Method and apparatus for supporting voice handoff in a wireless communication system

Abstract

The present disclosure relates to a 5G or pre-5G communication system for supporting a higher data transmission rate than a 4G communication system such as LTE. The present invention relates to a method and apparatus for supporting voice switching and improving quality of service in a mobile communication system, and more particularly, to a method for a UE connected to a first network to communicate with a network in a wireless communication system, the method including the steps of connecting a voice call to a second network; receiving a message including control information for controlling radio access of the UE from a base station of the second network; and determining a radio access technology (RAT) to be used and a PLMN to be accessed after the voice call is completed using the control information, wherein the first network and the second network communicate using different RATs, and the voice call is connected to the second network through a circuit switched (CS).

Description

TECHNICAL FIELD

[0001] The disclosure relates to a method of improving quality of service in a mobile communication system, and more particularly, to a method of providing control information to a user equipment (UE) during a voice call handover. BACKGROUND

[0002] Efforts are being made to develop an advanced fifth generation (5G) communication system or a pre-5G communication system in order to meet the increasing demand for wireless data traffic after commercialization of a fourth generation (4G) communication system. To this end, the 5G communication system or the pre-5G communication system is also called a beyond 4G network communication system or a post long term evolution (LTE) system. In order to achieve a high data rate, implementation of the 5G communication system in a frequency band of a terahertz (millimeter wave (mmWave)) band (e.g., 60 GHz band) is considered. To reduce a path loss of radio waves and increase a propagation distance of radio waves in the terahertz band, beamforming, massive multiple input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beam forming, and large scale antenna technologies are being discussed for the 5G communication system. In addition, to improve network efficiency, technologies such as evolved small cell, advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device communication (D2D), wireless backhaul, mobile network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation are being developed for the 5G communication system. In addition, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) technologies, and filter bank multi-carrier (FBMC), orthogonal time frequency space (OTFS), and sparse code multiple access (SCMA), which are advanced access technologies, are being developed for the 5G system.

[0003] The Internet is evolving from the human-centered connection network, where humans create and consume information, to the Internet of Things (IoT), where distributed components such as objects exchange and process information. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology and the like, has also emerged recently. To implement the IoT, technology elements such as a sensing technology, wired / wireless communication and network infra, service interface technology, and a security technology are required. In recent years, a great deal of research has been conducted to develop technologies for the sensor network, Machine-to-Machine (M2M) communication, and Machine Type Communication (MTC) for connection between objects, and the like. In the IoT environment, intelligent Internet Technology (IT) services can be provided to collect and analyze data generated from connected objects and to create new value in people's lives. Through convergence of the existing IT with various industries, it is possible to apply the services to fields such as smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, health care, smart home appliances, advanced medical services, and the like.

[0004] Accordingly, various attempts have been made to apply the 5G communication system to the IoT network. For example, technologies such as a sensor network, M2M, and MTC are implemented by means of the 5G communication technologies such as beamforming, MIMO, and array antennas. It can be said that the application of cloud RAN, which is the above-described Big Data processing technology, is an example of convergence between the 5G technology and the IoT technology. SUMMARY

[0005] TECHNICAL PROBLEM

[0006] Single radio voice call continuity (SRVCC) is a system that allows a voice call to be handed over from packet data to circuit switched data and inter-RAT (inter-Radio Access Technology) handover. When a user equipment (UE) leaves a fifth generation (5G) service area, it is necessary to hand over to a legacy network (e.g., a 3G RAT). Therefore, there is a need for a method of controlling a RAT to be used by a UE or a public land mobile network (PLMN) to be accessed by the UE when a voice call is completed after 5G to 3G SRVCC of the voice call by initiation or termination of the voice call in a 3G network. Because there are no parameters related to a 5G network in a 3G network, and SRVCC is only applicable to connected mode mobility, a RAT / frequency selection priority (RFSP) index or a service profiling identity (SPID) delivered to the UE in idle mode mobility can not be transmitted to the UE.

[0007] Therefore, there is a need for a method of controlling a RAT to be used by a UE or a PLMN to be accessed by the UE when a voice call is completed after 5G to 3G SRVCC of the voice call by initiation or termination of the voice call in a 3G network.

[0008] Technical Solution

[0009] According to an embodiment of the disclosure, a method of communicating, by a user equipment (UE) connected to a first network, with a network in a wireless communication system can include connecting a voice call to a second network, receiving, from a base station (BS) of the second network, a message including control information for controlling radio access of the UE, and determining, after completion of the voice call, a radio access technology (RAT) to be used and a public land mobile network (PLMN) to be accessed using the control information. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a circuit switched (CS) manner.

[0010] The method can further include communicating with a network of the determined PLMN using the determined RAT.

[0011] The connection can be a single radio voice call continuity (SRVCC) handover, the control information can include at least one of a subscriber profile id (SPID) and a PLMN ID, and the message can be a radio resource control (RRC) release message.

[0012] The message can be received after a voice call of the UE is completed.

[0013] The first network can be a fifth generation (5G) network, and the second network can be a third generation (3G) network.

[0014] The control information can include priority information about the RATs and the PLMNs.

[0015] The UE can communicate with the first network using the first RAT before the connection, and the priority information can prioritize the PLMN of the first network and the first RAT as a first priority.

[0016] According to an embodiment of the disclosure, a UE connected to a first network for communicating with a network in a wireless communication system can include a transceiver that receives a message including control information for controlling radio access of the UE from a base station (BS) of a second network, and a controller that connects a voice call to the second network and determines a RAT to be used and a PLMN to be accessed after the voice call is completed using the control information. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a circuit switched (CS) manner.

