Patent ID: 12225423

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

FIG.1illustrates an exemplary LTE 4G or new radio (NR) 5G network100supporting improvement for initial IP Multimedia Subsystem (IMS) registration in accordance with one novel aspect. LTE/NR network100comprises a user equipment (UE)101, a 3GPP radio access network RAN102, a non-3GPP radio access network RAN103, an Access and Mobility Management Function (AMF)110, a Session Management Function (SMF)111, an Non-3GPP Interworking Function (N3IWF)112, a User Plane Function (UPF)113, and a 5G core network or evolved packet core network (5GC/EPC)120. The AMF communicates with the base station, SMF and UPF for access and mobility management of wireless access devices in 5G NR network100. The SMF is primarily responsible for interacting with the decoupled data plane, creating, updating and removing Protocol Data Unit (PDU) sessions and managing session context with the UPF. The N3IWF functionality interfaces to 5G core network control plane functions, responsible for routing messages outside 5G RAN. UE101may be equipped with a radio frequency (RF) transceiver or multiple RF transceivers for services via different RATs/CNs. UE101may be a smart phone, a wearable device, an Internet of Things (IoT) device, a tablet, etc. InFIG.1, LTE/NR network100also comprises application servers including IMS server115that provides various services by communicating with a plurality of UEs including UE101. IMS server115and a packet data network gateway (PDN GW or P-GW)114belong to part of the 5GC/EPC120.

LTE and NR networks are packet-switched (PS) Internet Protocol (IP) networks. This means that the networks deliver all data traffic in IP packets, and provide users with Always-On IP Connectivity. When UE joins an LTE/NR network, a Packet Data Network (PDN) address (i.e., the one that can be used on the PDN) is assigned to the UE for its connection to the PDN. LTE/NR calls the UE's “IP access connection” an evolved packet system (EPS) bearer, which is a connection between the UE and the P-GW. The P-GW is the default gateway for the UE's IP access. LTE/NR has defined a Default EPS Bearer to provide the IP Connectivity that is Always-On. UE may establish additional data radio bearers for data communication.

IMS is a core network that provides IP multimedia services to UEs over an IP network. IMS contains several application services such as voice call (VoLTE or VoNR), SMS, instant message (IM), discovery presence (DP), etc. over the IP network. UE will send a Session initiation protocol (SIP) REGISTER to the IMS server to inform UE's capability and to request for IMS service. The initial IMS registration from the UE may fail due to subscription specific reason or due to some temporary failures in the network. In one application scenario, when both WiFi and cellular RAN are available and UE101is WiFi preferred for IMS, UE101may first try to register IMS on WiFi. However, if there are issues between UE and EPC/5GC through WiFi (e.g., a temporally connection issue as depicted by130), it would cause the registration failure and UE101will enter a retry procedure. Before concluding that WiFi is not available and find the alternate RAN, UE101will retry to register over WiFi 4 times (when retry count=4). These retry may take more than 60 sec and would result in UE101not being registered for 60 sec (when maximum retry count=4 and retry timer=15 sec). It causes UE101not able to use IMS service in that duration which will result in bad user experience.

In accordance with one novel aspect, a method of improving user experience for initial IMS registration is proposed. In the example ofFIG.1, as depicted by140, UE101performs rapid IMS registration as follows: 1) UE101boots up or leaves flight mode or turns on IMS setting, 2) UE101starts IMS registration by sending an IMS PDN setup request over a preferred RAT (non-3GPP WiFi access); 3) the processor of the UE starts a guard timer Tn for the IMS PDN initial setup on WiFi, starting from the sending of the IMS PDN setup request; 4) upon expiration of Tn, UE101aborts the current IMS PDN set up, and performs IMS PDN set up on another RAT (3GPP cellular access); 5) continue try PDN handover to the preferred WiFi access (in background). As a result, the proposed initial IMS registration procedure allows UE101to rapidly use IMS service when boots up or leaves flight mode or turns on IMS setting, when there are connection issues between UE101and EPC/5GC120over the preferred RAT.

