CN103763232A - Wavelet multi-carrier spread spectrum communication system and method with frequency changing - Google Patents

Abstract

The invention discloses a wavelet multi-carrier spread spectrum communication system and method with frequency changing. The system comprises a signal transmission device and a signal receiving device. The signal transmission device comprises an encoder, a spread spectrum unit, a carrier modulation unit and a parallel-series conversion unit all of which are connected in sequence; the signal receiving unit comprises a series-parallel conversion unit, a wavelet carrier unit, a dispreading unit, a data demodulation unit and a decoder all of which are connected in sequence. The system carries out wavelet reverse transformation on multi-carrier spread spectrum signals according to channel frequency changing to finish the parallel-series conversion, the system can be answerable for a time-frequency selective channel, and the stability of the system is improved; meanwhile, the fast wavelet transformation is adopted, the system has high adaptation and low calculation complexity.

Description

The small echo multi-carrier spread spectrum communication system and method that a kind of time-frequency changes

Technical field

The present invention relates to wireless communication technology field, be specifically related to small echo multi-carrier spread spectrum communication system, particularly relate to the small echo multi-carrier spread spectrum communication that can change with channel time-frequency.

Background technology

Wireless channel has the characteristic of T/F selective attenuation and is subject to Multi-Path Effects, in existing wireless communication technology, in order to overcome the problems referred to above, the main multi-carrier modulation technology that adopts, be that orthogonal frequency division multiplexi and spread spectrum combine, adopt multi-carrier spread spectrum communication system to realize transfer of data.Although yet the technical scheme of current existing multi-carrier spread spectrum communication system has higher modulation efficiency, reach gratifying transmission rate, but the collection of letters mechanism of Orthodoxy Frequency Division Multiplex is complicated, the agreement requiring is also complicated, what build is with high costs, and because Orthodoxy Frequency Division Multiplex adopts fast fourier transform, realize, between its subcarrier, frequency interval is fixed and reaches minimum, thereby very responsive to carrier frequency error. simultaneouslyIf cause that owing to producing relative motion between transmitter and receiver Doppler effect and clock jitter cause carrier frequency to produce any error, carrier frequency can lose orthogonality and produce larger inter-carrier interference, makes the reliability of communication system and adaptability unsatisfactory.In addition, for frequency-selective channel, OFDM is the method that proportion disperses, and the performance of its operation can reach good effect; And for time-selective channel or T/F selective channel, OFDM cannot be tackled the variation of channel, the performance of its operation often can not reach good effect.In addition, OFDM disturbs very responsive to very noisy, and as larger in impulse noise interference in the situation that, reliability and adaptability are all unsatisfactory.For in multi-carrier spread spectrum communication system, overcome the problem that changes the hydraulic performance decline bringing due to channel time-frequency, the new multi-carrier spread spectrum communication that exploitation can change with channel time-frequency and to process that very noisy disturbs be necessary simultaneously, but the method for developing at present all has higher computation complexity, be difficult to really realize in real-time communication system.

Summary of the invention

The shortcoming that the object of the invention is to overcome prior art, with not enough, provides a kind of small echo multi-carrier spread spectrum communication system that can change with channel time-frequency, and this system has higher adaptability and low computation complexity.

Another object of the present invention is to, a kind of method of the small echo multi-carrier spread spectrum communication system changing based on time-frequency is provided.

In order to reach above-mentioned the first object, the present invention by the following technical solutions:

The small echo multi-carrier spread spectrum communication system that a kind of time-frequency changes, comprise sender unit and signal receiving device, described sender unit comprises encoder, spectrum-spreading unit, carrier modulation unit and the parallel serial conversion unit being linked in sequence, and described signal receiving device comprises string converting unit, wavelet filtering unit, despread unit, data demodulation unit and the decoder being linked in sequence.

