23 Others

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

23.1 Support for real time IMS services

23.1.1 IMS Emergency Call

IMS emergency calls are supported in this release of the specification and UE may initiate an IMS emergency call on the PS domain if the network supports it. IMS Emergency call support indication is provided to inform the UE that emergency bearer services are supported. This is sent via NAS messaging for normal service mode UE and via a BCCH indicator for limited service mode UE TS 23.401 [17]. The BCCH indicator is set to ‘support’ if any of the MMEs in a non-shared environment or one of PLMNs in a shared network environment supports IMS emergency bearer services.

If at the time of an IMS emergency call origination, the UE is already RRC connected to a CN that does not support IMS emergency calls, it should autonomously release the RRC connection and originate a fresh RRC connection in a cell that is capable of handling emergency calls. Call admission control for IMS emergency call is based on bearer QoS (e.g. the ARP).

Security procedures are activated for emergency calls. For UE in limited service mode and the UE is not authenticated (as defined in TS 33.401 [22], clause 15.2.2), ‘NULL’ algorithms for ciphering and integrity protection are used and the related keys are set to specified value and may be ignored by the receiving node. During handover from cell in non-restricted area to restricted area, security is handled normally with normal key derivation etc. for both the intra-LTE and inter-RAT handover. For inter-RAT handover from LTE, if ‘NULL’ Integrity Protection algorithms are used in LTE, security is stopped after the handover. For inter-RAT handover to LTE, security is activated after the handover with ‘NULL’ algorithms if security is not activated in the source RAT.

23.2 Subscriber and equipment trace

23.2.0 General

Support for subscriber and equipment trace for E-UTRAN and EPC shall be as specified in TS 32.421 [29], TS 32.422 [30] and TS 32.423 [31].

23.2.1 Signalling activation

All traces are initiated by the core network, even if the trace shall be carried out in the radio network.

If the eNB has received an UE CONTEXT RELEASE COMMAND message where the UE is associated to an E-UTRAN Trace Id then the eNB shall terminate the on-going Trace.

The following functionality is needed on the S1 and X2 interface:

– Support for inclusion of subscriber and equipment trace information in INITIAL CONTEXT SETUP REQUEST message over the S1 interface.

– Support for an explicit TRACE START message over the S1 interface.

– Support for inclusion of subscriber and equipment trace information in the HANDOVER REQUEST message over the X2 interface.

– Support for inclusion of subscriber and equipment trace information in the HANDOVER REQUEST message over the S1 interface.

– Support for TRACE FAILURE INDICATION for the purpose of informing MME that the requested trace action cannot be performed due to an on-going handover preparation over the X2 interface.

A trace setup in the radio network will be propagated at handover. If the eNB receives trace information for a given UE, and a handover preparation is not already ongoing for the same UE, it shall store the trace information and propagate it to the target eNB in the case of a X2 based HO. In the case of S1 based HO, the propagation is handled by the MME.

23.2.2 Management activation

All conditions for Cell Traffic Trace are defined by the O&M. When the condition to start the trace recording is fulfilled the eNB will allocate a Trace Recording Session Reference and send it together with the Trace Reference to the MME in a CELL TRAFFIC TRACE message over the S1 interface.

Cell Traffic trace actions will not be propagated on the X2 interface or on the S1 interface in case of handover.

23.3 E-UTRAN Support for Warning Systems

23.3.0 General

The E-UTRAN provides support for warning systems through means of system information broadcast capability. The E-UTRAN performs scheduling and broadcasting of the "warning message content" received from the CBC, which is forwarded to the E-UTRAN by the MME. The schedule information for the broadcast is received along with the "warning message content" from the CBC. The E-UTRAN is also responsible for paging the UE to provide indication that the warning notification is being broadcast. The "warning message content" received by the E-UTRAN contains an instance of the warning notification. Depending on the size, E-UTRAN may segment the secondary notification before sending it over the radio interface.

23.3.1 Earthquake and Tsunami Warning System

ETWS is a public warning system developed to meet the regulatory requirements for warning notifications related to earthquake and/or tsunami events. ETWS warning notifications can either be a primary notification (short notifications delivered within 4 seconds, see TS 22.168 [37]) or secondary notification (providing detailed information). The ETWS primary notification is broadcast in SystemInformationBlockType10 while the secondary notification is broadcast in SystemInformationBlockType11.

23.3.2 Commercial Mobile Alert System

CMAS is a public warning system developed for the delivery of multiple, concurrent warning notifications (see TS 22.268 [34]). The CMAS warning notifications are short text messages (CMAS alerts). The CMAS warning notifications are broadcast in SystemInformationBlockType12. The E-UTRAN manages the delivery of multiple, concurrent CMAS warning notifications to the UE and is also responsible for handling any updates of CMAS warning notifications.

23.3.3 Korean Public Alert System

KPAS is a Korean public warning system developed for the delivery of multiple, concurrent warning notifications (see TS 22.268 [34]). The Korean Public Alarm System (KPAS) uses the same AS mechanisms as CMAS. Therefore, the E-UTRAN procedures defined for CMAS equally apply for KPAS.

23.3.4 EU-Alert

The European Union Warning System EU-Alert is a public warning system developed for the delivery of multiple, concurrent warning notifications (see TS 22.268 [34]). The EU-Alert warning system uses the same AS mechanisms as CMAS. Therefore, the E-UTRAN procedures defined for CMAS equally apply for EU-Alert.

23.4 Interference avoidance for in-device coexistence

23.4.1 Problems

In order to allow users to access various networks and services ubiquitously, an increasing number of UEs are equipped with multiple radio transceivers. For example, a UE may be equipped with LTE, WiFi, and Bluetooth transceivers, and GNSS receivers. Due to extreme proximity of multiple radio transceivers within the same UE operating on adjacent frequencies or sub-harmonic frequencies, the interference power coming from a transmitter of the collocated radio may be much higher than the actual received power level of the desired signal for a receiver. This situation causes In-Device Coexistence (IDC) interference and is referred to as IDC problems. The challenge lies in avoiding or minimizing IDC interference between those collocated radio transceivers, as current state-of-the-art filter technology might not provide sufficient rejection for certain scenarios (see TR 36.816 [50]). IDC problem can happen when the UE (intends to) uses WLAN on the overlapped carrier/band or adjacent carrier/band to the unlicensed carrier used for LAA operation, e.g. when related UE hardware components, such as antennas, are shared between LAA and WLAN operations. If there is a risk of IDC problem which cannot be avoided (e.g. by level of regulation), the IDC functionality for a UE should be configured by the eNB when the UE is configured for LAA operation.

23.4.2 Solutions

When a UE experiences IDC problems that it cannot solve by itself and a network intervention is required, it sends an IDC indication via dedicated RRC signalling to report the IDC problems to the eNB. The UE may rely on existing LTE measurements and/or UE internal coordination to assess the interference and the details are left up to UE implementation.

NOTE: For instance, the interference is applicable over several subframes/slots where not necessarily all the subframes/slots are affected and consists of interference caused by the aggressor radio to the victim radio during either active data exchange or upcoming data activity which is expected in up to a few hundred milliseconds.

A UE that supports IDC functionality indicates related capabilities to the network, and the network can then configure by dedicated signalling whether the UE is allowed to send an IDC indication. The IDC indication can only be triggered for frequencies for which a measurement object is configured and when:

– for the primary frequency, the UE is experiencing IDC problems that it cannot solve by itself;

– for a secondary frequency, regardless of the activation state of the corresponding SCell, the UE is experiencing or expects to experience upon activation IDC problems that it cannot solve by itself;

– for a non-serving frequency, the UE expects to experience IDC problems that it cannot solve by itself if that non-serving frequency becomes a serving one.

When notified of IDC problems through an IDC indication from the UE, the eNB can choose to apply a Frequency Division Multiplexing (FDM) solution or a Time Division Multiplexing (TDM) solution:

– The basic concept of an FDM solution is to move the LTE signal away from the ISM band by e.g., performing inter-frequency handover within E-UTRAN, removing SCells from the set of serving cells or de-activation of affected SCells, or in case of uplink CA operations, allocate uplink PRB resources on CC(s) whose inter-modulation distortion and harmonics does not fall into the frequency range of the victim system receiver.

– The basic concept of a TDM solution is to ensure that transmission of a radio signal does not coincide with reception of another radio signal. LTE DRX mechanism is used to provide TDM patterns (i.e. periods during which the LTE UE may be scheduled or is not scheduled) to resolve the IDC issues. DRX based TDM solution should be used in a predictable way, i.e. the eNB should ensure a predictable pattern of unscheduled periods by means of e.g. DRX mechanism or de-activation of affected SCells.

To assist the eNB in selecting an appropriate solution, all necessary/available assistance information for both FDM and TDM solutions is sent together in the IDC indication to the eNB. The IDC assistance information contains the list of E-UTRA carriers suffering from IDC problems, the direction of the interference and, depending on the scenario (see TR 36.816 [50]), it also contains TDM patterns or parameters to enable appropriate DRX configuration for TDM solutions on the serving E-UTRA carrier. Furthermore, the IDC indication can also be configured to include uplink CA related assistance information containing the victim system as well as the list of supported uplink CA combinations suffering from IDC problems. Furthermore, the IDC indication can also be configured to indicate that the cause of IDC problems is hardware sharing between LAA and WLAN operation, in which case the UE may omit the TDM assistance information. The IDC indication is also used to update the IDC assistance information, including for the cases when the UE no longer suffers from IDC problems. In case of inter-eNB handover, the IDC assistance information is transferred from the source eNB to the target eNB.

IDC interference situation can be divided into following three phases as shown in Figure 23.4.2-1:

– Phase 1: The UE detects start of IDC interference but does not initiate the transmission of the IDC indication to the eNB yet.

– Phase 2: The UE has initiated the transmission of the IDC indication to the eNB and no solution is yet configured by the eNB to solve the IDC issue.

– Phase 3: The eNB has provided a solution that solved the IDC interference to the UE.

Figure 23.4.2-1: Different phases of IDC interference related operations by UE

In different phases, UE behaviours related to RRM, RLM, and CSI measurements are shown in Table 23.4.2-1.

Table 23.4.2-1: RRM/RLM/CSI measurements in different phases of IDC interference

Phases of IDC Interference	RRM Measurements	RLM Measurements	CSI Measurements
Phase 1	Up to UE implementation and RRM measurement requirements (see TS 36.133 [21]) apply	Up to UE implementation and RLM measurement requirements (see TS 36.133 [21]) apply	Up to UE implementation and CSI measurement requirements (see TS 36.101 [52]) apply
Phase 2	UE shall ensure the measurements are free of IDC interference and RRM measurement requirements (see TS 36.133 [21]) apply (NOTE 4)	UE shall ensure the measurements are free of IDC interference and RLM measurement requirements (see TS 36.133 [21]) apply (NOTE 1)	(NOTE 4)
Phase 3	UE shall ensure the measurements are free of IDC interference and RRM measurement requirements (see TS 36.133 [21]) apply	UE shall ensure the measurements are free of IDC interference and RLM measurement requirements (see TS 36.133 [21]) apply
NOTE 1: The UE should attempt to maintain connectivity to LTE in this phase meaning that RLM measurements are not impacted by IDC interference. If no solution is provided within a time which is up to UE implementation, the UE may need to declare RLF or it may continue to deny the ISM transmission. In DC, when the UE experiences IDC problems in SCG, if no solution is provided within a time which is up to UE implementation, the UE may need to declare RLF in SCG or it may continue to deny the ISM transmission in SCG. NOTE 2: If the UE determines in Phase 2 that the network does not provide a solution that resolves its IDC problems, it performs measurements as defined for Phase 1. NOTE 3: If the IDC indication message reports the IDC interference on a neighbour frequency, it performs RRM measurements for that frequency as defined for Phase 2. NOTE 4: When experiencing IDC problem caused by the hardware sharing between LAA and WLAN the UE shall be allowed to relax the existing RRM/CSI measurement requirement during phase 2 (see TS 36.133 [21]).

