CN116232499A - Method and system for detecting subcarrier interference in PLC system - Google Patents

Abstract

The invention relates to a method and a system for detecting subcarrier interference in a PLC system, and belongs to the technical field of broadband carrier communication. The system comprises: the system comprises an effective front-end data module, a local front-end data module, a channel estimation module, a channel equalization module, an error vector magnitude calculation module, an error vector magnitude statistics module and a subcarrier interference judgment module; according to the known characteristics of leading symbol receiving and transmitting in power communication, in the power communication process, calculating the condition that subcarriers of leading symbols of frame burst data are interfered, adopting a method of each subcarrier EVM, counting each subcarrier EVM value in continuous multiple frame bursts, then adopting an operation average mode to calculate each subcarrier EVM value, and finally using the EVM value to judge whether the subcarriers are interfered or not. The invention can eliminate the interfered sub-carrier from the OFDM system, and is no longer used for bearing frame control and frame load data.

Description

Method and system for detecting subcarrier interference in PLC system

Technical Field

The invention belongs to the technical field of broadband carrier communication, and relates to a method and a system for detecting subcarrier interference in a broadband carrier (PLC) system of a voltage power line.

Background

The existing electric meter reading mainly has two communication modes, one is to use a power line as a transmission medium for communication, and the other is to use a public ISM frequency band for wireless communication. Both of these approaches can address most meter reading scenarios. However, the initial laying of the power line is mainly used for power transmission, and is not specially used for communication transmission, and various power devices are mounted on the power line, and the power devices can generate noise with various different frequencies and periods, so that the transmission performance of broadband carrier communication is greatly affected. The same problem exists in the wireless meter reading mode, and mainly because the wireless meter reading uses the public frequency bands, whether other systems are in use or not can not be determined on the frequency bands, so that the wireless meter reading performance is reduced.

At present, whether a power line mode or a wireless mode is adopted, an Orthogonal Frequency Division Multiplexing (OFDM) technology is adopted for modulation and transmission, and the OFDM modulation technology divides a broadband carrier frequency into a plurality of subcarriers for use, so that in the data transmission process of an OFDM system, the subcarriers which are interfered in one OFDM bandwidth can be shielded for use, and the influence of the interference on the performance of the whole OFDM system can be eliminated, namely, only the subcarriers which are not interfered are used by the power meter reading system.

As described above, in the electricity meter reading usage scenario, the application scenario is complex, and there is no strict index requirement on the wired or wireless communication medium, so that the interference situation of each electricity meter reading usage scenario is also different. In practical engineering, to shield these interfering subcarriers, a key issue is how to accurately locate which subcarriers are interfered.

Disclosure of Invention

Accordingly, the present invention is directed to a method and system for detecting subcarrier interference in a PLC system, which eliminates the interfered subcarriers from an Orthogonal Frequency Division Multiplexing (OFDM) system, and is no longer used for carrying frame control and frame load data.

In order to achieve the above purpose, the present invention provides the following technical solutions:

scheme 1: a system for detecting subcarrier interference in a PLC system, as shown in fig. 1, the system comprising: the system comprises an effective front-end data module, a local front-end data module, a channel estimation module, a channel equalization module, an error vector magnitude calculation module, an error vector magnitude statistics module and a subcarrier interference judgment module;

the effective front-end data guiding module is used for completing the function of extracting front-end symbol data from frame burst data, namely, a receiving end receives the frame burst data, firstly carries out automatic gain adjustment, time synchronization and frequency synchronization processing, then extracts effective front-end symbol data from the frame burst data, and carries out normalization operation on the frequency domain subcarrier amplitude;

the local preamble data module is used for completing the production process of preamble data in frame burst data, transmitting and receiving known information according to the technical specification of a power line communication system, and generating preamble symbol data which are completely the same as those transmitted by a transmitting end according to standard requirements at a receiving end;

the channel estimation module adopts local leading data and receives first effective leading symbol data to carry out channel estimation in a frequency domain so as to obtain channel response parameters of each subcarrier;

the channel equalization module performs channel equalization on the effective preamble symbol by using the channel response obtained by the channel estimation module, namely performs channel compensation;

the error vector magnitude calculation module is used for completing EVM value calculation of each subcarrier;

the error vector magnitude statistics module only stores a plurality of effective leading symbols when a receiving end receives burst data of one frame, and subcarrier EVM statistics is needed to be carried out in real time to truly reflect the interference condition of subcarriers;

the subcarrier interference judging module is used for representing the interference characteristics of subcarriers by the statistical EVM value of each subcarrier; when the subcarrier statistical EVM value is greater than a threshold, it indicates that the subcarrier cannot be used.