[0017] According to an embodiment of the disclosure, a method of communicating with a network by a BS of a second network in a wireless communication system can include connecting a voice call from a first network to the second network, receiving control information for a UE from an entity of the second network, and transmitting a message including the control information to the UE. The first network and the second network can communicate using different RATs, and the UE and the second network connect the voice call in a CS manner.

[0018] According to an embodiment of the disclosure, a BS of a second network for communicating with a network in a wireless communication system can include a transceiver that receives control information for a UE from an entity of the second network, and a controller that controls the transceiver to transmit a message including the control information to the UE. The control information can be received after a voice call is connected from a first network to the second network, the first network and the second network can communicate using different RATs, and the UE and the second network can connect the voice call in a CS manner.

[0019] According to an embodiment of the disclosure, a method for a UE connected to a first network to communicate with a network in a wireless communication system can include receiving control information for the UE from an entity of the first network, connecting a voice call to a second network, and determining a RAT to be used and a PLMN to be accessed after the voice call is completed using the control information. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0020] The method can further include communicating with a network of the determined PLMN using the determined RAT.

[0021] The control information can be included in a non-access stratum (NAS) message received from the entity.

[0022] The control information can be transmitted from the entity to a BS and then included in a message received from the BS.

[0023] The control information can be received from the entity periodically or when a certain condition is met.

[0024] According to an embodiment of the disclosure, a UE connected to a first network for communicating with a network in a wireless communication system can include a transceiver that receives control information for the UE from an entity of the first network, and a controller that connects a voice call to a second network and determines a RAT to be used and a PLMN to be accessed after the voice call is completed using the control information. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0025] According to an embodiment of the disclosure, a method for a first entity of a first network to communicate with a network in a wireless communication system can include receiving control information for a UE from a second entity of the first network, transmitting the control information to the UE, and connecting a voice call from the first network to a second network. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0026] The control information can be included in and received in a first message from the second entity of the first network periodically or when a certain condition is met, and the first message can be received from the second entity of the first network.

[0027] According to an embodiment of the present disclosure, a first entity for communicating with a network in a wireless communication system can include a transceiver that receives control information for a UE from a second entity of a first network, and a controller that controls the transceiver to transmit the control information to the UE and to connect a voice call from the first network to the second network. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0028] According to an embodiment of the present disclosure, a method of communicating with a network by a UE connected to a first network in a wireless communication system can include receiving control information for the UE from a BS of the first network with a voice call connection triggered to a second network, and determining a RAT to be used and a PLMN to be accessed after the voice call is completed using the control information. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0029] The control information can be included in a handover message received from the BS.

[0030] According to an embodiment of the present disclosure, a UE connected to a first network in a wireless communication system can include a transceiver that receives control information for the UE from a BS of the first network, and a controller that determines a RAT to be used and a PLMN to be accessed after a voice call is completed using the control information. The control information can be received after a voice call connection is triggered from the first network to a second network, the first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0031] According to an embodiment of the present disclosure, a method of communicating with a network by a BS of a first network in a wireless communication system can include having a voice call connection triggered from the first network to a second network, receiving control information for a UE from an entity of the first network, and transmitting the control information to the UE. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0032] The control information can be included in and received in a first handover message from the entity.

[0033] The control information can be included in a second handover message and transmitted to the UE.

[0034] According to an embodiment of the disclosure, a BS of a first network for communicating with a network in a wireless communication system can include a transceiver that receives control information for a UE from an entity of the first network, and a controller that transmits the control information to the UE. The control information can be received after a voice call connection is triggered from the first network to a second network, the first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0035] According to an embodiment of the disclosure, a method of communicating with a network by a first entity of a first network in a wireless communication system can include receiving control information for a UE from a second entity of the first network, triggering a voice call connection from the first network to a second network, and transmitting the control information to a BS of the first network. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0036] The control information can be received during registration of the UE in the first network.

[0037] The control information can be included in a handover message transmitted to the BS.

[0038] According to an embodiment of the disclosure, a first entity of a first network for communicating with a network in a wireless communication system can include a transceiver that receives control information for a UE from a second entity of the first network, and a controller that controls the transceiver to transmit the control information to a BS of the first network. The control information can be received before triggering a voice call connection from the first network to a second network. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0039] Advantageous effects

[0040] Through the various embodiments of the disclosure, the disclosure advantageously improves a voice service quality in a wireless communication system.

[0041] According to the disclosure, after 5G to 3G Single Radio Voice Call Continuity (SRVCC) that initiates or terminates a voice call through a 3G network, a radio access technology (RAT) to be used by a user equipment (UE) or a public land mobile network (PLMN) to be accessed by the UE can be controlled when a voice call is completed.

[0042] According to the disclosure, even in a connected mode mobility of a UE other than idle mode mobility, a RAT / frequency selection priority (RFSP) index or a service profile identification (SPID) can be received from a network.

[0043] According to the present disclosure, the RAT to be used by the UE or the public land mobile network (PLMN) to be accessed by the UE can be provided upon completion of a voice call after 5G to 3G SRVCC of the voice call through initiation or termination of a voice call in a 3G network without any modification to existing third generation (3G) network parameters and standards of the 3G network device. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 FIG. 1 is a diagram illustrating a fifth generation (5G) system structure based on a service-based architecture (SBA) according to an embodiment of the present disclosure.

