause 6
– 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
> The filtering process allows to filter out cells from the target list before sending them to the ORDER or GRADE evaluation process.
> It can be enabled/disabled on-line on a per cell basis from the OMC-R with the flag EN_PBGT_FILTERING.
> The candidate cells are filtered on their power budget in relation to a handover margin threshold based on the handover cause.
> Note: the average window used for this process is A_PBGT_HO (even for emergency handovers, where handover alarm could have been raised through A_LEV_HO or A_QUAL_HO samples).
> Warning: HO_MARGIN_xx (LEV, DIST or QUAL) has nothing to do with a handover margin value, specific for certain handover causes (anyway, these handovers cause only tackle source cell and are not looking at level of targets for handover detection).
> HO_MARGIN is used for handover detection (cause 12 or 23).
> HO_MARGIN_xx are used for candidate cell evaluation.
> Thus, there is no having HO_MARGIN = HO_MARGIN_xx! Let us see three examples:
1) If HO_MARGIN_xx = HO_MARGIN = 5 dB
In that case, when an emergency handover is triggered (level, quality, distance, etc.), all neighboring cells are filtered regarding their PBGT compared to 5 dB! By the way, if a cell that is not greater than the serving one + 5 dB will be filtered out: this handover, detected as an emergency case, is in fact a better cell one.
2) If HO_MARGIN_xx is very small (for example, -30 dB), risk of ping-pong handovers.
For example, all cells have L_RXLEV_DL_H = -97dBm. If Lev(cell1)=-98dBm, HO can be triggered to cell2 with level -99dBm (-99>-98-30), and then, as -99<-97, HO is triggered back to cell1: ping-pong of emergency HO.
3) HO_MARGIN_xx can be used to simulate PBGT HO (for example, usage of distance HO to simulate 900-1800 PBGT HO before it was existing). HO_MARGIN_DIST is very small (e.g., 2 on 1800). Thus, a Distance HO alarm is raised very early. If HO_MARGIN_DIST (1800,900)= 8 dB, no HO will be in fact triggered before the level of the 900 neighboring cell is greater than the one of 1800 + 8 dB: this distance HO is in fact a PBGT HO between bands.
• LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
• FREEfactor are TCH traffic based bonus/penalty to rank cells
If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
ORDER (n) = PBGT(n) + LINK_FACTOR(0,n) - HO_MARGIN_XX(0,n)
Cell "n" is kept if:
• AV_RXLEV_NCELL (n) > RXLEVmin (n) + max [0;(MS_TXPWR_MAX(n)-P)]
2.9 Candidate cell evaluation ORDER evaluation
> 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
> 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 andno further action is carried out.
> Note: the A_PBGT_HO average window is used for this process.
• LINK_FACTOR(0,n) is an operator parameter to give a bonus/penalty to a cell
• LOADfactor(n) is a weighting factor that takes into account the relative load of traffic channels in a cell
If EN_LOAD_ORDER = DISABLED or cell n is external to the BSC
GRADE (n) = PBGT(n) + LINK_FACTOR(0,n)
Cell "n" is kept if:
� AV_RXLEV_NCELL (n) > RXLEVmin(n) + max [0;(MS_TXPWR_MAX(n)-P)]
2.9 Candidate cell evaluation GRADE Evaluation
> LINKfactor(0,n) is a parameter set by OMC command for each cell(n).
> LINKfactor(n1,n2) allows the operator to handicap or to favor the cell n1 with respect to its neighboring cell n2. In particular, it can be used to disadvantage an external cell when an internal cell is also a possible candidate.
> 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 GRADE(n). If no cell fulfils the condition and the serving cell does not belong to the target cell list, the target cell list isempty and no further action is carried out.
> Note: the A_PBGT_HO average window is used for this process.
