TW201640922A - Mobile communication devices and methods for service continuity with proximity-based service (ProSe) user equipment (UE)-to-network relay - Google Patents

Abstract

A mobile communication device located within a radio signal coverage of a service network to serve as a relay User Equipment (UE) for Proximity-based Service (ProSe) UE-to-network relay is provided. The mobile communication device includes a wireless transceiver and a controller. The wireless transceiver performs wireless transmission and reception to and from the service network and a remote UE which is located out of the radio signal coverage of the service network. The controller receives a measurement report message from the remote UE via the wireless transceiver, and transmits a relay discovery message to other relay UEs via the wireless transceiver when the measurement report message indicates that the connection status between the remote UE and the relay UE falls below a predetermined threshold, so as to trigger other relay UEs to transmit a Device-to-Device Synchronization Signal (D2DSS).

Description

Mobile communication device and service continuous method

The present invention relates to a wireless communication technology, and in particular to a service for a Proximity-based Service (ProSe) User Equipment (UE) for a UE-to-network relay. method.

In recent years, due to the significant increase in demand for ubiquitous computing and network communications, various wireless technologies have emerged, including: Global System for Mobile communications (GSM) technology, universal packet wireless services ( General Packet Radio Service (GPRS) technology, Enhanced Data Rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, code division multiplexing access -2000 (Code Division Multiple Access 2000, CDMA-2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access, WiMAX) technology, long-term Long Term Evolution (LTE) technology, Long Term Evolution Enhanced (LTE-A) technology, and Time-Division LTE (TD-LTE) technology. By using one of the above wireless technologies, a mobile communication device (or a user device) can be wirelessly connected to the Internet or a service network to obtain mobile services including proximity services anytime and anywhere, including proximity services. The development of the system has risen in response to the demand for social science and technology in recent years.

Taking long-term evolution technology as an example, the proximity service department was proposed in the specification standard book developed by the 3rd Generation Partnership Project (3GPP) organization of the 12th edition. The user device with the proximity service function can explore other nearby user devices that also have the proximity service function by the performance of the device itself or with the assistance of the long term evolution network. In addition to proximity service discovery, a user device with proximity service function can also serve as a relay between two other user devices with proximity service functions, or as another user device with proximity service function and long term evolution. Relay between networks to provide proximity service communication between the two. However, according to the specification standard TR 23.713 developed by the 3rd Generation Partnership Project, the user device acting as a relay (also referred to as a relay user device) must be connected to the Long Term Evolution network and require proximity. Serving the radio resources used by the user equipment to the ProSe UE-to-network relay, and continuing to transmit the Device-to-Device Synchronization Signal (D2DSS) to give way The user device (also referred to as the remote user device) outside the signal of the long term evolution network can transmit data to the long term evolution network through the relay user device. As a result, the relay user device will face the problem of power consumption/waste, and the long-term evolution network The wireless resources of the road are prone to inefficiencies in use, especially when nearby remote user devices do not need to use the proximity service user device to service the network relay.

On the other hand, when the remote user device or the relay user device moves, the service of the ProSe UE-to-network relay between the two may be disconnected. . Therefore, how to enable the remote user device to continue to obtain services has become an urgent problem to be solved.

A first embodiment of the present invention provides a mobile communication device having a wireless transceiver and a controller, which is located within a signal range of a service network for use as a proximity service user device to one of the network relays. Relay user device. The wireless transceiver is configured to perform wireless transmission and reception with the service network and a remote user device located outside the coverage of the service network. The controller is configured to receive a measurement report message from the remote user device through the wireless transceiver, and indicate, by using the measurement report message, a connection between the remote user device and the mobile communication device. When the state is lower than a predetermined threshold, a relay discovery message is transmitted to the other relay user devices through the wireless transceiver to trigger the other relay user devices to start transmitting a device-to-device synchronization signal.

A second embodiment of the present invention provides a service persistence method, which is applicable to a proximity service user device relaying a network and being performed by a relay user device located in a signal coverage area of a service network, the service The continuous method includes: receiving a measurement report from a remote UE (remote UE) And transmitting a relay discovery message to the other relay user device when the measurement report message indicates that the connection state between the remote user device and the mobile communication device is lower than a predetermined threshold, Initiating transmission of a device-to-device synchronization signal by triggering the other relay user devices described above.

