CN113676215A - double-M-element coding spread spectrum method and system in high dynamic environment - Google Patents
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Abstract
The invention belongs to the technical field of spread spectrum communication, and particularly relates to a spread spectrum communication method and system in a high dynamic environment. A double M element coding spread spectrum method under high dynamic environment comprises the following steps: a transmitting terminal generates an original signal and performs double modulation processing on the original signal to obtain a transmitting signal; the receiving end receives the transmitted signal, processes the received signal and restores the original signal. The invention provides a method for generating a spread spectrum code by adopting a double-M-element coding mode, which reduces the complexity of generating the spread spectrum code; the PMF-H-FFT-LF capturing algorithm is adopted, synchronous capturing of the spread spectrum codes is ensured, the working efficiency of the whole spread spectrum communication system is improved, and good performances in the aspects of fading resistance, multipath interference resistance and the like are presented.
Description
Technical Field
The invention belongs to the technical field of spread spectrum communication, and particularly relates to a spread spectrum communication method and system in a high dynamic environment.
Background
As early as the 40 s of the 20 th century, scientific researchers began researching spread spectrum communication technologies. Spread spectrum communication technology was primarily used in the military field initially due to its good interference, fading, and multipath resistance. With the development of spread spectrum communication technology, the technology has penetrated into various fields of civil communication, and is widely applied to various fields such as measurement and control, satellite navigation positioning and the like. Direct sequence spread spectrum technology is the most common spread spectrum technology, but mainly aims at the conditions of low transmission data rate and limited frequency band utilization rate. With the development of modern technology level, people have higher and higher requirements on the performance of communication systems, and more services are provided for high-data-rate and multi-user data transmission. Therefore, it is an urgent need to improve the transmission efficiency and the anti-interference capability of the spread spectrum communication system and reduce the design complexity of the system. In addition, it is particularly critical to establish a fast and accurate synchronization mechanism in spread spectrum technology, and the synchronization process is roughly divided into acquisition and tracking. In the acquisition method, the circuit design and operation of the serial search method are simpler, but when the length of the spread spectrum code is increased, the search time is increased; the parallel search method has short search time and complicated circuit design and operation. In addition, under a high dynamic environment, the capture probability of a common algorithm is low, and the capture performance is poor. Therefore, how to effectively improve the phase tracking accuracy and the frequency offset estimation accuracy of the spreading codes in the spread spectrum system is very important.
Some scholars apply a classical capture algorithm to a direct sequence spread spectrum communication system, and some scholars combine a part of matched filters and fast Fourier transform to improve a capture effect, but the performance of the direct sequence spread spectrum communication system is poor, and the existing capture method has the problems of low parameter estimation precision and the like, so that the anti-interference performance of the spread spectrum communication system under a high dynamic environment is poor, the capture probability is low, and the practical application value is lacked.
Disclosure of Invention
The invention aims to solve the problems of complex generation mode, poor anti-interference performance, low acquisition speed and acquisition precision of a spread spectrum code and the like of the existing spread spectrum system in a high dynamic environment.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a dual M-ary encoded spread spectrum system in a high dynamic environment, comprising:
the transmitting terminal is used for generating an original signal and carrying out double modulation processing on the original signal to obtain a transmitting signal;
and the receiving end is used for receiving the sending signal, processing the received signal and recovering the original signal.
As a preferred mode of the present invention, the double modulation processing procedure is: based on a double-M-element coding spread spectrum mode, a spread spectrum code is generated, the generated spread spectrum code and an original signal are subjected to spread spectrum modulation to obtain a spread spectrum signal, and the spread spectrum signal is subjected to BPSK secondary modulation to obtain a transmission signal.
Further, the dual M-ary encoding spreading mode specifically includes:
randomly selecting a spreading code as a prototype spreading code, the length of the spreading code being L, using c0～L-1Denotes a chip in a spreading code, where L ≧ M, M ═ 2K(ii) a K represents the bit number of an information sequence corresponding to one transmission symbol;
moving the prototype spread spectrum code in the same direction by d unit lengths each time, wherein d is a positive integer
After the secondary cyclic shift, corresponding generation
A stripe spreading code;
for generated
Strip spreading code negation to obtain the remainder
A stripe spreading code.