Further, in the error vector magnitude calculation module, the calculation formula of the EVM is:

wherein EVM (k) represents an EVM value of the kth subcarrier; s is S _k Representing data transmitted by the kth subcarrier, R _k (i) Indicating that the kth subcarrier data in the ith preamble symbol in the valid preamble data is received, and N indicates the number of valid preamble symbols.

Further, in the error vector magnitude statistics module, a specific calculation method for performing subcarrier EVM statistics is as follows: assume that the j-1 th frame burst data statistics EVM is recorded as EVM _j-1 (k) Calculating the EVM of the burst data of the current effective frame as EVM (k), and recording the EVM of the burst data statistics of the j frame as EVM _j (k)；

Scheme 2: according to the known characteristics of leading symbol receiving and transmitting in power communication, in the power communication process, the subcarrier receiving interference condition of the leading symbol of frame burst data is calculated, the EVM value of each subcarrier in a plurality of continuous frame bursts is counted by adopting a method of the EVM value of each subcarrier error vector, then the EVM value of each subcarrier is calculated in a running average mode, and finally whether the subcarrier is interfered or not is judged by using the EVM value.

The method specifically comprises the following steps:

step 1: the receiving end receives the burst data of the power line frame, firstly utilizes the preamble symbol data to carry out frame synchronization, frame timing and frequency deviation processing, then takes out complete preamble symbol data from the frame burst, carries out Fast Fourier Transform (FFT) to obtain pilot frequency domain data PilotData _i Wherein i (1, 2,3,.. N; 1.ltoreq.i.ltoreq.N) represents that a valid preamble symbol number is received; as shown in step 1 of fig. 2.

Step 2: according to the technical specifications of a power line communication system (national electric network release 'technical specifications of broadband carrier communication of a power line of low voltage'), a receiving end generates front pilot frequency domain data S which is the same as a transmitting end _k The local preamble data is called; then uses the data and receives the first previous pilot field data PilotData ₁ Channel estimationCalculating to obtain subcarrier channel response H (k); as in step 2 of fig. 2.

H (k) =channel estimation (PilotData) ₁ ,S _k )

Wherein k represents a subcarrier number;

step 3: channel equalization processing is carried out on the residual preamble symbols by utilizing subcarrier channel response H (k), and preamble symbol data R sent by a sending end is estimated _k (i)；

R _k (i)＝PilotData _i (k)*H(k)

Wherein i (i.gtoreq.2) represents that a valid preamble symbol number is received; k denotes a subcarrier number.

Step 4: by R _k (i) And the local front derivative calculates a subcarrier EVM value, which is marked as EVM (k), wherein k represents a subcarrier number; as in step 4 of fig. 2. The EVM calculation formula is:

step 5: each time the receiving end receives an effective frame burst data, an EVM (k) value is calculated, and the statistical EVM value of the j-1 th frame burst is assumed to be EVM _j-1 (k) Then the statistical EVM value of the jth frame burst is EVM _j (k) The method comprises the steps of carrying out a first treatment on the surface of the As shown in step 5 of fig. 2. The calculation formula for the statistical EVM is:

step 6: the receiving end is not used for subcarrier interference judgment in the statistical EVM value of the initial m (m is an integer) frame bursts; when m frame bursts are used for counting that the number of the front derivatives of the EVM reaches L (L is an integer), sub-carrier interference judgment is started; one subcarrier EVM is greater than the decision threshold EVM, indicating that the subcarrier is not available. As shown in step 6 of fig. 2.

The invention has the beneficial effects that:

1) The method for detecting the subcarrier interference does not need to change the frame burst structure or change the signal processing flow of the existing communication system, and is easy to realize.

2) In the power line communication system, interference has certain randomness, and any measuring method has measuring errors, so that whether the interference is received or not cannot be determined by adopting single measurement.

3) Conventionally, EVM is used to evaluate the transmission performance of a transmitter in a communication system, and a receiving end adopts a signal-to-noise ratio (SNR) to evaluate the quality of a received signal, but it is inconvenient to evaluate the SNR of a single subcarrier; the present invention solves this problem.

