A relay method and system for point-to-multipoint network communication

Abstract

This invention discloses a relay method and system for point-to-multipoint network communication, comprising: in PMP network communication mode, according to the PMP network system frame structure, a second slave station and a third slave station simultaneously communicate with the master station, and simultaneously detect whether the second slave station and the third slave station have left the network. The slave station that has left the network becomes an unknown node and re-enters the network. The slave station that has left the network simultaneously receives information from the master station and the slave station that has not left the network; the network enters relay communication mode, and according to the relay system frame structure, the slave station that has not left the network is designated as a relay node, the master station is designated as the central node, and the slave station that has left the network is designated as a remote node. The communication link is communication between the central node and the relay node, and communication between the relay node and the remote node; both the relay node and the remote node perform time synchronization and frequency synchronization. After synchronization is completed, the relay node and the remote node adjust their transmission time slots respectively. After the entire network completes the transmission time adjustment, it enters the relay data communication stage, thereby improving the transmission performance of the system.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and more specifically to a relay method and system for point-to-multipoint network communication. Background Technology

[0002] The characteristics of radio wave propagation are the first problem encountered when studying any wireless communication system. The characteristics of the wireless propagation environment are not only the foundation of all theoretical research in wireless communication, but also directly relate to a series of system design issues in engineering design, such as the capabilities of communication equipment, the determination of antenna height, the calculation of communication distance, and the technical measures that must be adopted to achieve high-quality and reliable communication.

[0003] The wireless propagation environment is one that changes over time, depending on environmental factors and other external conditions. Radio waves not only experience diffusion loss as the propagation distance increases, but they are also affected by terrain and buildings, resulting in a "shadowing effect." This can cause terminal devices to fail to receive the signal waveform emitted by the base station, leading to a loss of communication links and a severe deterioration in system communication performance.

[0004] Therefore, how to provide a relay method and system for point-to-multipoint network communication is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a relay method and system for point-to-multipoint network communication, which solves the problem of signal fading and failure to receive signals due to communication distance and environmental influences, thereby improving the transmission performance of the system.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A relay method for point-to-multipoint network communication includes:

[0008] In PMP network communication mode, according to the PMP network system frame structure, the second and third slave stations communicate with the master station simultaneously and simultaneously detect whether the second and third slave stations have left the network. The slave station that has left the network becomes an unknown node and re-enters the network. The slave station that has left the network simultaneously receives information from the master station and the slave station that has not left the network.

[0009] The network enters relay communication mode. According to the relay system frame structure, the slave stations that have not left the network are regarded as relay nodes, the master station is regarded as the central node, and the slave stations that have left the network are regarded as remote nodes. The communication link is that the central node communicates with the relay node, and the relay node communicates with the remote node.

[0010] In the relay communication mode, both the relay node and the remote node perform timing synchronization and frequency synchronization. After synchronization is completed, the relay node and the remote node respectively adjust the transmission time slots. After the entire network completes the transmission time adjustment, it enters the relay data communication stage.

[0011] Preferably, the specific steps for detecting whether the second slave station and the third slave station are out of the network are as follows:

[0012] Calculate the channel quality between the second slave station and the master station and the channel quality between the third slave station and the master station, including the signal-to-noise ratio SNR and the error vector magnitude value EVM. At the same time, set the signal-to-noise ratio threshold SNR_TH and the error vector magnitude threshold EVM_TH;

[0013] Judge the quality of the signals received by the second slave station and the third slave station: If the SNR of the second slave station or the third slave station > SNR_TH and EVM < EVM_TH, the communication is normal. If SNR ≤ SNR_TH and EVM ≥ EVM_TH, the communication quality is poor and it is out of the network. SNR is the signal-to-noise ratio of the second slave station or the third slave station, and EVM is the error vector magnitude value of the second slave station or the third slave station.

[0014] Preferably, the specific steps for both the relay node and the remote node to perform timing synchronization and frequency synchronization are as follows:

[0015] When the relay node communicates with the central node, the relay node is timed and synchronized to the central node, and synchronization window opening and tracking processing are performed;

[0016] When the remote node communicates with the relay node, the remote node is timed and synchronized to the relay node, and synchronization window opening and tracking processing are performed. The synchronization window opening meets the delay of the maximum transmission distance d km. N is the number of points of the synchronization window opening, f s is the sampling rate, v is the speed of light 3e 8 m / s, d is the transmission distance;

[0017] The relay node performs frequency synchronization with the central node. The receiving end of the relay node performs frequency offset estimation and compensation processing, and the transmitting end of the relay node performs transmitting data frequency offset correction with the frequency offset estimation value of the receiving end of the relay node;

[0018] The remote node performs frequency synchronization with the relay node. The receiving end of the remote node performs frequency offset estimation and compensation processing, and the transmitting end of the remote node performs transmitting data frequency offset correction with the frequency offset estimation value of the receiving end of the remote node.

