Method and system for communicating GPS signals over the air in a wireless communication relay system

Abstract

The application discloses a method and system for transmitting GPS signals through an air interface in a wireless communication relay system, and realizes wireless coverage of each level area and communication with terminals in the corresponding area through multi-level relay stations; a main base station sends a source GPS synchronization signal to a first-level relay station; each level relay station generates a GPS signal of the level according to second boundary information of the received GPS signal, and sends the GPS signal of the level to a next-level relay station through an air interface; and the main base station and the multi-level relay stations transmit GPS signals through an air interface to realize synchronization of the relay system.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and in particular relates to a method and system for transmitting GPS signals over an air interface in a wireless communication relay system. Background Technology

[0002] EUHT-5G (Enhanced Ultra High Throughput) is a wireless communication technology developed under the leadership of Newshore Technology, which meets all the technical requirements of the fifth-generation mobile communication technology proposed by the International Telecommunication Union (ITU).

[0003] EUHT-5G technology has been applied in industries and scenarios such as tunnels, mines, and underground rail transit, meeting the requirements of high reliability and low latency transmission. At the same time, due to the complex terrain and many curves in these scenarios, it is difficult to cover the entire area with a single base station.

[0004] Because the current 5G communication system operates at a very high frequency, the spatial loss of the signal is significant, making it difficult for the wireless signal to cover indoor spaces. For common 5G communication systems, vehicle-to-everything (V2X) and rail transit systems that require wireless signal coverage indoors, or other enclosed spaces due to environmental obstructions, the conventional solution is to rebuild micro base stations indoors. This makes the deployment of the entire communication system complex and significantly increases the cost, which is not conducive to the rapid deployment and implementation of the system.

[0005] To this end, the EUHT-5G system uses a Relay Amplifier Unit (RAU) for wireless communication relay transmission, enabling communication between the remote access unit (EAU) and the engineering command center; current relay transmission systems such as Figure 1 As shown:

[0006] The main base station EBU_1 is connected to the engineering command center via optical fiber. Terminal devices such as EAU_1, EAU_2, and EAU_3 are responsible for data collection and transmission when connected to the network. Multi-level repeaters RAU_1, RAU_2, and RAU_3 are set up in bends or areas with significant wireless signal attenuation to provide wireless coverage and terminal access for lower-level areas. The EUHT system adopts a TDD frame structure. To avoid uplink and downlink interference between different main base stations EBU and repeaters RAU, strict synchronization between EBU and RAU is required. In the past, the method used was to directly connect the GPS antenna with optical fiber. However, in scenarios such as mines and tunnels, this would severely restrict construction and site layout. Therefore, the method of achieving synchronization by directly connecting the GPS antenna with optical fiber cannot be implemented. Summary of the Invention

[0007] In view of this, for scenarios such as mines, tunnels, and rail transit where enclosed spaces are formed due to environmental obstruction, this invention discloses a method and system for transmitting GPS signals over the air interface in a wireless communication relay system. This can avoid laying synchronous optical fibers on site, while also improving the flexibility and mobility of relay station deployment, and reducing engineering costs and construction difficulty.

[0008] A method for transmitting GPS signals over an air interface in a wireless communication relay system includes:

[0009] The main base station acquires the source GPS synchronization signal through an external GPS antenna;

[0010] Wireless coverage in various areas is achieved through multi-level relay stations, as well as communication with terminals in the corresponding areas;

[0011] The main base station and multiple relay stations transmit GPS signals over the air interface. The GPS signals are used to synchronize the relay system. The main base station sends the source GPS synchronization signal to the first-level relay station. Each relay station generates its own GPS signal based on the second boundary information of the received GPS signal and sends the GPS signal to the next level relay station over the air interface.

[0012] The system information includes a control field used to identify second boundary information, indicating whether this frame is the last frame within a second, and the control field is 1 bit long;

[0013] The main base station and multi-level relay stations count frames per second based on the received GPS signals from the previous level and mark the frame number accordingly;

[0014] The relay station receives GPS signals sent by the main base station or the previous level relay station, parses system information, and when it identifies the last frame within a second, it outputs the last frame trigger signal within a second. Based on the last frame trigger signal within a second, the receiving control signal, and the time advance difference, it generates the local GPS signal.