Further preferably, the receiving end includes a spreading code capturing unit, and the spreading code capturing unit is configured to perform spreading code synchronization processing on the received signal, specifically:
mixing the sampled signal with a local oscillation signal generated by a local NCO;
inputting the mixing signal into a partial matched filter to carry out correlation operation;
carrying out Haiming window adding processing on data output by the partial matching filter;
performing frequency domain analysis by adopting an FFT algorithm;
and (5) performing threshold approximation judgment to complete two-dimensional search of the phase and frequency deviation of the spread spectrum code.
Further preferably, the receiving end further includes a despreading and demodulating unit, configured to recover a frequency band of the captured signal to a bandwidth of an original information sequence, and then perform demodulation processing to recover the transmitted information.
The invention also provides a double M-element coding spread spectrum method under the high dynamic environment, which comprises the following steps:
a transmitting terminal generates an original signal and performs double modulation processing on the original signal to obtain a transmitting signal;
the receiving end receives the transmitted signal, and performs despreading demodulation processing on the received signal to recover the original signal.
Further, the performing of the double modulation processing on the original signal includes: based on a double-M-element coding spread spectrum mode, a spread spectrum code is generated, the generated spread spectrum code and an original signal are subjected to spread spectrum modulation to obtain a spread spectrum signal, and the spread spectrum signal is subjected to BPSK secondary modulation to obtain a transmission signal.
Further, the dual M-ary encoding spreading mode specifically includes:
randomly selecting a spreading code as a prototype spreading code, the length of the spreading code being L, using c0～L-1Denotes a chip in a spreading code, where L ≧ M, M ═ 2K(ii) a K represents the bit number of an information sequence corresponding to one transmission symbol;
moving the prototype spread spectrum code in the same direction sequentially, each time moving d unit length, d is positive integer
After the secondary cyclic shift, corresponding generation
A stripe spreading code;
for generated
Strip spreading code negation to obtain the remainder
A stripe spreading code.
Further preferably, the receiving end performs spreading code synchronization processing on the received signal by the following method:
mixing the sampled signal with a local oscillation signal generated by a local NCO;
inputting the mixing signal into a partial matched filter to carry out correlation operation;
carrying out Haiming window adding processing on data output by the partial matching filter;
performing frequency domain analysis by adopting an FFT algorithm;
and (5) performing threshold approximation judgment to complete two-dimensional search of the phase and frequency deviation of the spread spectrum code.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method adopts a double-M-element coding mode to generate the spread spectrum code, and reduces the complexity of generating the spread spectrum code.
(2) The PMF-H-FFT-LF capturing algorithm is provided, namely, correlation processing is carried out through a partial matched filter, a Hamming window is added to data output by the partial matched filter, Fourier transform is carried out, and finally required parameters are estimated by using a likelihood function, so that correct search of a spread spectrum code phase and accurate evaluation of frequency deviation are completed, synchronous capturing of the spread spectrum code is ensured, the working efficiency of the whole spread spectrum communication system is improved, and good performances in the aspects of fading resistance, multipath interference resistance and the like are presented.
Drawings
Fig. 1 is a block diagram of a dual M-ary encoding spread spectrum system in a high dynamic environment according to an embodiment of the present invention;
FIG. 2 is a flowchart of a dual M-ary encoding spread spectrum method under high dynamic environment according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a spreading code generator according to an embodiment of the present invention;
fig. 4 is a schematic diagram of generating a spreading code by using a dual M-ary spreading code according to an embodiment of the present invention;
FIG. 5 is a simulation diagram of a Hamming window provided by an embodiment of the present invention;
FIG. 6 is a schematic flow chart of a PMF-H-FFT-LF capture algorithm provided by an embodiment of the present invention;
Detailed Description
In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. Preferred embodiments of the present invention are shown in the drawings. 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.
