Optimization Methodology for Dual Band Markets

Optimization Methodology for Dual Band Markets

Schema Confidential & Proprietary May 2008 of 45


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Table of Contents 1 Introduction ..............................................................................................5 2 Project Workflow.......................................................................................6 3 Creating MS Recordings.............................................................................7

3.1 Pre-project Neighbor Optimization .................................................................... 7 3.2 BSIC Check ................................................................................................... 7 3.3 Recording Implementation............................................................................... 7

3.3.1 Recording Length ................................................................................. 7 3.3.2 Shadow-Breaking ................................................................................. 8 3.3.3 Conclusion........................................................................................... 9

4 Neighbor Optimization ............................................................................10 5 Frequency Planning.................................................................................11

5.1 Available Frequency Planning Strategy ............................................................ 11 5.1.1 Theoretical Background of Frequency Hopping ........................................ 11 5.1.2 Frequency Hopping............................................................................. 11

5.2 Hopping Method........................................................................................... 12 5.3 BCCH Planning for SFH.................................................................................. 13 5.4 Taking Advantage of Forté Planning Capabilities................................................ 14

6 Project Planning ......................................................................................16 7 Parameter Optimization ..........................................................................17

7.1 Introduction ................................................................................................ 17 7.2 General Optimization Methodology.................................................................. 17

7.2.1 Favoring Frequency Bands ................................................................... 18 7.3 Alcatel ........................................................................................................ 20

7.3.1 Idle Mode Behavior............................................................................. 20 7.3.2 Active Mode Behavior.......................................................................... 21

7.4 Siemens ..................................................................................................... 24 7.4.1 Idle Mode Behavior............................................................................. 24 7.4.2 Active Mode Behavior.......................................................................... 25

7.5 Ericsson...................................................................................................... 28 7.5.1 Idle Mode Behavior............................................................................. 28 7.5.2 Active Mode Behavior.......................................................................... 30

7.6 Nokia ......................................................................................................... 30 7.6.1 Idle Mode Behavior............................................................................. 30 7.6.2 Active Mode Behavior.......................................................................... 31 7.6.3 Common BCCH at 900......................................................................... 33

7.7 Nortel ......................................................................................................... 36 7.7.1 Idle Mode Behavior............................................................................. 36 7.7.2 Active Mode Behavior.......................................................................... 37

7.8 Huawei ....................................................................................................... 38 7.8.1 Idle Mode Behavior............................................................................. 38



7.8.2 Active Mode Behavior.......................................................................... 39 7.9 Motorola…Hello Moto! ................................................................................... 41

7.9.1 Idle Mode Behavior............................................................................. 41 7.9.2 Active Mode Behavior.......................................................................... 43



List of Figures Figure 1: HO Cause 21................................................................................................. 22 Figure 2: Umbrella Handover and Handover Due to Level.................................................. 32 Figure 3: BTS Handling Command Group Parameters ....................................................... 34 Figure 4: Umbrella Handover and Handover Due to Level (2) ............................................ 40



1 Introduction The goal of the document is to present the methodology used to optimize dual band markets (GSM900/DCS1800 or GSM850/PCS1900). The idea is to implement a complete optimization cycle including:

• Preliminary analysis

• Recording set up

• Neighbor optimization

• Frequency planning

• Parameter optimization: traffic management between bands.

This document does not replace the existing vendor-specific documentation, but instead, offers a general approach to the optimization process.



2 Project Workflow

INITIAL GSM 900 RECORDING

INITIAL GSM 900 RETUNE

FINAL GSM 900 RECORDING

FINAL RETUNE (BOTH BANDS)

NEIGHBOR OPTIMIZATION

DUAL BAND TRAFFIC PARAMETER OPTIMIZATION

PRE-PROJECT KPIs COLLECTION

NEIGHBOR DELETION/ BSIC CHECK

DUAL BAND TRAFFIC PARAMETERS FINE TUNING

DCS 1800 RECORDING (optional)

FINAL DCS1800 RECORDING

INITIAL DCS 1800 RETUNE (optional)



3 Creating MS Recordings The MS recording process must be performed carefully to minimize the length of the project, especially with regard to Siemens, Alcatel, Motorola, Huawei, or Nortel, since the user cannot modify the BA list, but can only create fake neighbors.

3.1 Pre-project Neighbor Optimization Before starting the MS recording, the neighbor list should be analyzed using Forté in order to identify all cells with more than 25 neighbors.

Based on this analysis, a list should be created with neighbors to be deleted, using only Handover Statistics, (as a model is not yet available) according to the following workflow:

1. Identify all cells in the optimization set with more than 25 neighbors.

2. Rank each neighbor relation by descending number of handover attempts.

3. Delete 6 of the last 12 neighbor relations by targeting inter-band HO relations first (in dual band markets).

3.2 BSIC Check Before beginning recording, the Forté BCCH-BSIC Reuse report should be checked to ensure that the BSIC plan does not include any close BCCH/BSIC reuses.

Any reuse below 5 or 10 km (depending on the willingness of the customer to make changes) should be corrected, and a new BSIC implemented, to avoid decoding problems during the modeling phase.

3.3 Recording Implementation

3.3.1 Recording Length

The length of recordings varies for each band, based on the number of BCCHs to measure and on the vendor.

Markets using free BCCH/TCH planning (with or without Base band hopping) may require several recording sessions per cell when more than 30 BCCHs are used.



Since the DCS1800 (PCS1900) layer is normally the capacity layer with more available spectrum, it uses more potential BCCH. On average, it takes twice as long to record the DCS layer as it does to record the GSM layer.

In theory, cross band measurements are only needed:

• If a network has a mixed configuration of Common BCCH or CBCCH (e.g., BCCH on band 850/900 and TCH on band 1900/1800– within the same sector) and Multiple BCCH or MBCCH (e.g., two co-sited sectors, one with 850/900 BCCH and one with 1900/1800 BCCH); all sectors should consider measuring interferences from both bands (mandatory).

• If cross-band HO optimization is required: The C/I between sectors belonging to different bands must be available for the user to optimize the handovers between bands. Therefore, measurement recording on both bands should be activated. If this not possible (as in Siemens), Forté can estimate cross-band measurements in the model by using intra-band measurements, and applying an attenuation value based on the difference in propagation between the bands (BAND_OFFSET parameters are defined in Ultima Forte Advanced Network Properties/Modeler).

The Ultima Forté Cross Band Measurements feature is available for dual band networks. While it is possible and recommended to measure cross-band interference in a dual band network, when more than one band is measured, the measurement recording time increases. Therefore, this feature should only be used in one of the circumstances described above.

Note than cross-band measurements are not available in Siemens, so the Forté Cross Band Measurements feature is the only way to evaluate cross-band impacts (and optimize cross-band Handover) for Siemens.

3.3.2 Shadow-Breaking

Recordings should provide the most accurate model possible. Because of shadowing (blind spots), it may be useful to perform an initial retune and collect two sets of recordings (before and after the initial retune). For example, two sectors using the same BCCH will be considered shadowed. The interference between the two will only be estimated except if measurements can be collected before and after the BCCH has been changed.

Shadow breaking may be required when the number of BCCHs used is limited (below 20) In most cases, an initial retune is recommended for the 850/900 layer.

Check the following for shadowing:



• The BCCH reuse report before a project. A high number of close BCCH reuses below 5 km may indicate poor BCCH planning and high shadowing

• Correlation. A low correlation with an under-predicted model may indicate a high level of shadowing (but the first recording session must be finished before it is possible to see the shadowing).