> Note: an example summarizing all steps of candidate cell evaluation, in case of a multi-band network, can be given here: MS on a 1800 cell, 3 possible neighboring cells (1*900 + 2*1800). P(1800,900)=1 and P(1800,1800)=0. All HO_MARGIN_xx = 0 dB. PBGT:
• PBGT (900) = +5 (second cell seen in the book-keeping list)
• PBGT (1800_1) = -2 (first cell seen in the book-keeping list)
• PBGT (1800_2) = +2 (third cell seen in the book-keeping list)
• Emergency alarm or Forced DR: the traffic distribution is driven by the parameter PRIORITY(0,n) because PREF_LAYER = upper + single is the layer to which both 900 and 1800 cells belong
> Umbrella 900 + mini 1800
• Emergency alarm: the traffic distribution is first driven by the layer because PREF_LAYER = upper + single for umbrella 900 cells and lower for mini 1800 cells (according to parameter EN_RESCUE_UM)
• Forced DR: the traffic distribution is first driven by the parameter PRIORITY(0,n)because PREF_LAYER = none, then the same band is preferred
– In case of a dual layer solution, almost no parameter is to be tuned to obtain an expected emergency handovers behavior
– Easy and fast introduction of the new band
3.2 Adding a 1800 band in an existing 900 network Single 1800 versus Mini 1800 (1/2)
> The strategy of parameter setting for a dualband 900/1800 configuration will depend on the coverage of the 1800 layer on the one hand and on the capacity of the 1800 cells on the other hand:
• if 1800 coverage is good and 1800 capacity is good:
– it is better to stay on the 1800 band for both FDR and Emergency alarm:
– mono-layer case (umbrella+single 900 & 1800): use the Priority(0,n) parameter to favor1800 cells or keep the same Priority to 900 and 1800 neighboring cells knowing that cells of the same band are preferred in the candidate cell evaluation process
– bi-layer case (umbrella 900 + mini 1800): set EN_RESCUE_UM to disabled to have "lower" as Preferred layer for Emergency HO and use the Priority(0,n) parameter to favor 1800 cells for FDR or keep the same Priority to 900 and 1800 neighboring cells knowing that cells of the same band are preferred in the candidate cell evaluation process.
– it is better to favor the 1800 band in case of congestion on the 900 band (especially the 1800 cells co-site of the congested 900 cell): use Priority(0,n) since the Preferred layer is "none" in both mono-layer or bi-layer configurations
– it is better to stay on the 900 band for an Emergency alarm: no specific parameter setting is needed since Preferred Layer = "upper+single" and cells of the same band are preferred in both mono-layer or bi-layer configurations.
• if 1800 coverage is not good and 1800 capacity is good:
– it is better to leave the 1800 band for the 900 band for both FDR and Emergency alarm:
– mono-layer case (umbrella+single 900 & 1800): use the Priority(0,n) parameter to favor 900 cells
– bi-layer case (umbrella 900 + mini 1800): set EN_RESCUE_UM to “enabled” to have "upper+single" as Preferred layer for Emergency HO and use the Priority(0,n) parameter to favor 900 cells for FDR.
– it is better to stay on the 900 band for Emergency HO and FDR (except for co-sector 1800 cell): no specific parameter setting is needed since (even if Preferred Layer = "none" for FDR) cells of the same band are preferred in both mono-layer or bi-layer configurations. Use Priority(0,n) to eventually favorthe co-sector 1800 cell but only in case of a bi-layer configuration.
• if 1800 capacity is not good:
– it is better to leave the 1800 band for the 900 band for FDR: use Priority(0,n) to favor the 900 neighboring cells since the Preferred layer is "none" in both mono-layer or bi-layer configurations.
– it is better to stay on the 900 band for FDR: no specific parameter setting is needed since cells of the same band are preferred in both mono-layer or bi-layer configurations.
– FDR (cause 20) is triggered when the average level of a neighboring cell is higher than L_RXLEV_NCELL_DR(n)
3.2 Adding a 1800 band in an existing 900 network Mini 1800: Call Setup
umbrella 900
EN_DR = Enabled
EN_FORCED_DR = Enabled
L_RXLEV_NCELL_DR(n) = -85 dBm
FREElevel_DR(n) = 0
mini 1800
EN_RESCUE_UM = Disabled
EN_DR = Enabled
EN_FORCED_DR = Enabled
L_RXLEV_NCELL_DR(n) = -90 dBm
FREElevel_DR(n) = 0
DR & FDR
PRIORITY(1800, 900) = 1
DR & FDR
PRIORITY(900, 900) = 2
DR & FDR
PRIORITY(900, 1800) = 1
Priority is not favoring FDR
towards 1800 neighboring cells
but frequency band criterion is
DR & FDR
PRIORITY(1800, 1800) = 1
DR only
PRIORITY(900, 1800) = 2
Priority is favoring FDR
towards co-site 1800
neighboring cells
> This example corresponds to a network design where the 1800 band has a good coverage and sufficient capacity.
> EN_RESCUE_UM is set to “Disabled” for an emergency handovers behavior (keep multi-band MS in the 1800 layer).
> Setting PRIORITY(0,n) is very important for FDR also for the Mini 1800 configuration since network behavior will not be driven by PREF_LAYER which is equal to "none" in case of FDR.