In addition, once configured by the network, the UE can autonomously deny LTE UL transmission in all phases to protect ISM in rare cases if other solutions cannot be used. Conversely, it is assumed that the UE also autonomously denies ISM transmission in order to ensure connectivity with the eNB to perform necessary LTE procedures, e.g., RRC connection reconfiguration and paging reception, etc. The network may configure a long-term denial rate by dedicated RRC signalling to limit the amount of LTE UL autonomous denials. Otherwise, the UE shall not perform any LTE UL autonomous denials.

23.5 TDD Enhanced Interference Management and Traffic Adaptation (eIMTA)

TDD enhanced Interference Management and Traffic Adaptation (eIMTA) allows adaptation of uplink-downlink configuration via L1 signalling. The E-UTRAN configures which UEs are subject to the TDD eIMTA operation.

For Uplink scheduling and HARQ timing, the UE follows the reference uplink-downlink configuration based on the one provided in SIB1. For Downlink HARQ timing, the UE follows the reference uplink-downlink configuration provided through dedicated signalling.

Downlink subframes in the reference configuration provided in SIB1 remain unchanged whereas only a subset of uplink and special subframes may be reconfigured to downlink subframes. E-UTRAN sends a L1 signalling to the UE on PCell PDCCH to indicate which uplink-downlink configuration defined in TS 36.211 [4] is currently used for one or more serving cell(s). This uplink-downlink configuration provided by the L1 signalling applies for a RRC-configured number of radio frames.

The UE uses the L1-signalled uplink-downlink configuration for (E)PDCCH monitoring and CSI measurements.

The UE RRM/RLM measurements are not affected by the TDD eIMTA configuration.

For DL CSI measurements of each serving cell, two subframe sets may be configured via RRC signalling.

For PUSCH/SRS UL power control of each serving cell, two subframe sets with separate power control parameters may be configured via RRC signalling.

Subframe-set dependent overload indication and uplink-downlink configuration intended to be used by a cell may be exchanged between eNBs over the X2 interface to facilitate the TDD eIMTA operation.

23.6 RAN assisted WLAN interworking

23.6.0 General

This clause describes the mechanisms to support traffic steering between E-UTRAN and WLAN.

23.6.1 General principles

This version of the specification supports E-UTRAN assisted UE based bi-directional traffic steering between E-UTRAN and WLAN for UEs in RRC_IDLE and RRC_CONNECTED.

E-UTRAN provides assistance parameters via broadcast and dedicated RRC signalling to the UE. The RAN assistance parameters may include E-UTRAN signal strength thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, WLAN signal strength thresholds and Offload Preference Indicator (OPI). E-UTRAN can also provide a list of WLAN identifiers to the UE via broadcast signalling. The UE uses the RAN assistance parameters in the evaluation of:

– Access network selection and traffic steering rules defined in TS 36.304 [11]; or

– ANDSF policies defined in TS 24.312 [58].

for traffic steering decisions between E-UTRAN and WLAN as specified in TS 23.402[19].

The OPI is only used in ANDSF policies as specified in TS 24.312 [58].

WLAN identifiers are only used in access network selection and traffic steering rules defined in TS 36.304 [11].

If the UE is provisioned with ANDSF policies it shall forward the received RAN assistance parameters to upper layers, otherwise it shall use them in the access network selection and traffic steering rules defined in clause 23.6.2 and in TS 36.304 [11]. The access network selection and traffic steering rules defined in clause 23.6.2 and in TS 36.304 [11] are applied only to the WLANs of which identifiers are provided by the E-UTRAN.

The UE in RRC_CONNECTED shall apply the parameters obtained via dedicated signalling if such have been received from the serving cell; otherwise, the UE shall apply the parameters obtained via broadcast signalling.

The UE in RRC_IDLE shall keep and apply the parameters obtained via dedicated signalling, until selection/reselection of another cell than the one where these parameters were received or a timer has expired since the UE entered RRC_IDLE upon which the UE shall apply the parameters obtained via broadcast signalling.

In the case of RAN sharing, each PLMN sharing the RAN can provide independent sets of RAN assistance parameters.

23.6.2 Access network selection and traffic steering rules

The UE indicates to upper layers when (and for which WLAN identifiers) access network selection and traffic steering rules defined in TS 36.304 [11] are fulfilled. The selection among WLANs that fulfil the access network selection and traffic steering rules is up to UE implementation.

When the UE applies the access network selection and traffic steering rules defined in TS 36.304 [11], higher layers perform traffic steering between E-UTRAN and WLAN.

23.7 Support of Low Complexity UEs

Low complexity UEs are targeted to low-end (e.g. low average revenue per user, low data rate, delay tolerant) applications, e.g. some Machine-Type Communications.

A low complexity UE has reduced Tx and Rx capabilities compared to other UE of different categories.

A Category 0 low complexity UE may access a cell only if SIB1 indicates that access of Category 0 UEs is supported. If the cell does not support access of Category 0 UEs, the UE considers the cell as barred.

The eNB determines that a UE is a Category 0 UE based on the LCID for CCCH and the UE capability.

The S1 signalling has been extended to include the UE Radio Capability for paging. This paging specific capability information is provided by the eNB to the MME, and the MME uses this information to indicate to the eNB that the paging request from the MME concerns a low complexity UE.

23.7a Support of Bandwidth Reduced Low Complexity UEs

A bandwidth reduced low complexity (BL) UE can operate in any LTE system bandwidth but with a limited channel bandwidth of 6 PRBs (corresponding to the maximum channel bandwidth available in a 1.4 MHz LTE system) in downlink and uplink. Interworking with NR is not supported by BL UE (e.g. functions like NR measurement reporting, reselection to NR, handover to NR, redirection to NR are not supported).

To enable higher data rates a BL UE can optionally support a larger maximum PDSCH/PUSCH channel bandwidth of 24 PRBs in downlink and a non-BL UE operating in enhanced coverage can optionally support a larger maximum PDSCH/PUSCH channel bandwidth of 24 or 96 PRBs in downlink, and 24 PRBs in uplink in connected mode for unicast transmission. Table 23.7.a-1 summarizes the maximum PDSCH/PUSCH bandwidth in connected mode for unicast transmission depending on the UE category and enhanced coverage mode (see clause 23.7b). The maximum PDSCH/PUSCH channel bandwidth is configured separately for PDSCH and PUSCH via dedicated RRC signaling.

Table 23.7a-1: Maximum PDSCH/PUSCH bandwidth (in PRBs)

UE category/CE mode	CE mode A	CE mode B
BL (Category M1)	6/6	6/6
BL (Category M2)	24/24	24/6
Non-BL (Category 0 and higher)	96 (or 24)/24	96 (or 24)/6

A BL UE may access a cell only if the MIB of the cell indicates that scheduling information for SIB1 specific for BL UEs is scheduled. If not, the UE considers the cell as barred.

A BL UE receives a separate occurrence of system information blocks (sent using different time/frequency resources). A BL UE has a transport block size (TBS) limited to 1000 bit for broadcast. The BL UE determines the scheduling information for SIB1 specific for BL UEs based on information in MIB. Scheduling information for other SIBs is given in SIB1 specific for BL UEs. The BCCH modification period for BL UEs is a multiple of the BCCH modification period provided in SIB2. The SIB transmission occasions within an SI-window are provided in the SIB1 specific for BL UEs. A BL UE can acquire SI messages across SI windows. The maximum number of SI messages that can be acquired across SI windows is 4. A BL UE is not required to detect SIB change when in RRC_CONNECTED.

A BL UE is paged based on paging occasions in time domain, and paging narrowbands in frequency domain. The starting subframe of a paging occasion is determined in the same way as the paging occasion in the legacy paging mechanism.

A set of PRACH resources (e.g. time, frequency, preamble), each associated with BL UEs in normal coverage, is provided in SIB. Number of PRACH repetitions and number of maximum preamble transmission attempts for BL UEs in normal coverage are provided in SIB. Time/frequency resources and repetition factor for random access response messages for BL UEs are derived from the used PRACH resources.

23.7b Support of UEs in Enhanced Coverage

A UE in enhanced coverage is a UE that requires the use of enhanced coverage functionality to access the cell. In this release of the specification two enhanced coverage modes (mode A, mode B) are supported. The support of enhanced coverage mode A is mandatory for a BL UE. The maximum PDSCH/PUSCH bandwidth in connected mode for unicast transmission depends on the UE category and enhanced coverage mode as summarized in table 23.7a-1.

A UE may access a cell using enhanced coverage functionality only if the MIB of the cell indicates that scheduling information for SIB1 specific for BL UEs is scheduled. System information procedures for UEs in enhanced coverage are identical to the system information procedures for bandwidth reduced low complexity UEs. A UE capable of enhanced coverage acquires, if needed, and uses legacy system information when in normal coverage if it is not a BL UE. A UE capable of enhanced coverage acquires, if needed, and uses system information specific for UEs in enhanced coverage. A UE in enhanced coverage is not required to detect SIB change when in RRC_CONNECTED.

A set of PRACH resources (e.g. time, frequency, preamble); each associated with a coverage enhancement level, is provided in SIB. Number of PRACH repetitions and number of maximum preamble transmission attempts per coverage enhancement level are provided in SIB. UEs in same enhanced coverage level use random access resources associated with the same enhanced coverage level. Time/frequency resources and repetition factor for random access response messages for UEs in enhanced coverage are derived from the used PRACH resources.

A UE in enhanced coverage is paged using the same mechanism for paging BL UEs. The starting subframe of a paging occasion and the repetition pattern (in both time and frequency domain for downlink common control signaling) of that paging occasion are determined irrespective of the UEs enhanced coverage level.

The paging request from the MME or the AMF for a UE supporting enhanced coverage functionality may contain enhanced coverage level related information and corresponding cell ID. If neither the UE Radio Capability for Paging IE nor the Assistance Data for Paging IE is included in the paging request from the MME or the AMF, the (ng-)eNB may need to page the UE in both PDCCH and MPDCCH.

A UE in RRC_IDLE does not inform the network when it changes the enhanced coverage level.

A UE in enhanced coverage camps on a suitable cell where S criterion for UEs in enhanced coverage is fullfilled.The UE shall re-select to inter-frequency cells in which it is able to operate in normal coverage over cells in which it has to be in enhanced coverage.

Connected mode mobility mechanisms such as measurement reporting, network controlled handover etc., are supported for UEs in enhanced coverage. At handover from a source cell in normal or enhanced coverage mode to a target cell in enhanced coverage mode, the network may provide SIB1-BR to the UE in the handover command. No additional mechanisms are introduced to support the use of enhanced coverage functionality to access an E-UTRA cell during inter-RAT handovers.

Reconfiguration of a UE in connected mode from normal to enhanced coverage mode (and vice versa) is supported by a means of intra-cell handover or RRC configuration without handover.

23.8 Support for Radio Interface based Synchronization

Radio-interface based synchronization (RIBS) enables an eNB to monitor the reference signals of another eNB for the purpose of over the air synchronization by means of network listening. This requires OAM to configure the eNBs with reference signal information, i.e. pattern, periodicity and offset, where the reference signals are available. The OAM should coordinate the reference signal information, for example via one to one mapping between stratum level and reference signal. To improve the hearability of reference signals, the listening eNB may request the interfering eNB(s) to enable subframe muting by means of network signalling.