The dual M-ary coding spread spectrum method provided in this embodiment is an accurate transmitting and synchronous capturing receiving method for a spread spectrum communication system in a high dynamic environment, and specifically includes, as shown in fig. 1:
step S1, generation and processing of digital signal
Signal s generated by the transmitting endkIs an information stream, then sendsThe signal s (t) can be expressed as:
wherein R issIs the symbol velocity, TsIs the symbol width, snIn order to be the information code,
Ts＝1/Rs。
in addition, serial-to-parallel conversion processing needs to be performed on the signal stream, and initialization parameter setting is performed according to the design requirements of the spread spectrum system.
Step S2 is to perform double modulation processing on the transmission signal.
And carrying out double modulation processing on the transmission signal, namely spread spectrum modulation and BPSK modulation. The spread spectrum modulation is carried out based on a double-M-element coding spread spectrum mode, and the spread spectrum codes generated by the spread spectrum mode not only ensure good autocorrelation characteristics, but also can reduce the code selection difficulty and reduce the complexity of actual system development.
1. Spread spectrum modulation
In the present invention, a spreading code with good performance is constructed based on an m-sequence. A sequence is typically represented by a generating function, as shown in FIG. 3, if { b }m}＝{b0,b1,b2…, the output sequence of the shift register is represented, and the subscript number represents time, the generating function g (x) of the output sequence is:
if it is
In the invention, the information sequence to be transmitted is divided into a symbol according to each K bits, and then the required M spreading codes correspondingly transmit the information content of each input symbol. The specific steps of the double M-element coding are as follows:
(1) firstly, randomly selecting a spread spectrum code as prototype spread spectrum code, the length of said spread spectrum code is L, using c0～L-1Denotes a chip in a spreading code, where L ≧ M, M ═ 2K；
(2) Moving the prototype spread spectrum code in the same direction in sequence, each time moving d unit length, d is positive integer, d value is needed to ensure that the spread spectrum code after cyclic shift is not repeated with the generated spread spectrum code, and the method is implemented
After the secondary cyclic shift, corresponding generation can be performed
A stripe spreading code;
(3) the rest of
The bar spreading code can be obtained by inverting the generated spreading code; the meaning of negation is: for generated
The-1 in the stripe spreading code corresponds to 1 and the 1 corresponds to-1.
Available q of spreading code after cyclic shiftiThe specific production mode is shown in figure 4.
Because of adopting double M-element coding spread spectrum mode, only need to generate
The stripe spreading code is enough, and the complexity of generating the spreading code is greatly reduced.
And carrying out spread spectrum modulation on the generated M spread spectrum codes and the original signal to obtain a spread spectrum signal.
BPSK modulation
The spread signal needs to be modulated twice by BPSK. After the signal is double-modulated, it can be expressed as:
wherein E represents average power, p (t) is spreading code waveform, theta is random carrier phase, fcIs the carrier frequency, τ is the received spreading code phase offset, fdIs the frequency deviation.
For unknown τ and fdThe average likelihood function of the two is the desired limit on θ in the conditional probability density function of r. It is expressed as:
step S3, inputting channel for transmission
In the channel transmission process, the hypothetical interference is not existed, only the noise of AWGN channel is existed to generate interference to signal, the noise signal is represented by n (t), E [ n (t)]0. Since the noise is zero-mean, E [ r ]i]＝si，
And the autocorrelation function of Gaussian white noise is
Step S4, obtaining the received signal
After passing through the AWGN channel, the received signal can be expressed as:
r(t)＝s(t)+n(t)0≤t≤T
where s (T) is the transmitted signal, n (T) is additive white gaussian noise, and T is the observation duration.
Since the complete set of basis functions that remain orthogonal over the time interval T satisfies:
the transmitted signal and the received signal may be expressed as:
and (3) obtaining the expansion coefficients of the above formula by using the complete set of basis functions, wherein the expansion coefficients are respectively expressed as:
step S5, spread code acquisition process
As shown in fig. 6, the spreading code acquisition process mainly includes: after mixing the sampled signal with a local oscillator signal generated by local NCO, inputting the mixed signal into a partial matching filter for correlation operation; and performing Haiming window processing on data output by the partial matched filter, performing frequency domain analysis by adopting an FFT algorithm, and finally performing threshold approximation judgment, thereby completing two-dimensional search of the phase and frequency deviation of the spread spectrum code.
