Patent Publication Number: US-2022225294-A1

Title: Method and apparatus for sidelink resource control

Description:
INCORPORATION BY REFERENCE 
     This application is a continuation of application Ser. No. 16/601,092, filed Oct. 14, 2019, which claims the benefit of U.S. Provisional Application No. 62/772,062, “METHOD OF CROSS-RAT SIDELINK RESOURCE CONTROL BETWEEN EPS AND 5GS” filed on Nov. 27, 2018. The disclosures of the prior applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Wireless communication systems can provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. With continuous developments of wireless communication technologies, multiple radio access technologies that adopt different telecommunication standards may co-exist. For example, new radio (NR), which is also referred to as fifth generation (5G), is new radio access technology (RAT) beyond Long Term Evolution (LTE) which is also referred to as fourth generation (4G). NR may coexist with LTE during network deployments of the new generation. 
     SUMMARY 
     Aspects of the disclosure provide methods, apparatuses and systems for wireless communication. In some embodiments, a wireless communication system includes processing circuitry. The processing circuitry of the wireless communication system operates based on a first radio access technology. The processing circuitry receives a sidelink control request from a first user equipment that accesses the wireless communication system using the first radio access technology. The sidelink control request requests sidelink control information for a second radio access technology. The processing circuitry then obtains the sidelink control information for the second radio access technology, and provides, via the first radio access technology, the sidelink control information for the second radio access technology, to the first user equipment. The sidelink control information is used to configure a sidelink between the first user equipment and a second user equipment using the second radio access technology. 
     In some examples, the first radio access technology is evolved universal terrestrial radio access (E-UTRA) technology, and the second radio access technology is new radio (NR) technology. In some examples, the first radio access technology is new radio (NR) technology, and the second radio access technology is evolved universal terrestrial radio access (E-UTRA) technology. 
     In an embodiment, the processing circuitry communicates with another wireless communication system configured based on the second radio access technology to obtain the sidelink control information for the second radio access technology. 
     In another embodiment, the processing circuitry acquires, from a control function server in the wireless communication system, sidelink control information for the first radio access technology. The processing circuitry communicates with another wireless communication system to provide the sidelink control information for the first radio access technology to the other wireless communication system. The other wireless communication network provides, using the second radio access technology, the sidelink control information for the first radio access technology to the second user equipment to enable the second user equipment to configure the sidelink between the first user equipment and the second user equipment using the first radio access technology. 
     In some embodiments, the processing circuitry provides sidelink control information for the first radio access technology to an application function (AF) server system. The AF server system provides the sidelink control information for the first radio access technology to the first user equipment and the second user equipment via channels in an application layer. The sidelink control information for the first radio access technology is used to configure a sidelink between the first user equipment and the second user equipment using the first radio access technology. 
     Aspects of the disclosure provide methods for an application function server system to control sidelink resource. In some embodiments, an application function (AF) server system receives sidelink control information for a first radio access technology from a first network configured based on the first radio access technology. Then, the AF server system coordinates with a first user equipment that accesses the first network using the first radio access technology, and a second user equipment that accesses a second network using a second radio access technology, via channels in an application layer. The AF server system provides the sidelink control information for the first radio access technology to the first user equipment and the second user equipment using the channels in the application layer for configuring a sidelink between the first user equipment and the second user equipment. 
     In some examples, the first radio access technology and the second radio access technology are evolved universal terrestrial radio access (E-UTRA) technology and new radio (NR) technology respectively. 
     In an embodiment, the AF server system receives sidelink control information for the radio access technology from the second network configured based on the first radio access technology. The AF server system can provide the sidelink control information for the second radio access technology to the first user equipment and the second user equipment using the channels in the application layer for configuring the sidelink between the first user equipment and the second user equipment. 
     In an example, the AF server system encrypts the sidelink control information for the first radio access technology in a message to be transmitted via the channels in the application layer. 
     Aspects of the disclosure also provide methods for sidelink resource control in user equipment. In some examples, a first user equipment establishes a radio connection with a first network using a first radio access technology. The first user equipment discovers a second user equipment that accesses a second network using a second radio access technology. The first user equipment sends a request to the first network that requests sidelink control information for the second radio access technology. Then, the first user equipment receives wireless signals in the first radio access technology that carries the sidelink control information for the second radio access technology. The sidelink control information for the second radio access technology is sourced from the second network in an example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of this disclosure that are proposed as examples will be described in detail with reference to the following figures, wherein like numerals reference like elements, and wherein: 
         FIG. 1  shows a diagram of a wireless communication scenario according to some embodiments of the disclosure; 
         FIG. 2  shows an example for a coordination procedure for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 3  shows another example for a coordination procedure for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 4  shows another example for a coordination procedure for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 5  shows another example for a coordination procedure for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 6  shows a flow chart outlining a process example for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 7  shows another flow chart outlining a process example for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 8  shows a flow chart outlining a process example for cross-RAT wireless communication according to an embodiment of the disclosure; 
         FIG. 9  shows a diagram of a user equipment according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Aspects of the disclosure provide techniques of radio resource control for cross-radio access technology (RAT) scenarios. In some embodiments, the techniques of radio resource control are used for controlling sidelink radio resources for wireless communication of user data directly between two devices without going through a base station, such as vehicle to vehicle (V2V) communication, vehicle to pedestrian (V2P) communication, vehicle to device (V2D) communication, user equipment to user equipment communication, cell phone to cell phone communication, device to device (D2D) wireless communication, and the like. While V2V wireless communication is used as examples in the present disclosure, the examples can be suitably modified for other sidelink communication scenarios, such as vehicle to everything (V2X) communication, vehicle to pedestrian (V2P) communication, vehicle to device (V2D) communication, user equipment to user equipment communication, cell phone to cell phone communication, and the like. 