23.9 Network-assisted interference cancellation/suppression

A UE that supports network assisted interference cancellation/suppression (NAICS) receiver functionality can mitigate PDSCH and CRS interference from aggressor cells in order to better receive a PDSCH from its serving cell.

The network may configure the UE with NAICS information of the aggressor cells in order to help the UE to mitigate the PDSCH and CRS interference of the aggressor cells. To support NAICS, an eNB may exchange NAICS information with its neighbour eNBs through X2 signalling.

23.10 Support for sidelink communication

23.10.1 General

Sidelink communication is a mode of communication whereby UEs can communicate with each other directly over the PC5 interface, as specified in TS 23.303 [62]. This communication mode is supported when the UE is served by E-UTRAN and when the UE is outside of E-UTRA coverage. Only those UEs authorised to be used for public safety operation can perform sidelink communication.

In order to perform synchronisation for out of coverage operation UE(s) may act as a synchronisation source by transmitting SBCCH and a synchronisation signal. SBCCH carries the most essential system information needed to receive other sidelink channels and signals. SBCCH along with a synchronisation signal is transmitted with a fixed periodicity of 40ms. When the UE is in network coverage, the contents of SBCCH are derived from the parameters signalled by the eNB. When the UE is out of coverage, if the UE selects another UE as a synchronisation reference, then the content of SBCCH is derived from the received SBCCH; otherwise UE uses pre-configured parameters. SIB18 provides the resource information for synchronisation signal and SBCCH transmission. There are two pre-configured subframes every 40ms for out of coverage operation. UE receives synchronisation signal and SBCCH in one subframe and transmit synchronisation signal and SBCCH on another subframe if UE becomes synchronisation source based on defined criterion, as specified in [16].

UE performs sidelink communication on subframes defined over the duration of Sidelink Control period. The Sidelink Control period is the period over which resources allocated in a cell for sidelink control information and sidelink data transmissions occur. Within the Sidelink Control period the UE sends sidelink control information followed by sidelink data. Sidelink control information indicates a Layer 1 ID and characteristics of the transmissions (e.g. MCS, location of the resource(s) over the duration of Sidelink Control period, timing alignment).

The UE performs transmission and reception over Uu and PC5 with the following decreasing priority order in case Sidelink Discovery Gap is not configured:

– Uu transmission/reception (highest priority);

– PC5 sidelink communication transmission/reception;

– PC5 sidelink discovery announcement/monitoring (lowest priority).

The UE performs transmission and reception over Uu and PC5 with the following decreasing priority order in case Sidelink Discovery Gap is configured:

– Uu transmission/reception for RACH;

– PC5 sidelink discovery announcement during a Sidelink Discovery Gap for transmission;

– Non-RACH Uu transmission;

– PC5 sidelink discovery monitoring during a Sidelink Discovery Gap for reception;

– Non-RACH Uu reception;

– PC5 sidelink communication transmission/reception.

23.10.2 Radio Protocol Architecture

23.10.2.0 General

In this clause, the UE radio protocol architecture for sidelink communication is given for the user plane and the control plane.

23.10.2.1 User plane

Figure 23.10.2.1-1 shows the protocol stack for the user plane, where PDCP, RLC and MAC sublayers (terminate at the other UE) perform the functions listed for the user plane in clause 6.

The Access Stratum protocol stack in the PC5 interface consists of PDCP, RLC, MAC and PHY as shown below in Figure 23.10.2.1-1.

Figure 23.10.2.1-1: User-Plane protocol stack for sidelink communication

User plane details of sidelink communication:

– There is no HARQ feedback for sidelink communication;

– RLC UM is used for sidelink communication;

– A receiving UE needs to maintain at least one RLC UM entity per transmitting peer UE;

– A receiving RLC UM entity used for sidelink communication does not need to be configured prior to reception of the first RLC UMD PDU;

– ROHC Unidirectional Mode is used for header compression in PDCP for sidelink communication;

– UDC is not used for sidelink communication.

A UE may establish multiple logical channels. LCID included within the MAC subheader uniquely identifies a logical channel within the scope of one Source Layer-2 ID and Destination Layer-2 ID combination. Parameters for logical channel prioritization are not configured. The Access stratum (AS) is provided with the PPPP of a protocol data unit transmitted over PC5 interface by higher layer. There is a PPPP associated with each logical channel.

23.10.2.2 Control plane

A UE does not establish and maintain a logical connection to receiving UEs prior to one-to-many a sidelink communication. Higher layer establishes and maintains a logical connection for one-to-one sidelink communication including ProSe UE-to-Network Relay operation.

The Access Stratum protocol stack for SBCCH in the PC5 interface consists of RRC, RLC, MAC and PHY as shown below in Figure 23.10.2.2-1.

Figure 23.10.2.2-1: Control-Plane protocol stack for SBCCH

The control plane for establishing, maintaining and releasing the logical connection for one-to-one sidelink communication is shown in Figure 23.10.2.2-2.

Figure 23.10.2.2-2: Control-Plane protocol stack for one-to-one sidelink communication

23.10.3 Radio resource allocation

23.10.3.0 General

The UE supporting sidelink communication can operate in two modes for resource allocation:

– Scheduled resource allocation is characterized by:

– The UE needs to be RRC_CONNECTED in order to transmit data;

– The UE requests transmission resources from the eNB. The eNB schedules transmission resources for transmission of sidelink control information and data;

– The UE sends a scheduling request (D-SR or Random Access) to the eNB followed by a Sidelink BSR. Based on the Sidelink BSR the eNB can determine that the UE has data for a sidelink communication transmission and estimate the resources needed for transmission. eNB can schedule transmission resources for sidelink communication using configured SL-RNTI.

– UE autonomous resource selection is characterized by:

– A UE on its own selects resources from resource pools and performs transport format selection to transmit sidelink control information and data;

– There can be up to 8 transmission pools either pre-configured for out of coverage operation or provided by RRC signalling for in-coverage operation. Each pool can have one or more PPPP associated with it. For transmission of a MAC PDU, the UE selects a transmission pool in which one of the associated PPPP is equal to the PPPP of a logical channel with highest PPPP among the logical channel identified in the MAC PDU. It is up to UE implementation how the UE selects amongst multiple pools with same associated PPPP. There is a one to one association between sidelink control pool and sidelink data pool;

– Once the resource pool is selected, the selection is valid for the entire Sidelink Control period. After the Sidelink Control period is finished the UE may perform resource pool selection again.

NOTE: The UE is allowed to perform multiple transmissions to different destinations in a single Sidelink Control period.

A UE in RRC_CONNECTED may send a Sidelink UE Information message to eNB when UE becomes interested in sidelink communication. In response eNB may configure the UE with a SL-RNTI.

A UE is considered in-coverage for sidelink communication whenever it detects a cell on a Public Safety ProSe Carrier as per criteria specified in, as specified in TS 36.331 [16]. The following rules apply for the UE:

– If the UE is out of coverage for sidelink communication it can only use UE autonomous resource selection;

– If the UE is in coverage for sidelink communication it may use scheduled resource allocation or UE autonomous resource selection as per eNB configuration;

– If the UE is in coverage for sidelink communication it shall use only the resource allocation mode indicated by eNB configuration unless one of the exceptional cases as specified in TS 36.331 [16] occurs:

– When an exceptional case occurs the UE is allowed to use UE autonomous resource selection temporarily even though it was configured to use scheduled resource allocation. Resource pool to be used during exceptional case may be provided by eNB.

A UE that is camped or connected on one carrier frequency but interested in sidelink communication operation on another carrier frequency (i.e. Public Safety ProSe Carrier) shall attempt to find cells on the Public Safety ProSe Carrier.

– An RRC_IDLE UE camped on a cell in another carrier frequency, but in the coverage area of an E-UTRA cell on Public Safety ProSe Carrier may consider the Public Safety ProSe carrier to be the highest priority; and reselects to the cell on the Public Safety ProSe Carrier. UE may consider a frequency (non-Public Safety ProSe carrier) to be the highest priority if it can perform sidelink communication only while camping on the frequency.

– An RRC_CONNECTED UE served by a cell in another carrier frequency may send a Sidelink UE Information message to its serving cell when it wants to perform sidelink communication. The indication contains the intended Public Safety ProSe Carrier:

– The serving cell indicates with the presence of SIB18 whether the UE is allowed to send a ProSe UE Information indication;

– The serving cell may configure an inter-frequency RRM measurement on the Public Safety ProSe Carrier;

– Once the UE enters coverage of a cell on the Public Safety ProSe Carrier, based on measurement report the eNB performs inter-frequency mobility to the Public Safety ProSe Carrier;

– If inter-frequency mobility is not performed by the serving cell (e.g. the serving cell does not broadcast SIB18 or if handover fails), the UE may still perform sidelink communication using UE autonomous resource selection from the resource pools, if any, broadcasted by the detected E-UTRA cell on the Public Safety ProSe Carrier.

– If the UE does not detect an E-UTRA cell on the Public Safety ProSe Carrier, the UE can use Public Safety ProSe Carrier resources preconfigured in the UICC or ME for out of coverage sidelink communication;

– If the UE detects an E-UTRA cell on the Public Safety ProSe Carrier, the UE stops using resources preconfigured in the UICC or ME. UE may use UE autonomous resource selection from the resource pools, if any, broadcasted by the detected E-UTRA cell on the Public Safety ProSe Carrier.

NOTE: For Rel-12 all ProSe communication (for a UE) is performed on a single preconfigured Public Safety ProSe Carrier, which is valid in the operating region. Higher layers check validity of the Public Safety ProSe Carrier in the operating region.

The cell on the Public Safety ProSe Carrier may select one of the following options:

– The cell on the Public Safety ProSe Carrier may provide a transmission resource pool for UE autonomous resource selection in SIB18:

– UEs that are authorized for sidelink communication may use these resources for sidelink communication in RRC_IDLE in the cell on the same carrier (i.e. Public Safety ProSe Carrier);

– UEs that are authorized for sidelink communication may use these resources for sidelink communication in RRC_IDLE or RRC_CONNECTED in a cell on another carrier.

– The cell on the Public Safety ProSe Carrier may indicate in SIB18 that it supports sidelink communication but does not provide transmission resources. UEs need to enter RRC_CONNECTED to perform sidelink communication transmission. In this case the cell on the Public Safety ProSe Carrier may provide in broadcast signalling an exceptional transmission resource pool for UE autonomous resource selection, to be used by the UE in exceptional cases, as specified in TS 36.331 [16]:

– A UE in RRC_CONNECTED that is authorized to perform sidelink communication transmission indicates to the serving eNB that it wants to perform sidelink communication transmissions;

– The eNB validates whether the UE is authorized for sidelink communication transmission using the UE context received from MME;

– The eNB may configure a UE by dedicated signalling with a transmission resource pool for UE autonomous resource selection; that may be used without constraints while the UE is in RRC_CONNECTED. Alternatively, the eNB may configure a UE to use the exceptional transmission resource pool for UE autonomous resource selection which the UE is allowed to use only in exceptional cases, as specified in TS 36.331 [16], and rely on scheduled resource allocation otherwise.

23.10.3.1 Resource Pool for sidelink control information

A set of transmission and reception resource pools for sidelink control information when the UE is out of coverage for sidelink communication is pre-configured in the UE.

The resource pools for sidelink control information when the UE is in coverage for sidelink communication are configured as below:

– The resource pools used for reception are configured by the eNB via RRC, in broadcast signalling;

– The resource pool used for transmission is configured by the eNB via RRC, in dedicated or broadcast signalling, if UE autonomous resource selection is used;

– The resource pool used for transmission is configured by the eNB via RRC, in dedicated signalling if scheduled resource allocation is used:

– The eNB schedules the specific resource(s) for sidelink control information transmission within the configured reception pools.