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 OFDM symbol subcarrier interference detection in a PLC system;

fig. 2 is a flow of OFDM symbol subcarrier interference detection in a PLC system;

FIG. 3 is a block diagram of a receive link in a PLC system;

FIG. 4 is a frame burst structure of a PLC system;

FIG. 5 is a diagram of a preamble block of a PLC system;

fig. 6 is a chart showing the EVM value per subcarrier at 1 frame burst statistics;

fig. 7 is a chart showing the EVM value per subcarrier for 100 frame bursts;

fig. 8 is a QPSK constellation.

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.

Referring to fig. 1 to 8, in the national power grid distribution PLC system, a mechanism for detecting subcarrier interference is not provided, and each manufacturer completes the implementation process according to actual conditions. The invention provides a method for detecting subcarrier interference based on the existing PLC communication system. As particularly shown in fig. 3.

And the normal PLC receiving end does not need an error vector amplitude calculation, error vector amplitude statistics and subcarrier interference judgment module. But still requires a PLC front end receive circuit, PLC time and frequency synchronization processing, PLC frame burst data collection, local front end data production, channel estimation and channel equalization, and frame control and frame load extraction from the frame burst data for parsing.

The following describes in detail how the present invention detects interfering sub-carriers from frame bursts.

In the PLC system, the national power grid issues a PLC technical specification, and a physical layer protocol data unit (abbreviated as PPDU) signal frame structure (frame burst structure) transmitted by the physical layer is shown in fig. 4. The PPDU consists of preamble, frame control and payload data. The preamble is a periodic sequence, and the number of carriers of control and load data of each symbol frame is 512. The type of the symbol guard interval includes a guard interval of frame control, guard intervals of 1 st and 2 nd symbols of payload data, and guard intervals of 3 rd and subsequent symbols of the payload data. Wherein the preamble in the frame burst structure is shown in fig. 5.

The preamble consisted of 10.5 SYNCPs and 2.5 SYNCMs. SYNCP is defined as:

where C is the set of available carriers, here N is 1024.

In addition, the formula of the inverse fast fourier transform (hereinafter referred to as IFFT) is:

taking complex signals

The method can obtain the following steps:

that is, SYNCP may be obtained by taking the real part of the IFFT transformation of X (k), i.e., the preamble symbol is time domain data.

SYNCM＝-SYNCP

Wherein the first 0.5 SYNCPs of the preamble are the latter half of SYNCPs, and the last 0.5 SYNCMs are the former half of SYNCMs. Where X (k) is the frequency domain data of the preamble symbol, in the X (k) calculation

The specification gives a certain phase table, as shown in table 1. />

TABLE 1 leading phase table

This preamble phase table is fixed, and both the transmitting end and the receiving end are already pre-approximated prior to communication, so the receiving end knows the time-domain and frequency-domain specific data used by the preamble transmitted by the transmitting end.

In this embodiment, the specific flow of subcarrier interference in the PLC system is as follows:

step 1: the receiving end receives the burst data of the power line frame, firstly performs frame synchronization, frame timing and frequency deviation processing by utilizing the content of the preamble symbol, and the process is the same as that of the normal receiving end.

Then the complete leading symbol data is taken out from the frame burst, and fast Fourier change (FFT) is carried out to obtain the pilot frequency domain data PilotData _i Wherein i (1, 2,3,) N, N.gtoreq.i.gtoreq.1, indicates receipt of a valid preamble symbol number.

In practical engineering, the receiving end receives the frame burst data, wherein the preamble symbol is also used for the receiving end to complete the automatic gain control and frame head searching processes, so that the number N of the preamble symbols which can be used is less than 12.

Step 2: according to the national power grid release 'technical Specification for broadband Carrier communication of Low Voltage Power line', the receiving end generates front Pilot frequency domain data S identical to the transmitting end _k =x (k), referred to as local preamble data. I.e. generated by the following formula

Wherein, the liquid crystal display device comprises a liquid crystal display device,

table 1 contents provided by reference standards.

Then, using the data and receiving the first preamble symbol data PilotData ₁ And carrying out channel estimation to obtain the channel response H (k) of each subcarrier. There are many channel estimation algorithms, and this embodiment recommends using Minimum Mean Square Error (MMSE) channel estimation.