     In a cross-RAT scenario, two vehicles are respectively connected into two radio access networks with different radio access technologies. In some embodiments, a first vehicle is connected into an evolved packet system (EPS) that is deployed based on LTE technology, and a second vehicle is connected into a 5G system (5GS) that is deployed based on NR technology. In some examples, the EPS is deployed with evolved packet core (EPC) network and evolved universal terrestrial radio access (E-UTRA) network for air interface; and the 5GS is deployed with 5G core (5GC) network and 5G access network for air interface. To enable sidelink communication of user data directly between the two vehicles without going through base stations, coordination of sidelink resource control over the EPS and 5GS are performed in some examples. In some embodiments, the coordination of the sidelink resource control is through an application server system. 
       FIG. 1  shows a diagram of a cross-RAT wireless communication system  100  according to some embodiments of the disclosure. The cross-RAT wireless communication system  100  includes two access networks that are respectively connected to two core networks. Coordination over the two core networks are performed for sidelink resource control to enable sidelink communication between two user devices, such as two vehicles that are respectively connected to the two radio access networks. 
     Specifically, in the  FIG. 1  example, the cross-RAT wireless communication system  100  includes a first sub-system  110  and a second sub-system  140 . In some examples, the first sub-system  110  is an EPS  110  that is configured based on LTE technology, and the second sub-system  140  is a 5GS  140  that is configured based on the NR technology. For example, the EPS  110  includes an evolved packet core (EPC) network  120  and an evolved universal terrestrial radio access network (E-UTRAN)  130  for air interface, and the 5GS  140  includes a 5G core 5GC) network  150  and a next generation (NG) radio access network (NG-RAN)  160  for air interface. It is noted that the cross-RAT wireless communication system  100  can include other suitable sub-systems, such as an application server system  170  and the like. The sub-systems  110 ,  140  and  170  are suitably connected, for example by Internet, and the like to enable control signals and/or data communication among the sub-systems. 
     The E-UTRAN  130  includes one or more base stations that air-interface with user equipment using LTE technology and can provide control plane and user plane to user equipment. The base stations in the E-UTRAN  130  are generally fixed stations that communicate with the user equipment and are also referred to as other suitable terminology, such as evolved node-B (eNB), a base transceiver system, an access point and the like. 
     The NG-RAN  160  includes one or more base stations that air-interface with user equipment using NR technology and can provide control plane and user plane to user equipment. The base stations in the NG-RAN  160  are generally fixed stations that communicate with the user equipment and are also referred to as other suitable terminology, such as next generation Node-B (gNB), a base transceiver system, an access point and the like. 
     According to some aspects of the disclosure, a first user equipment (UE)  180  and a second UE  190  are respectively connected into the EPS  110  and the 5GS  140 . For example, the first UE  180  is connected with the EPC  120  via the E-UTRAN  130 , and the second UE  190  is connected with the 5GC  150  via the NG-RAN  160 . In the  FIG. 1  example, the first UE  180  is connected into the EPS  110  via an eNB  131 , and the second UE  190  is connected into the 5GS  140  via a gNB  161 . 
     Further, according to some aspects of the disclosure, the first UE  180  and the second UE  190  may perform data communication directly via a sidelink without going through a base station. In an example, both the first UE  180  and the second UE  190  support LTE technology and NR technology, and may communicate directly over a LTE sidelink or an NR sidelink based on coordination of the EPS  110  and 5GS  140  in the cross-RAT wireless communication system  100 . In another example, the first UE  180  supports LTE technology, and the second UE  190  supports both LTE and NR technology, and the first UE  180  and the second UE  190  may communicate directly over a LTE sidelink based on coordination of the EPS  110  and 5GS  140  in the cross-RAT wireless communication system  100 . In another example, the first UE  180  supports both LTE technology and NR technology, and the second UE  190  supports the NR technology, and the first UE  180  and the second UE  190  may communicate directly over an NR sidelink based on coordination of the EPS  110  and 5GS  140  in the cross-RAT wireless communication system  100 . In some embodiments, the coordination oft the EPS  110  and 5GS  140  may go through a third party, such as the application server system  170  and the like. 
     It is noted that, in the  FIG. 1  example, wireless signals in the LTE technology is shown with thin dash lines, and wireless signals in the NR technology is shown with thick dash lines. 
     The first UE  180  and the second UE  190  can be any suitable fixed devices or mobile devices, and may be referred to as other suitable terminology, such as mobile stations, user terminals, wireless devices, and the like. Following description uses a first vehicle  180  and a second vehicle  190  as an example of the first UE  180  and the second UE  190 , and the description can be modified to suit for other devices. 
