CN114826455A

CN114826455A - Method for automatically selecting frequency band in PLC system

Info

Publication number: CN114826455A
Application number: CN202210492386.7A
Authority: CN
Inventors: 段红光; 刘怡豪; 文淳; 郑建宏; 罗一静
Original assignee: Chongqing University of Post and Telecommunications
Current assignee: Chongqing University of Post and Telecommunications
Priority date: 2022-05-07
Filing date: 2022-05-07
Publication date: 2022-07-29
Anticipated expiration: 2042-05-07
Also published as: CN114826455B

Abstract

The invention relates to a method for automatically selecting a frequency band in a PLC (programmable logic controller) system, belonging to the field of communication of the Internet of things. The method comprises a node frequency spectrum sensing process in the PLC system and an automatic frequency band selection process in the PLC system; the existing PLC system does not provide an automatic frequency band sensing function, the instrument is required to be independently tested every time the frequency band is changed, and then a new working frequency band is selected according to the tested interference condition, so that the system operation cost is high. The invention does not need to adopt a special detection instrument to carry out interference analysis, but the system automatically completes the interference analysis. The conventional frequency band interference test has limitation on interference detection time period, only one fixed time period can be analyzed, and the conventional method has limited test point selection and cannot support the interference test of all sites. The invention can be used for real-time interference analysis and site location test, and supports the real-time frequency band changing process.

Description

Method for automatically selecting frequency band in PLC system

Technical Field

The invention belongs to the field of communication of the Internet of things, and relates to a method for automatically selecting a frequency band in a PLC (programmable logic controller) system.

Background

With the development of the communication industry, people have more and more demand on frequency spectrum, and the current independent frequency spectrum allocation mode cannot meet the demand of the communication industry. Especially in the internet of things industry, the expensive spectrum use cost cannot be paid, so that many system designs are shifted to the shared spectrum part.

At present, a low-voltage power line broadband carrier communication system uses a low-voltage power line as a communication medium to realize a communication network for converging, transmitting and interacting power consumption information of low-voltage power users, mainly adopts an orthogonal frequency division multiplexing technology, uses 2 MHz-12 MHz in frequency band, and supports 4 frequency bands in total, as shown in table 1.

TABLE 1 broadband carrier communication frequency band of low-voltage power line

The physical layer architecture of the low-voltage power line broadband carrier communication is shown in fig. 1.

At the transmitting end, the physical layer receives input from the data link layer and uses two separate links to process frame control data and payload data, respectively. After the frame control data is encoded by Turbo, channel interleaving and frame control diversity copying are carried out; after scrambling, Turbo coding, channel interleaving and load diversity copying, constellation point mapping is carried out on load data and frame control data, cyclic prefixes are added to the mapped data after IFFT processing to form OFDM symbols, after windowing processing is carried out on the OFDM symbols, PPDU signals are formed, sent to an analog front end and finally sent to a power line channel.

At the receiving end, the data received from the analog front end is coordinated with Automatic Gain Control (AGC) and time synchronization to respectively adjust the frame control and the load data, and after FFT conversion is carried out on the frame control and the load data, the frame control and the load data enter a demodulation and decoding module, and finally the original data of the frame control information and the original data of the load are recovered.

And according to the technical specification, technical parameters of the OFDM symbols are defined, and the physical layer OFDM symbols are based on a clock sampling rate of 25MHz in a time domain. After the data is subjected to 1024-point inverse fourier transform (IFFT), a real number part is taken, and a cyclic prefix is added to form an OFDM symbol, where the cyclic prefix is composed of a roll-off interval and a guard interval, as shown in table 2.

TABLE 2 OFDM symbol characteristics

Symbol parameter	Number of time domain points	Time (us)
			Preamble IFFT Length	1024	40.96
Frame control/payload data IFFT Length	1024	40.96

Since the system uses a 25MHz clock and the fourier transform (FFT) takes 1024 points, the subcarrier spacing in this system is 24.414 KHz.

In the low-voltage power line broadband carrier communication system, the networking mode is as shown in fig. 2. For the electricity consumption information collection system, the broadband carrier communication network generally forms a tree network that is connected with all STAs (smart meter/I type collector communication unit, broadband carrier II type collector) in a multi-level association with a CCO as a center and a PCO (smart meter/I type collector communication unit, broadband carrier II type collector) as a relay agent, as shown in fig. 2, which is a topology of a typical broadband carrier communication network.

The PLC system consists of three types of nodes, namely a central coordinator, a site and an agent coordinator.