A third embodiment of the present invention provides a mobile communication device having a wireless transceiver and a controller, which is located outside the coverage of a service network to serve as a proximity service user device to the network relay. From the user device. The wireless transceiver is configured to perform wireless transmission and reception with the service network and one of the relay user devices within the coverage of the service network. The controller is configured to transmit, by the wireless transceiver, a relay discovery message to the other relay user through the wireless transceiver when the connection state of one of the relay user devices is lower than a predetermined threshold And receiving, by the wireless transceiver, one or more device-to-device synchronization signals from the other relay user devices, and transmitting a direct communication to one of the other relay user devices according to the device synchronization signal selection Request a message to establish a connection.

A fourth embodiment of the present invention provides a service persistence method, which is suitable for a proximity service user device to relay a network and is executed by a remote user device located outside a signal range of a service network, the service The continuation method includes: transmitting a relay discovery message to other relay user devices when measuring a connection state with one of the relay user devices below a predetermined threshold; receiving from the other relay user devices And one or more devices synchronize the signals to the device; and, according to the device, select a direct communication request message to the one of the other relay user devices to establish a connection.

With regard to other additional features and advantages of the present invention, those skilled in the art can make some modifications to the mobile communication device and service continuation method disclosed in the method of the present invention without departing from the spirit and scope of the present invention. Retouched and got.

100‧‧‧Wireless communication environment

110~140‧‧‧Mobile communication device

150‧‧‧Service Network

151‧‧‧Access network

152‧‧‧ core network

10‧‧‧Wireless transceiver

11‧‧‧RF device

12‧‧‧Base frequency processing device

13‧‧‧Antenna

20‧‧‧ Controller

30‧‧‧Storage device

40‧‧‧ display device

50‧‧‧ input device

S310~S390, S510~S550‧‧‧ steps

1 is a schematic diagram of a wireless communication environment according to an embodiment of the invention.

2 is a schematic diagram of a mobile communication device according to an embodiment of the invention.

3A and 3B are message sequence diagrams of a network relay by a proximity service user device according to an embodiment of the invention.

Fig. 4A is a message sequence diagram of the mode of exploration of mode A according to the embodiment of Figs. 3A and 3B.

Fig. 4B is a message sequence diagram of the mode of exploration of mode B according to the embodiment of Figs. 3A and 3B.

Figure 5 is a sequence diagram of a message established by a connection to a communication in accordance with an embodiment of Figures 3A and 3B of the present invention.

FIG. 6A is a message sequence diagram of the measurement and return of the connection state according to an embodiment of the invention.

FIG. 6B is a message sequence diagram of the measurement and return of the connection state according to another embodiment of the present invention.

Figure 7 is a message sequence diagram of a relay discovery procedure initiated by a relay user device in accordance with an embodiment of Figures 3A and 3B.

The present invention is described in the following as a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. It should be understood that the following embodiments may be via software, hardware, firmware, or the like. Arbitrarily combined to achieve. The specifications of the third-generation partner program described in this document are for the purpose of promoting the spirit of the invention and are not intended to limit the scope of the invention.

1 is a schematic diagram of a wireless communication environment according to an embodiment of the invention. The wireless communication environment 100 includes mobile communication devices 110-140 and a service network 150. The mobile communication devices 110-130 are located within the coverage of the service network 150 (marked by a cut line in FIG. 1) and can be wirelessly connected. To the service network 150 to obtain mobile services including proximity services. The mobile communication device 140 is located outside the coverage of the service network 150, but is adjacent to the mobile communication devices 110-130, that is, within a range in which wireless communication is possible (indicated by a broken line in FIG. 1). The mobile communication devices 110-140 are all user devices having a proximity service function. The mobile communication devices 110-130 can be used as relay user devices because they are located in the service area of the service network 150. The mobile communication device 140 can be used as a remote user device because it is located outside the service area of the service network 150. That is to say, the mobile communication devices 110-130 can serve as relay stations for providing proximity service communication between the mobile communication device 140 and the service network 150. The mobile communication devices 110-140 can be functional phones, smart phones, tablets, notebook computers, or any electronic computing device as long as they can support the wireless communication technology used by the service network 150.

