10.3 Mobility between E-UTRAN and Non-3GPP radio technologies

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

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

10.3.1 UE Capability Configuration

A UE shall be able to communicate with the E-UTRAN about its radio access capability, such as the system (including the release and frequency band) it supports and its receive and transmit capabilities (single/dual radio, dual receiver). UE shall transfer its capability about other radio technologies over E-UTRAN using the same procedure used to carry its E-UTRAN radio capability.

10.3.2 Mobility between E-UTRAN and cdma2000 network

This clause describes the E-UTRAN mechanisms to support idle and active mode mobility between E-UTRAN and cdma2000 HRPD or 1xRTT. The overall system is described in TS 23.401 [17].

10.3.2.1 Tunnelling of cdma2000 Messages over E-UTRAN between UE and cdma2000 Access Nodes

In order to efficiently support handover procedures when on E-UTRAN with a cdma2000 target system, cdma2000 messages are sent transparently to the target system over the E-UTRAN, with the eNB and MME acting as relay points.

To support the MME in its selection of the correct target system node to which it should route an Uplink tunnelled message and to provide the target system with information that is needed to resolve technology-specific measurement information (RouteUpdate and pilot strength measurements) that are delivered to the cdma2000 system, each eNB cell is associated with a cdma2000 HRPD SectorID and/or with a cdma2000 1xRTT SectorID (generically referred to as cdma2000 reference cellid). This cdma2000 reference cellid is provided by the eNB to the MME using the cdma2000 message transfer capability over S1-AP and forwarded to the target system via the S101 interface and corresponding interface to the cdma2000 1xRTT system.

Tunnelling is achieved over the E-UTRAN radio interface by encapsulating tunnelled cdma2000 messages in the UL Information Transfer (for pre-registration signalling) or UL Handover Preparation transfer (for handover signalling) and DL Information Transfer RRC messages (e.g., similar to UMTS Uplink/Downlink Direct Transfer). The reason for using different UL transfer messages is so that the UL Handover Preparation transfer messages can use a higher priority signalling radio bearer. For the UL/DL Information Transfer messages a specific IE in these RRC messages is used to identify the type of information contained in the message (e.g., NAS, TunneledMsg). Additionally if the message is carrying a tunnelled message, an additional IE is included to carry cdma2000 specific RRC Tunnelling Procedure Information (e.g. RAT type).

AS level security will be applied for these UL Information Transfer / UL Handover Preparation Transfer and DL Information Transfer RRC messages as normal but there is no NAS level security for these tunnelled cdma2000 messages.

Figure 10.3.2.1-1: Downlink Direct Transfer

Figure 10.3.2.1-2: Uplink Direct Transfer

Tunnelling to the MME is achieved over the S1-MME interface by encapsulating the tunnelled cdma2000 message in a new S1 CDMA tunnelling messages. These S1 messages carry in addition to the tunnelled message some additional cdma2000 specific IEs (e.g. cdma2000 Reference Cell Id, RAT type, cdma2000 message type).

10.3.2.2 Mobility between E-UTRAN and HRPD

10.3.2.2.1 Mobility from E-UTRAN to HRPD

10.3.2.2.1.1 HRPD System Information Transmission in E-UTRAN

The HRPD system information block (SIB) shall be sent on the E-UTRAN BCCH. The UE shall monitor the E-UTRAN BCCH during the RRC_IDLE and RRC_CONNECTED modes to retrieve the HRPD system information for the preparation of cell reselection or handover from the E-UTRAN to HRPD system. HRPD system information may also be provided to the UE by means of dedicated signalling. The HRPD system information contains HRPD neighbouring cell information, cdma timing information, as well as information controlling the HRPD pre-registration.

10.3.2.2.1.2 Measuring HRPD from E-UTRAN

Measurement events and parameters for HRPD measurements are to be aligned with those defined in clause 10.2.3.

10.3.2.2.1.2.1 Idle Mode Measurement Control

UE shall be able to make measurements on the HRPD cells in RRC_IDLE mode to perform cell re-selection.

The intra-3GPP inter-RAT idle mode measurement control is re-used to control the idle mode measurements on HRPD. The UE performs measurement on HRPD when the signal quality from E-UTRAN serving cell falls below a given threshold.