[0045] Figure 2 FIG. 2 is a diagram illustrating a structure of a voice service support network according to an embodiment of the present disclosure.

[0046] Figure 3 FIG. 3 is a flowchart illustrating a method of transmitting a radio access technology (RAT) and a public land mobile network (PLMN) to be used by a user equipment (UE) to the UE after completion of a single radio voice call continuity (SRVCC) based voice call of the UE according to an embodiment of the present disclosure.

[0047] Figure 4 FIG. 4 is a flowchart illustrating a method of communicating with a network by a UE connected to a first network in a wireless communication system according to an embodiment of the present disclosure.

[0048] Figure 5 FIG. 5 is a flowchart illustrating a method of communicating with a network by a base station (BS) of a second network in a wireless communication system according to an embodiment of the present disclosure.

[0049] Figure 6 FIG. 6 is a flowchart illustrating a method of transmitting a RAT and a PLMN to be used by a UE to the UE after completion of a SRVCC based voice call of the UE according to another embodiment of the present disclosure.

[0050] Figure 7 FIG. 7 is a flowchart illustrating a method of communicating with a network by a UE connected to a first network in a wireless communication system according to another embodiment of the present disclosure.

[0051] Figure 8 FIG. 8 is a flowchart illustrating a method of communicating with a network by a first entity of a first network in a wireless communication system according to another embodiment of the present disclosure.

[0052] Figure 9 FIG. 9 is a flowchart illustrating a method of transmitting a RAT and a PLMN to be used by a UE to the UE after completion of a SRVCC based voice call of the UE according to another embodiment of the present disclosure.

[0053] Figure 10 FIG. 11 is a flowchart illustrating a method of communicating with a network by a UE connected to a first network in a wireless communication system according to another embodiment of the disclosure.

[0054] Figure 11 FIG. 12 is a flowchart illustrating a method of communicating with a network by a BS of a first network in a wireless communication system according to another embodiment of the disclosure.

[0055] Figure 12 FIG. 13 is a flowchart illustrating a method of communicating with a network by a first entity of a first network in a wireless communication system according to another embodiment of the disclosure.

[0056] Figure 13 FIG. 14 is a diagram illustrating a method of reducing a voice call setup time of a UE according to another embodiment of the disclosure.

[0057] Figure 14 FIG. 15 is a block diagram illustrating a configuration of a UE according to an embodiment of the disclosure.

[0058] Figure 15 FIG. 16 is a block diagram illustrating a configuration of a BS of a second network according to an embodiment of the disclosure.

[0059] Figure 16 FIG. 17 is a block diagram illustrating a configuration of an entity (access and mobility management function (AMF)) in a first network according to an embodiment of the disclosure.

[0060] Figure 17 FIG. 18 is a block diagram illustrating a configuration of a BS in a first network according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0061] The operational principles of the disclosure will be described in detail below with reference to the accompanying drawings. Detailed descriptions of known functions or configurations will be avoided in order not to obscure the subject matter of the disclosure. Although the terms described later are defined in consideration of the functions in the disclosure, the terms can be changed according to the intention or habit of a user or an operator. Therefore, the definition should not be simply based on the terms actually used, but should be based on the meaning of each term.

[0062] In the following description, for the convenience of description, terms identifying an access node, terms indicating a network entity or a network function (NF), terms indicating a message, terms indicating an interface between network objects, terms indicating various types of identification information, and the like are provided by way of example. Therefore, the disclosure is not limited to the terms described below, and other terms indicating objects having equivalent technical meanings can be used.

[0063] For convenience of description, terms and names defined in the 3rd generation partnership project long term evolution (3GPP LTE) standard and 5G standard are used in the disclosure. However, the disclosure is not limited by the terms and names, and can be equally applied to systems conforming to other standards.

[0064] Although the description of the embodiments of the disclosure focuses on a method of improving voice service quality in an environment in which a fifth generation (5G) system and a legacy system coexist, the main subject matter of the disclosure is applicable to any type of wireless communication system and is applicable to other types of services (video call, game, chat, etc.) as well as voice services.

[0065] To support various 5G services, a new system structure and a new protocol are required, and 3GPP has decided to introduce a new technology called service-based architecture (SBA). The key feature of the SBA is that, considering the introduction of virtualization technology, a cloud environment, and network-based service expansion, the functions of NFs defined in the 3GPP standard are divided based on services, and these services are implemented using hypertext transfer protocol version 2 (HTTP / 2).

[0066] Figure 1 FIG. 1 is a diagram illustrating a structure of a 5G system based on SBA according to an embodiment of the disclosure.

[0067] Referring to Figure 1 , an access and mobility management function (AMF) is an NF that manages wireless network access and mobility of a user equipment (UE). A session management function (SMF) is an NF that manages a session for the UE, and session information includes quality of service (QoS) information, charging information, and packet processing information. A user plane function (UPF) is an NF that processes user plane traffic, and can be controlled by the SMF. Although not shown in Figure 1 , the 5G system can include an unstructured data storage network function (UDSF). The UDSF is an NF that stores unstructured data, and can store or retrieve any type of data according to a request of an NF (e.g., AMF, SMF, etc.) other than the UDSF.

[0068] Figure 2 FIG. 2 is a diagram illustrating a structure of a voice service support network according to an embodiment of the disclosure.

