PLC ad hoc network method and system based on three-phase line frequency division multiplexing

Abstract

The invention discloses a PLC ad hoc network method and system based on three-phase line frequency division multiplexing, and relates to the technical field of electric power communication. The method comprises the following steps: a central node firstly uses a common communication frequency band to send phase line identification signals on three phase lines at the same time, and then uses respective communication frequency bands of the three phase lines to send networking beacons on the corresponding phase lines; the method comprises the following steps that: a first-layer station firstly receives a phase line identification signal on a shared communication frequency band, carries out phase line identification, switches the frequency band to a communication frequency band corresponding to a phase line to which the first-layer station belongs to receive a networking beacon, and initiates a network access application to a central node; in the other levels of stations, the previous layer of station accessing the network uses the common communication frequency band to send phase line identification signals on the three phase lines at the same time, and then uses the respective communication frequency bands of the three phase lines to send networking beacons on the corresponding phase lines; and the next-layer website initiates a network access application to the central node according to a method consistent with that of the first-layer website. According to the invention, the communication time delay of the PLC network is reduced, and the network throughput is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power communication, in particular to a PLC ad hoc network method and system based on three-phase line frequency division multiplexing. BACKGROUND

[0002] In a general power line communication (PLC) network, there are three physical line branches of A, B and C phases. A CCO (Central Control Unit) generally works on the three phases A, B and C simultaneously and communicates with terminal devices on the three phases A, B and C. A terminal device, such as a STA (Station), generally works on only one of the three phase branches A, B and C. When the CCO performs channel access, the phase factor of the power line needs to be considered. When the STA on a different phase of the power line communicates with the CCO, the phase factor of the power line also needs to be considered.

[0003] At present, under the condition of three-phase communication, when the STA needs to communicate with the CCO, the STA needs to use the time slots of the three phases according to the time slot planning of the three phases. The STA on a different phase can only send a message to the CCO in the time slot of the corresponding phase. This is actually a mechanism of three-phase time division multiplexing. The communication between the first-level STA and the CCO becomes the bottleneck of the entire network. The STA needs to wait for the corresponding time slot to arrive before performing the corresponding communication, which increases the communication delay. In addition, the division of the phase time slots causes the problem of invalid time fragments, which causes channel competition and conflict and reduces the network throughput. SUMMARY

[0004] The present application aims to provide a PLC ad hoc network method and system based on three-phase line frequency division multiplexing to solve the technical problems of increasing communication delay and reducing network throughput caused by the above-mentioned mechanism of three-phase time division multiplexing. The preferred technical solutions in the technical solutions provided by the present application can produce the technical effects described below.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions: The PLC ad hoc network method based on three-phase line frequency division multiplexing provided by the present application initiates network formation from a center node to each layer station, including the following steps: A corresponding communication frequency band and a common communication frequency band are defined for each of the three phases; The center node first sends a phase recognition signal on the three phases using the common communication frequency band, and then sends a network formation beacon on the corresponding phase using the communication frequency band of each of the three phases; The first layer site first receives phase line identification signals on a common communication frequency band to identify the phase line, and after the phase line identification is completed, switches the frequency band to the communication frequency band corresponding to the phase line to which the site belongs to receive the network group beacon, and initiates a network access application to the center node; In the remaining layer sites, the last layer site in the network uses a common communication frequency band to send phase line identification signals on three phase lines, and then uses the communication frequency band of each of the three phase lines to send a network group beacon on the corresponding phase line; the next layer site first receives phase line identification signals on a common communication frequency band to identify the phase line, and after the phase line identification is completed, switches the frequency band to the communication frequency band corresponding to the phase line to which the site belongs to receive the network group beacon, and initiates a network access application to the center node through the last layer site in the network; After the center node receives the network access application, the site in the white list is added to the network.

[0006] In one or more embodiments, the bandwidths of the communication frequency bands of the three phase lines are equal, and the frequencies are higher than the frequency of the common communication frequency band.

[0007] In one or more embodiments, the communication frequency band ranges of the four communication frequency bands are defined as follows: The communication frequency band range of the A phase line is [1.953MHz, 5.127MHz]; The communication frequency band range of the B phase line is [5.371MHz, 8.545MHz]; The communication frequency band range of the C phase line is [8.789MHz, 11.963MHz]; The communication frequency band range of the A phase line, the B phase line and the C phase line is [0.708MHz, 1.709MHz].