Spectrum-spreading unit in described sender unit first carries out spread processing by the data after encoder encodes, then by carrier modulation unit, the signal of spread spectrum is done and met the multi-carrier modulation of orthogonality condition and complete parallel-serial conversion and be sent to signal receiving device by wireless channel through the wavelet inverse transformation that time-frequency changes.

String in described signal receiving device converting unit complete and go here and there and change through wavelet transformation, by wavelet filtering unit, the signal receiving is done to wavelet filtering successively again, again to signal by despread unit despreading, then by data demodulation unit by signal demodulation, finally by decoder decoding, obtain data.

In order to reach above-mentioned the second object, the present invention by the following technical solutions:

A method for the small echo multi-carrier spread spectrum communication system that time-frequency changes, comprises the steps:

S1, in sender unit, concrete processing method is:

S11, by spectrum-spreading unit, each channel symbol data after encoder encodes are done to spread processing;

S12, by carrier modulation unit, adjust between line frequency difference, subcarrier frequency between frequency difference and subcarrier, and spread-spectrum signal s (t) is sent to parallel serial conversion unit;

S13, by parallel serial conversion unit after wavelet inverse transformation, the data-signal y (t) that time-frequency diagram data will convert series connection to is sent to receiving terminal through wireless channel;

S2, in sender unit, concrete processing method is:

S21, obtain symbol data signal r (t);

S22, string converting unit are first sampled the chip data-signal r (t) receiving to obtain the data of the form of connecting;

S23, wavelet filtering unit reduce impulsive noise by multicarrier spectrum-spread signal s (t) signal in order to the filter of lower design:

$r_j\left(k\right)=\sqrt{\frac{{\mathrm{\σ}}_W^2}{{\mathrm{\σ}}_W^2+{\mathrm{\σ}}^2}}{s}_j\left(k\right)---\mathrm{VI})$

In likes VI), σ ²the estimated value of noise variance, σ _w ²the mean-square value of each sub-carrier signal, s _j(k) be in j sub-carrier signal, to be identified as being subject to the signal data of impulse noise interference, r _j(k) be the signal data after filtering is processed;

S24, despread unit by the spread spectrum pseudo-random binary symbol signal of each subcarrier by following formula VII) make auto-correlation processing,

r _i(t)=F ^-1[R _i(f)S _i(f)]VII）

In likes VII), r _i(t) be i the sub-carrier signal obtaining, F ^-1the inverse transformation of Fourier transform, R _i(f) be the Fourier transform value of i the sub-carrier signal after wavelet filtering is processed received, S _i(f) be i subcarrier spread spectrum pseudo-random binary symbol signal s _i(t) Fourier transform value;

S25, the data demodulation unit signal after to despreading is done binary phase shift keying demodulation, restores the data that described sender unit sends;

S26, decoder are again by the data decode after reduction;

S27, by decoder again by reduction after data decode send equipment to.

Step S11 is specially:

S111, according to the size of data rate and the channel width allowing, by data allocations to be sent to a plurality of subcarriers of Permissible bandwidth, and according to frequency difference between line frequency difference, data sampling length computation and setting subcarrier, make sub-carrier frequencies in frequency domain, show as continuous ascending single frequency, obtain the subcarrier binary code metadata of frequency orthogonal and gap variable;

S112, each subcarrier binary code metadata d by spreading code c (t) with frequency orthogonal and gap variable _i(t) cos (2 π f _cit+ θ) multiply each other, obtain the mutually orthogonal continually varying modulation signal of centre frequency of symbol data signal;

S113, by the binary element of modulation signal by following formula I) carry out spread processing and be added operation, thereby obtain spread-spectrum signal s (t):

$s\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{A}_i{d}_i\left(t\right)c\left(t\right)\cos (2\mathrm{\π}{f}_{c_i}t+\mathrm{\θ})---I)$

In likes I), the quantity that N is subcarrier, d _i(t) be t binary code metadata constantly in i channel, c (t) for the value producing with the shift register of linear feedback in band spectrum modulation unit be+1 or-1 t moment spread spectrum pseudo-random binary chip, f _cibe the subcarrier centre frequency in i channel, A _ibe the signal amplitude of i channel, θ is the initial phase of signal in this channel, d _i(t) cos (2 π f _cit+ θ) be the subcarrier binary code metadata of frequency orthogonal and gap variable.