[0069] When operating through access to 5G (and next generation RAN (NG-RAN)), a UE can initiate or terminate a voice call. When the UE moves out of a 5G service area, there is a better 3G network, or other conditions for handover to 3G are met, the UE can be handed over to a 3G network by the network during a voice call. To support the transfer of information of the UE and call processing between a 5G network (AMF) and a 3G network (mobile switching center (MSC) server), a fourth generation (4G) network (MME_SRVCC) can be implemented to support single radio voice call continuity (SRVCC) between the 5G network and the 3G network, so that the MME_SRVCC of the 4G network can be connected between the AMF of the 5G network and the MSC server of the 3G network.

[0070] At the completion of a voice call made by handover to 3G, the UE can simply remain in the 3G network or move to another network (e.g., the UE selects a 5G network). If a communication service provider intends to preferentially move the UE to a 5G network, functions to support this operation are required. In addition, when a 5G network and a 3G network use different public land mobile network (PLMN) IDs, or when the UE is to be converted to a specific PLMN after voice completion, functions to inform the UE of the conversion are required. In other words, when the PLMN ID of the 3G network being handed over and the PLMN ID of the 5G network to which the UE is to move after handover are different, functions to inform the UE of the PLMN ID of the 5G network to which the UE is to move are required. Alternatively, when the UE is to move to a specific PLMN after completion of handover of a voice call, functions to inform the UE of the ID of the specific PLMN to which the UE is to move after completion of handover of a voice call are required.

[0071] Figure 3 is a flowchart illustrating a method of transmitting information about a radio access technology (RAT) and a PLMN to be used by a UE to the UE after completion of a voice call based on SRVCC of the UE according to an embodiment of the disclosure.

[0072] The UE 100 that has been registered in the 5G network can exchange information indicating support for 5G-3G SRVCC (hereinafter referred to as SRVCC) with the 5G network in a registration step or an additional information exchange procedure. A voice call can be started (initiated or terminated) for the UE (subscriber), and an SRVCC procedure is performed by triggering SRVCC for the UE 100 according to the state and location of the UE 100 and network configuration (S310). The SRVCC procedure is basically a procedure of transferring UE information including a voice call from the 5G network to the 3G network, and specifically, performing handover of a voice call from a 5G packet switched (PS) network (based on an IP multimedia subsystem (IMS)) to a circuit switched (CS) network. The UE 100 receives a message indicating handover to the 3G network from the NG-RAN.

[0073] The UE 100 performs handover from the 5G network to the 3G network. In this procedure, a voice call transmitted and received through the PS network is transferred to the CS network (S320).

[0074] When needed, the UE 100 performs an operation for accessing the 3G PS network (S330). This procedure can start with the UE 100 transmitting a registration request (routing area update or attach request) message to a mobility management device (referred to as a serving GPRS support node (SGSN)) 130 of the 3G PS network through a 3G base station (BS) 120.

[0075] During the registration procedure to the 3G PS network, a home subscriber server (HSS) / visitor location register (VLR) 140 can transmit control information to the SGSN 130 (S340), and the information can include information indicating a priority of a radio access frequency or RAT (e.g., 5G / 4G / 3G) to be selected by the UE 100 after a voice call is completed. The control information can also include a PLMN ID that the UE 100 will preferentially select when a voice call is completed after the SRVCC operation of the UE.

[0076] The SGSN 130 can include information indicating priorities of radio access frequencies or RATs (e.g., 5G / 4G / 3G) to be selected (S350) by the UE 100 in an idle state or after a voice call is completed during an access procedure or a context configuration procedure for data transmission. The information can be in the form of an index indicating preset priorities of specific frequencies or RATs. The information can be a subscriber profile ID of RAT / frequency priorities. In addition, a PLMN ID to be preferentially selected by the UE 100 when a voice call is completed after an SRVCC operation can be included in the information.

[0077] The voice call is completed (S360).

[0078] The UE 100 determines frequencies, RATs, and PLMN IDs to be preferentially accessed by using the information received in step S350 (S380). When the corresponding information is configured to prioritize a 5G network as a high access priority, the UE 100 operates to preferentially access the 5G network.

[0079] Figure 4 FIG. 4 is a flowchart illustrating a method of communicating with a network by a UE 100 connected to a first network in a wireless communication system according to an embodiment of the disclosure.

[0080] Referring to Figure 4 In the method of communicating with a network by a UE 100 connected to a first network in a wireless communication system, a voice call can be connected to a second network (S410). The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network. The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner.

[0081] The UE 100 can receive a message including control information for controlling radio access of the UE 100 from a BS of the second network (S420). The control information can include at least one of a subscriber profile identity (SPID) and a PLMN ID, and the message can be a radio resource control (RRC) release message. The message can be received after a voice call of the UE is completed.

[0082] The UE 100 can determine a RAT to be used and a PLMN to be accessed after a voice call is completed using the control information (S430). The control information can include priority information about RATs and PLMNs. Before the voice call is connected, the UE 100 communicates with the first network using a first RAT, and the priority information can prioritize a PLMN of the first network and the first RAT as a first priority.

[0083] The UE 100 can communicate with the network of the determined PLMN using the determined RAT (S440).

[0084] Figure 5 is a flowchart illustrating a method of communicating by a BS of a second network with a network in a wireless communication system according to an embodiment of the disclosure.

[0085] Referring to Figure 5 In the method of communicating by a BS 120 of a second network with a network in a wireless communication system, a voice call can be connected from a first network to the second network (S510). The first network and the second network can communicate using different RATs, and the voice call can be connected in a CS manner between a UE and the second network.