[0015] Furthermore, after the main base station and multi-level relay stations detect the rising edge of the previous level GPS signal, they begin internal frame counting and mark the frame number; after detecting the rising edge of the GPS signal again, they restart internal frame counting and mark the frame number.

[0016] The relay station identifies the last frame identifier within a second, sets the last frame trigger signal to a high level, and sets it to a low level after a period of 1 frame.

[0017] Based on the uplink / downlink subframe ratio information contained in the system information, the relay station sets the receive control signal to a high level after the uplink frame ends. The receive control signal is used to instruct the relay station to start receiving downlink data.

[0018] When the receive control signal is on the rising edge, the trigger signal of the last frame within the second is high, setting the local reference GPS signal to the rising edge.

[0019] The local reference GPS signal is shifted according to the time advance difference ΔT of the received control signal, and the pulse width of the local reference GPS signal is set to obtain the local GPS signal.

[0020] The timing difference ΔT for receiving the control signal is calculated according to Formula 1:

[0021] △T=△t1-△t2 Formula 1

[0022] Among them, the first time advance △t1 is the air interface delay, and the second time advance △t2 is the time advance of raising the receive control signal before the end of the current frame and the start of the next frame.

[0023] The time interval by shifting the rising edge of the current level reference GPS signal by |△T| is the rising edge of the current level GPS signal.

[0024] When the time advance difference ΔT is greater than 0, the reference GPS signal is shifted forward;

[0025] When the time advance difference ΔT is less than 0, the reference GPS signal is shifted backward.

[0026] The present invention also discloses a wireless communication relay system, comprising:

[0027] The main base station acquires the source GPS synchronization signal through an external GPS antenna;

[0028] Multi-level relay stations are used to achieve wireless coverage in various areas and to communicate with terminals in the corresponding areas;

[0029] The main base station and multiple relay stations transmit GPS signals over the air interface. The GPS signals are used to synchronize the relay system. The main base station sends the source GPS synchronization signal to the first-level relay station. Each relay station generates its own GPS signal based on the second boundary information of the received GPS signal and sends the GPS signal to the next level relay station over the air interface.

[0030] The relay station includes:

[0031] The communication unit is used to communicate with the main base station or the next-level relay station. It acquires GPS signals sent by the main base station or the next-level relay station through the air interface, parses system information, and generates the last frame trigger signal within a second based on the second boundary information in the system information of the received GPS signal. It then sends the last frame trigger signal within a second, the receive control signal, and the timing advance to the processing unit at this level.

[0032] The processing unit generates the local GPS signal based on the trigger signal of the last frame within the second sent by the communication unit, the received control signal, and the time advance measurement.

[0033] The communication unit includes:

[0034] The first processing module is used to identify the last frame identifier within a second and generate a last frame trigger signal: the last frame trigger signal is set to a high level, and after a period of 1 frame, it is set to a low level.

[0035] The second processing module is used to generate a receiving control signal based on the uplink / downlink subframe ratio information contained in the system information: the receiving control signal is used to instruct the relay station to start receiving downlink data; after the uplink frame ends, the receiving control signal is set to a high level;

[0036] The sending module sends the trigger signal of the last frame within the second, the receive control signal, and the timing advance to the processing unit at this level.

[0037] The receiving module receives GPS signals sent by the main base station or the previous level relay station, as well as the air interface delay Δt1.

[0038] The processing unit includes:

[0039] The counting module divides the second interval according to the frame structure, counts frames within the second, and marks the frame number: when the communication unit detects the rising edge of the GPS signal, it starts internal frame counting; when it detects the rising edge of the GPS signal again, it restarts internal frame counting.

[0040] The processing module is used to generate the local GPS signal: when the receiving control signal is on the rising edge, the trigger signal of the last frame within the second is high level, generating the local reference GPS signal at a high level; the local reference GPS signal is shifted according to the time advance difference △T of the receiving control signal, and the pulse width is set to obtain the local GPS signal.

