Content for  TS 43.064  Word version:  18.0.0

EC-GSM-IoT is an evolution of EGPRS providing a streamlined protocol implementation, reducing MS complexity while supporting energy efficient operation with extended coverage compared to GPRS/EGPRS. EC-GSM-IoT also mandates the use of an improved security framework by both the network and the mobile station. EC-GSM-IoT makes use of a 9 bit BSIC wherein the 6 bit BSIC is supplemented with a 3 bit Radio frequency Colour Code with the purpose to help distinguish between cells in tight frequency reuse networks. EC-GSM-IoT makes use of Fixed Uplink Allocation for allocating uplink resources for EC-PDTCHs and hence does not support USF based uplink allocation. No simultaneous uplink and downlink packet transfer is supported. A MS that has enabled EC operation makes use of EC-channels (e.g. EC-PDTCH), except for the FCCH. An EC-GSM-IoT MS shall also support RACH and AGCH, in addition to EC-RACH and EC-AGCH. RACH and AGCH can be used by the MS when in GPRS/EGPRS coverage range (CC1, see subclause 3.3.9.2) if indicated by the network. EC-channels are used in idle mode as well as in packet transfer mode. The MS shall disable EC operation in case it enters a cell that does not support EC-GSM-IoT. The MS may also disable EC operation (see TS 45.008) at any time, in which case it operates as if it was in a cell that does not support EC-GSM-IoT. The MS shall inform the network that EC operation has been disabled by e.g. a cell update. A MS that has disabled EC operation is no longer subject to the relaxed mobility related requirements (see sub-clause 3.3.9.3). An EC-GSM-IoT mobile station need not comply with GPRS requirements, but shall comply with EGPRS requirements unless otherwise stated, see TS 45.005. An EC-GSM-IoT mobile station need only support EC operation. The mobile station can optionally also support other PS services, such as GPRS, EGPRS and/or EGPRS2, or CS related services. EC-GSM-IoT supports overload control by PLMN specific barring in the EC SI (see TS 44.018) and optionally by using the Implicit Reject Status field within the EC-SCH (see TS 44.018). EC-GSM-IoT shall not be operated in reduced latency TBF mode, see subclause 3.3.5, nor shall it support the Fast Ack/Nack reporting procedure. DTM is not supported in EC operation. The EGPRS modulation and coding schemes for PDTCH are reused for EC-PDTCH. The EC-BCCH and EC-RACH CC1 to CC4 re-uses the same coding scheme as the BCCH and RACH respectively. Modified coding schemes, or specific coding schemes, are defined for EC-SCH, EC-PCH, EC-AGCH, EC-RACH CC5 and EC-PACCH, see TS 45.003. The support of EC-GSM-IoT is optional for the mobile station and the network. A MS that supports EC-GSM-IoT shall support Overlaid CDMA (see subclause 3.3.10). The presence of EC-SCH indicates that a cell supports EC-CCCH and therefore allows an EC-GSM-IoT mobile station to camp on it. A MS supporting EC-GSM-IoT as well as the network may support the restricted use of enhanced coverage (see subclause 3.3.9.5).

In idle mode, energy efficient operation is enabled by the use of relaxed mobility related requirements (see subclause 3.3.8.1, and TS 45.008) and optionally eDRX (see TS 45.002) or Power Saving Mode (see TS 23.682), PSM. A mobile station supporting EC-GSM-IoT may support eDRX and/or PSM, and shall support the use of relaxed mobility related requirements. The paging monitoring procedure is also optimized compared to GPRS/EGPRS where

• A two burst block is used on EC-PCH (compared to a four burst block in EGPRS/GPRS), with the possibility to decode it after only one burst has been received.
• Early suspension of paging block reception is possible, by inclusion of the DL CC in downlink messages, as well as by using different training sequences depending on which CC the EC-CCCH/D block is intended for. For the former case, a MS that has selected a lower CC than what is indicated by DL CC can suspend the monitoring for the remainder of the EC-CCCH/D block. For the latter case, a MS that has selected CC2, CC3 or CC4 and that detects, through TSC detection, that CC1 is transmitted, can suspend reception for the remainder of the EC-CCCH/D block of the selected CC.