If an initial BCCH retune is performed for shadow-breaking reason, the Reveal shadowing option must be used in the initial plan. That option should not be used for the second and final plan.

Note: the initial BCCH retune goal, also called mini-BCCH retune, is not to improve the network statistics, but simply to reveal shadowed impacts (and eventually clean up the BSIC plan). It is recommended that Forté change all the BCCHs in the retune area. Otherwise, the Minimum change option can be used to allow only a pre-determined number of changes.

If no initial BCCH reuse is run, the user may or may not use that option in the Frequency plan.

3.3.3 Conclusion

An initial retune is recommended for markets having less than 20 BCCHs. MS statistics should be recorded before and after the retune.

In dual band markets, the capacity layer (DCS 1800/ PCS1900) does not always require a shadow-breaking retune. Since twice the recording time is required, only one retune (one set of recordings) should be implemented for that layer. The recordings should be made after dual-band parameter optimization is implemented, if possible.

If additional time is available, inter-band (cross-band) measurements could be recorded.



4 Neighbor Optimization Neighbor optimization should be prepared with a shadow-free model, if possible, and implemented before the final retune.

The main goal of the neighbor optimization is to decrease the constraints on the BCCH plan, not to improve network statistics (HO Success Rate), since most customers already have a reasonable HO list.

Forté uses neighbor relations as logical constraints when planning BCCH to avoid using co-channel BCCHs between neighbors, the use of which is usually not permitted in the OSS. A large number of intra-band neighbors, creates many logical constraints (not physical constraints), which are not based on measured interference from MS.

The Handover optimizer should be run on the layer with the most frequency planning constraints. Minimizing the number of neighbor relations will improve the quality of Forté’s BCCH FP output.

Optimizing inter-band HO for dual band markets reduces the length of the recording process, but does not necessarily improve performance.

If cross-band MS cannot be recorded because of the extra length associated with it, Forté should not be used to optimize inter-band HO relations, since those relations are only based on HO Statistics (not measured interference).

The 1800 to 1800 (1900 to 1900) Handover relations can be optimized along with 900 to 900 (850 to 850), but this will usually not result in significant improvement in the performance or quality of the Forté 1800/1900 BCCH plan because of the high number of available BCCH frequencies.



5 Frequency Planning Frequency planning can be prepared for both bands separately in accordance with the methodology normally used, as discussed in Section 3.3.2.

5.1 Available Frequency Planning Strategy

Several frequency planning strategies, which involve BCCH vs. TCH planning, hopping vs. non-hopping strategy, and base band hopping vs. synthesized hopping are available to operators.

Activating frequency hopping maximizes improvement to the network.

5.1.1 Theoretical Background of Frequency Hopping

GSM networks evolve with the goals of providing better quality of service and more system capacity. Frequency hopping helps to achieve these goals.

Cellular systems are limited by interference. Multiple co-channel interference, though controlled, is normal, and determines the limits of the service area. The higher the interference level, the harder it is to reuse available frequencies within the smallest area. Since quality of service depends on the carrier/interference ratio (C/I) more than on the signal/noise ratio, the system can tolerate the trade-off between quality and capacity.

Higher levels of capacity and quality are needed to support fast network growth. All possible techniques should be used to progressively enhance radio and network performance. GSM has some powerful mechanisms to reduce the effect of interference through frequency hopping, discontinuous transmission (DTX), and power control.

5.1.2 Frequency Hopping

Frequency hopping can be classified as either Base Band hopping (BB) or as Synthesized Frequency Hopping (SFH). SFH uses only one transmitter for all bursts in a specific connection, while base band hopping uses as many transmitters as frequencies in the hopping sequence. Hopping can be cyclic or random, but in random hopping, a HSN other than 0 should be chosen.

SFH involves changing channel frequency in every transmitted burst (217 hops per second) thus providing frequency diversity and interference averaging. This randomizes the risk of interference and improves channel behavior (for selective fading).

The following factors affect SFH performance:



1. Number of Hopping Frequencies A higher number of hopping frequencies improves system performance by increasing frequency diversity. It is not helpful to use more than eight hopping frequencies since the GSM interleaving period consists of eight bursts.

2. Hopping frequencies separation A larger frequency separation between hopping frequencies, improves system performance as the effects of propagation become more uncorrelated. Frequency spacing directly affects Fast Fading. A separation of three to five channels between hoppers provides the maximum gain.

3. System load Since a low system load results in lower interference probability in each hopping frequency, this directly affects SFH performance.

The choice of frequency hopping strategy depends on each network’s optimization level and available spectrum.

5.2 Hopping Method

Frequency hopping should be activated before using any frequency planning methodology.

The choice of one method over another (Base band vs. SFH) depends on the available spectrum, the system load (number of TRXs and EFL), and the maturity of the market (either fast growing or mature with very few new site activations). The hopping strategy influences BCCH planning strategy.

4. Base band hopping does not require separating the BCCH and the TCH bands and therefore, allows free BCCH/TCH planning (BCCH and TCH use all available frequencies). In addition, although all traffic TSs on the BCCH TRX are hopping, it has two main disadvantages:

o There is no gain, or a limited gain, for cells with a low number of TRXs (2 or fewer).

o Extensive planning is required, since a new frequency must be planned for every new TRX in the system (TRX addition or new cells)

5. The standard SFH (SFH1:1 or SFH1:3), involves splitting a spectrum into two separate groups of frequencies for BCCH and TCH -- two blocks or a staggered allocation (1 BCCH, 1 TCH…). The disadvantages are:



• A specific number of frequencies must be reserved for BCCH planning only (between 12 and 21), potentially affecting the quality of the BCCH plan.

• The traffic TS on the BCCH TRX will not hop.

• Without frequency planning, the random collisions between cells cannot be controlled.

The main advantage of SFH is that it does not requires extensive planning, so that TRX or new sites can easily be added to the network, which is especially good for fast-growing markets. In addition, SFH brings the quality gain of hopping even to cells with low number of TRXs, since the number of hoppers is much greater than the number of TRXs.

3. SFH Ad Hoc is a different version of SFH that allows planning a specific MAL (with a different frequency and length) for each sector, instead of a fixed MAL used by all sectors (SFH 1:1). MAL length is based on the number of TRXs in each cell. Normally, a minimum of three or four hoppers is used for each cell with a MAL length equal to the number of TRXs+1.

SFH Ad Hoc planning reintroduces frequency planning within SFH, and keeps SFH quality gain even for cells with few TRXs. Random collisions are avoided through the Interference matrix that Forté creates.

5.3 BCCH Planning for SFH

Two dedicated groups of frequencies for BCCH and TCH should be used with SFH (especially with fixed MAL), but this does not necessarily mean that there will be two frequency blocks.

A staggered BCCH vs. TCH plan can be used, interleaving some blocks of BCCH and TCH within the spectrum:

• Example 1: available spectrum 1-24, channels 1-2 will be TCH, 3-4 BCCH…

• Example 2: available spectrum 1-24, channels 1will be TCH, 2 BCCH…



The main advantages of using a staggered plan are:

• Capacity: Along with SFH1:1 or SFH1:3, the staggered plan allows use of all available MAIO, so that more TRXs can be planned.

• Quality: The staggered plan increases frequency diversity more than does using two blocks, especially when limited frequencies are available.

5.4 Taking Advantage of Forté Planning Capabilities

Forté offers a highly accurate Interference Matrix, based on real traffic distribution within the network.

