Cell Selection & Reselection
When the mobile (MS) is turned on, it begun to measure all received power level from all cells within range. Then the MS calculate the average power level received from each cell and stored it in RXLEV parameters. Then the C1 parameter is calculated fo
r each cell based on RXLEV parameter. MS compare the cell which gives positive C1 values and hold on to the cell which gives highest positive C1 value.
Cell reselection is achieved by comparing current cell C1 value with neighboring cell C1 value
Based on the calculated C1 value, the MS decide which cell to connect. This connection process called as “camps-on” to that cell.
Once camps-on the MS to cell, in idle mode the MS must measure the received power level periodically from each BCCH frequencies of each cell and stored them for calculation of C1 value. Any C1 values below 0 are ignored and keep best six neighboring cells.
In order to optimize cell reselection, additional cell reselection parameters can be optionally broadcast on the BCCH of each cell. The cell reselection process can optionally employ a parameter C2.
Path Loss Criterion (C1)
C1 = (RXLEV – RXLEV_ACCESS_MIN) – (MS_TXPWR_MAX_CCH – P)
Reselection Criterion (C2)
C2 = C1 + CELL_RESELECT_OFFSET – (TEMPORARY_OFFSET x H (PENELTY_TIME - T)
- Cell Reselection Offset - This optional parameter is a positive or negative offset applied to each cell to encourage or discourage MSs to reselect that cell.
- Penalty Time - When the MS places the cell on the list of the strongest carriers, it starts a timer which expires after the PENALTY_TIME. This timer will be reset when the cell is taken off the list. For the duration of this timer, C2 is given a negative offset. This will tend to prevent fast moving MSs from selecting the cell
- Temporary Offset - This is the amount of the negative offset described in the ‘Penalty Time’ above. An infinite value can be applied, but a number of finite values are also possible.