[0019] Preferably, the specific steps for the relay node and the remote node to respectively adjust the transmission time slots are as follows:

[0020] When the relay node communicates with the central node, the relay node adjusts the transmitting signal time slot according to the ranging information of the central node received;

[0021] When a relay node communicates with a remote node, the relay node receives signals from the remote node. The relay node calculates the difference between the peak position d1 of the received synchronization signal and the peak position d2 of the synchronization signal in the static state, and records it as d. is =d1-d2 and return it to the remote node. The remote node receives the distance information d. is The distance measurement value variable is calculated, and the remote node adjusts the transmission time slot according to the distance measurement value variable. The entire network completes the transmission time adjustment and enters the relay data communication stage.

[0022] Preferably, the PMP network system frame structure is used to allocate downlink time slots, uplink time slots, and ranging time slots when establishing data transmission in PMP network communication mode;

[0023] The relay system frame structure is used to allocate time slots for the central node, relay nodes, remote nodes, and ranging when establishing data transmission in relay communication mode.

[0024] A relay system for point-to-multipoint network communication includes:

[0025] PMP network communication module: Used in PMP network communication mode, according to the PMP network system frame structure, for the second and third slave stations to communicate with the master station simultaneously.

[0026] Signal detection module: used to simultaneously detect whether the second and third slave stations have left the network, and to re-enter the network as unknown nodes. The slave stations that have left the network can simultaneously receive information from the master station and the slave stations that have not left the network.

[0027] Relay communication module: Used for the network to enter relay communication mode. According to the relay system frame structure, the slave stations that have not left the network are used as relay nodes, the master station is used as the central node, and the slave stations that have left the network are used as remote nodes. The communication link is between the central node and the relay node, and between the relay node and the remote node.

[0028] Timed synchronization module: Used for timed synchronization of both relay nodes and remote nodes in relay communication mode;

[0029] Frequency synchronization module: used for frequency synchronization between relay nodes and remote nodes in relay communication mode; and

[0030] Transmit time slot adjustment module: After synchronization is completed, in relay communication mode, the relay node and the remote node adjust the transmit time slot respectively, and the entire network enters the relay data communication stage after the transmit time adjustment is completed.

[0031] Preferably, the specific steps for detecting whether the second and third slave stations have left the network are as follows:

[0032] Calculate the channel quality between the second slave station and the master station and the channel quality between the third slave station and the master station, including the signal-to-noise ratio SNR and the error vector magnitude value EVM. At the same time, set the signal-to-noise ratio threshold SNR_TH and the error vector magnitude threshold EVM_TH;

[0033] Judge the quality of the received signals at the second slave station and the third slave station: If the SNR of the second slave station or the third slave station > SNR_TH and EVM < EVM_TH, the communication is normal. If SNR ≤ SNR_TH and EVM ≥ EVM_TH, the communication quality is poor and the network exit occurs. SNR is the signal-to-noise ratio of the second slave station or the third slave station, and EVM is the error vector magnitude value of the second slave station or the third slave station.

[0034] Preferably, both the relay node and the remote node perform timing synchronization and frequency synchronization. The specific steps are as follows:

[0035] When the relay node communicates with the central node, the relay node is timed and synchronized to the central node, and synchronization window opening and tracking processing are performed;

[0036] When the remote node communicates with the relay node, the remote node is timed and synchronized to the relay node, and synchronization window opening and tracking processing are performed. The synchronization window opening satisfies the delay of the maximum transmission distance d km. N is the number of points of the synchronization window opening, f s is the sampling rate, v is the speed of light 3e 8 m / s, and d is the transmission distance;

[0037] The relay node and the central node perform frequency synchronization. The receiving end of the relay node performs frequency offset estimation and compensation processing, and the transmitting end of the relay node performs transmit data frequency offset correction with the frequency offset estimation value of the receiving end of the relay node;

[0038] The remote node and the relay node perform frequency synchronization. The receiving end of the remote node performs frequency offset estimation and compensation processing, and the transmitting end of the remote node performs transmit data frequency offset correction with the frequency offset estimation value of the receiving end of the remote node.