[0041] The processing module:

[0042] △T=△t1-△t2; where, the first time advance △t1 is the air interface delay, and the second time advance △t2 is the time advance by which the terminal module raises the receive control signal before the end of the current frame and the start of the next frame;

[0043] When △T is greater than 0, the reference GPS signal shifts forward;

[0044] When ΔT is less than 0, the reference GPS signal shifts backward;

[0045] When the time advance difference ΔT equals 0, the reference GPS signal does not move.

[0046] The main base station includes:

[0047] The processing unit divides the second interval according to the frame structure, performs frame counting within the second, and marks the frame number: after the rising edge of the GPS signal, the internal frame counting begins; after the rising edge of the GPS signal is detected again, the internal frame counting restarts.

[0048] The processing unit is also used to communicate with the communication unit of the next-level repeater.

[0049] The beneficial technical effects achieved by this invention are as follows:

[0050] 1. Relay stations at all levels can restore GPS synchronization signals without distortion to achieve synchronization;

[0051] 2. By transmitting GPS signals over the air interface for use by multi-level relay systems, the need to lay synchronous optical fibers in scenarios such as tunnels or mines is avoided, thus reducing project costs;

[0052] 3. Not limited by optical fiber, the lower-level relay station can be moved at any time, and the location of the RAU can be changed according to the actual channel environment, which improves the flexibility of cell coverage and terminal network access.

[0053] For the foregoing and related purposes, one or more embodiments include features that will be described in detail below and particularly pointed out in the claims. The following description and accompanying drawings detail certain exemplary aspects and indicate only a few of the various ways in which the principles of the various embodiments can be utilized. Other benefits and novel features will become apparent upon consideration of the following detailed description in conjunction with the accompanying drawings, and the disclosed embodiments are intended to include all such aspects and their equivalents. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of a wireless communication relay system that achieves indoor wireless signal coverage in the existing technology;

[0055] Figure 2 This is a block diagram of the relay station provided in Embodiment 1 of the present invention;

[0056] Figure 3 This is a flowchart of a method for transmitting GPS signals over the air interface between a main base station and relay stations at all levels, as provided in Embodiment 2 of the present invention.

[0057] Figure 3a This is a schematic diagram of generating the last frame trigger signal provided in Embodiment 2 of the present invention;

[0058] Figure 3b This is a schematic diagram of the generated local GPS signal provided in Embodiment 2 of the present invention;

[0059] Figure 3c This is a schematic diagram illustrating the principle of generating the time advance difference provided in Embodiment 2 of the present invention. Detailed Implementation

[0060] The following description and accompanying drawings fully illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, procedural, and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Some portions and features of some embodiments may be included in or replace portions and features of other embodiments. The scope of embodiments of the invention includes the entire scope of the claims and all available equivalents thereof. In this document, these embodiments of the invention may be referred to individually or collectively with the term "invention," which is merely for convenience and is not intended to automatically limit the scope of the application to any single invention or inventive concept if more than one invention is disclosed.

[0061] Example 1

[0062] This embodiment provides a wireless communication relay system, including:

[0063] The main base station EBU_1 is connected to the engineering command center via fiber optic cable; it acquires source GPS synchronization signals through an external GPS antenna.

[0064] Multi-level relay stations (RAUs) are used to achieve wireless coverage in various areas and to communicate with terminals (EAUs) in the corresponding areas.

[0065] When the terminal EAU is connected to the network, it is responsible for data collection and transmission;

[0066] In wireless communication relay systems, GPS signals are transmitted over the air interface to achieve synchronization.

[0067] The main base station EBU_1, which is connected to the engineering control center, is the first level of the entire wireless communication system. It is usually placed at the tunnel entrance or wellhead. EBU_1 has an external GPS antenna to accurately obtain GPS synchronization signals as the basis for frame synchronization of the system. In the entire relay system, the source GPS signal of EBU_1 is sequentially sent to each level of relay station RAU_1, RAU_2, etc.