Wherein, adopting the Hamming window to process can make the sidelobe reduce apparently, its sequence is:
as shown in fig. 5, the processing performed through the hamming window can reduce the degree of attenuation of the fourier transform output spectral peak and reduce the spectral leakage.
And if the spectrum peak value calculated by the FFT is higher than the preset threshold value of the capturing judgment, judging that the phase of the spread spectrum code of the current received signal is consistent with that of the local spread spectrum code, and thus finishing the two-dimensional search of the phase and the frequency deviation of the spread spectrum code. At this time, the received signal has a spreading code length of L and a frequency offset of fdAnd after the number of the partial matched filters with the length of W is Q, normalization processing is carried out, and N-point FFT operation is carried out on the correlation values output by the Q partial matched filters, the normalized amplitude-frequency response of the k point in the FFT result is as follows:
if Q ≠ 2nThen the normalized amplitude-frequency response at the k-th point in the FFT result is:
and step S6, parameter estimation and optimization.
In the r (t) expansion, the coefficients are Gaussian, statistically independent, and the variance is
Therefore, the temperature of the molten metal is controlled,
and (3) substituting the solution formula of the likelihood function, eliminating the maximum likelihood estimation irrelevant factor, and obtaining:
by integrating, exchanging the order of the limit and integration operations, we can get:
the average likelihood function is then:
where S is the energy of the signal waveform over the observation time interval. Since S does not vary much within the selected parameters, the factors that comprise it can be deleted, yielding:
assuming that the phase θ of the received carrier is uniformly distributed within [0,2 π ], the trigonometric expansion and integration with respect to θ can be written as:
wherein,
by traversing τ and fdAnd R (τ, f) is selectedd) To determine the value of the estimated parameter, then:
step S7, despreading and demodulating the recovered signal
In order to obtain effective data information at a receiving end, the receiving end needs to correctly de-spread received signals, and the de-spread premise is the synchronization of spread spectrum codes. And carrying out de-spreading processing at a receiving end, and restoring the frequency band of the signal to the bandwidth of the original signal sequence, namely the intermediate frequency modulation signal. Then, demodulation processing is carried out, and finally, the transmitted information s (t) is recovered, and the information transmission is completed.
Another embodiment of the present invention is a dual M-ary encoded spread spectrum system in a highly dynamic environment, as shown in fig. 2, the system includes a transmitting end 101, a receiving end 102, and a transmission channel 103.
The transmitting terminal 101 is configured to generate an original digital signal, perform serial-to-parallel conversion on the original signal, generate a spreading code based on a dual M-ary coding spreading mode, perform spreading modulation on the generated spreading code and the original signal to obtain a spreading signal, and perform BPSK secondary modulation on the spreading signal to obtain a transmission signal.
The transmission signal is transmitted to the receiving end 102 via the transmission channel 103.
At first, the receiving end 102 adopts a PMF-H-FFT-LF capture algorithm to the received signal to achieve synchronization of the spreading codes, which specifically includes:
the capture unit mixes the sampled sending signal with a local oscillator signal generated by local NCO and inputs the mixed signal into a partial matching filter for correlation operation; and performing Haiming window processing on data output by the partial matched filter, performing frequency domain analysis by adopting an FFT algorithm, and finally performing threshold approximation judgment, thereby completing two-dimensional search of the phase and frequency deviation of the spread spectrum code.
Then, the despreading and demodulating unit despreads the received effective signal, and restores the frequency band of the signal to the bandwidth of the original signal sequence, that is, the intermediate frequency modulated signal. Then, demodulation processing is carried out, and finally, the transmitted information is recovered, and the information transmission is completed.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. A double M element coding spread spectrum method under high dynamic environment comprises the following steps:
a transmitting terminal generates an original signal and performs double modulation processing on the original signal to obtain a transmitting signal;
the receiving end receives the transmitted signal, processes the received signal and restores the original signal.