[0039] Preferably, the relay node and the remote node respectively adjust the transmission time slots. The specific steps are as follows:

[0040] When the relay node communicates with the central node, the relay node adjusts the transmit signal time slot according to the ranging information of the central node received;

[0041] When the relay node communicates with the remote node, the relay node receives the signal of the remote node. The relay node calculates the difference between the peak position d1 of the received synchronization signal and the peak position d2 of the synchronization signal in the stationary state, and records it as d is = d1 - d2 and returns it to the remote node. The remote node adjusts the transmission time slot through the received distance information d isThe distance measurement value variable is calculated, and the remote node adjusts the transmission time slot according to the distance measurement value variable. The entire network completes the transmission time adjustment and enters the relay data communication stage.

[0042] Preferably, the PMP network system frame structure is used to allocate downlink time slots, uplink time slots, and ranging time slots when establishing data transmission in PMP network communication mode;

[0043] The relay system frame structure is used to allocate time slots for the central node, relay nodes, remote nodes, and ranging when establishing data transmission in relay communication mode.

[0044] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a relay method and system for point-to-multipoint network communication, which solves the problem of signal fading and failure to receive signals due to communication distance and environmental influences, thereby improving the transmission performance of the system. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0046] Figure 1 The attached figure is a block diagram of the relay communication mode of the present invention;

[0047] Figure 2 The attached figure is a flowchart of a point-to-multipoint network communication relay method according to the present invention;

[0048] Figure 3 The attached figure is a frame structure diagram of the PMP network system of the present invention;

[0049] Figure 4 The attached figure is a frame structure diagram of the relay system of the present invention;

[0050] Figure 5 The attached figure is a flowchart of the frequency synchronization process of the present invention;

[0051] Figure 6 The attached figure is a flowchart of the time slot adjustment process of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] This invention discloses a relay method for point-to-multipoint network communication, such as... Figure 1 and Figure 2 As shown, it includes:

[0054] In PMP network communication mode, according to the PMP network system frame structure, the second and third slave stations communicate with the master station simultaneously, while the slave stations do not communicate with each other. At the same time, it is detected whether the second and third slave stations have left the network. The slave station that has left the network becomes an unknown node and re-enters the network. The slave station that has left the network receives information from both the master station and the slave stations that have not left the network.

[0055] The network enters relay communication mode. According to the relay system frame structure, the slave stations that have not left the network are regarded as relay nodes, the master station is regarded as the central node, and the slave stations that have left the network are regarded as remote nodes. The communication link is that the central node communicates with the relay node, and the relay node communicates with the remote node.

[0056] In relay communication mode, both relay nodes and remote nodes perform timed synchronization and frequency synchronization. After synchronization is completed, relay nodes and remote nodes adjust their transmission time slots respectively. After the entire network completes the transmission time adjustment, it enters the relay data communication stage.

[0057] In this embodiment, the specific steps for detecting whether the second and third slave stations are out of the network are as follows:

[0058] Calculate the channel quality of the second slave station and the master station, as well as the channel quality of the third slave station and the master station, including the signal-to-noise ratio (SNR) and the error vector magnitude (EVM). Where S is the average signal power and N is the average noise power. I k Q is the theoretical value for in-phase of the k-th symbol; k This is the theoretical value for the orthogonal phase (90° offset) of the k-th symbol; This is the in-phase estimate of the k-th symbol; is the quadrature phase estimate of the k-th symbol; N is the input vector length. Simultaneously, the signal-to-noise ratio threshold SNR_TH and the error vector amplitude threshold EVM_TH are set.

[0059] Judge the signal quality received by the second slave station and the third slave station: If the SNR of the second slave station or the third slave station > SNR_TH and the EVM < EVM_TH, the communication is normal. If the SNR ≤ SNR_TH and the EVM ≥ EVM_TH, the communication quality is poor and it will leave the network. SNR is the signal-to-noise ratio of the second slave station or the third slave station, and EVM is the error vector magnitude value of the second slave station or the third slave station.

[0060] More specifically, for example: If the signal quality received by the second slave station is: SNR2 > SNR_TH and EVM2 < EVM_TH, the communication of the second slave station is normal; If the signal quality received by the third slave station is: SNR3 ≤ SNR_TH and EVM3 ≥ EVM_TH, the communication quality of the third slave station is poor and it will leave the network. The third slave station becomes an unknown node and re-enters the network, and at the same time receives information from the master station and the second slave station.

