BSC RF OPTIMIZATION

 

HandoverIt is the transfer of call from one cell to another cell.

Triggering Factors * Meeting the defined thresholds (urgent)

a. Interference b. Quality

c. Signal Level * Periodic better cell evaluation (non-urgent)

a. Power Budget b. Umbrella

* Forced handover

Handover Target EvaluationIn dedicated mode, the BSC sends the list of frequencies (max. of 32, 16 ch. 

from each band) the mobile has to tune in, in order to decode the BSIC and report the signal strength measurements of the 6 strongest adjacent cells in 1 SACCH.

An adjacent cell is only included in the target cell evaluation list in the BSC if and only if the first criterion is met, that is,

                                       RxLevNcell > RX LEV MIN CELL

(ZEAO) RX LEV MIN CELL.........…...(SL)………………-100 dBm (ZEQO) RXLEV ACCESS MIN............(RXP)..…………...-105 dBm

(ZEHO) AVERAGING WINDOW SIZE ADJ CELL ..…… 06

The target cell evaluation list in the BSC is constantly updated as the call is going on. When HO is triggered due to meeting either quality or signal level threshold, the adjacent cell has to satistfy the second criterion, that is, meeting the required QMRG or LMRG.

Handover Due to Interference Interference affects signal quality.C/I ratio is directly proportional to QUALITY.C/I requirement is 12, 9 for hopping channels.C/A allowed is 3.

BER(%) QUALITY Note: Handover due to Interference0.0 - 0.2 0 is associated with quality 0.2 - 0.4 1 measurements. It is triggered 0.4 - 0.8 2 if and only if QMRG is not met 0.8 - 1.6 3 by any of the adjacent cells. 1.6 - 3.2 43.2 - 6.4 56.4 - 12.8 6 12.8 up 7

 

Handover Due to Quality In ZEHO,HO THRESHOLDS QUAL DL RX QUAL ...... 3.2% - 6.4% PX .. 04 NX .. 06HO THRESHOLDS QUAL UL RX QUAL ...... 3.2% - 6.4% PX .. 04 NX .. 06

In ZEAO,HO MARGIN QUAL.....................……… (QMRG).. 0 dBENABLE HO MARGIN LEV QUAL...... (MRGS).. Y

A QMRG equal to 0dB means that the adjacent cell, after passing the first criterion, and the serving cell should be equally strong to qualify in the final list. The final list contains all the adjacent cells that passed the two criteria. Finally, the BSC will rank these qualified cells based on BTS load and PRIORITY.

If MRGS is set to N, it means that this adjacent cell will not be included in the target cell evaluation when the serving cell meets either the quality or signal level thresholds for handover.

Handover Due to Signal LevelHO THRESHOLDS LEV  DL  RX LEVEL ............     -092 dBm PX .. 01  NX .. 01HO THRESHOLDS LEV  UL  RX LEVEL ............     -095 dBm PX .. 01  NX .. 01

HO AVERAGING LEV  DL       WINDOW SIZE ............ 06    HO AVERAGING LEV  UL       WINDOW SIZE ............ 06    HO AVERAGING QUAL DL     WINDOW SIZE ............ 01    HO AVERAGING QUAL UL     WINDOW SIZE ............ 01

In ZEAO,HO MARGIN LEV..........................(LMRG)..    3 dB

An LMRG of 3dB means that this adjacent cell, after passing the first criterion, should be stronger than the serving cell by 3dB in order to be included in the final list.

Umbrella HandoverUmbrella is basically designed to handle fast moving MS. It should be a tall site with very wide coverage. It eliminates multiple handovers.

But now, umbrella is not used in this way. It is activated to push voice traffic from a

congested cell to another cell, that is, TRAFFIC OFFLOADING. Umbrella is activated only in the CONGESTED cell. Then, AUCL is individually set in

each of its adjacent cells. To trigger umbrella, RxLevNcell > HoLevelUmbrella(AUCL)

AUCL = -47dBm to -110dBm (difficult to easy triggering)  

Power Budget HandoverTo ensure  that the MS is always handed over to the cell with the minimum path loss ( EIRPbts – RxLev).                                    X YPBGT = (RxLevNcell – RxLevScell) + (PMAXsCell – PMAXnCell)               PMAX is the assumed maximum tx power of MS in that cell

To trigger PBGT HO,             PBGT > PMRG

Example: 1800 to 900 PBGT = X + ( 30 – 33), if PMRG = 6dB, then X should be 10PBGT = 10 – 3 = 7 , PBGT > PMRG, 7 > 6Therefore, 900 should be 10dB stronger to trigger the HO.PBGT HO and UMBRELLA HO are periodically evaluated every 6 SACCH ( 3 sec ).

Rapid Field Drop HandoverWhen the mobile moves so fast from one cell to another cell, the signal can drop very quickly. The usual averaging process takes approximately 3 sec before HO decision is made. If this feature is not activated, the call may just be dropped. Sudden signal (fading) obstruction can also result to rapid field drop.

In ZEHO,     HO THRESHOLDS LEV  UL FOR RAPID FIELD DROP …  -110 dBm    PX .. 00 (DISABLED) In ZEAO,      CHAINED ADJACENT CELL..................(CHAIN)….Y 

Chained adjacent cell  parameter is used to identify which cells are to be included in the target evaluation (minimum of 1).

  handover decision.