To obtain the best possible quality vs. capacity ratio, a non-random frequency planning strategy should be used, such as:

Example 1 Example 21 TCH 1 TCH2 TCH 2 BCCH3 BCCH 3 TCH4 BCCH 4 BCCH5 TCH 5 TCH6 TCH 6 BCCH7 BCCH 7 TCH8 BCCH 8 BCCH9 TCH 9 TCH

10 TCH 10 BCCH11 BCCH 11 TCH12 BCCH 12 BCCH13 TCH 13 TCH14 TCH 14 BCCH15 BCCH 15 TCH16 BCCH 16 BCCH17 TCH 17 TCH18 TCH 18 BCCH19 BCCH 19 TCH20 BCCH 20 BCCH21 TCH 21 TCH22 TCH 22 BCCH23 BCCH 23 TCH24 BCCH 24 BCCH



• Base band hopping for markets with many TRXs/ cells (3 or more TRX/cells), including free BCCH/ TCH planning.

• SFH Ad Hoc planning, preferably with dedicated BCCH and TCH channels (blocked or staggered to increase frequency diversity) for markets with limited spectrum or few TRX/cell (2 TRX/cells average).

Both methods have advantages and disadvantages, but also significantly increase network performance and capacity.



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Project Preparation and Logistic

Kickoff meeting NBR Clean-up MS Statistics Collection (900 ) (*) N1 N2 N3 Network Modeling/Planning Dual-band Parameters Optimization Frequency plan implementation MS Statistics Collection (1800 cross band ) (**) N1 N2 MS Statistics Collection (900 and 1800 ) (***) N1 N2 N3 N4 N5 Network Modeling/Analysis Neighbor list implementation Frequency Plan Implementation Fine tuning of fP and parameters BB Hopping Activation Performance collection/Analysis Performance Benchmarking Before Performance Benchmarking After Final Report Preparation

(*) N1 to N3 for 900 (N1 to N5 for 1800 optional)

(**) N1 and N2 for 1800 measuring 900 BCCH (optional)

(*) N1 to N3 for 900 and N1 to N5 for 1800



7 Parameter Optimization

7.1 Introduction The goal of the parameter optimization is to maximize the amount of traffic that the DCS1800/ PCS1900 layer carries. The 1800/1900 layer may be defined as the capacity layer since its spectrum is larger, while the 900/850 layer may be defined as the coverage/quality layer, since it propagates better at 900MHz. The GSM layer is, on average, 10 dB better than the DCS layer.

Traffic should be maintained, as much as possible, on the 1800/1900 layer (as long as there is sufficient quality) in order to reserve the 900/850 layer for mobiles, which need it more (due to low signal strength traffic).

Maintaining traffic on the 1800/1900 layer will achieve the following:

• Network capacity is maximized, since the DCS layer is usually underused and the GSM layer is usually congested.

• Network quality is improved by reserving the GSM layer for calls that require it the most (and which might have been previously denied due to GSM layer congestion).

• Data throughput is improved, since only the 900/850 layer is used for GPRS cell reselection.

In Idle mode, each call should originate on the GSM layer (the 900/850 layer), and then hand the call over to the to the 1800/1900 layer (active mode).

Advantages:

• Less SDCCH TS will be needed on the DCS layer, making more voice capacity available. Initially, the settings will be COMB SDCCH/4 for all 1800/1900 with 1 Dynamic SDCCH TS (if failure of the 900 cell results in congestion).

• No PDCH (dedicated packet TS) will be required on the 1800/1900 cell, resulting in greater voice capacity.

Data traffic will always camp on 900/850 for better throughput.

7.2 General Optimization Methodology Some factors should be considered in order to define coverage and parameter settings for Dual Band networks. To optimize network capacity, the load balance between the two bands should be evaluated. This will prevent expensive procedures, such as LAC optimization (which leads to



frequent location updates) or network topology (for inter-BSS handovers). Additional factors to consider include the percentage of dual band handsets and the percentage of coverage for each band.

Either adjacent coverage (one layer) or super-imposed coverage (at least, two layers), also called C-BCCH or M-BCCH (Common vs. Multiple BCCH) may be applied.

The following section explains how to set parameters for a multi-layer network, a method that resembles the method used for microcells.

7.2.1 Favoring Frequency Bands

Theoretical Background -- Cell Selection

MS accesses the system as follows:

1. PLMN is correct

2. Access is authorized

3. Cell_Bar_Access_Switch = 0 = « Cell not barred » for Phase 1 MS

4. Combination of Cell_Bar_Access_Switch and Cell_Bar_Qualify for phase 2 MS

5. Does not belong to forbidden LAC

6. C1 > 0

Theoretical Background -- Reselection

1. MS phase 1: C1

2. MS phase 2,: C1 and C2 si if specified by carrier

Reselection occurs when:

• The C1 of the selected cell becomes negative for more than 5 sec, or

• The selected cell becomes barred, or

• The C2 of one of the neighbors becomes greater than the selected cell for more than 5 sec (using Cell_Reselect_Hysteresis if belongs to a different LAC).

Cell Selection

A multiband MS (phase 2 MS) only selects an 1800 cell if no 900 cells are found with a positive C1.



To compute C1:

In both bands, Max (B, 0) is usually zero (0). The recommended value for rxLevAccessMin is -104 to -106 dBm for GSM 900, and -98 to -100 dBm for GSM 1800.

GSM900/850 is naturally favored by radio propagation conditions, and is always 10-12 dB stronger than DCS1800/ PCS1900.

Cell Reselection

Multiband mobile stations are Phase 2 mobile stations. Cell reselection involves C2 computation, based on the following formula:

A cell reselect offset can be used to compute C2 criteria to give an advantage to one frequency band. Two different cellReselectOffset values can be used, based on the cell frequency band. The higher the cellReselectOffset value is, the greater the C2 value.

In order to always allow cell reselection on the best layer (the GSM900/850), the same value should be used for cellReselectOffset on both bands.

Handovers

An offset must be considered in order to force traffic to go to the weakest layer (1800/1900), or to avoid going back to another band because it is the best cell (GSM900/850),). Alternatively, power budget handovers can be inhibited from a priority to a non-priority band.

The preferred band option is preferable to the HO margin whenever possible (for Ericsson, Nokia, Alcatel and Nortel), since this allows one band (or a group of cells) to be favored according to the priority definitions in various layers.



SETTINGS GSM 900 BAND

GSM1800 BAND

COMMENTS

CellBarQualify FALSE TRUE

CellReselectOffset 6 dB 6 dB

RxLevAccessMin -106 dBm -100 dBm

Layer Definition Lower Priority Higher Priority

Multiband Reporting

3 2 Number of opposite band neighbors reported as part of the 6 strongest

7.3 Alcatel

7.3.1 Idle Mode Behavior

Recommended Settings

On the cell level:

• RxLevAccessMin (Network access threshold):

o This parameter should equal 0 (-110 dBm) for all 900 cells in order to capture all possible traffic.

o This parameter should equal 6 (-104 dBm) for 1800 cells that are collocated with 900 cells.

o This parameter should equal 0 (-110 dBm) for standalone 1800 cells.

• CELL_RESELECT_OFFSET: Schema recommends 3 (6 dB).

• CellReselectionHysteresis Schema recommends 5 for all cells (10 dB).