2. The method for spreading double-M-ary codes under high dynamic environment according to claim 1, wherein: the double modulation processing specifically comprises: based on a double-M-element coding spread spectrum mode, a spread spectrum code is generated, the generated spread spectrum code and an original signal are subjected to spread spectrum modulation to obtain a spread spectrum signal, and the spread spectrum signal is subjected to BPSK secondary modulation to obtain a transmission signal.
3. The method according to claim 2, wherein the double M-ary coding spreading method under the high dynamic environment comprises: the spread spectrum mode based on the double M-element coding specifically comprises the following steps:
randomly selecting a spreading code as a prototype spreading code, the length of the spreading code being L, using c0～L-1Denotes a chip in a spreading code, where L ≧ M, M ═ 2K(ii) a K represents the bit number of an information sequence corresponding to one transmission symbol;
moving the prototype spread spectrum code in the same direction sequentially, each time moving d unit length, d being positive integer
After the secondary cyclic shift, corresponding generation
A stripe spreading code;
for generated
Strip spreading code negation to obtain the remainder
A stripe spreading code.
4. The method for spreading double-M-ary codes under high dynamic environment according to claim 1, wherein: the receiving end carries out spread spectrum code synchronization processing on the received signals by the following method:
mixing the sampled signal with a local oscillation signal generated by a local NCO;
inputting the mixing signal into a partial matched filter to carry out correlation operation;
carrying out Haiming window adding processing on data output by the partial matching filter;
performing frequency domain analysis by adopting an FFT algorithm;
and (5) performing threshold approximation judgment to complete two-dimensional search of the phase and frequency deviation of the spread spectrum code.
5. A dual M-ary encoded spread spectrum system in a high dynamic environment, comprising:
the transmitting terminal is used for generating an original signal and carrying out double modulation processing on the original signal to obtain a transmitting signal;
and the receiving end is used for receiving the sending signal, processing the received signal and recovering the original signal.
6. The dual M-ary encoded spread spectrum system according to claim 5, wherein the dual modulation process comprises: based on a double-M-element coding spread spectrum mode, a spread spectrum code is generated, the generated spread spectrum code and an original signal are subjected to spread spectrum modulation to obtain a spread spectrum signal, and the spread spectrum signal is subjected to BPSK secondary modulation to obtain a transmission signal.
7. The dual-M-ary encoded spread spectrum system according to claim 5, wherein the dual-M-ary encoded spread spectrum scheme is specifically:
randomly selecting a spreading code as a prototype spreading code, the length of the spreading code being L, using c0～L-1Denotes a chip in a spreading code, where L ≧ M, M ═ 2K(ii) a K represents the bit number of an information sequence corresponding to one transmission symbol;
moving the prototype spread spectrum code in the same direction sequentially, each time moving d unit length, d being positive integer
After the secondary cyclic shift, corresponding generation
A stripe spreading code;
for generated
Strip spreading code negation to obtain the remainder
A stripe spreading code.
8. The dual-M-ary coding spread spectrum system according to claim 5, wherein the receiving end comprises a spread spectrum code capturing unit, and the spread spectrum code capturing unit is configured to perform spread spectrum code synchronization processing on the received signal, specifically:
mixing the sampled signal with a local oscillation signal generated by a local NCO;
inputting the mixing signal into a partial matched filter to carry out correlation operation;
carrying out Haiming window adding processing on data output by the partial matching filter;
performing frequency domain analysis by adopting an FFT algorithm;
and (5) performing threshold approximation judgment to complete two-dimensional search of the phase and frequency deviation of the spread spectrum code.
9. The dual-M-ary coded spread spectrum system according to claim 8, wherein the receiving end further comprises a de-spreading demodulation unit for recovering the frequency band of the received signal to the bandwidth of the original information sequence, and then performing demodulation processing to recover the transmitted information.
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