[0061] In this embodiment, as Figure 5 shown, the slave station 2 marked in the attached figure is the second slave station, and the slave station 3 is the third slave station. The relay node and the remote node both perform timing synchronization and frequency synchronization. First, perform timing synchronization, and then perform frequency synchronization. The specific steps are as follows:

[0062] When the relay node communicates with the central node, the relay node is timed and synchronized to the central node, and synchronization window opening and tracking processing are performed;

[0063] When the remote node communicates with the relay node, the remote node is timed and synchronized to the relay node, and synchronization window opening and tracking processing are performed. The synchronization window opening meets the time delay of the maximum transmission distance of d km. N is the number of points of the synchronization window opening, f s is the sampling rate, v is the speed of light 3e 8 m / s, and d is the transmission distance;

[0064] The relay node and the central node perform frequency synchronization. The receiving end and the transmitting end of the central node do not perform frequency offset estimation and compensation processing. The receiving end of the relay node performs frequency offset estimation and compensation processing. The frequency offset estimation value is Δf2. The transmitting end of the relay node performs frequency offset correction of the transmitted data with the frequency offset estimation value Δf2 of the receiving end of the relay node;

[0065] The remote node and the relay node perform frequency synchronization. The receiving end and the transmitting end of the relay node do not perform frequency offset estimation and compensation processing. The receiving end of the remote node performs frequency offset estimation and compensation processing. The frequency offset estimation value is Δf3. The transmitting end of the remote node performs frequency offset correction of the transmitted data with the frequency offset estimation value Δf3 of the receiving end of the remote node.

[0066] It should be noted that in relay transmission mode, relay nodes periodically synchronize with the central node, and remote nodes periodically synchronize with the relay nodes. They are allocated different time slot resources and each uses its own time slot for periodic synchronization. However, each node only performs periodic synchronization with the remote node when it cannot receive information from the central node. Similarly, relay nodes synchronize frequencies with the central node, and remote nodes synchronize frequencies with the relay nodes. They are allocated different time slot resources and each uses its own time slot for frequency synchronization. However, each node only performs frequency synchronization with the remote node when it cannot receive information from the central node.

[0067] In this embodiment, as Figure 6 As shown, the specific steps for adjusting the transmission time slots of the relay node and the remote node are as follows:

[0068] When a relay node communicates with a central node, the relay node adjusts its signal transmission time slot based on the ranging information received from the central node.

[0069] When a relay node communicates with a remote node, the relay node receives signals from the remote node. The synchronization window of the relay node satisfies a distance of d km. The relay node calculates the difference between the peak position d1 of the received synchronization signal and the peak position d2 of the synchronization signal in the stationary state, and records it as d. is =d1-d2 and return it to the remote node. The remote node receives the distance information d. is The distance measurement value variable is calculated, and the remote node adjusts the transmission time slot according to the distance measurement value variable. The entire network completes the transmission time adjustment and enters the relay data communication stage.

[0070] This invention provides a relay system for point-to-multipoint network communication, comprising:

[0071] PMP network communication module: Used in PMP network communication mode, according to the PMP network system frame structure, for the second and third slave stations to communicate with the master station simultaneously.

[0072] Signal detection module: used to simultaneously detect whether the second and third slave stations have left the network, and to re-enter the network as unknown nodes. The slave stations that have left the network can simultaneously receive information from the master station and the slave stations that have not left the network.

[0073] Relay communication module: Used for the network to enter relay communication mode. According to the relay system frame structure, the slave stations that have not left the network are used as relay nodes, the master station is used as the central node, and the slave stations that have left the network are used as remote nodes. The communication link is between the central node and the relay node, and between the relay node and the remote node.

[0074] Timed synchronization module: Used for timed synchronization of both relay nodes and remote nodes in relay communication mode;

[0075] Frequency synchronization module: used for frequency synchronization between relay nodes and remote nodes in relay communication mode; and

[0076] Transmit time slot adjustment module: Used in relay communication mode, relay nodes and remote nodes adjust the transmit time slots respectively, and the entire network enters the relay data communication stage after the transmit time adjustment is completed.

[0077] The specific functions and methods implemented in each module correspond to each other, and will not be elaborated here.

[0078] In this embodiment, the PMP network system frame structure is used to establish the downlink time slots, uplink time slots, and ranging time slots allocated during data transmission in the PMP network communication mode; such as Figure 3 As shown, the system is configured with time slot numbers [0:4], where time slot [0:1] represents the downlink time slot sent by the master station to the second and third slave stations, time slot [2] represents the ranging time slots of the second and third slave stations to the master station respectively, and time slot [3:4] represents the uplink time slots sent by the second and third slave stations to the master station respectively.

