CN114553339B - Single-channel mixed communication signal interference detection method based on high-order cyclic accumulation - Google Patents
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Abstract
The invention relates to a single-channel mixed communication signal interference detection method based on a high-order cyclic accumulation amount. For narrowband wireless communication systems, co-frequency/adjacent frequency interference exceeding the interference threshold will cause communication disruption. The invention comprises the following steps: generating a plurality of modulation signals, and performing oversampling, shaping filtering and carrier wave modulation processing; mixing a plurality of signals to obtain experimental signals, and defining one of the experimental signals as a desired signal; and adding additive Gaussian white noise to the experimental signal and the expected signal, then performing fourth-order cyclic accumulation amount calculation, setting a judgment threshold after subtraction, and performing discrete spectrum line detection, wherein if the prominent discrete spectrum line exists, the existence of interference is indicated. The method can detect the same-frequency/adjacent-frequency interference of the mixed signal under the condition that the sequence value of the mixed signal is not known and any priori knowledge is not needed, has good anti-noise performance under the signal-to-noise ratio condition required by the subway operation environment, and has high detection accuracy and low calculation complexity.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a single-channel mixed communication signal interference detection method based on high-order cyclic accumulation.
Background
At present, the system and the frequency band used by each type of train-ground wireless communication system of urban rail transit mainly comprise an 800MHz TETRA system, a 2.4GHz Wi-Fi system, a 5.8GHz Wi-Fi system and a 1.8GHz LTE-M system, and are respectively used for train-ground communication services of a wireless cluster dispatching system, a signal CBTC system and a passenger information system. The 2.4G frequency band and the 5.8G frequency band belong to a public frequency band, and are used for bearing rail traffic operation services and then inevitably face interference from external public user equipment at any time. The signal CBTC service of the new line of the urban rail transit is mainly carried by adopting a 1.8GHz LTE-M system, the frequency band belongs to a special shared frequency band, and besides the rail transit, the frequency band can be used in industries such as electric power, airports, heavy-duty railways, petroleum and the like, so that the same-frequency interference risk exists. Meanwhile, the LTE-M system and an operator system in an adjacent frequency band are easy to generate interference, such as a China telecom FDD-LTE system and a China mobile DCS1800 system, so that the base station and the terminal of the LTE-M system are affected.
For narrowband wireless communication systems, co-frequency/adjacent frequency interference exceeding the interference threshold will cause communication disruption. Wi-Fi and LTE-M are broadband wireless communication systems based on OFDM, and service data is carried by a plurality of discrete sub-carriers in a band, so that the interference is random interference and random collision. A lower level of co-channel/adjacent channel interference will result in reduced throughput and, in severe cases, interruption of communication. The subway communication system terminal is mostly single antenna or two antennas, and the interference detection can not be carried out by adopting the traditional array signal processing method, so that the interference detection of single-channel time-frequency overlapping signals is a key technology for guaranteeing the normal operation of the subway communication system, how to improve the interference monitoring capability of the wireless communication system, and how to find a means for effectively detecting the co-frequency/adjacent-frequency interference of the wireless communication becomes a problem to be solved in the engineering field.
Disclosure of Invention
The invention aims to provide a single-channel mixed communication signal interference detection method based on a high-order cyclic accumulation amount, which at least solves the problems of improving the interference monitoring capability of a wireless communication system and effectively detecting the same-frequency/adjacent-frequency interference of wireless communication.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a single-channel mixed communication signal interference detection method based on a high-order cyclic accumulation amount comprises the following steps:
generating a plurality of modulated signals;
oversampling the modulated signal;
shaping and filtering the signal after the oversampling treatment;
carrying out carrier wave modulation processing on the signals after the shaping and filtering processing;
mixing a plurality of signals subjected to the upper carrier modulation processing, wherein the obtained mixed signals are experimental signals, and one of the signals is specified to be a desired signal;
adding additive Gaussian white noise to the experimental signal and the expected signal, and then calculating a fourth-order cycle accumulation amount to obtain the fourth-order cycle accumulation amount of the experimental signal and the fourth-order cycle accumulation amount of the expected signal;
subtracting the fourth-order cyclic accumulation amount of the expected signal from the fourth-order cyclic accumulation amount of the experimental signal to obtain the processed fourth-order cyclic accumulation amount, setting a decision threshold to detect discrete spectral lines of the processed fourth-order cyclic accumulation amount, and if the prominent discrete spectral lines exist, indicating that interference exists.