[0008] In one or more embodiments, the following conditions need to be met simultaneously when sending the phase line identification signal: The phase line identification signals sent on the three phase lines are orthogonal; the phase line identification signals sent on the three phase lines have the same power; and the phase line identification signals on the three phase lines are sent simultaneously.

[0009] In one or more embodiments, the phase line identification signal includes a preamble and a payload, the preambles of the phase line identification signals sent on the three phase lines are the same, the payloads are orthogonal, and contain multiple groups of orthogonal symbols.

[0010] In one or more embodiments, the payload is modulated by OFDM, and the subcarrier modulation mode is BPSK.

[0011] In one or more embodiments, each layer site identifies the phase line to which it belongs by comparing the power of the phase line identification signals from different phase lines at the same time.

[0012] In one or more embodiments, after a certain station receives the mixed signal, phase line identification signals sent by three phase lines are obtained through signal decomposition, and the sending phase line corresponding to the maximum power value in the three signals is the phase line to which the station belongs.

[0013] In one or more embodiments, each layer station needs to select a target network and a parent node before initiating a network access application.

[0014] According to another aspect of the present application, a PLC ad hoc network system based on three-phase line frequency division multiplexing is also provided, based on the PLC ad hoc network method based on three-phase line frequency division multiplexing described above, comprising a center node, a relay node and a terminal node, the center node working on three-phase lines at the same time, the relay node and the terminal node working on one phase line in the three-phase lines.

[0015] The center node comprises a communication frequency band definition module and an ad hoc network module, the communication frequency band definition module being used to define corresponding communication frequency bands for the three phase lines and a common communication frequency band, and the ad hoc network module being used to realize networking of the relay node and the terminal node according to the four communication frequency bands defined by the communication frequency band definition module; the relay node and the terminal node comprise a phase line identification module, which identifies the phase line to which the relay node and the terminal node belong by comparing the power of the phase line identification signals from different phase lines at the same time.

[0016] Implementing one of the technical solutions of the present application has the following advantages or beneficial effects: The present application enables the stations of the A-phase line, the B-phase line and the C-phase line to simultaneously communicate with the center node using different frequency bands, without waiting for the time slots corresponding to the phase lines, so that each station can send messages to the center node at any time, greatly reducing the communication time delay of the PLC network and improving the network throughput. Meanwhile, the A-phase line, the B-phase line and the C-phase line time division multiplexing network is divided into three three-phase line frequency division multiplexing sub-networks, the three sub-networks work in parallel, solving the problem of invalid time fragments caused by phase line time slot division, avoiding channel competition and conflict, and effectively improving the network throughput. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings. Figure 1 is a PLC ad hoc network method flowchart based on three-phase line frequency division multiplexing according to an embodiment of the present application; Figure 2is a three-phase line frequency division multiplexing PLC system networking process (n-layer node) schematic diagram of an embodiment of the present application; Figure 3 is a PLC ad hoc network system structure block diagram based on three-phase line frequency division multiplexing of an embodiment of the present application; Figure 4 is a three-phase line frequency division multiplexing PLC system protocol stack structure schematic diagram of an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, various exemplary embodiments to be described below will be described with reference to corresponding drawings, which constitute a part of the exemplary embodiments, and various exemplary embodiments that can be used to implement the present application are described. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation described in the following exemplary embodiments does not represent all implementations consistent with the present disclosure. It should be understood that they are only examples of processes, methods and devices, etc. consistent with some aspects of the present disclosure as described in the appended claims, and other embodiments can be used, or modifications can be made to the embodiments listed herein in structure and function, without departing from the scope and spirit of the present application.

[0019] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the elements referred to must have a particular orientation, structure and operation. The terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. The term "a plurality of" means two or more. The terms "connected", "connected" should be broadly understood, for example, it can be fixedly connected, detachably connected, integrally connected, mechanically connected, electrically connected, communicatively connected, directly connected, indirectly connected through an intermediate medium, it can be the internal communication of two elements or the interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more related listed items. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0020] In order to illustrate the technical solutions described in the present application, the following will be described by specific embodiments, only showing the parts related to the embodiments of the present application.