The master node role in a Central Coordinator (CCO) communication network is responsible for completing networking control, network maintenance management and other functions, and its corresponding device entity is a concentrator local communication unit.

A slave node role in a Station (STA) communication network, and a corresponding device entity is a communication unit, which includes an electric energy meter communication unit, an I-type collector communication unit or an II-type collector.

A Proxy Coordinator (PCO) is a site for relaying and forwarding data between a central coordinator and a site or between sites, which is called a proxy for short.

In the PLC system, data transmission is performed in a frame burst manner, as shown in fig. 3.

The frame structure of the physical layer transmitted PPDU signal is shown in fig. 3. The PPDU consists of a preamble, a frame control and payload data. The preamble is a periodic sequence, and the number of subcarriers of the frame control and payload data of each symbol is 512. The types of the guard interval of the symbol include a frame control guard interval, a guard interval of the 1 st and 2 nd symbols of the payload data, and a guard interval of the 3 rd and later symbols of the payload data.

At present, a low-voltage power line broadband carrier communication system does not support a spectrum sensing function and also does not support a frequency band automatic configuration function, and various problems still exist in practical application due to the adoption of a fixed working frequency band configuration mode. The method comprises the following specific steps:

firstly, the method comprises the following steps: before the low-voltage power line broadband carrier communication system is deployed, the use condition of 0-12MHz wireless frequency bands needs to be checked, and the wireless frequency bands are coupled to a power line and interfere with normal communication of the power line. In practical engineering, an optimal operating frequency band cannot always be selected in real time due to the variation of interference.

Secondly, the method comprises the following steps: the low-voltage power line broadband carrier communication system is inflexible in use frequency band, a working frequency band needs to be preset in the deployment process, automatic configuration is not supported in the use process, and only a manual mode can be adopted. The low-voltage power line broadband carrier communication system is unstable in operation and high in maintenance cost.

Due to the two reasons, communication failure often occurs in the low-voltage power line broadband carrier communication system in the using process. Communication represents a situation of unstable performance and requires a professional to perform field testing, which is costly to maintain.

Disclosure of Invention

In view of the above, the present invention is directed to a method for automatic band selection in a PLC system. The basic principle is that nodes in a PLC system carry out spectrum analysis on received data by a receiving end if effective frame burst data sent by a sending end is not found in the real-time receiving process, the average power of the frequency band background noise is counted, and the node of the PLC system is adopted to periodically report a heartbeat message and periodically report the average power of the frequency band background noise to a central coordinator. The central coordinator collects the frequency band background noise average power of all nodes in the PLC system, calculates the interference minimum frequency band in the PLC system as the optimal working frequency band, and determines whether to start the optimal working frequency band. And finally, the central coordinator adopts the beacon middle frequency band change item to configure the selected optimal working frequency band to each node in the PLC system.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for automatically selecting frequency bands in a PLC system comprises a node frequency spectrum sensing flow in the PLC system and an automatic frequency band selection flow in the PLC system;

the node frequency spectrum sensing process in the PLC system is as follows;

step 11: the node in the PLC system monitors whether effective frame burst data exists on a PLC line in real time, a receiving end node firstly receives 1024-point time domain data which is recorded as a _ rx _ time _ data, then detects whether the time domain data is the frame burst data, and if the time domain data is the frame burst data, a normal frame burst receiving process of the node is started; if the frame burst data is not the frame burst data, starting spectrum sensing measurement;

step 12: the receiving end node performs 1024-point Fourier transform FFT on the received a _ rx _ time _ data time domain data; obtaining 1024 sub-carrier frequency domain data, and recording the data as a _ rx _ frequency _ data;

step 13: extracting frequency domain information of the first 512 subcarriers from the a _ rx _ frequency _ data, calculating a background noise power value of each subCarrier, and recording the background noise power value as a _ rx _ subCarrier _ power;

a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))

wherein abs () represents the modulo calculation; i represents the number of the subcarrier, and the value range is 1-512;

step 14: accumulating and averaging the subCarrier background noise power corresponding to the a _ rx _ subCarrier _ power and the locally recorded a _ rx _ subCarrier _ average _ power, and calculating the subCarrier background noise average power;

a_rx_subCarrier_average_power(i)＝(a_rx_subCarrier_average_power(i)+a_rx_subCarrier_power(i))/2；

wherein i represents a subcarrier number, and the value range is 1 to 512;

step 15: calculating the subCarrier background noise average power of each frequency band, and recording as a _ rx _ subCarrier _ band _ power;