• Priority(0,n) will be used to favor co-site 1800 neighboring cells in case of FDR from a 900 cell.
• Priority(0,n) may not be used to favor 1800 neighboring cells from a 1800 cell since neighboring cells with the same frequency band are preferred in the candidate cell evaluation process.
3.2 Adding a 1800 band in an existing 900 network Mini 1800: Better condition handovers (1/2)
umbrella 900
MULTI_BAND_TRAFFIC_CONDITION
= ANY_LOAD
EN_SPEED_DISC = Disabled
EN_PBGT_HO = Enabled
EN_PREFERRED_BAND_HO = Enabled
EN_MCHO_NCELL =?
mini 1800
EN_PBGT_HO = Enabled
EN_SPEED_DISC = Disabled
HIGH_TRAFFIC_LOAD = 70%
Cause 21 or Cause 14
PRIORITY(900, 1800) = 1
L_RXLEV_CPT_HO(900, 1800)
= -85 dBm
Cause 12 / 23
PRIORITY(900, 900) = 2
HO_MARGIN(900, 900) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12 / 23
PRIORITY(1800, 1800) = 1
HO_MARGIN(1800, 1800) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
No better condition HO from 1800 to 900
(different layers)
Only Emergency HO
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> Use Priority(0,n) to favor 1800 neighboring cells when cause 12 and cause 21 (or 14) HO alarms are triggered at the same time in a 900 cell.
> To make sure that cause 21 is triggered whatever the load of the 1800 cell, one may choose HIGH_TRAFFIC_LOAD = 100% on a Mini 1800 cell.In case HIGH_TRAFFIC_LOAD = 100% in a 1800 layer, Cause 23 is unusable (Traffic(1800) is never HIGH).
> As the proportion of multi-band MSs in the network is increasing (about 80% by the end of year 2002, compared to 15% in summer 2000), MULTIBAND_TRAFFIC_CONDITION can be tuned to avoid sending MS to the 1800 cell when the traffic in the 900 cell is low.Consequently the 900 band could then be preferred to the 1800 band on Emergency alarm on a 1800 layer.
> cause 21 is triggered:– When a 1800 cell is received with an average level higher than -85 dBm
– When traffic condition in 1800 cell is not HIGH
– whatever the load of the macro 900 serving cell if MULTIBAND_TRAFFIC_CONDITION= ANY_LOAD (can be tuned)
> cause 14 is triggered:– When a 1800 cell is received with an average level higher than -85 dBm
– during L_MIN_DWELL_TIME seconds as EN_SPEED_DISC = DISABLED (speed discrimination to avoid capture of fast MS)
> it is necessary to choose between causes 21 and 14– cause 14 only in case of a new of speed discrimination
– In case a microcell 900 is added in the network: no more choice!
> cause 12 is used to make intra-layer handovers (PBGT > 5dB)
3.2 Adding a 1800 band in an existing 900 network Mini 1800: Better condition handovers (2/2)
> To make sure that cause 21 is triggered whatever the load of the 1800 cell, one may choose HIGH_TRAFFIC_LOAD = 100% on a Mini 1800 cell.
> As the proportion of multi-band MSs in the network is increasing (about 80% by the end of year 2002, compared to 15% in summer 2000), MULTIBAND_TRAFFIC_CONDITION can be tuned to avoid sending MSs to the 1800 cell when the traffic in the 900 cell is low.
3.2 Adding a 1800 band in an existing 900 network Mini 1800: Emergency handovers
umbrella 900
PREF_LAYER = upper + single
mini 1800
EN_RESCUE_UM = Disabled
PREF_LAYER = lower
PRIORITY(900, 1800) = 1
PRIORITY(900, 900) = 2
PRIORITY(1800, 1800) = 1
PRIORITY(900, 1800) = 1
PRIORITY(900, 1800) = 2
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> EN_RESCUE_UM is set to “Disabled” for an emergency handovers behavior (keep multi-band MSs in the 1800 layer).
> Setting PRIORITY(0,n) is not very important for an Emergency alarm in case of a Mini 1800 configuration as the network behavior will be mainly driven by PREF_LAYER.Indeed, in case of an Emergency alarm in a 900 cell, MS will be kept on the 900 band thanks to the Preferred Layer which will be equal to "upper+single" in this case. Even if Priority(0,n) settings favor the 1800 neighboring cells, 900 cells will be preferred since they belong to the "upper+single" layer whereas 1800 cells belong to the "lower" layer as being declared as mini.
