Patent Description:
The disclosed embodiments relate generally to wireless communication, and, more particularly, to performing inter-system change and handling indication of interworking without N26 interface supported when received over non-3GPP access.

Third generation partnership project (3GPP) and <NUM> New Radio (NR) mobile telecommunication systems provide high data rate, lower latency and improved system performances. In 3GPP NR, <NUM> terrestrial New Radio (NR) access network (includes a plurality of base stations, e.g., Next Generation Node-Bs (gNBs), communicating with a plurality of mobile stations referred as user equipment (UEs). Orthogonal Frequency Division Multiple Access (OFDMA) has been selected for NR downlink radio access scheme due to its robustness to multipath fading, higher spectral efficiency, and bandwidth scalability. Multiple access in the downlink is achieved by assigning different sub-bands (i.e., groups of subcarriers, denoted as resource blocks (RBs)) of the system bandwidth to individual users based on their existing channel condition.

In 5GS, as e.g. defined in 3GPP TS <NUM> version <NUM>. <NUM> Release <NUM>, UEs can be simultaneously registered and connected to both 3GPP access and non-3GPP access (using NAS signalling), thus the 5GS is able to take advantage of these multiple accesses to improve the user experience and optimize the traffic distribution across various accesses. When a UE registers to 3GPP or non-3GPP access, the UE will receive a REGISTRATION ACCEPT message, carrying a 5GS network feature support IE, which in turn carries an indication "interworking without N26 interface supported" or an indication "interworking without N26 interface not supported". In another word, an IWK N26 bit in the 5GS network feature support IE can be set to "interworking without N26 interface supported" or "interworking without N26 interface not supported".

In current protocol, if a UE is registered to 3GPP access to first network with a first configuration: "interworking without N26 interface supported" or "interworking without N26 interface not supported", and the UE is registered to non-3GPP access to second network with a second configuration. Then the UE will consider using the second configuration in the first network, the first network and second network can be same PLMN, or different PLMNs, same SNPN, or different SNPNs. However, such UE behavior may not be correct.

A method and a user equipment according to the invention are defined in the independent claims. The dependent claims define preferred embodiments thereof. A method of performing intersystem change without N26 interface supported or not supported when a UE is registered to the same or different networks over 3GPP and non-3GPP accesses is proposed. UE registers to one or more PLMN/SNPN over 3GPP access and non-3GPP access. UE receives a REGISTRATION ACCEPT message over 3GPP access, which carries a first 5GS network feature support IE, which indicates that interworking without N26 interface not supported. UE also receives a REGISTRATION ACCEPT message over non-3GPP access, which carries a second 5GS network feature support IE, which indicates that interworking without N26 interface supported. UE ignores the second indication received over non-3GPP access and considers that N26 interface is supported for interworking. As a result, after intersystem change from <NUM> to <NUM>, UE triggers a TAU procedure over LTE in <NUM> EPS.

In one embodiment, a UE maintains one or more Protocol Data Unit (PDU) sessions in 5GS, wherein the UE is registered to a first network via a first access type, and wherein the first network indicates interworking without N26 interface not supported. The UE receives a REGISTRATION ACCEPT message over a second access type from a second network, wherein the second network indicates interworking without N26 interface supported. The UE performs an intersystem change from 5GS to EPS. The UE ignores the indication from the second network. The UE triggers a tracking area update (TAU) procedure in EPS. The first access type is 3GPP access, and the second access type is non-3GPP access.

Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. In the following, the invention is best understood in view of <FIG> and <FIG>. The remaining embodiments, aspects, or examples are included in order to help the reader better understand the invention.

The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

<FIG> illustrates an exemplary <NUM> network and a method of performing intersystem change without N26 interface supported or not supported when a User Equipment (UE) is registered to the same or different networks over 3GPP access and non-3GPP accesses in accordance with one novel aspect. <NUM>/<NUM> network <NUM> comprises a user equipment (UE) <NUM>, a 3GPP access <NUM> (e.g., a 3GPP radio access network (E-UTRAN or NG-RAN)), a non-3GPP access <NUM> (e.g., a non-3GPP WiFi), an access and mobility management function (AMF) <NUM> or a mobility management entity (MME) <NUM>, a session management function (SMF) <NUM> or a serving gateway (SGW) <NUM>, a non-3GPP interworking function (N3IWF) <NUM>, a user plane function (UPF) <NUM>, and a <NUM> core or evolved packet core (5GC or EPC) data network <NUM>. In <NUM>, the AMF <NUM> communicates with the base stations in the 3GPP access <NUM>, the SMF <NUM>, and the UPF <NUM> for access and mobility management of wireless access devices in the <NUM> network <NUM>. The SMF <NUM> is primarily responsible for interacting with the decoupled data plane, creating, updating, and removing PDU sessions and managing session context with the UPF <NUM>. The N3IWF <NUM> interfaces to <NUM> core network control plane functions, responsible for routing messages outside <NUM> RAN.