[0021] Embodiment one: As Figure 1As shown, the application provides a PLC self-networking method based on three-phase line frequency division multiplexing, which initiates networking from the center node to each layer site, including the following steps: S100, define a corresponding communication frequency band and a common communication frequency band for each of the three-phase lines; S200, the center node first sends a phase line identification signal on the three-phase lines using the common communication frequency band, and then sends a networking beacon on the corresponding phase line using the communication frequency band of each phase line; S300, the first layer site first receives the phase line identification signal on the common communication frequency band, performs phase line identification, and after completing the phase line identification, switches the frequency band to the communication frequency band corresponding to the phase line to which it belongs to receive the networking beacon, and initiates a network access application to the center node. Wherein, after completing the target network and parent node selection, the first layer site initiates the network access application; S400, among the remaining layer sites, the last layer site that has accessed the network sends a phase line identification signal on the three-phase lines using the common communication frequency band, and then sends a networking beacon on the corresponding phase line using the communication frequency band of each phase line; the next layer site first receives the phase line identification signal on the common communication frequency band, performs phase line identification, and after completing the phase line identification, switches the frequency band to the communication frequency band corresponding to the phase line to which it belongs to receive the networking beacon, and initiates a network access application to the center node through the last layer site that has accessed the network. Wherein, after completing the target network and parent node selection, the next layer site initiates the network access application through the last layer site; S500, after the center node receives the network access application, the site in the white list is added to the network.

[0022] The PLC self-networking method of the embodiment supports three-phase line frequency division multiplexing, the sites (STA) of the A-phase line, the B-phase line and the C-phase line use different frequency bands to simultaneously communicate with the center node (CCO), without waiting for the time slot corresponding to the phase line, and can send messages to the CCO at any time, greatly reducing the communication delay of the PLC network and improving the network throughput. In addition, the embodiment divides a three-phase line time division multiplexing network into three three-phase line frequency division multiplexing sub-networks, and the three sub-networks work in parallel, solving the problem of invalid time fragments caused by phase line time slot division, avoiding channel competition and conflict, and effectively improving the network throughput.

[0023] For the convenience of understanding, since there are sometimes multiple central nodes networking at the same time at the work site, the STA will receive beacons from multiple networks at the same time, and needs to select the target network to which it wants to join. If the application to join the first network is rejected, it can select the second network to apply to join, until it joins the network to which it belongs. Therefore, each station needs to select a target network before initiating the network access application, and the selection of the target network can determine the network to which the STA belongs. In addition, each station also needs to select a parent node before initiating the network access application, and a multi-level tree network can be formed through the parent node.

[0024] To support three-phase frequency division multiplexing, four communication frequency bands are defined in the above step S100, including frequency band A, frequency band B, frequency band C and frequency band D. Frequency band A is allocated to phase A, frequency band B is allocated to phase B, frequency band C is allocated to phase C, and frequency band D is a common frequency band for phase A, phase B and phase C.

[0025] In one or more embodiments, the bandwidths of the communication frequency bands of the three phase lines are equal, and the frequencies are higher than the frequency of the common communication frequency band. In a specific embodiment, the bandwidths of frequency band A, frequency band B and frequency band C are about 3.2 MHz, and the bandwidth of frequency band D is about 1.0 MHz. The adjacent frequency bands are separated by about 0.2 MHz.

[0026] In one or more embodiments, the communication frequency band ranges of the four communication frequency bands are defined as shown in Table 1.

[0027] Table 1 Communication frequency band range table In one or more embodiments, the transmission of the phase line identification signal needs to meet the following conditions at the same time: 1) The phase line identification signals transmitted on the three phase lines are orthogonal; 2) The phase line identification signals transmitted on the three phase lines have the same power; 3) The phase line identification signals on the three phase lines are transmitted at the same time.

[0028] For the convenience of understanding, since the signals among the three phase lines will interfere with each other, i.e. the signals transmitted by phase A can also be received on phase B and phase C, the signals transmitted by phase B can also be received on phase A and phase C, and the signals received by a certain STA are the superimposed mixture of the signals of the three phase lines, therefore the phase line identification signals transmitted on the three phase lines are orthogonal, so as to separate the signal of one phase line from the mixed signal.

[0029] The powers of the three phase lines are the same, and only the relative size needs to be compared to identify the phase line, without the need for further calculation of channel attenuation, which is simple and reliable to implement.

[0030] Since the power line channel is time-varying, the attenuation of the channel at a previous time and a next time is different, and the accuracy of phase line identification by comparing the signal power of three phase lines at the same time is higher than that at different times. Therefore, the phase line identification signals on the three phase lines are transmitted at the same time.

[0031] In one or more embodiments, the phase line identification signal includes a preamble and a payload. The preamble is used for automatic gain control adjustment, frame detection and synchronization. The payload is modulated by OFDM, and the subcarrier modulation mode is BPSK. The OFDM symbol is based on a 25MHz sampling rate, the data is processed by a 1024-point IFFT, and the real part is taken, and a 512-point cyclic prefix is added to form an OFDM symbol.

[0032] In specific embodiments, the phase line identification signals transmitted on the three phase lines have the same preamble and orthogonal payloads, and the payloads include multiple groups of orthogonal symbols. Each group of four symbols, the phase relationship between each group of symbols on the A phase line is [+1 -1 +1 +1], the phase relationship between each group of symbols on the B phase line is [+1 +1 -1 +1], and the phase relationship between each group of symbols on the C phase line is [+1 +1 +1 -1].

[0033] In one or more embodiments, each layer site identifies the phase line to which it belongs by comparing the power of the phase line identification signals from different phase lines at the same time. Further, the mixed signal received by a certain site is decomposed into three phase line identification signals transmitted by the three phase lines, and the transmission phase line corresponding to the maximum power in the three signals is the phase line to which the site belongs.

[0034] It should be further pointed out that considering the transmission function and noise of the channel, the signal received at the frequency domain subcarrier k can be represented as: (1) ; Wherein: is the transmission signal on the A, B and C three phase lines, is the received signal on the A, B and C three phase lines, is the received noise on the A, B and C three phase lines, is the 3x3 channel matrix of the subcarrier k.

[0035] (2) ; In the channel matrix represents the transmission function of subcarrier k from the transmission phase line Lt to the receiving phase line Lr. Lt and Lr are substituted into the A, B and C three phase lines, and the matrix can be obtained.

[0036] If a certain site is on the A phase line, the received signal of the site can be obtained from equation (1) and equation (2) as follows: (3); Equation (3) shows that the received signal at this station is the transmitted signal on the three phase lines A, B, and C. After transmission through the channel, it is mixed with noise. The superimposed mixed signals. Utilizing the orthogonality of the signals, equation (4) can be used to obtain the received signals. The signals transmitted from the three phase lines A, B, and C are separated.

[0037] (4); Where: N is the number of OFDM symbols. For subcarrier k, the signal transmitted from transmitting phase line A to receiving phase line A. For subcarrier k, the signal is transmitted from the transmitting phase line B to the receiving phase line A. The subcarrier k is the signal transmitted from the transmitting phase line C to the receiving phase line A.

[0038] because For direct communication channel transfer functions, and For non-direct communication channel transfer functions, The channel attenuation is less than and Channel attenuation, and [ The transmission power of the signals is the same, therefore the signals The power is greater than The power of the signal is calculated by adding the power of all subcarriers together. By comparing the magnitude of the signal power, the location of the station on phase A can be identified.

[0039] Similarly, for stations on phase B and phase C lines, the above method can be used to identify their respective phase lines.

[0040] like Figure 2 As shown in the diagram, the end nodes are the STAs (stations) in each layer of stations. In this embodiment, only the central node can initiate network formation. The network formation process mainly involves the central node sending phase line identification signals and beacons to trigger phase line identification and network access applications from the end nodes level by level, thereby completing the entire network formation. If there are n layers of stations, the specific network formation process is as follows: After the central node is powered on, it first uses frequency band D to simultaneously send phase line identification signals on phase lines A, B, and C, so that the end nodes can identify the phase lines. After the phase line identification signals are sent, it uses frequency bands A, B, and C to send beacons on phase lines A, B, and C, respectively. After the beacon transmission is completed, it waits for the end nodes to apply for network access.

[0041] After the end node is powered on, it first receives the phase line identification signal on frequency band D and performs phase line identification. After the phase line identification is completed, it switches the frequency band to the frequency band A, B or C allocated to the phase line to which the site belongs to receive beacons. If the phase line to which the site belongs is phase line A, it switches the frequency band to frequency band A to receive network beacons. After completing the selection of the target network and parent node, it initiates a network access application.

[0042] After receiving a network access application, the central node checks whether the applying site is in the whitelist. If the site is in the whitelist, it allows the site to join the network; otherwise, it refuses the site to join the network.

[0043] After the first-tier sites complete their network access, the central node instructs them to send phase line identification signals and beacons, triggering the second-tier sites to initiate network access applications. The first-tier sites first use frequency band D to simultaneously send phase line identification signals. After the phase line identification signals are sent, they then use the frequency band A, B, or C allocated to the phase line to which the site belongs to send beacons. If the phase line to which the site belongs is phase line A, the frequency band is switched to frequency band A to send the beacons.