[0068] Each relay station generates its own GPS signal based on the second boundary information of the received GPS signal, and transmits the GPS signal to the next level relay station via the air interface. The relay station can accurately reconstruct the GPS signal for its own use and serve as the source of the reconstructed GPS signal for the next level RAU. In this way, the relay system is synchronized.

[0069] It should be noted that the relay station can be a base station, or other relay devices including a communication unit 10 and a processing unit 20, that is, other relay devices that can realize the relay function of the present invention, and are not limited here.

[0070] Furthermore, such as Figure 2 As shown, the relay station RAU includes:

[0071] The communication unit 10 is used to communicate with the main base station or the next-level relay station, acquire the GPS signal sent by the main base station or the next-level relay station through the air interface, parse the system information, generate the last frame trigger signal within the second based on the second boundary information in the system information in the received GPS signal, and send the last frame trigger signal within the second, the receive control signal, and the time advance to the processing unit at this level.

[0072] The processing unit 20 generates a local GPS signal based on the trigger signal of the last frame within a second sent by the communication unit, the received control signal, and the time advance difference.

[0073] In the EUTH communication system, the communication unit 10 is a baseband chip and radio frequency chip that supports the EUTH protocol and can be connected to the first-level EBU or RAU processing unit on the network.

[0074] Specifically, the communication unit 10 includes:

[0075] The first processing module 11 is used to identify the last frame identifier within a second and generate a last frame trigger signal: the last frame trigger signal is set to a high level, and after a period of 1 frame, it is set to a low level.

[0076] The second processing module 12 is used to generate a receiving control signal based on the uplink and downlink subframe ratio information contained in the system information: the receiving control signal is used to instruct the relay station to start receiving downlink data; after the uplink frame ends, the receiving control signal is set to a high level;

[0077] The sending module 13 sends the last frame trigger signal, the receiving control signal, and the timing advance within the second to the processing unit at this level.

[0078] Communication unit 10 communicates with processing unit 20 through standard Ethernet interface Eth to transmit data. Communication unit 10 obtains the second boundary of the upper-level EBU / RAU processing unit 20 through the air interface, and sends the obtained second boundary information and frame header start information to the local processing unit 20 in the form of signals through the ETH interface. At the same time, the local processing unit can also obtain the timing advance information sent by the communication unit through eth.

[0079] The receiving module 14 receives the GPS signal sent by the main base station or the previous level relay station, as well as the first time advance △t1.

[0080] The processing unit 20 includes:

[0081] The counting module 21 divides the second interval according to the frame structure, performs frame counting within the second, and marks the frame number: when the communication unit detects the rising edge of the GPS signal, it starts internal frame counting; when it detects the rising edge of the GPS signal again, it restarts internal frame counting.

[0082] Processing module 22 is used to generate the local GPS signal: when the receiving control signal is on the rising edge, the trigger signal of the last frame within the second is high level, generating the local reference GPS signal at a high level; the local reference GPS signal is shifted according to the time advance difference △T of the receiving control signal, and the pulse width is set to obtain the local GPS signal.

[0083] △T = △t1 - △t2; where △t1 is the air interface delay, sent by the local communication unit and obtained through the eth interface; △t2 is the time advance by which the terminal module raises the rx_en signal before the end of the current frame and the start of the next frame;

[0084] When △T is greater than 0, the reference GPS signal shifts forward;

[0085] When ΔT is less than 0, the reference GPS signal shifts backward;

[0086] When the time advance difference ΔT equals 0, the reference GPS signal does not move.

[0087] The main base station, including the aforementioned processing unit 20, divides the second interval according to the frame structure, performs frame counting within the second, and marks the frame number: after the rising edge of the GPS signal, the internal frame counting begins; after the rising edge of the GPS signal is detected again, the internal frame counting restarts.

[0088] The processing unit is also used to communicate with the communication unit of the next-level repeater.