NOTE: In order to perform communication even when some UEs are in-coverage and some UEs are out of coverage, all UEs (i.e. both in and out of coverage) should be configured with resource pools for reception of sidelink control information which are the union of the resource pools used for transmission of sidelink control information from a) the serving cell, b) neighbour cells and c) out of coverage (i.e. pre-configured transmission resource pools).

23.10.3.2 Resource Pool for sidelink data

A set of transmission and reception resource pools for data when the UE is out of coverage for sidelink communication is pre-configured in the UE.

The resource pools for data when the UE is in coverage for sidelink communication are configured as below:

– The resource pools used for transmission and reception are configured by the eNB via RRC, in dedicated or broadcast signalling, if UE autonomous resource selection is used;

– There is no resource pool for transmission and reception if scheduled resource allocation is used.

23.10.4 Sidelink Communication via ProSe UE-to-Network Relay

A ProSe UE-to-Network Relay provides a generic L3 forwarding function that can relay any type of IP traffic between the Remote UE and the network. One-to-one and one-to-many sidelink communications are used between the Remote UE(s) and the ProSe UE-to-Network Relay. For both Remote UE and Relay UE only one single carrier (i.e., Public Safety ProSe Carrier) operation is supported (i.e., Uu and PC5 should be same carrier for Relay/ Remote UE). The Remote UE is authorised by upper layers and can be in-coverage of the Public Safety ProSe Carrier or out-of-coverage on any supported carriers including Public Safety ProSe Carrier for UE-to-Network Relay discovery, (re)selection and communication. The ProSe UE-to-Network Relay is always in-coverage of EUTRAN. The ProSe UE-to-Network Relay and the Remote UE perform sidelink communication and sidelink discovery as described in clause 23.10 and 23.11 respectively.

The eNB controls whether the UE can act as a ProSe UE-to-Network Relay:

– If the eNB broadcast any information associated to ProSe UE-to-Network Relay operation, then ProSe UE-to-Network Relay operation is supported in the cell;

– The eNB may provide:

– Transmission resources for ProSe UE-to-Network Relay discovery using broadcast signalling for RRC_IDLE state and dedicated signalling for RRC_CONNECTED state;

– Reception resources for ProSe UE-to-Network Relay discovery using broadcast signalling;

– The eNB may broadcasts a minimum and/or a maximum Uu link quality (RSRP) threshold(s) that the ProSe UE-to-Network Relay needs to respect before it can initiate a UE-to-Network Relay discovery procedure. In RRC_IDLE, when the eNB broadcasts transmission resource pools, the UE uses the threshold(s) to autonomouslystartor stop the UE-to-Network Relay discovery procedure. In RRC_CONNECTED, the UE uses the threshold(s) to determine if it can indicate to eNB that it is a Relay UE and wants to start ProSe UE-to-Network Relay discovery;

– If the eNB does not broadcast transmission resource pools for ProSe-UE-to-Network Relay discovery, then a UE can initiate a request for ProSe-UE-to-Network Relay discovery resources by dedicated signalling, respecting these broadcasted threshold(s).

– If the ProSe-UE-to-Network Relay is initiated by broadcast signalling, it can perform ProSe UE-to-Network Relay discovery when in RRC_IDLE. If the ProSe UE-to-Network Relay is initiated by dedicated signalling, it can perform relay discovery as long as it is in RRC_CONNECTED.

A ProSe UE-to-Network Relay performing sidelink communication for ProSe UE-to-Network Relay operation has to be in RRC_CONNECTED. After receiving a layer-2 link establishment request or TMGI monitoring request (upper layer message), as specified in TS 23.303 [62], from the Remote UE, the ProSe UE-to-Network Relay indicates to the eNB that it is a ProSe UE-to-Network Relay and intends to perform ProSe UE-to-Network Relay sidelink communication. The eNB may provide resources for ProSe UE-to-Network Relay communication.

The remote UE can decide when to start monitoring for ProSe UE-to-Network Relay discovery. The Remote UE can transmit ProSe UE-to-Network Relay discovery solicitation messages while in RRC_IDLE or in RRC_CONNECTED depending on the configuration of resources for ProSe UE-to-Network Relay discovery. The eNB may broadcast a threshold, which is used by the Remote UE to determine if it can transmit ProSe UE-to-Network Relay discovery solicitation messages, to connect or communicate with ProSe UE-to-Network Relay UE. The RRC_CONNECTED Remote UE, uses the broadcasted threshold to determine if it can indicate to eNB that it is a Remote UE and wants to participate in ProSe UE-to-Network Relay discovery and/or communication. The eNB may provide, transmission resources using broadcast or dedicated signalling and reception resources using broadcast signalling for ProSe UE-to-Network Relay Operation. The Remote UE stops using ProSe UE-to-Network Relay discovery and communication resources when RSRP goes above the broadcasted threshold.

NOTE: Exact time of traffic switching from Uu to PC5 or vice versa is up to higher layer.

The Remote UE performs radio measurements at PC5 interface and uses them for ProSe UE-to-Network Relay selection and reselection along with higher layer criterion, as specified in TS 23.303 [62]. A ProSe UE-to-Network Relay is considered suitable in terms of radio criteria if the PC5 link quality exceeds configured threshold (pre-configured or provided by eNB). The Remote UE selects the ProSe UE-to-Network Relay, which satisfies higher layer criterion and has best PC5 link quality among all suitable ProSe UE-to-Network Relays.

The Remote UE triggers ProSe UE-to-Network Relay reselection when:

– PC5 signal strength of current ProSe UE-to-Network Relay is below configured signal strength threshold;

– It receives a layer-2 link release message (upper layer message), as specified in TS 23.303 [62], from ProSe UE-to-Network Relay.

23.11 Support for sidelink discovery

23.11.1 General

Sidelink discovery is defined as the procedure used by the UE supporting sidelink discovery to discover other UE(s) in its proximity, using E-UTRA direct radio signals via PC5. Sidelink discovery is supported both when UE is served by EUTRAN and when UE is out of EUTRA coverage. Only ProSe-enabled Public safety UE can perform sidelink discovery when it is out of EUTRA coverage. For public safety sidelink discovery the allowed frequency is pre-configured in the UE, and is used even when UE is out of coverage of EUTRA in that frequency. The pre-configured frequency is the same frequency as the Public Safety ProSe Carrier.

Figure 23.11.1-1: PC5 interface for sidelink discovery (see TS 23.303 [62])

Upper layer handles authorization for announcement and monitoring of discovery message.

Content of discovery message is transparent to Access Stratum (AS) and no distinction in AS is made for sidelink discovery models and types of sidelink discovery, as specified in TS 23.303 [62]. However higher layer informs whether the sidelink discovery announcement is related to public safety or non-Public safety discovery. Higher layer also informs whether the discovery announcement/monitoring is related to ProSe UE-to-Network Relay discovery or other public safety discovery.

NOTE: The ProSe Protocol ensures that only valid discovery messages are delivered to AS for announcement.

The UE can participate in announcing and monitoring of discovery message in both RRC_IDLE and RRC_CONNECTED states as per eNB configuration. The UE announces and monitors its discovery message subject to the half-duplex constraint.

The UE that participates in announcing and monitoring of discovery messages maintains the current UTC time. The UE that participates in announcing transmits the discovery message, which is generated by the ProSe Protocol taking into account the UTC time upon transmission of the discovery message. In the monitoring UE, the ProSe Protocol provides the message to be verified together with the UTC time upon reception of the message to the ProSe Function.

NOTE: UE may obtain UTC time from the RAN via SIB16 or from other sources such as NITZ, NTP, and GNSS depending on their availability.

In order to perform synchronisation UE(s) participating in announcing of discovery messages may act as a synchronisation source by transmitting SBCCH and a synchronisation signal based on the resource information for synchronisation signals provided in SIB19.

There are three range classes. Upper layer authorisation provides applicable range class of the UE. Maximum allowed transmission power for each range class is signalled in SIB19. UE uses the applicable maximum allowed transmission power corresponding to its authorised range class. This puts an upper limit on the determined transmit power based on open loop power control parameters.

23.11.2 Radio Protocol Architecture

The Access Stratum protocol stack for sidelink discovery consists of only MAC and PHY.

The AS layer performs the following functions:

– Interfaces with upper layer (ProSe Protocol): The MAC layer receives the discovery message from the upper layer (ProSe Protocol). The IP layer is not used for transmitting the discovery message;

– Scheduling: The MAC layer determines the radio resource to be used for announcing the discovery message received from upper layer;

– Discovery PDU generation: The MAC layer builds the MAC PDU carrying the discovery message and sends the MAC PDU to the physical layer for transmission in the determined radio resource. No MAC header is added.

23.11.3 Radio resource allocation

There are two types of resource allocation for discovery message announcement.

– UE autonomous resource selection: A resource allocation procedure where resources for announcing of discovery message are allocated on a non UE specific basis, further characterized by:

– The eNB provides the UE(s) with the resource pool configuration used for announcing of discovery message. The configuration may be signalled in broadcast or dedicated signalling;

– The UE autonomously selects radio resource(s) from the indicated resource pool and announces discovery message;

– The UE can announce discovery message on a randomly selected discovery resource during each discovery period.

– Scheduled resource allocation: A resource allocation procedure where resources for announcing of discovery message are allocated on per UE specific basis, further characterized by:

– The UE in RRC_CONNECTED may request resource(s) for announcing of discovery message from the eNB via RRC;

– The eNB assigns resource(s) via RRC;

– The resources are allocated within the resource pool that is configured in UEs for announcement.

For UEs in RRC_IDLE:

– The eNB may select one of the following options:

– The eNB may provide resource pools for UE autonomous resource selection based discovery message announcement in SIB19. UEs that are authorized for sidelink discovery use these resources for announcing discovery message in RRC_IDLE;

– The eNB may indicate in SIB19 that it supports sidelink discovery but does not provide resources for discovery message announcement. UEs need to enter RRC_CONNECTED in order to request resources for discovery message announcement.

For UEs in RRC_CONNECTED:

– A UE authorized to perform sidelink discovery announcement indicates to the eNB that it wants to perform sidelink discovery announcement. A UE can also indicate to the eNB the frequency(s) in which sidelink discovery announcement is desired;

– The eNB validates whether the UE is authorized for sidelink discovery announcement using the UE context received from MME;

– The eNB may configure the UE with resource pool for UE autonomous resource selection for discovery message announcement via dedicated signalling;

– The eNB may configure resource pool along with dedicated resource in the form of time and frequency indices for discovery message announcement via dedicated RRC signalling;

– The resources allocated by the eNB via dedicated signalling are valid until;

– The eNB re-configures the resource(s) by RRC signalling or;

– The UE enters RRC_IDLE.

Authorised receiving UEs in RRC_IDLE and RRC_CONNECTED monitor resource pools used for UE autonomous resource selection and resource pools for scheduled resource allocation. The eNB provides the resource pool configuration used for discovery message monitoring on intra frequency, inter frequency of same or different PLMNs cells in RRC signalling (SIB19). The RRC signalling (SIB19 or dedicated) may contain detailed sidelink discovery configuration used for announcement of sidelink discovery in cells of intra-frequency, inter-frequency of same or different PLMNs.

Synchronous and asynchronous deployments are supported. Discovery resources can be overlapping or non-overlapping across cells.