On the TRX level:

• BCCH type changed to BCCH COMB SDCCH/4 for all 1800 collocated cells

• One Fixed SDCCH TS defined for all 900 cells (1 SDC) and 1800 only cells

• No Fixed SDCCH TS defined for 1800 collocated cells

• One Dynamic SDCCH TS defined for all cells (1 SDD)

• One Fixed PDCH TS defined for all 900 cells (AgprsMinPdch = 1) and 1800- only cells

• No PDCH defined for 1800 collocated cells (AgprsMinPdch = 0)

Additional Optimization

In order to further decrease SDCCH traffic, unnecessary registration at the LAC border can be minimized by increasing the CellReselectHysteresis parameter from 3 to 5. This only impacts a limited number of cells on the border between LACs.

7.3.2 Active Mode Behavior

Schema recommends use of the Preferred Band option to hand off traffic from the GSM to the DCS layer after a TCH has been assigned to the 900 layer.

The system-preferred band is defined via a BSC parameter called the “PREFERRED_BAND” (cell_band_type = preferred_band), which in this case, is 1800MHz (DCS1800).

The preferred band option triggers an HO Cause 21 to occur, based on a defined, fixed SS threshold, which will be set to the same value for all adjacencies of each cell. Sometimes carriers use HO Cause 13 (PBGT HO) to force traffic on 1800 through High HO Margin values (typically –9 dB from 900 to 1800 and +18 from 1800 to 900)

Cause 21 HO occurs when the HO goes from any cell not in the “preferred” band to any cell in the preferred band.

HO Cause 21 = High Level in the Neighboring Cell in the Preferred Band, as shown in the following diagram:



Figure 1: HO Cause 21

The HO trigger is defined by the signal level of the neighboring cells in 1800MHz (which is in the preferred band) and by the traffic evaluation of the sectors involved (900MHz cell and neighboring sectors in 1800MHz), via the following algorithm.

AV_RXLEV_NCELL(n)>L_RXLEV_CPT_HO(0,n)+Max(0,[MS_TXPWR_MAX(n)-P])

And

Traffic_load(0) = MULTIBAND_TRAFFIC_CONDITION

and

Traffic_load(n) ≠ HIGH

and

EN_PREFERRED_BAND_HO = ENABLE

900MHz

HO Cause 21

1800MHz 1800MHz

900MHz



Where:

• L_RXLEV_CPT_HO = Minimum signal level of the 1800MHz cell (single) for HO cause 21 to occur.

• MULTIBAND_TRAFFIC_CONDITION = Verifies the condition of the 900 read traffic for HO cause 21 to occur.

• EN_PREFERRED_BAND_HO = Enable HO Cause 21

• LOW_TRAFFIC_LOAD = Threshold used to verify if the read traffic in the target sector is low.

• HIGH_TRAFFIC_LOAD = Threshold used to verify if the traffic in the sector is high.

• EN_MULTIBAND_PBGT_HO = Enables the HO for power budget (cause 12) between cells of different bands.

To prevent handing over PB to the 900 cell, immediately after a HO cause 21 occurs:

• Disable the handover Power Budget between bands (EN_MULTIBAND_PBGT_HO = DISALBE) in the 1800MHz cell neighbors of the 900 cell. This 1800MHz sector will not hand over via PB to any cell of a different band (single 900MHz cells), but will hand over only in emergency cases or,

• Modify the specific HO relation HoMargin (1800, 900) to a value that totally prevents a handover to any 900 cell (e.g,, HM = 127dB).


BSC level :

• Preferred Band = DCS1800

Cell level (HO Control):

• For all 900 cells - EN_PREFERRED_BAND_HO = TRUE

• For all 1800 cells – HoThresholdLevParam - rxLevelDL = 17, meaning –93dB (should be lower than L_RXLEV_CPT_HO for at least 5 dB)

• For all collocated 1800 cells - EN_MULTIBAND_PBGT_HO = FALSE cells (this parameter disables the handover PB between cells of different bands).

• For all standalone 1800 cells - EN_MULTIBAND_PBGT_HO = TRUE

• For all cells - EN_RXLEV_DL = TRUE

• For all cells - EN_RXLEV_UL = FALSE

• MULTIBAND_TRAFFIC_CONDITION = ANY LOAD

• HIGH_TRAFFIC_LOAD = 90%

• RxlevMin(n)= -104 dBm for 900 and –93 dBm for 1800.



Adjacency level:

• All HO relations from 900 to 1800 (1800 cells are collocated) - L_RXLEV_CPT_HO = 20 (meaning–90 dBm)

• All HO relations from 900 to 1800 (1800 cells are standalone) - L_RXLEV_CPT_HO = 63 (meaning –47 dBm): disabled.

• All HO relations– HoMargin=6

Initial settings may not push enough traffic on the DCS layer for some cells, resulting in the need to lower the L_RXLEV_CPT_HO threshold in order to achieve the correct balance between traffic and quality.

While the –90 dBm (L_RXLEV_CPT_HO=20) should be appropriate, this depends on the site cluster. An appropriate value in the middle of the city may be –90 or –93, while in a rural area, it may be –93/ -95.

This optimization requires fine-tuning, since each site may benefit from different L_RXLEV_CPT_HO settings. Any sign of congestion should be closely monitored. Traffic based HO optimization, RxLev, and the Urgency HO threshold should also be tested.

7.4 Siemens



On the Cell level:

• RXLEVAMI (Network access threshold):

o For all 900 cells, this parameter should equal 0 (-110 dBm), in order to capture all possible traffic.

o For 1800 cells collocated with 900 cells, this parameter should equal 6 (-104 dBm).

o For standalone 1800 cells, this parameter should equal 0 (-110 dBm)



• CRESOFF: Cell Reselect Offset. Schema recommends 3 (6 dB) for all cells.

• CRESPARI: Set to 1 for use of C2 criteria.

• CBQ: Set to 1 for 1800 cells (0 for 900 cells) so that GSM cells are given higher priority in the cell selection process (not reselection).

• SDCCHGONG: set to 80 to properly use the Dynamic SDCCH allocation.

On the TRX Level:

• One Fixed SDCCH TS (at least) defined for all 900 cells (CREATE CHAN:NAME=BTSM:0/BTS:0/TRX:0/CHAN:1, CHTYPE=SCBCH or SDCCH) and 1800-only cells

• No more than one Fixed SDCCH TS defined for 1800 collocated cells (Siemens requirement)

• One Dynamic SDCCH TS defined for all cells via Smooth Channel Allocation (CREATE CHAN:NAME=BTSM:0/BTS:0/TRX:0/CHAN:2, CHTYP=TCHSD, CHPOOLTYP=TCHSDPOOL)

• GPRS TS defined on 900, with CHAN 4 to 7 used for data on demand (CREATE CHAN:NAME=BTSM:0/BTS:0/TRX:0/CHAN:3,CHTYP=TCH or TCH_HALF, GDCH=<NULL>, CHPOOLTYP=TCHPOOL)

More Dynamic SDCCH TS may be defined on 900 if necessary (CHAN 3). GPRS on-Demand TS may be defined on 1800 for security purposes, if the 900 cell is down.


In order to further decrease SDCCH traffic, unnecessary registration at the LAC border can be minimized by increasing the Cell Reselection Hysteresis parameter (CELLRESH) from 3 to 5. This only impacts a limited number of cells on the border between LACs.


HCS (Hierarchical Cell Structure) should be activated to ensure that calls are served by the DCS station.

