CN114826455B - Automatic frequency band selection method in PLC system - Google Patents

Automatic frequency band selection method in PLC system Download PDF

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Publication number
CN114826455B
CN114826455B CN202210492386.7A CN202210492386A CN114826455B CN 114826455 B CN114826455 B CN 114826455B CN 202210492386 A CN202210492386 A CN 202210492386A CN 114826455 B CN114826455 B CN 114826455B
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frequency band
power
subcarrier
plc system
data
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CN114826455A (en
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段红光
刘怡豪
文淳
郑建宏
罗一静
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Chongqing University of Post and Telecommunications
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Chongqing University of Post and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/382—Monitoring; Testing of propagation channels for resource allocation, admission control or handover
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/46—Monitoring; Testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/54—Systems for transmission via power distribution lines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
    • Y02P90/02—Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

The invention relates to a method for automatically selecting a frequency band in a PLC system, and belongs to the field of communication of the Internet of things. The method comprises a node frequency spectrum sensing flow in a PLC system and an automatic frequency band selection flow in the PLC system; the existing PLC system does not provide an automatic frequency band sensing function, an instrument is required to be adopted for independent test each time the frequency band is changed, then a new working frequency band is selected according to the interference condition of the test, and the operation cost of the system is high. The invention does not need to adopt a special detection instrument to carry out interference analysis, but the system is automatically completed. The conventional frequency band interference test is adopted, the interference detection time period is limited, only one analysis of a fixed time period can be performed, the conventional method is adopted, the selection test points are limited, and the interference test of all site positions cannot be supported. The invention can be used for real-time interference analysis and site position test, and supports the real-time frequency band changing process.

Description

Automatic frequency band selection method 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 system.
Background
With the development of the communication industry, the spectrum demand of people is also increasing, and the current independent spectrum allocation mode can not meet the demand of the communication industry. Particularly in the internet of things industry, expensive spectrum use fees cannot be paid, so that many system designs are transferred to the shared spectrum part.
The current low-voltage power line broadband carrier communication system takes a low-voltage power line as a communication medium to realize the communication network of convergence, transmission and interaction of low-voltage power user power consumption information, which mainly adopts an orthogonal frequency division multiplexing technology, uses 2 MHz-12 MHz in frequency bands, and totally supports 4 frequency bands, as shown in a table 1.
Table 1 voltage power line broadband carrier communication frequency band
The physical layer architecture for the broadband carrier communication of the voltage power line is shown in fig. 1.
At the transmitting end, the physical layer receives input from the data link layer, and processes frame control data and payload data respectively using two separate links. After the frame control data is coded 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 the load data and frame control data, cyclic prefix is added to form OFDM symbols after IFFT processing is carried out on the mapped data, and the OFDM symbols are added to form PPDU signals after windowing processing is carried out on the lead symbols, and the PPDU signals are sent to an analog front end and finally sent to a power line channel.
At the receiving end, the data is received from the analog front end, automatic Gain Control (AGC) and time synchronization are adopted in cooperation to respectively adjust frame control and load data, after FFT conversion is carried out on the frame control and load data, the frame control and load data enter a demodulation and decoding module, and finally the original data of frame control information and the original data of load are recovered.
And according to the technical specification, the technical parameters of the OFDM symbol are defined, and the physical layer OFDM symbol is based on the clock sampling rate of 25MHz in the time domain. The data is subjected to 1024-point inverse fourier transform (IFFT) and then takes the real part, 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 Time domain point number 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) uses 1024 points, the subcarrier spacing in the system is 24.414KHz.
In the broadband carrier communication system of the voltage power line, the networking mode adopted is shown in fig. 2. For the electricity consumption information collection system, the broadband carrier communication network generally forms a tree network with CCO as a center and PCO (smart meter/type I collector communication unit, broadband carrier type II collector) as a relay agent, and connects all STAs (smart meter/type I collector communication unit, broadband carrier type II collector) in multistage association, 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 a proxy coordinator.