     The EPC network  120  includes various network elements. In some examples, the EPC network  120  includes a mobility management entity (MME)  122 , serving gateways (not shown), packet data network (PDN) gateways (not shown), and some other network elements such as vehicle to everything control function (V2X-CF)  121 , and the like. 
     It is noted that, in an example, each network element in the EPC network  120  can be implemented as circuits (e.g., processing circuitry, memory circuitry, input/output circuitry, and the like) or can be implemented as a processor that operates based on software instructions. In another example, a network element can be implemented as a server system with multiple servers. The multiple servers can be disposed at a location or can be distributed at different locations and are connected to work together as to appear as a single server to for example, user equipment. In another example, multiple network elements can be implemented by one physical component. 
     The serving gateways and the PDN gateways are configured for handling the user plane, such as transport data traffic between the user equipment and external networks of the EPS  110 . The serving gateways are the points of interconnection between the E-UTRAN  130  and the EPC network  120 . The serving gateways serve the user equipment by routing the incoming and outgoing IP packets in an example. The PDN gateways are the points of interconnection between the EPC network  120  and the external IP networks. The PDN gateways route packets to and from the packet data networks for example. 
     In some examples, the MME  122  is configured to handle with the control plane. For example, the MME  122  handles the signaling related to mobility and security for accessing E-UTRAN  130 . 
     It is noted that, in some examples, the MME  122  and the serving gateways are combined into a network element for performing both functions. 
     The V2X-CF  121  is a network element for managing vehicle to everything (V2X) related services in a network. In an example, the V2X-CF assists with network relation actions, such as providing the user equipment (e.g., vehicle, terminal device, smart phone, and the like) with the parameters necessary to use V2X communications. 
     According to an aspect of the disclosure, the 5GC network  150  includes various service functions for providing services. In some examples, the 5GC network  150  includes a core access and mobility management function (AMF)  152 , policy control function (PCF)  151 , user plane function (UPF) (not shown), session management function (SMF) (not shown) and some other service functions, and the like. In an example, an application function (AF) is implemented as part of the operator network and thus in the 5GC network  150 . In another example, an AF is implemented in the domain of a third party, such as in the application server system  170 , in user equipment, and the like.  FIG. 1  shows that the application server system  170  includes an AF  171 . 
     It is noted that, in an example, each function in the 5GC network  150  can be implemented in circuits (e.g., processing circuitry, memory circuitry, input/output circuitry, and the like) or can be implemented as a processor that operates based on software instructions. In another example, a function can be implemented as a server system with multiple servers. The multiple servers can be disposed at a location or can be distributed at different locations and are connected to work together as to appear as a single server to external components, such as user equipment. In another example, multiple functions can be performed by one physical component. 
     In some examples, the UPF combines the functions of the serving gateways and the PDN gateways in the LTE technology. 
     In some examples, the AMF  152  receives connection and session related information from user equipment and is responsible for handling connection and mobility management tasks. It is noted that messages related to session management are forwarded to the SMF, and handled by the SMF. 
     In some examples, the PCF  151  provides policy rules for control plane functions, such as network slicing, roaming and mobility management. Further, the PCF  151  can access subscription information for policy decisions, and supports the quality of service (QoS) policy and charging control functions. In an example, the PCF  151  can provide sidelink resource policy and configuration parameters. It is noted that, in another example, the sidelink resource policy and configuration parameters can be provided by other suitable function in the 5GC network  150 . 
     In some embodiments, user equipments use valide V2X policy and parameters provisioned by core networks for sidelink communication. For example, the V2X CF  121  can provide V2X policy and parameters for configuring LTE sidelinks for V2X communication; and the PCF  151  can provide V2X policy and parameters for configuring NR sidelinks for V2X communication. 
     According to an aspect of the disclosure, the EPC network  120  and the 5GC network  150  coordinate to provide suitable V2X policy and parameters to enable cross RAT radio resource control on the sidelink communication between the first UE  180  and the second UE  190 . Some coordination procedures for cross-RAT sidelink control are shown in  FIG. 2  and  FIG. 3 . 
     According to another aspect of the disclosure, the coordination of the EPC network  120  and the 5GC network  150  for providing suitable V2X policy and parameters go through the AF  171 . In an example, the application server system  170  is a vehicle application server system  170  that provides V2X communication service. Some coordination procedures for cross-RAT sidelink control are shown in  FIG. 4  and  FIG. 5 . It is noted that the application server system  170  can include one or more servers. The one or more servers can be disposed at one location, or can be distributed at different locations and are suitably connected. 
       FIG. 2  shows an example of a coordination procedure  200  in the cross-RAT wireless communication system  100  according to an embodiment of the disclosure. The coordination procedure  200  enables the cross-RAT wireless communication system  100  to provide valid V2X policy and parameters to the first UE  180  and the second UE  190  for configuring sidelink communication. In the  FIG. 2  example, the first UE  180  supports both LTE and NR technologies, and the second UE  190  supports NR technology. 
     At S 205 , the first UE  180  establishes a radio resource control (RRC) connection with the eNB  131 , and is connected into the EPS  110 . 