3.2 Adding a 1800 band in an existing 900 network Mini 1800: Candidate cells evaluation process
umbrella 900
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Enabled
CELL_EV = GRADE
mini 1800
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Enabled
CELL_EV = GRADE
EN_RESCUE_UM = Disabled
PRIORITY(900, 900) = 2
HO_MARGIN_LEV(900, 900)= 0 dB
HO_MARGIN_QUAL(900, 900)= -1 dB
HO_MARGIN_DIST(900, 900)= 0 dB
PRIORITY(1800, 900) = 1
HO_MARGIN_LEV(1800, 900)= -127 dB
HO_MARGIN_QUAL(1800, 900)= -127 dB
HO_MARGIN_DIST(1800, 900)= -127 dB
PRIORITY(900, 1800) = 1
HO_MARGIN_LEV(900, 1800)= 0 dB
HO_MARGIN_QUAL(900, 1800)= -1 dB
HO_MARGIN_DIST(900, 1800)= 0 dB
PRIORITY(1800, 1800) = 1
HO_MARGIN_LEV(1800, 1800)= 0 dB
HO_MARGIN_QUAL(1800, 1800)= -1 dB
HO_MARGIN_DIST(1800, 1800)= 0 dB
PRIORITY(900, 1800) = 2
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> 900 is a rescue layer for 1800: thus, all HO_MARGIN_XX(1800, 900) are set to -127 dB. In case no good 1800 neighboring cell is found (all of them are filtered through the PBGT filtering process) then the MS will be sent to the 900 neighboring cell having the best GRADE value.
– FDR (cause 20) is triggered when the average level of a neighboring cell is higher than L_RXLEV_NCELL_DR(n)
3.2 Adding a 1800 band in an existing 900 network Single/Umbrella 1800: Call Setup
Umbrella or single 900
EN_DR = Enabled
EN_FORCED_DR = Enabled
L_RXLEV_NCELL_DR(n) = -85 dBm
FREElevel_DR(n) = 0
Umbrella or single 1800
EN_DR = Enabled
EN_FORCED_DR = Enabled
L_RXLEV_NCELL_DR(n) = -90 dBm
FREElevel_DR(n) = 0
DR & FDR
PRIORITY(900, 900) = 1
DR & FDR
PRIORITY(900, 1800) = 1
DR & FDR
PRIORITY(1800, 1800) = 1
DR only
PRIORITY(900, 1800) = 2Priority is favoring FDR
towards co-site 1800
neighboring cells and 900
ones
DR & FDR
PRIORITY(1800, 900) = 1
Priority is not favoring FDR
towards 1800 neighboring cells
but frequency band criterion is
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> EN_RESCUE_UM is set to “Disabled” for an emergency handovers behavior (keep multi-band MSs in the 1800 layer).
> In case of dual band and mono-layer configuration, there is no way to favor the 1800 band for traffic catching during an FDR occurring in a 900 cell since setting of PRIORITY(0,n) parameters interacts with the MS behavior during an Emergency alarm. Therefore Priority(0,n) settings shall be chosen in order to favor 900 neighboring cells in case of Emergency alarm in a 900 cell (see the next slides).
> Priority(0,n) may not be used to favor 1800 neighboring cells from 1800 cell since neighboring cells with same frequency band are preferred in the candidate cell evaluation process. It is the same for an Emergency alarm where 1800 neighboring cells are preferred.
3.2 Adding a 1800 band in an existing 900 network Single/Umbrella 1800: Better condition handovers
Umbrella or single 900
MULTI_BAND_TRAFFIC_CONDITION
= ANY_LOAD
EN_PBGT_HO = Enabled
EN_PREFERRED_BAND_HO = Enabled
Umbrella or single 1800
EN_PBGT_HO = Enabled
HIGH_TRAFFIC_LOAD = 70%
Cause 21
PRIORITY(900, 1800) = 1
L_RXLEV_CPT_HO(900, 1800)
= -85 dBm
HO_MARGIN(900, 1800) = 0 dB
Cause 12 / 23
PRIORITY(900, 900) = 1
HO_MARGIN(900, 900) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12 / 23
PRIORITY(1800, 1800) = 1
HO_MARGIN(1800, 1800) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
PRIORITY(1800, 900) = 1
HO_MARGIN(1800, 900) = +127 dB
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> PBGT HO has to be avoided from 1800 to 900 cells as it will create ping-pong handover with capture. This is done by setting HO_MARGIN(1800, 900) to +127 dB.