wherein, i identifies the subcarrier number, startSubCarrier represents the frequency band starting subcarrier number, endSubCarrier represents the frequency band ending subcarrier number; n represents the number of subcarriers in the frequency band;

the automatic frequency band selection process in the PLC system is as follows:

step 21: in the first process of PLC system deployment, firstly, determining a used frequency band by a conventional method for deployment, and completing a networking process according to the technical requirements of a low-voltage power line broadband carrier communication system;

step 22: each node in the PLC system comprises a site, an agent coordinator and a central coordinator, and the spectrum sensing measurement process is carried out on the nodes, the background noise average power of each frequency band of the PLC system is obtained in the process, and the average of the background noise power of all subcarriers in the frequency band is adopted for representation;

step 23: the PLC node reports the average power a _ rx _ subCarrier _ band _ power of the bottom noise subCarrier of each frequency band to a central coordinator by adopting a heartbeat detection message according to a heartbeat detection message reporting period configured by a system;

step 24: the central protocol device collects heartbeat detection messages from each node, and takes out the average power of the background noise of the frequency band reported by each node, and records the average power as a _ rx _ band _ power; average calculation is carried out on the average power of the background noise of the frequency band reported by each node, and the average power is used as a frequency band interference analysis result;

wherein, M represents the number of nodes which finish spectrum sensing and are collected by the central coordinator;

step 25: selecting a frequency band corresponding to the minimum a _ rx _ band _ power as an optimal working frequency band from results of calculating all frequency bands a _ rx _ band _ power of the PLC system, comparing the a _ rx _ band _ power of the optimal working frequency band with the current working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is less than a threshold bandPowerOffset of the current working frequency band;

step 26: and the central protocol unit configures the newly selected formal working frequency band to each site according to the requirements of the low-voltage power line broadband carrier communication technical standard, and then each site performs working frequency band replacement according to the requirements of the central coordinator.

The invention has the beneficial effects that:

firstly, the method comprises the following steps: the existing PLC system does not provide an automatic frequency band sensing function, the instrument is required to be independently tested every time the frequency band is changed, and then a new working frequency band is selected according to the tested interference condition, so that the system operation cost is high. The invention does not need to adopt a special detection instrument to carry out interference analysis, but the system automatically completes the interference analysis.

Secondly, the method comprises the following steps: the conventional frequency band interference test has limitation on interference detection time period, only one fixed time period can be analyzed, and the conventional method has limited test point selection and cannot support the interference test of all sites. The invention can be used for real-time interference analysis and site location test, and supports the real-time frequency band changing process.

Thirdly, the steps of: the invention adds the function of the invention on the existing system, does not need to upgrade the hardware, and can be finished only by upgrading the software.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.

Drawings

For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of the physical layer overall architecture;

FIG. 2 is a topology diagram of a broadband carrier communication network;

FIG. 3 is a frame burst structure;

FIG. 4 is a block diagram of an automatic frequency band configuration in a PLC system;

FIG. 5 is a node spectrum sensing process in a PLC system;

FIG. 6 is a flow of automatic frequency band selection in a PLC system;

FIG. 7 is a frame for implementing automatic band selection in the embodiment;

FIG. 8 is a spectrum sensing flow of a site and agent coordinator in an embodiment;

fig. 9 is an exemplary automatic band selection procedure of the central coordinator.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.

Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.

The invention consists of three modules, namely a frequency spectrum detecting and reporting module, a frequency band interference analyzing module and a frequency band selecting and configuring module. The frequency spectrum detecting and reporting module completes frequency-mode sensing measurement of each node in the PLC system, calculates the average power of the frequency band background noise, namely the average power of the background noise of all subcarriers in the frequency band, and reports the average power to the central coordinator through heartbeat detection messages. And the frequency band interference analysis module completes the frequency band background noise average power analysis of all the nodes collected by the PLC system, calculates the average background noise of each frequency band of the PLC system, and expresses the average background noise average power in the frequency band reported by all the nodes. The frequency band selection and configuration module completes the working frequency band selection of the PLC system, selects the optimal working frequency band, and configures the optimal working frequency band to each node through the configuration working frequency band unit in the beacon. As shown in fig. 4.

The invention includes two processes, one of which is: a node frequency spectrum sensing process in the PLC system; the second step is as follows: and (3) automatic frequency band selection process in the PLC system.

The first process comprises the following steps: the node spectrum sensing process in the PLC system is shown in FIG. 5.