[0086] The BS 120 of the second network can receive control information for the UE from a network entity (SGSN) 130 of the second network (S520). The control information can include at least one of an SPID and a PLMN ID.

[0087] The BS 120 of the second network can transmit a message including the received control information for controlling radio access to the UE 100 (S530). The message can be an RRC release message. The message can be transmitted to the UE 100 after a voice call of the UE 100 is completed. The control information can include priority information about a RAT and a PLMN. Before the voice call is connected, the UE 100 communicates with the first network using a first RAT, and the priority information can prioritize a PLMN of the first network and the first RAT as a first priority.

[0088] Upon receiving the control information, the UE 100 can determine a RAT to be used and a PLMN to be accessed after the voice call is completed, and communicate with a network of the determined PLMN using the determined RAT.

[0089] Figure 6 is a flowchart illustrating a method of transmitting a RAT and a PLMN to be used by a UE to the UE after a voice call of the UE based on SRVCC is completed according to another embodiment of the disclosure.

[0090] Referring to Figure 6 The UE 100 that has registered in a 5G network can exchange information indicating support for 5G-3G SRVCC (hereinafter referred to as SRVCC) with the 5G network in a registration step or an additional information exchange procedure (S610).

[0091] The NF (hereinafter referred to as the UDM) 160 storing the control information (subscription data) can transmit information indicating the priority of the radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE to the NF (hereinafter referred to as the AMF) 150 for the access and mobility control function of the UE 100 (S620). The information can be an RFSP ID (or index). In addition, a PLMN ID that is preferentially selected by the UE upon completion of the voice call after the SRVCC operation can be included. The information can be transmitted in the registration procedure of step S610 or in a separate procedure.

[0092] After completion of the voice call, the AMF 150 can transmit a message including information indicating the priority of the radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 to the UE 100 (S630). The information indicating the priority of the radio access frequency or RAT to be selected by the UE 100 after completion of the voice call can be an SPID. In addition, further, the message transmitted from the AMF 150 to the UE 100 can include a PLMN ID that the UE 100 will preferentially select upon completion of the voice call after the SRVCC operation. The AMF 150 can determine the information to be selected and transmitted using the information received from the UDM 160 at step S630 and the operator configuration within the AMF 150. The AMF 150 can instruct the UE 100 to preferentially select the current wireless network (the frequency of 5G as the current RAT) and the current PLMN (the registered PLMN), and to return to the current wireless network and the PLMN after completion of the voice call through the message.

[0093] The message transmitted by the AMF 150 to the UE 100 can be a non-access stratum (NAS) message. The information indicating the priority of the radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 after completion of the voice call and the information about the PLMN ID that will be preferentially selected by the UE 100 upon completion of the voice call after the SRVCC operation can be transmitted to the UE 100 through the registration accept message during the above-described registration procedure or through the UE configuration update message or other NAS message. Upon receipt of the information, the UE 100 can store the corresponding information and maintain the information even when moving to other networks (3G or 4G networks), and the information can be applied to the return operation after the voice call is switched to 3G. In other words, after completion of the voice call, the UE 100 can use the received information to select the radio access frequency or RAT to be preferentially selected and the PLMN ID to be preferentially selected.

[0094] A voice call is started, and SRVCC to a 3G network occurs according to a condition (S640).

[0095] Upon completion of the voice call, the UE 100 can determine the frequency, RAT, and PLMN ID to be accessed with priority by using the information received in step S630 (S650). When the information is configured such that the access priority of the 5G network is high, the UE 100 operates to access the 5G network with priority. When the information is configured to select the radio network and the PLMN ID with priority before SRVCC occurs, the UE 100 can select the 5G network and the PLMN ID used in the 5G network with priority.

[0096] By modifying step S630 of the embodiment, the AMF 150 can transmit information to the NG-RAN 110, and the NR-RAN 110 can transmit information for the UE 100 to use upon return to the UE 100, instead of the AMF 150 transmitting information for the UE 100 to use upon return to the UE 100. The AMF 150 can include information on the priority of the radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 upon completion of the voice call in a message (e.g., UE context setup, etc.) transmitted to the NG-RAN 110. In addition, the message can include the PLMN ID to be selected with priority by the UE 100 upon completion of the voice call after the SRVCC operation. The AMF 150 can determine the information to be selected and transmitted using the information received from the UDM 160 and the operator configuration of the AMF 150. The NG-RAN 110 can then include information on the priority of the radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 upon completion of the voice call in a message (e.g., RRC release) transmitted to the UE. The information can be in the form of an index indicating the preset priority of a specific frequency or RAT. The information can be a subscriber profile ID of an RFSP index (SPID). The information can also include the PLMN ID to be selected with priority by the UE 100 upon completion of the voice call after the SRVCC operation. Alternatively, the information can include information indicating that the UE 100 selects the current wireless network (the frequency of 5G as the current RAT) and the currently connected PLMN (the registered PLMN) with priority and returns to the current wireless network and the PLMN after the voice call is completed.

[0097] Figure 7 FIG. 7 is a flowchart illustrating a method of communicating by a UE connected to a first network with a network in a wireless communication system according to another embodiment of the disclosure.

[0098] Referring to Figure 7In a method of communicating with a network by a UE 100 connected to a first network in a wireless communication system, the UE 100 can receive control information for the UE 100 from an entity (AMF) 150 of the first network (S710). The control information can be included in a NAS message received from the entity (AMF) 150 of the first network. Alternatively, the control information can be transmitted from the entity (AMF) 150 of the first network to a BS 110 of the first network, and then included in a message received by the UE 100 from the BS 110. The control information can be received from the entity (AMF) 150 of the first network periodically or when a certain condition is met.

