CN116017486A - Frequency spectrum scanning method based on frequency domain accumulation - Google Patents
Frequency spectrum scanning method based on frequency domain accumulation Download PDFInfo
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- CN116017486A CN116017486A CN202211406529.4A CN202211406529A CN116017486A CN 116017486 A CN116017486 A CN 116017486A CN 202211406529 A CN202211406529 A CN 202211406529A CN 116017486 A CN116017486 A CN 116017486A
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Abstract
The invention relates to a frequency spectrum scanning method based on frequency domain accumulation, which belongs to the technical field of wireless communication, and along with the development of wireless communication technology, communication means are more and more abundant, but frequency spectrum resources used for communication are also more and more tense. In order to alleviate the above problem, it becomes necessary to find available communication frequency points within a certain bandwidth, such as short wave communication or very low limit communication. The traditional spectrum scanning method mostly adopts a pseudo-random sequence sliding correlation method, but the method has more limitations. The method based on frequency domain accumulation provided by the invention has the advantages of simple principle, convenience in implementation and small limitation.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a frequency spectrum scanning method based on frequency domain accumulation.
Background
With the development of wireless communication technology, communication means are becoming more and more abundant, but spectrum resources used by communication are also becoming more and more intense. In order to alleviate the above problem, it becomes necessary to find available communication frequency points within a certain bandwidth, such as short wave communication or very low limit communication. The traditional spectrum scanning method mostly adopts a pseudo-random sequence sliding correlation method, but the method has more limitations.
Disclosure of Invention
The invention aims to provide a frequency spectrum scanning method based on frequency domain accumulation, which is used for solving the technical problems in the prior art, the frequency spectrum resources used for communication are more and more tense, and the searching of available communication frequency points in a certain bandwidth becomes necessary, such as short-wave communication or extremely low-limit communication; the traditional spectrum scanning method mostly adopts a pseudo-random sequence sliding correlation method, but the method has more limitations.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a frequency spectrum scanning method based on frequency domain accumulation comprises the following steps:
s1, setting a reasonable symbol period according to the specific situation of a communication system;
s2, designing a frequency point interval delta f and a processing bandwidth W, wherein the total scanning is required in the bandwidth W
Frequency points;
s3, designing a repeated transmission frame period N;
s4, carrying out N on the data acquired by the receiver fft Fourier transform of the points; the frequency resolution is required to satisfy F s /N fft Delta f, namely ensuring that a plurality of frequency domain sample points exist for accumulation and use in the frequency point interval;
s5, calculating a ratio xi;
s6, sliding window judgment is carried out on the comparison value xi, and the most frequency points which exceed the threshold and fall in the appointed delta f interval are selected as the basis for judging the carrier frequency points of the transmitting end;
s7, setting a fixed scanning mode at the transmitting end, and matching the detected frequency point with the scanning rule of the transmitting end at the receiving end.
Further, a reasonable symbol period in step S1 means that the signal satisfies frequency selective fading in the frequency domain.
Further, in step S3, let x (t) represent the transmitted signal, one branch y of the receiving end 1 (t) is expressed as
y 1 (t)＝x(t)+n 1 (t) (1)
Another branch y 2 (t) is expressed as
y 2 (t)＝x(t)+n 2 (t) (2)
Wherein n is 1 (t)、n 2 (t) represents gaussian white noise with a mean of 0 and a variance of 1; order the
y(t)＝y 1 (t)+y 2 (t)＝2x(t)+n 1 (t)+n 2 (t) (3)
Performing Fourier transform on the formula (1) and the formula (2) respectively
Y 1 (ω)＝X(ω)+N 1 (ω) (4)
Y 2 (ω)＝X(ω)+N 2 (ω) (5)
Wherein Y is 1 (ω)、N 1 (ω)、Y 2 (omega) and N 2 (ω) represents y respectively 1 (t)、n 1 (t)、y 2 (t) and n 2 Fourier transform of (t), X (ω) represents fourier transform of X (t), and equal gain combining equation (4) and equation (5) in the frequency domain
Y(ω)＝Y 1 (ω)+Y 2 (ω)＝2X(ω)+N 2 (ω)+N 1 (ω) (6)；
The carrier wave is scanned and sent by a transmitting end, and the carrier wave is extracted by a receiving end through frequency accumulation according to the combination gain of the formula (6);
the transmitted frames are identical, and the signal is received in the same frame period from the time when the signal is sampled by the receiver, so as to obtain a repeated transmission frame period N.