Further, generating the plurality of modulated signals includes:
for transmitting end single polarity binary bit sequence b n Performing BPSK, QPSK,16QAM and 64QAM modulation to generate corresponding BPSK modulation signals, QPSK modulation signals, 16QAM modulation signals and 64QAM modulation signals;
wherein,,
b n ∈[0,1]
n is the sequence number of the binary data.
Further, the oversampling of the modulated signal includes:
and (3) performing oversampling processing on the BPSK modulation signal, the QPSK modulation signal, the 16QAM modulation signal and the 64QAM modulation signal, wherein the sampling frequency is 19200Hz, and obtaining an oversampling time sequence s (t).
Further, performing shaping filtering processing on the signal after the oversampling processing includes:
and filtering s (t) by adopting a root raised cosine shaping filter with a roll-off coefficient of 0.35 to obtain an output signal u (t).
Further, performing the carrier modulation processing on the signal after the shaping filtering processing includes:
and (3) carrying out upper carrier modulation on the u (t) to obtain a signal x (t) after upper carrier modulation processing, wherein the expression is as follows:
x(t)＝u(t)exp(j2πf c t)
wherein:
f c is the carrier frequency;
j is the imaginary unit;
t is time.
Further, mixing the plurality of signals after the uplink carrier modulation processing, the obtained mixed signal being an experimental signal, and specifying one of the signals as a desired signal includes:
obtaining x based on four modulation signals i (t)，i＝1,2,3,4；
Mixing p of the above materials, wherein p is more than or equal to 1 and less than or equal to 3, and obtaining a mixed signal y (t) serving as an experimental signal;
one of the signals to be mixed is denoted as a desired signal as q (t).
Further, performing fourth-order cycle accumulation amount calculation after adding additive gaussian white noise to the experimental signal and the expected signal, and obtaining the fourth-order cycle accumulation amount of the experimental signal and the fourth-order cycle accumulation amount of the expected signal includes:
adding y (t) to the additive white gaussian noise for fourth-order cycle cumulative calculation, comprising:
adding y (t) into the additive Gaussian white noise to obtain a cyclostationary signal r (t);
wherein:
n (t) is additive white gaussian noise;
the second-order moment, conjugate moment and fourth-order moment of the cyclostationary signal r (t) are respectively:
m r,21 (t,τ)＝E{r(t)r * (t+τ)}
m r,20 (t,τ)＝E{r(t)r(t+τ)}
m r,40 (t,τ)＝E{r(t)r(t+τ 1 )r(t+τ 2 )r(t+τ 3 )}
wherein:
r * (t) is a conjugated sequence of r (t);
τ，τ 1 ，τ 2 ，τ 3 is a fixed time delay;
e { } is the mean operation;
according to the relation between the time-varying moment and the time-varying accumulation amount, for the cyclostationary signal with zero mean value, the second-order time-varying variable and the conjugate time-varying accumulation amount are respectively the same as the second-order time-varying moment and the conjugate time-varying moment, namely
c y,21 (t,τ)＝m y,21 (t,τ),c y,20 (t,τ)＝m y,20 (t,τ)
And the fourth-order time-varying accumulation amount is:
c y,40 (t,τ 1 ,τ 2 ,τ 3 )＝m y,40 (t,τ 1 ,τ 2 ,τ 3 )-m y,20 (t,τ 1 )m y,20 (t+τ 2 ,t+τ 3 )-m y,20 (t,τ 2 )m y,20 (t+τ 1 ,t+τ 3 )-m y,20 (t,τ 3 )m y,20 (t+τ 2 ,t+τ 1 )
the fourth-order cyclic accumulation amount of y (t) is
C y,40 (α,τ 1 ,τ 2 ,τ 3 )＝<c y,40 (t,τ 1 ,τ 2 ,τ 3 )e -j2παt > t
Wherein:
<> t is time averaged;
alpha is the circulation frequency;
adding the desired signal to the additive white gaussian noise, and performing fourth-order cycle cumulative calculation, wherein the method comprises the following steps:
r q (t)＝q(t)+n(t)
r q (t) the fourth-order cycle cumulative amount is:
further, subtracting the fourth-order cyclic accumulation amount of the expected signal from the fourth-order cyclic accumulation amount of the experimental signal to obtain a processed fourth-order cyclic accumulation amount, and setting a decision threshold to perform discrete spectral line detection on the processed fourth-order cyclic accumulation amount includes:
the fourth-order cyclic accumulation amount of the experimental signal is represented by C40_mixed, the fourth-order cyclic accumulation amount of the desired signal is represented by C40_ex, the fourth-order cyclic accumulation amount of the desired signal is subtracted from the fourth-order cyclic accumulation amount of the experimental signal, and the processed fourth-order cyclic accumulation amount, i.e., the cyclic accumulation amount to be detected, is represented by C40_test
C40_test＝C40_mixed-C40_ex
Setting the decision threshold as
δ＝10E{C40_test}+8σ{C40_test}
Wherein:
e is the mean value and sigma is the standard deviation;
definition |C y,40 (α)|/mean|C y,40 I is fourth-order cyclic accumulationThe amount of line protrusion at the cyclic frequency alpha, where mean|C y,40 I is C y,40 And comparing the average value of the amplitude with a set judgment threshold by using the degree of protrusion, and if the degree of protrusion of the spectral line is larger than the judgment threshold, indicating that a discrete spectral line exists at the circulating frequency, namely that interference exists.
Compared with the prior art, the invention has the following beneficial effects:
the method is implemented based on the high-order cyclic accumulation amount, the high-order cyclic accumulation amount is based on the statistical characteristics of signals, the characteristics only need to know the signal sequence value and do not need to know the signal characteristics such as carrier frequency, bandwidth and the like, the method has good suppression capability on additive Gaussian or non-Gaussian white noise in a channel, and the cyclic accumulation amount meets the linear additivity, so that the cyclic accumulation operation on a received signal can well reflect the cyclic characteristics of each source signal, and the purpose of detecting whether the same-frequency/adjacent-frequency interference signal exists in the received signal under the condition that the expected signal characteristics are known is achieved by detecting whether the cyclic accumulation amount amplitude spectrum has prominent discrete spectral lines or not.
The method can detect the same-frequency/adjacent-frequency interference of the mixed signal under the condition that the sequence value of the mixed signal is not known and any priori knowledge is not needed, has good anti-noise performance under the signal-to-noise ratio condition required by the subway operation environment, and has high detection accuracy and low calculation complexity.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other embodiments of the drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of the method of the present invention.
Fig. 2 is a schematic diagram of the amplitude spectrum of a single fourth-order cyclic accumulation of a BPSK modulated signal and a QPSK modulated signal used in the method of the present invention and the fourth-order cyclic accumulation of the mixed signal with respect to the cyclic frequency.
Fig. 3 is a schematic diagram of the amplitude spectrum of a single fourth-order cyclic accumulation amount of a BPSK modulated signal, a QPSK modulated signal, and a 16QAM modulated signal used in the present invention, and a mixed signal fourth-order cyclic accumulation amount with respect to a cyclic frequency.
Fig. 4 is a graph of the amplitude obtained by subtracting the fourth-order cyclic accumulation amount of the desired signal 16QAM from the fourth-order cyclic accumulation amount of the 16qam+qpsk mixed signal used in the present invention.
Fig. 5 is a graph of the amplitude of the fourth-order cyclic accumulation amount of the bpsk+qpsk+16QAM mixed signal used in the present invention minus the fourth-order cyclic accumulation amount of the desired signal 16 QAM.
Fig. 6 is a graph of detection accuracy for interference detection using a single QPSK modulated signal, a 16qam+qpsk mixed signal, and a bpsk+qpsk+16QAM mixed signal, respectively, according to the present invention.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. The drawings illustrate preferred embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It should be noted that like reference numerals and letters refer to like items, and thus once an item is defined in one embodiment, no further definition or explanation thereof is necessary in subsequent embodiments. Furthermore, the terms "comprises," "comprising," and the like, as well as any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements that are expressly listed or inherent to such process, method, article, or apparatus.