10.3.2.2.1.2.2 Active Mode Measurement Control

In RRC_CONNECTED mode, the UE shall perform radio measurements on the HRPD network when directed by the E-UTRAN network. The network provides the required HRPD neighbour cell list information and measurement controls to the UE through dedicated RRC signalling. When needed the eNB is responsible for configuring and activating the HRPD measurements on the UE via the dedicated RRC signalling message. Periodic and event-triggered measurements are supported.

For single-radio terminals, measurement gaps are needed to allow the UE to switch into the HRPD network and do radio measurements. These measurement gaps are network-controlled. The eNB is responsible for configuring the gap pattern and providing it to the UE through RRC dedicated signalling. Terminals with a dual receiver perform measurements on HRPD neighbour cells without tuning away from the E-UTRAN network. No DL gap patterns will be required for UEs which are capable of simultaneous reception on the involved frequency bands. No UL gap patterns will be required for UEs which are capable simultaneous transmission in one access and measuring on another access.

10.3.2.2.1.2.3 Active Mode Measurement

In RRC_CONNECTED mode, the UE measures the strengths of each of the HRPD neighbour cells and reports them in an RRC message.

10.3.2.2.1.3 Pre-registration to HRPD Procedure

Pre-registration allows a UE to establish a presence with an HRPD system in advance of a cell re-selection or handover. E-UTRAN network instructs the UE whether the pre-registration is needed over broadcast channel and in a dedicated RRC message.

The signalling procedure is transparent to E-UTRAN network. In the pre-registration to HRPD, messages shall be tunnelled inside RRC and S1-AP messages between the UE and MME and in a generic "transfer" message between source MME and target access network.

The UE is responsible for maintaining the HRPD context e.g. by performing periodic re-registrations if needed. The UE will use pre-registration zone information (including the current HRPD Pre-registration Zone and a list of HRPD Secondary Pre-registration Zone ID) to decide whether a re-registration shall be performed. A dual-receiver UE can ignore the parameter. E-UTRAN will provide the pre-registration zone information on the E-UTRAN system information broadcast channel or dedicated RRC signalling (unless it is determined that the UE will read the E-UTRAN system information broadcast channel in RRC_CONNECTED). Re-registrations are only allowed in areas where pre-registration is requested.

The managing of pre-registration and re-registration is handled by HRPD upper layer. The UE should indicate if it is pre-registered when sending measurement reports on cdma2000 cells.

10.3.2.2.1.4 E-UTRAN to HRPD Cell Re-selection

For the "Optimized Idle-mode Mobility" in TS 23.402 [19], the pre-condition for cell re-selection from E-UTRAN to HRPD is that the UE has previously established a presence in the target HRPD network, either through the pre-registration procedure or previous HRPD attachment.

For the "Non-optimized Handover" in TS 23.402 [19], the above pre-condition does not apply.

The UE performs Cell re-selection to HRPD while in RRC_IDLE.

Cell reselection from E-UTRAN to HRPD should be aligned with 3GPP inter RAT cell reselection mechanism.

10.3.2.2.1.5 E-UTRAN to HRPD Handover

The pre-condition for the E-UTRAN to HRPD Handover procedure is that the UE is attached in the E-UTRAN network in E-UTRAN_ACTIVE state and has pre-registered with the HRPD network. Based on measurement reports received from the UE the eNB initiates a handover by sending an RRC Handover FROM E-UTRA PREPARATION REQUEST message to the UE to indicate to the UE that it should begin the handover procedure. This message shall include the specified target RAT type and any cdma2000 specific HRPD parameters needed by the UE to create the appropriate HRPD messages needed to request a connection. Upon reception of this message the UE should begin handover signalling towards the HRPD access. The HRPD handover signalling is tunnelled through E-UTRAN between the UE and HRPD network. These HRPD parameters and HRPD messages are transparent to E-UTRAN. The set of the required HRPD parameters are out of scope of this specification.

The messages are transferred inside RRC transfer messages and S1 CDMA2000 tunnelling messages. The MME will, based on indication provided by the HRPD network, get information about if the handover succeeded or failed making it possible for the MME set the handover status in the S1 CDMA2000 tunnelling messages (e.g. handover success, handover failure). In case the handover succeeded E-UTRAN will include the tunnelled "CDMA2000 handover command", which will be sent to the UE, inside the RRC MOBILITY from E-UTRA COMMAND message.

The UE can continue to send and receive data on the E-UTRAN radio until it receives the RRC MOBILITY from E-UTRA COMMAND message including a tunnelled "CDMA2000 handover command". After this message is received by the UE, the UE shall leave the E-UTRAN radio and start acquiring the HRPD traffic channel. The HRPD handover signalling is tunnelled between the UE and HRPD network.