Step 1: the node in the PLC system monitors whether effective frame burst data exists on a PLC line in real time, the receiving end node firstly receives 1024-point time domain data which is recorded as a _ rx _ time _ data, then detects whether the time domain data is the frame burst data, and if the time domain data is the frame burst data, the normal frame burst receiving process of the node is started. If not, spectrum sensing measurement is started. As in step 1 of fig. 5.

Step 2: the receiving end node performs 1024-point Fourier transform (FFT) on the received a _ rx _ time _ data time domain data to obtain 1024 subcarrier frequency domain data, and the frequency domain data is recorded as a _ rx _ frequency _ data. As shown in step 2 of fig. 5.

And 3, step 3: and extracting the frequency domain information of the first 512 subcarriers from the a _ rx _ frequency _ data, calculating a background noise power value of each subCarrier, and recording the background noise power value as a _ rx _ subCarrier _ power. As in step 3 of fig. 5.

a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))

Wherein abs () represents the modulo calculation. i represents a subcarrier number, and ranges from 1 to 512.

And 4, step 4: and accumulating and averaging the subCarrier background noise power corresponding to the a _ rx _ subCarrier _ power and the locally recorded a _ rx _ subCarrier _ average _ power, and calculating the subCarrier background noise average power. As in step 4 of fig. 5.

a_rx_subCarrier_average_power(i)＝(a_rx_subCarrier_average_power(i)+a_rx_subCarrier_power(i))/2。

Wherein i represents a subcarrier number, and the value range is 1 to 512.

And 5: and calculating the average power of the subCarrier background noise of each frequency band, and recording as a _ rx _ subCarrier _ band _ power. As shown in step 5 of fig. 5.

Wherein, i identifies the subcarrier number, startSubCarrier represents the frequency band starting subcarrier number, endSubCarrier represents the frequency band ending subcarrier number. N represents the number of subcarriers in the frequency band.

And a second process: an automatic frequency band selection process in the PLC system;

step 1: in the first process of PLC system deployment, firstly, a used frequency band is determined by a conventional method for deployment, and the networking process is completed according to the technical requirements of the low-voltage power line broadband carrier communication system. As in step 1 of fig. 6.

Step 2: each node in the PLC system comprises a site, an agent coordinator and a central coordinator, the spectrum sensing measurement process is carried out, the background noise average power of each frequency band of the PLC system is obtained in the process, and the average of the background noise power of all subcarriers in the frequency band is adopted for representation. As shown in step 2 of fig. 6.

And step 3: and the PLC node reports the average power a _ rx _ subCarrier _ band _ power of the bottom noise subCarrier of each frequency band to the central coordinator by adopting a heartbeat detection message according to a heartbeat detection message reporting period configured by the system. As in step 3 of fig. 6.

And 4, step 4: and the central protocol device collects heartbeat detection messages from each node, and takes out the average power of the background noise of the frequency band reported by each node, and records the average power as a _ rx _ band _ power. Namely, the average calculation is carried out on the average power of the background noise of the frequency band reported by each node, and the average power is used as the result of frequency band interference analysis. As shown in step 4 of fig. 6.

and 5: and selecting a frequency band corresponding to the minimum a _ rx _ band _ power as an optimal working frequency band from results of calculating all frequency bands a _ rx _ band _ power of the PLC system, comparing the a _ rx _ band _ power of the optimal working frequency band with the current working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is less than a threshold bandPowerOffset of the current working frequency band. As shown in step 5 of fig. 6.

Step 6: and the central protocol unit configures the newly selected formal working frequency band to each site according to the requirements of the low-voltage power line broadband carrier communication technical standard, and then each site performs working frequency band replacement according to the requirements of the central coordinator. As shown in steps 6 and 7 of fig. 6.

In order to clearly illustrate the application of the present invention in practical engineering, a specific PLC system implementation network will be described below. The system consists of 9 stations (STA1 to STA 9); 3 proxy coordinators (PCO1 to PCO3) and 1 Central Coordinator (CCO), and the PLC networking is completed as shown in FIG. 2.

According to the requirement of the low-voltage power line broadband carrier communication technical specification (short for technical specification), each station needs to periodically send a discovery list message for acting the station to judge whether the station is active on line. The proxy site sends the site activity information in the locally maintained discovery list to the CCO through a heartbeat detection message with a fixed period so that the CCO can summarize the information whether the sites of the whole network are on line. And sending the heartbeat detection message at least once in a period. In the technical specification, the definition of the existing heartbeat detection message is shown in table 3.