The service network 150 is a network with proximity service functions, such as: Long-term evolution network, long-term evolution enhanced network, or time-sharing long-term evolution network. Specifically, the service network 150 includes an access network 151 for processing radio signals, supporting terminal radio protocols, and connecting machine type communication devices 110-130 and a core network, and a core network 152. Path 152, and core network 152 is used to perform mobility management, network-side authentication, and interfacing with a public network (e.g., the Internet). Access network 151 and core network 152 may each include one or more network nodes to perform the functions described above. For example, the access network 151 may be an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) including at least one evolved Node B (eNB), for example The home evolved base station, the wide base station, and the pico base station; and the core network 152 may be an Evolved Packet Core (EPC), which includes: a home user server ( Home Subscriber Server, HSS), Mobility Management Entity (MME), Serving Gateway (S-GW), Packet Data Network Gateway (PDN-GW/P-) GW), Secure User Plane Location (SUPL) positioning platform (SUL Location Platform, SLP), and proximity service function nodes.

Although not shown, the core network 152 can be further coupled to an Access Stratum (AS) for providing public safety related services. For example, the Public Safety Access Layer can be used as a control center or information return center for dealing with emergencies such as major natural disasters and large-scale regional power outages.

2 is a mobile communication device according to an embodiment of the invention. Schematic diagram. The mobile communication device shown can be broadly representative of mobile communication devices 110-140, including wireless transceiver 10, controller 20, storage device 30, display device 40, and input device 50. The wireless transceiver 10 is configured to provide wireless transmission and reception functions with the service network 150 and other nearby mobile communication devices. Specifically, the wireless transceiver 10 includes a radio frequency (RF) device 11, a baseband processing device 12, and an antenna 13. The baseband processing device 12 is configured to perform baseband signal processing and control communication between a subscriber number card (eg, a Universal Subscriber Identity Module (USIM) card) (not shown) and the radio frequency device 11. . The baseband processing device 12 may include a plurality of hardware devices to perform baseband signal processing, including analog-to-digital conversion (ADC)/digital-to-analog conversion (DAC), gain ( Gain) adjustment, modulation and demodulation, and encoding/decoding. The radio frequency device 11 can receive the radio frequency wireless signal from the antenna 13, convert the radio frequency wireless signal into a baseband signal for further processing by the baseband processing device 12, or receive the baseband signal from the baseband processing device 12, and the baseband signal. It is converted into a radio frequency wireless signal for transmission through the antenna 13. The radio frequency device 11 may also include a plurality of hardware devices to perform the above-described radio frequency conversion. For example, the radio frequency device 11 may include a mixer to multiply the baseband signal by one of the radio frequencies used by the wireless technology. Carrier, where the radio can be 900 MHz, 2100 MHz, or 2.6 GHz, or other radio frequency used by Long Term Evolution, Long Term Evolution, or Time-Shifted Long Term Evolution, eg, unlicensed band ( Such as: 2.4 GHz) or licensed bands used by other wireless technologies.

The controller 20 can be a general purpose processor, a microprocessor (Micro-Control Unit, MCU), application processor, or digital signal processor (DSP), etc., for controlling the wireless transceiver 10 to execute between the service network 150 and other nearby mobile communication devices. Wireless transmission and reception, reading or writing data from the storage device 30, transmitting screens (including text, images, video) data to the display device 40, and receiving input signals from the input device 50, and the like. In particular, controller 20 is operative to coordinate control of wireless transceiver 10, storage device 30, display device 40, and input device 50 to perform the service continuation method of the present invention.

In another embodiment, controller 20 may be integrated into baseband processing device 12 as a baseband processor.

The storage device 30 can be a memory (for example, a random access memory (RAM), a flash memory, or a non-volatile memory (Non-Volatile Random Access Memory, NVRAM). ), magnetic storage devices (eg, magnetic tape or hard disk), optical storage devices (eg, Compact Disc Read-Only Memory (CD-ROM)), or any combination of the above, for storing instruction sets And the code of the application and / or communication protocol.