> Warning: setting EN_MULTIBAND_PBGT_HO to “disabled” is not the good solution, as it has to be used for 1800 zone exit.
> To make sure that cause 21 is triggered whatever the load of the 1800 cell, one may choose HIGH_TRAFFIC_LOAD = 100% on a Mini 1800 cell.
> As the proportion of multi-band MSs in the network is increasing (about 80% by the end of year 2002, compared to 15% in summer 2000), MULTIBAND_TRAFFIC_CONDITION can be tuned to avoid sending MSs to the 1800 cell when the traffic in the 900 cell is low.
> In case HIGH_TRAFFIC_LOAD = 100% in the 1800 layer, Cause 23 is unusable (Traffic(1800) is never HIGH).
3.2 Adding a 1800 band in an existing 900 network Single/Umbrella 1800: Candidate cells evaluation process
Umbrella or single 900
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Enabled
CELL_EV = GRADE
Umbrella or single 1800
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Enabled
CELL_EV = GRADE
PRIORITY(900, 900) = 1
HO_MARGIN_LEV(900, 900)= 0 dB
HO_MARGIN_QUAL(900, 900)= -1 dB
HO_MARGIN_DIST(900, 900)= 0 dB
PRIORITY(1800, 900) = 1
HO_MARGIN_LEV(1800, 900)= -127 dB
HO_MARGIN_QUAL(1800, 900)= -127 dB
HO_MARGIN_DIST(1800, 900)= -127 dB
PRIORITY(900, 1800) = 1
HO_MARGIN_LEV(900, 1800)= 0 dB
HO_MARGIN_QUAL(900, 1800)= -1 dB
HO_MARGIN_DIST(900, 1800)= 0 dB
PRIORITY(1800, 1800) = 1
HO_MARGIN_LEV(1800, 1800)= 0 dB
HO_MARGIN_QUAL(1800, 1800)= -1 dB
HO_MARGIN_DIST(1800, 1800)= 0 dB
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> 900 is a rescue layer for 1800: thus, all HO_MARGIN_XX(1800, 900) are set to -127 dB. In case no good 1800 neighboring cell is found (all of them are filtered through the PBGT filtering process) then the MS will be sent to the 900 neighboring cell having the best GRADE value.
3.2 Adding a 1800 band in an existing 900 network Twin 1800: Better condition handovers
Umbrella or single 900
EN_PBGT_HO = Enabled
EN_MULTIBAND_PBGT_HO = Enabled
EN_PREFERRED_BAND_HO = Disabled
Umbrella or single 1800
EN_PBGT_HO = Enabled
EN_MULTIBAND_PBGT_HO = Enabled
Cause 12
PRIORITY(900, Twin) = 1
HO_MARGIN(900, Twin) = 0 dB
Cause 12 / 23
PRIORITY(900, 900) = 1
HO_MARGIN(900, 900) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12 / 23
PRIORITY(Twin, Twin) = 1
HO_MARGIN(Twin, Twin) = 5 dB
DELTA_INC_HO_MARGIN = 2 dB
DELTA_DEC_HO_MARGIN = 2 dB
Cause 12
PRIORITY(Twin, 900) = 1
HO_MARGIN(Twin, 900) = +15 dB
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> Remark: cause 23 is not possible between different bands.
> An HO_MARGIN of 0 - 15 dB is taken between 900 and 1800 cells to avoid a ping-pong HO (levels of colocatedcells are correlated with a propagation difference around 10 dB).
> Due to PRIORITY(0,n) settings, if alarms towards cells of both bands are triggered at the same time:
• From a 900 cell, the best cell is chosen (same priority towards 900 and 1800 cells).
• From a 1800 cell, the best cell is chosen (same priority towards 900 and 1800 cells).
3.2 Adding a 1800 band in an existing 900 network Twin 1800: Candidate cells evaluation process
Umbrella or single 900
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Disabled
CELL_EV = GRADE
Umbrella or single 1800
EN_PRIORITY_ORDERING = Enabled
EN_PBGT_FILTERING = Disabled
CELL_EV = GRADE
PRIORITY(900, 900) = 1
HO_MARGIN_LEV(900, 900)= 0 dB
HO_MARGIN_QUAL(900, 900)= -1 dB
HO_MARGIN_DIST(900, 900)= 0 dB
PRIORITY(Twin, 900) = 1
HO_MARGIN_LEV(Twin, 900)= -127 dB
HO_MARGIN_QUAL(Twin, 900)= -127 dB
HO_MARGIN_DIST(Twin, 900)= -127 dB
PRIORITY(900, Twin) = 1
HO_MARGIN_LEV(900, Twin)= 0 dB
HO_MARGIN_QUAL(900, Twin)= -1 dB
HO_MARGIN_DIST(900, Twin)= 0 dB
PRIORITY(Twin, Twin) = 1
HO_MARGIN_LEV(Twin, Twin)= 0 dB
HO_MARGIN_QUAL(Twin, Twin)= -1 dB
HO_MARGIN_DIST(Twin, Twin)= 0 dB
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> 900 is a rescue layer for 1800: thus, all HO_MARGIN_XX(1800, 900) are set to -127 dB. In case no good 1800 neighboring cell is found (all of them are filtered through the PBGT filtering process) then the MS will be sent to the 900 neighboring cell having the best GRADE value.