It should also be noted that although the order of steps is referred to in the method description, in some cases it may be performed in a different order than here, and should not be construed as limiting the order of steps.
As shown in fig. 1, a wireless communication system includes a signal transmitter, a wireless channel, and a signal receiver. The signal transmitter carries out MPSK or MQAM modulation on the digital binary information, and then modulates the modulated signal onto a high-frequency carrier wave through the radio frequency module and transmits the modulated signal by using an antenna. The transmitted signal is received by a signal receiver through a wireless channel, the received signal is subjected to fourth-order cyclic accumulation processing to obtain an amplitude spectrum about cyclic frequency, the amplitude spectrum is subjected to prominent spectral line detection, and whether an interference signal exists or not can be known according to the detection result.
Through theoretical analysis of the fourth-order cyclic accumulation, its magnitude spectrum with respect to cyclic frequency is non-zero at 4fc and 4fc±k fb, k=0, 1,2. In the non-zero values, the amplitude value at 4fc is the maximum value and the amplitude value at 4fc±fb is the next largest value. And the fourth-order cyclic accumulation amount has linear additivity, so that the fourth-order cyclic accumulation amount of the sum signal after a plurality of signals are mixed is equal to the sum of the fourth-order cyclic accumulation amounts of the single signals. Further, the cyclic accumulation amount of additive gaussian or non-gaussian white noise higher than the third order is zero.
According to the above properties, the fourth-order cyclic cumulative magnitude of the mixed signal is subtracted from the fourth-order cyclic cumulative magnitude of the expected signal, the result is subjected to discrete spectrum line number detection, and if the detection result is not zero, the same frequency/adjacent frequency interference is indicated.
Fig. 3 is an amplitude spectrum diagram of a four-order cyclic accumulation amount of a single signal of a BPSK modulated signal, a QPSK modulated signal and a 16QAM modulated signal, and a signal-to-noise ratio of 10dB, which is used in the method of the present invention, with respect to a cyclic frequency. It can be seen from fig. 3 that the fourth-order cyclic accumulation of the mixed signal satisfies the theoretical analysis, providing theoretical support for the present invention. The four-order cyclic cumulative magnitude spectra of any other three mixed signals are equivalent to those of fig. 3.
Based on the principle, the invention provides a single-channel mixed communication signal interference detection method based on a high-order cyclic accumulation amount, which comprises the following steps:
s1: a plurality of modulated signals are generated.
For transmitting end single polarity binary bit sequence b n Performing BPSK, QPSK,16QAM and 64QAM modulation to generate corresponding BPSK modulation signals, QPSK modulation signals, 16QAM modulation signals and 64QAM modulation signals;
wherein,,
b n ∈[0,1]
n is the sequence number of the binary data.
S2: and carrying out oversampling processing on the modulated signal.
And (3) performing oversampling processing on the BPSK modulation signal, the QPSK modulation signal, the 16QAM modulation signal and the 64QAM modulation signal, wherein the sampling frequency is 19200Hz, and obtaining an oversampling time sequence s (t).
S3: and performing shaping filtering processing on the signal after the oversampling processing.
And filtering s (t) by adopting a root raised cosine shaping filter with a roll-off coefficient of 0.35 to obtain an output signal u (t).
S4: and carrying out the upper carrier modulation processing on the signal after the shaping filtering processing.
And (3) carrying out upper carrier modulation on the u (t) to obtain a signal x (t) after upper carrier modulation processing, wherein the expression is as follows:
x(t)＝u(t)exp(j2πf c t)
wherein:
f c is the carrier frequency;
j is the imaginary unit;
t is time.
S5: and mixing the plurality of signals subjected to the uplink carrier modulation processing, wherein the obtained mixed signal is an experimental signal, and one signal is specified as a desired signal.
Obtaining x based on four modulation signals i (t)，i＝1,2,3,4；
Mixing p of the above materials, wherein p is more than or equal to 1 and less than or equal to 3, and obtaining a mixed signal y (t) serving as an experimental signal;
one of the mixed signals is denoted as q (t) as a desired signal.
S6: and adding additive Gaussian white noise to the experimental signal and the expected signal, and then performing fourth-order cycle accumulation calculation to obtain the fourth-order cycle accumulation of the experimental signal and the fourth-order cycle accumulation of the expected signal.