[0089] Example 2

[0090] This embodiment specifically illustrates how the main base station and relay stations at all levels transmit GPS signals through the air interface, such as... Figure 3 As shown, it includes the following steps:

[0091] S21. The processing unit 20 of the main base station and relay stations at all levels counts frames per second based on the received GPS signal from the previous level and marks the frame number;

[0092] As an example, with a frame length of 2 milliseconds, after the processing unit of the main base station EBU_1 or each level of relay station successfully acquires the rising edge of the GPS signal at the physical layer, it begins to perform internal frame counting. The internal clock frequency of the processing unit is 160MHz, so every 320,000 clock units, one frame is added to the count and the frame number is marked, with a duration of 2ms; and so on, until the rising edge of the GPS signal is acquired again, at which point the internal frame count restarts from 1.

[0093] This frame number can be obtained at any time during frame scheduling.

[0094] S22. The System Information SICH includes a control field used to identify second boundary information, indicating whether this frame is the last frame within a second. The control field is 1 bit long.

[0095] SICH, a broadcast message transmitted with every frame, carries various frame-level control information with distinct characteristics. To enable air interface transmission of GPS signals, one bit is added to SICH to identify whether the current frame is the last frame within a second. Taking a 2ms frame length as an example, one second contains 500 frames. The processing unit reconstructs SICH for each frame. When the frame number within the second is 500, i.e., the last frame, the EBU_1 or RAU processing unit sets this bit to 1. The system information field definition table is shown in Table 1. 18 Control field for identifying second boundary information:

[0096]

[0097]

[0098]

[0099] Table 1

[0100] S23. The communication unit of the relay station receives the GPS signal sent by the main base station or the previous level relay station, parses the system information, and when it identifies the last frame within the second, it outputs the last frame trigger signal last_f_s within the second.

[0101] The first processing module 11 of the communication unit identifies the last frame identifier within seconds, sets the last frame trigger signal to a high level, and sets it to a low level after a period of 1 frame.

[0102] Specifically, when b is identified 18 When the value is 1, it indicates that the current frame is the last frame within 1 second. At this time, the signal last_f_s of the first processing module 11 is set high, and the duration is 1 frame. As an example, Figure 3aAs shown: 301 is the GPS signal of the previous EBU or RAU processing unit, which is set to high level at the beginning of each second for 100ms, and then set to low level; 302 is the last_f_s signal output by this stage. After the first processing module 11 of this stage recognizes the last frame within the second, it sets this signal to high level for 1 frame, and then sets it to low level.

[0103] S24. The second processing unit 12 sets the receiving control signal rx_en to a high level after the uplink frame ends, based on the uplink and downlink subframe ratio information contained in the system information. The receiving control signal is used to instruct the relay station to start receiving downlink data.

[0104] The EUHT system uses a TDD frame structure. After the communication unit 10 synchronizes with the processing unit 20 of the previous level EBU_1 or RAU through the air interface, it parses the system information SICH. The SICH contains uplink and downlink subframe ratio information. After the uplink frame ends (including the uplink guard interval UGI interval), the receive control signal rx_en will be pulled high to start the reception processing of the next frame. The receive control signal rx_en is also used to generate the local GPS signal.

[0105] S25. The processing module 22 of the processing unit 20 generates a local GPS signal based on the last frame trigger signal last_f_s within the second, the receiving control signal rx_en, and the time advance difference; such as Figure 3b As shown:

[0106] S25a. When the receive control signal is on the rising edge, the last frame trigger signal within the second is at a high level, setting the local reference GPS signal to the rising edge;

[0107] When the rx_en signal 401 is at the rising edge, if the last_f_s signal 402 is also at a high level at this time, the rising edge 403 of the restored reference GPS signal will be generated.

[0108] S25b. Calculate the timing difference ΔT for receiving the control signal according to Formula 1:

[0109] △T=△t1-△t2 Formula 1

[0110] Among them, the first time advance △t1 is the air interface delay. After the communication unit of this level relay station enters the upper-level EBU or RAU processing unit, the upper-level EBU or RAU processing unit will schedule the communication unit to perform ranging at intervals and send the ranging result to this level communication unit in the form of △t1.

[0111] The local communication unit 10 sends data to the local processing unit 20 via the sending module 13;

[0112] The second time advance Δt2 marks the end of the current frame. The time advance for receiving control signals is increased before the start of the next frame, and this is configured on a per-sample-point basis.