In step S12, described carrier modulation unit is by Formula Il) adjust between line frequency difference, subcarrier frequency between frequency difference and subcarrier:

Line frequency difference: $\mathrm{\Δ}{f}_l=\frac{C}{2^n-1}$

Frequency difference between subcarrier: $\mathrm{\Δf}=\frac{m}{N}\mathrm{\Δ}{f}_l=\frac{\mathrm{mC}}{(2^n-1)N}---\mathrm{II})$

Sub-carrier frequencies: $\{f_c-(\frac{N}{2}-1)\mathrm{\Δf}\},\·\·\·,\{f_c-\mathrm{\Δf}\},\left\{f_c\right\},\{f_c+\mathrm{\Δf}\},\·\·\·,\{f_c+\left(\frac{N}{2}\right)\mathrm{\Δf}\}$

, in, C is the spreading rate of spread spectrum pseudo-random binary chip likes II), 2 ⁿ-1 is the chip lengths of this chip, 2 ⁿin-1, n represents the progression of the feedback shift register in carrier modulation unit, △ f _lfor the line frequency difference of spread spectrum pseudo-random binary chip, △ f is frequency difference between each subcarrier, the quantity that N is subcarrier, f _ccentered by channel subcarrier centre frequency, m is more than or equal to 1 positive integer;

At parallel serial conversion unit, multicarrier spectrum-spread signal s (t) is carried out to wavelet inverse transformation and complete parallel-serial conversion; Wherein N is that the quantity of subcarrier (is supposed N=2 ⁱ), representing frequency change, L is time span, and the time that represents changes, and N parallel time frequency signal is together in series from low to high and forms following a plurality of series units by frequency:

s ₁(t ₁)...s ₁(t _L)，

s ₂(t ₁)...s ₂(t _L)，

s ₃(t ₁)...s ₃(t _L)s ₄(t ₁)...s ₄(t _L),

s ₅(t ₁)...s ₅(t _L)s ₆(t ₁)...s ₆(t _L)s ₇(t ₁)...s ₇(t _L)s ₈(t ₁)...s ₈(t _L)，

…

$s_{2^{i-1}+1}\left(t_1\right)\·\·\·s_{2^{i-1}+1}\left(t_L\right)s_{2^{i-1}+2}\left(t_1\right)\·\·\·s_{2^{i-1}+2}\left(t_L\right)\·\·\·\·\·\·s_{2^i-1}\left(t_1\right)\·\·\·s_{2^i-1}\left(t_L\right)s_{2^i}\left(t_1\right)\·\·\·s_{2^i}\left(t_L\right).$

In step S21, obtain data symbols data-signal r (t) method and be:

$\begin{array}{c}r\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}[D\left(t\right)+R\left(t\right)]+n\left(t\right)\\ =\underset{i=1}{\overset{N}{\mathrm{\Σ}}}[A_i{d}_i(t-T_d)c(t-T_d)\cos (2\mathrm{\π}{f}_{\mathrm{ci}}t-{\mathrm{\φ}}_0)+\\ \mathrm{\α}{A}_i{d}_i(t-T_d-\mathrm{\Δ}{T}_d)c(t-T_d-\mathrm{\Δ}{T}_d)\cos (2\mathrm{\π}{f}_{\mathrm{ci}}t-{\mathrm{\φ}}_0-\mathrm{\Δ}{\mathrm{\φ}}_0)]+n\left(t\right)\end{array}---\mathrm{III})$

Formula III) in, D (t) is direct signal, and R (t) is reflected signal, and n (t) is noise, T _dfor propagation delay, φ ₀for sub-carrier phase, α be reflected signal compared to the relative propagation loss of direct signal, 0< α≤1 wherein, △ T _dfor relative propagation delay, △ φ ₀for relative phase difference;

