3.10 EC Operation

3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

3.10.1 General

EC-GSM-IoT is an optional feature that allows a MS to use relaxed mobility requirements, extended coverage and optionally, a power saving feature while in packet idle mode. The power saving feature consists of either extended DRX (eDRX – see 3GPP TS 23.060) or Power Saving Mode (PSM – see 3GPP TS 23.060). A cell indicates it supports EC-GSM-IoT operation by the presence of the EC-SCH (see 3GPP TS 45.002). The relaxed mobility related requirements supported by a MS that has enabled EC operation are described in 3GPP TS 43.064 [109].

An EC-GSM-IoT capable mobile station in a cell that supports EC-GSM-IoT operation may perform NAS signalling to negotiate the use of a power saving feature. An EC-GSM-IoT capable mobile station in a cell that supports EC-GSM-IoT operation attempts packet access by:

– transmitting an EC PACKET CHANNEL REQUEST message using the RACH (see sub-clause 3.5.2.1.2); or

– transmitting an EC PACKET CHANNEL REQUEST message using the 1TS EC-RACH Mapping method (see sub-clause 3.5.2.1.2a); or

– transmitting an EC PACKET CHANNEL REQUEST message using the 2TS EC-RACH Mapping method (see sub-clause 3.5.2.1.2a).

When sending a response to an EC PACKET CHANNEL REQUEST message a BSS shall only assign the MS packet resources in the frequency band corresponding to CCCH or EC-CCCH on which the EC PACKET CHANNEL REQUEST message was received.

When EC operation is enabled it shall be disabled in case the MS enters a cell that does not support EC operation or the MS decides to disable EC operation for any reason. When EC operation is disabled then the MS shall continue to use eDRX or PSM (if either one is enabled) as long as it remains in the same Routing Area it was in when it performed NAS signalling to enable eDRX/PSM. When EC operation is disabled the use of relaxed mobility related requirements and the use of the EC PACKET CHANNEL REQUEST message 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).

3.10.2 Power Saving States

A MS that has enabled EC operation where eDRX is used supports reachability while in packet idle mode when the Ready timer is running as described in sub-clause 3.9.2 for the case of a mobile station that uses PEO with eDRX.

A MS that has enabled EC operation where PSM with eDRX is used supports reachability while in packet idle mode when the Ready timer or Active timer is running as described in sub-clause 3.9.2 for the case of a mobile station that uses PEO with PSM and eDRX.

A MS that has enabled EC operation 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 lowest eDRX 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 eDRX information indicating the lowest eDRX cycle.

– While in packet idle mode the mobile station uses the lowest eDRX cycle while the Active timer is running. A PAGING-PS PDU received by the BSS for that mobile station shall not contain eDRX information.

– 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 EC operation where neither eDRX nor PSM is used supports reachability while in packet idle mode when the Ready timer is running as follows:

– The mobile station uses the lowest eDRX cycle while the Ready timer (see 3GPP TS 24.008 [79]) is running. A BSS that receives a DL-UNITDATA PDU (see 3GPP TS 48.018 [107]) containing coverage class information but no eDRX information shall always use the lowest eDRX cycle.

– Upon expiration of the Ready timer the mobile station shall continue using the lowest eDRX cycle.

3.10.3 Extended DRX (eDRX)

An EC-GSM-IoT capable mobile station in a cell that supports EC-GSM-IoT enables eDRX by selecting an eDRX cycle value from the set of available eDRX cycles (see 3GPP TS 45.002 [32]) and indicating it as its preferred eDRX cycle length when registering with the network (see 3GPP TS 24.008 [79]). If an eDRX value is successfully negotiated with the network, the mobile station shall use it when monitoring the paging channel of any cell within the Routing Area where the eDRX value was negotiated.The mobile station selects a nominal paging group on the EC-PCH of its selected EC-CCCH (see 3GPP TS 45.002 [32]) by taking into account its IMSI, its negotiated eDRX cycle and its selected downlink coverage class and monitors pages thereon (see 3GPP TS 45.002 [32]).

