6.5.6 Cell Re-selection

03.643GPPGeneral Packet Radio Service (GPRS)Overall description of the GPRS radio interfaceStage 2TS

NOTE: The text in this subclause is informative. The normative text is in GSM 03.22 and GSM 05.08 [15]. Where there is a conflict between these descriptions, the normative text has precedence.

In GPRS Packet Idle and Packet Transfer modes, cell re-selection is performed by the MS, except for a class A MS (see GSM 02.60 [2] ) while in dedicated mode in which case the cell is determined by the network according to the handover procedures.

The new cell re-selection criteria C31 and C32 are provided as a complement to the current GSM cell re-selection criteria. This provides a more general tool to make cell planning for GPRS as similar to existing planning in GSM as possible.C31 is a signal strength criterion used to decide whether prioritised cell re-selection shall be used. For cells that fulfil the C31 criterion, the cell with highest priority class shall be selected. If more than one cell has the highest priority, the one of those with the highest C32 value shall be selected. If no cell fulfils the C31 criterion, the one among all cells with the highest C32 value shall be selected.

C32 is an improvement of C2. It applies an individual offset and hysteresis value to each pair of cells, as well as the same temporary offsets as for C2. Additional hysteresis values apply for a cell re-selection that requires cell or routing area update.

Cell re-selection procedure apply to the MSs attached to GPRS if a PBCCH exists in the serving cell. If the PBCCH is not allocated, then the MS shall perform cell re-selection according to the C2 criteria.

In addition, the network may control the cell re-selection as described in subclause Measurements for Cell Re-selection

The MS shall measure the received RF signal strength on the BCCH frequencies of the serving cell and the neighbour cells as indicated in the BA-GPRS list, and calculate the received level average (RLA) for each frequency, as specified in GSM 05.08 [15]. In addition the MS shall verify the BSIC of the cells. Only channels with the same BSIC as broadcast together with BA-GPRS on PBCCH shall be considered for re-selection.

A COMPACT capable MS shall in addition perform the above tasks for any CPBCCH, either transmitted in the serving cell or indicated, by way of frequency and time group in the BA-GPRS list.

Any cell having a CPBCCH indicated in the BA-GPRS list shall be time synchronized to that cell, as specified in GSM 05.10 [16].

When the number of downlink PDCHs assigned to certain types of multislot MS (see GSM 05.02 [11] , annex B) does not allow them to perform measurements within the TDMA frame, the network shall provide measurement windows to ensure that the MS can perform a required number of measurements. The network shall provide periods of inactivity during a fixed allocation to allow the MS to make adjacent cell power measurements and BSIC detection. Broadcast Information

The PBCCH broadcasts GPRS specific cell re-selection parameters for serving and neighbour cells, including the BA (GPRS) list. A BA (GPRS) identifies the neighbour cells, including BSIC, that shall be considered for GPRS cell (re-selection (not necessary the same as for GSM in Idle or circuit switched mode)). Optional measurement reports and network controlled cell re-selection

It shall be possible for the network to order the mobile stations to send measurement reports to the network and to suspend its normal cell re-selection, and instead to accept decisions from the network. This applies to both Packet idle mode and Packet transfer mode.

The degree to which the mobile station shall resign its radio network control shall be variable, and be ordered in detail by the parameter NETWORK_CONTROL_ORDER.

Two sets of parameters are broadcast on PBCCH and are valid in Packet transfer and Packet idle modes respectively. NETWORK_CONTROL_ORDER can also be sent individually to an MS on PACCH, in which case it overrides the broadcast parameter.

Additionally, the network may request extended measurement reports from the MS and the reporting shall be maintained in packet idle mode. The reports may include interference measurements (see subclause Measurement reports shall be sent individually from each MS as RLC transmissions.

When a class A mobile station is simultaneously involved in a circuit switched service and in a GPRS transfer, the network controlled cell re-selection procedures (NC1 or NC2 modes of operation) should not be used. In this case, handover for the circuit switched service has precedence over GPRS network controlled cell re-selection, and the MS shall stop sending measurement reports and ignore cell change orders.