> Cell selection: same priority for macro 1800 and macro 900 cells
3.3 adding a 900 band in an existing 1800 network Idle mode parameters (1/2)
18001800CELL_BAR_QUALIFY = 0
900900
CELL_BAR_QUALIFY = 0
=> a dual band MS tries to select the best cell
> This type of configuration will for example happen in a network where the historical band was 1800, dedicated to urban coverage. A network coverage extension is done in a rural area by using 900 frequency (less sites required). We examine this case in this chapter. 900 cells introduction together with 1800 cells in a urban area may be extrapolated from the previous chapter.
3.4 adding a 1800 band in an existing 900 (macro+micro) network Better condition handovers (1/2)
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> In 900 macrocells:
• Priority is given to lower corporate microcells since we want MSs to be preferably transferred to them. This will have no drawback in case of Emergency HO in 900 macrocells since MSs will stay on the upper layer (900 or 1800 cells) thanks to Pref Layer = "upper+single".
• Priority can not be given to 1800 macrocells over 900 macros cells because multi-band MSs should stay on the 900 band on Emergency alarm.
• However giving the same Priority(0,n) to 900 and 1800 neighboring cells allow to choose the best Graded cell if cause 12 and cause 21 are triggered at the same time.
> In 1800 macrocells:
• Priority is given to lower corporate microcells since we want MSs to be preferably transferred to them. This will have no drawback in case of Emergency HO in 900 macrocells since MSs will stay on the upper layer (900 or 1800 cells) thanks to Pref Layer = "upper+single".
• The PBGT HO is disabled towards upper 900 macrocells by choosing HO_Margin(0,n) to +127 dB.
> In corporate 900 microcells:
• The PBGT HO will only occur towards neighboring microcells except for Fast MSs when Speed discrimination is enabled.
• In this latter case, Priority(0,n) will be used to favor umbrella 1800 macrocells compared to umbrella 900 macrocells.
3.4 adding a 1800 band in an existing 900 (macro+micro) network Better condition handovers (2/2)
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> In 900 macrocells:
• Priority is given to 1800 macrocells over 900 microcells since we want MS to be preferably transferred to them.
• Priority can not be given to 1800 macrocells over 900 macrocells because multi-band MS should stay on the 900 band on Emergency alarm.
• However giving the same Priority(0,n) to 900 and 1800 neighboring cells allow to choose the best Graded cell if cause 12 and cause 21 are triggered at the same time.
> In 1800 macrocells:
• The Better cell (capture cause 14) has to be disabled towards 900 microcells since 1800 band is preferred. This can be done by:
– disabling cause 14 in 1800 macrocells: EN_MCHO_NCELL=disabled in 1800 cells
– disabling cause 14 towards any 900 microcells:
– either L_RXLEV_CPT_HO(1800,micro)=-47dBm
– or EN_BI-BAND_MS=disabled in 1800 cells
• PBGT HO is disabled towards upper 900 macrocells by choosing HO_Margin(0,n) to +127 dB.
> In 900 microcells:
• PBGT HO will only occur towards neighboring microcells except for Fast MSs when Speed discrimination is enabled.
• In this latter case, Priority(0,n) will be used to favor umbrella 1800 macrocells compared to umbrella 900 macrocells.
3.4 adding a 1800 band in an existing 900 (macro+micro) network Emergency handovers
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> Priority(0,n) is the same between cells of the same band and cells from the other band since neighboring cells from the same band will be anyway preferred during the HO Candidate Cell Evaluation process.
3.4 adding a 1800 band in an existing 900 (macro+micro) network Candidate Cell Evaluation
> This example corresponds to a network design where the 1800 band has a good coverage and a sufficient capacity.
