3.9 Power Efficient Operation (PEO)

3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 16TS

3.9.1 General

Power Efficient Operation (PEO) is an optional feature used by a MS in a cell that supports PEO to reduce its power consumption through the use of relaxed mobility related requirements (see 3GPP TS 43.064 [109]) and a power saving feature while in idle mode. The power saving feature consists of either extended DRX (eDRX – see 3GPP TS 45.002 [32]) or Power Saving Mode (PSM – see 3GPP TS 23.060 [74]), and a PEO capable mobile station shall support at least one. A cell indicates its support of PEO by including the PEO_DSC field in the SI13 Rest Octets IE.

A PEO capable mobile station camping in a cell that supports PEO performs NAS signalling to negotiate the use of a power saving feature (i.e. eDRX or PSM – see 3GPP TS 23.060 [74]). A mobile station that has enabled PEO (see 3GPP TS 43.064 [109]) shall only transmit an EGPRS PACKET CHANNEL REQUEST message indicating ‘PEO One Phase Access Request’ (see Table 3.5.2.1.2.2 and 3GPP TS 44.060 [76]) when performing system access. A BSS that receives this message shall send a response that only assigns the MS packet resources in the frequency band corresponding to CCCH on which the EGPRS PACKET CHANNEL REQUEST message was received.

When PEO is enabled it shall be disabled in case the MS enters a cell that does not support PEO or the MS decides to disable PEO for any reason. When PEO is disabled the MS shall continue to use eDRX or PSM (whichever is enabled) as long as it remains in the same Routing Area it was in when it performed NAS signalling to enable eDRX/PSM (i.e. regardless of whether or not the serving cell indicates PEO is enabled). When PEO is disabled the use of relaxed mobility related requirements and the use of the EGPRS PACKET CHANNEL REQUEST message indicating ‘PEO One Phase Access Request’ shall be disabled. Upon reselecting to a cell in a new Routing Area a mobile station that has enabled eDRX/PSM shall consider it as disabled (i.e. the MS must perform additional NAS signalling in the new Routing Area to enable eDRX/PSM).

3.9.2 PEO Power Saving States

A MS that has enabled PEO where eDRX is used supports eDRX paging cycles that can range from multiple seconds to about 52 minutes (see 3GPP TS 45.002 [32]). In this case the mobile station supports reachability while in packet idle mode as follows:

– The mobile station uses the lowest eDRX cycle while the Ready timer (see 3GPP TS 24.008 [79]) is running.

– Upon expiration of the Ready timer or waking up and determining it has not been paged using its nominal paging group the mobile station re-enters the eDRX based power saving state for the time remaining until its next paging occasion.

– A BSS that receives a PAGING-PS PDU containing eDRX information uses it to determine when the corresponding MS is reachable (see 3GPP TS 48.018 [107]).

A MS that has enabled PEO where PSM with eDRX is used supports reachability while in packet idle mode as follows:

– While in packet idle mode the mobile station uses the lowest eDRX cycle while the Ready timer is running.

– While in packet idle mode the mobile station uses the negotiated eDRX cycle while the Active timer is running and a PAGING-PS PDU received by the BSS for that mobile station shall contain eDRX information indicating the negotiated eDRX cycle.

– The mobile station enters the PSM based power saving state upon expiration of the Ready timer if the Active timer is not used or upon expiration of the Active timer if a non-zero Active timer is used.

– A BSS that receives a PAGING-PS PDU containing eDRX information will use it to determine when the corresponding MS is reachable (see 3GPP TS 48.018 [107]).

A MS that has enabled PEO where PSM without eDRX is used supports reachability while in packet idle mode as follows:

– While in packet idle mode the mobile station uses the broadcasted DRX cycle while the Ready timer is running. A DL-UNITDATA PDU received by the BSS for a mobile station that has enabled PSM without eDRX shall contain DRX information (if available at the SGSN).

– While in packet idle mode the mobile station uses the broadcasted DRX cycle while the Active timer is running and a PAGING-PS PDU received by the BSS for that mobile station shall contain DRX information (if available at the SGSN).

– The mobile station enters the PSM based power saving state upon expiration of the Ready timer if the Active timer is not used or upon expiration of the Active timer if a non-zero Active timer is used.

– A BSS that receives a PAGING-PS PDU containing DRX information will use it to determine when the corresponding MS is reachable (see 3GPP TS 48.018 [107]).