Adding y (t) to the additive white gaussian noise for fourth-order cycle cumulative calculation, comprising:
adding y (t) into the additive Gaussian white noise to obtain a cyclostationary signal y (t);
adding y (t) into the additive Gaussian white noise to obtain a cyclostationary signal r (t);
wherein:
n (t) is additive white gaussian noise;
the second-order moment, conjugate moment and fourth-order moment of the cyclostationary signal r (t) are respectively:
m r,21 (t,τ)＝E{r(t)r * (t+τ)}
m r,20 (t,τ)＝E{r(t)r(t+τ)}
m r,40 (t,τ)＝E{r(t)r(t+τ 1 )r(t+τ 2 )r(t+τ 3 )}
wherein:
r * (t) is a conjugated sequence of r (t);
τ，τ 1 ，τ 2 ，τ 3 is a fixed time delay;
e { } is the mean operation.
According to the relation between the time-varying moment and the time-varying accumulation amount, for the cyclostationary signal with zero mean value, the second-order time-varying variable and the conjugate time-varying accumulation amount are respectively the same as the second-order time-varying moment and the conjugate time-varying moment, namely
c y,21 (t,τ)＝m y,21 (t,τ),c y,20 (t,τ)＝m y,20 (t,τ)
And the fourth-order time-varying accumulation amount is:
c y,40 (t,τ 1 ,τ 2 ,τ 3 )＝m y,40 (t,τ 1 ,τ 2 ,τ 3 )-m y,20 (t,τ 1 )m y,20 (t+τ 2 ,t+τ 3 )-m y,20 (t,τ 2 )m y,20 (t+τ 1 ,t+τ 3 )-m y,20 (t,τ 3 )m y,20 (t+τ 2 ,t+τ 1 )
the fourth-order cyclic accumulation amount of y (t) is
C y,40 (α,τ 1 ,τ 2 ,τ 3 )＝<c y,40 (t,τ 1 ,τ 2 ,τ 3 )e -j2παt > t
Wherein:
<> t is time averaged;
alpha is the circulation frequency;
adding the desired signal to the additive white gaussian noise, and performing fourth-order cycle cumulative calculation, wherein the method comprises the following steps:
r q (t)＝q(t)+n(t)
r q (t) the fourth-order cycle cumulative amount is:
s7: subtracting the fourth-order cyclic accumulation amount of the expected signal from the fourth-order cyclic accumulation amount of the experimental signal to obtain the processed fourth-order cyclic accumulation amount, setting a decision threshold to detect discrete spectral lines of the processed fourth-order cyclic accumulation amount, and if the prominent discrete spectral lines exist, indicating that interference exists.
The fourth-order cyclic accumulation amount of the experimental signal is represented by C40_mixed, the fourth-order cyclic accumulation amount of the desired signal is represented by C40_ex, the fourth-order cyclic accumulation amount of the desired signal is subtracted from the fourth-order cyclic accumulation amount of the experimental signal, and the processed fourth-order cyclic accumulation amount, i.e., the cyclic accumulation amount to be detected, is represented by C40_test
C40_test＝C40_mixed-C40_ex
Setting the decision threshold as
δ＝10E{C40_test}+8σ{C40_test}
Wherein:
e is the mean value and sigma is the standard deviation;
definition |C y,40 (α)|/mean|C y,40 I is the degree of protrusion of the line at the cycle frequency alpha of the fourth-order cyclic accumulation, where mean|C y,40 I is C y,40 And comparing the average value of the amplitude with a set judgment threshold by using the degree of protrusion, and if the degree of protrusion of the spectral line is larger than the judgment threshold, indicating that a discrete spectral line exists at the circulating frequency, namely that interference exists.
In the detection, firstly detecting the highest spectral line, if the protruding degree of the highest spectral line is larger than a judgment threshold, indicating that interference exists, setting the spectral line to zero, and detecting the next highest spectral line until the protruding degree of the highest spectral line is smaller than the judgment threshold, and ending the spectral line detection process. If the number of the prominent spectrum lines in the detection result is 0, the interference is not caused; otherwise, the number of the prominent spectral lines is the number of the interference signals.