A UE, if authorised by the NW, can announce discovery messages in the same as well as other frequencies than the serving cell, in same or different PLMNs. The UE can monitor discovery resources in the same as well as other frequencies than the serving cell, in same or different PLMNs:

– The serving cell may provide in SIB19 a list of frequencies along with PLMN ID on which the UE may aim to monitor discovery message. The serving cell may provide in SIB19 a list of frequencies along with PLMN ID on which the UE is allowed to announce discovery message.

– The serving cell may not provide detailed sidelink discovery configuration and cell (re)selection parameters for other carrier frequencies of same or other PLMNs in RRC signalling.

– If detailed sidelink discovery configuration and cell (re)selection parameters for other frequencties of same or different PLMN is not provided by serving cell in SIB19, the eNB may indicate if the UE should read SIB19 and other relevant SIBs on other carriers or the UE should request detailed sidelink discovery configuration from serving cell, if it wants to perform discovery message announcement on those carriers of same or other PLMNs. A UE only reads SIB19 and other relevant SIBs of authorised carriers and authorised PLMN:

– Obtaining sidelink discovery configuration by reading SIB19 (and other SIBs) of an inter-frequency and/or inter-PLMN cell shall not affect the UE’s Uu reception on the serving cell(s).

– If a UE performs sidelink discovery announcement on another frequency, irrespective of whether the eNB provides cell (re)selection parameters for the other frequency of same or different PLMN, the UE follows the same legacy cell (re)selection procedure.

– If SIB19 is not broadcasted by the serving cell, the UE may perform sidelink discovery announcement and monitoring on another carrier of same or different PLMN that is authorised by the network, as long as it does not affect Uu operation.

– The UE is not expected to perform any PLMN change for the purpose of inter-PLMN sidelink discovery announcement.

– If the UE autonomously reads SIB 19 of the other carrier of same or different PLMN to acquire resource for sidelink discovery announcement and that carrier does not provide resources for sidelink discovery announcement in SIB19, then the UE shall not perform sidelink discovery announcement on that carrier.

– The UE performs intra-frequency and inter-frequency of same or different PLMN sidelink discovery announcement or monitoring in subframes in which a sidelink discovery resource pool is configured.

– To enhance intra-frequency and inter-frequency sidelink discovery performance for the non-dedicated transceiver case the eNB may provide gaps to the UE, so that RF transmitter/receiver chain can be reused for sidelink discovery transmissions/receptions:

– The gaps provided for sidelink discovery transmission and/or reception takes into account any additional overhead (e.g. for synchronization, subframe offset between serving carrier and sidelink discovery carrier, interruption time for retuning). The eNB can deconfigure a configured sidelink discovery transmission and /or reception gaps.

– Configured discovery gaps are applicable for all configured cells of a UE.

– If SIB19 is not broadcasted by the serving cell the UE shall not enter RRC_CONNECTED on the serving cell to request gaps or resources for sidelink discovery announcement.

– The eNB may indicate in broadcast or dedicated signalling if the UE can request gaps. Based on implementation the UE can trigger a gap request for sidelink discovery announcement or monitoring. In the request the UE informs the eNB of the subframes (with respect to the timing of serving cell) on which the UE needs gaps.

NOTE: The UE is not expected to monitor any physical downlink channels during sidelink discovery reception gaps. During transmission gap, the UE prioritizes discovery announcement over Uu uplink transmission and sidelink communication transmission only when a conflict with sidelink discovery announcement occurs. The UE prioritizes the RACH procedure over the sidelink gaps.

NOTE: Measurement requirements on the serving frequency should not be affected by sidelink gaps.

– If network does not configure transmission and reception gaps for sidelink discovery.

– Intra-frequency, inter-frequency of same and other PLMN sidelink discovery announcement shall not affect Uu transmission:

– Intra-frequency, inter-frequency and inter-PLMN sidelink discovery monitoring shall not affect Uu reception:

– The UE shall not create autonomous gaps for announcement or monitoring of sidelink discovery.

– The UE uses DRX occasions in RRC_IDLE and RRC_CONNECTED or second RX chain if it is available, for intra- frequency, inter-frequency and inter-PLMN discovery message monitoring;

– An RRC_CONNECTED UE sends a Sidelink UE Information message to the serving cell if it is interested or no longer interested in intra-frequency, inter-frequency or inter-PLMN discovery message monitoring.

If the S-Criteria on the ProSe carrier for Public Safety is not met, the UE can use Public Safety ProSe Carrier discovery resources preconfigured in the UICC or ME for out of coverage sidelink discovery.

NOTE: All sidelink discovery for Public Safety (for a UE) is performed on a single preconfigured Public Safety ProSe Carrier, which is valid in the operating region. Higher layers check validity of the Public Safety ProSe Carrier in the operating region.

23.12 Resource usage reporting for shared networks

The eNB may be configured to report the resource usage as data volume for the different PLMN identities of the operators in a shared network. The measurements, which are defined in TS 36.314 [63], are based on the QoS parameter values exchanged at E-RAB setup/modification.

OAM configures data volume reporting criteria. The configured data volume criteria define the PLMN IDs and the QoS profile criteria for the collection and reporting. The data volume reports are per configured PLMN ID and per configured QoS profile per DL/UL.

The QoS profile configuration shall be the same for all configured PLMN IDs and for all eNBs. The configured QoS profile criteria can differ in UL and DL in terms of GBR ranges. It shall be possible to collect and report up to 200 counter types and a maximum of 200 counter instances.

Data volumes for the DL/UL direction of a GBR bearer shall be collected within a given DL/UL GBR range if the DL/UL E-RAB guaranteed bit rate is within a configured DL/UL range delimited by a minimum and maximum value. The GBR ranges shall be five in number for DL and five in number for UL. GBR ranges shall be non-overlapping and configurable. The configured set of GBR ranges applies to the whole RAN and to all PLMN IDs in the RAN.

23.13 Optimising signalling load and resource usage for paging

23.13.1 General paging optimisation

Paging can be optimised by the MME and the E-UTRAN as described in TS 23.401 [17].

As a part of this, an eNB may inform the MME about a list of recommended eNBs for paging. If a recommended eNB in this list is a HeNB behind a HeNB GW, the paging target is identified by the TAI instead of the eNB identity.

Paging Attempt Information consists of a Paging Attempt Count and the Intended Number of Paging Attempts and may include the Next Paging Area Scope. If Paging Attempt Information is included in the Paging message, each paged eNB receives the same information during a paging attempt. The Paging Attempt Count shall be increased by one at each new paging attempt. The Next Paging Area Scope, when present, indicates whether the MME plans to modify the paging area currently selected at next paging attempt. If the UE has changed its mobility state to ECM CONNECTED the Paging Attempt Count is reset.

23.13.2 Paging optimisation for UEs in enhanced coverage

Information on the coverage enhancement (CE) level, if available for the UE, is provided transparently by the serving eNB to the MME at transition to ECM_IDLE together with the respective cell identifier and is provided to the E-UTRAN during paging. The Paging Attempt Information, as defined in 23.13.1, is always provided to all paged eNBs for UEs for which the information on the coverage enhancement level has been received.

23.14 Support for V2X services

23.14.1 General

23.14.1.0 Overview

Vehicular communication services, represented by V2X services, can consist of the following four different types: V2V, V2I, V2N and V2P, as specified in TS 22.185 [71].

V2X services can be provided by PC5 interface and/or Uu interface. Support of V2X services via PC5 interface is provided by V2X sidelink communication as specified in TS 23.285 [72] and/or NR sidelink communication as specified in TS 23.287 [93], which are modes of communication whereby UEs can communicate with each other directly over the PC5 interface. Both communication modes may be supported when the UE is served by E-UTRAN and when the UE is outside of E-UTRA coverage. Only the UEs authorised to be used for V2X services can perform V2X sidelink communication and/or NR sidelink communications for V2X services.

23.14.1.1 Support for V2X sidelink communication

The user plane protocol stack and functions, as specified in clause 23.10.2.1 for sidelink communication, are also used for V2X sidelink communication. In addition, for V2X sidelink communication:

– STCH for sidelink communication is also used for V2X sidelink communication.

– Non-V2X (e.g. Public Safety) data is not multiplexed with V2X data transmitted in resources configured for V2X sidelink communication.

– The Access Stratum (AS) is provided with the PPPP and PPPR of a protocol data unit transmitted over PC5 interface by upper layers. The packet delay budget (PDB) of the protocol data unit can be determined from the PPPP. The low PDB is mapped to the high priority PPPP value (TS 23.285 [72]).

– The Access Stratum (AS) is provided with a transmit profile (TS 23.285 [72]) of a protocol data unit transmitted over PC5 interface by upper layers.

– The logical channel prioritization based on PPPP is used for V2X sidelink communication.

Control plane protocol stack for SBCCH as specified in clause 23.10.2.2 for sidelink communication is also used for V2X sidelink communication.

The UE supporting V2X sidelink communication can operate in two modes for resource allocation:

– Scheduled resource allocation, characterized by:

– The UE needs to be RRC_CONNECTED in order to transmit data;

– The UE requests transmission resources from the eNB. The eNB schedules transmission resources for transmission of sidelink control information and data. Sidelink SPS is supported for scheduled resource allocation;

– UE autonomous resource selection, characterized by:

– The UE on its own selects resources from resource pools and performs transport format selection to transmit sidelink control information and data;

– If mapping between the zones and V2X sidelink transmission resource pools is configured, the UE selects V2X sidelink resource pool based on the zone UE is located in.

– The UE performs sensing for (re)selection of sidelink resources. Based on sensing results, the UE (re)selects some specific sidelink resources and reserves multiple sidelink resources. Up to 2 parallel independent resource reservation processes are allowed to be performed by the UE. The UE is also allowed to perform a single resource selection for its V2X sidelink transmission.

In order to assist the eNB to provide sidelink resources, the UE in RRC_CONNECTED may report geographical location information to the eNB. The eNB can configure the UE to report the complete UE geographical location information based on periodic reporting via the existing measurement report signaling.

Geographical zones can be configured by the eNB or pre-configured. When zones are (pre)configured, the world is divided into geographical zones using a single fixed reference point (i.e. geographical coordinates (0, 0)), length and width. The UE determines the zone identity by means of modulo operation using length and width of each zone, number of zones in length, number of zones in width, the single fixed reference point and the geographical coordinates of the UE’s current location. The length and width of each zone, number of zones in length and number of zones in width are provided by the eNB when the UE is in coverage and pre-configured when the UE is out of coverage. The zone is configurable for both in coverage and out of coverage.

For in coverage UE, when the UE uses UE autonomous resource selection, the eNB can provide the mapping between zone(s) and V2X sidelink transmission resource pools in RRC signalling. For out of coverage UEs, the mapping between the zone(s) and V2X sidelink transmission resource pools can be pre-configured. If a mapping between zone(s) and V2X sidelink transmission resource pool is (pre-)configured, the UE selects transmission sidelink resources from the resource pool corresponding to the zone where it is currently located. The zone concept is not applied to exceptional V2X sidelink transmission pools as well as reception pools. Resource pools for V2X sidelink communication are not configured based on priority.