Then, adopt following formula I V) r (t) is transformed into plural form,

$\begin{array}{c}r\left(t\right)=h\left(t\right)*y\left(t\right)=h\left(t\right)*[s\left(t\right)+n\left(t\right)]=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}h(\mathrm{\&tau;},t)y(t-\mathrm{\&tau;})=\\ \underset{i=1}{\overset{N_p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i\exp \left[j{\mathrm{\&phi;}}_i\left(t\right)\right]y(t-\mathrm{\&tau;})\end{array}---\mathrm{IV})$

In likes IV), the impulse response that h (t) is receive channel, y (t) is for transmitting, and τ is time delay, φ _i(t) be phase place, * is convolution sign, N _pquantity for the y that transmits (t); The time selectivity characteristic of channel can be showed by the impulse response h (t) of channel, and the frequency selectivity characteristic of channel can be showed by the frequency response H (f) of channel.

In step S22, carry out as follows the operation of wavelet transformation:

$W_{j,k}={\left|2^j\right|}^{-\frac{1}{2}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}r\left(t\right)\stackrel{-}{\mathrm{\&psi;}}\left(\frac{t-k{2}^j}{2^j}\right)\mathrm{dt}$

, in, upper line represents conjugate function likes V); In order to realize wavelet inverse transformation, the time-frequency diagram data of input can be regarded as to serial wavelet coefficient w _j,k(s ₂(t ₁) ... s ₂(t _l), s ₃(t ₁) ... s ₃(t _l) s ₄(t ₁) ... s ₄(t _l), s ₅(t ₁) ... s ₅(t _l) s ₆(t ₁) ... s ₆(t _l) s ₇(t ₁) ... s ₇(t _l) s ₈(t ₁) ... s ₈(t _l) ..., $s_{2^{i-1}+1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+1}\left(t_L\right)s_{2^{i-1}+2}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+2}\left(t_L\right)\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_L\right)s_{2^i}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i}\left(t_L\right))$ With approximation coefficient a _j,k(s ₁(t ₁) ... s ₁(t _l)), while carrying out multi-carrier modulation, carrier wave will be respectively small echo Ψ _j,k(t)=2 ^-j/2Ψ (2 ^-jt-k) and scaling Equations

through parallel serial conversion unit, can obtain output signal y (t).

The expression formula of output signal y (t) is:

For adaptive channel time-frequency changes, the value of adjustable parameters N and L; According to the T/F selectivity characrerisitic of channel, if frequency selectivity is strong, N value is optional larger, and L value is optional smaller; If time selectivity is strong, N value is optional smaller, and L value is optional larger; After wavelet inverse transformation, the data-signal y (t) that time-frequency diagram data will convert series connection to is sent to receiving terminal through wireless channel.

The present invention has following advantage and effect with respect to prior art:

A) the method for the invention is first pressed formula

frequency difference between subcarrier is tuned up, greatly reduce the impact of multipath decline and carrier frequency error, the stability of communication is significantly improved.

B) owing to adopting binary phase shift keying (BPSK) as carrier modulation mode, and according to the bandwidth of sender unit data rate to be sent and wireless channel, determine that the quantity of subcarrier makes frequency orthogonal between subcarrier, thereby can use simple frequency division multiple access (FDMA) technology to realize the multiple access access of N sub-carrier signal.Again owing to only using a unique spreading code, and the despreading process of receiving terminal is a kind of auto-correlation processing based on FFT (fast fourier transform), and the complexity of its calculating reduces greatly.

C) because system provided by the invention changes and to carry out wavelet inverse transformation and complete parallel-serial conversion by channel time-frequency multicarrier spectrum-spread signal, make system can tackle T/F selective channel, thereby improved the stability of system; Owing to adopting wavelet transformation fast, this system has higher adaptability and low computation complexity simultaneously.

D) because system provided by the invention has added wavelet filtering unit at signal receiving device, in wavelet field, the noise of identification is carried out to filtering, greatly reduce the impact of Noise and Interference, more improved the stability of system.

E) due to system, adopt the simple ripe technology such as simple spreading code, fast Fourier transform (FFT), fast wavelet transform and binary phase shift keying (BPSK) modulation to complete the transmission of system is controlled, greatly reduce the construction cost of system.

Accompanying drawing explanation

Fig. 1 is the topological structure schematic diagram of a specific embodiment of the small echo multi-carrier spread spectrum communication system that changes of a kind of time-frequency of the present invention.

Fig. 2 is the structured flowchart of a specific embodiment of communication equipment of the present invention.

The communication flow diagram that Fig. 3 (a) is sender unit of the present invention.

The communication flow diagram of Fig. 3 (b) and signal receiving device.

Fig. 4 is time-frequency datagram of the present invention.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited to this.

Embodiment

Referring to Fig. 1, wireless communication system shown in this example is comprised of communication equipment A, communication equipment B and communication equipment C, in this system, communication equipment B can be processed data to be sent or that receive to be sent to communication equipment A and C or to receive from data communication equipment A and C and process small echo multi-carrier spread spectrum modem processes by small echo multi-carrier spread spectrum modulator-demodulator.

By the communication data that sends 8 channels in communication equipment B, the small echo multi-carrier spread spectrum wireless communication process process to communication equipment A and C is described in detail below:

Referring to Fig. 2, communication equipment A or communication equipment C comprise a sender unit and a signal receiving device, wherein,

Described sender unit is comprised of the encoder connecting successively, spectrum-spreading unit, carrier modulation unit and parallel serial conversion unit (wavelet inverse transformation); Described signal receiving device is comprised of the string connecting successively converting unit (wavelet transformation), wavelet filtering unit, despread unit, data demodulation unit and decoder.

Referring to Fig. 3 (a) and Fig. 3 (b), in the present embodiment, get the numerical value that N=8(N gets other and be equally applicable to technical scheme of the present invention), the communication data that sends 8 channels in communication equipment B is as follows to the multi-carrier spread spectrum radio communication control flow of communication equipment A and C:

In sender unit, first, by described spectrum-spreading unit, each channel symbol data after encoder encodes are done to spread processing, step is as follows:

A) according to the channel width of the size of data rate and permission, by data allocations to be sent to 8 subcarriers of Permissible bandwidth, and according to frequency difference between line frequency difference and data sampling length computation and setting subcarrier, make sub-carrier frequencies in frequency domain, show as continuous ascending single frequency, obtain the subcarrier binary code metadata of frequency orthogonal and gap variable;

B) each subcarrier binary code metadata d with frequency orthogonal and gap variable by spreading code c (t) _i(t) cos (2 π f _cit+ θ) multiply each other, obtain the mutually orthogonal continually varying modulation signal of centre frequency of symbol data signal;

C) by the binary element of modulation signal by following formula I) carry out spread processing and be added operation, thereby obtain spread-spectrum signal s (t):

$s\left(t\right)=\underset{i=1}{\overset{8}{\mathrm{\&Sigma;}}}{A}_i{d}_i\left(t\right)c\left(t\right)\cos (2\mathrm{\&pi;}{f}_{c_i}t+\mathrm{\&theta;})---I)$

In likes I), d _i(t) be t binary code metadata constantly in i channel, c (t) for the value producing with the shift register of linear feedback in band spectrum modulation unit be+1 or-1 t moment spread spectrum pseudo-random binary chip (PN code), f _cibe the subcarrier centre frequency in i channel, A _ibe the signal amplitude of i channel, θ is the initial phase of signal in this channel, d _i(t) cos (2 π f _cit+ θ) be the subcarrier binary code metadata of frequency orthogonal and gap variable;

Then, by described carrier modulation unit by Formula Il) adjust between line frequency difference, subcarrier frequency between frequency difference and subcarrier, and spread-spectrum signal s (t) is sent to parallel serial conversion unit (wavelet inverse transformation):

Line frequency difference: $\mathrm{\&Delta;}{f}_l=\frac{C}{2^n-1}$

Frequency difference between subcarrier: $\mathrm{\&Delta;f}=\frac{m}{N}\mathrm{\&Delta;}{f}_l=\frac{\mathrm{mC}}{(2^n-1)N}---\mathrm{II})$

Sub-carrier frequencies: $\{f_c-(\frac{N}{2}-1)\mathrm{\&Delta;f}\},\&CenterDot;\&CenterDot;\&CenterDot;,\{f_c-\mathrm{\&Delta;f}\},\left\{f_c\right\},\{f_c+\mathrm{\&Delta;f}\},\&CenterDot;\&CenterDot;\&CenterDot;,\{f_c+\left(\frac{N}{2}\right)\mathrm{\&Delta;f}\}$

, in, C is the spreading rate of spread spectrum pseudo-random binary chip likes II), 2 ⁿ-1 is the chip lengths of this chip, 2 ⁿin-1, n represents the progression of the feedback shift register in carrier modulation unit, △ f _lfor the line frequency difference of spread spectrum pseudo-random binary chip, △ f is frequency difference between each subcarrier, the quantity that N is subcarrier, f _ccentered by channel subcarrier centre frequency, the spreading rate C of spread spectrum pseudo-random binary chip (PN code) is 1MHz in the present embodiment, chip lengths is 2 ⁹-1=511, setting frequency difference adjustment parameter m between subcarrier is 72, can obtain like this line frequency difference △ f of spread spectrum pseudo-random binary chip _land between each subcarrier, frequency difference △ f is respectively:

$\mathrm{\&Delta;}{f}_l=\frac{1000000}{511}=1.957\mathrm{KHz}$

$\mathrm{\&Delta;f}=\frac{m}{N}\mathrm{\&Delta;}{f}_l=\frac{72\&times;1000000}{511\&times;8}=17.6\mathrm{KHz}$

Make f _cfor 1000KHz, the centre frequency of the subcarrier after each modulation is respectively: 947.2KHz, 964.8KHz, 982.4KHz, 1000KHz, 1017.6KHz, 1035.2KHz, 1052.8KHz, 1070.4KHz.

As shown in Figure 4, at parallel serial conversion unit (wavelet inverse transformation), multicarrier spectrum-spread signal s (t) is carried out to wavelet inverse transformation and complete parallel-serial conversion.Process in parallel-serial conversion is got N=8, L=1024, and 8 parallel time frequency signals are together in series from low to high and form 4 following series units by frequency:

s ₁(t ₁)...s ₁(t _L)，

s ₂(t ₁)...s ₂(t _L)，

s ₃(t ₁)...s ₃(t _L)s ₄(t ₁)...s ₄(t _L),

s ₅(t ₁)...s ₅(t _L)s ₆(t ₁)...s ₆(t _L)s ₇(t ₁)...s ₇(t _L)s ₈(t ₁)...s ₈(t _L)，

Then, by described parallel serial conversion unit (wavelet inverse transformation), after wavelet inverse transformation, (can adopt 9/7 lifting wavelet transform fast), the data-signal y (t) that time-frequency diagram data will convert series connection to is sent to receiving terminal through wireless channel.

In signal receiving device, first,

1) signal of described reception is by following formula III) explain and obtain symbol data signal r (t),

$\begin{array}{c}r\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}[D\left(t\right)+R\left(t\right)]+n\left(t\right)\\ =\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}[A_i{d}_i(t-T_d)c(t-T_d)\cos (2\mathrm{\&pi;}{f}_{\mathrm{ci}}t-{\mathrm{\&phi;}}_0)+\\ \mathrm{\&alpha;}{A}_i{d}_i(t-T_d-\mathrm{\&Delta;}{T}_d)c(t-T_d-\mathrm{\&Delta;}{T}_d)\cos (2\mathrm{\&pi;}{f}_{\mathrm{ci}}t-{\mathrm{\&phi;}}_0-\mathrm{\&Delta;}{\mathrm{\&phi;}}_0)]+n\left(t\right)\end{array}---\mathrm{III})$