In Access Stratum (AS) layer, an RAN provides radio access for the UE <NUM> via a radio access technology (RAT). In Non-Access Stratum (NAS) layer, the AMF <NUM> and the SMF <NUM> communicate with RAN and 5GC for access and mobility management and PDU session management of wireless access devices in the <NUM> network <NUM>. The 3GPP access <NUM> may include base stations (gNBs or eNBs) providing radio access for the UE <NUM> via various 3GPP RATs including <NUM>, <NUM>, and <NUM>/<NUM>. The non-3GPP access <NUM> may include access points (APs) providing radio access for the UE <NUM> via non-3GPP RAT including WiFi. The UE <NUM> can obtain access to data network <NUM> through 3GPP access <NUM>, AMF <NUM>/MME <NUM>, SMF <NUM>/SGW <NUM>, and UPF <NUM>. The UE <NUM> can obtain access to data network <NUM> through non-3GPP access <NUM>, N3IWF <NUM>, AMF/MME, SMF/SGW, and UPF <NUM>. The UE <NUM> may be equipped with a single radio frequency (RF) module or transceiver or multiple RF modules or transceivers for services via different RATs/CNs. In some examples, UE <NUM> may be a smart phone, a wearable device, an Internet of Things (IoT) device, a tablet, etc..

In 5GS, a protocol data unit (PDU) session defines the association between a UE and the data network that provides a PDU connectivity service. The PDU session establishment is a parallel procedure of PDN connection (bearer) procedure in <NUM>/LTE. When the UE has at least one active PDU session, an intersystem change from <NUM> N1 mode to <NUM> S1 mode may occur, it involves an N26 interface: an interface between a mobility management entity (e.g., MME <NUM>) in EPS and an access and mobility management function (e.g., AMF <NUM>) in 5GS.

When a UE registers to 3GPP or non-3GPP access, the UE will receive a REGISTRATION ACCEPT message, carrying a 5GS network feature support IE, which in turn carries an indication "interworking without N26 interface supported" or an indication "interworking without N26 interface not supported". In another word, an IWK N26 bit in the 5GS network feature support IE can be set to "interworking without N26 interface supported" or "interworking without N26 interface not supported". In current protocol, if a UE is registered to 3GPP access to a first network with a first configuration: "interworking without N26 interface supported" or "interworking without N26 interface not supported", and the UE is registered to non-3GPP access to a second network with a second configuration. Then the UE will consider using the second configuration in the first network. However, such UE behavior may not be correct, especially if the second configuration is related to interworking feature support that is received over non-3GPP access type, because N26 is a 3GPP-specific configuration and it can be ignored when the UE receives related information over non-3GPP access.

In accordance with one novel aspect, a method of performing intersystem change without N26 interface supported or not supported when UE is registered to the same or different networks over 3GPP and non-3GPP accesses is proposed. As depicted in <FIG>, UE <NUM> registers to one or more Public Land Mobile Network (PLMN) or Standalone Non-Public Network (SNPN) over 3GPP access <NUM> and non-3GPP access <NUM>. UE <NUM> receives a REGISTRATION ACCEPT message over 3GPP access, which carries a first 5GS network feature support IE, which indicates that interworking without N26 interface not supported (e.g., N26 interface is supported for interworking). UE <NUM> also receives a REGISTRATION ACCEPT message over non-3GPP access, which carries a second 5GS network feature support IE, which indicates that interworking without N26 interface supported (e.g., N26 interface is not supported for interworking). UE <NUM> ignores the second indication received over non-3GPP access and considers that N26 interface is supported for interworking. As a result, after intersystem change from <NUM> to <NUM>, UE <NUM> triggers a TAU procedure (not ATTACH procedure) over LTE in <NUM> EPS.