Further, the step S5 specifically includes:
according to the time delay characteristics of Fourier transformation, i.e.
The time delay difference of the signal received by the receiver relative to the transmitter can be known, and according to the formula (7), the phase error caused by the receiving and transmitting time delay difference is eliminated through the modulo operation;
according to the analysis, let
Wherein the method comprises the steps of
Representing the fourier transform of the receiver samples into the ith signal frame containing a delay difference relative to the transmitted signal, equation (8) can be expressed as follows according to equation (7)
Wherein Y is i (ω) represents the fourier transform of the ith signal frame transmitted by the transmitter.
Further, in combination with formulas (4), (5) and (6), formula (9) can be written as
According to the absolute value inequality |a+b| is less than or equal to |a|+|b|, there are
Then equation (10) has a maximum value, i.e
And when N i When (ω) =0, ζ=1;
therefore, by defining the ratio ζ, a frequency domain signal detection operation is performed on the basis.
Further, in step S7, the transmitting end performs continuous scanning, and if the frequency point detected by the receiving end has no continuity, the receiving end considers the frequency point as a false alarm.
Compared with the prior art, the invention has the following beneficial effects:
the frequency spectrum scanning method based on the frequency domain accumulation has the advantages that a pseudo-random sequence sliding correlation method is mostly adopted for a frequency spectrum scanning method of short-wave communication or extremely low-limit communication, but the frequency domain accumulation-based method is limited, and the frequency spectrum scanning method based on the frequency domain accumulation is simple in principle, convenient to achieve and small in limitation.
Drawings
Fig. 1 is a diagram illustrating frequency domain combining at a negative signal-to-noise ratio according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of an originating frame according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a frame format of a transceiver end according to an embodiment of the present invention.
Fig. 4 is a graph showing the variation of the ratio ζ with the signal-to-noise ratio according to an embodiment of the present invention.
FIG. 5 is a diagram showing the discrimination between the ratio and the sliding window threshold according to one embodiment of the present invention.
Fig. 6 is a graph of probability of detection for different signal-to-noise ratios of an AWGN channel according to one embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made more fully with reference to the accompanying drawings, 1-6, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Examples:
with the development of wireless communication technology, communication means are becoming more and more abundant, but spectrum resources used by communication are also becoming more and more intense. In order to alleviate the above problem, it becomes necessary to find available communication frequency points within a certain bandwidth, such as short wave communication or very low limit communication. The traditional frequency spectrum scanning method mostly adopts a pseudo-random sequence sliding correlation method, and a frequency domain accumulation-based method is provided, so that the principle is simple and the implementation is convenient.
Let x (t) denote the transmitted signal, one branch y at the receiving end 1 (t) can be expressed as
y 1 (t)＝x(t)+n 1 (t) (1)
Another branch y 2 (t) can be expressed as
y 2 (t)＝x(t)+n 2 (t) (2)
Wherein n is 1 (t)、n 2 And (t) represents Gaussian white noise with a mean value of 0 and a variance of 1. Order the
y(t)＝y 1 (t)+y 2 (t)＝2x(t)+n 1 (t)+n 2 (t) (3)
Since n (t) =n 1 (t)+n 2 (t) is still Gaussian white noise with 0 mean and 1 variance, so the above combination mode can improve the signal-to-noise ratio of the signal at the receiving end.
Performing Fourier transform on the formula (1) and the formula (2) respectively
Y 1 (ω)＝X(ω)+N 1 (ω) (4)
Y 2 (ω)＝X(ω)+N 2 (ω) (5)
Wherein Y is 1 (ω)、N 1 (ω)、Y 2 (omega) and N 2 (ω) represents y respectively 1 (t)、n 1 (t)、y 2 (t) and n 2 The fourier transform of (t),x (ω) represents the Fourier transform of X (t), and the equal gain combination of equation (4) and equation (5) in the frequency domain can be obtained
Y(ω)＝Y 1 (ω)+Y 2 (ω)＝2X(ω)+N 2 (ω)+N 1 (ω) (6)
Since the fourier transform of the gaussian white noise still satisfies the (complex) gaussian characteristic, if the signal processing is performed in the frequency domain, the combining manner in the frequency domain can still improve the signal-to-noise ratio of the signal at the receiving end in the frequency domain, as shown in fig. 1.