H(k)＝MMSE(PilotData ₁ ,S _k )

Wherein k represents a subcarrier number; MMSE () means channel estimation using MMSE; mean () means an average calculation operation on elements in brackets; abs () represents a modulo operation on an element in brackets.

Remarks: in actual engineering, a channel estimation method in the normal processing process of a PLC system is adopted, and normalization operation is carried out on H (k).

Step 3: channel equalization processing is carried out on the residual preamble symbols by utilizing subcarrier channel response H (k), and preamble symbol data R sent by a sending end is estimated _k (i)。

R _k (i)＝PilotData _i (k)*H(k)

Wherein i (i.gtoreq.2) represents that a valid preamble symbol number is received; k denotes a subcarrier number.

Remarks: in PilotData data, the first valid preamble symbol received has been used for channel estimation, so R is calculated _k (i) The calculation starts with the receipt of a valid second preamble symbol.

Step 4: by R _k (i) And local preamble data S _k And calculating the EVM value of the subcarrier, namely EVM (k), wherein k represents the subcarrier number, and the receiving end calculates the EVM value of each subcarrier once every time when one frame burst data is received. The EVM calculation formula is:

step 5: each time the receiving end receives an effective frame burst data, an EVM (k) value is calculated, and the statistical EVM value of the j-1 th frame burst is assumed to be EVM _j-1 (k) Then the statistical EVM value of the jth frame burst is EVM _j (k) As shown in step 5 of fig. 2. The calculation formula for counting EVM by adopting the running average method is as follows:

step 6: the receiving end is not used for subcarrier interference decision in the statistical EVM value of the initial m (m is an integer) frame bursts. Subcarrier interference decisions are only initiated when m frame bursts are used to count the number of forward derivatives of EVM up to L (L is an integer). One subcarrier EVM is greater than the decision threshold EVM, which indicates that the subcarrier is not usable, in this embodiment, L is taken as 100 and threshold EVM is 0.7.

In order to verify the effectiveness of the invention, a PLC preamble link is simulated, 4 preamble symbols are adopted, and two modulation modes of quadrature phase shift keying (QPSK for short) and 16 quadrature amplitude modulation (16 QAM for short) are respectively used. Different gaussian white noise is added for 1024 subcarriers, i.e. with signal-to-noise ratio snr=5, 10, 15, 20 gaussian white noise, and fixed noise is added on subcarriers 5, 15 and 1000, wherein the noise amplitude of the added subcarriers 15 and 1000 is smaller than the signal amplitude and the noise sign of the subcarrier 15 is larger than the signal amplitude. The simulation results are shown in fig. 6 and 7.

It can be derived from fig. 6 that the EVM value of each subcarrier is not enough to indicate that the subcarrier is interfered in only one frame burst, but that only the subcarrier numbers 5 and 1000 are clearly recognized that there is significant interference, but that the interference of other subcarriers cannot be evaluated.

The algorithm method provided by the invention is shown in fig. 7. The subcarrier statistical EVM value of 100 frame bursts is counted, and not only is that subcarriers 5, 10 and 1000 are subjected to strong single-carrier interference obviously obtained from fig. 7, but also the statistical EVM value of each subcarrier under the condition that each subcarrier is subjected to white gaussian noise can be estimated according to specific evaluation, and the statistical EVM value of each subcarrier tends to be stable, and can be used for judging the interference evaluation parameters of the subcarriers.

In this embodiment, threshold EVM takes on a value of

If the EVM value of the statistical subcarrier is greater than 0.7, it indicates that the subcarrier is not available. As shown in particular in fig. 8.

In fig. 8, the QPSK constellation is such that the EVM value of the received a-point data is smaller than that of the first quadrant a-point of the coordinates when the transmitting end transmits the data

I.e., threshhold evm is selected to be 0.7, since the analytic signal quality of 16qam,64qam is higher than that of QPSK in actual use, threshhold evm is set to be 0.7 as the decision threshold in this embodiment. If the statistic EVM value of one subcarrier is greater than 0.7, it indicates that the subcarrier is interfered and cannot be used for data transmission normally.