[0099] The UE 100 can connect a voice call to a second network (S720). The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner. The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network.

[0100] After completing the voice call, the UE 100 can determine a RAT to be used and a PLMN to be accessed after completing the voice call using the control information (S730). The control information can include priority information about the RAT and the PLMN. Before the voice call connection, the UE 100 communicates with the first network using the first RAT, and the priority information can prioritize the PLMN of the first network and the first RAT as a first priority.

[0101] The UE 100 can communicate with a network of the determined PLMN using the determined RAT (S740).

[0102] Figure 8 FIG. 8 is a flowchart illustrating a method of communicating with a network by a first entity (AMF) 150 of a first network according to an embodiment of the disclosure.

[0103] Referring to Figure 8 In a method of communicating with a network by a first entity (AMF) 150 of a first network in a wireless communication system, the first entity (AMF) 150 of the first network can receive control information for a UE from a second entity (UDM) 160 of the first network (S810). The control information can be received in a first message received from the entity of the first RAT periodically or when a certain condition is met, and the first message can be received from the entity of the first RAT.

[0104] The first entity (ANF) 150 can transmit control information (S820). The control information can include priority information about RATs and PLMNs. Before a voice call connection, the UE 100 can communicate with a first network using a first RAT, and the priority information can prioritize a PLMN of the first network and the first RAT as a first priority.

[0105] The voice call can be connected from the first network to the second network (S830). The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner. The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network.

[0106] Figure 9 FIG. 9 is a flowchart illustrating a method of transmitting, to a UE, RATs and PLMNs to be used by the UE after a voice call of the UE is completed based on SRVCC according to another embodiment of the disclosure.

[0107] Referring to Figure 9 , the UE 100 has been registered in a 5G network, and the UE 100 and the 5G network can exchange information indicating that 5G-3G SRVCC (hereinafter referred to as SRVCC) functionality is supported with each other in a registration step or an additional information exchange procedure (S910).

[0108] An NF (hereinafter referred to as a UDM) 160 that stores control information (subscription data) can transmit information indicating priorities of radio access frequencies or RATs (5G / 4G / 3G) to be selected by the UE 100 for access and mobility control functions of the UE 100 to an NF (hereinafter referred to as an AMF) 150 (S920). The information can be an RFSP ID (or index). In addition, a PLMN ID that is preferentially selected by the UE 100 when a voice call is completed after an SRVCC operation can be included. The information can be transmitted in the registration procedure of step S910 or in a separate procedure.

[0109] A voice call is started (initiated or terminated) for the UE (subscriber), and when SRVCC is triggered for the UE according to a state and a location of the UE and network configuration, SRVCC is performed (S930). The SRVCC procedure is basically a procedure of transferring UE information including a voice call from a 5G network to a 3G network, and specifically, a handover of a voice call from a 5G PS network (based on IMS) to a CS network is performed.

[0110] During the SRVCC procedure, when a handover request (i.e., a request to hand over the UE 100 from the 5G network to the 3G network) is received from the NG-RAN (BS) 110, the AMF 150 can process the handover request and transmit a response to the handover request to the NG-RAN 110 (S940). The response message can include information indicating a priority of a radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 after the voice call is completed. Also, a PLMN ID that is preferentially selected by the UE 100 when the voice call is completed after the SRVCC operation can be included. The response message can be a handover required message, a first handover command message, or a first handover message. The AMF 150 can determine which information to select and transmit using the information received from the UDM 160 in step S920 and the operator configuration of the AMF 150.

[0111] The NG-RAN 110 transmits a message for transitioning the UE 100 to the 3G network to the UE 100 during the SRVCC procedure (S950). The message can be a mobility command message, a second handover command message, or a second handover message. The message can include information indicating that the network to be transitioned to is 3G, information about a 3G BS to be selected by the UE 100, and information about a 3G cell or frequency to be selected by the UE 100. Also, the message transmitted from the NG-RAN to the UE can include information indicating a priority of a radio access frequency or RAT (5G / 4G / 3G) to be selected by the UE 100 after the voice call is completed. The information can be in the form of an index indicating a preset priority of a specific frequency or RAT. The information can be an SPID. Also, a PLMN ID that is preferentially selected by the UE 100 when the voice call is completed after the SRVCC operation can be included. Alternatively, the NG-RAN can transmit information indicating that the UE, after completing the voice call, preferentially selects the current wireless network (a frequency of 5G as the current RAT) and the currently connected PLMN (a registered PLMN) and returns to the current wireless network and the PLMN.

[0112] The UE 100 performs handover to the 3G network according to the command (S960). Then, the voice call proceeds in the 3G network and then ends (S960).

[0113] Upon completion of the voice call, the UE 100 determines a frequency, a RAT, and a PLMN ID to be preferentially accessed using the information received in step S950 (S970). When the information is configured such that the priority of access to the 5G network is high, the UE preferentially accesses the 5G network.

[0114] Figure 10is a flowchart illustrating a method of communicating by a UE connected to a first network with a network in a wireless communication system according to another embodiment of the disclosure.

[0115] Referring to Figure 10 In the method of communicating by a UE 100 connected to a first network with a network in a wireless communication system, a voice call connection to a second network can be triggered (S1010). The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner. The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network.

[0116] The UE 100 can receive control information for the UE 100 from a BS of the first network (S1020). The control information can be received in a handover message.

