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Content for  TS 43.022  Word version:  16.0.0

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5  Group receive mode

5.1  General description

The purpose of the group receive mode process is for a MS to determine the most suitable cell while listening to a group or broadcast call.
There are various requirements that a cell must satisfy before an MS can perform group receive mode on it:
  1. The radio path loss between MS and BTS must be below a threshold set by the PLMN operator. This is estimated as shown in subclause 3.6. That means that the cell is suitable for transmission and reception.
  2. It should not be "barred" (see subclause 3.5.1);
  3. The NCC of the PLMN should be permitted;
The choice of a cell is based on the C2 criterion, as defined in TS 45.008. When in group receive mode on a cell the MS regularly looks to see if there is a better cell in terms of the cell reselection criterion C2, as defined in TS 45.008. C2 is determined by the MS from reception measurements on the BCCH frequency on the cell and reselection parameters relative to the cell. The reselection parameters are the same as those used in idle mode.
If there is a better cell which is suitable, the better cell is selected. (This is called "cell reselection in group receive mode").
The switching from idle or dedicated or group transmit mode to group receive mode is controlled by the Radio Interface Layer 3 protocols, see TS 44.018.
If no suitable cell can be found the MS immediately returns to idle mode by choosing a cell like releasing a dedicated channel (see TS 45.008).
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5.2  Requirements and technical solutions

5.2.1  Network provisions

For group and broadcast calls, the network provides a BA list in the SI TYPE 5, 5bis or 5ter message on the SACCH of the channel used for the group or broadcast call. The BA list indicates the BCCH carriers of the surrounding cells that MSs engaged in the call should monitor. The list shall include the cell on which it is sent. The cells in the list may belong to different PLMNs.
The network also provides the SI TYPE 6 message including an NCC permitted information element on the SACCH of the channel used for the group or broadcast call.
The network shall provide in SI TYPE 10 messages the necessary information for computation of the cell reselection criterion for all neighbour cells as given by SI TYPE 5, 5 bis and /or 5ter.
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5.2.2  Group receive mode cell monitoringWord‑p. 19

A MS in group receive mode shall perform synchronization, identification and receive signal strength measurements of the BCCH carriers in the BA(SACCH) list of BCCH frequencies which was provided by the network in the serving cell. The regularity for performing synchronization and identification of the BCCH carriers shall be performed with a regularity as specified in TS 45.008 for a MS in dedicated mode. The regularity of performing receive signal strength measurements of the BCCH carriers shall be as specified in TS 45.008 for a MS in idle mode.
As long as no BA(SACCH) list is available on the SACCH, the last received BA(BCCH) list of the current cell shall be used instead if available.
The MS does not have to monitor cells for with NCC not permitted. The NCC permitted information is provided on the SACCH of the current cell. As long as no NCC permitted information is available on the SACCH, the last received NCC permitted information on the BCCH of the current cell shall be used instead if available.
The MS must also read the parameters affecting cell reselection of the surrounding cells. These parameters are:
  • MS txpwr max cch;
  • rxlev access min;
  • cell reselect offset;
  • temporary offset;
  • penalty time;
  • location identity.
The MS receives this information in SI TYPE 10 messages on the SACCH, however if the necessary information for a neighbour cell is not available, the MS shall get the information from the BCCH of that neighbour cell.
The MS shall attempt to decode this information within 15s after there are less than six stronger suitable cells and the MS is allowed to discard up to 6 speech frames during this period. The MS shall attempt to update the information at least every five minutes.
If ciphering is not used in the call then, before selecting a cell in group receive mode the MS must have read the information which is presented in SI TYPE 1 and 3 messages transmitted in the target cell, or have received in the serving cell valid information relating to the target cell obtained from a SI TYPE 10bis, SI TYPE 10ter, or VGCS Neighbour Cell Information message. SI TYPE 3 information shall override information received in SI10.
If ciphering is used in the call then, before selecting a cell in group receive mode the MS must have read the information which is presented in SI TYPE 3 messages transmitted in the target cell and either:
  • have received in the serving cell valid information relating to the target cell obtained from a SI TYPE 10bis, SI TYPE 10ter, or VGCS Neighbour Cell Information message, or
  • have read the information which is presented in SI TYPE 1 messages transmitted in the target cell.
On this basis, the MS determines which of the cells in the list are suitable and computes their reselection criterion, and decides on its own whether one of the surrounding cells should be selected instead of the current one, as described in the next subclause.
The procedures above do not consider whether the cell supports the call or not.
To perform cell change, the MS shall at least have performed measurements on cells of the BA list received and read the corresponding BSIC.
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5.2.3  Group receive mode cell changeWord‑p. 20