The display device 40 can be a Liquid-Crystal Display (LCD), a Light-Emitting Diode (LED) display, or an Electronic Paper Display (EPD) to provide a display function. Alternatively, the display device 40 may further include one or more touch sensors for detecting the proximity/contact of an object such as a finger or a stylus.

The input device 50 can include one or more buttons, a keyboard, a mouse, Touch panels, video lenses, microphones, and/or speakers are used to interact with the user as a human interface.

It is to be understood that the elements shown in FIG. 2 are only used to provide an illustrative example and are not intended to limit the scope of the invention.

3A and 3B are message sequence diagrams of a network relay by a proximity service user device according to an embodiment of the invention. First, the mobile communication devices 110-130 respectively perform a connection establishment procedure for the service network 150, but do not require wireless resources for the neighboring service user device to relay the network, and do not transmit the device-to-device synchronization signal (step S310). Specifically, the mobile communication devices 110-130 notify the service network 150 via the connection establishment program that they want to act as a relay user device. The connection establishment procedure may include the establishment of an attach procedure and/or a packet data network (PDN) connection.

Next, the mobile communication device 140 executes a relay search program to find a relay user device in its vicinity (step S320). Specifically, the mobile communication device 140 broadcasts a relay discovery message, and the mobile communication devices 110-130 start transmitting the device-to-device synchronization signal in a time zone after receiving the relay discovery message. For example, the mobile communication devices 110-130 can initiate a guard timer to count the time segment and receive a Direct Communication Request message from the mobile communication device 140 before the guard timer expires. Then, the transmission device stops the device synchronization signal.

In an embodiment, the relay search procedure of step S320 may be the mode of exploring mode A, as shown in FIG. 4A, wherein the relay discovery message is a Discovery Announcement message, and the mobile communication device 110~130 does not need to reply to the mobile communication device 140 when receiving the discovery announcement message. The mobile communication devices 110-130 only need to receive the discovery announcement message, and start the protection timer and periodically transmit the device-to-device synchronization signal before the protection timer expires.

In another embodiment, the relay discovery procedure of step S320 may be the mode B mode of exploration, as shown in FIG. 4B, wherein the relay discovery message is a Discovery Solicitation message, and the mobile communication device 110~ The 130 must reply to a Discovery Response message to the mobile communication device 140 upon receiving the discovery request message. In FIG. 4B, although the mobile communication devices 110-130 start the protection timer and start the transmission device-to-device synchronization signal before replying to the discovery response message, the mobile communication devices 110-130 may also choose to respond to the response in response. After the message, the guard timer is started and the transmitter-to-device sync signal is started. It should be noted that in the mode B mode of exploration, the mobile communication devices 110-130 can individually determine whether they are willing to act as a relay station of the mobile communication device 140, and if so, reply to the discovery response message to the mobile communication device 140.

Returning to FIG. 3A, after step S320, the mobile communication device 140 measures the received signal strength/quality of the received device-to-device synchronization signal, and selects the best received signal from the mobile communication devices 110-130. Intensity/Quality (step S330). Specifically, the received signal strength/quality of the device synchronization signal can be determined according to the following information: Received Signal Strength Indication (RSSI), Signal-to-Noise Ratio (SNR), proximity Adjacent Channel Interference (ACI), Packet Error Rate (Packet Error Rate, PER), or Bit Error Rate (BER).

Thereafter, the mobile communication device 140 establishes a connection with the mobile communication device selected in step S330 for one-to-one communication (step S340). In this embodiment, it is assumed that the device transmitted by the mobile communication device 110 has the best received signal strength/quality for the device synchronization signal, that is, the mobile communication device 110 is selected in step S330.

Once the connection of the one-to-one communication is successfully established, the mobile communication device 110 becomes an active relay user device, responsible for transferring one-way data between the mobile communication device 140 and the service network 150. . The mobile communication devices 120-130 become non-active relay user devices.