For V2X sidelink transmission, during handover, transmission resource pool configurations including exceptional transmission resource pool for the target cell can be signaled in the handover command to reduce the transmission interruption. In this way, the UE may use the V2X sidelink transmission resource pools of the target cell before the handover is completed as long as either synchronization is performed with the target cell in case eNB is configured as synchronization source or synchronization is performed with GNSS in case GNSS is configured as synchronization source. If the exceptional transmission resource pool is included in the handover command, the UE uses randomly selected resources from the exceptional transmission resource pool, starting from the reception of handover command. If the UE is configured with scheduled resource allocation in the handover command, the UE continues to use the exceptional transmission resource pool while the timer associated with handover is running. If the UE is configured with autonomous resource selection in the target cell the UE continues to use the exceptional transmission resource pool until the sensing results on the transmission resource pools for autonomous resource selection are available. For exceptional cases (e.g. during RLF, during transition from RRC IDLE to RRC CONNECTED or during change of dedicated V2X sidelink resource pools within a cell), the UE may select resources in the exceptional pool provided in serving cell’s SIB21 or in dedicated signalling based on random selection, and uses them temporarily. During cell reselection, the RRC_IDLE UE may use the randomly selected resources from the exceptional transmission resource pool of the reselected cell until the sensing results on the transmission resource pools for autonomous resource selection are available.

In order to avoid interruption time in receiving V2X messages due to delay in acquiring reception pools broadcasted from the target cell, synchronisation configuration and reception resource pool configuration for the target cell can be signaled to RRC_CONNECTED UEs in the handover command. For RRC_IDLE UE, it is up to UE implementation to minimize V2X sidelink transmission/reception interruption time associated with acquisition of SIB21 of the target cell.

A UE is considered in-coverage on the carrier used for V2X sidelink communication whenever it detects a cell on that carrier as per criteria specified in TS 36.331 [16]. If the UE that is authorized for V2X sidelink communication is in-coverage on the frequency used for V2X sidelink communication or if the eNB provides V2X sidelink configuration for that frequency (including the case where UE is out of coverage on that frequency), the UE uses the scheduled resource allocation or UE autonomous resource selection as per eNB configuration. When the UE is out of coverage on the frequency used for V2X sidelink communication and if the eNB does not provide V2X sidelink configuration for that frequency, the UE may use a set of transmission and reception resource pools pre-configured in the UE. V2X sidelink communication resources are not shared with other non-V2X data transmitted over sidelink.

An RRC_CONNECTED UE may send a Sidelink UE Information message to the serving cell if it is interested in V2X sidelink communication transmission in order to request sidelink resources.

If the UE is configured by upper layers to receive V2X sidelink communication and V2X sidelink reception resource pools are provided, the UE receives on those provided resources.

Reception of V2X sidelink communication in different carriers/PLMNs can be supported by having multiple receiver chains in the UE.

For sidelink SPS, maximum 8 SPS configurations with different parameters can be configured by eNB and all SPS configurations can be active at the same time. The activation/deactivation of SPS configuration is signalled via PDCCH by eNB. The existing logical channel prioritization based on PPPP is used for sidelink SPS.

UE assistance information can be provided to eNB. Reporting of UE assistance information is configured by eNB for V2X sidelink communication. The UE assistance information used for V2X sidelink communication includes traffic characteristic parameters (e.g. a set of preferred SPS interval, timing offset with respect to subframe 0 of the SFN 0, PPPP, PPPR, Destination Layer-2 ID, and maximum TB size based on observed traffic pattern) related to the SPS configuration. The UE assistance information can be reported in case either SPS is already configured or not. Triggering of UE assistance information transmission is left to UE implementation. For instance, the UE is allowed to report UE assistance information when change in estimated periodicity and/or timing offset of packet arrival occurs. SR mask per traffic type is not supported for V2X sidelink communication.

The serving cell can provide synchronization configuration for the carrier used for V2X sidelink communication. In this case, the UE follows the synchronization configuration received from serving cell. In case there is no cell detected on the carrier used for V2X sidelink communication and the UE does not receive synchronization configuration from serving cell, the UE follows preconfigured synchronization configuration. There are three types of synchronization reference, namely eNB, UE and GNSS. In case GNSS is configured as synchronization source, the UE utilizes the UTC time and (pre)configured DFN offset to calculate direct frame number and subframe number. In case eNB timing is configured as synchronization reference to the UE, for synchronization and DL measurements, the UE follows the cell associated with the concerned frequency (when in-coverage on this frequency), or the PCell or the serving cell (when out of coverage on the concerned frequency). UE can indicate the current synchronization reference type it is using to the eNB. One transmission pool for scheduled resource allocation is configured, taking into account the synchronization reference of the UE.

For controlling channel utilization, the network is able to indicate how the UE adapts its transmission parameters for each transmission pool depending on the Channel Busy Ratio (CBR). The UE measures all the configured transmission pools including exceptional pool. If a pool is (pre)configured such that a UE shall always transmit PSCCH and PSSCH in adjacent resource blocks the UE measures PSCCH and PSSCH resources together. If a pool is (pre)configured such that a UE may transmit PSCCH and the corresponding PSSCH in non-adjacent resource blocks in a subframe then PSSCH pool and PSCCH pool are measured separately.

A UE in RRC_CONNECTED can be configured to report CBR measurement results. For CBR reporting, periodic reporting and event triggered reporting are supported. Two reporting events are introduced for event-triggered CBR reporting. In case PSSCH and PSCCH resources are placed non-adjacently, only PSSCH pool measurement is used for event-triggered CBR reporting. In case PSSCH and PSCCH resources are placed adjacently, CBR measurement of both the PSSCH and PSCCH resources is used for event-triggered CBR reporting. Event-triggered CBR reporting is triggered by overloaded threshold and/or less-loaded threshold. The network can configure which of the transmission pools the UE needs to report.

A UE (regardless of its RRC state) performs transmission parameter adaptation based on the CBR. In case PSSCH and PSCCH resources are placed non-adjacently, only PSSCH pool measurement is used for transmission parameter adaptation. In case PSSCH and PSCCH resources are placed adjacently, CBR measurement of both the PSSCH and PSCCH resources is used for transmission parameter adaptation. When CBR measurements are not available, the default transmission parameters are used. The exemplary adapted transmission parameters include maximum transmission power, range of the number of retransmission per TB, range of PSSCH RB number, range of MCS, maximum limit on channel occupancy ratio. The transmission parameter adaption applies to all transmission pools including exceptional pool.

A UE using scheduled resource allocation may be configured to perform sensing and periodically report the sensing result. The UE performs sensing only in the V2X sidelink transmission resource pool(s) for which reporting is configured.

For V2X sidelink communication, sidelink transmission and/or reception resources including exceptional pool for different frequencies for scheduled resource allocation and UE autonomous resource selection may be provided. The sidelink resources for different frequencies can be provided via dedicated signalling, SIB21 and/or preconfiguration. The serving cell may indicate to the UE only the frequency on which the UE may acquire the resource configuration for V2X sidelink communication. If multiple frequencies and associated resource information are provided, it is up to UE implementation to select the frequency among the provided frequencies. The UE shall not use preconfigured transmission resource if the UE detects a cell providing resource configuration or inter-carrier resource configuration for V2X sidelink communication. Frequencies which may provide V2X sidelink communication resource configuration or cross-carrier configuration can be signalled in SIB21 or pre-configured in the UE. The RRC_IDLE UE may prioritize the frequency that provides cross-carrier resource configuration for V2X sidelink communication during cell reselection.

If the UE supports multiple transmission chains, it may simultaneously transmit on multiple carriers via PC5. For the case where multiple frequencies for V2X are supported, a mapping between V2X service types and V2X frequencies is configured by upper layers. The UE should ensure a V2X service to be transmitted on the corresponding frequency. For scheduled resource allocation, the eNB can schedule a V2X transmission on a frequency based on the Sidelink BSR, as specified in TS 36.321 [13], in which the UE includes the Destination Index uniquely associated with a frequency reported by the UE to the eNB in Sidelink UE Information message as specified in TS 36.331 [16].

Carrier aggregation (CA) in sidelink is supported for V2X sidelink communication. It applies to both in coverage UEs and out of coverage UEs. For CA in sidelink, neither primary component carrier nor secondary component carriers are defined. Each resource pool (pre)configured for V2X sidelink communication transmission or reception is associated to a single carrier. When a UE supporting CA in sidelink uses autonomous resource selection, it performs carrier selection and may select one or more carriers used for V2X sidelink communication transmission. The carrier selection is performed at MAC layer, depending on the CBR of the (pre)configured carriers for V2X sidelink communication and the PPPP(s) of the V2X messages to be transmitted. The carrier reselection may be performed when resource reselection is triggered and is triggered for each sidelink process. In order to avoid frequent switching across different carriers, the UE may keep using a carrier already selected for transmission, if the measured CBR on this carrier is lower than a (pre)configured threshold. All selected carriers should have the same synchronization reference or the same synchronization priority configuration. For a UE using autonomous resource selection, logical channel prioritization is performed for a sidelink resource on a carrier depending on the CBR measured on the carrier and the PPPP of the sidelink logical channels as specified in TS 36.321 [13].

Sidelink packet duplication is supported for V2X sidelink communication and is performed at PDCP layer of the UE. For sidelink packet duplication for transmission, a PDCP PDU is duplicated at the PDCP entity. The duplicated PDCP PDUs of the same PDCP entity are submitted to two different RLC entities and associated to two different sidelink logical channels respectively. The duplicated PDCP PDUs of the same PDCP entity are only allowed to be transmitted on different sidelink carriers. A UE can activate or deactivate sidelink packet duplication based on (pre)configuration. Sidelink packet duplication does not apply to transmission with Rel-14 transmit profile (TS 23.285 [72]). The PPPR value(s) for which sidelink packet duplication is supported can be (pre)configured via a PPPR threshold. For UE autonomous resource selection and scheduled resource allocation, the UE shall perform sidelink packet duplication for the data with the configured PPPR value(s) until packet duplication is deconfigured for these PPPR value(s). For scheduled resource allocation, the UE reports the amount of data associated with one or more PPPR values, and the destination(s) to which the data belongs via sidelink BSR(s). A mapping of PPPR values to logical channel groups can be configured by the eNB, and the PPPR value(s) are reflected by the associated logical channel group ID included in the sidelink BSR(s). A list of PPPR value(s) may be reported in Sidelink UE information by an RRC_CONNECTED UE.

For a UE using scheduled resource allocation, two non-overlapped sets of carriers are configured by the eNB per Destination reported by the UE to the network, and they apply to all the PPPR(s) that are configured for sidelink packet duplication. The UE then associates two duplicated sidelink logical channels corresponding to the same PDCP entity respectively with the two sets of carriers configured for the Destination of the two sidelink logical channels. The association between the duplicated sidelink logical channel and the carrier set is up to UE implementation. Data of a duplicated sidelink logical channel can only be transmitted on the carrier(s) in the associated carrier set.

For V2X sidelink communication reception, packet duplication detection is performed at PDCP layer of the UE. Reordering function is also supported at PDCP layer and how to set the reordering timer at the PDCP layer is up to UE implementation. There are specific logical channel identities which apply to the sidelink logical channel used for sidelink packet duplication exclusively as specified in TS 36.321 [13].

The UE may receive the V2X sidelink communication of other PLMNs. The serving cell can indicate to the UE the resource configuration for V2X sidelink communication reception for inter-PLMN operation directly or only the frequency on which the UE may acquire the inter-PLMN resource configuration for V2X sidelink communication reception. V2X sidelink communication transmission in other PLMNs is not allowed.

When UL transmission overlaps in time domain with V2X sidelink transmission in the same frequency, the UE prioritizes the V2X sidelink transmission over the UL transmission if the PPPP of sidelink MAC PDU is lower than a (pre)configured PPPP threshold; otherwise, the UE prioritizes the UL transmission over the V2X sidelink transmission. When UL transmission overlaps in time domain with V2X sidelink transmission in different frequency, the UE may prioritize the V2X sidelink transmission over the UL transmission or reduce UL transmission power if the PPPP of sidelink MAC PDU is lower than a (pre)configured PPPP threshold; otherwise, the UE prioritizes the UL transmission over the V2X sidelink transmission or reduces V2X sidelink transmission power. However, if UL transmission is prioritized by upper layer as specified in TS 24.386 [75] or random access procedure is performed, the UE prioritizes UL transmission over any V2X sidelink transmission (i.e. irrespectively of the sidelink MAC PDU’s PPPP).