The central coordinator (central coordinator, abbreviated as CCO) takes charge of completing functions of network control, network maintenance management and the like in a master node role in the communication network, and the corresponding equipment entity is a local communication unit of the concentrator.
The slave node role in the Station (STA) communication network is that the corresponding equipment entity is a communication unit, including an electric energy meter communication unit, an I-type collector communication unit or an II-type collector.
The agent coordinator (proxy coordinator, abbreviated as PCO) is a site for relaying and forwarding data between the central coordinator and the site or between sites, abbreviated as agent.
In the PLC system, data transmission is performed in a frame burst manner, as shown in fig. 3.
The PPDU signal frame structure transmitted by the physical layer is shown as 3. The PPDU consists of preamble, frame control and payload data. The preamble is a periodic sequence, and the number of subcarriers of frame control and payload data of each symbol is 512. The type of the guard interval of the symbol includes the guard interval of frame control, the guard interval of the 1 st and 2 nd symbols of the payload data, the guard interval of the 3 rd symbol of the payload data and the following.
At present, the broadband carrier communication system of the voltage power line does not support a frequency spectrum sensing function and 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 steps:
first: before the deployment of the broadband carrier communication system of the power line of the voltage, the use condition of the wireless frequency bands of 0-12MHz needs to be checked, and the wireless frequency bands are coupled to the power line to interfere with the normal communication of the power line. In practical engineering, an optimal working frequency band cannot be selected in real time all the time due to the change of interference.
Second,: the broadband carrier communication system of the voltage power line is inflexible in use frequency band, and in the deployment process, the working frequency band needs to be preset, and in the use process, automatic configuration is not supported, and only a manual mode can be adopted. Resulting in unstable operation of the voltage power line broadband carrier communication system and high maintenance costs.
For both of these reasons, communication is often unsuccessful in use of the low voltage power line broadband carrier communication system. Communication shows unstable performance, and requires professional to perform field test, and has high maintenance cost.
Disclosure of Invention
In view of the above, the present invention is directed to a method for automatic frequency band selection in a PLC system. The basic principle is that in the process of receiving in real time, if the node in the PLC system does not find that the transmitting end transmits effective frame burst data, the receiving end performs spectrum analysis on the received data, counts the average power of the frequency band background noise, adopts the node period of the PLC system to report heartbeat messages, and periodically reports the average power of the frequency band background noise to the 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 the optimal working frequency band is started. And finally, configuring the selected optimal working frequency band to each node in the PLC system by adopting a frequency band change item in the beacon by the central coordinator.
In order to achieve the above purpose, the present invention provides the following technical solutions:
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 selecting flow in the PLC system;
the node spectrum sensing flow in the PLC system is as follows;
step 11: the node in the PLC system monitors whether effective frame burst data exist on a PLC line in real time, a receiving end node firstly receives 1024-point time domain data, the 1024-point time domain data is recorded as a_rx_time_data, then whether the time domain data is the frame burst data is detected, 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 generated, 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 subcarrier frequency domain data, and recording the data as a_rx_frequency_data;
step 13: the frequency domain information of the first 512 subcarriers is taken out from the a_rx_frequency_data, the bottom noise power value of each subCarrier is calculated, and the bottom noise power value is recorded as a_rx_sub carrier_power;
a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))
wherein abs () represents performing modulo computation; i represents the number of the sub-carrier, and the value range is 1-512;
step 14: accumulating and averaging the subCarrier background noise power corresponding to the a_rx_sub-carrier_power and the locally recorded a_rx_sub-carrier_average_power, and calculating 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 average power of the subCarrier background noise of each frequency band, and marking the average power as a_rx_sub carrier_band_power;
wherein i identifies a subcarrier number, startsub-carrier represents a frequency band start subcarrier number, endsub-carrier represents a frequency band end subcarrier number; n represents the number of subcarriers in the frequency band;
the automatic frequency band selection flow in the PLC system is as follows:
step 21: in the first deployment process of the PLC system, firstly, a conventional method is adopted to determine a used frequency band for deployment, and the networking process is completed according to the technical requirements of a broadband carrier communication system of a voltage power line;
step 22: each node in the PLC system comprises a site, an agent coordinator and a central coordinator for performing a spectrum sensing measurement process, wherein the process obtains the average power of the background noise of each frequency band of the PLC system, and the average power of the background noise of all subcarriers in the frequency band is used for representing;
step 23: the PLC node reports the average power a_rx_sub-carrier wave of the background noise of each frequency band to the central coordinator by adopting a heartbeat detection message according to the heartbeat detection message reporting period configured by the system;
step 24: the central protocol device collects heartbeat detection messages from all nodes, takes out the average background noise power of the frequency band reported by each node, and records the average background noise power as a_rx_band_power; 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 the interference analysis of the frequency band;
wherein M represents the number of nodes which are collected by the central coordinator and finish spectrum sensing;
step 25: selecting a frequency band corresponding to the minimum a_rx_band_power as an optimal working frequency band in the result of calculating all frequency bands a_rx_band_power of the PLC system, comparing the frequency band corresponding to the minimum a_rx_band_power with a current working frequency band by adopting the a_rx_band_power of the optimal working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is smaller than a current working frequency band threshold band PowerOffset;
step 26: the central protocol unit configures the reselected formal working frequency band to each station according to the technical standard requirements of the broadband carrier communication of the low-voltage power line, and then each station performs the replacement of the working frequency band according to the requirements of the central coordinator.
The invention has the beneficial effects that:
first: the existing PLC system does not provide an automatic frequency band sensing function, an instrument is required to be adopted for independent test each time the frequency band is changed, then a new working frequency band is selected according to the interference condition of the test, and the operation cost of the system is high. The invention does not need to adopt a special detection instrument to carry out interference analysis, but the system is automatically completed.
Second,: the conventional frequency band interference test is adopted, the interference detection time period is limited, only one analysis of a fixed time period can be performed, the conventional method is adopted, the selection test points are limited, and the interference test of all site positions cannot be supported. The invention can be used for real-time interference analysis and site position test, and supports the real-time frequency band changing process.
Third,: the invention adds the functions of the invention on the existing system, does not need to upgrade hardware, and can be completed only by upgrading 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 objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.
Drawings
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in the following preferred detail with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of the overall architecture of a physical layer;
fig. 2 is a topology of a broadband carrier communication network;
FIG. 3 is a frame burst structure;
FIG. 4 is a block diagram of automatic frequency band configuration in a PLC system;
FIG. 5 is a node spectrum sensing flow in a PLC system;
FIG. 6 is a flow of automatic frequency band selection in a PLC system;
FIG. 7 is an automatic band selection implementation framework in an embodiment;
FIG. 8 is a flow diagram of site and proxy coordinator spectrum awareness in an embodiment;
fig. 9 is a flowchart of automatic frequency band selection by the central coordinator in the embodiment.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the illustrations provided in the following embodiments merely illustrate the basic idea of the present invention by way of illustration, and the following embodiments and features in the embodiments may be combined with each other without conflict.
Wherein the drawings are for illustrative purposes only and are shown in schematic, non-physical, and not intended to limit the invention; for the purpose of better illustrating embodiments of the invention, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the size of the actual product; it will be appreciated 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 numbers in the drawings of embodiments of the invention correspond to the same or similar components; in the description of the present invention, it should be understood that, if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc., that indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but not for indicating or suggesting that the referred device or element must have a specific azimuth, be constructed and operated in a specific azimuth, so that the terms describing the positional relationship in the drawings are merely for exemplary illustration and should not be construed as limiting the present invention, and that the specific meaning of the above terms may be understood by those of ordinary skill in the art according to the specific circumstances.