     At S 210 , the second UE  190  establishes an RRC connection with the gNB  161  and is connected into the 5GS  140 . It is noted that S 205  and S 210  may happen at the same time or in a different sequence. 
     At S 220 , the first UE  180  and the second UE  190  respectively execute a V2X application. In an example, the first UE  180  performs a suitable discovery process to find the second UE  190  that is nearby for sidelink communication. In another example, the second UE  190  performs a suitable discovery process to find the first UE  180  that is nearby for sidelink communication. It is noted that, in the present disclosure, the discovery process can be any suitable discovery process, such as an in-application discovery process, a discovery process independent of applications, and the like. In the  FIG. 2  example, NR technology is supported by both the first UE  180  and the second UE  190 , and the NR technology is determined for use in sidelink communication between the first UE  180  and the second UE  190 . 
     At S 225 , the first UE  180  checks whether valid V2X policy and parameters for NR technology is available at the first UE  180 . When the first UE  180  does not have valid V2X policy and parameters, the first UE  180  sends a request to the EPC network  120 . In an example, the MME  122  receives the request. 
     At S 230 , the second UE  190  checks whether valid V2X policy and parameters for the NR technology is available at the second UE  190 . When the second UE  190  does not have valid V2X policy and parameters, the second UE  190  sends a request to the 5GC network  150 . In an example, the AMF  152  receives the request. 
     At S 240 , the 5GC network  150  obtains valid V2X policy and parameters for the NR technology. In an example, the PCF  151  provides the valid V2X policy and parameters for the NR technology to the AMF  152 . It is noted that, in another example, the valid V2X policy and parameters for the NR technology can be provided from other suitable network function to the AMF  152 . 
     At S 250 , the EPC network  120  and the 5GC network  150  coordinates the cross RAT sidelink resource control. In an example, the MME  122  and the AMF  152  interact with suitable interfaces, such as via a PDN gateway, a UPF, and connections between the EPS  110  and the 5GS  140 . For example, the AMF  152  provides the valid V2X policy and parameters for the NR technology to the MME  122 . 
     At S 255 , the EPC network  120  provides the valid V2X policy and parameters for the NR technology to the first UE  180 . In an example, the MME  122  provides the valid V2X policy and parameters for the NR technology to the first UE  180  via eNB  131 . Then, the air interface between the eNB  131  and the first UE  180  carries, using the LTE technology, the valid V2X policy and parameters for the NR technology. 
     At S 260 , the 5GC network  150  provides the valid V2X policy and parameters for the NR technology to the second UE  190 . In an example, the AMF  152  provides the valid V2X policy and parameters for the NR technology to the second UE  190  via gNB  161 . Then, the air interface between the gNB  161  and the second UE  190  carries, using the NR technology, the valid V2X policy and parameters for the NR technology. 
     It is noted that S 255  and S 260  may be performed at the same time or in a different sequence. In some examples, S 260  may be performed before S 250  and after S 240 . 
     At S 270 , both the first UE  180  and the second UE  190  have valid V2X policy and parameters for NR technology, and thus can setup sidelink communication in the NR technology to transmit data in the user plane between the first UE  180  and the second UE  190  without go through the base stations. 
       FIG. 3  shows an example for a coordination procedure  300  in the cross-RAT wireless communication system  100  according to an embodiment of the disclosure. The coordination procedure  300  enables the cross-RAT wireless communication system  100  to provide valid V2X policy and parameters to the first UE  180  and the second UE  190  for sidelink communication. In the  FIG. 3  example, the first UE  180  supports the LTE technology, and the second UE  190  supports both LTE and NR technologies. 
     At S 305 , the first UE  180  establishes a radio resource control (RRC) connection with the eNB  131 , and is connected into the EPS  110 . 
     At S 310 , the second UE  190  establishes an RRC connection with the gNB  161  and is connected into the 5GS  140 . It is noted that S 305  and S 310  may happen at the same time or in a different sequence. 
     At S 320 , the first UE  180  and the second UE  190  respectively execute a V2X application. In an example, the first UE  180  performs a suitable discovery process to find the second UE  190  that is nearby for sidelink communication. In another example, the second UE  190  performs a suitable discovery process to find the first UE  180  that is nearby for sidelink communication. It is noted that, in the present disclosure, the discovery process can be any suitable discovery process, such as an in-application discovery process, a discovery process independent of applications, and the like. In the  FIG. 3  example, the LTE technology is supported by both the first UE  180  and the second UE  190 , and the LTE technology is determined for use in sidelink communication between the first UE  180  and the second UE  190 . 
     At S 325 , the first UE  180  checks whether valid V2X policy and parameters for the LTE technology is available at the first UE  180 . When the first UE  180  does not have valid V2X policy and parameters, the first UE  180  sends a request to the EPC network  120 . In an example, the MME  122  receives the request. 
     At S 330 , the second UE  190  checks whether valid V2X policy and parameters for LTE technology is available at the second UE  190 . When the second UE  190  does not have valid V2X policy and parameters, the second UE  190  sends a request to the 5GC network  150 . In an example, the AMF  152  receives the request. 