Figure 5 is a sequence diagram of a message established by a connection to a communication in accordance with an embodiment of Figures 3A and 3B of the present invention. The mobile communication device 140 transmits a direct communication request message to the mobile communication device 110 (step S510). When receiving the direct communication request message, the mobile communication device 110 requests the service network 150 for the wireless resource configuration for the mobile communication device 140. Specifically, the mobile communication device 110 transmits a Scheduling Request (SR) message or The Buffer Status Report (BSR) message is sent to the access network 151 (step S520), and then an uplink grant (UL Grant) message including the radio resource configuration setting is received from the access network 151 (step S530). Next, the mobile communication device 110 and the mobile communication device 140 perform verification and establish a secure connection (step S540). Specifically, the mobile communication device 110 first initiates two-way verification to the mobile communication device 140, and then through the PC5 interface (detailed definition can be referred to Specification Standards developed by the Third Generation Partnership Project 23.703) Initiate the establishment of a second layer of secure links. Thereafter, the mobile communication device 110 can selectively transmit the radio resource configuration setting obtained in step S530 to the mobile communication device 140 in a message (step S550), however, if the mobile communication device 110 and the mobile communication device 140 decide to If one-to-one communication is performed on the unlicensed band, step S550 may be omitted. In an embodiment, the message in step S550 may be a Radio Resource Control (RRC) reset request message.

Returning to FIG. 3A, after step S340, the mobile communication device 140 performs the measurement and return of the connection state (step S350). The connection state refers to a connection state of one-to-one communication between the mobile communication device 140 and the mobile communication device 110.

Regarding an embodiment of the measurement and return of the connection state, as shown in FIG. 6A, the mobile communication device 110 transmits a MEASUREMENT CONTROL message to the mobile communication device 140, requesting the mobile communication device 140 to be connected. The measurement. Next, the mobile communication device 140 transmits a MEASUREMENT REPORT message including the measurement result to the mobile communication device 110. The connection status can be determined by measuring the following values: received signal strength indicator, signal to interference ratio, adjacent channel interference, packet error rate, and/or bit error rate. Thereafter, it is determined by the mobile communication device 140 whether the measured connection status is lower than a predetermined threshold, and if so, the mobile communication device 140 initiates the relay search procedure of the next step S360.

Regarding another embodiment of the measurement and return of the connection status, as shown in FIG. 6B, similar to the embodiment of FIG. 6A, the mobile communication device 110 transmits a measurement control message to the mobile communication device 140, requesting mobile communication. Device 140 Perform the measurement of the connection status. Next, the mobile communication device 140 transmits a measurement report message including the measurement result to the mobile communication device 110. However, unlike the embodiment of FIG. 6A, after that, it is determined by the mobile communication device 110 whether the measured connection status is lower than a predetermined threshold, and if so, the next step S360 is initiated by the mobile communication device 110. Relay discovery program.

Returning to FIG. 3A, following step S350, the relay discovery program is initiated by the mobile communication device 110 or 140 to find the relay user device in the vicinity of the mobile communication device 140 (step S360).

In an embodiment, the relay discovery procedure of step S360 may be initiated by the mobile communication device 140, as in the mode A of FIG. 4A, the mobile communication devices 120-130 are configured to receive the discovery announcement message. The guard timer is activated and the device-to-device sync signal is transmitted periodically before the guard timer expires. Alternatively, as shown in the mode B of FIG. 4B, when receiving the discovery announcement message, the mobile communication devices 120-130 activate the protection timer and start the transmission device to synchronize the signal with the device, and then reply to the search response message.

In another embodiment, the relay discovery procedure of step S360 may be initiated by the mobile communication device 110, as shown in FIG. 7, wherein the mobile communication device 110 broadcasts a relay discovery message, and the mobile communication device 120-130 When the relay discovery message is received, the protection timer is started and the device-to-device synchronization signal is periodically transmitted before the protection timer expires. In an embodiment, the relay discovery message may be a discovery announcement message. Although not shown, the mobile communication device 140 may also receive the relay discovery message transmitted by the mobile communication device 110, and upon receiving, initiate the mode A exploration mode as shown in FIG. 4A, or The mode B is shown in FIG. 4B. The only difference is that the mobile communication device 120-130 does not need to transmit the guard timer and the device to the device synchronization signal when receiving the relay discovery message transmitted by the mobile communication device 140. Process it.

