1) PLMN Selection An MS will need to make a PLMN selection only incase: a. MS is powered ON for the 1st time i.e. No PLMN was registered on before (No Information on MCC&MNC is stored on SIM) b. Old PLMN is not available any more. PLMN Selection Criterion 1) 2) 3) 4)
Automatic PLMN Selection Mode steps: Home PLMN. Each PLMN stored on the SIM card in priority order. Other PLMNs have Signal Strength > -85 dBm in random order. All other PLMNs in order of decreasing Signal Strength.
- Manual PLMN Selection Mode: 1) Home PLMN. 2) All other available PLMNs and give the user the choice to select.
2) Cell Selection
The Cell Selection algorithm tries to find the most suitable cell in the selected PLMN and make the MS camp on. Cell Selection is done by the MS itself.
Scan RF Frequencies one by one and calculates the Average received signal strength over 3 5 seconds Tune to the RF Frequency with the highest average received signal strength
Check if the chosen frequency is a BCCH carrier frequency or not
Tune to the next higher frequency that wasn’t tried before
Yes MS will synchronize to the BCCH frequency and read system information (LAI,BA List,…etc) Check if PLMN is desired or not Yes Check if Cell is barred or not No Check if C1 > 0 or not
No Yes No
Camp on the Cell
Scanning RF Frequencies may occur in 2 ways: 1) Normal Scanning: Scan all Frequencies in the band ex:124 freq. in GSM900 Band.
2) Stored List Scanning: Scan the Frequencies in the Idle BA list (BCCH Allocation) stored on the MS SIM before being switched off. (BA list can have maximum 32 frequencies) C1 is called “Cell Selection Quantity” It is calculated at the MS based on the below equation:
C1 = (Received SS – ACCMIN) – max (CCHPWR-P,0) - ACCMIN Minimum allowed DL received SS at the MS in order to access the system - CCHPWR Maximum allowed transmitting power by the MS in the UL. - P Maximum output power of the MS according to its class. N.B: 1.
ACCMIN and CCHPWR are cell parameters sent to the MS at the BCCH channel.
If CCHPWR > P then C1 will decrease and so the Received SS should be large enough to keep C1 > 0 (May be this cell is not designed of this MS class)
3. ACCMIN, CCHPWR, P are all measured in dBm, where C1&C2 are measured in dBs
3) Cell Reselection After a cell has been selected, the MS will start the cell reselection measurements to know if it is better to stay on the current cell or to camp on another cell.
Cell reselection measurements summary: BSIC
BCCH Data (System Information)
Every 30 Seconds
Six Strongest Neighbors
Every 30 Seconds
Every 5 Minutes
When will Cell Reselection occur ?!!! 1) Serving Cell became barred ( CB = YES ) 2) C1 serving cell falls below zero for more than 5 seconds. 3) MS tried to access the network through this cell unsuccessfully for the allowed no. of times defined by the parameter MAXRET 4) C2 neighbor cell ( one of the six strongest neighbors) became greater than C2 serving cell
for more than 5 seconds.
5) MS detects Downlink Signaling Failure.
C2 is called “Cell Reselection Quantity” C2 = C1 + CRO – TO * H( PT – T ) C2 = C1 – CRO