[0117] The UE 100 can determine a RAT to use and a PLMN to access after a voice call is completed using the control information (S1030).

[0118] The control information can include priority information about the RAT and the PLMN. Before the voice call connection, the UE 100 communicates with the first network using the first RAT, and the priority information can prioritize the PLMN of the first network and the first RAT as a first priority.

[0119] Figure 11 is a flowchart illustrating a method of communicating by a BS of a first network with a network in a wireless communication system according to another embodiment of the disclosure.

[0120] Referring to Figure 11 In the method of communicating by a BS 110 of a first network with a network in a wireless communication system, a voice call connection from the first network to a second network can be triggered (S1110). The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner. The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network.

[0121] The BS 110 of the first network can receive control information for a UE from an entity (AMF) 150 of the first network (S1120). The control information can be received in a first handover message from the BS.

[0122] The BS 110 of the first network can transmit control information to the UE (S1130). The control information can be transmitted to the UE 100 in a second handover message. The control information can include priority information about the RATs and the PLMNs. The UE 100 uses the first RAT to communicate with the first network before the voice call connection, and the priority information can prioritize the PLMN of the first network and the first RAT as a first priority.

[0123] Figure 12 FIG. 13 is a flowchart illustrating a method of communicating with a network by a first entity of a first network in a wireless communication system according to another embodiment of the disclosure.

[0124] Referring to Figure 12 In the method of communicating with a network by a first entity of a first network in a wireless communication system, the UE 100 can receive control information from a second entity (UDM) 160 of the first network (S1210). The control information can be received in a process of registering the UE 100 in the first network or in a separate process.

[0125] A voice call connection from the first network to a second network can be triggered (S1220). The first network and the second network can communicate using different RATs, and the voice call can be connected to the second network in a CS manner. The voice call connection can be an SRVCC handover. The first network can be a 5G network, and the second network can be a 3G network.

[0126] The first entity (AMF) 150 can transmit the control information to a BS of the first network (S1230). The control information can be included in a handover message transmitted to the BS.

[0127] Figure 13 FIG. 14 is a diagram illustrating a method of reducing a voice call setup time of a UE according to another embodiment of the disclosure.

[0128] Referring to Figure 13 The UE 100 has been registered in a 5G network and registered in an IMS network for a voice service. A voice call (origination / termination) occurs for the UE 100 (S1305).

[0129] During the processing of the voice call, the SMF 170 creates a new QoS flow for transmitting and receiving voice media, and transmits a request message for adding the QoS flow to a session to the AMF 150 (S1310).

[0130] The AMF 150 sends a response message to the SMF 170. This step can be performed after step S1320 or step S1325. When the transmission is performed after step S1325, the response message sent from the AMF 150 to the SMF 170 can include an indication indicating that fallback has occurred. When the transmission is performed after step S1325, steps S1330 and S1335 can be skipped.

[0131] The AMF 150 sends, to the NG-RAN 110, a session modification request message for adding a QoS flow for transmitting and receiving voice media to the session, according to the request received from the SMF 170 (S1320).

[0132] The NG-RAN 110 determines whether EPS fallback or inter-RAT fallback is needed to provide the voice service. When fallback occurs, the NG-RAN 110 can send a session modification response message to the AMF 170, and the message can include an indicator indicating that fallback should occur (S1325).

[0133] The AMF 150 sends a message to the SMF 170 indicating that fallback has occurred (S1330).

[0134] The SMF 170 sends a response message to the AMF 150 (S1335).

[0135] The AMF 150 can determine whether to apply the function of reducing fallback time. The AMF 150 can determine that the function is applicable when the configuration of the AMF 150 and the supported features received from the SMF 170 indicate that the SMF 170 also supports the fallback time reduction function after the AMF 150 recognizes that fallback has been triggered for the UE 100.

[0136] When the fallback time reduction function is applied, the AMF 150 can even send a request to the SMF 170 to receive an SM context (used in the same sense as PDU session context) for the UE in advance before receiving a context request for the UE from the MME (S1345). When the AMF 150 applies the fallback time reduction function, sends a request for SM context transmission for the UE to the SMF 170, and then receives a context request for the UE from the MME, the AMF 150 should not send an SM context request to the SMF 170 again. When two or more PDU sessions are configured for the UE, the AMF 150 can request SM context transmission for each PDU session.

[0137] When the SMF 170 needs to perform N4 session modification with the UPF before receiving the PDU session in response to the AMF 150 request, the SMF 170 exchanges N4 messages with the UPF (S1350).

[0138] The SMF 170 can transmit information about the PDU session to the AMF 150 according to the request of the AMF 150 (S1355).

[0139] The AMF 150 can store the SM context received from the SMF 170, and when receiving a context transfer request for the UE from the MME, transmit a context response to the MME using the corresponding information without exchanging additional information with the SMF 170 (S1360).

[0140] Figure 14 is a block diagram illustrating a configuration of a UE according to an embodiment of the disclosure.

[0141] Referring to Figure 14 In a wireless communication system, a UE 100 connected to a first network and communicating with the network can include a transceiver 101 and a controller 102. The transceiver 101 can receive a message including control information for controlling radio access of the UE from a BS of a second network, and receive a message including control information for controlling radio access of the UE from a BS of the first network. The controller 102 can connect a voice call to the second network, and determine a RAT to be used after the voice call is completed and a PLMN to be accessed using the control information.

[0142] Figure 15 is a block diagram illustrating a configuration of a BS of a network according to an embodiment of the disclosure.