The invention is composed of three modules, namely a frequency spectrum detecting and reporting module, a frequency band interference analysis module and a frequency band selection and configuration module. The frequency spectrum detection 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 all the subcarrier background noise in the frequency band, and reports the average power to the central coordinator through the heartbeat detection message. The frequency band interference analysis module is used for completing frequency band base noise average power analysis of all nodes collected by the PLC system, calculating average base noise of each frequency band of the PLC system, and representing by adopting average base noise average power in the frequency band reported by all the nodes. The frequency band selection and configuration module completes the selection of the working frequency band 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: node frequency spectrum sensing flow in the PLC system; and two,: and (3) an automatic frequency band selection flow in the PLC system.
Process one: the node spectrum sensing flow in the PLC system is shown in fig. 5.
Step 1: and a 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, marks the 1024-point time domain data 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, starts a normal frame burst receiving process of the node. If not, a spectrum sensing measurement is initiated. As shown 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 sub-carrier frequency domain data, and records the data as a_rx_frequency_data. As shown in step 2 of fig. 5.
Step 3: the frequency domain information of the first 512 subcarriers is taken out from the a_rx_frequency_data, and the base noise power value of each subCarrier is calculated and recorded as a_rx_sub carrier_power. As shown in step 3 of fig. 5.
a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))
Where abs () represents modulo computation. i represents the subcarrier number and ranges from 1 to 512.
Step 4: and accumulating and averaging the subCarrier background noise power corresponding to the a_rx_subclier_power and the locally recorded a_rx_subclier_average_power, and calculating the subCarrier background noise average power. As shown in step 4 of fig. 5.
a_rx_subCarrier_average_power(i)＝(a_rx_subCarrier_average_power(i)+a_rx_subCarrier_power(i))/2。
Where i represents a subcarrier number and ranges from 1 to 512.
Step 5: the average power of the subCarrier background noise of each frequency band is calculated and is marked as a_rx_sub carrier_band_power. As shown in step 5 of fig. 5.
Wherein i identifies the subcarrier number, startsub-carrier represents the band start subcarrier number, endsub-carrier represents the band end subcarrier number. N represents the number of subcarriers within a frequency band.
And a second process: an automatic frequency band selection flow in the PLC system;
step 1: in the first process of the deployment of the PLC system, a conventional method is adopted to determine a used frequency band for deployment, and the networking process is completed according to the technical requirements of a broadband carrier communication system of a voltage power line. As shown in step 1 of fig. 6.
Step 2: and each node in the PLC system comprises a station, an agent coordinator and a central coordinator for performing a spectrum sensing measurement process, wherein the process obtains the average power of the background noise of each frequency band of the PLC system, and the average power of the background noise of all subcarriers in the frequency band is used for representing. As shown in step 2 in fig. 6.
Step 3: and the PLC node reports the average power a_rx_sub-carrier wave average power a_sub-carrier wave_band_power of the bottom noise of each frequency band to the central coordinator by adopting a heartbeat detection message according to the heartbeat detection message reporting period configured by the system. As shown in step 3 of fig. 6.
Step 4: the central protocol device collects heartbeat detection messages from all nodes, takes out the average background noise power of the frequency band reported by each node, and records the average background noise power as a_rx_band_power. And carrying out average calculation on the average power of the background noise of the frequency band reported by each node, and taking the average power as a result of frequency band interference analysis. As shown in step 4 of fig. 6.
Wherein M represents the number of nodes which are collected by the central coordinator and finish spectrum sensing;
step 5: and selecting a frequency band corresponding to the minimum a_rx_band_power as an optimal working frequency band in the result of calculating all frequency bands a_rx_band_power of the PLC system, comparing the frequency band corresponding to the minimum a_rx_band_power with the current working frequency band by adopting the a_rx_band_power of the optimal working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is smaller than a current working frequency band threshold bandPowerOffset. As shown in step 5 of fig. 6.