[0113] The advance of △t2 is related to the time required for the downlink path to prepare normally, and is in units of 100ns. A suitable configuration value can be selected according to the differences in the radio frequency link. A typical configuration is an advance time of 1.5us after the start of the uplink protection interval UGI.

[0114] S25c. Processing module 22 shifts the local reference GPS signal according to the received control signal time advance difference ΔT, sets the pulse width of the local reference GPS signal, and obtains the local GPS signal; such as Figure 3c As shown:

[0115] The time interval by which the rising edge 403 of the current level reference GPS signal is shifted by |△T| is the rising edge 404 of the current level GPS signal; when the time advance difference △T is greater than 0, △T is a positive value and the reference GPS signal is shifted forward; when the time advance difference △T is less than 0, △T is a negative value and the reference GPS signal is shifted backward.

[0116] The processing module 22 can convert the two parameters △t1 and △t2, which are based on sampling points, into parameters based on time (microseconds) according to the sampling frequency, so as to determine the position of the rising edge of the restored GPS signal pulse.

[0117] S25d. Set the pulse width of the local reference GPS signal.

[0118] The GPS signal pulse width is set according to actual needs. For example, the processing module 22 is configured to 1ms, 2ms, 4ms, and 8ms respectively according to the frame length of the relay station at this level, and generates the local GPS signal.

[0119] Those skilled in the art will also understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments herein can be implemented as electronic hardware, computer software, or a combination thereof. To clearly illustrate the interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps described above are generally described in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art can implement the described functionality in alternative ways for each specific application; however, such implementation decisions should not be construed as departing from the scope of this disclosure.

[0120] The steps of the methods or algorithms described in conjunction with the embodiments herein can be directly embodied in hardware, software modules executed by a processor, or a combination thereof. The software modules can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user terminal. Alternatively, the processor and storage medium can exist as discrete components in the user terminal.

[0121] For software implementation, the techniques described in this application can be implemented using modules (e.g., procedures, functions, etc.) that perform the functions described in this application. This software code can be stored in memory units and executed by a processor. The memory units can be implemented within the processor or outside the processor; in the latter case, they are communicatively coupled to the processor via various means, as is well known in the art.

Claims

1. A method for transmitting GPS signals over an air interface in a wireless communication relay system, characterized in that, include: The main base station acquires the source GPS synchronization signal through an external GPS antenna; Wireless coverage in various areas is achieved through multi-level relay stations, as well as communication with terminals in the corresponding areas; The main base station and multiple relay stations transmit GPS signals over the air interface. The GPS signals are used to achieve synchronization of the relay system: the main base station sends the source GPS synchronization signal to the first-level relay station; each level of relay station generates its own GPS signal based on the second boundary information of the received GPS signal, and sends its own GPS signal to the next level of relay station over the air interface. The main base station and multi-level relay stations count frames within a second based on the received GPS signal from the previous level and mark the frame number; the relay station receives the GPS signal sent by the main base station or the previous level relay station, parses the system information, and when it identifies the last frame within a second, it outputs the last frame trigger signal within a second; the station generates the local level GPS signal based on the last frame trigger signal within a second, the receive control signal, and the time advance difference. The relay station identifies the last frame identifier within a second, sets the last frame trigger signal to a high level, and sets it to a low level after a period of 1 frame. Based on the uplink and downlink subframe ratio information contained in the system information, the relay station sets the receive control signal to a high level after the uplink frame ends. The receive control signal is used to instruct the relay station to start receiving downlink data. When the received control signal is on the rising edge, the trigger signal of the last frame within the second is high level, and the local reference GPS signal is set to the rising edge; the local reference GPS signal is shifted according to the time advance difference △T of the received control signal, and the pulse width of the local reference GPS signal is set to obtain the local GPS signal; Calculate the timing difference ΔT for receiving the control signal according to Formula 1: △T = △t1 - △t2 Formula 1 Among them, the first time advance △t1 is the air interface delay, and the second time advance △t2 is the time advance of raising the receive control signal before the end of the current frame and the start of the next frame. The time interval by which the rising edge of the current-level reference GPS signal is shifted by |ΔT| is the rising edge of the current-level GPS signal. When the time advance difference ΔT is greater than 0, the reference GPS signal is shifted forward; when the time advance difference ΔT is less than 0, the reference GPS signal is shifted backward; when the time advance difference ΔT is equal to 0, the reference GPS signal does not move.