Theoritical Background

The Siemens handover algorithm always performs the handover decision for imperative handovers before a decision regarding a power budget handover is made. Assuming that no imperative handover is required beforehand, an inter-cell handover (power budget) is performed if all of the following conditions are met:

A) A neighbor cell is considered a suitable target cell, and is placed in the target cell list of the HANDOVER CONDITION INDICATION if



C1. RXLEV_NCELL(n) > RXLEVMIN(n) + Max(0,Pa)

• RXLEV_NCELL(n) = received level average of the neighbor cell (n)

• RXLEVMIN(n) = RXLEVMIN (CREATE ADJC) = minimum receive level of the neighbor cell (n)

• MS_TXPWR_MAX(n) = MSTXPMAXGSM/DCS/PCS (BTS object or TGTBTS object), value in [dBm] = max. allowed transmit power of neighbor cell (n)

• P = power capability of the mobile in [dBm]

o Max(0,Pa) = MS_TXPWR_MAX(n) - P if MS_TXPWR_MAX(n) - P > 0

o Max(0,Pa) = 0 if MS_TXPWR_MAX(n) - P < 0

and

C2. PBGT(n) > HO_MARGIN(n)

where PBGT(n) = RXLEV_NCELL(n) - (RXLEV_DL + PWR_C_D) +

Min(MS_TXPWR_MAX, P) - Min(MS_TXPWR_MAX(n),P)

• PBGT (n) = power budget of the neighbor cell (n)

• HO_MARGIN(n) = HOM (CREATE ADJC) = handover margin of the neighbor cell (n)

• RXLEV_NCELL(n) = received level average of the neighbor cell (n)

• RXLEV_DL = received level average downlink of the serving cell

• PWR_C_D = BS_TXPWR_MAX - BS_TXPWR = averaged difference between the maximum downlink RF power and the actual downlink due to power budget.

• MS_TXPWR_MAX = MSTXPMAXGSM (resp. MSTXPMAXDCS or MSTXPMAXPCS) (CREATE BTS [BASICS]), value in [dBm] = max. allowed transmit power of serving cell (n)

• MS_TXPWR_MAX(n) = MSTXPMAXGSM/DCS/PCS (BTS object or TGTBTS object), value in [dBm] = max. allowed transmit power of neighbor cell (n)

• P = power capability of the mobile in [dBm]

o Min(MS_TXPWR_MAX,P) = MS_TXPWR_MAX if MS_TXPWR_MAX < P

o Min(MS_TXPWR_MAX,P) = P if MS_TXPWR_MAX > P

and

C3. PRIO_NCELL(n) <= PRIO_SCELL

• PRIO_NCELL = PLNC (CREATE ADJC) = priority layer assigned to the neighbor cell

• PRIO_SCELL = PL (SET HAND) = priority layer assigned to the serving cell

Note: The lower the value of the parameters PL and PLNC, the higher the priority level!



B) The cells in the target cell list of the HANDOVER CONDITION INDICATION message are ordered by priority (not by their level).

Cells with the same priority level are ordered according to the value of PBGT(n) - HO_MARGIN(n).

Feature Activation

To activate the feature, the cell parameter HIERC must be set to TRUE for all cells; this flag enables the hierarchical cell structures feature. If it is set to TRUE, the target cell list generation process in the BTS considers the priority levels of the serving cell (see parameter PL, which is only relevant for power budget and traffic handovers) and the neighbor cells (see parameters PLNC and PPLNC in the ADJC object, which is only relevant for all imperative handovers, except for the fast uplink handover).

The PL parameter defines the priority layer of each cell, while the PLNC parameter defines the priority of neighbor cells.

RXLEVMIN is used to set the desired Level threshold to access an 1800 cell. All handovers from 1800 to 900 will be handled via an urgency condition (Level and Quality). Traffic HO will be allowed between 1800 cells.


Cell level (HAND):

• HIERC= TRUE for all cells.

• PL=5 for 1800 cells and 9 for 900 cells. Priority layer, if hierarchical cell handover is enabled (HIERC=TRUE) this parameter determines the priority layer of the cell, and is only evaluated for the Power Budget handover decision and the traffic handover decision (see parameter TRFKPRI).

• TRFKPRI=TRUE: HO Traffic priority; this parameter determines which neighbor cells are allowed as target cells for traffic handovers if the hierarchical cell structure feature is enabled (parameter HIERC=TRUE).

o If TRFKPRI=TRUE, an adjacent cell may only be a traffic handover target cell if it has the same priority level as the serving cell.

o If TRFKPRI=FALSE, an adjacent cell may be a traffic handover target cell if it has the same, or higher, priority level as the serving cell.

• RXLEVHO=TRUE: Enables HO due to low SS

• HOLTHLVDL=12 (-98 dBm) for 1800 cells and 5 (-105) for 900 cells: Handover lower threshold level downlink, defines the receive signal level threshold on the downlink for inter-cell level handover decisions. This parameter is only relevant if inter-cell handover due to



level is enabled (RXLEVHO=TRUE). The actual threshold value in [dBm] is calculated as follows: Handover Threshold (dBm) = -110dBm + HOLTHLVDL.

• NMULBAC: Number of reported Multi Band cells. Currently set to 0. Schema recommends a setting of 2 in order to report at least 2 cells from the opposite band for collocated cells.

Adjacency level (ADJ):

• PLNC (Priority layer of neighbor cell) = 5 for 900 to 1800 neighbor relations, and 9 for all neighbor relations; this parameter determines the priority layer of the adjacent cell.

• HO margin

o HOM= 69 (+6 dB) for 900 to 900

o HOM= 49 (-14 dB) for 900 to 1800

o HOM= 69 (+6 dB) for 1800 to 900 (does not matter)

• RXLEVMIN= 6 (-104 dBm) for 900 and 17 (–93 dBm) for 1800

7.5 Ericsson


Generally, path loss and clutter result in the GSM cell being stronger than a co-located DCS cell. However, the settings noted in the following paragraphs will improve the likelihood of MS operating on the GSM channels.


On the cell level:

• ACCMIN (Network access threshold):

o For all 900 cells this parameter should equal -110 (dBm) in order to capture all possible traffic.

o For 1800 cells, collocated with 900 cells, this parameter should equal -104.

o For standalone 1800 cells this parameter should equal -110 dBm.



• CRO: Cell Reselect Offset. Schema recommends 3 (6 dB) for all cells (PT should also be set to 0).

• CHAP: Schema recommends 6.

• ESCM= TRUE for all cells

• CBQ= HIGH for GSM cells and LOW for DCS to favor GSM cells in the cell selection process (not reselection).

On the TRX level:

• BCCH type changes to BCCH COMB SDCCH/4 for all 1800 collocated cells

• One fixed SDCCH TS (at least) defined for all 900 cells

• No fixed SDCCH TS defined for 1800 collocated cells

• Dynamic SDCCH allocation active on all cells (ACSTATE=ON)

• One fixed GPRS TS defined on 900 cells only (FPDCH=1)



Additional Optimization To further decrease unnecessary SDCCH traffic, unnecessary registration should be minimized on the LAC border by setting the Cell Reselection Hysteresis parameter (CRH) to 5 (10dB). This only impacts a limited number of cells on the BSC borders (1LAC= 1BSC).


The HCS – Hierarchical Cell Structure should be activated to ensure that calls are served by the DCS station.

The Hierarchical Cell Structure (HCS) feature can be used to force traffic onto 1800 MHz channels when calls are active by setting the 1800 MHz cells to a higher priority than the 900 MHz cells (i.e., by setting the HCSBAND parameter to 2 for the 1800 MHz cells and to 3 for the 900 MHz cells, with layer 1 reserved for micro-cells).