10.3.2.2.2 Mobility from HRPD to E-UTRAN

Mobility from HRPD to E-UTRAN has no impact on the E-UTRAN.

10.3.2.3 Mobility between E-UTRAN and cdma2000 1xRTT

10.3.2.3.1 Mobility from E-UTRAN to cdma2000 1xRTT

10.3.2.3.1.1 cdma2000 1xRTT System Information Transmission in E-UTRAN

The cdma2000 1xRTT system information block (SIB) shall be sent on E-UTRAN BCCH. The UE shall monitor the E-UTRAN BCCH during the RRC_IDLE and RRC_CONNECTED modes to retrieve the 1xRTT system information for the preparation of handover from the E-UTRAN to cdma2000 1xRTT system. 1xRTT system information may also be provided to the UE by means of dedicated signalling. The 1xRTT system information contains 1xRTT neighbouring cell information, cdma timing information, and 1xRTT CS Fallback information.

10.3.2.3.1.2 Measuring cdma2000 1xRTT from E-UTRAN

Measurement events and parameters for 1xRTT measurements are to be aligned with those defined in clause 10.2.3.

10.3.2.3.1.2.1 Idle Mode Measurement Control

UE shall be able to make measurements on the 1xRTT system cells in LTE_IDLE mode to perform cell re-selection. UE shall perform cdma2000 1xRTT neighbour cell measurements during DRX periods, between paging occasions.

The intra-3GPP inter-RAT idle mode measurement control is re-used to control the idle mode measurements on cdma2000 1xRTT. The UE performs measurement on cdma2000 1xRTT when the signal quality from E-UTRAN serving cell falls below a given threshold.

10.3.2.3.1.2.2 Active Mode Measurement Control

In the E-UTRAN network, in RRC_CONNECTED mode, the UE shall perform radio measurements on the cdma2000 1xRTT network when directed by the E-UTRAN network. The network provides the required cdma2000 1xRTT neighbour cell list information and measurement controls to the UE through dedicated RRC signalling. When needed the eNB is responsible for configuring and activating the cdma2000 1xRTT measurements on the UE via the dedicated RRC signalling message. As for intra-3GPP inter-RAT measurement reporting, periodic and event-triggered measurements are supported.

For single-radio terminals, measurement gaps are needed to allow the UE to switch into the cdma2000 1xRTT network and do radio measurements. These Measurement gaps are network-controlled. The eNB is responsible for configuring the gap pattern and providing it to the UE through RRC dedicated signalling. Terminals with a dual receiver perform measurements on cdma2000 1xRTT neighbour cells without tuning away from the E-UTRAN network. No DL gap patterns will be required for UEs which are capable of simultaneous reception on the involved frequency bands. No UL gap patterns will be required for UEs which are capable simultaneous transmission in one access and measuring on another access.

10.3.2.3.1.2.3 Active Mode Measurement

In RRC_CONNECTED mode, the UE measures the strengths of each of the cdma2000 1xRTT neighbour cells and reports them in an RRC Message.

10.3.2.3.1.3 E-UTRAN to cdma2000 1xRTT Cell Re-selection

UE performs Cell re-selection to cdma2000 1xRTT while in RRC_IDLE.

Cell reselection from E-UTRAN to 1xRTT should be aligned with 3GPP inter RAT cell reselection mechanism.

10.3.2.3.1.4 E-UTRAN to cdma2000 1xRTT Handover

In the high level procedure for handover from E-UTRAN to cdma2000 1xRTT except 1xRTT CS Fallback, registration and handover is performed directly after the handover decision has been made. Based on measurement reports received from the UE the eNB initiates a handover by sending a RRC Handover FROM E-UTRA PREPARATION REQUEST message to the UE to indicate to the UE that it should begin the handover procedure. This message shall include the specified target RAT type and any cdma2000 specific 1xRTT access parameters needed by the UE to create the appropriate 1xRTT Origination Request message. The 1xRTT handover signalling is tunnelled between the UE and 1xRTT network. The 1xRTT access parameters and 1xRTT messages are transparent to E-UTRAN. The set of the required 1xRTT access parameters are out of scope of this specification.