<FIG> illustrates simplified block diagrams of wireless devices, e.g., a UE <NUM> and a network entity <NUM> in accordance with an exemplary aspect. Network entity <NUM> may be a base station and/or an AMF/SMF. Network entity <NUM> has an antenna <NUM>, which transmits and receives radio signals. A radio frequency RF transceiver module <NUM>, coupled with the antenna, receives RF signals from antenna <NUM>, converts them to baseband signals and sends them to processor <NUM>. RF transceiver <NUM> also converts received baseband signals from processor <NUM>, converts them to RF signals, and sends out to antenna <NUM>. Processor <NUM> processes the received baseband signals and invokes different functional modules to perform features in base station <NUM>. Memory <NUM> stores program instructions and data <NUM> to control the operations of base station <NUM>. In the example of <FIG>, network entity <NUM> also includes protocol stack <NUM> and a set of control function modules and circuits <NUM>. Protocol stacks <NUM> includes Non-Access-Stratum (NAS) layer to communicate with an AMF/SMF/MME entity connecting to the core network, Radio Resource Control (RRC) layer for high layer configuration and control, Packet Data Convergence Protocol/Radio Link Control (PDCP/RLC) layer, Media Access Control (MAC) layer, and Physical (PHY) layer. In one example, control function modules and circuits <NUM> includes a registration circuit <NUM> that handles registration procedures, a connection handling circuit <NUM> that handles signaling connections, and a configuration and control circuit <NUM> that provides different parameters to configure and control UE of related functionalities including registration and paging. The network entity <NUM> can be one 5GS network component or more than one 5GS network components (e.g., access network + AMF + N3IWF + SMF, etc.).

Similarly, UE <NUM> has memory <NUM>, a processor <NUM>, and radio frequency (RF) transceiver module <NUM>. RF transceiver <NUM> is coupled with antenna <NUM>, receives RF signals from antenna <NUM>, converts them to baseband signals, and sends them to processor <NUM>. RF transceiver <NUM> also converts received baseband signals from processor <NUM>, converts them to RF signals, and sends out to antenna <NUM>. Processor <NUM> processes the received baseband signals and invokes different functional modules and circuits to perform features in UE <NUM>. Memory <NUM> stores data and program instructions <NUM> to be executed by the processor to control the operations of UE <NUM>. Suitable processors include, by way of example, a special purpose processor, a digital signal processor (DSP), a plurality of micro-processors, one or more micro-processor associated with a DSP core, a controller, a microcontroller, application specific integrated circuits (ASICs), file programmable gate array (FPGA) circuits, and other type of integrated circuits (ICs), and/or state machines. A processor in associated with software may be used to implement and configure features of UE <NUM>.

UE <NUM> also includes protocol stacks <NUM> and a set of control function modules and circuits <NUM>. Protocol stacks <NUM> includes NAS layer to communicate with an AMF/SMF/MME entity connecting to the core network, RRC layer for high layer configuration and control, PDCP/RLC layer, MAC layer, and PHY layer. Control function modules and circuits <NUM> may be implemented and configured by software, firmware, hardware, and/or combination thereof. The control function modules and circuits, when executed by the processors via program instructions contained in the memory, interwork with each other to allow UE <NUM> to perform embodiments and functional tasks and features in the network. In one example, control function modules and circuits <NUM> includes a registration handling circuit <NUM> that performs registration procedure with the network, a connection handling circuit <NUM> that handles RRC and NAS signaling connection, a intersystem change handling circuit <NUM> for performing intersystem change, and a config and control circuit <NUM> that handles configuration and control parameters including obtaining and determining network feature support.

<FIG> illustrates the content of a REGISTRATION ACCEPT message and a 5GS NETWORK FEATURE SUPPORT IE with IWK N26 interface support indication. When a UE tries to register to a network, the UE sends a REGISTRATION REQUEST message to the network. In response, the UE receives a REGISTRATION ACCEPT message from the network. The REGISTRATION ACCEPT message comprises many information elements (IEs), including a 5GS network feature support IE, as depicted in table <NUM>. The contents of the 5GS network feature support IE in turn are carried by certain bits, each bit indicates whether certain network feature is supported or not supported.

For example, bit <NUM> of the 5GS network feature support IE carries an IWK N26 indication, which indicates whether interworking without N26 interface is supported or not supported. If IWK N26 (bit <NUM>) == <NUM>, it indicates interworking without N26 interface not supported (e.g., interworking with N26 interface is supported), and if IWK N26 (bit <NUM>) == <NUM>, it indicates interworking without N26 interface supported (e.g., interworking with N26 interface is not supported). Note that the N26 interface is the interface between a mobility management entity (MME) in EPS and an access and mobility management function (AMF) in 5GS. If N26 interface is supported, then upon intersystem change from 5GS to EPS, the PDU session(s) in 5GS will be transferred to corresponding PDN connections by the network, and the UE only needs to initiate a tracking area update (TAU) procedure. On the other hand, if N26 interface is not supported, then upon intersystem change from 5GS to EPS, the UE needs to send an ATTACH REQUEST message containing a PDN CONNECTIVITY REQUEST message with request type set to "handover" or "handover of emergency bearer services" to transfer the PDU session(s) from N1 mode to S1 mode. The UE also needs to initiate PDN connectivity activation procedures for each of the corresponding PDU sessions.