     At S 340 , the EPC network  120  obtains valid V2X policy and parameters for the LTE technology. In an example, the V2X CF  121  provides the valid V2X policy and parameters for the LTE technology to the MME  122 . 
     At S 350 , the EPC network  120  and the 5GC network  150  coordinate the cross RAT sidelink resource control. In an example, the MME  122  and the AMF  152  interact with suitable interfaces, such as via a PDN gateway, a UPF, and connections between the EPS  110  and the 5GS  140 . In an example, the MME  122  provides the valid V2X policy and parameters for LTE technology to the AMF  152 . 
     At S 355 , the EPC network  120  provides the valid V2X policy and parameters for the LTE technology to the first UE  180 . In an example, the MME  122  provides the valid V2X policy and parameters for LTE technology to the first UE  180  via eNB  131 . Then, the air interface between the eNB  131  and the first UE  180  carries, using the LTE technology, the valid V2X policy and parameters for LTE technology. 
     At S 360 , the 5GC network  150  provides the valid V2X policy and parameters for the LTE technology to the second UE  190 . In an example, the AMF  152  provides the valid V2X policy and parameters for LTE technology to the second UE  190  via gNB  161 . Then, the air interface between the gNB  161  and the second UE  190  carries, using the NR technology, the valid V2X policy and parameters for LTE technology. 
     It is noted that S 355  and S 360  may be performed at the same time or in a different sequence. In another example, S 355  is performed before S 350  and after S 340 . 
     At S 370 , both the first UE  180  and the second UE  190  have valid V2X policy and parameters for the LTE technology, and thus can setup sidelink communication in the LTE technology to transmit data in the user plane between the first UE  180  and the second UE  190  without go through the base stations. 
     It is noted that, in another example, both the first UE  180  and the second UE  190  support both LTE and NR technology. During the discovery step, one of the first UE  180  and the second UE  190  may determine the technology for the sidelink communication. When the NR technology is determined for the sidelink communication, the coordination procedure is similar to the coordination procedure  200 ; and when the LTE technology is determined for the sidelink communication, the coordination procedure is similar to the coordination procedure  300 . 
       FIG. 4  shows an example for a coordination procedure  400  in the cross-RAT wireless communication system  100  according to an embodiment of the disclosure. The coordination procedure  400  enables the cross-RAT wireless communication system  100  to provide valid V2X policy and parameters to the first UE  180  and the second UE  190  for sidelink communication. In the  FIG. 4  example, the first UE  180  supports both LTE and NR technologies, and the second UE  190  supports NR technology. 
     At S 405 , the first UE  180  establishes a radio resource control (RRC) connection with the eNB  131 , and is connected into the EPS  110 . 
     At S 410 , the second UE  190  establishes an RRC connection with the gNB  161  and is connected into the 5GS  140 . It is noted that S 505  and S 510  may happen at the same time or in a different sequence. 
     At S 420 , the first UE  180  and the second UE  190  respectively execute a V2X application. For example, the first UE  180  and the second UE  190  are connected with the application server system  170  and executes functions provided by the AF  171 . In an example, the first UE  180  performs a suitable discovery process to find the second UE  190  that is nearby for sidelink communication. In another example, the second UE  190  performs a suitable discovery process to find the first UE  180  that is nearby for sidelink communication. It is noted that, in the present disclosure, the discovery process can be any suitable discovery process, such as an in-application discovery process, a discovery process independent of applications, and the like. In the  FIG. 4  example, NR technology is supported by both the first UE  180  and the second UE  190 , and the NR technology is determined for use in sidelink communication between the first UE  180  and the second UE  190 . 
     At S 425 , the first UE  180  checks whether valid V2X policy and parameters for NR technology is available at the first UE  180 . When the first UE  180  does not have valid V2X policy and parameters, the first UE  180  sends a request to the EPC network  120 . In an example, the MME  122  receives the request. 
     At S 430 , the second UE  190  checks whether valid V2X policy and parameters for NR technology is available at the second UE  190 . When the second UE  190  does not have valid V2X policy and parameters, the second UE  190  sends request to the 5GC network  150 . In an example, the AMF  152  receives the request. 
     At S 440 , the 5GC network  150  obtains valid V2X policy and parameters for the NR technology, and provides to the AF  171  in the application server system  170 . In an example, the PCF  151  provides the valid V2X policy and parameters for the NR technology to the AMF  152 . The AMF  152  interacts with suitable interfaces, such as via a PDN gateway, and connections between the 5GS  140  and the application server system  170  to provide the valid V2X policy and parameters for the NR technology to the AF  171 . In some embodiments, the EPC network  120  obtains valid V2X policy and parameters for the LTE technology, and provides to the AF  171  in the application server system  170 . In an example, the V2X CF  121  provides the valid V2X policy and parameters for the LTE technology to the MME  122 . The MME  122  interacts with suitable interfaces, such as via UPN, and connections between the EPS  110  and the application server system  170  to provide the valid V2X policy and parameters for the LTE technology to the AF  171 . 
