PT(s)

PT(s)

The Cell Reselect Penalty Time (PT for short) is used to ensure the safety and validity of cell reselection because it helps to avoid frequent cell reselection. For details, see GSM Rec. 05.08 and 04.08.

This parameter applies to only GSM Phase II MSs.

[0,31]

0

Seconds

-

None

None

None

TO

None

Parameters About Radio Resources

Generally, upon completion of cell selection, the MS camps on the selected cell and starts to measure the receive levels of the BCCH carriers for the six strongest non-serving cells. In addition, the MS obtains various system information and control messages from the six best neighbor cells.

If certain conditions are met, an MS leaves the serving cell and camps on another cell. This procedure is called cell reselection. The required conditions include many factors, such as the cell priority and whether accessing the cell is allowed. Signal quality is an important requirement. In other words, cell reselection is initiated when the signal strength of a neighbor cell is better than that in the serving cell. The reselection criterion C2 indicates the channel quality standard. The value of C2 is defined by the following formula:

If PENALTY_TIME is not equal to 11111, C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET x H(PENALTY_TIME - T)

Here,

if X < 0, H (x) = 0; if X >= 0, H (x) = 1.

T is a timer and the initial value of timer T is 0. If a cell is recorded in the neighbor cell list because the receive level of the cell is among the top six, timer T of the cell is started. The precision of T is calculated by one TDMA frame (about 4.62 ms). If a cell is removed from the top-six neighbor cell list, timer T of the cell is reset.

After a cell reselection is complete, the original serving cell becomes a neighbor cell, and timer T of the original serving cell is set to PT. If PT minus T is less than 0, that is, C2 = C1 + CRO, no penalty is performed on the original serving cell.

If PT is 11111, C2 = C1-CRO.

CRO is used to manually modify C2.

The function of TEMPORARY_OFFSET: during the period between the time timer T is started and the time timer T reaches PENALTY_TIME, a penalty is performed on C2 of the original serving cell so that the MS is not reselected to the original serving cell.

PT specifies the period during which TO affects C2. The value of 11111 is reserved for changing the effect of CRO on C2.

CRO, TO, and PT are parameters related to cell reselection. If PI is 1, these parameters are broadcast over the BCCH. If PI is 0, these parameters are 0, so C2 equals C1.

If the MS finds that the value of C2 for a neighbor cell (being in the same location area as the serving cell) exceeds the value of C2 for the serving cell for a period of 5 seconds, the MS initiates a cell reselection to camp on the neighbor cell. If the MS finds that the value of C2 for a neighbor cell (being in a different location area) exceeds the value of C2 for the serving cell by at least CELL_RESELECT_HYSTERESIS dB as defined by the BCCH data from the current serving cell, for a period of 5 seconds, the MS initiates a cell reselection to camp on the neighbor cell. In addition, at least an interval of 15s is required for C2-based cell reselection to avoid frequent cell reselection.

Signal strength-based cell reselection is implemented based on C2. C2, a parameter based on C1, takes into consideration manual adjustments to preferably select some cells or reject some cells, thus achieving better traffic balance.