<FIG> illustrates a sequence flow between a UE and a network entity for performing intersystem change based on N26 interface (not) supported indication received over 3GPP or non-3GPP access in accordance with one novel aspect. In step <NUM>, UE <NUM> registers to PLMN1 by sending a REGISTRATION REQUEST message over 3GPP access <NUM>, the request message carries UE-Requested information. In step <NUM>, UE <NUM> receives a REGISTRATION ACCEPT message over 3GPP access, the REGISTRATION ACCEPT message carries a list of information elements (IEs), e.g., a 5GS network feature support IE. For example, the 5GS network feature support IE carries a first IWK N26 indicator (e.g., bit <NUM> == <NUM>) to indicate that interworking without N26 interface is not supported. In other words, PLMN1 indicates to UE that interworking with N26 interface is supported.

In step <NUM>, UE <NUM> UE <NUM> registers to PLMN2 by sending a REGISTRATION REQUEST message over non-3GPP access <NUM>, the request message carries UE-Requested information. In step <NUM>, UE <NUM> receives a REGISTRATION ACCEPT message over non-3GPP access, the REGISTRATION ACCEPT message carries a list of information elements (IEs), e.g., a 5GS network feature support IE. For example, the 5GS network feature support IE carries a second IWK N26 indicator (e.g., bit <NUM> == <NUM>) to indicate that interworking without N26 interface is supported. In other words, PLMN2 indicates to UE that interworking with N26 interface is not supported. Typically, UE should update its configuration based on the newly received 5GS network feature support IE. However, because the second IWK N26 indicator is provided via non-3GPP access, and N26 interface is a 3GPP-specific configuration, therefore such indication should be ignored by the UE for intersystem change from 5GS to EPS to handover PDU sessions to PDN connections.

Accordingly, in step <NUM>, UE <NUM> performs an intersystem change from 5GS to EPS (N1 mode to S1 mode). In step <NUM>, UE <NUM> ignores the second IWK N26 indicator that is provided via non-3GPP access from PLMN2. As a result, UE <NUM> knows that interworking with N26 interface is supported by the network, and the PDU sessions in 5GS will be handover to the corresponding PDN connections in EPS by the network. In step <NUM>, UE <NUM> triggers a TAU procedure (not an ATTACH procedure) in LTE to complete the intersystem change.

The benefit of triggering the TAU procedure is that the UE and the network can carry the <NUM> registration information and the <NUM> PDU sessions to <NUM> in a single TAU procedure. If IWK N26 is not supported, then the UE needs to perform multiple procedures, e.g., an ATTACH procedure and one or more PDN connectivity activation procedures to complete the intersystem change. Note that the first network PLMN1 and the second network PLMN2 can be the same PLMN, or can be different PLMNs. In addition, the first network can be SNPN1, and the second network can be SNPN2, and SNPN1 and SNPN2 can be the same SNPN, or can be different SNPNs. In general, for configurations received over 3GPP and non-3GPP from the first network and the second network, if the first network and the second network are the same, then UE maintains a common configuration; if the first network and the second network are different, then UE maintains two independent configurations. In the case of IWK N26 however, since N26 is a 3GPP-specific configuration, UE should ignore the IWK N26 indicator received over non-3GPP access.

<FIG> is a flow chart of a method of performing intersystem change without N26 interface supported or not supported when UE is registered to the same or different networks over 3GPP and non-3GPP accesses in accordance with one novel aspect of the present invention. In step <NUM>, a UE maintains one or more Protocol Data Unit (PDU) sessions in 5GS, wherein the UE is registered to a first network via a first access type, and wherein the first network indicates interworking without N26 interface not supported. In step <NUM>, the UE receives a REGISTRATION ACCEPT message over a second access type from a second network, wherein the second network indicates interworking without N26 interface supported. In step <NUM>, the UE performs an intersystem change from 5GS to EPS. In step <NUM>, the UE triggers a tracking area update (TAU) procedure in EPS.

Claim 1:
A method performed by a User Equipment, UE, the method comprising:
maintaining one or more Protocol Data Unit, in the following also referred to as PDU, sessions by the UE in 5GS, wherein the UE is registered to a first network via a first access type, and wherein the first network indicates interworking without N26 interface not supported (<NUM>);
receiving a REGISTRATION ACCEPT message over a second access type from a second network, wherein the second network indicates interworking without N26 interface supported (<NUM>);
performing an intersystem change from 5GS to EPS (<NUM>) ;
ignoring the indication from the second network (<NUM>); and
triggering a tracking area update, in the following also referred to as TAU, procedure in EPS (<NUM>),
wherein the first access type is 3GPP access, and wherein the second access type is non-3GPP access.