> 900 is a rescue layer for 1800: thus, all HO_MARGIN_XX(1800, 900) are set to -127 dB. In case no good 1800 neighboring cell is found (all of them are filtered through the PBGT filtering process) then the MS will be sent to the 900 neighboring cell having the best GRADE value.
> All other HO_MARGIN_XX(0,n) are set to their default values:
4.1 Load & Traffic evaluation Long term evaluation (1/4)
> 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_LOADcalculated from Nb free TCH samples updated every A_TRAFFIC_LOAD x TCH_INFO_PERIOD s
• MS reports measurements on both cells for the handover algorithms
> BSICINNER = BSICOUTER
• INNER cell can decode the RACH received on OUTER BCCH frequency
> INNER cell always BARRED
• MS always camps on OUTER cell
> At the border of the two cells, an overlapping area allows to provide a continuous coverage. When the MS moves from one cell to the other, a handover is triggered in the overlap zone. Two BCCH channels are needed (one for the inner cell, one for the outer cell), so that the MS reports measurements on both cells for the handover algorithms.
> The TRXs of the inner cell and of the outer cell are synchronised, but the reception of the outer cell is delayed by 60bits period to account for the propagation delay.
> In the inner cell, the MS can receive the BCCH inner frequency as wells as the outer BCCH frequency. To avoid to manage RACH reception on two different frequencies in the inner cell, the MS is forced to access the inner cell on the outer BCCH frequency. For this purpose, the RACH reception (BCCH TRX) of the inner cell is tuned to the outer BCCH frequency, and the inner cell is barred1. So on time slot 0 of the inner cell, transmission is done on the inner cell BCCH frequency, and reception is done on outer BCCH frequency.
> The chosen implementation allows to make use of all timeslots2 of the TDMA frame and to use the combined configuration for the CCCH channel.
4.2 Extended cell overview 4.2.2 Radio Link Establishment - MS located in the outer cell area
> The inner cell is always barred, so the MS cannot camp on the inner cell, even if located in the inner cell range. In the whole extended cell coverage, the MS has a good reception of the outer cell BCCH, so the MS will always be camping in the outer cell, whether in the inner cell or outer cell range.
> For this reason, a special radio and link establishment procedure is used to cope with this behaviour .
> It consists of receiving the CHANNEL REQUEST messages on outer BCCH frequency, and allocating the SDCCH channel according to the MS estimated position. The IMMEDIATE ASSIGNMENT COMMAND for an SDCCH is sent on the outer cell BCCH frequencies, but the SDCCH may be allocated in either inner or outer cell, depending on the MS position.
> (1) The MS camping on the outer cell sends an access burst on the RACH on outer cell BCCH frequency. These bursts will be received successfully in the inner cell by the BCCH TRE. In the outer cell, the access burst arrives too early and cannot be decoded.
> (2) The inner 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 to the transaction in the inner cell and asks the BTS to activate this subchannel.
> (4) The BTS activates the requested channel and sends back and acknowledgement, once this is done.
> (5) 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.
> (6) The IMMEDIATE ASSIGNMENT message is sent over the air to the MS on the AGCH of the outer cell.
> (6') The IMMEDIATE ASSIGNMENT message sent by the inner cell is lost, because the MS listens to the outer cell frequency.
> (7) The mobile switches its transceiver to the SDCCH allocated in the inner cell 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.
4.2 Extended cell overview 4.2.2 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.
4.2 Extended cell overview 4.2.2 Radio Link Establishment - MS located in the overlap zone (2/2)
> (1a&b) The MS camping on the outer cell sends an access burst on the RACH. This burst is correctly received by the inner cell BCCH TRE and outer cell BCCH TRE.
> (2a&b) The inner cell and outer cell BCCH TRE send 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.
> (3a&b) Both TCUs controlling the TREs having BCCH allocate an SDCCH subchannel to the transaction and ask the BTS to activate this subchannel.
> (4a&b) The BTS activates the requested channels and sends back an acknowledgement for each, once this is done.
> (5b) The TCU controlling the outer cell, sends the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the outer cell to the outer cell BCCH TRE.
> (5a&c)The TCU controlling the inner cell sends in the IMMEDIATE ASSIGNMENT COMMAND with SDCCH description in the inner cell. Two cases are possible:
• Access Delay IE > 59 the inner cell TCU will not send a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This is the desired behaviour.
• Access Delay in [58,59] range, the inner cell TCU sends a copy of the IMMEDIATE ASSIGNMENT command to the outer cell TCU. This is not the desired behaviour (corresponds to inner cell scenario). This is due to the fact that the BSC definition of the overlap zone does not match the exact BTS overlap area (negative values of TOA in the outer cell up to –2, are clipped to 0).