[0079] The relay system frame structure is used to allocate time slots for the central node, relay nodes, remote nodes, and ranging during data transmission in relay communication mode. For example... Figure 4 As shown, in the relay communication mode, the system is configured with time slots [0:4], where time slot [0] represents the data time slot sent by the central node (master station) to the relay node, time slot [1] represents the data time slot sent by the relay node to the remote node, time slot [2] represents the distance measurement time slot between the relay node and the central node, time slot [3] represents the data time slot sent by the remote node to the relay node, and time slot [4] represents the data time slot sent by the relay node to the central node. The distance measurement between the remote node and the relay node is carried out through the distance protection of the time slots.

[0080] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A relay method for point-to-multipoint network communication, characterized in that, It includes: In the PMP network communication mode, according to the PMP network system frame structure, the second slave station and the third slave station communicate with the master station simultaneously, and at the same time detect whether the second slave station and the third slave station are out of the network. The slave station that is out of the network becomes an unknown node and re-enters the network. The slave station that is out of the network receives the information of the master station and the slave stations that are not out of the network at the same time; The network enters the relay communication mode. According to the relay system frame structure, the slave stations that are not out of the network are used as relay nodes, the master station is used as the central node, and the slave stations that are out of the network are used as remote nodes. The communication link is the communication between the central node and the relay node, and the communication between the relay node and the remote node; In the relay communication mode, both the relay node and the remote node perform timing synchronization and frequency synchronization. After synchronization is completed, the relay node and the remote node respectively adjust the transmission time slot. After the entire network completes the transmission time adjustment, it enters the relay data communication stage; The specific steps for both the relay node and the remote node to perform timing synchronization and frequency synchronization are as follows: When the relay node communicates with the central node, the relay node is timed and synchronized to the central node, and synchronization window opening and tracking processing are performed; When a remote node communicates with a relay node, the remote node periodically synchronizes with the relay node and performs synchronization windowing and tracking processing. The synchronization windowing satisfies the time delay required for the maximum transmission distance d km. N is the number of points for simultaneous windowing, f s Where v is the sampling rate and v is the speed of light (3e). 8 m / s, d is the transmission distance; The relay node performs frequency synchronization with the central node. The receiving end of the relay node performs frequency offset estimation and compensation processing, and the transmitting end of the relay node corrects the frequency offset of the transmitted data with the frequency offset estimation value of the receiving end of the relay node; The remote node performs frequency synchronization with the relay node. The receiving end of the remote node performs frequency offset estimation and compensation processing, and the transmitting end of the remote node corrects the frequency offset of the transmitted data with the frequency offset estimation value of the receiving end of the remote node; The specific steps for the relay node and the remote node to respectively adjust the transmission time slot are as follows: When the relay node communicates with the central node, the relay node adjusts the transmission signal time slot according to the ranging information of the central node received; When a relay node communicates with a remote node, the relay node receives signals from the remote node. The relay node calculates the difference between the peak position d1 of the received synchronization signal and the peak position d2 of the synchronization signal in the static state, and records it as d. is =d1-d2 and return it to the remote node. The remote node receives the distance information d. is The distance measurement value variable is calculated, and the remote node adjusts the transmission time slot according to the distance measurement value variable. The entire network completes the transmission time adjustment and enters the relay data communication stage.

2. The relay method for point-to-multipoint network communication according to claim 1, characterized in that, The specific steps for detecting whether the second slave station and the third slave station are out of the network are as follows: Calculate the channel quality between the second slave station and the master station and the channel quality between the third slave station and the master station, including the signal-to-noise ratio SNR and the error vector magnitude value EVM. At the same time, set the signal-to-noise ratio threshold SNR_TH and the error vector magnitude threshold EVM_TH; Judge the quality of the signals received by the second slave station and the third slave station: If the SNR of the second slave station or the third slave station > SNR_TH and EVM < EVM_TH, the communication is normal. If SNR ≤ SNR_TH and EVM ≥ EVM_TH, the communication quality is poor and out of the network. SNR is the signal-to-noise ratio of the second slave station or the third slave station, and EVM is the error vector magnitude value of the second slave station or the third slave station.