TABLE 3 Heartbeat detection message Format

In the invention, the background noise average power content of the frequency band reported by the site is added in the heartbeat detection message format in the table 3. Modified to the contents of table 4.

TABLE 4 updated heartbeat detection message format

In the invention, the newly added 'average power of noise floor of frequency band' is 4 bytes in length. The first byte represents the average power of the noise floor of frequency band 1; the second byte represents the average power of the noise floor of frequency band 2; the third byte represents the average power of the noise floor of band 3; the fourth byte represents the average power of the noise floor for band 4.

The implementation framework of the present invention in this embodiment is as shown in fig. 7, and in the embodiment, the implementation framework is composed of three functional modules, namely, a site STA and a PCO spectrum detection and reporting module, a central coordinator frequency band interference analysis module, and a central coordinator CCO evaluation selection and configuration module.

The site STA and PCO spectrum detection and reporting module is completed by 9 STA sites and 3 PCO agent coordinators in the embodiment. And each node calculates the average power of the subcarrier background noise of each working frequency band. And then reports the heartbeat detection message to the central coordinator through a table 4.

The central coordinator collects the subcarrier background noise average power of the working frequency band reported by the 9 STA sites and the 3 proxy coordinators in this embodiment, and the subcarrier background noise average power of the working frequency band collected by the central coordinator. And then calculating the average value of the average power of the background noise of each frequency band as the basis for judging the frequency band interference, wherein the larger the calculation result is, the larger the background noise interference is.

The selection and configuration module of the CCO frequency band of the central coordinator is completed by the central coordinator, the central coordinator selects the optimal frequency band according to the average power value of the background noise of each frequency band, in order to avoid that the central coordinator constantly changes the working frequency band, the average power value of the background noise of the optimal working frequency band is required to be lower than a threshold value of the current working frequency band according to the requirement of the invention, and is selected to be 8 in the embodiment. If the working frequency band changes, the central coordinator configures a new working frequency band through the beacon.

In this embodiment, the specific implementation involves two processes.

The first process is as follows: spectrum sensing process of 9 sites and 3 agent coordinators. As shown in fig. 8.

Step 1: each node monitors whether effective frame burst data exists on a PLC line in real time or not by 9 stations and 3 agent coordinators in the PLC system. The nodes firstly carry out AGC adjustment through a power line adapter, adopt 25MHz of the nodes to collect PLC time domain signals by adopting a clock, obtain 1024-point PLC time domain data which are recorded as a _ rx _ time _ data, then receive signal time domain power and carry out a correlation calculation method with a local preamble, detect whether the time domain data are effective frame burst data, and if the time domain data are the frame burst data, start the normal frame burst receiving process of the nodes. If not, spectrum sensing measurement is started. In the process, if the data is valid frame burst data, the data does not participate in the spectrum sensing measurement process. As in step 1 of fig. 8.

Step 2: the receiving end node performs 1024-point Fourier transform (FFT) on the received a _ rx _ time _ data time domain data to obtain 1024 subcarrier frequency domain data, wherein the frequency domain data consists of a real part and an imaginary part and is recorded as a _ rx _ frequency _ data. As shown in step 2 of fig. 8.

And step 3: in the PLC system, there is no up-conversion process, and only the real part is used in the transmission process, so that only 1 to 512 sub-carriers make sense. And (3) extracting the frequency domain information of the first 512 subcarriers from the a _ rx _ frequency _ data, and calculating the subcarrier background noise power of each subcarrier, namely adopting a square sum of a real part and an imaginary part and then adopting a root number calculation method. The result is recorded as a _ rx _ subCarrier _ power. As in step 3 of fig. 8.

a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))

Wherein abs () represents performing a modulo calculation, i.e. representing a power calculation of a subcarrier. i represents a subcarrier number, and ranges from 1 to 512.

And 4, step 4: the a _ rx _ subCarrier _ power and the locally recorded a _ rx _ subCarrier _ average _ power corresponding to the subCarrier background noise average power are subjected to accumulative averaging in many ways, and in this embodiment, an average calculation method is adopted, that is, each subCarrier background noise power recorded by using the a _ rx _ subCarrier _ power and the subCarrier background noise average power recorded in the a _ rx _ subCarrier _ average _ power corresponding to the a _ rx _ subCarrier _ average _ power are added, then an averaging method is taken, and the average power is updated to the a _ rx _ subCarrier _ average _ power variable. As shown in step 4 of fig. 8.

Wherein i represents a subcarrier number, and the value range is 1 to 512.

Remarking: running averages methods popular in the industry may also be employed in calculating the cumulative average.