In the communication system of frequency domain scanning, the two communication parties do not have available frequency points to synchronize any signals. The scheme designs a method for realizing spectrum scanning by periodically transmitting a completely repeated modulation signal by a transmitting end, as shown in fig. 2. The implementation principle is that the transmitting end scans and transmits the carrier wave, and the receiving end extracts the scheme of the carrier wave through frequency accumulation according to the combination gain of the formula (6).
The position at which the receiving end starts to receive the signal is random because of no synchronization. Since the frames transmitted are identical, the signal is received with the same frame period from the time the receiver samples the signal, a periodic frame can still be obtained, as shown in fig. 3.
According to the time delay characteristics of Fourier transformation, i.e.
It can be known that the signal received by the receiver has a delay difference with respect to the transmitter, and according to formula (7), that is, the phase of the received signal changes with respect to the transmitting end in the frequency domain, but the amplitude still has the characteristic of the signal at the transmitting end, and the phase error caused by the delay difference of receiving and transmitting can be eliminated by the modulo operation.
According to the analysis, let
Wherein the method comprises the steps of
Representing the fourier transform of the receiver samples into the ith signal frame containing a delay difference relative to the transmitted signal, equation (8) can be expressed as follows according to equation (7)
Wherein Y is i (ω) represents the fourier transform of the ith signal frame transmitted by the transmitter, and as can be seen from equation (9), the definition of equation (8) excludes the effect of the transmit-receive sampling time difference. In combination with equations (4), (5) and (6), equation (9) can be written as
According to the absolute value inequality |a+b| is less than or equal to |a|+|b|, there are
Then equation (10) has a maximum value, i.e
And when N i When (ω) =0, ζ=1.
As can be seen from fig. 4, the value of the ratio ζ gradually approaches 1 as the signal-to-noise ratio increases (noise gradually decreases). Therefore, the frequency domain signal detection operation can be performed by defining the ratio ζ and based thereon.
The frequency spectrum scanning method based on frequency domain accumulation comprises the following steps:
1) Setting a reasonable symbol period according to the specific condition of a communication system;
the symbol period is set reasonably, and the signal is mainly made to meet the frequency selective fading in the frequency domain so as to meet the condition of equal gain combination. Taking the short wave as an example, assuming that the symbol period is 3k, according to the ITU-520-2 protocol, the maximum multipath delay of the short wave is 5ms, and the coherence bandwidth can be roughly calculated as the inverse of the maximum multipath delay, which is about 200Hz. Because the used short wave symbol period is more than 200Hz, the signal undergoes frequency selective fading in the frequency domain, and the equal gain combination condition is satisfied;
2) Reasonably designing a frequency point interval delta f and a processing bandwidth W;
within the frequency band W, a total of scans are required
Frequency points. The smaller the delta f is, the more frequency points need to be scanned, and the calculation amount of the system is large; the greater Δf, the poorer the accuracy of the scan.
3) Reasonably designing a repeated transmission frame period N;
comparing equation (6), it can be known that the larger N is, the larger the signal-to-noise ratio gain obtained by the receiving end is.
4) N is carried out on the data acquired by the receiver fft Fourier transform of the points;
in order to ensure the accuracy of the subsequent frequency domain accumulation detection, the frequency resolution thereof needs to satisfy F s /N fft And delta f, namely ensuring that a plurality of frequency domain samples exist for accumulation in the frequency point interval.
5) Calculating a ratio xi according to a formula (8);
6) Performing sliding window judgment on the comparison value xi, and selecting the most frequency points which exceed a threshold and fall within a designated delta f interval as a judgment basis of the carrier frequency points of the transmitting end, wherein a schematic diagram is shown in fig. 5;
7) In order to prevent false alarm, a fixed scanning mode can be set at the transmitting end, and the detected frequency point and the scanning rule of the transmitting end are matched at the receiving end. For example, the transmitting end performs continuous scanning, and if the frequency points detected by the receiving end have no continuity, the receiving end is considered as a false alarm.
Taking short-wave frequency domain accumulation scanning as an example, the simulation adopts a symbol period of 3kBand, a frequency point interval deltaf=3 kHz, and a repeated transmission frame period of n=20, N fft The detection probability is shown in fig. 6 for AWGN channel, =2626144.
As can be seen from fig. 6, under the AWGN channel, with the spectrum scanning method herein, the detection probability exceeds 90% when the snr= -14dB is obtained by repeating transmission of 20 times; since the number of repeated transmissions is adjustable, a user can select a reasonable value according to the system requirements, for example, the scheme can realize spectrum scanning in very low-limit (SNR < -30 dB) communication.