By forcing traffic onto the 1800 MHz cells, 1800 MHz candidate cells are always evaluated before the 900 MHz cells.

Cell level (HAND):

• LAYER= 2 for DCS cells and 3 for GSM cells.

• LAYERTHR= -95 (dBm) for GSM cells and –85 for DCS cells.

• LAYERHYST=3 for all cells.

• MBCR: Number of reported Multi-Band cells. Schema recommends 2 for GSM cells and 3 for DCS cells to report at least 2 cells from opposite bands for collocated cells.


• The HO margin should be set to 5 dB for all neighbor relations.

7.6 Nokia


Generally, path loss and clutter make the GSM cell stronger than a co-located DCS cell. However, the settings noted in the following paragraphs should further improve the likelihood of MS operating on the GSM channels.


On the Cell level:



• RxLevAccssMin (“Receive Level Access Minimum”)

o For all 900 cells, this parameter should equal -110 (dBm), in order to capture all possible traffic.

o For 1800 cells that are collocated with 900 cells, this parameter should equal –104 dBm.

o For standalone 1800 cells, this parameter should equal -110 dBm.

• CRO: Cell Reselect Offset. Schema recommends 3 (6 dB) for all cells.

• EarlySendingIndication = YES for all cells

• CellBarQualify (CBQ)= HIGH for GSM cells and LOW for DCS to favor GSM cells in the cell selection process (not reselection).

On the TRX level:

• BCCH type changes to BCCH COMB SDCCH/4 for all 1800 collocated cells

• One Fixed SDCCH TS (at least) defined for all 900 cells


• Dynamic SDCCH Allocation active on all cells

• One Fixed GPRS TS defined only for 900 cells


To further decrease SDCCH traffic, unnecessary registration can be minimized on the LAC border by setting the cellReselectHysteresis (CRH) to 5 (10dB). This only impacts a limited number of cells on the BSC borders (1LAC= 1BSC).


The Umbrella structure should be activated to ensure that calls are served by the DCS station.

This feature can be used to force traffic into the 1800 MHz channels in active mode by setting the 1800 MHz cells at a higher priority than the 900 MHz cells (i.e., by setting the enable_umbrella_HO parameter to 2 for the 1800 MHz cells and to 3 for the 900 MHz cells, with layer 1 reserved for micro-cells).

By forcing traffic onto the 1800 MHz cells, 1800 MHz candidate cells will always be evaluated before 900 MHz cells.

Theoretical Background

Umbrella Handover can be used in multilayer networks to push traffic from macro cells to micro cells or from GSM cells to DCS cells (with combined umbrella and power budget handovers.).



Figure 2: Umbrella Handover and Handover Due to Level

The Combined Umbrella and Power Budget Handover is separate from the MS speed used in the Network.

The serving Cell can be Macro (GSM), Micro or Middle _sized (DCS), based on the msTxPwrMax.

Finally, the adjacent cell can be a Micro, a Macro (GSM) or a Middle-sized (DCS), based on the msTxPwrMax (n).

When enablePowerBudgetHo = Yes & enableUmbrellaHo = Yes

• Power Budget Handover takes place only among cells in the same layer

• Umbrella Handover takes place on cells in different layers.

Based on the AdjCellLayer parameter setting, either the adjacent cell layer or the conventional method may be used.

Implementation

On the Cell level (HAND):



• enable_umbrella_HO=1; allows umbrella Handover

• HoLevelUmbrella= -95 (dBm) for GSM cells and –85 for DCS cells; this parameter defines the minimum signal level of an adjacent cell when a handover is allowed in an adjacent umbrella cell.

• multiBandCellReporting: Number of reported Multi-Band cells. Schema recommends 2 for GSM cells and 3 for DCS cells in order to report at least 2 cells from opposite bands for collocated cells.

On the Adjacency level (ADJ):

• The HO margin should be set to 5 dB for all neighbor relations.

7.6.3 Common BCCH at 900

The new S10 features, “Common BCCH Control” and “Multi BCF Control” are optional and introduce a new architecture and radio network object, called a “segment.” Up to S9, a segment is used in the same sense as a telecom cell, which consists of only one BTS. In BSC S10, a cell can be configured for different BTS objects, and the BTSs of a segment are co-located and synchronized.

The TRXs inside a BTS-object must have capabilities that are common to both features. For instance, they must be both EDGE-capable and non-EDGE-capable. TRXs must be configured as separate BTS-objects. (E)GPRS territory can be defined separately for each BTS-object.

A Segment can have BTS objects that differ in frequency bands (GSM850 and GSM 1900), power levels (Talk-family and UltraSite BTSs), regular and super-reuse frequencies, normal and extended cell radius frequencies, and EDGE capabilities.

Common BCCH parameters are defined in several command groups, required to control the Common BCCH Control feature. The groups are BSC Parameter Handling in BSC, BTS Handling in BSC, Adjacent Cell Handling, Handover Control Parameter Handling, and Power Control Parameter Handling.

Some parameters are required to handle the segment environment in general, while others are required to handle the resources of different frequency bands in a segment. The most important general parameters of the segment environment are the segment identification and the segment name (provided on PRFILE/FIFILE level). These general parameters are available in all command groups with specific cell parameters that are common to all the BTSs of a segment.

Most of the parameters related to the Common BCCH Control are defined per segment object. Parameters related to the feature in Adjacent Cell Handling, Handover Control Parameter Handling and Power Control Parameter Handling are all defined as common values for the BTSs of one segment. In the BTS Handling command group, most of the parameters are segment



level parameters, but there are also BTS-specific parameters, used to define separate values for the different BTS objects in a segment.

In the BTS Handling command group, two BTS-specific parameters have been introduced, along with the Common BCCH Control feature.

• NonBcchLayerOffset is used to estimate the signal level of the non- BCCH layer resources.

• BTSLoadInSEG is used to control the traffic load in different BTSs of a segment.

Figure 3: BTS Handling Command Group Parameters

Three groups of parameters, which existed before the Common BCCH functionality, have been preserved mainly as BTS-specific parameters in the segment environment, and are related to Frequency Hopping, HSCSD and GPRS.

In BTS Handling in BSC, the former cell-specific parameter, MsTxPwrMax, has been replaced by MsTxPwrMaxGsm and MsTxPwrMaxGsm1x00, due to the Common BCCH Control. These parameters are used whether or not the Common BCCH Control options are enabled. MsTxPwrMaxGsm is used in the GSM900 and the GSM850 frequency bands, while MsTxPwrMaxGsm1x00 is used in the GSM1800 and the GSM1900 frequency bands.

In the Handover Control Parameter Handling (not in E/GPRS) command group, the SuperReuseGoodRxLevThreshold parameter is used to evaluate the usability of the non-BCCH layer in a segment with resources originating from different frequency bands.

In Adjacent Cell Handling, the former cell-specific parameter, MsTxPwrMaxCell, has been replaced with two separate parameters (MsTxPwrMaxGsm and MsTxPwrMaxGsm1x00), just as MsTxPwrMax has been replaced in the Base Transceiver Station Handling in BSC. These parameters are used whether or not the Common BCCH Control options is used.

In BSC Parameter Handling, the IntraSegSdcchHoGuard parameter controls the transfer of SDCCH reservations from the BCCH resource layer in segments under BSC control.