     At S 455 , the application server system  170  provides the valid V2X policy and parameters for NR technology to the first UE  180 , for example in the application layer. In an example, a channel in the application layer is setup between the application server system  170  and the first UE  180 , and the valid V2X policy and parameters for NR technology is included in a message and provided via the channel from the AF  171  to the first UE  180 . It is noted that, in some examples, suitably encryption and authentication techniques are used on the message. It is noted that in some examples, the application server system  170  also provides the valid V2X policy and parameters for the LTE technology to the first UE  180 , for example in the application layer 
     At S 460 , the application server system  170  provides the valid V2X policy and parameters for the NR technology to the second UE  190 , for example in the application layer. In an example, a channel in the application layer is setup between the application server system  170  and the second UE  190 , and the valid V2X policy and parameters for NR technology is included in a message and provided via the channel from the AF  171  to the second UE  190 . It is noted that, in some examples, suitably encryption and authentication techniques are used on the message. It is noted that in some examples, the application server system  170  provides the valid V2X policy and parameters for the LTE technology to the second UE  190 , for example in the application layer. 
     It is noted that S 455  and S 460  may be performed at the same time or in a different order. 
     At S 470 , both the first UE  180  and the second UE  190  have valid V2X policy and parameters for NR technology, and thus can setup sidelink communication in the NR technology to transmit data in the user plane between the first UE  180  and the second UE  190  without go through the base stations. 
       FIG. 5  shows an example for a coordination procedure  500  in the cross-RAT wireless communication system  100  according to an embodiment of the disclosure. The coordination procedure  500  enables the cross-RAT wireless communication system  100  to provide valid V2X policy and parameters to the first UE  180  and the second UE  190  for sidelink communication. In the  FIG. 5  example, the first UE  180  supports both LTE technology, and the second UE  190  supports both LTE and NR technologies. 
     At S 505 , the first UE  180  establishes a radio resource control (RRC) connection with the eNB  131 , and is connected into the EPS  110 . 
     At S 510 , the second UE  190  establishes an RRC connection with the gNB  161  and is connected into the 5GS  140 . It is noted that S 505  and S 510  may happen at the same time or in a different sequence. 
     At S 520 , the first UE  180  and the second UE  190  respectively execute a V2X application. In an example, the first UE  180  performs a suitable discovery process to find the second UE  190  that is nearby for sidelink communication. In another example, the second UE  190  performs a suitable discovery process to find the first UE  180  that is nearby for sidelink communication. It is noted that, in the present disclosure, the discovery process can be any suitable discovery process, such as an in-application discovery process, a discovery process independent of applications, and the like. In the  FIG. 5  example, the LTE technology is supported by both the first UE  180  and the second UE  190 , and the LTE technology is determined for use in sidelink communication between the first UE  180  and the second UE  190 . 
     At S 525 , the first UE  180  checks whether valid V2X policy and parameters for LTE technology is available at the first UE  180 . When the first UE  180  does not have valid V2X policy and parameters, the first UE  180  sends a request to the EPC network  120 . In an example, the MME  122  receives the request. 
     At S 530 , the second UE  190  checks whether valid V2X policy and parameters for LTE technology is available at the second UE  190 . When the second UE  190  does not have valid V2X policy and parameters, the second UE  190  sends a request to the 5GC network  150 . In an example, the AMF  152  receives the request. 
     At S 540 , the EPC network  120  obtains valid V2X policy and parameters for the LTE technology, and provides to the AF  171  in the application server system  170 . In an example, the V2X CF  121  provides the valid V2X policy and parameters for the LTE technology to the MME  122 . The MME  122  interacts with suitable interfaces, such as via UPN, and connections between the EPS  110  and the application server system  170  to provide the valid V2X policy and parameters for the LTE technology to the AF  171 . In some embodiments, the 5GC network  150  obtains valid V2X policy and parameters for the NR technology, and provides to the AF  171  in the application server system  170 . In an example, the PCF  151  provides the valid V2X policy and parameters for the NR technology to the AMF  152 . The AMF  152  interacts with suitable interfaces, such as via a PDN gateway, and connections between the 5GS  140  and the application server system  170  to provide the valid V2X policy and parameters for the NR technology to the AF  171 . 
     At S 555 , the application server system  170  provides the valid V2X policy and parameters for the LTE technology to the first UE  180 , for example in the application layer. In an example, a channel in the application layer is setup between the application server system  170  and the first UE  180 , and the valid V2X policy and parameters for the LTE technology is included in a message and provided via the channel from the AF  171  to the first UE  180 . It is noted that, in some examples, suitably encryption and authentication techniques are used on the message. It is noted that, in some examples, the application server system  170  provides the valid V2X policy and parameters for the NR technology to the first UE  180 , for example in the application layer. 
     At S 560 , the application server system  170  provides the valid V2X policy and parameters for the LTE technology to the second UE  190 , for example in the application layer. In an example, a channel in the application layer is setup between the application server system  170  and the second UE  190 , and the valid V2X policy and parameters for the LTE technology is included in a message and provided via the channel from the AF  171  to the second UE  190 . It is noted that, in some examples, suitably encryption and authentication techniques are used on the message. It is noted that, in some examples, the application server system  170  provides the valid V2X policy and parameters for the NR technology to the second UE  190 , for example in the application layer. 
     It is noted that S 555  and S 560  may be performed at the same time or in a different sequence. 