3.9.3 Extended DRX (eDRX)

A PEO capable mobile station in a cell that supports PEO that wants to use eDRX selects an eDRX cycle value from the set of available eDRX cycles (see 3GPP TS 45.002 [32]) and indicates it as its preferred eDRX cycle length when registering with the network (see 3GPP TS 24.008 [79]). A mobile station may negotiate the use of both eDRX and PSM when registering with the network in which case its power saving feature is considered to be PSM and the mobile station only makes use of eDRX based reachability when the Active timer is running (see 3GPP TS 23.060 [74] and 3GPP TS 23.682 [108]). The mobile station selects a nominal paging group determined using IMSI and its eDRX cycle and monitors pages thereon (see 3GPP TS 45.002 [32]).

3.9.4 BCCH Acquisition

A MS that has enabled PEO shall read the PEO_BCCH_CHANGE_MARK field when performing the packet access procedure (see sub-clause 3.5.2.1.2). If a change of PEO_BCCH_CHANGE_MARK is detected it shall first read SI13 before proceeding with the packet access procedure. If no change is detected and the time elapsed since it last read SI13 exceeds 24 hours it should read SI13 before proceeding with the packet access procedure.

To help avoid the case where a change in PEO_BCCH_CHANGE_MARK is detected when a MS reads its paging subchannel it may acquire an AGCH/PCH message (for the purpose of checking PEO_BCCH_CHANGE_MARK and acquiring the RCC field) before the next instance of its paging subchannel. It shall use the 6 bit BSIC from the most recently read SCH and the acquired RCC field to establish a BSIC. If the BSIC does not match the BSIC value decoded upon first entering the serving cell (see 3GPP TS 45.008) or if the RCC and PEO_BCCH_CHANGE_MARK fields are not included in the message it shall consider PEO as disabled and attempt cell re-selection.

The network indicates a change to the PEO_BCCH_CHANGE_MARK field within an IMMEDIATE ASSIGNMENT message using the IA Rest Octets IE (see sub-clause 10.5.2.16) or within an IMMEDIATE ASSIGNMENT REJECT or an IMMEDIATE ASSIGNMENT EXTENDED or an IMMEDIATE PACKET ASSIGNMENT message using the Feature Indicator IE (see sub-clause 10.5.2.76) or within a PAGING REQUEST TYPE 1 message using the P1 Rest Octets IE (see sub-clause 10.5.2.23) or within a PAGING REQUEST TYPE 2 message using the P2 Rest Octets IE (see sub-clause 10.5.2.24) or within a PAGING REQUEST TYPE 3 message using the P3 Rest Octets IE (see sub-clause 10.5.2.25).

Considering the time spanned by the longest eDRX cycle, changes to the PEO_BCCH_CHANGE_MARK field should not occur more frequently than 3 times within a 24 hour time period.

If a mobile station determines that more than 3 changes to the PEO_BCCH_CHANGE_MARK field have occurred within a 24 hour time period it shall disable PEO_BCCH_CHANGE_MARK monitoring for 1 hour (i.e. it shall ignore changes to the PEO_BCCH_CHANGE_MARK field when performing the packet access procedure for 1 hour), re-read system information and then resume PEO_BCCH_CHANGE_MARK monitoring. If it then determines that more than 3 changes to the PEO_BCCH_CHANGE_MARK field occur in the next hour it shall disable PEO_BCCH_CHANGE_MARK monitoring for 24 hours (i.e. it shall ignore changes to the PEO_BCCH_CHANGE_MARK field when performing the packet access procedure for 24 hours), re-read system information and then resume PEO_BCCH_CHANGE_MARK monitoring.

A mobile station in PEO may support deferred system information acquisition (see subclause 3.9.4.1).

3.9.4.1 Deferred System Information Acquisition for PEO

A mobile station that supports deferred system information acquisition for PEO, shall read BCCH after cell selection and determine from SI13 message (see subclause 9.1.43a), if the serving cell provides the PEO Idle Mode Mobility (IMM) Cell Group Definition IE, by this indicating the use of common cell parameters across a group of cells in order to potentially defer reading of BCCH data after performing a cell reselection to one of these non-serving cells.

– If not provided, the MS in idle mode shall apply legacy operation for BCCH acquisition until it reselects to a cell which provides the PEO Idle Mode Mobility (IMM) Cell Group Definition IE in SI13.

