CN108736921B - Power line carrier communication preamble detection method for resisting random impulse noise - Google Patents

Power line carrier communication preamble detection method for resisting random impulse noise Download PDF

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CN108736921B
CN108736921B CN201710260656.0A CN201710260656A CN108736921B CN 108736921 B CN108736921 B CN 108736921B CN 201710260656 A CN201710260656 A CN 201710260656A CN 108736921 B CN108736921 B CN 108736921B
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preamble
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李松斌
刘鹏
钟永捷
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Nanhai Research Station Institute Of Acoustics Chinese Academy Of Sciences
Institute of Acoustics CAS
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/54—Systems for transmission via power distribution lines
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B15/00—Suppression or limitation of noise or interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
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    • H04B3/46—Monitoring; Testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
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Abstract

The invention provides a power line carrier communication preamble detection method for resisting random impulse noise, which caches a local preamble sequence segment, performs impulse noise reduction processing on a signal, performs cross-correlation calculation on the locally cached preamble sequence segment and an input signal, performs autocorrelation calculation on the input signal, and substitutes the cross-correlation and autocorrelation calculation results into a normalization decision function; and finally, comparing the set threshold value with the calculation result of the decision function to obtain the detection result of the preamble cyclic sequence unit. Compared with the traditional preamble detection method, the preamble detection method provided by the invention has better robustness to random impulse noise, and the method can not generate an interference peak value at the end of a frame, thereby effectively avoiding the false appearance of another frame signal.

Description

Power line carrier communication preamble detection method for resisting random impulse noise
Technical Field
The invention relates to the field of digital information transmission, in particular to a power line carrier communication preamble detection method for resisting random impulse noise.
Background
With the development of network technology, power line carrier communication has received great attention in applications such as information appliances and building intelligence due to its advantages of wide distribution and low laying cost.
The transmission environment of power line carrier communication is very complex, and in the communication process, random impulse noise greatly interferes a power line carrier communication system due to the characteristic of high power of the random impulse noise, so that the random impulse noise becomes an important factor for hindering the performance of power line communication.
In power carrier communication, a preamble is an important component of a frame structure, and mainly functions include frame detection, symbol synchronization, channel estimation, frequency offset estimation, AGC (automatic gain control), and the like. Therefore, in the power carrier communication process, preamble detection plays a very important role in communication.
The conventional preamble detection method mainly includes: 1. the sequence self-correlation detection algorithm is that when a signal arrives, self-correlation detection is carried out according to the number of leader sequences in leader symbols, and then the frame starting position is determined by judging a threshold value. The method is troublesome in determining the correlation threshold value and poor in robustness to random impulse noise. 2. The delay correlation algorithm introduces energy terms on the basis of a sequence autocorrelation detection algorithm, utilizes the ratio of the energy terms of the correlation terms, namely normalization processing, and then determines a threshold value to determine the frame starting position. Compared with the sequence autocorrelation detection algorithm, the delay correlation algorithm does not need to consider the actual threshold value. However, since the energy window index leads the correlation window, when the energy drops rapidly, the correlation value does not drop rapidly, resulting in a period of interference peaks at the end of the frame, which may cause artifacts in the arrival of another frame.
In view of the above situation, in a complex power line carrier communication environment, it is very important for power line carrier communication to implement stable and reliable data transmission, which is an urgent task for power line carrier communication system design.
Disclosure of Invention
The invention aims to provide a power line carrier communication preamble detection method resisting random impulse noise in order to overcome the influence of the random impulse noise on preamble detection in a low-voltage power line carrier communication system.
In order to achieve the above object, the present invention provides a preamble detection method based on correlation operation between a local preamble sequence and an input signal at a power carrier communication receiving end. The method specifically comprises the following steps:
step 1) locally caching a single leader sequence segment, wherein the leader sequence segment is required to be consistent with the structure of a leader cyclic sequence unit in an input signal;
step 2) determining the position of the input signal interfered by random impulse noise by detecting the amplitude value of the input signal by combining the characteristics of the preamble cyclic sequence unit, and carrying out amplitude limiting processing on the position;
step 3) performing cross-correlation calculation on the locally cached leader sequence fragment and the input signal, performing self-correlation calculation on the input signal, and substituting the cross-correlation and self-correlation calculation results into a normalization decision function;
and 4) comparing the set threshold with the calculation result of the decision function to obtain the detection result of the preamble cyclic sequence unit.