Returning to FIG. 3A, after step S360, the mobile communication device 140 measures the received signal strength/quality of the received device-to-device synchronization signal, and selects the best received signal from the mobile communication devices 120-130. The strength/quality person or the person having the highest priority level is selected from the mobile communication devices 120 to 130 according to the priority level indicated by the received device to the device synchronization signal (step S370). For example, if the mobile communication devices 120-130 each provide a relay service on different frequency bands, different priority levels may be set according to different operating frequency bands, and priority levels are included in the device-to-device synchronization signals transmitted by the respective devices. Information, and the mobile communication device 140 may first select the mobile communication devices 120-130 according to the received signal strength/quality of the device synchronization signal. If the received signal strength/quality is the same, the mobile communication device 140 further selects according to its priority level. .

Thereafter, the mobile communication device 140 establishes a connection with the mobile communication device selected in step S370 for one-to-one communication (step S380). In this embodiment, it is assumed that the device transmitted by the mobile communication device 120 has the best received signal strength/quality for the device synchronization signal, that is, the mobile communication device 120 is selected in step S370. The establishment of the one-to-one communication connection is similar to the step S340. For a detailed description, reference may be made to FIG. 5, and therefore no further details are provided herein.

Once the connection of the one-to-one communication is successfully established, the mobile communication device 120 becomes an active relay user device, and is responsible for transferring one-way data between the mobile communication device 140 and the service network 150. Then, OK The mobile communication device 140 transmits a connection interruption request message to the mobile communication device 110 (step S390), so that the mobile communication device 110 becomes a non-active relay user device. As a result, the mobile communication device 140 is successfully reselected from the mobile communication device 110 to the mobile communication device 120 so that data transmission/reception between the mobile communication device 150 and the service network 150 can be continued without interruption.

According to the embodiments of the foregoing 3A and 3B, it can be understood that in the proximity service user device to the network relay process of the present invention, the relay user device only needs to be in a certain time period. The transmitting device needs to synchronize the signal to the device, and only needs to request the wireless network configuration from the service network when receiving the direct communication request message sent by the remote user device. Therefore, the power consumed by the relay user device due to the transmission device synchronizing the signal to the device is greatly reduced, and the use efficiency of the radio resources of the long term evolution network is also improved.

It should be noted that, regarding the proximity service user device described in the embodiments of FIG. 3A and FIG. 3B, the network relay process, other details not in the scope of the present invention can be referred to the third generation partner program organization. Specification standards TR 23.713 and 36.843.

The present invention has been described above with reference to various embodiments, which are intended to be illustrative only and not to limit the scope of the invention, and those skilled in the art can make a few changes without departing from the spirit and scope of the invention. With retouching. The above-described embodiments are not intended to limit the scope of the invention, and the scope of the invention is defined by the scope of the appended claims.

10‧‧‧Wireless transceiver

11‧‧‧RF device

12‧‧‧Base frequency processing device

13‧‧‧Antenna

20‧‧‧ Controller

30‧‧‧Storage device

40‧‧‧ display device

50‧‧‧ input device

Claims (20)