Both BCCH allocation and the sending of system information in the common BCCH networks are similar to methods used in traditional networks with single BTS cells. The adjacency information sent to the MS is based on the BCCH frequency of a common BCCH segment. Other frequency layers in the segment are invisible to MSs.



However, since the BSC must decide which handovers are made for an MS on the GSM1900 layer of a segment, the BCCH frequency of the segment, itself, is added to the BCCH frequencies that the MS measures when it is on the GSM1900 band. A modified BA list is sent to an MS on the GSM1900 layer in an SI 5 message on the SACCH.

When the Common BCCH Control feature is enabled there can be only 31 frequencies in adjacent cell and BA lists. Only five of the strongest neighbors are included in the adjacent cell measurements in a multi-band segment since the BCCH of the serving segment is added to the measured frequencies.

7.6.3.1 TCH Allocation and Common BCCH Control

When the BSC has determined that a mobile accessing the SDCCH is capable of dual band operation, it determines whether to send the call to the 850 or 1900 MHz BTS by applying the BTS-specific parameter, NonBcchLayerOffset, to the 850 BCCH measurements to estimate what the signal level would be at 1900. A single value is used even though it may actually vary, based on the MS location relative to the cell.

When a call is on a GSM1900 frequency band TCH channel, the BSC defines the usability of the GSM850 band, based on the measurement of the serving GSM1900 TCH. The BTS-specific offset parameter, NonBcchLayerOffset, is used to determine whether a call should be handed over to a particular BTS. The criterion for accepting a resource type to be used in channel allocation is

RXLEV_DL - NonBcchLayerOffset>= SuperReuseGoodRxLevThreshold.

If the MS uses a GSM1900 TCH, the RXLEV_DL is the downlink signal level of the BCCH carrier of the segment.

7.6.3.2 Internal Inter-cell TCH Handover

When the BSC has defined a need for an inter-cell handover based on the measurements of the serving TCH channel, the usability of the different resource types of each candidate segment are determined on the basis of the BCCH measurement results for the segment and the values of NonBcchLayerOffset parameter for different resource types in the segment. The resulting level is compared to an existing threshold parameter RxLevMinCell(n):

AV_RXLEV_NCELL(n) - NonBcchLayerOffset>= RxLevMinCell(n).

The signal level in the adjacent segment must exceed the RxLevMinCell(n) level to perform the handover to the adjacent segment.



7.6.3.3 External TCH Handover

It is not possible to define the usability of the GSM1900 resources on the target side of a handover between two BSCs. The radio link measurements related to the target segment are only available on the source side BSC. The TCH allocation on the target side of a BSC external handover is limited to the GSM850 frequencies of the segment.

7.7 Nortel


Generally, path loss and clutter result in a GSM cell being stronger than a co-located DCS cell. However, the settings outlined in the following paragraphs will improve the likelihood of MS operating on the GSM channels.


On the cell level:

• RxLevMinCell (Network access threshold):

o For all 900 cells, this parameter should equal -110 (dBm), to capture all possible traffic.

o For 1800 cells, collocated with 900 cells, this parameter should equal -104.

o For standalone 1800 cells, this parameter should equal -110 dBm.

• CellReselectOffset: Schema recommends 3 (6 dB) for all cells (PT set to 0).

• CellBarQualify= FALSE for GSM cells and TRUE for DCS to favor GSM cells in the cell selection process (not reselection)

On the TRX level:




• Dynamic SDCCH allocation active on all cells (ACSTATE=ON)

• One Fixed GPRS TS defined on 900 cells only (FPDCH=1)




In order to further decrease SDCCH traffic, unnecessary registration can be minimized on the LAC border by setting the cellReselectHysteresis parameter to 5 (10dB), which only impacts a limited number of cells at the BSC borders (1LAC= 1BSC).


To ensure that calls are served by the DCS station, it is best to activate the handover decision based on adjacent cell Priorities and the load (from v12).

This feature helps optimize traffic distribution between layers (based on cell priorities) and cells on the same layer (based on overload conditions).

Traffic can be forced to the 1800 MHz channels when calls are active by setting the 1800 MHz cells to a higher priority than the 900 MHz cells (that is, by setting the offsetPriority parameter to 2 for 1800 MHz cells and to 3 for 900 MHz cells, layer 1 being reserved for micro-cells).

By forcing traffic to the 1800 MHz cells, 1800 MHz candidate cells will always be evaluated before the 900 MHz cells.

In the selection phase, the BSC places cells in descending priority order (offsetPriority), but for same priority cells, the order in the Handover Indication message is maintained. The BSC calculates the following for those cells:

EXP4(n) = EXPi(n) – [offset_load(n) * state_load(n)] where EXPi(n) = EXP1(n) For handover causes, capture, or directed retries in distant mode, EXPi(n) = EXP2(n) for other causes ; EXP1 or EXP2 are added to the “handover indication” message from V12 ; offset_load is a neighbor cell parameter in dB and state_load is an overload status parameter ; state_load=1 for an intra BSS neighbor cell which is overloaded and 0 otherwise including an inter-BSS neighbor cell overloaded ; the BSC sorts same priority cells by decreasing the EXP4 values before reducing the preferred cell list from six to three.

• offset_load(n) corresponds to the new offsetLoad parameter.

• offsetPriority defines the priority range from 1 to 5 (1 is the highest level).

Overload detection relies on the ”handover for traffic reasons” principle. If the overload detection is not activated, priority is the only criterion considered.

Priority is important in a multi-layer network, and overload is important in a network containing same-priority cells.

A problem may occur in multi-layer networks when the higher priority cell (which captures traffic) is overloaded, and induces HOs for traffic in adjacent cells.



Cell level (HAND):

• offsetPriority = 2 for DCS cells and 3 for GSM cells.

• multiband reporting: Number of reported Multi Band cells. Schema recommends two for GSM cells and three for DCS cells in order to report at least two cells from opposite band for collocated cells.

• rxLevMinCell= 6 (-104 dBm) for 900 and 17 (–93 dBm) for 1800. Minimum received signals for neighbor to be eligible for Handover.

• LRxLevDLH: Urgency Handover threshold due to poor SS DL. LRxLevDLH = 12 (-98 dBm) for 1800 cells and 5 (-105) for 900 cells: Handover lower threshold level downlink defines the receive signal level threshold on the downlink for the inter-cell level handover decision. The actual threshold value in [dBm] is calculated as follows: Handover Threshold (dBm) = -110dBm + LRxLevDLH.


• HO margin should be set to 5 dB for all neighbor relations.

7.8 Huawei


Generally, path loss and clutter result in a GSM cell being stronger than a co-located DCS cell. However, the settings listed in the following paragraphs improve the likelihood of MS operating on GSM channels.


On the cell level:

• RXLEV_ACCESS_MIN (“Receive Level Access Minimum”)

o For all 900 cells this parameter should equal -110 dBm (0), to capture all possible traffic.

o For 1800 cells that are collocated with 900 cells, this parameter should equal–104 (6).

o For standalone 1800 cells this parameter should equal -110 dBm (0).

• CRO: Cell Reselect Offset. Schema recommends 3 (6 dB) for all cells.

• EarlySendingIndication = YES for all cells

• CellBarQualify (CBQ)= YES (HIGH) for GSM cells and NO (LOW) for DCS to favor GSM cells in the cell selection process (not reselection).



On the TRX level:




• Dynamic SDCCH Allocation active on all cells (SD Dynamic Allocation Allowed= YES)

• One Fixed GPRS TS defined on 900 cells only


In order to further decrease SDCCH traffic, unnecessary registration can be minimized on the LAC border by setting the cellReselectHysteresis (CRH) to 5 (10dB), which only impacts a limited number of cells on the BSC borders (1LAC= 1BSC).


