Cell
Selection Procedure
• First MS
powers-on
• MS starts
measuring received power level from all cells in range
• MS calculates
average power level received from each cell:
• Stored in
RXLEV(n) parameter
• MS calculates
C1 parameter for each cell based on RXLEV(n)
• Mobile
compares cells which give a positive value of C1 and ‘camps-on’ to the cell
with the highest C1 value.
On switch-on,
an MS periodically measures the received power level on each of the BCCH
frequencies of all cells within range. From these periodic measurements the MS
calculates the mean received level value from each cell, stored in the
parameter RXLEV (n) where n=neighboring cell number.
Cell
Re-selection – GSM Phase 1 Mobiles
For GSM Phase 1
mobiles, cell reselection is achieved by comparing current cell C1 with neighboring
C1 cell measurements:
• Between cells
within a Location Area:
C1 (new) > C1 (old) (for
more than 5 seconds)
• Between cells
on a Location Area boundary:
C1 (new) > C1 (old) + OFFSET (for
more than 5 seconds)
Cell
Re-selection – GSM Phase 2 Mobiles
• GSM Phase 2
introduced a separate cell re-selection parameter, C2
• Intended to:
• Prevent
multiple handovers for fast-moving mobiles
• Ensure MS
camps on to cell with greatest chance of successful communications
• The C2
calculated is:
C2 = C1 + OFFSET – (TEMPORARY_OFFSET x H(PENALTY_TIME –T)