Resource pool for transmission of pedestrian UE (P-UE) may be overlapped with resources for V2X sidelink communication. For each transmission pool, resource selection mechanism (i.e. random selection, partial sensing based selection or either random selection or partial sensing based selection), which is allowed to be used in this pool, is also configured. If P-UE is configured to use either random selection or partial sensing based selection for one transmission pool, it is up to UE implementation to select a specific resource selection mechanism. If the P-UE is configured to use partial sensing based selection only, the P-UE shall use partial sensing based selection in the pool. The P-UE shall not do random selection in the pool wherein only partial sensing is allowed. If the eNB does not provide a random selection pool, the P-UEs that support only random selection cannot perform sidelink transmission. In exceptional pool, the P-UE uses random selection. The P-UE can send Sidelink UE Information message to indicate that it requests resource pools for P2X-related V2X sidelink communication transmission as specified in TS 36.331 [16].

It is not mandatory for P-UE to support zone based resource selection. The P-UE reports whether it supports zone based resource selection as part of UE capability signalling. If the P-UE supports zone based resource selection, the network can provide zone based configuration via only dedicated signalling.

Power saving of P-UE can be achieved by UE implementation and upper layer mechanisms. P-UE does not perform CBR measurement. However, P-UE adjusts the transmission parameters based on the default transmission parameter configuration, which can be provided to the P-UE via RRC signalling.

To support the co-existence of CEN DSRC and V2X sidelink communication, the upper layers of the UE which is performing V2X sidelink communication send an indication to lower layers when the UE is within the proximity of CEN DSRC tolling station(s).

23.14.1.2 Support for V2X communication via Uu

For V2X communication in uplink, maximum 8 SPS configurations with different parameters can be configured by eNB and all SPS configurations can be active at the same time. The activation/deactivation of each SPS configuration is signalled via PDCCH by eNB. The existing logical channel prioritization for Uu is used.

For V2X communication, UE assistance information can be provided to eNB. Reporting of UE assistance information is configured by eNB. The UE assistance information includes parameters (e.g. a set of preferred SPS interval, timing offset with respect to subframe 0 of the SFN 0, LCID and maximum TB size based on observed traffic pattern) related to the SPS configuration. Triggering of UE assistance information transmission is left to UE implementation. For instance, the UE is allowed to report the UE assistance information when change in estimated periodicity and/or timing offset of packet arrival occurs. For V2X communication via Uu, SR mask as per legacy mechanism can be used.

For unicast transmission of V2X messages, the V2X message can be delivered via Non-GBR bearers as well as GBR bearers. In order to meet the QoS requirements for V2X message delivery for V2X services, a Non-GBR QCI value and a GBR QCI value for V2X messages are used as specified in TS 23.285 [72].

For broadcasting V2X messages, SC-PTM or MBSFN transmission can be used. In order to reduce SC-PTM/MBSFN latency, shorter (SC-)MCCH repetition period for SC-PTM/MBSFN, modification period for SC-PTM/MBSFN and MCH scheduling period for MBSFN are supported. Reception of downlink broadcast of V2X messages in different carriers/PLMNs can be supported by having multiple receiver chains in the UE. A GBR QCI value is used for the delivery of V2X messages over MBMS bearers as specified in TS 23.285 [72].

23.14.1.3 Void

23.15 Support for MMTEL voice and video enhancements

23.15.1 RAN-assisted codec adaptation

RAN-assisted codec adaptation provides a means for the eNB to send codec adaptation indication with recommended bit rate to assist the UE to select or adapt to a codec rate for MMTEL voice or MMTEL video. The RAN-assisted codec adaptation mechanism supports the uplink/downlink bit rate increase or decrease. For a bearer associated with configuration of MBR greater than GBR (see clauses 11.4 and 13.2), the recommended uplink/downlink bit rate is within boundaries set by the MBR and GBR of the concerned bearer.

For uplink or downlink bit rate adaptation, eNB may send a recommended bit rate to the UE to inform the UE on the currently recommended transport bit rate on the local uplink or downlink, which the UE may use in combination with other information to adapt the bit rate, e.g. the UE may send a bit rate request to the peer UE via application layer messages as specified in TS 26.114 [74], which the peer UE may use in combination with other information to adapt the codec bit rate. The recommended bit rate is in kbps at the physical layer at the time when the decision is made.

The recommended bit rate for UL and DL is conveyed as a MAC Control Element (CE) from the eNB to the UE as outlined in Figure 23.15.1-1.

Figure 23.15.1-1: UL or DL bit rate recommendation

Based on the recommended bit rate from the eNB, a UE may initiate an end-to-end bit rate adaptation with its peer (UE or MGW). The UE may also send a query message to its local eNB to check if a bit rate recommended by its peer can be provided by the eNB. The UE is not expected to go beyond the recommended bit rate from the eNB.

The recommended bit rate query message is conveyed as a MAC Control Element (CE) from the UE to the eNB as outlined in Figure 23.15.1-2.

Figure 23.15.1-2: UL or DL bit rate recommendation query

A prohibit timer can be configured per logical channel by the network to limit UEs sending frequent query MAC CEs. Independent prohibit timers are used for each direction (uplink and downlink) to prohibit the UE from retransmitting exactly the same query MAC CE to the eNB during the configured time.

23.15.2 MMTEL signalling optimisation

In case of network congestion (e.g. maximum number of users that can be connected, poor radio conditions, etc), an operator may want to prioritize MMTEL voice/MMTEL video access. For both type of accesses, the MO voice call cause value is used.

During the re-direction procedure, if the UE receives the RRC Connection Release message with redirection and the voice call is ongoing, the UE keeps the call in the application layer. After the UE re-accesses the network, the voice GBR bearer can be recovered immediately.

23.15.3 MMTEL voice quality/coverage enhancements

In order to enhance the voice quality and coverage, the techniques for PUSCH coverage enhancement introduced in Rel-13 for CE Mode A can be configured also for UEs in non-CE mode. These techniques are applied in a new PUSCH enhancement mode and include:

– PUSCH subframe repetition with intra-bundle or inter-bundle frequency hopping and

– UL asynchronous HARQ operation.

The PUSCH enhancement mode can be enabled only on PCell. In the PUSCH enhancement mode, the PUSCH maximum bandwidth is 20MHz. The UE transition between normal mode and PUSCH enhancement mode is controlled and triggered by RRC signalling, As part of the transition procedure, the UL HARQ operation switches between synchronous (normal mode) and asynchronous (PUSCH enhancement mode), with a partial MAC reset.

PUSCH coverage enhancement requires that air interface delay budget can be relaxed to increase the robustness of the transmission. Such relaxation may be achieved when a UE in good coverage indicates a preference to the eNB to reduce the local air interface delay by sending a UEAssistanceInformation message with delayBudgetReport set to type1 to decrease the DRX cycle length, so that the E2E delay and jitter can be reduced. The peer UE in bad coverage can send a UEAssistanceInformation message with delayBudgetReport set to type2 to its eNB to indicate a preference on Uu air interface delay adjustments, see TS 36.331 [16], TS 36.211 [4] and TS 36.213 [6]. Based on the UE report and other information, the E-UTRAN may configure the UE with coverage enhancement techniques. When the UE detects changes such as end-to-end MMTEL voice quality or local radio quality, the UE may inform the eNB its new preference by sending UEAssistanceInformation messages with updated contents.

23.16 Application Layer Measurement Collection

This function enables collection of application layer measurements from the UE. The supported service types are QoE Measurement Collection for streaming services and QoE Measurement Collection for MTSI services. The feature is activated by Trace Function from the MDT framework (see clause 19.2.1.17 and TS 37.320 [43]). Both signalling based and management based initiation cases are allowed. For the signalling based case, the Application Layer Measurement Collection is initiated towards a specific UE from CN nodes using the MDT mechanism as described in clause 5.1.3 of TS 37.320 [43]; for the management based case, the Application Layer Measurement Collection is initiated from OAM targeting an area (without targeting a specific UE).

Application layer measurement configuration received from OAM or CN is encapsulated in a transparent container, which is forwarded to UE in a downlink RRC message. Application layer measurements received from UE’s higher layer are encapsulated in a transparent container and sent to network in an uplink RRC message, as specified in TS 36.331 [16]. The application layer measurement configuration and measurement reporting are supported in RRC_CONNECTED state only. E-UTRAN can release the application layer measurement configuration towards the UE at any time.

23.17 Support for Aerial UE communication

23.17.1 General

E-UTRAN based mechanisms providing LTE connection to UEs capable of Aerial communication are supported via the following functionalities:

– subscription-based Aerial UE identification and authorization, as specified in TS 23.401 [17], clause 4.3.31.

– height reporting based on the event that the UE’s altitude has crossed a network-configured reference altitude threshold.

– interference detection based on a measurement reporting that is triggered when a configured number of cells (i.e. larger than one) fulfills the triggering criteria simultaneously.

– signalling of flight path information from UE to E-UTRAN.

– Location information reporting, including UE’s horizontal and vertical velocity.

23.17.2 Subscription based identification of Aerial UE function

Support of Aerial UE function is stored in the user’s subscription information in HSS. HSS transfers this information to the MME during Attach, Service Request and Tracking Area Update procedures.

The subscription information can be provided from the MME to the eNB via the S1-AP Initial Context Setup Request during Attach, Tracking Area Update and Service Request procedures. The subscription information can also be updated via the S1-AP UE Context Modification Request message. In addition, for X2-based handover, the source eNodeB can include the subscription information in the X2-AP Handover Request message to the target eNodeB.

For the intra and inter MME S1 based handover, the MME provides the subscription information to the target eNB after the handover procedure.

23.17.3 Height based reporting for Aerial UE communication

An aerial UE can be configured with event based height reporting. UE sends height report when the altitude of the aerial UE is above or below a configured threshold. The report contains height and location if configured as described in 23.17.6.

23.17.4 Interference detection and mitigation for Aerial UE communication

For interference detection, an aerial UE can be configured with RRM event A3, A4 or A5 that triggers measurement report when individual (per cell) RSRP values for a configured number of cells fulfill the configured event. Once such condition is met and a measurement report is sent, the list of triggered cells is updated when subsequent cell(s) fulfil the event, however further measurement reports are not sent while the list of triggered cells remains larger than the configured number of cells. The report contains RRM results and location if configured, as described in 23.17.6.

For interference mitigation an aerial UE can be configured with a dedicated UE-specific alpha parameter for PUSCH power control.

23.17.5 Flight path information reporting

E-UTRAN can request a UE to report flight path information consisting of a number of waypoints defined as 3D locations as defined in TS 36.355 [78]. A UE reports up to configured number of waypoints if flight path information is available at the UE. The report can consist also time stamps per waypoint if configured in the request and if available at the UE.

23.17.6 Location reporting for Aerial UE communication

Location information for Aerial UE communication can include horizontal and vertical speed if configured. Location information can be included in RRM report and in height report.

23.18 PDCP packet duplication

PDCP packet duplication is configured for a RB by RRC where two logical channels are configured for the RB. The two logical channels can either belong to the same MAC entity (referred to as CA duplication) or different MAC entities (referred to as DC duplication). When activated, PDCP packet duplication allows sending the same PDCP PDU on two independent transmission paths: via the primary RLC entity and a secondary RLC entity, thus increasing reliability and reducing latency.