And 5: and reporting the heartbeat detection message time on the site or the proxy coordinator, calculating the average power of the background noise of each frequency band, and recording as a _ rx _ subCarrier _ band _ power. As shown in step 5 of fig. 8.

Wherein i identifies the subcarrier number, startSubCarrier represents the frequency band start subcarrier number, and enSubCarrier represents the frequency band end subcarrier number. N represents the number of subcarriers in the frequency band.

In the PLC system, as shown in table 1. The system has 4 frequency bands, and the number of the sub-carriers of the frequency band 0 is from 80 to 490; the frequency band 1 sub-carriers are numbered from 100 to 230; the frequency band 2 sub-carriers are numbered from 32 to 120; the band 3 subcarriers are numbered from 72 to 120.

In the step, the average power values of the background noises of 4 frequency bands are respectively calculated and recorded as a _ rx _ subCarrier _ band _ power, the variable is 32 bits, and the first 8 bits records the average power of the background noises of the frequency band 0; recording the average power of the background noise of the frequency band 1 by the second 8 bits; the average power of the background noise of the third 8-bit recording frequency band 2; the fourth 8 bits record the band 3 noise floor average power.

Remarking: in the process, the central coordinator also needs to calculate the average power of the background noise of each frequency band, but does not need to start the reporting process.

And a second process: and (3) carrying out interference analysis and working frequency band configuration process on the central coordinator. As shown in fig. 9.

Step 1: in the first process of PLC system deployment, engineering personnel use a spectrum analysis instrument to analyze the spectrum interference condition of the deployment site, determine a used frequency band for deployment, and then the PLC system completes the networking process according to the technical requirements of the low-voltage power line broadband carrier communication system. As in step 1 of fig. 9.

Step 2: in each node in the PLC system, the node includes 9 sites, 3 agent coordinators and a central coordinator perform a spectrum sensing measurement process, and the process obtains the average power of the background noise of each frequency band of the PLC system, and is represented by an average of all the average powers of the background noise in the frequency band, in the system of this embodiment, 4 frequency bands (frequency band 0, frequency band 1, frequency band 2, and frequency band 3) are summarized, as shown in table 1. As in step 2 of fig. 9.

And 3, step 3: and the PLC node reports the background noise average value a _ rx _ subCarrier _ band _ power of each frequency band to the central coordinator by adopting a heartbeat detection message according to a heartbeat detection message reporting period configured by the system. The content of the heartbeat detection packet used in the present invention is shown in table 4. As in step 3 of fig. 9.

And 4, step 4: and the central protocol device collects heartbeat detection messages from each node, and takes out the frequency band background noise average power reported by each node, and records the frequency band background noise average power as a _ rx _ band _ power. Namely, the average calculation is carried out on the frequency band background noise average power reported by each node, and the average calculation is used as a frequency band interference analysis result. As in step 4 of fig. 9.

Wherein, M represents the number of nodes that the central coordinator collects to complete spectrum sensing, and in this embodiment, the nodes include 9 sites, 3 agent coordinators and one central coordinator; i.e., M-12.

And 5: selecting a frequency band corresponding to the minimum a _ rx _ band _ power as an optimal working frequency band from the calculated results of all frequency bands a _ rx _ band _ power of the PLC system, comparing the a _ rx _ band _ power of the optimal working frequency band with the current working frequency band, and if the optimal working frequency band is smaller than a threshold bandPowerOffset of the current working frequency band, and setting the bandPowerOffset to be 8 in the embodiment, selecting the optimal working frequency band as a formal working frequency band. As shown in step 5 of fig. 9.

In the present invention, bandPowerOffset is used to prevent the central coordinator from "ping-pong" selection between the two available frequency bands, resulting in degraded network performance.

Step 6: the central protocol unit configures the reselected formal working frequency band to each station by adopting a beacon message according to the technical standard requirement of the low-voltage power line broadband carrier communication, specifically participates in the target frequency band in the table 5, and then each station carries out working frequency band replacement according to the requirement of the central coordinator. As shown in steps 6 and 7 of fig. 9.

Table 5 band announcement entry

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.

Claims

1. A method for automatically selecting frequency bands in a PLC system is characterized in that: the method comprises a node frequency spectrum sensing process in the PLC system and an automatic frequency band selection process in the PLC system;

the node frequency spectrum sensing process in the PLC system is as follows;

a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))

wherein i represents a subcarrier number, and the value range is 1 to 512;

the automatic frequency band selection process in the PLC system is as follows: