CN1168255C - A joint spread spectrum communication device - Google Patents

Abstract

The present invention discloses a novel communication method for combined spread spectra. A two-dimensional spread spectrum module 1 is composed of a discrete multi-carrier spread spectrum 3, a direct sequence spread spectrum 2 and inverse discrete Fourier transform 4, and the two-dimensional spread spectrum module 1, a frequency hopping spread spectrum 6 and a time hopping spread spectrum 10 together form an emitting part of the combined spread spectrum communication method. An inverse discrete multi-carrier 29, a direct sequence de-spread spectrum 30 and discrete Fourier transform 28 together form a two-dimensional de-spread spectrum module 27, and the two-dimensional de-spread spectrum module 27, a de-time hopping spread spectrum unit 17 and a de-frequency hopping spread spectrum unit 20 together form a receiving part of the combined spread spectrum communication method. The adoption of the communication method of the present invention makes the randomness of information in a wireless channel stronger and also makes illegal users (for instance, enemies and deliberate destroyers) more difficult to capture legal users' information.

Description

A joint spread spectrum communication device

technical field

The invention belongs to the field of electromagnetic wave technology, such as wireless communication, optical communication, ultrasonic communication, wired communication and other related data transmission and processing technologies, and particularly relates to a communication device using spread spectrum.

Background technique

As is well known, spread spectrum communication devices are widely used in existing communication technologies. The traditional spread spectrum uses the method of multiplying the spread spectrum code and the original signal to expand the spectrum of the original signal. Therefore, the advantages of the communication device using the spread spectrum are: the widening of the spectrum means that the probability of intercepting the original signal is reduced; the enhancement of the anti-interference performance means the reduction of the communication bit error rate; Enhanced capabilities.

The existing main methods (techniques) for spreading the spectrum are:

扩频序列如图2所示。(1) Direct Sequence Spread Spectrum (DS-CDMA) (also known as time-domain spread spectrum method): module 2 in Figure 1, it uses a spread spectrum sequence with a higher rate than the original data to compare with the original data Multiplied, thereby expanding the spectrum of the original data. For its working principle, please refer to: "Digital Communication Principles" third edition, written by JG Proakis, Electronic Industry Press, published in September 1998. The working principle of direct sequence spread spectrum (direct spread) can be briefly described as: b(t) is the original input information, after direct sequence spread spectrum 2 spread spectrum, the output $d\left(t\right)=\underset{j=1}{\overset{N}{\mathrm{\Σ}}}b\left(t\right){\mathrm{\α}}_{j}p(t-(j-1)T_c),$ Among them, α _I is the spreading sequence α corresponding to direct sequence spreading: α ₁ , α ₂ , ..., the elements in α _N , N is the processing gain of direct sequence spreading, p(t) is the width equal to T _c The unit amplitude pulse,

The spread spectrum sequence is shown in Figure 2.

(2) The working principle of multi-carrier spread spectrum (MC-CDMA) is: each bit of the original data is transmitted with different sub-carriers in the multi-carrier system, and then scrambled with a spreading sequence. For details, see: Shinsuke Hara and Ramjee Prasad, "Overview of Multicarrier CDMA," IEEE Communications Magazine, pp.126-133, Dec.1997.

(3) The working principle of Time Hopping Spread Spectrum (TH-SS) is: different time periods in communication use different carrier center frequencies, and the carrier center frequency is controlled by the frequency hopping sequence. For details, see: "Spread Spectrum Communication", written by Zha Guangming and Xiong Xianzuo, Xidian University Press, published in 1990.

(4) The working principle of Frequency Hopping Spread Spectrum (FH-SS) is: the time period and moment of connection in the communication are controlled by the time hopping sequence. For details, see: "Spread Spectrum Communication", written by Zha Guangming and Xiong Xianzuo, Xidian University Press, published in 1990.

The existing spread spectrum communication devices are all one-dimensional spread spectrum, such as DS-CDMA, MC-CDMA, etc., and its disadvantages are:

(1) The spread spectrum is not uniform, and it is easy for the enemy to detect the specific value of some modulation parameters; (2) It is difficult to realize when the spread spectrum gain is high; (3) The design of the spread spectrum gain is not flexible; (4) The sampling rate is too high during digital reception; (5) The implementation of adaptive interference suppression is complicated.

Contents of the invention

The task of the present invention is to provide a communication device with a lower probability of information being intercepted, that is, using the communication device of the present invention, the randomness of information on the wireless channel is stronger, making illegal users (such as enemies, vandals) more It is difficult to intercept legitimate user information.

A joint spread spectrum communication device of the present invention includes a transmitting part and a receiving part, and the transmitting part includes a direct sequence spreading unit 2, an inverse discrete Fourier transform 4, a frequency hopping spreading unit 6, and a time hopping spreading unit 10 The receiving part includes a time-hopping spread spectrum unit 17, a frequency-hopping spread spectrum unit 20, a discrete Fourier transform 28, and a direct sequence despread spectrum unit 30; it is characterized in that the transmitting part also includes a discrete multi-carrier spread spectrum unit 3 , the discrete multi-carrier spread spectrum unit 3 together with the direct sequence spread spectrum unit 2 and the inverse discrete Fourier transform 4 form a two-dimensional spread spectrum module 1, and the matrix expression of the two-dimensional spread spectrum process is: $f\left(t\right)=\mathrm{s\βU\αp}\sqrt{2P_T}b\left(t\right),$ Among them, f(t) is the signal after the joint spread spectrum, and the elements in s=(cos(2πΔft), cos(2π2Δft),..., cos(2πMΔft)) correspond to each subcarrier in the multi-carrier, Δf is the spacing between subcarriers, β=(β ₁ , β ₂ ,..., β _N ) is the spreading sequence matrix of discrete multi-carrier spreading, N is the total number of β columns, β _j =(β _{j, 1,} β _{j, 2,} ..., β _{j, M} ) ^T is the jth column of the spreading matrix, j=1, 2, ..., N, M is the total number of rows of β, (·) ^T means Transpose operation, U=diag{p(t), p(tT _c ), ..., p(t-(N-1)T _c )}, diag{ } represents a diagonal matrix, p(t) is the amplitude pulse whose width is equal to T _c , α is the spreading sequence corresponding to the direct sequence spreading, α=diag(α ₁ , α ₂ ,...,α _N ); p=(p(t), p(tT _c ),..., p(t-(N-1)T _c )) ^T ; P _T is the transmission power of any subcarrier, b(t) is the signal to be spread spectrum; two-dimensional spread spectrum module 1 Together with the frequency hopping spread spectrum unit 6 and the time hopping spread spectrum unit 10, the transmitting part of the device for joint spread spectrum communication is formed; the receiving part also includes an inverse discrete multi-carrier unit 29, an inverse discrete multi-carrier unit 29 and a direct sequence despreading unit 30. The discrete Fourier transform 28 together forms a two-dimensional despreading module 27, and the matrix expression of the two-dimensional despreading process is $\hat{b}\left(t\right)=\mathrm{N\; M}{T}_c\sqrt{\frac{P_T}{2}}b\left(t\right)+{\left(\mathrm{\βU\αp}\right)}^T{\∫}_0^{T_c}{\mathrm{the\; s}}^T\mathrm{no}\left(t\right)\mathrm{dt},$ Among them, N is the total number of columns of β, M is the total number of rows of β, β=(β ₁ , β ₂ ,..., β _N ) is the spreading sequence matrix of discrete multi-carrier spread spectrum, β _j =(β _{j , 1,} β _{j, 2,} ..., β _{j, M} ) ^T is the jth column of the spreading matrix, j=1, 2, ..., N; T _c is the spreading sequence of direct sequence spreading α is the width of one symbol; P _T is the transmission power of any subcarrier; b(t) is the signal to be spread spectrum: U=diag{p(t), p(tT _c ),...,p( t-(N-1)T _c )}, diag{ } represents a diagonal matrix, p(t) is an amplitude pulse whose width is equal to T _c ; p=(p(t), p(tT _c ), .. ., p(t-(N-1)T _c )) ^T ; s=(cos(2πΔft), cos(2π2Δft), ..., cos(2πMΔft)) corresponds to each sub-carrier in the multi-carrier Δf is the spacing between subcarriers; n(t) is additive white Gaussian noise; the two-dimensional despreading module 27 forms a joint spread spectrum communication with the de-hopping time-spreading unit 17 and the de-frequency-hopping spreading unit 20 the receiving part of the device.

Transmitter part of the present invention is made up: the transmitting part of the present invention comprises by direct sequence (Direct Sequence, be called for short DS) spread spectrum unit 2, discrete multi-carrier (Discrete MultiCarrier, be called for short DMC) spread spectrum unit 3, inverse discrete Fourier transform (Inverse Discrete Forierr Transform (IDFT for short) 4 forms a two-dimensional spread spectrum module 1 to complete the function of two-dimensional spread spectrum. communication device. The transmitter also includes units such as adding a guard time slot unit 5, a frequency hopping sequence 7, a local oscillator 8, a time hopping sequence 11, a time hopping switch 12, a radio frequency part 13, an antenna 14, and a central control unit 31, as shown in Figure 3 .

The principle of the transmitter part of the present invention (the working process of the module 1 of the two-dimensional spread spectrum function):

Here, BPSK modulation is taken as an example to illustrate the idea of the present invention, and such setting does not affect the application of the idea of the present invention to systems of other modulation modes. The present invention adopts a joint spread spectrum communication device composed of two-dimensional spread spectrum joint frequency hopping and time hopping spread spectrum. Its working principle is shown in FIG. 3 . In Figure 3, module 1 completes the function of two-dimensional spread spectrum, where DS is Direct Sequence Spread Spectrum (Direct Sequence), DMC is Discrete MultiCarrier (Discrete MultiCarrier), IDFT is Inverse Discrete Forierr Transform (Inverse Discrete Forierr Transform) ). b(t) is the original input information, after direct sequence spread spectrum 2 spread spectrum, output d(t):

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, α _I is the element in the spreading sequence α corresponding to direct sequence spreading: α ₁ , α ₂ , ..., α _N , N is the processing gain of direct sequence spreading, and p(t) is the width equal to T Unit amplitude pulse of _c :

Of course, p(t) can also be other forms of pulse shapes, and the assumption of formula (2) does not affect the generality of the present invention.

The signal after the direct-sequence spreading unit (DS) 2 spread spectrum is sent to the discrete multi-carrier spreading unit (DMC) 3, and the duplicator 33 in the discrete multi-carrier spreading unit 3 inputs 1 symbol (chip), as shown in FIG. As shown in 5, M channels of signals with the same width of 1 symbol are output, and each channel of signals is multiplied by the frequency-domain spread spectrum sequence β _{j, i} respectively. The working principle is shown in Figure 5.

d _i (t)=d(t)β _{j, i} p(t-(j-1)T _c )i=1, 2,..., M; j=1, 2,..., N ( 3) Among them:

β _j = (β _{j, 1,} β _{j, 2,} ..., β _{j, M} ) ^T j = 1, 2, ..., N (4)

β=(β ₁ , β ₂ ,..., β _N ) (5) β is the spreading sequence matrix of discrete multi-carrier spreading, and its column vectors correspond to a spreading sequence, β _{j, I} are frequency domain Spread spectrum sequence, d _i (t) is the signal output by DMC spread spectrum 3.

The signal d _i (t) output by DMC spread spectrum 3 is sent to inverse discrete Fourier transform (IDFT) module 4, and the model of IDFT4 is shown in FIG. 6 . In actual engineering, IDFT4 generally uses the Fast Fourier Transform (IFFT) algorithm; here, in order to illustrate the idea of the present invention, only IDTF is used to describe; but whether it is IDFT or FFT, it does not affect the generality of the present invention. In FIG. 6 , Δf is the distance between any nearest two subcarriers in the multi-carrier, and there are M subcarriers in total, so the total frequency bandwidth is MΔf. The output f(t) of the inverse discrete Fourier transform unit is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; s\&beta;U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Where _PT is the transmit power of any subcarrier. Substituting equations (1), (3)~(5) into equation (6), the output of the inverse discrete Fourier transform unit is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;i\&Delta;ft</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

The matrix expression of f(t) is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; s\&beta;</span>}\mathrm{<span\; class="notranslate">\; U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

in,

s=(cos(2πΔft), cos(2π2Δft),..., cos(2πMΔft)) (9)

U=diag{p(t), p(tT _c ), ..., p(t-(N-1)T _c )} (10)

α=diag(α ₁ , α ₂ , . . . , α _N ) (11)

p=(p(t), p(tT _c ), . . . , p(t-(N-1)T _c )) ^T (12)

Conclusion: The working principle of module 1, which is composed of DS2, DMC3, and IDFT4 to complete the two-dimensional spread spectrum function, has been theoretically discussed above, and the frequency-hopping spread-spectrum unit 6 and the time-hopping spread-spectrum unit 10 are both prior art Therefore, the communication device proposed by the present invention can jointly spread the frequency spectrum of the original data through two-dimensional spread spectrum joint frequency hopping and time-hopping spread spectrum, so that the interception rate of communication information is lower than that of the prior art. The reason is easy to see from the above: to intercept the communication information transmitted by the method of the present invention, not only need to intercept the law of frequency hopping and time hopping, but also need to further search for detection methods in two-dimensional space.

Some innovative points of the transmitter of the present invention: (1) in the existing communication device of spread frequency spectrum, its spread spectrum is one-dimensional spread spectrum, for example adopts direct sequence spread spectrum (DS-CDMA), multi-carrier spread spectrum (MC -CDMA) and other methods. The present invention adopts full DMC discrete multi-carrier (DiscreteMultiCarrier) spread spectrum on the basis of Direct Sequence Spread Spectrum (DS-CDMA), and its feature is that the spread spectrum sequence is different in the adjacent time segment multi-carrier spread spectrum sequence, namely by DS2 , DMC3, and IDFT4 form the module 1 that completes the two-dimensional spread spectrum function to realize the purpose of two-dimensional spread spectrum. (2) Two-dimensional spread spectrum is combined with two spread spectrum methods of frequency hopping and time hopping to form the joint spread spectrum communication method of the present invention.

The essence of the transmitter part of the present invention: with respect to methods such as traditional time hopping, frequency hopping, multi-carrier spread spectrum, direct sequence spread spectrum, the core idea of the present invention is: the time of each hop in the time hopping and frequency hopping process Within the width, the two-dimensional spread spectrum (TwoDimension Spread Spectrum) method is used to spread the spectrum of the information, and the randomness of the information on the wireless channel is stronger, making it more difficult for illegal users (such as the enemy, malicious actors, etc.) to intercept legitimate user information.

Receiver part of the present invention:

The receiver part of the present invention consists of: including: receiving antenna 15, radio frequency part 16, time-hopping unit 17, frequency-hopping unit 20, A/D converter 24, time-hopping sequence 19, time-hopping switch 18, frequency-hopping sequence 21 , frequency, time synchronization 25, central control unit 31, guard slot module 26, it also includes: two-dimensional demodulation part 27, it is despread by discrete Fourier transform (DFT) unit 28, DMC despreading unit 29, DS Unit 30 is composed. As shown in Figure 3.

The working principle of two-dimensional spread spectrum despreading (the working process of two-dimensional spread spectrum despreading 27):

In the receiver, there are many traditional methods for the time and frequency synchronization of the frequency-time synchronization unit 25, which will not be described here. The demodulation mode may be non-coherent demodulation, differential coherent demodulation, pilot symbol-assisted coherent demodulation, coherent demodulation and other modes. Regardless of the demodulation method, the time-frequency two-dimensional spread spectrum method in the present invention can be used. Only the time-frequency two-dimensional despreading method during BPSK coherent demodulation is described here. In order to highlight the principle of two-dimensional spread spectrum despreading, it is assumed here that the time and frequency are synchronized, and the radio frequency signal passes through the additive white Gaussian noise channel. The system does not use the addition of guard time slots and the removal of guard time slot units. The radio frequency transmitting part, The influence of frequency hopping and de-hopping, time hopping and de-hopping, and radio frequency on f(t) can be ignored. This assumption does not affect the generality of the invention. Then there are:

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; s\&beta;U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Where r(t) is the output of the guard slot module 26 removed, f(t) is the output of the two-dimensional spread spectrum module 1, and n(t) is the additive white Gaussian noise with a power spectral density of N ₀ . According to the model shown in Figure 3, the signal of r(t) after Discrete Fourier Transform (DFT)28 is:

$\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; s\&beta;</span>}\mathrm{<span\; class="notranslate">\; U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; m</span>}}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}$

Wherein I _M×M is an M×M identity matrix, g=(g ₁ , g ₂ , . . . , g _M ) ^T . g is sent to the DMC despreading 29 for processing, and g is multiplied by (βU) ^T to the left to obtain the output h(t) of the DMC despreading 29:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;\; U</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;\; U</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

According to the properties of p on the time axis defined in formula (2), formula (14) can be simplified as:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Omega;\&alpha;p</span>}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;\; U</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

Where Ω is: Ω=diag{|β ₁ | ² p(t), |β ₂ | ² p(tT _c ), ..., |β _N | ² p(t-(N-1)T _c ) } (17) where $|{\mathrm{\&beta;}}_j{|}^2={\mathrm{\&beta;}}_j^T{\mathrm{\&beta;}}_j,j=\mathrm{1,2},...,N.$

h(t) is sent to DS despreading unit 30, output (t):

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&alpha;p</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}$ $\mathrm{<span\; class="notranslate">\; \&Omega;\&alpha;p</span>}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}$ $\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>$ ${<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}$ ${<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 18</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}{<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}$

Substitute formula (2) into formula (18), without loss of generality, let α _i =±1, β _{j, i} =±1, j=1, 2,..., M, i=1, 2,. .., N, then there are:

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N\; M</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 19</span>}<span\; class="notranslate">\; )</span>$

Among them, N is the total number of columns of β, M is the total number of rows of β, β=(β ₁ , β ₂ ,..., β _N ) is the spreading sequence matrix of discrete multi-carrier spread spectrum, β _j =(β _{j , 1,} β _{j, 2,} ..., β _{j, M} ) ^T is the jth column of the spreading matrix, j=1, 2, ..., N; T _c is the spreading sequence of direct sequence spreading α is the width of one symbol; _PT is the transmission power of any subcarrier; b(t) is the signal to be spread spectrum; U=diag{p(t), p(tT _c ),...,p( t-(N-1)T _c )}, diag{ } represents a diagonal matrix, p(t) is an amplitude pulse whose width is equal to T _c ; p=(p(t), p(tT _c ), .. ., p(t-(N-1)T _c )) ^T ; s=(cos(2πΔft), cos(2π2Δft), ..., cos(2πMΔft)) corresponds to each sub-carrier in the multi-carrier Δf is the spacing between subcarriers; n(t) is additive white Gaussian noise.

The working principle of the two-dimensional despreading module 27 composed of DFT28, DMC despreading 29, and DS despreading has been discussed in theory from the above, and the two despreading methods of de-frequency hopping 20 and de-hopping 17 are traditional techniques, so , the receiver proposed by the present invention performs joint despreading on the original information after joint spreading by performing two-dimensional despreading, de-frequency hopping, and de-hopping time-hopping method on the jointly spread-spectrum information. feasible. From formula (18), since $(\mathrm{\&beta;U\&alpha;}{p)}^T{\&Integral;}_0^{T_c}{\mathrm{the\; s}}^T\mathrm{no}\left(t\right)\mathrm{dt}$ is a Gaussian noise process with a mean value of zero, and obviously the detection result (t) is an unbiased estimate of b(t), which shows that the receiver structure in the present invention is an optimal method.

It should be noted that, according to the requirements of the system indicators and the like, the system of the present invention may not use the two units of adding guard time slot unit 5 and removing guard time slot unit 26 . Whether to add the guard slot unit 5 or remove the guard slot unit 26 does not affect the generality of the present invention.

In addition, the time and frequency synchronization information in the system of the present invention is used as the time and frequency reference for direct sequence spread spectrum despreading and discrete multi-carrier spread spectrum despreading.

The innovative point of the receiver part of the present invention is: on the basis of DS despreading, DMC despreading is added, and the methods of frequency hopping and time hopping are jointly understood, and the original information after joint spreading of the present invention is jointly despread.

The essence of the receiver part of the present invention: corresponding to the DMC spread spectrum signal of the transmitter of the present invention, DMC despreading is performed, and the direct sequence spread spectrum despreading, frequency hopping and time hopping are combined simultaneously.

In Figure 3, the two-dimensional spread spectrum is DS spread spectrum first, and then DMC spread spectrum. Since both DS spread spectrum and DMC spread spectrum are linear operations, the sequence can be exchanged. Therefore, it does not affect the generality of the present invention whether DS spreads first and then DMC spreads, or DMC spreads first and then DS spreads.

The discrete Fourier transform 4 may adopt a discrete Fourier transform technique (as shown in FIG. 3 ), or a fast Fourier transform technique.

The engineering realization of the present invention is compared with traditional one-dimensional spread spectrum joint frequency hopping, time-hopping low-interception wireless communication system, has the following characteristics:

(1) The interception rate of the present invention is lower than that of the prior art. This is because to intercept the wireless communication information of the inventive method, not only need to intercept the frequency hopping rule and the time hopping rule, but also need to further search for a detection method in two-dimensional space ; while the interception of traditional time-hopping frequency-hopping direct sequence spread spectrum wireless communication information is to find a detection method in one-dimensional space after de-hopping when de-hopping and de-frequency hopping. Obviously, it is much more difficult to intercept the wireless communication information of the method of the present invention.

(2) The frequency band involved in each hop of frequency hopping in the present invention is more uniform. In the traditional frequency-hopping direct-sequence spread spectrum wireless communication, its spectrum is a sin(2πΔf)/(2πΔf) function. The signal near the center point of each hop carrier (when Δf=0) has the strongest energy, and the farther away from the center point of the carrier The weaker the energy of the signal, the weaker the energy, thus causing the spread spectrum to be uneven, and it is easy for the enemy to detect the specific value of some modulation parameters. However, in each hop, the present invention consists of multiple subcarriers with the same spectrum width in the frequency domain. The shifts together form a total signal, so it is much more difficult to detect the carrier center frequency of each hop in the wireless communication system of the present invention.

(3) Since DFT is used for demodulation, adaptive interference suppression is not needed, and a single limiting algorithm is only needed to achieve a good ability to resist multi-frequency blocking interference.

(4) Facilitate the realization of digital wireless communication. IDFT of the present invention, DFT can use very mature IFFT, FFT in the project to implement, compared with traditional direct sequence spread spectrum low intercept wireless communication, the low intercept wireless communication receiver that uses the method of the present invention realizes and realizes cost is low, The performance is more stable.

(5) The ability to suppress the influence of fading channels is stronger. On the premise of satisfying a certain bit error rate requirement, it is illustrated that the low-interception wireless communication receiver realized by the method of the present invention does not require a transmitter to transmit more energy, thereby further increasing the anti-interception ability.

(6) adopt the receiver of wireless communication system of the present invention to realize more simply, under the same spread spectrum gain premise, realize the wireless communication of cost ratio time hopping frequency hopping direct sequence spread spectrum (FT-FH-DS-SS) System low.

As mentioned above, adopting the communication device of the present invention, the randomness of information on the wireless channel is stronger, making it more difficult for illegal users (such as enemies and vandals) to intercept the information of legitimate users, and it can be used for wireless communication, optical Communication, ultrasonic communication, wired communication and other technologies related to information (data) transmission provide technical guarantee for the security of information (data) transmission.

Description of drawings:

Figure 1 is a working principle diagram of a traditional direct sequence spread spectrum joint frequency hopping and time hopping low intercept wireless communication system

Among them, the transmitter part: 2 is a direct sequence (DS) spread spectrum unit, 6 is a transmit frequency hopping spread spectrum unit, 7 is a transmit frequency hopping sequence, 8 is a transmit local oscillator, 9 is filter one, and 10 is a transmit hop Time-spreading unit, 11 is a time-hopping sequence for transmitting, 12 is a transmitting switch, 13 is a transmitting radio frequency part, 14 is an antenna; 15 is a receiving antenna; receiver part: 16 is a radio frequency part, 17 is a time-spreading unit for de-hopping, 18 is time hopping receiving switch, 19 is time hopping sequence, 20 is receiver frequency mixing and frequency hopping part, 21 is frequency hopping sequence, 22 is local oscillator, 23 is filter, 24 is A/D conversion, 25 is A frequency and time synchronization unit, 30 is a DS despreading unit.

b(t) is the original input information, d(t) is the output information after direct sequence spreading 2, and (t) is the output of the two-dimensional despreading module 30 .

Figure 2 is a schematic diagram of the spreading sequence of direct sequence spreading

Wherein, the horizontal axis is the time axis, and α ₁ , α ₂ , . . . , α _N are specific values of the direct sequence spread spectrum sequence.

Fig. 3 is a schematic diagram of the principle of the communication method of the present invention

Among them, the transmitter part: 1 is a two-dimensional spread spectrum module, 2 is a direct sequence (DS) spread spectrum unit, 3 is a discrete multi-carrier (DMC) spread spectrum unit, 4 is an inverse discrete Fourier transform (IDFT) module, 5 Is to add guard time slot unit, 6 is to transmit frequency hopping spread spectrum unit, 7 is to transmit frequency hopping sequence, 8 is to transmit local oscillator, 9 is filter one, 10 is time hopping spread spectrum unit, 11 is to transmit time hopping sequence , 12 is a transmitting switch, 13 is a transmitting radio frequency part, 14 is an antenna; the receiver part: 15 is a receiving antenna, 16 is a radio frequency part, 17 is a spread spectrum unit when de-hopping, 18 is a receiving time-hopping switch, and 19 is a time-hopping sequence , 20 is the frequency mixing and de-frequency hopping part, 21 is the frequency hopping sequence, 22 is the local oscillator, 23 is the filter, 24 is the A/D conversion, 25 is the frequency time synchronization unit, 26 is the removal of the guard time slot unit, 27 is a two-dimensional despreading unit, 28 is a DFT module, 29 is a DMC spreading unit, and 30 is a DS despreading unit.

b(t) is the original input information; d(t) is the output information after direct sequence spread spectrum 2 spreading; f(t) is the output of the inverse discrete Fourier transform unit (4), that is, the two-dimensional spread spectrum module 1 r (t) is the input of the two-dimensional despreading module (27); g is the output signal after the discrete Fourier transform (20); h (t) is the output of the inverse discrete multi-carrier (29);  (t) is the output of the two-dimensional despreading module (27).

Figure 4 is a schematic diagram of the elements corresponding to the two-dimensional spread spectrum matrix

Wherein, the horizontal axis is the time axis, the vertical axis is the frequency, α _I is the element in the spreading sequence α=(α ₁ , α ₂ ,..., α _N ) ^T corresponding to the direct sequence spreading, and N is the direct sequence Spread spectrum processing gain, β _j = (β _{j, 1,} β _{j, 2,} ..., β _{j, M} ) ^T , j = 1, 2, ..., N; β = (β ₁ , β ₂ ,..., β _N ), β is a spreading sequence matrix corresponding to discrete multi-carrier spreading, and its different column vectors correspond to a frequency-domain spreading sequence of different data (chips) in frequency-domain spreading, α _j β _{j, i} is an element of a two-dimensional spread spectrum matrix, where i=1, 2, ..., M, j = 1, 2, ..., N.

Figure 5 is a schematic diagram of the spread spectrum principle of discrete multi-carrier spread spectrum 3

Wherein, 33 is a duplicator, and the duplicator 33 in the discrete multi-carrier spreading unit 3 inputs 1 symbol (chip), outputs the signal of the same 1 symbol width of M road, and every road signal is spread with frequency domain separately again Multiply frequency sequence β _j, i, d _i (t)=d(t)β _{j, i} p(t-(j-1)T _c )i=1, 2,..., M; j=1 , 2, ..., N, where: β _j = (β _{j, 1,} β _{j, 2,} ..., β _{j, M} ) ^T j = 1, 2, ..., N, β = ( β ₁ , β ₂ ,..., β _N ), β is the spreading sequence matrix of discrete multi-carrier spreading, and its different column vectors correspond to a frequency domain spreading of different data (chip) in frequency domain spreading sequence.

Fig. 6 is a schematic diagram of the working principle of the inverse discrete Fourier transform module (IDFT) 4

Wherein, Δf is the distance between any nearest two subcarriers in the multi-carrier, and there are M subcarriers in total, so the total frequency bandwidth is MΔf. The output of the inverse discrete Fourier transform unit is: $f\left(t\right)=\underset{i=1}{\overset{m}{\mathrm{\&Sigma;}}}\sqrt{2P_T}{d}_i\left(t\right)\cos \left(2\mathrm{\&pi;i\&Delta;ft}\right),$ _PT is the transmission power of any subcarrier, and d _i (t) is the Mth channel signal output from DMC3 spread spectrum.

Figure 7 is a schematic diagram of the addition of guard slot 5

Among them, G is the width of the guard slot, and T _c is the effective length of the symbol. Guard slots are used to combat intersymbol interference caused by multipath.

Detailed ways:

The main innovation of the transmitting part of the present invention is a joint spread spectrum communication system formed by combining two-dimensional spread spectrum, frequency hopping and time hopping spread spectrum methods, wherein frequency hopping spread spectrum and time hopping spread spectrum are existing spread spectrum method, the matrix expression (8) of the two-dimensional spread spectrum method is:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; s\&beta;U\&alpha;p</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Equation (8) can be realized by programming, and the existing technology can be used to make corresponding hardware to realize the process of two-dimensional spread spectrum; then, combined with the existing spread spectrum technology of frequency hopping spread spectrum and time hopping spread spectrum, the composition The transmitter system of the present invention.

Transmitter part work process of the present invention: the transmitting part of the present invention is at first by DS Direct Sequence Spread Spectrum (DirectSequence) unit 2, DMC discrete multi-carrier (Discrete MultiCarrier) unit 3, IDFT is inverse discrete Fourier transform (Inverse Discrete Forierr Transform) 4 form the module 1 that completes the two-dimensional spread spectrum function, which is the main innovation of the present invention; then by adding the output of the guard time slot unit 5, it is sent to the frequency hopping unit 6; the transmission frequency hopping sequence 7 controls the transmission local oscillator 8 The output frequency is mixed with the output of the added guard time slot 5, filtered and then sent to the time-hopping spread spectrum unit 10, wherein the transmitting time-hopping switch 12 is controlled by the transmitting time-hopping sequence 11. The central control unit 31 separately controls the DS spreading unit 2, the DMC spreading unit 3, the transmitting frequency hopping sequence 7, and the transmitting time hopping sequence 11 by controlling the timing and frequency in the whole system. The output of the transmitting time-hopping switch 12 is sent to the transmitting radio frequency part 13, and radiated into the electromagnetic wave transmission medium through the antenna 10. As shown in Figure 3.

The two-dimensional spread spectrum module 1 performs the spread spectrum operation on the user information, which can firstly perform direct sequence spread spectrum 2, and then perform discrete multi-carrier spread spectrum 3; or first perform discrete multi-carrier spread spectrum 3, and then perform direct sequence spread spectrum 2 ;

In the present invention, the spread spectrum operation sequence of the time-hopping spread spectrum 6, the frequency-hopping spread spectrum 10, and the two-dimensional spread spectrum 1 is variable, and the spread spectrum operation sequence of the three can be determined according to specific requirements. The inverse discrete Fourier transform 4 may adopt an inverse discrete Fourier transform technique, or may adopt a fast Fourier transform technique.

The method of two-dimensional spread spectrum can be briefly explained with Fig. 4 first. Multiply each bit b(t) of the original data with the two-dimensional spread spectrum matrix βUαp shown in Figure 4 to complete two-dimensional spread spectrum. In Figure 4, the horizontal axis is time, the vertical axis is frequency, and two-dimensional spread spectrum The mathematical expression of the two-dimensional spread spectrum output of module 1 is: $f\left(t\right)=\mathrm{s\&beta;U\&alpha;p}\sqrt{2P_T}b\left(t\right),$ Among them, f(t) is the signal after the joint spread spectrum; s=(cos(2πΔft), cos(2π2Δft),..., cos(2πMΔft)) corresponds to each subcarrier in the multi-carrier, Δf is the spacing between subcarriers; β=(β ₁ , β ₂ ,..., β _N ) is the spreading sequence matrix of discrete multi-carrier spreading, N is the total column number of β, β _j =(β _{j, 1,} β _{j, 2} ..., β _{j, M} ) ^T is the jth column of the spreading matrix, j=1, 2,..., N, M is the total number of rows of β, ( ) ^T represents the transfer Set operation; U=diag{p(t), p(tT _c ),..., p(t-(N-1)T _c )}, diag{ } represents a diagonal matrix, and p(t) is Width is equal to the amplitude pulse of T _c ; α is the spread spectrum sequence corresponding to direct sequence spread spectrum, α=diag(α ₁ ,α ₂ ,...,α _N ); p=(p(t),p(tT _c ),..., p(t-(N-1)T _c )) ^T ; P _T is the transmission power of any subcarrier; b(t) is the signal to be spread spectrum.

Each column in the spread spectrum matrix used by discrete multi-carrier spread spectrum 3 can be a different pseudo-random sequence, or the same pseudo-random sequence; the spread spectrum sequence used in the direct sequence spread spectrum 2 is a a pseudo-random sequence.

The function of adding the guard slot unit 5 is to reduce the intersymbol interference caused by channel multipath. The principle of adding the guard slot is shown in FIG. 7 , where G represents the length of the guard slot.

The main innovation of the receiving part of the present invention is a communication system composed of three spread spectrum methods: two-dimensional spread spectrum, frequency hopping, and time hopping, wherein the frequency hopping and time hopping are all existing spread spectrum methods, and the two-dimensional The principle of despreading is expressed by formula (13), (13), (14), (15), (18), and the final detection result is formula (19),

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N\; M</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&beta;U\&alpha;p</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 19</span>}<span\; class="notranslate">\; )</span>$

According to the method represented by the above formula, the communication device proposed by the present invention can be realized through programming, and then the corresponding hardware can be made by using the existing technology to form the receiver system of the present invention to realize the process of two-dimensional despreading.

Part of the working process of the receiver of the present invention: the signal received by the receiving antenna 15 in the receiver is sent to the A/D 24 after the time-hopping unit 17 and the frequency-hopping unit 20 are removed; wherein the time-hopping sequence 19 is controlled by the central control unit 31 The time-hopping sequence 19 controls the switch of the time-hopping switch 18; the frequency-hopping sequence 21 is controlled by the frequency and time synchronization 25 and the central control unit 31. The output of the A/D converter 24 removes the guard slot in the guard slot removal module 26 and sends it to the discrete Fourier transform (DFT) unit 28 in the two-dimensional despreading module 27 . The other signal output by the A/D converter 24 is sent to the frequency-time synchronization unit 25 to obtain time-frequency synchronization information, which is used for two-dimensional despreading and controlling the frequency accuracy of the local oscillator through the frequency hopping sequence. As shown in Figure 3.

Claims (6)

1. A communication device of combined spread spectrum comprises a transmitting part and a receiving part, wherein the transmitting part comprises a direct sequence spread spectrum unit (2), an inverse discrete Fourier transform (4), a frequency hopping spread spectrum unit (6) and a time hopping spread spectrum unit (10); the receiving part comprises a time hopping spreading unit (17), a frequency hopping spreading unit (20), a discrete Fourier transform (28) and a direct sequence despreading unit (30); the method is characterized in that the transmitting part also comprises a discrete multi-carrier spread spectrum unit (3), the discrete multi-carrier spread spectrum unit (3), a direct sequence spread spectrum unit (2) and an inverse discrete Fourier transform (4) form a two-dimensional spread spectrum module (1), and the two-dimensional spread spectrum module is two-dimensionalThe matrix expression for the spreading process is: <math> <mrow> <mi>f</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>s&beta;U&alpha;p</mi> <msqrt> <msub> <mrow> <mn>2</mn> <mi>P</mi> </mrow> <mi>T</mi> </msub> </msqrt> <mi>b</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> where f (t) is the signal after the joint spread spectrum, the elements in s ═ (cos (2 pi Δ ft), cos (2 pi 2 Δ ft), …, cos (2 pi M Δ ft)) correspond to each subcarrier in the multicarrier, Δ f is the spacing between subcarriers, β ═ (β M Δ ft) is the signal after the joint spread spectrum is applied, and β ═ is the signal after the joint spread spectrum is applied₁，β₂，…，β_N) A spreading sequence matrix for discrete multi-carrier spreading, N being the total number of columns, beta_j＝(β_j，1，β_j，2，…，β_j，M)^TIs the j column of the spreading matrix, j is 1, 2, …, N, M is the total row number of beta, (. cndot.)^TDenotes a transpose operation, U ═ diag { p (T), p (T-T)_c)，…，p(t-(N-1)T_c) Is a diagonal matrix, p (T) is equal in width to T_cα is a spreading sequence corresponding to direct sequence spreading, α ═ diag (α)₁，α₂，…，α_N)；p＝(p(t)，p(t-T_c)，…，p(t-(N-1)T_c))^T；P_TIs the transmission power of any subcarrier, b (t) is the signal of the spectrum to be spread; the two-dimensional spread spectrum module (1), the frequency hopping spread spectrum unit (6) and the time hopping spread spectrum unit (10) form a transmitting part of the device for joint spread spectrum communication; the receiving part also comprises an inverse discrete multi-carrier unit (29), the direct sequence despreading unit (30) and the discrete Fourier transform (28) form a two-dimensional despreading module (27), and the matrix expression of the two-dimensional despreading process is <math> <mrow> <mover> <mi>b</mi> <mo>^</mo> </mover> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>NMT</mi> <mi>c</mi> </msub> <msqrt> <mfrac> <msub> <mi>P</mi> <mi>T</mi> </msub> <mn>2</mn> </mfrac> </msqrt> <mi>b</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mi>&beta;U&alpha;p</mi> <mo>)</mo> </mrow> <mi>T</mi> </msup> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <msub> <mi>T</mi> <mi>c</mi> </msub> </msubsup> <msup> <mi>s</mi> <mi>T</mi> </msup> <mi>n</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mi>dt</mi> <mo>,</mo> </mrow> </math> Where N is the total number of columns of beta, M is the total number of rows of beta, beta is beta₁，β₂，…，β_N) Spreading sequence matrix, beta, for discrete multi-carrier spreading_j＝(β_j，1，β_j，2，…，β_j，M)^TJ is the jth column of the spreading matrix, j is 1, 2, …, N; t is_cA spreading sequence α that is direct sequence spread is one symbol wide; p_TIs the transmit power of any subcarrier; b (t) is a signal to be spread; u ═ diag { p (T), p (T-T)_c)，…，p(t-(N-1)T_c) Is a diagonal matrix, p (T) is equal in width to T_cThe amplitude pulse of (3); p ═ p (T), p (T-T)_c)，…，p(t-(N-1)T_c))^T(ii) a Elements in (cos (2 pi Δ ft), cos (2 pi 2 Δ ft), …, cos (2 pi M Δ ft)) correspond to each subcarrier in the multicarrier, and Δ f is the spacing between subcarriers; n (t) is additive white Gaussian noise; the two-dimensional despreading module (27) forms a receiving part of the device for joint spread spectrum communication together with the time hopping spreading unit (17) and the frequency hopping spreading unit (20).

2. A spread spectrum communication apparatus according to claim 1, wherein the two-dimensional spreading module (1) performs spreading operation on the user information in a sequence of direct sequence spreading (2) and discrete multi-carrier spreading (3); it is also possible to perform discrete multi-carrier spreading (3) first and then direct sequence spreading (2).

3. The spread spectrum communication apparatus according to claim 1, wherein the spreading operation sequence of the time hopping spreading (6), the frequency hopping spreading (10), and the two-dimensional spreading (1) is variable.

4. A spread spectrum combined communication device according to claim 1, wherein each column of the spreading sequence matrix used for the discrete multi-carrier spreading (3) may be a different pseudo-random sequence or the same pseudo-random sequence; the spreading sequence used by the direct sequence spreading (2) is a pseudo-random sequence.

5. A spread spectrum combined communication device according to claim 1, wherein the inverse discrete fourier transform (4) is an inverse discrete fourier transform technique or a fast fourier transform technique.

6. A combined spread spectrum communication device as claimed in claim 1, wherein the discrete fourier transform (4) is a discrete fourier transform technique or a fast fourier transform technique.

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