> (6b) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in outer cell, is sent to the MS on the outer cell BCCH frequency. In most cases this message should be received by the MS (except if 6c is received first)
> (6a) The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is lost on the inner cell air interface, because the MS does not listen to that frequency. The unused SDCCH will be released by the BSC when the supervising timer expires6.
> (6c) Access Delay in [58,59] range: The IMMEDIATE ASSIGNMENT message describing the SDCCH allocation in inner cell is sent on the BCCH frequency of the outer cell. In most cases, the MS should have received message (6b) before and has already switched to the SDCCH in the outer cell, and so this message is lost. It is however possible, in case the message (6b) is delayed in the inner cell, that the message (6c) is received earlier by the MS. In this case establishment will occur on the SDCCH allocated in the inner cell (not drawn).
> (7b) The mobile receives the IMMEDIATE ASSIGNEMENT describing the SDCCH allocation in outer cell on the BCCH outer cell frequency. It then switches to the designated channel and sends repeatedly an SABM frame to establish the layer 2 connection with the BTS in the outer cell. If the message (6c) is received before (6b), then the establishment will occur in the inner cell.
> (8b) The BTS acknowledges the establishment of the LapDm link to the MS with a UA frame sent on the SDCCH allocated to the MS.
> (9) The unused SDCCH is released in the inner cell (double SDCCH allocation). If message 6c arrives first, then the unused SDCCH release will occur in the outer cell.
4.2 Extended cell overview 4.2.3 Handover - from the INNER cell to the OUTER cell
> In the extended cell , the handover procedure is purely controlled by settings of the handover detection parameters. Two special causes allow handover from the inner cell to the outer cell and handover from the outer cell to the inner cell. There is no change in the BSC handover algorithm either for handover preparation or execution.
> From the inner cell to the outer cell , the handover alarm is only triggered by the handover cause “too long MS-BS distance”. When this cause is triggered the extended outer cell is always a candidate cell.
> However the operator setting of the handover parameters must insure that this cause is only triggered when the distance from the serving inner cell BTS is greater than the limit of the overlap zone (TA > 62) by setting U_TIME_ADVANCE to 62.
> In order to avoid the extended outer cell to be filtered by the filtering process the flag EN_PBGT_FILTERING must be set to DISABLE.
> The candidate cell evaluation process is recommended to be the GRADE mode.
4.2 Extended cell overview 4.2.3 Handover - from the OUTER cell to the INNER cell
> In the same way, from the outer cell to the inner cell , the handover alarm is only triggered by the handover cause “too short MS-BS distance”. When this cause is triggered the extended inner cell is always a candidate cell.
> However the operator setting of the handover parameters must insure that this cause is only triggered when the timing advance applied by the mobile reaches 0, this is achieved by setting L_TIME_ADVANCE to 0.
> In order to avoid the extended inner cell to be filtered by the filtering process the flag EN_PBGT_FILTERING must be set to DISABLE.
> The candidate cell evaluation process is recommended to be the GRADE mode.
> The OUTER or INNER cell is always present in the Candidate CellEvaluation
4.2 Extended cell overview 4.2.3 Handover - from the OUTER or INNER cell towards an other cell
> The setting of the handover parameter does not prevent any handover cause to trigger an alarm for a handover towards a third cell.
> It is possible to use exactly the same rules and parameters for handover towards a third cell as in the macro cellular normal cases.
> The synchronous handover does not work between the inner and the outer cell.
> In order to avoid call terminations due to directed retry into the inner or outer cell with an incorrect distance range it is recommended to disable the forced directed retry towards the inner and the outer cell. For this purpose, the parameter FREELEVEL_DR(n) is set to the maximum value (255) for the inner and the outer cell.
> If combined CCCH/SDCCH is used in the inner extended cell, then the same configuration is required in outer extended cell, and vice-versa (ie same in both cells)
> BSICINNER = BSICOUTER
> The TS 7 of BCCH TRX of outer cell must be set to IDLE
> The INNER cell and OUTER cell must belong to the same location area
> Synchronous handover must be disabled.
> U_TIME_ADVANCE = 62
> L_TIME_ADVANCE = 0
> EN_PBGT_FILTERING = DISABLE.
> CELL_EV = “Grade”
> FREELEVEL_DR(n) = 255 (this is done automatically, at configuration time)
> INNER cell and OUTER cell must be neighbour, handover relationship must exist in both directions