2. The method for transmitting GPS signals over an air interface in a wireless communication relay system as described in claim 1, characterized in that, The system information includes a control field used to identify second boundary information. The control field is 1 bit long and is used to identify whether this frame is the last frame within a second.

3. The method for transmitting GPS signals over an air interface in a wireless communication relay system as described in claim 1, characterized in that, After the main base station and multi-level relay stations detect the rising edge of the previous level GPS signal, they begin internal frame counting and mark the frame number; after detecting the rising edge of the GPS signal again, they restart internal frame counting and mark the frame number.

4. A wireless communication relay system, characterized in that, include: The main base station acquires the source GPS synchronization signal through an external GPS antenna; Multi-level relay stations are used to achieve wireless coverage in various areas and to communicate with terminals in the corresponding areas; The main base station and multiple relay stations transmit GPS signals over the air interface. The GPS signals are used to synchronize the relay system. The main base station sends the source GPS synchronization signal to the first-level relay station. Each level relay station generates its own GPS signal based on the second boundary information of the received GPS signal and sends the GPS signal to the next level relay station over the air interface. The communication unit is used to communicate with the main base station or the next-level relay station. It acquires GPS signals sent by the main base station or the next-level relay station through the air interface, parses system information, and generates the last frame trigger signal within a second based on the second boundary information in the system information of the received GPS signal. It then sends the last frame trigger signal within a second, the receive control signal, and the timing advance to the processing unit at this level. The processing unit generates a local GPS signal based on the trigger signal of the last frame within a second sent by the communication unit, the received control signal, and the time advance difference. The communication unit includes: a first processing module, used to identify the last frame identifier within a second and generate a last frame trigger signal: setting the last frame trigger signal to a high level, and after a period of 1 frame, setting it to a low level; a second processing module, used to generate a receive control signal based on the uplink / downlink subframe ratio information contained in the system information: the receive control signal is used to instruct the relay station to start receiving downlink data; after the uplink frame ends, the receive control signal is set to a high level; a sending module, sending the last frame trigger signal within a second, the receive control signal, and the timing advance to the current processing unit; and a receiving module, receiving the GPS signal sent by the main base station or the previous level relay station, and the first timing advance Δt1. The processing unit includes: a counting module, which divides the second interval according to the frame structure, counts frames within a second, and marks the frame number; when the communication unit detects the rising edge of the GPS signal, it starts internal frame counting; when it detects the rising edge of the GPS signal again, it restarts internal frame counting; and a processing module, which generates the local GPS signal: when the receiving control signal is at its rising edge, the trigger signal of the last frame within the second is at a high level, generating a high-level local reference GPS signal; and shifting the local reference GPS signal according to the time advance difference ΔT of the receiving control signal, setting the pulse width, to obtain the local GPS signal. The processing module specifically calculates the timing difference ΔT for receiving the control signal according to Formula 1: △T = △t1 - △t2; Formula 1 Wherein, the first time advance △t1 is the air interface delay, and the second time advance △t2 is the time advance by which the terminal module raises the reception control signal before the end of the current frame and the start of the next frame; when the time advance difference △T is greater than 0, the reference GPS signal shifts forward; when the time advance difference △T is less than 0, the reference GPS signal shifts backward; when the time advance difference △T is equal to 0, the reference GPS signal does not move.

5. The wireless communication relay system as described in claim 4, characterized in that, The main base station includes: The processing unit divides the second interval according to the frame structure, performs frame counting within the second, and marks the frame number: after the rising edge of the GPS signal, the internal frame counting begins; after the rising edge of the GPS signal is detected again, the internal frame counting restarts. The processing unit is also used to communicate with the communication unit of the next-level repeater.

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