PDCP packet duplication is supported in the following cases:

– for SRBs using RLC AM;

– for DRBs using RLC UM or AM.

For DRBs, duplication can be activated and deactivated by a MAC CE. In addition, for DRBs, PDCP packet duplication can be activated upon configuration by RRC signalling. For SRBs, once duplication is configured, it is always activated.

When PDCP packet duplication is activated, the associated logical channels are restricted to be sent only on certain serving cells to ensure the duplicates are sent on different serving cells. The restriction is lifted when PDCP packet duplication is deactivated. When CA duplication is configured for an SRB, one of the logical channels associated to the SRB is restricted to be sent only on the serving cells including PCell and PSCell.

At the receiver, PDCP enables reordering and duplication detection when PDCP packet duplication is configured.

When activating duplication for a DRB, E-UTRAN should ensure that at least one serving cell is activated for each logical channel of the DRB; and when the deactivation of SCells leaves no serving cells activated for a logical channel of the DRB, E-UTRAN should ensure that duplication is also deactivated.

23.19 E-UTRAN control for NR sidelink communication

NR sidelink communication may be used to support other services than V2X services as in clause 23.14.1.0. When the UE is served by E-UTRAN, if the UE supports and is authorized to perform NR sidelink communication in E-UTRAN, NR sidelink communication can be configured and controlled by E-UTRAN via dedicated signaling and/or system information, using the procedures specified in TS 38.300 [79], with the following restrictions to operation of NR sidelink communication controlled by E-UTRAN:

– Dynamic sidelink scheduling and the configured sidelink grant with type 2 are not supported for the UE served by E-UTRAN.

– The prioritization between EUTRA UL transmission and NR SL transmission, if needed, is performed based on the priority of sidelink MAC PDU only, except that the UL transmission is prioritized by upper layer as specified in TS 24.386 [75] or random access procedure is performed.

23.20 Support for Multi-USIM devices

23.20.1 General

E-UTRAN may support one or more of the following enhancements for MUSIM UE operation:

– Paging Collision Avoidance, as described in clause 23.20.2;

23.20.2 Paging Collision Avoidance

The purpose of paging collision avoidance is to address the overlap of paging occasions on both USIMs when a MUSIM (e.g. dual USIM device) is in RRC_IDLE/RRC_INACTIVE state in both the networks (e.g. Network A and Network B) associated with respective USIMs.

A MUSIM device UE may determine potential paging collision on two networks and may trigger actions to prevent potential paging collision on E-UTRA connected to EPC as specified in TS 23.401 [17] or E-UTRA connected to 5GC as specified in TS 23.501 [82].

Editor’s Note: It is left to UE implementation as to how it selects one of the two RATs/networks for paging collision avoidance.

23.21 Support for BL UEs, UEs in enhanced coverage and NB-IoT UEs over Non-Terrestrial Networks

23.21.1 General

Support for BL UEs, UEs in enhanced coverage and NB-IoT UEs over Non-Terrestrial Networks (see clause 4.12) is only applicable to E-UTRA connected to EPC. UEs not supporting NTN are barred from accessing an NTN cell.

In NTN, only BL UEs, UEs in enhanced coverage and NB-IoT UEs with GNSS capability are supported in this release of the specification.

To accommodate long propagation delays in NTN, increased timer values and window sizes, or delayed starting times are supported for the physical layer and for higher layers.

UL segmented transmission is supported for UL transmission with repetitions. The UE shall apply UE pre-compensation per segment of UL transmission of PUSCH/PUCCH/PRACH for BL UEs or UEs in enhanced coverage and NPUSCH/NPRACH for NB-IoT UEs from one segment to the next segment.

23.21.2 Timing and synchronization

23.21.2.1 Scheduling timing

DL and UL are frame aligned at the uplink time synchronization reference point (RP) with an offset given by .

To accommodate the long propagation delays in NTN, several timing relationships are enhanced by Common TA and two scheduling offsets: and illustrated in Figure 23.21.2.1-1:

– is a configured offset corresponding to the RTT between the RP and the NTN payload.

– is a configured scheduling offset approximately corresponding to the sum of the service link RTT and the common TA.

– is a configured offset approximately corresponding to the RTT between the RP and the eNB.

Figure 23.21.2.1-1 Timing relationship parameters

The scheduling offset is used to allow the UE sufficient processing time between a downlink reception and an uplink transmission, see TS 36.213 [6].

The offset is used to delay the application of a downlink configuration indicated by a MAC CE received on NPDSCH/PDSCH, see TS 36.213 [6], and to determine the UE-eNB RTT, see TS 36.321 [13].

23.21.2.2 Pre-compensation by the UE

For the serving cell, the network broadcast ephemeris information and common Timing Advance (common TA) parameters.

The UE shall have valid GNSS position as well as the satellite ephemeris and common TA before connecting to an NTN cell. To achieve synchronisation, before and during connection to a cell, the UE shall autonomously pre-compensate the Timing Advance (T_TA, see TS 36.211 [4] clause 8.1), see Figure 23.21.2.2-1, as well as the frequency doppler shift by considering the common TA, UE position and the satellite position through the satellite ephemeris.

In connected mode, the UE shall continuously update the Timing Advance and frequency pre-compensation, but the UE is not expected to perform GNSS acquisition. In connected mode, upon outdated satellite ephemeris and common Timing Advance, the UE re-acquires the broadcasted parameters and upon outdated GNSS position the UE moves to idle mode.

The UEs may be configured to report Timing Advance at initial access or in connected mode. In connected mode triggered reporting of the Timing Advance is supported.

Figure 23.21.2.2-1 Illustration of Uplink/Downlink Radio Frame Timing at the UE

While the pre-compensation of the instantaneous Doppler shift experienced on the service link is to be performed by the UE, the management of Doppler shift experienced over the feeder link and transponder frequency error, whether introduced in Downlink or Uplink, is left to network implementation.

23.21.3 Support of discontinuous coverage

As a satellite moves on a specified orbit, for example in case of a NGSO satellite, the satellite beam(s) coverage area may move and cover different portions of a geographical area due to the orbital movement of the satellite. As a consequence, a UE located in the concerned geographical area may experience a situation of discontinuous coverage, due to e.g. a sparse satellite constellation deployment.

To enable the UE, in RRC_IDLE, to save power during periods of no coverage, the network provides satellite assistance information (e.g. satellite ephemeris parameters, the start-time of upcoming satellite’s coverage) to enable the UE to predict when coverage will be provided by upcoming satellites. Predicting out of coverage and in coverage is up to UE implementation. When out of coverage, the UE is not required to perform AS functions.

23.21.4 Mobility Management

23.21.4.1 Mobility Management in ECM-IDLE

The principles described in clause 10.1.1 apply in NTN unless specified otherwise hereafter.

The network may broadcast more than one TAC per PLMN in a cell in order to reduce the signalling load at cell edge in NTN, in particular for Earth-moving cell coverage. The AS layer indicates all received TACs for the selected PLMN to the NAS layer. The network may update the UEs upon TAC removal. UEs may by UE implementation also check whether a TAC has been removed.

For quasi-Earth-fixed cells, timing information on when the cell is going to stop serving the area may be broadcast by the network. This may be used by the UE to start measurements on neighbour cells before the broadcast stop time of the serving cell, while the exact start of the measurements is up to UE implementation.

23.21.4.2 Mobility Management in ECM-CONNECTED

Radio link failure and RRC connection re-establishment are supported in NTN. The principles described in clause 10.1.6 apply unless specified otherwise.

To enable mobility in NTN, the network provides target cell satellite parameters needed to access the NTN cell in the handover command.

Conditional handover is supported for BL UEs and UEs in enhanced coverage.

23.21.5 Switchover

23.21.5.1 Definitions

A feeder link switchover is the procedure where the feeder link is changed from a source NTN Gateway to a target NTN Gateway for a specific NTN payload. The feeder link switchover is a Transport Network Layer procedure.

Both hard and soft feeder link switchover are applicable to NTN.

23.21.5.2 Assumptions

A feeder link switchover may result in transferring the established connection for the affected UEs between two eNBs.

For soft feeder link switchover, an NTN payload is able to connect to more than one NTN Gateway during a given period i.e. a temporary overlap can be ensured during the transition between the feeder links.

For hard feeder link switchover, an NTN payload only connects to one NTN Gateway at any given time i.e. a radio link interruption may occur during the transition between the feeder links.

23.21.5.3 Procedures

The NTN control function determines the point in time when the feeder link switchover between two eNBs is performed. For BL UEs and UEs in enhanced coverage, the transfer of the affected UEs’ context between the two eNBs at feeder link switchover is performed by means of either S1 based or X2 based handover, and it depends on the eNBs’ implementation and configuration information provided to the eNBs by the NTN Control function.

23.21.6 Signalling

The Cell Identity, as defined in TS 36.413 [25] and TS 36.423 [42], corresponds to a Mapped Cell ID, irrespective of the orbit of the NTN payload or the types of service links supported in the following cases:

– The Cell Identity indicated by the eNB to the Core Network as part of the User Location Information, or as E-UTRAN CGI in the related S1AP messages;

– The Cell Identity used for Paging Optimization in S1 interface;

– The Cell Identity used for PWS.

For a BL UE or a UE in enhanced coverage, the Cell Identity included within the target identification of the handover messages allows identifying the correct target cell.

The mapping between Mapped Cell ID(s) and geographical area(s) is configured in the RAN and Core Network.

NOTE 1: A specific geographical location may be mapped to multiple Mapped Cell ID(s), and such Mapped Cell IDs may be configured to indicate different geographical areas (e.g. overlapping and/or with different dimensions).

For a BL UE or a UE in enhanced coverage or a NB-IoT UE that supports S1-U data transfer or User Plane CIoT EPS optimisation, the eNB is responsible for constructing the Mapped Cell ID based on the UE location information received from the UE, if available. The mapping may be pre-configured (e.g., depending on operator’s policy) or up to implementation.

NOTE 2: As described in TS 23.401 [17], the User Location Information may enable the MME to determine whether the UE is allowed to operate at its present location. Special Mapped Cell IDs or TACs may be used to indicate areas outside the serving PLMN’s country.

The eNB reports the broadcasted TAC(s) of the selected PLMN to the MME. In case the eNB knows the UE’s location information, the eNB may determine the TAI the UE is currently located in and provide that TAI to the MME.

23.21.7 MME(Re-)Selection by eNB

The eNB implements the NAS Node Selection Function specified in TS 36.410 [95].

For a RRC_CONNECTED UE, the eNB is configured to ensure that the BL UE or the UE in enhanced coverage is using an MME that serves the country in which the UE is located. If the eNB detects that a BL UE or a UE in enhanced coverage is in a different country to that served by the serving MME, it should perform an S1 handover to change to an appropriate MME or initiate an UE Context Release Request procedure towards the serving MME (in which case the MME may decide to detach the UE).

For an RRC_CONNECTED NB-IoT UE, when the eNB is configured to ensure that the NB-IoT UE is using an MME that serves the country in which the UE is located. If the eNB detects that the UE is in a different country to that served by the serving MME, it should initiate a UE Context Release Request procedure towards the serving MME (in which case the MME may decide to detach the UE).

23.21.8 O&M Requirements

The NTN related parameters shall be provided by O&M to the eNB providing non-terrestrial access, as specified in TS 38.300 [79].

23.21.9 Coarse UE location reporting

Upon network request, after AS security is established in connected mode, BL UEs and UEs in enhanced coverage can report its coarse UE location information (most significant bits of the GNSS coordinates, ensuring an accuracy in the order of 2km) to the eNB.