Step 6: the central protocol unit configures the reselected formal working frequency band to each station according to the technical standard requirements of the broadband carrier communication of the low-voltage power line, and then each station performs the replacement of the working frequency band 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 will be used to implement a network. The system consists of 9 stations (STA 1 to STA 9); 3 proxy coordinators (PCO 1 to PCO 3) and 1 Central Coordinator (CCO), and after the PLC networking is completed, as shown in fig. 2.
According to the technical specification (short for technical specification) requirements of the broadband carrier communication of the voltage power line, each station needs to periodically send a discovery list message for judging whether the station is active or not by the agent station. And the proxy station transmits the station active information in the locally maintained discovery list to the CCO through a heartbeat detection message with a fixed period so that the CCO gathers information whether the stations of the whole network are online. And sending a heartbeat detection message at least once in the 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 station reporting frequency band is increased in the heartbeat detection message format of the table 3. The modifications are as in table 4.
Table 4 updated heartbeat detection message format
In the invention, the newly added frequency band background noise average power is 4 bytes long. The first byte represents the base noise average power for band 1; the second byte represents the background noise average power of band 2; the third byte represents the base noise average power for band 3; the fourth byte represents the floor noise average power for bin 4.
The implementation framework of the invention in this embodiment is shown in fig. 7, and in the embodiment, the invention is composed of three functional modules, namely a station STA and 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 station STA and the PCO spectrum sensing and reporting module are implemented by 9 STA stations and 3 PCO agent coordinators in the embodiment. And each node calculates the subcarrier background noise average power of each working frequency band. And then reporting the heartbeat detection message to the central coordinator through the heartbeat detection message in the table 4.
The central coordinator frequency band interference analysis module is completed by the central coordinator, and 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 the 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 base noise average power of each frequency band as the basis of the frequency band interference judgment, wherein the larger the calculation result is, the larger the base noise interference is.
The central coordinator CCO frequency band selection and configuration module is completed by the central coordinator, and the central coordinator selects an optimal frequency band according to the base noise average power value of each frequency band, so as to avoid the continuous change of the working frequency band of the central coordinator, and the base noise average power value of the optimal working frequency band is required to be lower than a threshold value of the current working frequency band according to the invention, and is selected to be 8 in the embodiment. If the operating frequency band changes, the central coordinator configures a new operating frequency band through the beacon.
In this embodiment, the specific implementation involves two processes.
Process one: spectrum sensing procedure of 9 sites and 3 proxy coordinators. As shown in fig. 8.
Step 1: 9 stations and 3 proxy coordinators in the PLC system, and each node monitors whether valid frame burst data exists on a PLC line in real time. The nodes firstly carry out AGC adjustment through a power line adapter, 25MHz of the nodes is adopted to acquire PLC time domain signals, 1024-point PLC time domain data are obtained and recorded as a_rx_time_data, then the time domain power of the received signals and a local preamble are subjected to a correlation calculation method, whether the time domain data are valid frame burst data or not is detected, and if the frame burst data are valid frame burst data, a normal frame burst receiving process of the nodes is started. If not, a spectrum sensing measurement is initiated. In this process, if it is valid frame burst data, it does not participate in the spectrum sensing measurement process. As shown 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 sub-carrier 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.
Step 3: in a PLC system, there is no up-conversion process, and only the real part is used in the transmission process, so only 1 to 512 subcarriers are significant. The frequency domain information of the first 512 subcarriers is taken out from the a_rx_frequency_data, and the subcarrier background noise power of each subcarrier is calculated, namely, a square sum of a real part and an imaginary part is adopted, and then a root number calculation method is adopted. The result is recorded as a_rx_sub-carrier_power. As shown in step 3 of fig. 8.
a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))
Where abs () represents modulo computation, i.e. represents the power computation of a subcarrier. i represents the subcarrier number and ranges from 1 to 512.