The invention utilizes the statistical characteristics of MPSK and MQAM modulation signals to calculate the fourth-order cyclic accumulation amount of the mixed signal, does not need any prior information except signal sequences, and detects the same frequency/adjacent frequency interference. Under the condition that the signal-to-noise ratio is greater than 6dB, the detection accuracy can reach 100%, the noise immunity is excellent, and the calculation complexity is low.
The accuracy of the invention is verified by simulation tests as follows:
in order to better show the simulation experiment result of the single-channel time-frequency overlapping signal interference detection method based on the fourth-order cyclic accumulation amount, the simulation parameters are set as follows: the sampling frequency is 19200Hz; carrier frequencies are 160 Hz,1000Hz and 1800Hz respectively; symbol rates are 1200baud,1600baud,1920baud, respectively; the data length is 30720 bytes; the roll-off coefficient of the root raised cosine filter is 0.35; the signal-to-noise ratio is from 6dB to 20dB, the step length is 2dB, the interference detection simulation verification under different signal-to-noise ratios is carried out, each signal-to-noise ratio is subjected to 100 Monte Carlo tests, and the interference detection accuracy is taken as a judgment standard.
Experiment one: simulation experiment verification of single signal interference detection
QPSK modulated signals are generated at a carrier frequency of 1600Hz, a symbol rate of 1200 Baud. A single QPSK signal is used as an experimental mix signal, while the generated QPSK signal is used as a desired signal. The four-order cycle cumulative amounts are calculated respectively, C40_test is obtained by subtracting C40_ex from C40_mixed, the C40_test is subjected to the prominent spectral line detection, the interference detection accuracy is as shown in FIG. 6, and the accuracy is 100%. According to the interference detection accuracy of fig. 6, it can be illustrated that the method of the present invention is feasible for detecting whether an interference signal exists, and the accuracy can reach 100% under different signal to noise ratios, and the noise immunity is excellent.
The carrier frequency 1600Hz and the code element rate 1200Baud are used for respectively generating BPSK,16QAM and 64QAM modulation signals, the single signal is used as a mixed signal, the single signal is used as an expected signal for carrying out interference detection simulation experiments, the interference detection accuracy can reach 100%, and the simulation result is ideal.
Experiment II: simulation experiment verification of two-signal mixed interference detection
BPSK, QPSK,16QAM,64QAM signals are generated at carrier frequencies of 1200 Hz and 1000Hz, respectively, and symbol rates of 1200Baud and 1600Baud, respectively. The sum of any two signals is a mixed signal, one signal is an expected signal, and an interference detection simulation experiment is carried out. Fig. 4 is a graph of c40_test amplitude at a signal-to-noise ratio of 10dB with 16QAM as the desired signal mixed with QPSK signals, and detection of the maximum of the spectral lines in the graph, i.e., the presence of a prominent one of the spectral lines, indicates the presence of an interfering signal in the mixed signal. 100 simulation experiments are carried out, the interference detection result is shown in fig. 6, and the accuracy is 100%. Fig. 4 is a graph of the amplitude obtained by subtracting the fourth-order cyclic accumulation amount of the desired signal 16QAM from the fourth-order cyclic accumulation amount of the 16QAM and QPSK mixed signal used in the present invention, and the maximum value of the spectral line in the graph is detected, that is, it is confirmed that there is interference.
In the subsequent experiments, the accuracy of interference detection can reach 100% under the condition that the signal-to-noise ratio is 6dB to 20dB and the step length is 2dB after any two signals are mixed. The result shows that the method has high interference detection accuracy and good stability for the mixing of two signals.
Experiment III: simulation experiment verification of three-signal mixed interference detection
BPSK, QPSK,16QAM,64QAM signals are generated at carrier frequencies of 1200 Hz,1000Hz, and 630 Hz, respectively, and symbol rates of 1200Baud, and 1920Baud, respectively. Any three signals are added to form a mixed signal, wherein any one signal is a known expected signal, and the same-frequency interference detection simulation experiment is carried out. Fig. 5 is a graph of c40_test amplitude at a signal-to-noise ratio of 10dB for a desired signal 16QAM mixed with bpsk+qpsk+16QAM signals, and the maximum and next largest of the spectral lines in the graph, i.e., the two line graphs that are prominent, are detected, indicating that two interfering signals are present. 100 simulation experiments are carried out, the interference detection result is shown in fig. 6, and the accuracy is 100%. Fig. 5 is a graph of the magnitudes of the fourth-order cyclic accumulation of the BPSK, QPSK and 16QAM mixed signals minus the fourth-order cyclic accumulation of the 16QAM desired signal used in the present invention, and the maxima and second-most values of the spectral lines in the graph are detected, i.e., the presence of interference is demonstrated.