     At S 570 , both the first UE  180  and the second UE  190  have valid V2X policy and parameters for the LTE technology, and thus can setup sidelink communication in the LTE technology to transmit data in the user plane between the first UE  180  and the second UE  190  without go through the base stations. 
     It is noted that, in another example, both the first UE  180  and the second UE  190  support both LTE and NR technology. During the discovery step, one of the first UE  180  and the second UE  190  may determine the technology for the sidelink communication. When the NR technology is determined for the sidelink communication, the coordination procedure is similar to the coordination procedure  400 ; and when the LTE technology is determined for the sidelink communication, the coordination procedure is similar to the coordination procedure  500 . 
       FIG. 6  shows a flow chart outlining a process  600  according to an embodiment of the disclosure. The process  600  is executed by a first network, such as the EPS  110 , the 5GS  140 , and the like. In some examples, the process  600  is executed by circuitry, such processing circuitry, transceiver circuitry, and the like. In some examples, one or more processors execute software instructions stored in memory circuitry to execute the process  600 . The process starts at S 601  and proceeds to S 610 . 
     At S 610 , the first network receives a request from a first UE. The first network is based on a first RAT. The first UE is connected with the first network based on the first RAT. The request requests sidelink control information for a second RAT. 
     At S 620 , first network obtains the sidelink control information for the second RAT. In some examples, the first network coordinates with a second network that is based on the second RAT to receive the sidelink control information for the second RAT from the second network. 
     At S 630 , the first network provides, via the first RAT, the sidelink control information for the second RAT to the first UE. Thus, in some examples, the first UE can setup a sidelink in the second RAT with a second UE in the second network. Then, the process proceeds to S 699  and terminates. 
       FIG. 7  shows a flow chart outlining a process  700  according to an embodiment of the disclosure. The process  700  is executed by an application function, such as the AF  171  in the application server system  170 , and the like. In some examples, the process  700  is executed by circuitry, such processing circuitry, transceiver circuitry, and the like. In some examples, one or more processors execute software instructions stored in memory circuitry to execute the process  700 . The process starts at S 701  and proceeds to S 710 . 
     At S 710 , the AF receives sidelink control information for a first RAT from a first network based on a first RAT and/or sidelink control information for a second RAT from a second network based on a second RAT. In an example, the EPC  120  receives a request from the UE  180  for sidelink control information for LTE. In response to the request, the EPC  120  provides the sidelink control information for LTE to the AF  171 . In an example, when the EPC  120  receives a request from the UE  180  for sidelink control information for NR, the EPC  120  does not have the sidelink control information for NR, and may forward the request to the AF  171 . It is noted that, the EPC  120  can forward the request for the sidelink control information of NR to the AF  171 , and provides the sidelink control information for LTE to the AF  171 . In an example, the 5GC  150  receives a request from the UE  190  for sidelink control information for NR. In response to the request, the 5GC  150  provides the sidelink control information for NR to the AF  171 . In an example, when the 5GC  150  receives a request from the UE  190  for sidelink control information for LTE, the 5GC  150  does not have the sidelink control information for LTE, and may forward the request to the AF  171 . It is noted that, the 5GC  150  can forward the request for the sidelink control information of LTE to the AF  171 , and provides the sidelink control information for NR to the AF  171 . 
     At S 720 , the AF coordinates with a first UE accessing the first NW and a second UE accessing the second UE using channels in the application layer. In an example, the application layer contains the communications protocols and interface methods used in process-to-process communications across, for, example, an Internet Protocol (IP) computer network. The application layer standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client-server or peer-to-peer networking model. For example, a first channel is setup between the AF  171  and the first UE  180 , messages are sent between the AF  171  and the first UE  180  by the first channel. The messages can be suitably encrypted, thus although the eNB  131  may transmit and receive signals carrying the messages, but is not able to decrypt messages in an example. Similarly, a second channel is setup between the AF  171  and the second UE  190 , messages are sent between the AF  171  and the second UE  190  by the second channel. 
     At S 730 , the AF provides at least one of the sidelink control information for the first RAT and the sidelink control information for the second RAT to the first UE and the second UE using the channels in the application layer. In an example, the AF  171  provides the sidelink control information for LTE to the first UE  180  via the first channel and provides the sidelink control information for the LTE to the second UE  190  via the second channel. Thus, the first UE  180  and the second UE  190  can setup LTE sidelink. In another example, the AF  171  provides the sidelink control information for NR to the first UE  180  via the first channel and provides the sidelink control information for the NR to the second UE  190  via the second channel. Thus, the first UE  180  and the second UE  190  can setup NR sidelink. In another example, the AF  171  provides the sidelink control information for LTE and NR to the first UE  180  via the first channel and provides the sidelink control information for the LTE and NR to the second UE  190  via the second channel. Thus, the first UE  180  and the second UE  190  can setup LTE or NR sidelink. Then, the process proceeds to S 799  and terminates. 
       FIG. 8  shows a flow chart outlining a process  800  according to an embodiment of the disclosure. The process  800  is executed by an UE, such as the first UE  180 , the second UE  190  and the like. In some examples, the process  800  is executed by circuitry in the UE, such processing circuitry, transceiver circuitry, and the like. In some examples, one or more processors in the UE execute software instructions stored in memory circuitry to execute the process  800 . The process starts at S 801  and proceeds to S 810 . 