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 (5)

1. A system for detecting subcarrier interference in a PLC system, the system comprising: the system comprises an effective front-end data module, a local front-end data module, a channel estimation module, a channel equalization module, an error vector magnitude calculation module, an error vector magnitude statistics module and a subcarrier interference judgment module;

the effective front-end data guiding module is used for completing the function of extracting front-end symbol data from frame burst data, namely, a receiving end receives the frame burst data, firstly carries out automatic gain adjustment, time synchronization and frequency synchronization processing, then extracts effective front-end symbol data from the frame burst data, and carries out normalization operation on the frequency domain subcarrier amplitude;

the local preamble data module is used for completing the production process of preamble data in frame burst data, transmitting and receiving known information according to the technical specification of a power line communication system, and generating preamble symbol data which are completely the same as those transmitted by a transmitting end according to standard requirements at a receiving end;

the channel estimation module adopts local leading data and receives first effective leading symbol data to carry out channel estimation in a frequency domain so as to obtain channel response parameters of each subcarrier;

the channel equalization module performs channel equalization on the effective preamble symbol by using the channel response obtained by the channel estimation module, namely performs channel compensation;

the error vector magnitude calculation module is used for completing EVM value calculation of each subcarrier;

the error vector magnitude statistics module is used for carrying out subcarrier EVM statistics in real time when a receiving end receives burst data of one frame;

the subcarrier interference judging module is used for representing the interference characteristics of subcarriers by the statistical EVM value of each subcarrier; when the subcarrier statistical EVM value is greater than a threshold, it indicates that the subcarrier cannot be used.

2. The detecting system of subcarrier interference in a PLC system according to claim 1, wherein in the error vector magnitude calculating module, a calculation formula of EVM is:

wherein EVM (k) represents an EVM value of the kth subcarrier; s is S _k Representing data transmitted by the kth subcarrier, R _k (i) Indicating that the kth subcarrier data in the ith preamble symbol in the valid preamble data is received, and N indicates the number of valid preamble symbols.

3. The system for detecting subcarrier interference in a PLC system according to claim 1, wherein the specific calculation method for performing subcarrier EVM statistics in the error vector magnitude statistics module is as follows: assume that the j-1 th frame burst data statistics EVM is recorded as EVM _j-1 (k) Calculating the EVM of the burst data of the current effective frame as EVM (k), and recording the EVM of the burst data statistics of the j frame as EVM _j (k)；

4. The method for detecting the subcarrier interference in the PLC system is characterized by comprising the following steps of:

step 1: the receiving end receives the burst data of the power line frame, firstly utilizes the preamble symbol data to carry out frame synchronization, frame timing and frequency deviation processing, then takes out complete preamble symbol data from the frame burst, carries out fast Fourier change to obtain the preamble domain data PilotData _i Wherein i (1, 2,3,.. N; 1.ltoreq.i.ltoreq.N) represents that a valid preamble symbol number is received;

step 2: according to the technical specification of the power line communication system, the receiving end generates front pilot frequency domain data S which are the same as the transmitting end _k The local preamble data is called; then uses the data and receives the first previous pilot field data PilotData ₁ Performing channel estimation to obtain subcarrier channel response H (k);

h (k) =channel estimation (PilotData) ₁ ,S _k )

Wherein k represents a subcarrier number;

step 3: channel equalization processing is carried out on the residual preamble symbols by utilizing subcarrier channel response H (k), and preamble symbol data R sent by a sending end is estimated _k (i)；

Step 4: by R _k (i) And the local front derivative calculates a subcarrier EVM value, which is marked as EVM (k), wherein k represents a subcarrier number; the EVM calculation formula is:

step 5: each time the receiving end receives an effective frame burst data, an EVM (k) value is calculated, and the statistical EVM value of the j-1 th frame burst is assumed to be EVM _j-1 (k) Then the statistical EVM value of the jth frame burst is EVM _j (k) The method comprises the steps of carrying out a first treatment on the surface of the The calculation formula for the statistical EVM is:

step 6: the receiving end is not used for subcarrier interference judgment in the statistical EVM value of the initial m frame bursts; when m frame bursts are used for counting L front derivative orders of EVM, sub-carrier interference judgment is started; one subcarrier EVM is greater than the decision threshold EVM, indicating that the subcarrier is not available.

5. The method for detecting subcarrier interference in a PLC system as claimed in claim 4, wherein in step 3, the preamble symbol data R transmitted from the transmitting end is estimated _k (i) The calculation formula of (2) is as follows;

R _k (i)＝PilotData _i (k)*H(k)

wherein i (i.gtoreq.2) represents that a valid preamble symbol number is received; k denotes a subcarrier number.

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