In the subsequent experiments, the interference detection simulation experiments are carried out under the conditions that the signal-to-noise ratio is 6dB to 20dB and the step length is 2dB after any three signals are mixed, and the interference detection accuracy can reach 100%.
Comparing the experimental results, the method has higher accuracy rate for detecting the interference signals of the single-channel time-frequency overlapped signals, has stronger stability and robustness under different signal-to-noise ratios, can be suitable for an LTE-M system in subway train-ground wireless communication to improve the wireless signal monitoring capability of the system, detects whether the same-frequency/adjacent-frequency interference exists, and timely performs interference early warning according to the result.
The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be limiting. Several simple deductions, modifications or substitutions may also be made by a person skilled in the art to which the invention pertains, based on the idea of the invention.
Claims (8)
1. A single-channel mixed communication signal interference detection method based on a high-order cyclic accumulation amount is characterized by comprising the following steps of:
the method comprises the following steps:
generating a plurality of modulated signals;
oversampling the modulated signal;
shaping and filtering the signal after the oversampling treatment;
carrying out carrier wave modulation processing on the signals after the shaping and filtering processing;
mixing a plurality of signals subjected to the upper carrier modulation processing, wherein the obtained mixed signals are experimental signals, and one of the signals is specified to be a desired signal;
adding additive Gaussian white noise to the experimental signal and the expected signal, and then calculating a fourth-order cycle accumulation amount to obtain the fourth-order cycle accumulation amount of the experimental signal and the fourth-order cycle accumulation amount of the expected signal;
subtracting the fourth-order cyclic accumulation amount of the expected signal from the fourth-order cyclic accumulation amount of the experimental signal to obtain the processed fourth-order cyclic accumulation amount, setting a decision threshold to detect discrete spectral lines of the processed fourth-order cyclic accumulation amount, and if the prominent discrete spectral lines exist, indicating that interference exists.
2. The method according to claim 1, characterized in that:
generating the plurality of modulated signals includes:
for transmitting end single polarity binary bit sequence b n Performing BPSK, QPSK,16QAM and 64QAM modulation to generate corresponding BPSK modulation signals, QPSK modulation signals, 16QAM modulation signals and 64QAM modulation signals;
wherein,,
b n ∈[0,1]
n is the sequence number of the binary data.
3. The method according to claim 2, characterized in that:
the oversampling of the modulated signal includes:
and (3) performing oversampling processing on the BPSK modulation signal, the QPSK modulation signal, the 16QAM modulation signal and the 64QAM modulation signal, wherein the sampling frequency is 19200Hz, and obtaining an oversampling time sequence s (t).
4. A method according to claim 3, characterized in that:
the shaping and filtering processing of the signal after the oversampling processing comprises:
and filtering s (t) by adopting a root raised cosine shaping filter with a roll-off coefficient of 0.35 to obtain an output signal u (t).
5. The method according to claim 4, wherein:
the performing the carrier wave modulation processing on the signal after the shaping and filtering processing includes:
and (3) carrying out upper carrier modulation on the u (t) to obtain a signal x (t) after upper carrier modulation processing, wherein the expression is as follows:
x(t)＝u(t)exp(j2πf c t)
wherein:
f c is the carrier frequency;
j is the imaginary unit;
t is time.
6. The method according to claim 5, wherein:
mixing the plurality of signals after the uplink carrier modulation processing, wherein the obtained mixed signal is an experimental signal, and the provision that one of the signals is a desired signal comprises:
obtaining x based on four modulation signals i (t)，i＝1,2,3,4；
Mixing p of the above materials, wherein p is more than or equal to 1 and less than or equal to 3, and obtaining a mixed signal y (t) serving as an experimental signal;
one of the signals to be mixed is denoted as a desired signal as q (t).