Formula III) in, D (t) is direct signal, and R (t) is reflected signal, and n (t) is noise, T _dfor propagation delay, φ ₀for sub-carrier phase, α be reflected signal compared to the relative propagation loss of direct signal, 0< α≤1 wherein, △ T _dfor relative propagation delay, △ φ ₀for relative phase difference;

Then, adopt following formula I V) r (t) is transformed into plural form,

$\begin{array}{c}r\left(t\right)=h\left(t\right)*y\left(t\right)=h\left(t\right)*[s\left(t\right)+n\left(t\right)]=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}h(\mathrm{\&tau;},t)y(t-\mathrm{\&tau;})=\\ \underset{i=1}{\overset{N_p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i\exp \left[j{\mathrm{\&phi;}}_i\left(t\right)\right]y(t-\mathrm{\&tau;})\end{array}---\mathrm{IV})$

In likes IV), the impulse response that h (t) is receive channel, y (t) is for transmitting, and τ is time delay, φ _i(t) be phase place, * is convolution sign, N _pquantity for the y that transmits (t); The time selectivity characteristic of channel can be showed by the impulse response h (t) of channel, and the frequency selectivity characteristic of channel can be showed by the frequency response H (f) of channel.

2) described string converting unit (wavelet transformation) first sampled the chip data-signal r (t) receiving to obtain the data of the form of connecting, then by following formula, carries out the operation of wavelet transformation,

$W_{j,k}={\left|2^j\right|}^{-\frac{1}{2}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}r\left(t\right)\stackrel{-}{\mathrm{\&psi;}}\left(\frac{t-k{2}^j}{2^j}\right)\mathrm{dt}$

In likes V), wavelet coefficient w _j,kcan the data of series connection form be reverted back to s by the time-frequency figure of transmitting terminal ₂(t ₁) ... s ₂(t _l), s ₃(t ₁) ... s ₃(t _l) s ₄(t ₁) ... s ₄(t _l), s ₅(t ₁) ... s ₅(t _l) s ₆(t ₁) ... s ₆(t _l) s ₇(t ₁) ... s ₇(t _l) s ₈(t ₁) ... s ₈(t _l), approximation coefficient a _j,kthe data of series connection form are reverted back to s ₁(t ₁) ... s ₁(t _l), thereby obtain multicarrier spectrum-spread signal s (t);

3) described wavelet filtering unit reduces impulsive noise by multicarrier spectrum-spread signal s (t) signal in order to the filter of lower design:

$r_j\left(k\right)=\sqrt{\frac{{\mathrm{\&sigma;}}_W^2}{{\mathrm{\&sigma;}}_W^2+{\mathrm{\&sigma;}}^2}}{s}_j\left(k\right)---\mathrm{VI})$

In likes VI), σ ²the estimated value of noise variance, σ _w ²the mean-square value of each sub-carrier signal, s _j(k) be in j sub-carrier signal, to be identified as being subject to the signal data of impulse noise interference, r _j(k) be the signal data after filtering is processed;

4) described despread unit by the spread spectrum pseudo-random binary symbol signal of each subcarrier by following formula VII) make auto-correlation processing,

r _i(t)=F ^-1[R _i(f)S _i(f)]VII）

In likes VII), r _i(t) be i the sub-carrier signal obtaining, F ^-1the inverse transformation of Fourier transform, R _i(f) be the Fourier transform value of i the sub-carrier signal after wavelet filtering is processed received, S _i(f) be i subcarrier spread spectrum pseudo-random binary symbol signal s _i(t) Fourier transform value;

5) signal of described data demodulation unit after to despreading done binary phase shift keying demodulation, restores the data that described sender unit sends;

6) described decoder is again by the data decode after reduction.