ZEAO CommandADJACENT CELL DATA BTS-001 S644PRDHN4 HAS ADJACENT CELL : BTS-003 S644PRDHN6 LOCATION AREA CODE.....................(LAC)....30001 CELL IDENTIFICATION....................(CI).....60644 NETWORK COLOUR CODE....................(NCC).... 0 BACKGROUND NETWORK COLOUR CODE.........(BNCC)... - BTS COLOUR CODE........................(BCC).... 3 BACKGROUND BTS COLOUR CODE.............(BBCC)... - FREQUENCY NUMBER OF BCCH...............(FREQ)... 69 BACKGROUND FREQUENCY NUMBER OF BCCH....(BFREQ).. - HO MARGIN PBGT.........................(PMRG).. 6 dB HO MARGIN LEV..........................(LMRG).. 3 dB HO MARGIN QUAL.........................(QMRG).. 0 dB ENABLE HO MARGIN LEV QUAL..............(MRGS).. Y HO PRIORITY LEVEL......................(PRI)... 3 HO LOAD FACTOR.........................(OF).... 1 RX LEV MIN CELL........................(SL)....-100 dBm HO LEVEL UMBRELLA......................(AUCL)..- 47 dBm MS TX PWR MAX CELL.....................(PMAX).. 33 dBm SYNCHRONIZED...........................(SYNC).. Y TRHO TARGET LEVEL......................(TRHO).. N (NOT IN USE) ADJACENT CELL LAYER....................(ACL)... N (NOT IN USE) FAST MOVING THRESHOLD..................(FMT)... 0 (NOT IN USE) MS PWR OPT LEVEL.......................(POPT).. N (NO OPTIMIZATION) CHAINED ADJACENT CELL..................(CHAIN). N DIRECTED RETRY THRESHOLD...............(DRT)...-100 dBm

ZEHO CommandHANDOVER CONTROL PARAMETERS OF BTS-001 S644PRDHN4 ENABLE INTRA HO INTERF UL ...... N ENABLE INTRA HO INTERF DL ...... N ENABLE PWRBUDGET HANDOVER ...... Y ENABLE MS DISTANCE PROCESS ..... N ENABLE SDCCH HANDOVER .......... Y ENABLE UMBRELLA HANDOVER ....... N ENABLE FAST AVE CALL SETUP ..... Y ENABLE FAST AVE PC ............. Y ENABLE FAST AVE HO ............. Y MIN INT BETWEEN HO REQ ............. 05 s HO PERIOD UMBRELLA ....... 06 MIN INT BETWEEN UNSUCC HO ATTEMPT .. 05 s HO PERIOD PBGT ........... 06 AVERAGING WINDOW SIZE ADJ CELL ..... 10 NUMBER OF ZERO RESULTS ... 2 ALL ADJACENT CELLS AVERAGED ........ N HO AVERAGING LEV DL WINDOW SIZE ............ 10 WEIGHTING .... 1 HO AVERAGING LEV UL WINDOW SIZE ............ 10 WEIGHTING .... 1 HO AVERAGING QUAL DL WINDOW SIZE ............ 10 WEIGHTING .... 1 HO AVERAGING QUAL UL WINDOW SIZE ............ 10 WEIGHTING .... 1 MS SPEED AVERAGING ............. 04 HO THRESHOLDS QUAL DL RX QUAL ...... 1.6% - 3.2% PX .. 08 NX .. 10 HO THRESHOLDS QUAL UL RX QUAL ...... 1.6% - 3.2% PX .. 08 NX .. 10 HO THRESHOLDS LEV DL RX LEVEL ............ -095 dBm PX .. 03 NX .. 04 HO THRESHOLDS LEV UL RX LEVEL ............ -095 dBm PX .. 03 NX .. 04 HO THRESHOLDS LEV UL FOR RAPID FIELD DROP . -110 dBm PX .. 00 (DISABLED)ENABLE ENHANCED RAPID FIELD DROP ........... DIS (DISABLED) THRESHOLD DEEP DROPPING EDGE ............... 10 dB PX .. 02 NX .. 03 DEEP DROPPING EDGE MONITORING WINDOW ....... 2 MODIFIED AVERAGING WINDOW .................. 2 MODIFIED NUMBER OF ZERO RESULTS ............ 1 ENHANCED RAPID FIELD DROP DURATION ......... 10 s HO THRESHOLDS INTERFERENCE DL RX LEVEL ..... -080 dBm PX .. 03 NX .. 04 HO THRESHOLDS INTERFERENCE UL RX LEVEL ..... -080 dBm PX .. 03 NX .. 04 MS DISTANCE AVERAGING PARAM WINDOW SIZE ..... 20 MS DISTANCE HO THRESHOLD PARAM MS RANGE MAX .... 63 PX .. 10 NX .. 16

HANDOVER EXAMPLE

RxLev(1800) = -92 dBm (HO due to DL Signal Level, as received by MS)

Neighbors                    LMRG    BSC CHK   PRI   BTS LD    OF    NPRI     RANKA  (900)  =  - 90  dBm          3dB         delB (1800)   =  - 93  dBm          0dB         delC (1800)   =  - 89  dBm          0dB         ok             5         72%       1          4             2ndD (1800)  =  - 92  dBm          0dB         ok             5         50%       1          5             1stE  (900)    =  - 70  dBm          3dB         ok             3         40%       1          3             3rdF  (900)    =  - 92  dBm          3dB         del

Note: BTS load of an adjacent cell belonging to different BSC is not evaluated.          If two or more cells have equal NPRI , ranking is then based on Signal Strength.