The messages are transferred inside RRC transfer messages and S1 CDMA2000 tunnelling messages. The MME will, based on indication provided by the 1xRTT network, get information about if the handover succeeded or failed making it possible for the MME set the handover status in the S1 CDMA2000 tunnelling messages (e.g. handover success, handover failure). In case the handover succeeded E-UTRAN will include the tunnelled "CDMA2000 handover command", which will be sent to the UE, inside the RRC MOBILITY from E-UTRA COMMAND message.

10.3.2.3.2 Mobility from cdma2000 1xRTT to E-UTRAN

Mobility from cdma2000 1xRTT has no impact on E-UTRAN.

10.3.2.3.3 1xRTT CS Fallback

CS fallback to 1xRTT enables the delivery of CS-domain services when a UE is being served by the E-UTRAN, as specified in TS 23.272 [23].

The UE initiates 1xCSFB (e.g. to perform a 1xCS call origination or accept a 1xCS call termination) by using NAS signalling to send a CSFB indication to the MME. The MME then indicates to the eNB that 1xCSFB is required, which triggers the eNB to execute one of the following 1xCSFB procedures depending on network support and UE capability:

– Rel-8 1xCSFB, characterized by RRC connection release with redirection to 1xRTT;

– enhanced 1xCSFB, characterized by 1xRTT handover signalling tunnelled between the UE and 1xRTT network;

– dual receiver 1xCSFB, characterized by RRC connection release without redirection information; or

– dual receiver/transmitter enhanced 1xCSFB, characterized by either 1xRTT handover signalling tunnelled between the UE and 1xRTT network, or redirection of the UE’s second radio to 1xRTT.

The network advertises its support for Rel-8 1xCSFB by broadcasting 1xRTT pre-registration parameters in system information (SIB8). The Rel-8 1xCSFB procedure is the default procedure, when no other 1xCSFB procedure can be performed. If Rel-8 1xCSFB is to be performed, the eNB optionally solicits 1xRTT measurements from the UE, and then sends an RRC Connection Release message with redirection to 1xRTT. The UE then performs the normal 1xCS call origination or termination procedure in the 1xRTT access network.

A network which advertises support for Rel-8 1xCSFB may also support enhanced 1xCSFB, in which case the eNB determines to perform enhanced 1xCSFB based on UE capability. If enhanced 1xCSFB is to be performed, the eNB optionally solicits 1xRTT measurements from the UE, and then sends it a Handover From EUTRA Preparation Request message. This triggers the UE to send the UL Handover Preparation Transfer message containing 1xRTT dedicated information. The 1xRTT information is contained inside RRC and S1-AP messages between the UE and MME and in a generic "transfer" message between MME and 1xRTT network. The response from the 1xRTT network triggers the eNB to send a Mobility From EUTRA Command message which includes a 1xRTT channel assignment message that causes the UE to acquire a traffic channel in the 1xRTT access network. In addition to enhanced 1xCSFB, the eNB may determine to perform concurrent mobility to HRPD based on UE capability; if so, then two separate UL Handover Preparation Transfer messages are triggered from the UE containing 1xRTT and HRPD dedicated information, respectively. The concurrent HRPD handover procedure is handled independently from the e1xCSFB procedure, except that responses from the 1xRTT and HRPD networks shall be combined by the eNB into a single Mobility From EUTRA Command message.

The network advertises support for dual receiver 1xCSFB by broadcasting the dual receiver 1xCSFB support indicator in system information (SIB8). The eNB determines to perform dual receiver 1xCSFB if the UE has a dual Rx configuration according to UE capability, and enhanced 1xCSFB cannot be performed (i.e. because enhanced 1xCSFB is not supported by both network and UE). If dual receiver 1xCSFB is to be performed, the eNB sends an RRC Connection Release message without including redirection information. The UE then performs the normal 1xCS call origination or termination procedure in the 1xRTT access network. A UE with dual Rx configuration may initiate 1xCSFB to a network broadcasting 1xRTT pre-registration parameters but not broadcasting the dual receiver 1xCSFB support indicator; in this case, the UE may receive an RRC Connection Release message with redirection to 1xRTT.