A mobile communication device is located in the coverage of a service network for use as a relay user of a Proximity-based Service (ProSe) user-to-network relay A relay UE, comprising: a wireless transceiver, configured to perform wireless transmission and reception with the service network and a remote UE located outside the coverage of the service network And a controller for receiving a measurement report message from the remote user device through the wireless transceiver, and indicating, between the remote user device and the mobile communication device, the measurement report message When the connection state is lower than a predetermined threshold, transmitting a relay discovery message to the other relay user device through the wireless transceiver to trigger the other relay user device to start transmitting a device-to-device synchronization signal (Device-to -Device Synchronization Signal, D2DSS). The mobile communication device of claim 1, wherein the controller further transmits a measurement control message to the remote user device through the wireless transceiver before receiving the measurement report message. The mobile communication device of claim 1, wherein the controller further receives a connection interruption message from the remote user device through the wireless transceiver. The mobile communication device of claim 1, wherein each of the other relay user devices is connected to one of the service networks before the controller receives the measurement report message. But does not require any The wireless resource does not transmit the device-to-device synchronization signal. The mobile communication device of claim 1, wherein each of the other relay user devices periodically transmits the device to the device in a time period after receiving the relay discovery message. And synchronizing the signal, and stopping transmitting the device-to-device synchronization signal when the direct communication request message is not received from the remote user device in the time period. The mobile communication device of claim 5, wherein one of the other relay user devices further requests a wireless resource from the wireless network through the wireless transceiver when receiving the direct communication request message. It is configured for use by the proximity service user device for network relay and establishes connection with one of the remote user devices. A service continuation method for Proximity-based Service (ProSe) user-to-network relay and relayed by one of the coverages of a service network The service continuation method includes: receiving a measurement report message from a remote UE (remote UE); and indicating, by the measurement report message, the remote user device and the action When a connection state between the communication devices is lower than a predetermined threshold, a relay discovery message is transmitted to the other relay user devices to trigger the other relay user devices to start transmitting a device-to-device synchronization signal (Device- to-Device Synchronization Signal, D2DSS). For example, the service continuation method described in claim 7 further includes: transmitting a measurement control message to the top before receiving the measurement report message The remote user device is described. The service continuation method of claim 7, further comprising: accepting a connection interruption message from the remote user device. The service continuation method of claim 7, wherein each of the other relay user devices establishes connection with one of the service networks before the controller receives the measurement report message. However, no radio resources are required, and the device-to-device synchronization signal is not transmitted. The service continuation method of claim 7, wherein each of the other relay user devices periodically transmits the device to the device within a time period after receiving the relay discovery message. And synchronizing the signal, and stopping transmitting the device-to-device synchronization signal when the direct communication request message is not received from the remote user device in the time period. The service continuation method of claim 11, wherein one of the other relay user devices further requests a wireless resource from the service network through the wireless transceiver when receiving the direct communication request message. It is configured for use by the proximity service user device for network relay and establishes connection with one of the remote user devices. A mobile communication device located outside a signal range of a service network for use as a Proximity-based Service (ProSe) user-to-network relay (UE-to-network relay) remote user device (remote UE), comprising: a wireless transceiver, configured to perform wireless transmission and reception with the service network and one of the relay UEs located in the coverage of the service network; as well as a controller configured to transmit a relay discovery message to the other relay user through the wireless transceiver when the connection status of one of the relay user devices is lower than a predetermined threshold through the wireless transceiver The device receives one or more Device-to-Device Synchronization Signals (D2DSS) from the other relay user devices through the wireless transceiver, and selects the device synchronization signals according to the device to One of the user devices transmits a direct communication request message to establish a connection. The mobile communication device of claim 13, wherein the controller receives the signal strength or quality, or the device-to-device synchronization signal, for each of the device synchronization signals according to the device. One of the priority levels is indicated to perform the selection of the other relay user devices described above. The mobile communication device of claim 13, wherein the controller further receives a measurement control message from the relay user device through the wireless transceiver, and transmits the connection status through the wireless transceiver One of the measurement report messages to the relay user device. The mobile communication device of claim 13, wherein the controller further transmits a connection interruption message to the relay user device via the wireless transceiver. A service continuation method for Proximity-based Service (ProSe) user-to-network relay and used by a remote location outside the coverage of a service network signal The service persistence method includes: transmitting a relay discovery message to other relay users when measuring a connection state with one of the relay user devices below a predetermined threshold Device Receiving one or more Device-to-Device Synchronization Signals (D2DSS) from the other relay user devices; and selecting one of the other relay user devices according to the device synchronization signal according to the device A direct communication request message is transmitted to establish a connection. The service continuation method of claim 17, wherein the other relay user device is selected according to whether the device receives signal strength or quality for each of the device synchronization signals, or the device synchronizes with the device. One of the priority levels indicated by each of the signals is performed. The service continuation method of claim 17, further comprising: receiving a measurement control message from the relay user device; and transmitting a measurement report message including the connection status to the relay user Device. The service continuation method of claim 17, further comprising: transmitting a connection interruption message to the relay user device.