Step 4: the average power of the sub-carrier background noise corresponding to a_rx_sub-carrier_average power of the local record is accumulated and averaged in a number of ways, in this embodiment, an average calculation method is adopted, that is, each sub-carrier background noise power recorded with a_rx_sub-carrier_power is added to the average power of the sub-carrier background noise corresponding to a_rx_sub-carrier_average power recorded with a_rx_sub-carrier_average power, and then the average method is taken and updated into the a_rx_sub-carrier_average power variable. As in step 4 of fig. 8.
a_rx_subCarrier_average_power(i)＝(a_rx_subCarrier_average_power(i)+a_rx_subCarrier_power(i))/2。
Where i represents a subcarrier number and ranges from 1 to 512.
Remarks: running average methods popular in the industry may also be employed when calculating the cumulative average.
Step 5: and obtaining the time for reporting the heartbeat detection message at the station or the proxy coordinator, calculating the average power of the background noise of each frequency band, and recording the average power as a_rx_sub-carrier_band_power. As shown in fig. 8 at step 5.
Wherein i identifies the subcarrier number, startsub-carrier represents the band start subcarrier number, and ensub-carrier represents the band end subcarrier number. N represents the number of subcarriers within a frequency band.
In the PLC system, as shown in table 1. 4 frequency bands exist in the system, and the subcarrier numbers of the frequency band 0 are from 80 to 490; band 1 subcarriers numbered from 100 to 230; the frequency band 2 subcarrier numbers from 32 to 120; the band 3 subcarriers number from 72 to 120.
In this step, the average power value of the background noise of 4 frequency bands is calculated and is recorded as a_rx_sub-carrier_band_power, the variable is 32 bits, and the first 8 bits record the average power of background noise of frequency band 0; the second 8 bits record the average power of the base noise of the frequency band 1; the third 8 bits record the average power of the 2 background noise of the frequency band; the fourth 8 bits record the band 3 background noise average power.
Remarks: in this process, the central coordinator also needs to calculate the average power of the background noise for each frequency band, but does not need to initiate the reporting process.
And a second process: the central coordinator interferes with the analysis and operating band configuration processes. As shown in fig. 9.
Step 1: in the first deployment process of the PLC system, engineering personnel use a spectrum analysis instrument to analyze the spectrum interference condition of the deployment site in the embodiment, determine a used frequency band for deployment, and then the PLC system completes the networking process according to the technical requirements of the broadband carrier communication system of the low-voltage power line. As shown at step 1 in fig. 9.
Step 2: each node in the PLC system comprises 9 stations, 3 proxy coordinators and a central coordinator for performing a spectrum sensing measurement process, where the process obtains the average power of the background noise of each frequency band of the PLC system, and the average power of all background noise in the frequency band is represented by the average power of all background noise in the frequency band, and 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 shown in step 2 of fig. 9.
Step 3: and the PLC node reports the background noise average value a_rx_sub carrier_band_power of each frequency band to the central coordinator by adopting a heartbeat detection message according to the heartbeat detection message reporting period configured by the system. The load content of the heartbeat detection message used in the invention is shown in table 4. As in step 3 of fig. 9.
Step 4: the central protocol device collects heartbeat detection messages from all nodes, takes out the average power of the frequency band background noise reported by each node, and records the average power as a_rx_band_power. And carrying out average calculation on the average power of the frequency band background noise reported by each node, and taking the average power as a frequency band interference analysis result. As shown at step 4 in fig. 9.
Where M represents the number of nodes that the central coordinator collects to complete spectrum sensing, and in this embodiment, includes 9 sites, 3 proxy coordinators and one central coordinator; i.e. m=12.