[0044] After the second-layer stations have completed their network access, the central node arranges for the second-layer stations to send phase line identification signals and beacons, triggering the third-layer stations to initiate network access applications. This process is repeated until the nth-layer stations have completed their network setup.

[0045] As an alternative implementation, the end node can first apply for network access using frequency band A. After all sites are connected to the network, since all sites have achieved time synchronization, phase line identification can be performed using a zero-time comparison method. After phase line identification is completed, the end node switches to the frequency bands A, B, and C allocated to its respective phase line to re-establish the network. This scheme requires two network setups, which takes a relatively long time.

[0046] Furthermore, the method for comparing the zero-crossing times of phase lines is as follows: the central node collects the zero-crossing times of its own three phase lines A, B, and C, and sends them to the terminal node; the terminal node collects the zero-crossing times of its own phase lines, calculates the difference between the zero-crossing times of the central node and the central node, and can identify its own phase line based on the difference.

[0047] Example 2: like Figure 3 As shown, this embodiment also provides a PLC self-organizing network system based on three-phase line frequency division multiplexing, which is based on the PLC self-organizing network method based on three-phase line frequency division multiplexing described in Embodiment 1 above, including a central node, a relay node, and an end node.

[0048] In one or more embodiments, the central node includes a communication frequency band definition module and a self-organizing network module. The communication frequency band definition module is used to define corresponding communication frequency bands for the three phase lines and a shared communication frequency band. The definition of the communication frequency bands is consistent with that described in Embodiment 1, and can be found in Embodiment 1 for details.

[0049] The self-organizing network module is used to network relay nodes and end nodes according to the four communication frequency bands defined by the communication frequency band definition module, specifically implementing the relevant processes in steps S200-S500 of Embodiment 1. See the corresponding sections in the embodiments for details, which will not be repeated here.

[0050] In one or more embodiments, the relay node and the terminal node include a phase line identification module. The phase line identification module identifies the phase line to which the relay node and the terminal node belong by comparing the power of phase line identification signals from different phase lines at the same time. See the corresponding sections of the embodiments for details, which will not be repeated here.

[0051] In a specific embodiment, the central node connects all relay nodes and terminal nodes via physical lines on three phase lines A, B, and C, forming three multi-level tree networks on these three phase lines. The central node operates on all three phase lines (A, B, and C) and can simultaneously transmit and receive signals on all three phase lines; the relay nodes and terminal nodes operate on one of the three phase lines (A, B, and C).

[0052] Furthermore, the central node is the control and management center of the network, responsible for the construction, maintenance, and management of the network, including access management and resource allocation for relay nodes and end nodes. Relay nodes are the network's routing nodes, responsible for relaying data between the central node and end nodes, as well as for data transmission within the node itself. End nodes access the network through the central node or relay nodes, completing their own data transmission.

[0053] like Figure 4 As shown, the protocol stack of a three-phase frequency division multiplexing PLC system consists of five layers: physical layer, data link layer, network layer, transport layer, and application layer. In addition to providing services to the network layer, the data link layer can also directly provide transmission services to the application layer.

[0054] Physical layer: Implements the encoding and modulation of data at the transmitting end, and the demodulation and decoding of power line carrier signals at the receiving end.

[0055] Data Link Layer: Divided into MAC sublayer and network management sublayer. The MAC sublayer mainly handles physical channel access, ensuring reliable data transmission; the network management sublayer mainly handles network topology, maintenance, routing management, and data aggregation and distribution at the data link layer.

[0056] Network layer: provides network service, complies with IPv6, 6LoWPAN protocol.

[0057] Transport layer: provides transport service, complies with UDP protocol.

[0058] Application layer: uses DL / T698.45, DL / T645 and other protocols to realize service data interaction between the center node and the relay node, and the end node.

[0059] To sum up, the PLC ad hoc network system supporting three-phase line frequency division multiplexing of the embodiment, the stations (STA) of the A-phase line, the B-phase line and the C-phase line use different frequency bands to simultaneously communicate with the center node (CCO), without waiting for the time slot corresponding to the phase line, and can send messages to the CCO at any time, greatly reducing the communication delay of the PLC network and improving the network throughput. In addition, the embodiment divides the A, B and C three-phase line time division multiplexing network into three three-phase line frequency division multiplexing sub-networks, and the three sub-networks work in parallel, solving the problem of invalid time fragments caused by phase line time slot division, avoiding channel competition and conflict, and effectively improving the network throughput.

[0060] It should be understood that the above embodiments are only one special case, and do not mean that the present application is in this way.