The network advertises support for dual receiver/transmitter enhanced 1xCSFB (dual Rx/Tx e1xCSFB) by broadcasting the dual Rx/Tx e1xCSFB support indicator in system information (SIB8). The eNB determines to perform dual Rx/Tx e1xCSFB if the UE supports dual Rx/Tx e1xCSFB according to UE capability. If the network does not advertise support for dual Rx/Tx e1xCSFB, UE which have dual Rx/Tx configuration may decide to keep the 1xRTT receiver/transmitter turned on in order to continuously operate in both 1xRTT and E-UTRAN. If dual Rx/Tx e1xCSFB is to be performed, the eNB optionally solicits 1xRTT measurements from the UE, and then sends a Handover From EUTRA Preparation Request message. This triggers the UE to perform one of the following:

– send the UL Handover Preparation Transfer message containing 1xRTT dedicated information. The 1xRTT information is contained inside RRC and S1-AP messages between the UE and MME and in a generic "transfer" message between MME and 1xRTT network. The response from the 1xRTT network triggers the eNB to send a DL Information Transfer message which includes a 1xRTT channel assignment message that causes the UE to acquire a traffic channel in the 1xRTT access network while continuing to be served by the E-UTRAN (for PS-domain services).

– direct its second radio to 1xRTT, where it performs the 1xCS call origination or termination procedure in the 1xRTT access network while continuing to be served by the E-UTRAN (for PS-domain services).

The following table summarizes the various CS fallback options for 1xRTT, necessary UE capabilities and FGI index which should be set to ‘1’. The meaning of FGI index is specified in TS 36.331 [16], Annex B.

Table 10.3.2.3.3-1: CS fallback options

Target RAT	Solutions	Release	UE Capability	FGI Index
CS fallback to 1xRTT	RRC Connection Release with Redirection	Rel-8	(NOTE 1) Mandatory for UEs supporting CS fallback to 1xRTT
	enhanced 1xCSFB	Rel-9	(NOTE 1) e-CSFB-1XRTT
	enhanced 1xCSFB with concurrent HRPD handover	Rel-9	(NOTE 1) e-CSFB-ConcPS-Mob1XRTT, Support of HRPD, supportedBandListHRPD	FGI12, FGI26
	dual receiver 1xCSFB (RRC Connection Release without Redirection)	Rel-9	(NOTE 1) rx-Config1XRTT (set to ‘dual’)
	dual receiver/transmitter enhanced 1xCSFB	Rel-10	(NOTE 1) e-CSFB-dual-1XRTT
NOTE 1: All CS fallback to 1xRTT capable UE shall indicate that it supports 1xRTT and supported band list in the UE capability. NOTE 2: The measurement may be performed before any of the above CS fallback solution is triggered to select the target cell or frequency layer more accurately based on eNB decision. eNB may trigger any of above CS fallback solutions blindly.

10.3.2.3.3.1 Pre-registration Procedure for 1xRTT CSFB

A 1xCSFB capable terminal may pre-register in the 1xRTT network via the E-UTRAN in order to establish CS services (e.g. originating and terminating voice calls) in the 1xRTT network. Pre-registration applies only to Rel-8 1xCSFB, enhanced 1xCSFB and dual receiver/transmitter enhanced 1xCSFB. It does not apply to dual receiver 1xCSFB, since the UE registers directly in the 1xRTT network using the normal 1xCS registration procedure.

The UE determines whether pre-registration is needed based on 1xRTT pre-registration parameters broadcast in system information (SIB8). Before performing a 1xRTT pre-registration, the UE requests from the eNB the necessary information to perform the 1xRTT pre-registration using the CDMA2000 CSFB Parameters Request message. The eNB provides the necessary parameters in the CDMA2000 CSFB Parameters Response message. These necessary parameters are pre-configured in the eNB and are transparent to E-UTRAN.

The UE is responsible for maintaining the 1xRTT context, e.g. by performing re-registrations if needed. The UE will use the 1xRTT pre-registration information to decide whether a re-registration shall be performed. A dual receiver UE which registers directly in the 1xRTT network can ignore these parameters. Re-registrations are only allowed in areas where pre-registration is allowed.

The management of the pre-registration and re-registration is handled by the 1xRTT upper layer in the UE.

10.3.3 CDMA2000 interworking in LTE shared networks

LTE system information (SIB8) can contain parameters for multiple CDMA2000 networks to allow the different PLMNs to inter-work with different CDMA2000 networks. There is a one to one mapping between PLMN and CDMA2000 network in that each LTE PLMN in SIB1 can inter-work with only one CDMA2000 network. Thus the UE, eNB and MME implicitly knows the CDMA2000 network from the UE’s RPLMN. All UEs not supporting the per-PLMN signalling inter-work with the same CDMA2000 network independent of their RPLMN.