FIG.2illustrates simplified block diagrams of a UE201in accordance with embodiments of the current invention. UE201has memory202, a processor203, and radio frequency (RF) transceiver module204. RF transceiver204is coupled with antenna205, receives RF signals from antenna205, converts them to baseband signals, and sends them to processor203. RF transceiver204also converts received baseband signals from processor203, converts them to RF signals, and sends out to antenna205. Processor203processes the received baseband signals and invokes different functional modules and circuits to perform features in UE201. Memory202stores data and program instructions210to be executed by the processor to control the operations of UE201. 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 UE201.

UE201also comprises a set of protocol stacks260and control circuits including various system modules and circuits270to carry out functional tasks of UE201. Protocol stacks260comprises Non-Access-Stratum (NAS) layer to communicate with a mobility management entity (MME) 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. System modules and circuits270may be implemented and configured by software, firmware, hardware, and/or combination thereof. The function modules and circuits, when executed by the processors via program instructions contained in the memory, interwork with each other to allow UE201to perform embodiments and functional tasks and features in the network.

In one example, system modules and circuits270comprise a configuration and control circuit206that obtains configuration and control information for IMS registration, a guard timer207that is started upon determining initial IMS registration, a PDN connection/PDU session handling circuit208that handles RRC connection for control and establishes DRB connection for data, and an IMS service handling circuit209for performing IMS functionalities. When the UE boots up or leaves flight mode, the processor of the UE determines a period Tn of time for IMS PDN initial setup on a single AS NW, starting from sending IMS PDN setup request. Upon expiration of Tn, the UE aborts the IMS PDN set up request, and performs IMS PDN set up on another AS NW. As a result, it allows the UE to rapidly get capability to use IMS service when boots up or leaves flight mode.

FIG.3illustrates a first embodiment of IMS registration using a new timer in accordance with one novel aspect. In step311, UE301powers on or turns off air-plane mode or activates IMS service. When both LTE and WiFi are available, and the UE is WiFi-preferred, or when the WiFi signal strength or quality is higher, then UE301(iWLAN) selects WiFi for IMS registration. In step321, UE301sends an IMS PDN setup request to ePDG302over the WiFi access. Meanwhile, at time T1, UE301also starts a guard timer Tn. In step331, ePDG302forwards the PDN setup request to ePDG-GW303, but does not receive any response due to a connection issue. Upon retry timer expiry, in step332, ePDG302re-sends the PDN setup request to ePDG-GW303, but does not receive any response due to a connection issue. In step333, ePDG302continues the retry process upon expiry of the retry timer. At time T2, the guard timer Tn expires. In response, in step341, UE301aborts the IMS registration procedure. In step351, UE301moves to LTE/5G and tries IMS registration over LTE/5G 3GPP access. Because UE301applies the guard timer Tn, in addition to the retry timer and retry count, the overall wait time for IMS registration is reduced, when the preferred access has a connection issue. The guard timer value can be configured based on operator/network conditions. This first embodiment has a simple design and is easy to implement, with a very clear and definite handling/action. However, the ePDG connection may need to be aborted midway if the guard timer expires before connection setup completed.

FIG.4illustrates a second embodiment of IMS registration using a new retry count in accordance with one novel aspect. In step411, UE401powers on or turns off air-plane mode. When both LTE and WiFi are available, and the UE is WiFi-preferred, or the WiFi signal strength or quality is higher, then UE401(iWLAN) selects WiFi for IMS registration. In step421, UE401sends an IMS PDN setup request to ePDG402over the WiFi access. In step431, ePDG402determines whether the requested IMS registration is for initial registration or for handover registration. If for initial registration, then the retry count is reduced to 2; if for handover registration, then the retry count is kept as its original value of 4. In the example ofFIG.4, since it is the initial registration, the retry count is set to 2. In step432, ePDG402forwards the PDN setup request to ePDG-GW403, but does not receive any response due to a connection issue. Upon retry timer expiry, in step433, ePDG402re-sends the PDN setup request to ePDG-GW403, but does not receive any response due to a connection issue. Because the retry count has already reached to 2, in step441, ePDG402sends an error message to UE401indicating the failure of the IMS registration over WiFi. Accordingly, in step451, UE401moves to LTE/5G and tries IMS registration over LTE/5G 3GPP cellular access. Because UE401applies reduced maximum retry count (2), the overall wait time for IMS registration is reduced, when the preferred access has a connection issue. This second embodiment can leverage the core retry logic algorithm. However, the UE needs to maintain separate logic to differentiate initial registration vs handover registration.