As a further improvement of the above technical solution, the step 2) specifically includes: step 201) calculating the maximum amplitude of the probability distribution of the leader sequence segment locally cached in the step 1), namely the amplitude value with the maximum probability appearing in the leader sequence segment;
step 202) reading the input signal rkAnd checking the input signal rkSetting a threshold value T1 for the amplitude value of each point, and assigning the maximum amplitude value of the probability distribution to the point corresponding to the amplitude value larger than the threshold value T1.
As a further improvement of the above technical solution, the step 3) specifically includes:
step 301) setting a sliding window and receiving an input signal;
step 302) performing cross-correlation calculation on the input signal and the locally cached leader sequence fragment, wherein the calculation formula is as follows:
Figure BDA0001274616920000021
wherein S iskFor locally cached leader sequence fragments, rk+nFor the input signal, N is the length of the leader sequence segment, L is the length of the input signal, N is the nth point in the input signal, k is the kth point in the leader sequence segment, CnCross-correlation calculation results for the nth point;
step 303) the autocorrelation calculation is performed on the input signal, and the calculation formula is expressed as:
Figure BDA0001274616920000022
wherein, PnThe autocorrelation calculation result of the nth point;
step 304) substitutes the results of the calculations of step 302) and step 303) into a normalized decision function expressed as:
Figure BDA0001274616920000023
wherein M isnThe result is calculated for the decision function at the nth point.
As a further improvement of the above technical solution, the step 4) specifically includes:
step 401) setting a threshold value T2, and executing step 402 if the calculation result of the decision function of each point in the input signal is judged to be larger than the threshold value T2);
step 402) continuously judging whether the point greater than the threshold value T2 is the maximum point of the decision function, if not, judging that the point is caused by random pulse noise interference, discarding the calculation result of the decision function corresponding to the point, if so, judging that the detection is finished by one leading cycle sequence unit, and executing step 403 after all leading cycle sequence units in the input signal are detected to be finished);
step 403), setting a threshold value T3, and judging whether the calculation result of the decision function of the point in the input signal is less than the threshold value T3, and then judging that the detection of all the preamble cyclic sequence units in the input signal is finished.
The power line carrier communication preamble detection method for resisting random impulse noise has the advantages that:
compared with the traditional preamble detection method, the preamble detection method provided by the invention has good robustness to random impulse noise, and the method can not generate an interference peak value at the end of a frame, thereby effectively avoiding the false appearance of another frame signal.
Drawings
Fig. 1 is a flowchart of a method for detecting a preamble of power line carrier communication resisting random impulse noise according to the present invention.
Fig. 2 is a diagram of a preamble data format provided in an implementation of the present invention.
Fig. 3 is a simulation result of a normalized decision function without introducing any noise.
Fig. 4 shows a preamble detection simulation result obtained by using a conventional delay correlation algorithm under the condition of introducing random impulse noise.
Fig. 5 is a simulation result obtained by using the preamble detection method of the present invention under the condition of introducing random impulse noise.
Fig. 6 is a simulation result obtained after random pulse suppression and normalization processing are performed by using the preamble detection method of the present invention under the condition of introducing random pulse noise.
Detailed Description
The following describes a preamble detection method for power line carrier communication resisting random impulse noise according to the present invention in detail with reference to the accompanying drawings and embodiments.