– A MS that has enabled EC operation where eDRX is used supports reachability while in packet idle mode as described in sub-clause 3.5.1a when in packet idle mode and the Ready timer is not running.

– A MS that has enabled EC operation where PSM is used supports reachability while in packet idle mode as described in sub-clause 3.5.1a when in packet idle mode and the Active timer is running.

3.10.4 EC-BCCH Acquisition

A MS that has enabled EC operation shall have read a complete set of EC SYSTEM INFORMATION messages set no longer than 24 hours prior to attempting packet access. In addition, if the mobile station detects a change to the EC-BCCH CHANGE MARK field when reading the EC-SCH INFORMATION message (see sub-clause 9.1.30c) it shall subsequently read one or more EC SYSTEM INFORMATION messages as needed before attempting packet access (see sub-clause 3.5.2a). The EC SI reading can occur immediately after the EC-SCH INFORMATION reading.

To help avoid the case where a MS detects a change in EC-BCCH CHANGE MARK shortly before any instance of its paging subchannel it may acquire the EC-SCH INFORMATION message sufficiently in advance of each instance of its paging subchannel (see 3GPP TS45.002).

Each EC SYSTEM INFORMATION message instance includes an EC SI_CHANGE_MARK bitmap used by a mobile station to determine which specific EC SYSTEM INFORMATION message(s) has changed after it first detects a change to the EC-BCCH CHANGE MARK field in the EC-SCH INFORMATION message. A mobile station makes use of this bitmap as follows:

– Upon detecting a change to the EC-BCCH CHANGE MARK field (sent using the EC-SCH INFORMATION message) a mobile station reads any EC SYSTEM INFORMATION message to acquire the EC SI_CHANGE_MARK bitmap.

– If the Overflow Control Bit therein (see sub-clause 9.1.43p) has not changed since the last time the corresponding bitmap was acquired the mobile station determines which of the message specific bits (i.e. EC SI 1, EC SI 2, EC SI 3 and EC SI 4 bits – see sub-clause 9.1.43p) in the EC SI_CHANGE_MARK bitmap have changed since the last time the bitmap was acquired.

– The mobile station then reads the subset of EC SYSTEM INFORMATION messages for which a change has been indicated by the message specific bits of the EC SI_CHANGE_MARK bitmap.

– If the Overflow Control Bit has changed since the last time the mobile station acquired the EC SI_CHANGE_MARK bitmap from any EC SYSTEM INFORMATION message it shall read all EC SYSTEM INFORMATION messages.

Changes to the EC-BCCH CHANGE MARK field should not occur more frequently than 7 times per 24 hours.

A network that follows the principle of not changing the EC-BCCH CHANGE MARK field more frequently than 7 times per 24 hours should manage changes to EC SYSTEM INFORMATION messages as follows:

– After using a given EC-BCCH_CHANGE_MARK field code point the network should not re-use the same code point for at least 24 hours.

– If the time between two successive changes for any given EC SYSTEM INFORMATION message is less than 24 hours the network shall change (toggle) the Overflow Control Bit (see sub-clause 9.1.43p).

– After changing the Overflow Control Bit the network shall not change it again for 24 hours regardless of how many additional changes to EC SYSTEM INFORMATION messages are made in that time period (i.e. once an overflow condition is indicated using the Overflow Control Bit it shall continue to be indicated for 24 hours).

If a mobile station determines that more than 7 changes to the EC-BCCH CHANGE MARK field have occurred within a 24 hour time period or that less than 24 hours have expired since the last time the Overflow Control Bit was changed in the serving cell it shall disable EC-BCCH CHANGE MARK monitoring for 1 hour (i.e. it shall ignore changes to the EC-BCCH CHANGE MARK field when performing the packet access procedure for 1 hour), re-read system information and then resume EC-BCCH CHANGE MARK monitoring. If it then determines that more than 7 changes to the EC-BCCH CHANGE MARK field occur in the next hour or that the Overflow Control Bit changes again in the next hour it shall disable EC-BCCH CHANGE MARK monitoring for 24 hours (i.e. it shall ignore changes to the EC BCCH-CHANGE MARK field when performing the packet access procedure for 24 hours), re-read system information and then resume EC-BCCH CHANGE MARK monitoring.