In packet transfer mode, energy efficient operation is enabled by e.g. the following functionality:

• As for EC-PCH in idle mode, a two burst block is also used on EC-AGCH minimizing reception time when in good radio conditions;
• Only one phase access is defined in EC operation;
• Efficient contention resolution that reduces the transmission time from the MS, by the use of a reduced TLLI;
• Early suspension of downlink reception possible, by inclusion of the DL CC in downlink messages;
• EC-PACCH on the downlink is possible to decode after only one burst has been received;
• Energy efficient initial resource allocation by inclusion of measured radio conditions in the channel request message;
• No neighbor cells monitoring

EC-GSM-IoT mandates the use of an improved security framework by both the network and the mobile station, see TS 43.020. In this context it should be noted that integrity protection has been limited to LLC unacknowledged operation [8].

Use of enhanced coverage, requiring extensive network resources including radio resources, may be restricted by the network for a given subscriber. An EC-GSM-IoT capable MS that supports restricted use of enhanced coverage, indicates this support during the GPRS Attach and Routing Area Update procedures (see TS 23.060 and TS 24.008. The network supporting restricted use of enhanced coverage provides the mobile station with the applicable restriction in the GPRS Attach Accept and Routing Area Update Accept. If the use of enhanced coverage is not restricted:

• The mobile station continues without modification of its operation, i.e. EC operation if camping on a EC-GSM-IoT supporting cell and (E)GPRS operation if camping on a non-EC-GSM-IoT supporting cell.

Otherwise, if the use of enhanced coverage is restricted:

• If, after applying the offset for Enhanced Coverage Authorization, the mobile station can still use EC operation, it remains in the serving cell (i.e. cell reselection is not necessary).
• If, after applying the offset for Enhanced Coverage Authorization, a mobile station in idle mode is unable to remain in EC operation in its serving cell, it performs cell reselection with modified cell reselection parameters for an EC-GSM-IoT supporting cell, based on the offset for Enhanced Coverage Authorization, according to TS 45.008, being broadcasted in (EC) System Information, according to TS 44.018. The offset effectively yields a desensitization of the mobile station in regard to each EC-GSM-IoT supporting cell, corresponding to the signalled range of 5 to 20 dB, but not further than normal coverage. Cell reselection to each non-EC-GSM-IoT supporting cell is left unchanged.
• For a mobile station in packet transfer mode with an ongoing downlink or uplink EC TBF, the network may need to adapt the downlink or uplink Coverage Class according to observed radio conditions and implementation based criteria. For this purpose, the BSS needs to be informed by the SGSN about whether the subscriber is authorized for use of enhanced coverage (see TS 48.018) in order to identify if adaptation to a higher Coverage Class is enabled. For this purpose, the SGSN shall have the latest EC restriction information.
• In case where the network decides to discontinue the use of enhanced coverage restriction for a mobile station, for which the Ready timer is not running, the SGSN initiates the packet paging procedure towards the BSS (see TS 48.018), which sends a paging request to the mobile station camping either on a non-EC-GSM-IoT supporting cell or an EC-GSM-IoT supporting cell and thereby the BSS informs the mobile station about the removed restriction for use of enhanced coverage (see TS 44.018). This paging request is sent using the appropriate Downlink Coverage Class based on the previously sent information from the mobile station to ensure proper reception. The mobile station sends a paging response acknowledging reception of the paging request and starts the cell reselection procedure by triggering measurements for cell re-selection, not applying the offset for Enhanced Coverage Authorization (see TS 45.008) for any EC-GSM-IoT supporting cell. This procedure of Enhanced Coverage Reauthorization is targeted for scenarios where a mobile station would be using a low coverage class due to enhanced coverage restriction and, once the restriction is removed, the mobile station should be able to move to an appropriate higher coverage class to improve the channel quality.
• In case where the network decides to discontinue the use of enhanced coverage restriction for a mobile station, for which the Ready timer is running the SGSN may initiate the transmission of a DL-UNITDATA PDU containing a zero length LLC-PDU (see TS 48.018) to indicate to the BSS whether the use of enhanced coverage is restricted or not for this mobile station. This information may be used in the BSS to decide the allowable coverage classes and is not propagated towards the mobile station.

The SGSN also sends the EC restriction information in all DL_UNITDATA_PDUs for EC capable mobiles (see TS 48.018).