– If provided, the MS in idle mode shall determine, based on the content of the PEO IMM Cell Group Definition IE in SI13 as well as common and specific cell parameters, broadcasted in SI2 and SI3 messages, the cell parameters related to cell selection / reselection, cell barring, RA assignment and paging reception, valid for all cells belonging to the same PEO IMM cell group as its serving cell.

Prior to receiving any instance of its paging subchannel, the MS supporting deferred system information acquisition for PEO shall identify, after evaluation of the PEO_BCCH_CHANGE_MARK field, as specified in subclause 3.9.4 and as specified below for the case of activation / deactivation of deferred system information acquisition for PEO, if the serving cell has modified the PEO IMM Cell Group Definition IE, by reading an SI 13 message and / or AGCH/PCH message in order to determine the PEO IMM Cell Group Identifier and the PEO IMM Change Mark. If either of both values is different to the previously stored one, the MS is obliged to read SI 13 to obtain the latest sent PEO IMM Cell Group Definition IE.

In case PEO IMM Cell Group Definition IE is provided by the current serving cell, the MS shall use the related information when triggering measurements for cell reselection (i.e. BCCH frequencies, specific BSIC’s, PEO IMM Cell Group Identifier and PEO IMM Change Mark fields) and shall determine for non-serving cells, for which BSIC identification is required (see 3GPP TS 45.008 [34]) whether the non-serving cell supports broadcast of PEO IMM Cell Group Definition IE.. To this purpose it may acquire an SI13 message and / or an AGCH/PCH message (for the purpose of reading the RCC field, see subclause 3.9.4) which both contain the PEO IMM Cell Group Details IE (i.e. PEO IMM Cell Group Identifier and PEO IMM Change Mark fields) indicating whether the non-serving cell supports broadcast of PEO IMM Cell Group Definition IE and whether it is part of the same PEO IMM cell group as the serving cell. If the mobile station detects that the non-serving cell has the same values of the PEO IMM Cell Group Identifier and the PEO IMM Change Mark fields as its serving cell, it shall apply the common and specific cell parameters belonging to the PEO IMM cell group of its serving cell for this cell when evaluating if cell reselection is required and shall omit reading of the BCCH of this cell, else it shall read BCCH of this non-serving cell except cell reselection parameters are broadcasted for this non-serving cell in SI2n, i.e. the serving cell indicates SI2n support in SI13. If the MS detects that the PEO IMM Change Mark field in the non-serving cell, which belongs to the same PEO IMM cell group as the serving cell, has been incremented by 1 or more compared to the last one obtained in the serving cell, it immediately stops measuring non-serving cells and starts acquisition of the complete set of System Information messages in the serving cell. The MS shall use the common and specific cell parameters for all cells belonging to the same PEO IMM cell group when evaluating if cell reselection is required and identifying the target cell for reselection. If the MS has reselected to a cell that is part of the same PEO IMM cell group as its previous serving cell, it shall monitor in the new serving cell, i.e. the cell it has reselected to, its paging channel without reading the BCCH in this cell. Only in case

– a matching page is received, that requires to send a paging response, or

– the MS needs to perform an uplink data transmission, or

– a configurable timeout, i.e. Timeout Read Complete SI, since the last reading of the complete set of System Information messages in a different than the current serving cell is expired,

the MS is required to immediately read the complete set of System Information messages in the current serving cell.

The network may choose to deactivate deferred SI acquisition for PEO in network deployments for which System Information needs to be reconfigured rather frequently or for which adjacent cells’ idle mode mobility parameters differ too much. In this case the support of deferred SI acquisition for PEO is discontinued by removing the PEO IMM Cell Group Definition IE from SI13 and PEO IMM Cell Group Details IE from AGCH/PCH messages.

Otherwise the network may choose to activate deferred SI acquisition for PEO in specific cells. In this case the support of deferred SI acquisition in EC operation is indicated by addition of the PEO IMM Cell Group Definition IE to SI 13 and PEO IMM Cell Group Details IE to AGCH/PCH messages.

The requirement for reading PEO_BCCH_CHANGE_MARK in the serving cell, as specified in subclause 3.9.4, applies also for deferred SI acquisition for PEO. In addition, in case of activation or deactivation of deferred SI acquisition for PEO, the PEO_BCCH_CHANGE_MARK field shall be incremented in the respective cells whilst in case of modification (reconfiguration) of the PEO IMM Cell Group Definition IE it shall not be incremented (rather the PEO IMM Change Mark field is incremented).