A mobile station that supports deferred system information acquisition in EC operation, shall read EC-BCCH after cell selection and determine from EC SI type 2 message (see subclause 9.1.43q), if the serving cell provides the Idle Mode Mobility (IMM) Cell Group Definition, by this indicating the use of common cell parameters across a group of cells in order to potentially defer reading of EC-BCCH data after performing a cell reselection to one of these cells.

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

– If provided, the MS shall determine, based on the content of the IMM Cell Group Definition as well as common and specific cell parameters, broadcasted in EC SI type 2 and EC SI type 3 messages, the cell parameters related to cell selection / reselection, cell barring, downlink coverage class selection in idle mode, RA assignment and paging reception, valid for all cells belonging to the same IMM Cell Group as its serving cell.

Prior to receiving any instance of its paging subchannel, the MS supporting deferred system information acquisition in EC operation shall identify, after evaluation of the EC-BCCH CHANGE MARK field as specified above, if the current serving cell provides the IMM Cell Group Definition, by reading two consecutive EC-SCH Information messages, starting in the 51-multiframe M with M mod 8 = 0, in order to determine the IMM Cell Group Identifier and the IMM Change Mark. If either of both values is different to the previously stored one, the MS is obliged to read EC SI 2 to either obtain the latest sent IMM Cell Group Definition, if its provision is indicated by the cell, or, if its provision is not indicated by the cell, to obtain cell parameters related to legacy operation for EC-BCCH acquisition.

In case IMM Cell Group Definition is provided by the current serving cell, the MS in idle mode shall use the related information when triggering measurements for cell reselection (i.e. BCCH frequencies, specific BSIC’s, IMM Cell Group Identifier and IMM Change Mark) and shall identify, by reading two consecutive EC-SCH Information messages in the non-serving cell, starting in the 51-multiframe M with M mod 8 = 0, whether the non-serving cell supports broadcast of IMM Cell Group Definition (see subclause 9.1.30c) and if yes, whether a non-serving cell is part of the same IMM Cell Group as the current serving cell. If the mobile station detects that the non-serving cell is part of the same IMM Cell Group and the IMM Change Mark has the same value as in the serving cell, it shall apply the common and specific cell parameters belonging to the IMM Cell Group for this cell when evaluating if cell reselection is required and shall omit reading of the EC-BCCH of this cell, else it shall read EC-BCCH of this non-serving cell in case no cell reselection parameters are broadcasted for this cell in EC SI type 3 message. If the MS detects that the IMM Change Mark in the non-serving cell, belonging to the same IMM Cell Group as the current 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 to acquire a full set of EC System Information messages in the serving cell.

The MS shall use the common and specific cell parameters for all cells belonging to the same 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 IMM Cell Group which the previous serving cell belongs to, it shall monitor in the current serving cell, i.e. the cell it has reselected to, its paging channel and, if applicable, its paging indication channel, without reading the EC-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 EC System Information messages in a different than the current serving cell is expired,

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

The network may choose to deactivate deferred SI acquisition in EC operation in network deployments for which EC 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 in EC operation is discontinued by removing the IMM Cell Group Definition IE from EC SI 2 and indicating in the IMM CGI field of the EC-SCH Information message ‘IMM Cell Group Definition is not broadcasted or not supported in the cell’.

Otherwise the network may choose to activate deferred SI acquisition in EC operation in specific cells. In this case the support of deferred SI acquisition in EC operation is indicated by addition of the IMM Cell Group Definition IE to EC SI 2 and by the IMM CGI field in the EC-SCH Information message indicating ‘Cell belongs to IMM Cell Group Identity X’ with X being 1, 2, …, or 7.