The network may configure EC Paging Indication Channel (EC-PICH) for MS capable to receive EC-PICH in higher coverage class condition (CC3 or CC4) which occurs prior to the EC-CCCH/D blocks corresponding to the paging block of the MS to optimise the energy consumption for paging reception. Separate EC-PICH blocks are used for paging indication for CC3 and CC4 MS (see TS 45.002). An EC-PICH block for CC4 contains the paging indication for single paging block of CC4 within four 51 multiframes, whereas an EC-PICH block for CC3 serves for indicating a page to one or two CC3 MS per two 51-multiframes. The MS in CC3 or CC4 coverage condition checks the EC-PICH block corresponding to its paging block (see TS 45.002), whether containing a wake-up indication, and if yes, listens to the paging block. If the EC-PICH block indicates that no paging message is scheduled in the EC-CCCH/D blocks corresponding to its paging block, the MS enters into sleep mode until the next paging occasion after completion of current (e)DRX cycle thus reducing energy consumption due to avoiding reading multiple repetitions of the EC-CCCH/D block of the higher coverage class which may or not contain a matching page. The message sent on EC-PICH (EC PAGING INDICATION, see TS 44.018) to convey wake-up or sleep indication(s) is designed such that it can be received by legacy EC-GSM-IoT mobile stations in CC1 condition, expecting an EC-AGCH, without decoding failure, as the EC-PICH burst uses the same training sequence number as the EC-CCCH/D CC1 burst and the legacy EC-GSM-IoT mobile station detects an unknown message type. The message sent on EC-PICH (EC PAGING INDICATION, see TS 44.018) carries a specific paging indication sequence for a mobile station, capable to receive EC-PICH in coverage class condition CC3 or CC4, which depends on the coverage class, training sequence number, indication (wake-up or sleep) and referred paging block. The set of paging indication sequences is designed such that the mobile station can detect the transmitted sequence by correlation (see TS 44.018). The support of EC-PICH logical channel is broadcasted in EC System Information. An MS supporting EC-PICH indicates its capability support to the network.

In order to reduce energy consumption in packet idle mode, the network may broadcast information to assist the MS to apply deferred system information acquisition (see TS 45.008). To this purpose it reconfigures EC System Information type 2 for a cell to include an Idle Mode Mobility cell group description comprising cells, geographically adjacent or close to each other, with shared cell parameters related to cell (re)selection, Routing Area assignment, paging monitoring, DL Coverage class selection, mobility support and cell barring and assigns it a broadcast frequency list containing BCCH carriers allocated in these cells. To better match cell deployments, some cell parameters may deviate from the common values and are separately indicated on a per cell basis (see TS 44.018). To allow for different settings of shared cell parameters in geographic adjacent areas, different Idle Mode Mobility cell groups are defined with an identifier to distinguish one from the other, thus providing a spatially definite assignment of cells to Idle Mode Mobility cell groups. Since values of shared or non-shared cell parameters in a particular Idle Mode Mobility cell group are subject to change in time, a change mark is assigned to the Idle Mode Mobility cell group. An increment of the change mark for a particular Idle Mode Mobility cell group hence indicates to the MS to acquire the complete EC SI in the serving cell. To enable fast detection if a cell is part of a specific Idle Mode Mobility cell group or not, the MS identifies from EC-SCH reception the Idle Mode Mobility cell group identifier and the related change mark. Thus, an MS reselecting to a cell in the same IMM cell group as the last serving cell has read the EC-SCH and decoded both the IMM cell group identifier and the IMM cell group change mark. If both values match with those of the last serving cell, it will not need to read the EC-BCCH for this cell prior to the decision for cell reselection, neither after cell reselection to this cell for subsequent cell reselections and for paging monitoring in packet idle mode. Only in case a valid page is received, that requires to send a paging response, or the MS needs to perform an uplink data transmission, or a timeout since the last reading of the complete EC SI in a different than the current serving cell is expired, the MS is required to read the complete EC System Information in the current serving cell. The network may choose to deactivate deferred SI acquisition in network deployments for which EC System Information needs to be reconfigured more frequently or for which adjacent cells' idle mode mobility parameters differ too much. The support of deferred system information acquisition is broadcasted in EC System Information.