presentation to warid for selection reselection

1Huawei Confidential

Cell Selection and Cell Reselection


Cell Selection

When MS is powered on, it will try to find a GSM PLMN. MS will select an appropriate cell and read system information. This process is called cell selection

GSM specification stipulates one parameter called path loss principle C1. The appropriate cell must ensure the C1>0. C1 is obtained by the calculation of cell selection parameters.

After MS selects cell, MS will settle in the selected cell


C1 = RLA_C - RXLEV_ACCESS_MIN - MAX((MS_TXPWR_MAX_CCH- P), 0) RLA_C: mean receiving level of MS

RXLEV_ACCESS_MIN: minimum receiving level of MS permitted to access

P: maximum physical transmitting power level of MS.

Cell Selection


MS_TXPWR_MAX_CCH Value range: 0~31 Content: This parameter determines the max. allowed output

power of the MS when it begins to access a cell and has not yet received power command.

Recommendation: 5(900MHz), 0(1800MHz) List is the corresponding dBm values related to the 32 For

GSM900:{39, 39, 39, 37, 35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5}For GSM1800:{30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 36, 34, 32}

Cell Selection


RXLEV_ACCESS_MIN Value range: 0~63 Unit: Level Content: It means the minimum received signal level required

for MS to access a cell. Recommendation: 8

Cell Selection


If SIM card of MS does not store any BCCH, it will search all the 124 RF channels and 374 more GSM1800 channels for dual-band MS, measure the receiving signal level of each.

The whole process lasts about 3s to 5s. During this, MS obtains at least 5 measurement samples from each channel

Then MS tunes to the carrier with strongest receiving level, and judge whether it is BCCH (by searching for FCCH)

If yes, MS tries to decode SCH and enable it synchronous with that BCCH, and reads system information on it

If MS can correctly read the system information and verify this cell belongs to the selected PLMN and C1 is larger than 0 and cell priority is normal, then MS conducts location update

Cell Selection


After passing, MS resides in that cell. Otherwise, MS will tune to second BCCH and go on with the same procedure

If it is impossible to access, MS will try to access the cell with low cell selection priority level

If still unsuccessful, MS will use PLMN allowed on SIM card to try on

If fail again, MS will go on monitoring all RF channels and find out a cell (Signal is the strongest. C1 is larger than 0. Access is not prohibited.) without considering the PLMN , and MS enters emergency call mode

Cell Selection


When MS is powered off, it will store some BCCH carrier information. When powered on, it will first search the BCCH carrier that have been stored

If MS can decode the BCCH data of this cell but cannot reside, it will check the BCCH in BA1 table of this cell

If it still cannot pass, MS will start the cell selection process without BCCH table.

Cell Selection


CBQ & CBA Value range: Yes(1) , No(0) Unit: None Content: Cell Bar Qualify. CBQ only affects the selection of

cells but is not related to cell reselection. It works with CBA to define the access priorities of cells.

Recommendation: CBQ=No CBA=Yes.

Cell Selection


CBQ CBA Cell selection priority Cell reselection priority

No Yes Normal Normal

No No Disabled Disabled

Yes Yes Low Normal

Yes No Low Normal

Cell Selection


Cell Reselection

Cell reselection for cells in same location area– If the C2 value of the target cell is higher than that of the serving cell

and last for longer than 5 seconds, a cell reselection process will be performed and the MS tunes to the new cell.

Cell reselection for cells in different location areas– If the C2 value of the target cell is higher than that of the serving cell

by at least the value of CRH and last for longer than 5 seconds, a location updating process and the cell reselection process will be performed.

Cell reselections caused by C2 have a time interval of 15 seconds

If current serving cell is prohibited, or down link fails, or C1 is less than 0 continuously for 5s, cell reselection will also be triggered.


C2=C1+CRO-TO*H(PT-T)When PT is not equal to 31:

C2=C1-CROWhen PT is equal to 31.

Function H(x)=0, when x<0; H(x)=1, when x>0 T is a timer with initial value 0. When a certain cell becomes

of one of the six neighbor cells with highest signal level, T corresponding to this cell begins to count with accuracy of one TDMA frame (about 4.62ms). When it is out of the six strongest neighbor cells, the corresponding timer is reset.

CRO is used for manually correct the cell reselection parameter C2.

Cell Reselection


PI Value range: Yes (1), No (0). Unit: None Content: Cell Reselect Parameters Indication, sent on the

broadcast channel of the cell. It is an indication of existence of “Cell Reselect Offset (CRO)”, “Temporary Offset (TO)” and “Penalty Time (PT)”.

Recommendation: Yes.

Cell Reselection


CRO Value range: 0~63, the corresponding level value: 0~126dB,

stepped every 2dB. Unit: None Content: Cell Reselect Offset. It is a parameter in C2

calculation to give a manual modification in MS cell reselection.

Recommendation: 0

Cell Reselection


TO Value range: 0~7 , the corresponding value is 0~60dB, 7

corresponds to “Infinite” Unit: None Content: Cell Reselect Temporary Offset. It is a parameter in

C2 criterion to give a temporary modification within PT time. Recommendation: 0

Cell Reselection


PT Value range: 0~31, the corresponding time is 20~620s. 31 is to

change the function direction of CRO on C2. Unit: None Content: Cell Reselect Penalty Time. Recommendation: 0

Cell Reselection


CRH Value range: 0~14 , the step size is 2 Unit: dB Content: Cell Reselection Hysteresis. It is the parameter used

when cell reselection happens between two location areas. Recommendation: 4

Cell Reselection


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presentation to warid for selection reselection

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