7. The method according to claim 6, wherein:
adding additive Gaussian white noise to the experimental signal and the expected signal, and then performing fourth-order cycle accumulation calculation to obtain the fourth-order cycle accumulation of the experimental signal and the fourth-order cycle accumulation of the expected signal, wherein the method comprises the following steps:
adding y (t) to the additive white gaussian noise for fourth-order cycle cumulative calculation, comprising:
adding y (t) into the additive Gaussian white noise to obtain a cyclostationary signal r (t);
wherein:
n (t) is additive white gaussian noise;
the second-order moment, conjugate moment and fourth-order moment of the cyclostationary signal r (t) are respectively:
m r,21 (t,τ)＝E{r(t)r * (t+τ)}
m r,20 (t,τ)＝E{r(t)r(t+τ)}
m r,40 (t,τ)＝E{r(t)r(t+τ 1 )r(t+τ 2 )r(t+τ 3 )}
wherein:
r * (t) is a conjugated sequence of r (t);
τ，τ 1 ，τ 2 ，τ 3 is a fixed time delay;
e { } is the mean operation;
according to the relation between the time-varying moment and the time-varying accumulation amount, for the cyclostationary signal with zero mean value, the second-order time-varying variable and the conjugate time-varying accumulation amount are respectively the same as the second-order time-varying moment and the conjugate time-varying moment, namely
c y,21 (t,τ)＝m y,21 (t,τ),c y,20 (t,τ)＝m y,20 (t,τ)
And the fourth-order time-varying accumulation amount is:
c y,40 (t,τ 1 ,τ 2 ,τ 3 )＝m y,40 (t,τ 1 ,τ 2 ,τ 3 )-m y,20 (t,τ 1 )m y,20 (t+τ 2 ,t+τ 3 )-m y,20 (t,τ 2 )m y,20 (t+τ 1 ,t+τ 3 )-m y,20 (t,τ 3 )m y,20 (t+τ 2 ,t+τ 1 )
the fourth-order cyclic accumulation amount of y (t) is
C y,40 (α,τ 1 ,τ 2 ,τ 3 )＝<c y,40 (t,τ 1 ,τ 2 ,τ 3 )e -j2παt > t
Wherein:
<> t is time averaged;
alpha is the circulation frequency;
adding the desired signal to the additive white gaussian noise, and performing fourth-order cycle cumulative calculation, wherein the method comprises the following steps:
r q (t)＝q(t)+n(t)
r q (t) the fourth-order cycle cumulative amount is:
8. the method according to claim 7, wherein:
subtracting the fourth-order cyclic accumulation amount of the expected signal from the fourth-order cyclic accumulation amount of the experimental signal to obtain a processed fourth-order cyclic accumulation amount, and setting a decision threshold to perform discrete spectrum line detection on the processed fourth-order cyclic accumulation amount comprises:
the fourth-order cyclic accumulation amount of the experimental signal is represented by C40_mixed, the fourth-order cyclic accumulation amount of the desired signal is represented by C40_ex, the fourth-order cyclic accumulation amount of the desired signal is subtracted from the fourth-order cyclic accumulation amount of the experimental signal, and the processed fourth-order cyclic accumulation amount, i.e., the cyclic accumulation amount to be detected, is represented by C40_test
C40_test＝C40_mixed-C40_ex
Setting the decision threshold as
δ＝10E{C40_test}+8σ{C40_test}
Wherein:
e is the mean value and sigma is the standard deviation;
definition |C y,40 (α)|/mean|C y,40 I is the degree of protrusion of the line at the cycle frequency alpha of the fourth-order cyclic accumulation, where mean|C y,40 I is C y,40 And comparing the average value of the amplitude with a set judgment threshold by using the degree of protrusion, and if the degree of protrusion of the spectral line is larger than the judgment threshold, indicating that a discrete spectral line exists at the circulating frequency, namely that interference exists.
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| CN110557209A (en) * | 2019-07-19 | 2019-12-10 | 中国科学院微电子研究所 | Broadband signal interference monitoring method |
| CN112347871A (en) * | 2020-10-23 | 2021-02-09 | 中国电子科技集团公司第七研究所 | Interference signal modulation identification method for communication carrier monitoring system |
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