     At S 810 , a first UE establishes an RRC with a first NW based on a first RAT. In an example, the first UE  180  in the  FIG. 1  example establishes an RRC with the E-UTRAN  130  based on LTE, and is then connected into the EPS  110 . The second UE  190  in the  FIG. 1  example establishes an RRC with NG-RAN  160 , and is then connected into the 5GS  140 . 
     At S 820 , the first UE sends a request to the first NW requesting sidelink control information for a second RAT. In an example, the first UE  180  and the second UE  190  conduct a discovery process, and decides to setup NR sidelink between the first UE  180  and the second UE  190 . The first UE  180  checks whether the first UE  180  has valid sidelink control information for NR, and sends a request for valide sidelink control information for NR to the EPC  120 . 
     At S 830 , the first UE receives the sidelink control information for the second RAT. In an example, the EPC  120  and the 5GC  150  coordinate, and the 5GC  150  provides the valid sidelink control information (e.g., sidelink policy and parameters) for NR to the EPC  120 , and the EPC  120  provides the valid sidelink control information for NR to the first UE  180 . In another example, the 5GC  150  provides the valid sidelink control information for NR to the AF  171 , and then the AF  171  then sends the valid sidelink control information for NR to the first UE  180  via a channel in the application layer. The AF  171  may also sends the valid sidelink control information for NR to the second UE  190  via a channel in the application layer. 
     At S 840 , the first UE and the second UE set up a sidelink of the second RAT based on the sidelink control information for the second RAT, and transmit user data in the sidelink. Then, the process proceeds to S 899  and terminates. 
       FIG. 9  shows a block diagram of a UE  900  according to embodiments of the disclosure. In an example, the first UE  180  and the second UE  190  can be respectively configured in the same manner as the UE  900 . The UE  900  can be configured to perform various functions in accordance with one or more embodiments or examples described herein. Thus, the UE  900  can provide means for implementation of techniques, processes, functions, components, systems described herein. For example, the UE  900  can be used to implement functions of the first UE  180  or the second UE  190  in various embodiments and examples described herein. The UE  900  can be a general purpose computer in some embodiments, and can be a device including specially designed circuits to implement various functions, components, or processes described herein in other embodiments. The UE  900  can include processing circuitry  910 , a memory  920 , a radio frequency (RF) module  930 , and an antenna  940 . 
     In various examples, the processing circuitry  910  can include circuitry configured to perform the functions and processes described herein in combination with software or without software. In various examples, the processing circuitry can be a digital signal processor (DSP), an application specific integrated circuit (ASIC), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), digitally enhanced circuits, or comparable device or a combination thereof. 
     In some other examples, the processing circuitry  910  can be a central processing unit (CPU) configured to execute program instructions to perform various functions and processes described herein. Accordingly, the memory  920  can be configured to store program instructions. The processing circuitry  910 , when executing the program instructions, can perform the functions and processes. The memory  920  can further store other programs or data, such as operating systems, application programs, and the like. The memory can include transitory or non-transitory storage medium. The memory  920  can include a read only memory (ROM), a random access memory (RAM), a flash memory, a solid state memory, a hard disk drive, an optical disk drive, and the like. 
     The RF module  930  receives processed data signal from the processing circuitry  910  and transmits the signal in a beam-formed wireless communication network via an antenna  940 , or vice versa. The RF module  930  can include a digital to analog convertor (DAC), an analog to digital converter (ADC), a frequency up convertor, a frequency down converter, filters, and amplifiers for reception and transmission operations. The RF module  930  can include multi-antenna circuitry (e.g., analog signal phase/amplitude control units) for beamforming operations. The antenna  940  can include one or more antenna arrays. 
     The UE  900  can optionally include other components, such as input and output devices, additional or signal processing circuitry, and the like. Accordingly, the UE  900  may be capable of performing other additional functions, such as executing application programs, and processing alternative communication protocols. 
     The processes and functions described herein can be implemented as a computer program which, when executed by one or more processors, can cause the one or more processors to perform the respective processes and functions. The computer program may be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with, or as part of, other hardware. The computer program may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. For example, the computer program can be obtained and loaded into an apparatus, including obtaining the computer program through physical medium or distributed system, including, for example, from a server connected to the Internet. 
     The computer program may be accessible from a computer-readable medium providing program instructions for use by or in connection with a computer or any instruction execution system. The computer readable medium may include any apparatus that stores, communicates, propagates, or transports the computer program for use by or in connection with an instruction execution system, apparatus, or device. The computer-readable medium can be magnetic, optical, electronic, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. The computer-readable medium may include a computer-readable non-transitory storage medium such as a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a magnetic disk and an optical disk, and the like. The computer-readable non-transitory storage medium can include all types of computer readable medium, including magnetic storage medium, optical storage medium, flash medium, and solid state storage medium. 
     When implemented in hardware, the hardware may comprise one or more of discrete components, an integrated circuit, an application-specific integrated circuit (ASIC), etc. While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.