FIG.5illustrates a preferred embodiment of rapid initial IMS registration using a new timer in accordance with one novel aspect. In step511, UE501powers up or leaves airplane mode or activates IMS service. UE501has a preferred access type, e.g., WiFi, for performing IMS registration and establish PDN connection or PDU session. In step521, UE501sends an initial IMS PDN setup request over the WiFi access type. UE501determines that the IMS registration is an initial registration (as compared to a handover registration). UE501then determines a period Tn of guard time for the initial IMS PDN setup on a single AS NW (WiFi), starting from the sending of the IMS PDN setup request. Accordingly, at time T1, UE501starts the guard timer Tn. In the embodiment ofFIG.5, there are connection problem of the Internet over the WiFi access type. As a result, UE501is not able to register for IMS service over WiFi successfully. UE501then enters a retry procedure for the IMS PDN setup, subject to a retry timer and a retry count. At time T2, the guard timer Tn expires, before reaching the retry count.

In order to reduce the wait time for the initial IMS registration, in step531, UE501aborts the IMS PDN setup on WiFi in response to the guard timer expiry, and moves to 3GPP access for IMS registration. Note that from time T1to time T2, UE501continue to send and resend the IMS PDN setup request, based on a retry timer with a maximum retry count mechanism. At time T2, the UE has not reached the maximum retry count, but the guard timer expires. The value of the guard timer is configurable by the network. Typically, the length of the guard time (e.g., 7 sec) is much less than the total time of (retry timer) times (maximum retry count) (e.g., 60 sec=15×4). In step541, UE501sends an initial IMS PDN setup request over cellular RAN. In step542, the cellular RAN forwards the IMS PDN setup request to the EPC/5GC/IMS server. In step543, the cellular RAN receives IMS PDN setup confirm from the EPC/5GC/IMS server. In step544, the cellular RAN forwards the IMS PDN setup confirm back to UE501. In step551, a PDN connection or PDU session is established between UE501and the core network for receiving IMS services. Because WiFi is the preferred access type, in step561, UE501continues to try handover the PDN connection or PDU session over WiFi access in background.

FIG.6illustrates the difference between the original flow and the new flow of IMS registration and user experience. Under the original IMS registration flow, UE tries to attach to WiFi (that has a connection issue). UE will continue to send IMS PDN setup request until reaching maximum retry count with a retry timeout. As a result, the UE status remains at “trying to register”, and user needs to wait for 60 seconds for IMS registration. Under the new IMS registration flow, UE tries to attach to WiFi (that has a connection issue), UE will quickly conclude that WiFi is unstable and move to 3GPP (with the use of a guard timer). As a result, the UE status changes from “trying to register” to “IMS registered”, and user needs to wait for 7 seconds for IMS registration.

FIG.7is a flow chart of a method of supporting rapid IMS registration to improve user experience in accordance with one novel aspect. In step701, a UE initiates an IP Multimedia Subsystem (IMS) registration procedure in a mobile communication network, wherein the UE sends an initial IMS registration request to an IMS server over a first radio access type (RAT). In step702, the UE starts a guard timer upon sending the initial IMS registration request. In step703, the UE aborts the IMS registration procedure over the first RAT upon the guard timer expiry. In step704, the UE transmits another initial IMS registration request to the IMS server over a second RAT, wherein the UE establishes a connection with the network upon successful IMS registration over the second RAT.

Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.