To ensure that calls are served by the DCS station, it is best to activate the Umbrella structure, which forces traffic to 1800 MHz channels in active mode. The 1800 MHz cells are set to a higher priority than the 900 MHz cells (that is, the enable_umbrella_HO parameter is set to two for the 1800 MHz cells and to three for the 900 MHz cells, layer 1 being reserved for micro-cells).

By forcing traffic to the 1800 MHz cells, 1800 MHz candidate cells are always evaluated before the 900 MHz cells.


The Umbrella Handover can be used in multilayer networks to push traffic from macro cells to micro cells or from GSM cells to DCS cells (with combined umbrella and power budget handovers).



Figure 4: Umbrella Handover and Handover Due to Level (2)

The Combined Umbrella and Power Budget Handover can be used regardless of the MS speed used in the network.

The serving Cell can be Macro (GSM), Micro or Middle _sized (DCS), based on the msTxPwrMax.

Finally, the adjacent cell can be micro, macro (GSM) or a middle-sized (DCS), based on the msTxPwrMax (n).

When enablePowerBudgetHo = Yes & enableUmbrellaHo = Yes

• Power Budget Handover only operates on cells in the same layer

• Umbrella Handover operates on cells in a different layer

The AdjCellLayer parameter is set to either the Adjacent Cell Layer method or to the Conventional Method.

Implementation

Cell level (HAND):

• Layer of the cell (Range: 1~4), 2 for 1800 and 3 for 900; The smaller the layer value, the higher the priority.

• Inter-layer HO Thrsh = -95 (dBm) for GSM cells and –85 for DCS cells. The threshold for the inter-layer Hierarchical Handover should satisfy: Inter-layer HO Thrsh. ≥�Edge HO RX_LEV Thrsh. + Inter-cell HO hysteresis to ensure that the receiving level of the destination cell is higher than inter-layer HO threshold in hierarchical handover or load handover. Otherwise,



MS hands over from a large load high level cell (high priority cell) to a small load low level cell (low priority cell), and the MS may be disconnected.

• Inter-layer HO hysteresis is for inter-layer or inter-priority handover, and is used to avoid inter-layer Ping-Pong handover. Actual Inter-layer HO Thrsh. of serving cell = value of Inter-layer HO Thrsh. - Inter-layer HO hysteresis. Actual Inter-layer HO Thrsh. of neighboring cell = value of Inter-layer HO Thrsh. + Inter-layer HO hysteresis.

• multiBandCellReporting (MBR): For reported Multi-Band cells, Schema recommends 2 for GSM cells and 3 for DCS cells in order to report at least 2 cells from opposite band for collocated cells.

• Rx_Level_Drop HO allowed (Yes) on 1800; the parameter decides whether to use the emergency handover algorithm when the receiving level drops quickly.

• The PBGT HO allowed for both bands parameter determines whether to use the PBGT handover algorithm, which is based on path loss. To avoid Ping-Pong handover, the PBGT handover occurs only between cells of the same layer.


• HO margin should be set 5 dB for all neighbor relations.

Additional features: Cell Load sharing

• The Load HO allowed set to Yes on DCS1800 determines whether Traffic load-sharing handover is allowed. Load-sharing reduces cell congestion and balances the traffic load for each cell to improve network performance. This works only within the same BSC or for cells in the same layer, and is only used for TCH.

7.9 Motorola…Hello Moto!


Generally, the difference in path loss results in the GSM cell being stronger than a co-located DCS cell. However, the settings in the following paragraphs improve the likelihood that MS operates on the GSM channels.


Access



cell_bar_access_switc 0 Not barred

cell_bar_qualify 1/0 Normal priority/ Low

cell_bar_access_class 0 Deactivated

emergency_class_swit 0 All access classes

Immediate Assignmenmode

1 Allocate SDCCH or TCH basedon available resources

Option emergency Preempt

1 Preemption allowed for emergency calls

Selection / Reselection (900/1800)

Rxlev_access_min 4 / 12 - 106 dBm / - 98 dBm

Cell_reselect_hysteresis 4 8 dB

Cell_reselect_offset 0 / 4 0 dB / 8 dB

Cell_reselect_param_ind 1 / 1 C2 will be used for both bands

Penalty_time 0 0

Temporary_offset 0 0 dB

900 900 / 1800 900

900 1800 if 1800 > - 95 dBm and equal to 900 (CRO – Difference Rxlev_acc_min )

1800 900 if 900 equal to 1800 ( CRO – Différence Rxlev_acc_min )

On the TRX level:






• Dynamic SDCCH Allocation active on all cells (Immediate Assignment mode=1)

• One Fixed GPRS TS defined on 900 cells only


In order to further decrease SDCCH traffic, unnecessary registration can be minimized on the LAC border.

To do so, the Cell_reselect_hysteresis (CRH) can be reset to 5 (10dB). This will only impact a limited number of cells at the BSC borders (1LAC= 1BSC).


HO cause capture on PBGT (type 5) can be used to ensure that calls are served by the DCS station by forcing traffic to 1800 MHz channels in active mode, using a different HO-margin for type 5 HO only, and setting the specific Rxlev min to control traffic on 1800.




Serving cell: Causes HandOver activated

900 non collocated level UL/DL ; quality UL/DL ; distance and PBGT type 1

900 with 1800 collocated level UL/DL ; quality UL/DL ; distance ; PBGT type 1 towards 900 ; PBGT

type 5 towrds 1800 1800 non collocated level UL/DL ; quality UL/DL ;

PBGT type 1 ; distance Five types of HO on TCH should be activated:

• PBGT (normal)

• Quality (UL and DL): urgency

• Level (UL and DL): urgency

• Distance: urgency

• Congestion: urgency

In a dual band environment, the following HO should be activated: Cell macro umbrella (900): Same + capture (5) Cell 1800:

• PBGT

• Quality (UL and DL)

• Level (UL and DL)

• Congestion

Algorithm PBGT Type 5 (capture)

Equation

Neighbor SS must meet the requirement for qualify_delay_time_type_5 PBGT(n) > ho_margin_cell (n) and rlev_dl ( n ) > rxlev_ncell_h(n) during qualify_delay_time_type_5



Implementation

Cell level:

• interband_ho_allowed: allow inter band HO

• band_preference: indicate preferred band (4 = DCS 1800)

• band_preference_mode: The band_preference_mode parameter specifies the method the system uses to program a Multiband MS with the preferred frequency band for a given cell in the BSS. The BSS attempts to hand a Multiband MS over to the strongest neighbour that the MS reported when a handover is required for normal radio resource reasons. Indicates when to change band ( 3 = on SDCCH and TCH for all 900 cells and 0 = for better cell between 1800).

• multiband_reporting (MBR): Number of reported Multi Band cells. Schema recommends 2 for GSM cells and 3 for DCS cells in order to report at least 2 cells from opposite band for collocated cells.

• early_classmark_sending: Activate early classmark on A and Air interface ( BSC parameter)

• mb_preference: Activation of dual band on Motorola BSS (BSC parameter)

• The rxlev_min_def parameter specifies the default value for rxlev_min_cell.

• The option_alg_a5_5 parameter enables or disables the encryption algorithm A5/5.

Handover:

• The ho_margin_type5 parameter sets the power budget type 5 handover margin.

Optimization Methodology for Dual Band Markets

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