As shown in fig. 1, the present invention provides a method for detecting a preamble of power line carrier communication resisting random impulse noise, which comprises the following steps:
step 1) locally caching a single leader sequence segment, wherein the leader sequence segment is required to be consistent with the structure of a leader cyclic sequence unit in an input signal;
step 2) determining the position of the input signal interfered by random impulse noise by detecting the amplitude value of the input signal by combining the characteristics of the preamble cyclic sequence unit, and carrying out amplitude limiting processing on the position;
step 3) performing cross-correlation calculation on the locally cached leader sequence fragment and the input signal, performing self-correlation calculation on the input signal, and substituting the cross-correlation and self-correlation calculation results into a normalization decision function;
and 4) comparing the set threshold with the calculation result of the decision function to obtain the detection result of the preamble cyclic sequence unit.
For a conventional delay correlation algorithm decision function, it is defined as follows:
Figure BDA0001274616920000041
where r is the input signal, L represents the input signal length, j represents the current signal position, CnFor input signal autocorrelationC, PnIs an energy term. From the above formula, PnSubscript leading CnTherefore, when the energy drops rapidly, the correlation value does not drop rapidly, resulting in a period of interference peaks at the end of a frame, which may cause the appearance of an artifact of another frame, i.e., a situation as shown in fig. 4, where a plurality of interference peaks appear. And for continuous input signals, continuous correlation calculation is required, and the calculation amount is increased.
The invention carries out pulse noise reduction processing on the signals by detecting the input signals. Then buffer the local leading cycle sequence segment, set the sliding window, calculate the input signal, not only improve the calculation efficiency, but also can avoid PnSubscript leading CnInterference peaks that result in a period of time at the end of a frame are prevented, which may cause artifacts in the arrival of another frame.
Therefore, compared with the traditional sequence correlation detection method, the method has better anti-noise property. Compared with a delayed correlation algorithm, the method has the advantages that the interference peak value can not appear when the frame is ended, and the false appearance that another frame signal arrives can be effectively avoided.
Example one
Based on the foregoing power line carrier communication preamble detection method, in this example, the specific implementation steps of the preamble detection method specifically include:
step 1) referring to the preamble structure of the power line communication shown in fig. 2, the preamble structure is composed of 10.5 SYNCPs and 2.5 SYNCMs, where SYNCM is-SYNCP. SYNCP is defined as:
Figure BDA0001274616920000042
buffering a single preamble sequence segment S with length N-1024kTo home, SkIs generated by formula (1) for a single standard preamble, which means that a segment is cut from a single preamble cycle sequence SYNCP, the segment of the preamble sequence is combined with the input signal rkThe preamble cyclic sequence unit in (1) is consistent in structure, and the average value of the locally cached preamble sequence segments is calculated to be 2047.
Step 2) reading an input signal, checking the amplitude value of each point in the input signal, setting a threshold value to be 4096, and judging whether the signal amplitude value of each point is larger than the threshold value; and assigning the point corresponding to the amplitude value larger than the threshold value to the maximum amplitude value of the probability distribution.
And 3) setting the length of the sliding window to be N-1024, receiving an input signal, and in order to improve the calculation efficiency, calculating after all data do not need to be cached by setting the sliding window, only the data with the length of N need to be cached, and then calculating each point in a shifting mode.
Step 4) single leader sequence segment S cached locallykAnd an input signal rkAnd performing correlation calculation, wherein the calculation formula is represented as:
Figure BDA0001274616920000051
wherein S iskFor locally cached leader sequence fragments, rk+nFor the input signal, N is the length of the leader sequence segment, L is the length of the input signal, N is the nth point in the input signal, k is the kth point in the leader sequence segment, CnThe cross-correlation calculation result for the nth point.
Step 5) carrying out energy autocorrelation calculation on the input signal, wherein the calculation formula is as follows:
Figure BDA0001274616920000052
wherein, PnIs the result of the autocorrelation calculation for the nth point.
Step 6) normalization processing, substituting the calculation results of the step 4) and the step 5) into the following decision functions:
Figure BDA0001274616920000053
wherein M isnThe result is calculated for the decision function at the nth point.
Step 7) setting a threshold value of 0.9, and judgingBroken MnIf it is greater than the threshold. If M isnIf the input signal is more than 0.9, the next step can be executed.
Step 8) judging the current MnAnd if the position of the corresponding point is the maximum point of the decision function, the detection of the single preamble cycle sequence unit is finished. Combining the leader structure and calculating according to the correlation to obtain a normalized structure MnThe maximum position is at the last bit of a single preamble loop sequence unit and 12 peaks occur. The results shown in fig. 3 are simulation results without introducing any noise. If current M isnIf the position of the corresponding point is not the last bit of the single preamble cycle sequence unit, the result can be considered to be caused by noise interference, and the calculation result of the decision function corresponding to the point is discarded.
Step 9) finally setting a threshold value of 0.1, and judging MnAnd if so, determining that the detection of all the preamble cyclic sequence units in the input signal is finished.
As shown in fig. 5 and 6, the simulation results obtained in the embodiment by using the preamble detection method are shown. Under the condition that the noise reduction processing is not performed, the result of the decision function is as shown in fig. 5, and it can be seen from the figure that the result fluctuation is large, and it is troublesome to determine the threshold of the decision function for serious impulse noise interference. Fig. 6 shows simulation results after impulse noise processing and normalization processing, and compared with fig. 5, the decision function result shown in fig. 6 is smoother and more convenient for determining the decision function threshold.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (2)

1. A power line carrier communication preamble detection method resisting random impulse noise is characterized by comprising the following steps:
step 1) locally caching a single leader sequence segment, wherein the leader sequence segment is required to be consistent with the structure of a leader cyclic sequence unit in an input signal;
step 2) determining the position of the input signal interfered by random impulse noise by detecting the amplitude value of the input signal by combining the characteristics of the preamble cyclic sequence unit, and carrying out amplitude limiting processing on the position;
the step 2) specifically comprises the following steps:
step 201) calculating the maximum amplitude of the probability distribution of the leader sequence segment locally cached in the step 1), namely the amplitude value with the maximum probability appearing in the leader sequence segment;
step 202) reading the input signal rkAnd checking the input signal rkSetting a threshold value T1 for the amplitude value of each point, and assigning the maximum amplitude value of the probability distribution to the point corresponding to the amplitude value greater than the threshold value T1;
step 3) performing cross-correlation calculation on the locally cached leader sequence fragment and the input signal, performing self-correlation calculation on the input signal, and substituting the cross-correlation and self-correlation calculation results into a normalization decision function;
the step 3) specifically comprises the following steps:
step 301) setting a sliding window and receiving an input signal;
step 302) performing cross-correlation calculation on the input signal and the locally cached leader sequence fragment, wherein the calculation formula is as follows:
Figure FDA0002321613780000011
wherein S iskFor locally cached leader sequence fragments, rk+nFor the input signal, N is the length of the leader sequence segment, L is the length of the input signal, N is the nth point in the input signal, k is the kth point in the leader sequence segment, CnCross-correlation calculation results for the nth point;
step 303) the autocorrelation calculation is performed on the input signal, and the calculation formula is expressed as:
Figure FDA0002321613780000012
wherein, PnThe autocorrelation calculation result of the nth point;
step 304) substitutes the results of the calculations of step 302) and step 303) into a normalized decision function expressed as:
Figure FDA0002321613780000021
wherein M isnCalculating a result for the decision function of the nth point;
and 4) comparing the set threshold with the calculation result of the decision function to obtain the detection result of the preamble cyclic sequence unit.
2. The method for detecting a preamble of power line carrier communication resisting random impulse noise according to claim 1, wherein the step 4) specifically includes:
step 401) setting a threshold value T2, and executing step 402 if the calculation result of the decision function of each point in the input signal is judged to be larger than the threshold value T2);
step 402) continuously judging whether the point greater than the threshold value T2 is the maximum point of the decision function, if not, judging that the point is caused by random pulse noise interference, discarding the calculation result of the decision function corresponding to the point, if so, judging that the detection is finished by one leading cycle sequence unit, and executing step 403 after all leading cycle sequence units in the input signal are detected to be finished);
step 403), setting a threshold value T3, and judging whether the calculation result of the decision function of the point in the input signal is less than the threshold value T3, and then judging that the detection of all the preamble cyclic sequence units in the input signal is finished.
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