[0143] Referring to Figure 15 A BS 120 of a network communicating with other networks or other entities in a wireless communication system can include a transceiver 121 and a controller 122. The transceiver 121 can receive control information of a UE from other network entities. The controller 122 can control the transceiver to transmit a message including the received control information for controlling radio access to the UE.

[0144] Figure 16 is a block diagram illustrating a configuration of a network entity according to an embodiment of the disclosure.

[0145] Referring to Figure 16The network entity can include, for example, an AMF. The network entity 150 can include a transceiver 151 and a controller 152 to communicate with other networks or other entities in a wireless communication system. The transceiver 151 can receive control information for the UE from a second entity (UDM) 160, for example. The controller 152 can control the transceiver 151 to transmit the control information to the UE 100 and connect a voice call from the first network to the second network.

[0146] Figure 17 is a block diagram showing a configuration of a BS of a network according to an embodiment of the disclosure.

[0147] Referring to Figure 17 The BS 110 of the first network to communicate with other networks or other entities in a wireless communication system can include a transceiver 111 and a controller 112. The transceiver 111 can receive control information for the UE from an entity (AMF) 150. The controller 112 can transmit the control information to the UE 100.

[0148] The control information described in the specification can be replaced by subscription information.

[0149] It should be noted that Figures 1 to 17 The configuration diagrams shown in the above detailed description, the exemplary diagrams showing control / data signal transmission methods, the exemplary diagrams showing operation procedures, and the configuration diagrams are not intended to limit the scope of the disclosure. That is, referring to Figures 1 to 17 All components, entities, or operation steps described above should not be interpreted as essential components to implement the disclosure, and the disclosure can be implemented even with only some components within the subject matter of the disclosure.

[0150] The above-described operations of the BS or the UE can be implemented by providing a storage device storing corresponding program codes in any components of the BS or the UE. That is, the controller of the BS or the UE can perform the above-described operations by reading and executing the program codes stored in the memory device by a processor or a central processing unit (CPU).

[0151] The various components and modules of the entities, BSs, or UEs described in the specification can operate using hardware circuits (such as complementary metal-oxide semiconductor-based logic circuits) embedded in machine-readable media, firmware, software, and / or a combination of hardware and firmware and / or software. For example, various electrical structures and methods can be implemented using circuits such as transistors, logic gates, and dedicated semiconductors.

[0152] Although specific embodiments have been described in the detailed description of the disclosure, various modifications can be made without departing from the scope of the disclosure. Therefore, the scope of the disclosure should be defined by the claims described below and the claims and their equivalents, and not limited to the described embodiments.

Claims

1. A method for communication between a user equipment (UE) connected to a 5G network in a wireless communication system, the method comprising: During the registration process, information indicating support for SRVCC single radio voice call continuity handover is exchanged with the 5G network, wherein the SRVCC handover is from the 5G network to the 3G network. When the UE has already registered in the 5G network, the voice call will be connected to the 5G network; The Access and Mobility Management Function (AMF) in the 5G network receives a Non-Access Stratum (NAS) message including control information for controlling the radio access of the UE, wherein the control information includes a Subscriber Profile ID (SPID) for the priority of the frequency to be selected after the voice call is completed. When the SRVCC handover is triggered for the UE based on the UE's state and location and network configuration, the voice call is connected to the 3G network using the SRVCC handover from the 5G network to the 3G network; and The control information is used to determine the Radio Access Technology (RAT) to be used and the Public Land Mobile Network (PLMN) to be accessed after the voice call is completed. The voice call is connected to the 3G network via circuit-switched (CS) mode.

2. The method according to claim 1, wherein, The control information also includes the PLMN ID, and the message is a Radio Resource Control (RRC) release message.

3. The method according to claim 1, wherein, The control information includes priority information regarding the RAT and PLMN.

4. The method according to claim 3, in, The UE communicates with the 5G network using a first RAT before establishing a voice call connection to the 3G network, and The priority information prioritizes the PLMN of the 5G network and the first RAT as the first priority.

5. A user equipment (UE) connected to a 5G network, for communicating with the network in a wireless communication system, the UE comprising: transceiver; as well as The controller, coupled to the transceiver and configured to control: During the registration process, information indicating support for SRVCC single radio voice call continuity handover is exchanged with the 5G network, wherein the SRVCC handover is from the 5G network to the 3G network. When the UE has already registered in the 5G network, the voice call will be connected to the 5G network; The Access and Mobility Management Function (AMF) in the 5G network receives a Non-Access Stratum (NAS) message including control information for controlling the radio access of the UE, wherein the control information includes a Subscriber Profile ID (SPID) for the priority of the frequency to be selected after the voice call is completed. When an SRVCC handover is triggered for the UE based on the UE's state and location and network configuration, the voice call is connected to the 3G network using the SRVCC handover from the 5G network to the 3G network; and The control information is used to determine the Radio Access Technology (RAT) to be used and the Public Land Mobile Network (PLMN) to be accessed after the voice call is completed. The voice call is connected to the 3G network via circuit-switched (CS) mode.

6. The UE according to claim 5, wherein, The control information also includes PLMNID, and the message is a Radio Resource Control (RRC) release message.

7. The UE according to claim 5, wherein, The control information includes priority information regarding the RAT and PLMN.

8. The UE according to claim 7, in, The UE communicates with the 5G network using a first RAT before establishing a voice call connection to the 3G network, and The priority information prioritizes the PLMN of the 5G network and the first RAT as the first priority.

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