3.10.5 Extended Coverage

An EC-GSM-IoT capable mobile station supports extended coverage whereby blind physical layer transmissions are used on both the uplink and downlink according to the current coverage conditions and the logical channel used (see 3GPP TS 45.002). Four different coverage classes for downlink and five coverage classes for uplink are defined, each corresponding to a fixed number of blind physical layer transmissions for each logical channel, where the fixed number of blind physical layer transmissions need not be the same for different logical channels belonging to the same coverage class. A mobile station that has enabled EC operation selects its uplink and downlink coverage class based on thresholds broadcast by the network. The mobile station uses its selected uplink coverage class to determine the number of blind physical layer transmissions to use when sending an EC PACKET CHANNEL REQUEST message (see sub-clause 3.5.2a) and includes the selected downlink coverage class in the message (see sub-clause 9.1.65).

Upon determining that its currently selected downlink coverage class has changed, a mobile station that has enabled EC operation shall trigger the transmission of a cell update under certain conditions (see 3GPP TS 45.008).

Blind physical layer transmissions in a cell on EC-PDTCH and EC-PACCH channels in uplink and downlink are mapped on to either 4 consecutive PDCH resources or 2 consecutive PDCH resources. The number of consecutive PDCH resources used for EC TBF operation in an EC-GSM-IoT capable cell is controlled via the EC System information type 2 message. The mapping of EC channels onto physical channels shall be as specified in 3GPP TS 45.002.

3.10.6 EC-CCCH/D Operation

On EC-CCCH/D, the EC-CCCH blocks designated to mobile stations in CC1 and to mobile stations in the higher coverage classes (CC2, CC3 and CC4) use different training sequences. For EC-PCH and EC-AGCH, the TSC shall be selected from the TSC Set 1, if the EC-PCH / EC-AGCH block, is designated to MSs in CC1 only and shall be selected from TSC Set 2 if the EC-PCH / EC-AGCH block, is designated to at least one MS in a higher coverage class (CC2, CC3 or CC4).

A mobile station in idle mode which has selected a higher coverage class (CC2, CC3 or CC4) attempts to detect, based on the training sequence in the received bursts, whether the EC-CCCH/D block is sent to mobile stations in the lower coverage class CC1 and if detected, may suspend further reception of the EC-CCCH/D blocks belonging to the selected coverage class.

A mobile station in idle mode which has selected CC1 as downlink coverage class needs to decode the received EC-CCCH/D block, irrespective of whether the EC-CCCH/D block is designated to mobile stations in CC1 or mobile stations in the higher coverage classes (CC2, CC3 and CC4). In both cases it attempts to decode, based on the detected training sequence in the received bursts, the message sent on EC-CCCH/D.

A mobile station which supports monitoring of the EC paging indication channel, camps on a cell that indicates paging indication channel support and has selected CC3 or CC4 as downlink coverage class, shall monitor in idle mode the EC paging indication channel (EC-PICH) in a cell which indicates EC paging indication channel support in EC System Information type 2 (see subclause 9.1.43q). The mapping between the paging block of the mobile station and the EC-PICH block which the mobile station shall monitor is specified in 3GPP TS 45.002 [32]). If the EC-PICH block indicates that no paging message is scheduled in the EC-CCCH/D blocks corresponding to its paging block, the mobile station enters into sleep mode until the next paging occasion after completion of the current (e)DRX cycle. Else if the EC-PICH block indicates presence of a paging message in the EC-CCCH/D blocks corresponding to its paging block, the mobile station shall read its paging block.

On EC-PICH channel, for a mobile station that has selected CC4 as downlink coverage class, the paging indication sequence contained in the EC PAGING INDICATION message (see subclause 9.1.69) corresponds to the wake-up or go-to-sleep indication for the paging block mapped to the EC-PICH block. For a mobile station that has selected CC3 as downlink coverage class, the paging indication sequence contained in the EC PAGING INDICATION message (see subclause 9.1.69) corresponds to the wake-up or go-to-sleep indication for any of the two paging blocks mapped to the EC-PICH block (see 3GPP TS 45.002 [32]). A mobile station which supports monitoring of EC paging indication channel detects the paging indication sequence contained within the EC PAGING INDICATION message based on the received bursts of the EC-PICH block (e.g. based on correlation of the received bursts against the expected bursts from a candidate paging indication sequence as specified in subclause 9.1.69) and determines whether to further receive the EC-CCCH/D blocks corresponding to the EC-PICH block based on the detected sequence.