Step 5: and selecting a frequency band corresponding to the minimum a_rx_band_power from the calculated results of all frequency bands a_rx_band_power of the PLC system as an optimal working frequency band, comparing the frequency band corresponding to the minimum a_rx_band_power with the current working frequency band by adopting the a_rx_band_power of the optimal working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is smaller than a current working frequency band threshold bandPowerOffset, wherein the bandPowerOffset is set to 8 in the embodiment. As shown at step 5 in fig. 9.
In the present invention, the bandPowerOffset is used to prevent the central coordinator from making a "ping-pong" selection between the two available frequency bands, resulting in reduced 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 requirements of the broadband carrier communication of the low-voltage power line, and specifically participates in the target frequency band in the table 5, and then each station performs the replacement of the working frequency band according to the requirements of the central coordinator. As shown in steps 6 and 7 of fig. 9.
Table 5 band Notification entry
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.

Claims (1)

1. A method for automatically selecting frequency bands in a PLC system is characterized in that: the method comprises a node frequency spectrum sensing flow in a PLC system and an automatic frequency band selection flow in the PLC system;
the node spectrum sensing flow in the PLC system is as follows;
step 11: the node in the PLC system monitors whether effective frame burst data exist on a PLC line in real time, a receiving end node firstly receives 1024-point time domain data, the 1024-point time domain data is recorded as a_rx_time_data, then whether the time domain data is the frame burst data is detected, 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 generated, 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 subcarrier frequency domain data, and recording the data as a_rx_frequency_data;
step 13: the frequency domain information of the first 512 subcarriers is taken out from the a_rx_frequency_data, the bottom noise power value of each subCarrier is calculated, and the bottom noise power value is recorded as a_rx_sub carrier_power;
a_rx_subCarrier_power(i)＝abs(a_rx_frequency_data(i))
wherein abs () represents performing modulo computation; i represents the number of the sub-carrier, and the value range is 1-512;
step 14: accumulating and averaging the subCarrier background noise power corresponding to the a_rx_sub-carrier_power and the locally recorded a_rx_sub-carrier_average_power, and calculating 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 average power of the subCarrier background noise of each frequency band, and marking the average power as a_rx_sub carrier_band_power;
wherein i identifies a subcarrier number, startsub-carrier represents a frequency band start subcarrier number, endsub-carrier represents a frequency band end subcarrier number; n represents the number of subcarriers in the frequency band;
the automatic frequency band selection flow in the PLC system is as follows:
step 21: in the first deployment process of the PLC system, firstly, a conventional method is adopted to determine a used frequency band for deployment, and the networking process is completed according to the technical requirements of a broadband carrier communication system of a voltage power line;
step 22: each node in the PLC system comprises a site, an agent coordinator and a central coordinator for performing a spectrum sensing measurement process, wherein the process obtains the average power of the background noise of each frequency band of the PLC system, and the average power of the background noise of all subcarriers in the frequency band is used for representing;
step 23: the PLC node reports the average power a_rx_sub-carrier wave of the background noise of each frequency band to the central coordinator by adopting a heartbeat detection message according to the heartbeat detection message reporting period configured by the system;
step 24: the central protocol device collects heartbeat detection messages from all nodes, takes out the average background noise power of the frequency band reported by each node, and records the average background noise power as a_rx_band_power; 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 the interference analysis of the frequency band;
wherein M represents the number of nodes which are collected by the central coordinator and finish spectrum sensing;
step 25: selecting a frequency band corresponding to the minimum a_rx_band_power as an optimal working frequency band in the result of calculating all frequency bands a_rx_band_power of the PLC system, comparing the frequency band corresponding to the minimum a_rx_band_power with a current working frequency band by adopting the a_rx_band_power of the optimal working frequency band, and selecting the optimal working frequency band as a formal working frequency band if the optimal working frequency band is smaller than a current working frequency band threshold band PowerOffset;
step 26: the central protocol unit configures the reselected formal working frequency band to each station according to the technical standard requirements of the broadband carrier communication of the low-voltage power line, and then each station performs the replacement of the working frequency band according to the requirements of the central coordinator.
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