[0061] It should be understood that although each step in the flowchart involved in the above embodiments is displayed in sequence according to the arrow, these steps are not necessarily executed in the order indicated by the arrow. Unless otherwise stated herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other order. Moreover, at least part of the steps in the flowchart involved in the above embodiments can include multiple steps or stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least part of other steps or steps or stages in other steps.

[0062] The above only describes the preferred embodiments of the present application, and those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, these features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of protection of the present application.

Claims

1. A PLC ad hoc network method based on three-phase line frequency division multiplexing, characterized by, The center node initiates network group to each layer site step by step, including the following steps: Three phase lines are defined respectively corresponding communication frequency band and a common communication frequency band; The center node first uses the common communication frequency band to send phase line identification signal on three phase lines, and then uses the communication frequency band of each phase line to send network group beacon on the corresponding phase line; The first layer site first receives the phase line identification signal on the common communication frequency band to identify the phase line, and after the phase line identification is completed, the frequency band is switched to the communication frequency band corresponding to the phase line to which the site belongs to receive the network group beacon, and initiates the network application to the center node; In the remaining layer sites, the last layer site uses the common communication frequency band to send the phase line identification signal on three phase lines, and then uses the communication frequency band of each phase line to send the network group beacon on the corresponding phase line; the next layer site first receives the phase line identification signal on the common communication frequency band to identify the phase line, and after the phase line identification is completed, the frequency band is switched to the communication frequency band corresponding to the phase line to which the site belongs to receive the network group beacon, and initiates the network application to the center node through the last layer site which has entered the network; After the center node receives the network application, each site in the white list is added to the network.

2. The PLC ad hoc network method based on three-phase line frequency division multiplexing according to claim 1, characterized in that, The bandwidth of the communication frequency band of the three phase lines is equal, and the frequency is higher than the frequency of the common communication frequency band.

3. The PLC ad hoc network method based on three-phase line frequency division multiplexing according to claim 1, characterized in that, The communication frequency band range of the four communication frequency bands is defined as follows: The communication frequency band range of the A phase line is [1.953MHz, 5.127MHz]; The communication frequency band range of the B phase line is [5.371MHz, 8.545MHz]; The communication frequency band range of the C phase line is [8.789MHz, 11.963MHz]; The communication frequency band range of the A phase line, the B phase line and the C phase line is [0.708MHz, 1.709MHz].

4. The PLC ad hoc network method based on three-phase line frequency division multiplexing according to claim 1, characterized in that, The following conditions need to be met when sending the phase line identification signal: The phase line identification signals sent on the three phase lines are orthogonal; The phase line identification signals sent on the three phase lines have the same power; The phase line identification signals on the three phase lines are sent at the same time.

5. The PLC ad hoc network method based on three-phase line frequency division multiplexing according to claim 4, characterized in that, The phase line identification signal includes a preamble and a payload, the preambles of the phase line identification signals sent on the three phase lines are the same, the payloads are orthogonal, and contain multiple groups of orthogonal symbols.

6. The PLC ad hoc network method based on three-phase line frequency division multiplexing according to claim 5, characterized in that, The payload is modulated by OFDM, and the subcarrier modulation mode is BPSK.

7. The method according to claim 1, wherein the method is characterized by, Each layer site identifies the phase line to which it belongs by comparing the power of the phase line identification signals from different phase lines at the same time.

8. The method according to claim 7, wherein, After a site receives the mixed signal, three phase line identification signals sent by the three phase lines are obtained through signal decomposition, and the phase line corresponding to the maximum power in the three signals is the phase line to which the site belongs.

9. The method according to any one of claims 2-8, wherein, Each layer site needs to select a target network and a parent node before initiating the network application.

10. A PLC ad hoc network system based on three-phase line frequency division multiplexing, characterized by, The PLC self-networking method based on three-phase line frequency division multiplexing according to any one of claims 1-9, comprising a center node, a relay node and a terminal node, the center node works on three phase lines at the same time, the relay node and the terminal node work on one phase line in the three phase lines; The center node comprises a communication frequency band defining module and an ad hoc network module, the communication frequency band defining module is used for defining a corresponding communication frequency band and a common communication frequency band for three phase lines respectively; the ad hoc network module is used for realizing networking of the relay node and the terminal node according to the four communication frequency bands defined by the communication frequency band defining module; The relay node and the terminal node comprise a phase line identification module, the phase line identification module identifies the phase line to which the relay node and the terminal node belong by comparing the power of the phase line identification signals from different phase lines at the same time.

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