The above is a preferred embodiment of the present invention, and all changes made according to the technical solution of the present invention belong to the protection scope of the present invention when the generated functional effects do not exceed the scope of the technical solution of the present invention.
Claims (6)
1. The frequency spectrum scanning method based on the frequency domain accumulation is characterized by comprising the following steps of:
s1, setting a reasonable symbol period according to the specific situation of a communication system;
s2, designing a frequency point interval delta f and a processing bandwidth W, wherein the total scanning is required in the bandwidth W
Frequency points;
s3, designing a repeated transmission frame period N;
s4, carrying out N on the data acquired by the receiver fft Fourier transform of the points; the frequency resolution is required to satisfy F s /N fft Delta f, namely ensuring that a plurality of frequency domain sample points exist for accumulation and use in the frequency point interval;
s5, calculating a ratio xi;
s6, sliding window judgment is carried out on the comparison value xi, and the most frequency points which exceed the threshold and fall in the appointed delta f interval are selected as the basis for judging the carrier frequency points of the transmitting end;
s7, setting a fixed scanning mode at the transmitting end, and matching the detected frequency point with the scanning rule of the transmitting end at the receiving end.
2. The method of spectrum scanning based on frequency domain accumulation as claimed in claim 1, wherein the reasonable symbol period in step S1 means that the signal satisfies frequency selective fading in the frequency domain.
3. The spectrum scanning method based on frequency domain accumulation as claimed in claim 2, wherein in step S3, let x (t) represent the transmitted signal, a branch y of the receiving end 1 (t) is expressed as
y 1 (t)＝x(t)+n 1 (t) (1)
Another branch y 2 (t) is expressed as
y 2 (t)＝x(t)+n 2 (t) (2)
Wherein n is 1 (t)、n 2 (t) represents gaussian white noise with a mean of 0 and a variance of 1; order the
y(t)＝y 1 (t)+y 2 (t)＝2x(t)+n 1 (t)+n 2 (t) (3)
Performing Fourier transform on the formula (1) and the formula (2) respectively
Y 1 (ω)＝X(ω)+N 1 (ω) (4)
Y 2 (ω)＝X(ω)+N 2 (ω) (5)
Wherein Y is 1 (ω)、N 1 (ω)、Y 2 (omega) and N 2 (ω) represents y respectively 1 (t)、n 1 (t)、y 2 (t) and n 2 Fourier transform of (t), X (ω) represents fourier transform of X (t), and equal gain combining equation (4) and equation (5) in the frequency domain
Y(ω)＝Y 1 (ω)+Y 2 (ω)＝2X(ω)+N 2 (ω)+N 1 (ω) (6)；
The carrier wave is scanned and sent by a transmitting end, and the carrier wave is extracted by a receiving end through frequency accumulation according to the combination gain of the formula (6);
the transmitted frames are identical, and the signal is received in the same frame period from the time when the signal is sampled by the receiver, so as to obtain a repeated transmission frame period N.
4. A frequency spectrum scanning method based on frequency domain accumulation as claimed in claim 3, wherein step S5 is specifically as follows:
according to the time delay characteristics of Fourier transformation, i.e.
The time delay difference of the signal received by the receiver relative to the transmitter can be known, and according to the formula (7), the phase error caused by the receiving and transmitting time delay difference is eliminated through the modulo operation;
according to the analysis, let
Wherein the method comprises the steps of
Representing the fourier transform of the receiver samples into the ith signal frame containing a delay difference relative to the transmitted signal, equation (8) can be expressed as follows according to equation (7)
Wherein Y is i (ω) represents the fourier transform of the ith signal frame transmitted by the transmitter.
5. The frequency-domain accumulation based spectrum scanning method as claimed in claim 4 wherein in combination with formulas (4), (5) and (6), formula (9) can be written as
According to the absolute value inequality |a+b| is less than or equal to |a|+|b|, there are
Then equation (10) has a maximum value, i.e
And when N i When (ω) =0, ζ=1;
therefore, by defining the ratio ζ, a frequency domain signal detection operation is performed on the basis.
6. The spectrum scanning method based on frequency domain accumulation as claimed in claim 5, wherein in step S7, the transmitting end performs continuous scanning, and if there is no continuity of the frequency points detected by the receiving end, the frequency points are considered as false alarms.
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