Either of the following events trigger a cell change by a MS in group receive mode:
  1. The pass loss parameter C1 indicates that the path loss to the serving cell has become too high.
  2. There is a radio link time out.
  3. There is a better cell (in terms of the criterion C2) in the same LA, or a much better cell in another LA (using CRH parameter, subclause 3.4) and with NCC permitted.
After cell change, the MS either
  • leaves the group receive mode and goes to idle mode in order to establish a dedicated connection with the network to perform a location update if the cell belongs to a new LA
  • detects that the selected cell does not belong to an equivalent PLMN and therefore leaves the group receive mode and goes to idle mode;
  • detects that no NCH is present and therefore leaves the group receive mode and goes to idle mode;
  • reads the NCH but does not receive any notification message for the current group or broadcast call and therefore leaves the group receive mode and goes to idle mode;
  • reads the NCH and receives a notification message for the current group or broadcast call with the related channel position. If the channel is found, the MS changes to it and stays in group receive mode;
  • reads the NCH and receives a notification message for the current group or broadcast call without information on the related channel position. The MS leaves the group receive mode and goes to idle mode in order to establish a dedicated connection with the network to become informed on the related channel position.
  • moves directly to the group channel, if it had valid information describing the location of the group call which was received in the old cell.
During these procedures, the MS may not be able to listen to the group or broadcast call, in which case it should mute the downlink.
For all procedures, which require that the MS leaves group receive mode, the MS goes to idle mode by choosing a cell like releasing a dedicated channel (see TS 45.008).
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5.2.4  Uplink access in group calls

A MS assigned the uplink for the user to talk switches to group transmit mode.
It thus performs synchronisation, identification and measurements of the BCCH carriers according to the BA(SACCH) list as well as radio link measurements and reporting and is subject to hand over control from the network as for dedicated mode.

5a  Broadcast/multicast receive mode

5a.1  General description

The purpose of the broadcast/multicast receive mode process is for a MS to determine the most suitable cell while listening to an MBMS session. The broadcast/multicast receive mode is a substate of packet idle mode, and can only be entered by mobile stations that are GPRS attached.
If no suitable cell can be found the MS immediately returns to packet idle mode.

5a.2  Requirements and technical solutionsWord‑p. 21

5a.2.1  Network provisions

If the PBCCH is not allocated in the serving cell, the necessary information for the computation of the cell reselection criterion for all neighbour cells in the neighbour cell list shall not be read by the mobile station from the system information of the neighbour cells. Instead, this information shall be provided by the network (see TS 44.018 and/or TS 44.060).
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5a.2.2  Broadcast/multicast receive mode cell monitoring

The MS shall not read the parameters affecting cell reselection from the BCCH of the surrounding cells. Instead, this information shall be provided by the network. If the necessary information for a neighbour cell has not been received after entering broadcast/multicast receive mode, the MS shall use the the information read from the BCCH or PBCCH of that neighbour cell while in packet idle mode or, if not available, default parameters.
If the information is not available for a suitable cell within 30 seconds after it has become one of the six stronger cells, the mobile station shall read this information from the BCCH of the neighbouring cell. The MS is allowed to interrupt the reception of the MBMS session during this period. The MS shall not attempt to perform periodic updates of this information while in broadcast/multicast receive mode.
The MS determines which of the cells in the list are suitable and computes their reselection criterion, and decides on its own whether one of the surrounding cells should be selected instead of the current one. In computing the cell reselection criterion, the mobile station shall obey the intra-RAT and inter-RAT cell reselection algorithms defined for the GMM Ready state (see TS 45.008).
To perform cell change, the MS shall at least have performed measurements on cells of the BA(GPRS) list and read the corresponding BSIC.
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5a.2.3  Broadcast/multicast receive mode cell change

Either of the following events trigger a cell change by a MS in broadcast/multicast receive mode:
  1. The pass loss parameter C1 indicates that the path loss to the serving cell has become too high.
  2. There is a better cell (in terms of the criterion C2 or of the GPRS cell reselection criterion) in the same LA/RA, or a much better cell in another LA/RA and with NCC permitted.
After cell change, the MS either
  • leaves the broadcast/multicast receive mode and goes to packet idle mode in order to establish a dedicated connection with the network to perform a location update or routing area update if the cell belongs to a new LA/RA;
  • detects that the selected cell does not belong to the MBMS Service Area and therefore leaves the broadcast/multicast receive mode and goes to packet idle mode;
  • detects that the selected cell does not belong to an equivalent PLMN and therefore leaves the broadcast/multicast receive mode and goes to packet idle mode;
During these procedures, the MS may not be able to listen to the broadcast or multicast session.
If the mobile station has received information about the location of the p-t-m bearer in the cell that it has reselected to, the mobile station can resume the reception of the MBMS session without the need to complete the acquisition of the system information.
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6  Tables and figuresWord‑p. 22

(not reproduced yet)
Figure 3: Cell Selection State diagram
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In any state, a new PLMN selection causes an exit to 1 if a valid SIM is present in the MS
Go to 3 if no valid SIM in MS

$  Change HistoryWord‑p. 23


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