3. The relay method for point-to-multipoint network communication according to claim 1, characterized in that, The PMP network system frame structure is used for allocating downlink time slots, uplink time slots and ranging time slots when establishing data transmission in the PMP network communication mode; The relay system frame structure is used for allocating central node transmission time slots, relay node transmission time slots, remote node transmission time slots and ranging time slots when establishing data transmission in the relay communication mode.

4. A relay system for point-to-multipoint network communication, characterized in that, It includes: PMP network communication module: Used in the PMP network communication mode, according to the PMP network system frame structure, the second slave station and the third slave station communicate with the master station simultaneously; Signal detection module: Used to simultaneously detect whether the second slave station and the third slave station are out of the network, make the slave station that is out of the network become an unknown node and re-enter the network, and the slave station that is out of the network receives the information of the master station and the slave stations that are not out of the network at the same time; Relay communication module: It is used for the network to enter the relay communication mode. In accordance with the relay system frame structure, the slave stations that have not left the network are used as relay nodes, the master station is used as the central node, and the slave stations that have left the network are used as remote nodes. The communication links are the communication between the central node and the relay nodes, and the communication between the relay nodes and the remote nodes; Timing synchronization module: It is used for both the relay nodes and the remote nodes to perform timing synchronization in the relay communication mode; Frequency synchronization module: It is used for both the relay nodes and the remote nodes to perform frequency synchronization in the relay communication mode; and Transmission time slot adjustment module: After synchronization is completed, in the relay communication mode, the relay nodes and the remote nodes respectively adjust the transmission time slots. After the entire network completes the transmission time adjustment, it enters the relay data communication stage; The specific steps for both the relay nodes and the remote nodes to perform timing synchronization and frequency synchronization are as follows: When the relay node communicates with the central node, the relay node is timed and synchronized to the central node, and synchronization window opening and tracking processing are performed; When a remote node communicates with a relay node, the remote node periodically synchronizes with the relay node and performs synchronization windowing and tracking processing. The synchronization windowing satisfies the time delay required for the maximum transmission distance d km. N is the number of points for simultaneous windowing, f s Where v is the sampling rate and v is the speed of light (3e). 8 m / s, d is the transmission distance; The relay node performs frequency synchronization with the central node. The receiving end of the relay node performs frequency offset estimation and compensation processing, and the transmitting end of the relay node corrects the frequency offset of the transmitted data with the frequency offset estimation value of the receiving end of the relay node; The remote node performs frequency synchronization with the relay node. The receiving end of the remote node performs frequency offset estimation and compensation processing, and the transmitting end of the remote node corrects the frequency offset of the transmitted data with the frequency offset estimation value of the receiving end of the remote node; The specific steps for the relay nodes and the remote nodes to respectively adjust the transmission time slots are as follows: When the relay node communicates with the central node, the relay node adjusts the transmission signal time slot according to the ranging information of the central node received; When a relay node communicates with a remote node, the relay node receives signals from the remote node. The relay node calculates the difference between the peak position d1 of the received synchronization signal and the peak position d2 of the synchronization signal in the static state, and records it as d. is =d1-d2 and return it to the remote node. The remote node receives the distance information d. is The distance measurement value variable is calculated, and the remote node adjusts the transmission time slot according to the distance measurement value variable. The entire network completes the transmission time adjustment and enters the relay data communication stage.

5. A relay system for point-to-multipoint network communication according to claim 4, characterized in that, The specific steps for detecting whether the second slave station and the third slave station have left the network are as follows: Calculate the channel quality between the second slave station and the master station and the channel quality between the third slave station and the master station, including the signal-to-noise ratio SNR and the error vector magnitude value EVM. At the same time, set the signal-to-noise ratio threshold SNR_TH and the error vector magnitude threshold EVM_TH; Judge the quality of the signals received by the second slave station and the third slave station: If the SNR of the second slave station or the third slave station > SNR_TH and EVM < EVM_TH, the communication is normal. If SNR ≤ SNR_TH and EVM ≥ EVM_TH, the communication quality is poor and it has left the network. SNR is the signal-to-noise ratio of the second slave station or the third slave station, and EVM is the error vector magnitude value of the second slave station or the third slave station.

6. A relay system for point-to-multipoint network communication according to claim 4, characterized in that, The PMP network system frame structure is used for allocating the downlink time slot, uplink time slot, and ranging time slot when establishing data transmission in the PMP network communication mode; The relay system frame structure is used for allocating the central node transmission time slot, relay node transmission time slot, remote node transmission time slot, and ranging time slot when establishing data transmission in the relay communication mode.

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