Finally by described decoder, send the data decode after reduction to equipment again.

Above-described embodiment is preferably execution mode of the present invention; but embodiments of the present invention are not restricted to the described embodiments; other any do not deviate from change, the modification done under Spirit Essence of the present invention and principle, substitutes, combination, simplify; all should be equivalent substitute mode, within being included in protection scope of the present invention.

Claims (9)

1. the small echo multi-carrier spread spectrum communication system that a time-frequency changes, it is characterized in that, comprise sender unit and signal receiving device, described sender unit comprises encoder, spectrum-spreading unit, carrier modulation unit and the parallel serial conversion unit being linked in sequence, and described signal receiving device comprises string converting unit, wavelet filtering unit, despread unit, data demodulation unit and the decoder being linked in sequence.

2. the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 1 changes, it is characterized in that, spectrum-spreading unit in described sender unit first carries out spread processing by the data after encoder encodes, then by carrier modulation unit, the signal of spread spectrum is done and met the multi-carrier modulation of orthogonality condition and complete parallel-serial conversion and be sent to signal receiving device by wireless channel through the wavelet inverse transformation that time-frequency changes.

3. the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 1 changes, it is characterized in that, string in described signal receiving device converting unit complete and go here and there and change through wavelet transformation, by wavelet filtering unit, the signal receiving is done to wavelet filtering successively again, again to signal by despread unit despreading, then by data demodulation unit by signal demodulation, finally by decoder decoding, obtain data.

4. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 1 changes, is characterized in that, comprises the steps:

S1, in sender unit, concrete processing method is:

S11, by spectrum-spreading unit, each channel symbol data after encoder encodes are done to spread processing;

S12, by carrier modulation unit, adjust between line frequency difference, subcarrier frequency between frequency difference and subcarrier, and spread-spectrum signal s (t) is sent to parallel serial conversion unit;

S13, by parallel serial conversion unit after wavelet inverse transformation, the data-signal y (t) that time-frequency diagram data will convert series connection to is sent to receiving terminal through wireless channel;

S2, in sender unit, concrete processing method is:

S21, obtain symbol data signal r (t);

S22, string converting unit are first sampled the chip data-signal r (t) receiving to obtain the data of the form of connecting;

S23, wavelet filtering unit reduce impulsive noise by multicarrier spectrum-spread signal s (t) signal in order to the filter of lower design:

$r_j\left(k\right)=\sqrt{\frac{{\mathrm{\&sigma;}}_W^2}{{\mathrm{\&sigma;}}_W^2+{\mathrm{\&sigma;}}^2}}{s}_j\left(k\right)---\mathrm{VI})$

In likes VI), σ ²the estimated value of noise variance, σ _w ²the mean-square value of each sub-carrier signal, s _j(k) be in j sub-carrier signal, to be identified as being subject to the signal data of impulse noise interference, r _j(k) be the signal data after filtering is processed;

S24, despread unit by the spread spectrum pseudo-random binary symbol signal of each subcarrier by following formula VII) make auto-correlation processing,

r _i(t)=F ^-1[R _i(f)S _i(f)]VII）

In likes VII), r _i(t) be i the sub-carrier signal obtaining, F ^-1the inverse transformation of Fourier transform, R _i(f) be the Fourier transform value of i the sub-carrier signal after wavelet filtering is processed received, S _i(f) be i subcarrier spread spectrum pseudo-random binary symbol signal s _i(t) Fourier transform value;

S25, the data demodulation unit signal after to despreading is done binary phase shift keying demodulation, restores the data that described sender unit sends;

S26, decoder are again by the data decode after reduction;

S27, by decoder again by reduction after data decode send equipment to.

5. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 4 changes, is characterized in that, step S11 is specially:

S111, according to the size of data rate and the channel width allowing, by data allocations to be sent to a plurality of subcarriers of Permissible bandwidth, and according to frequency difference between line frequency difference, data sampling length computation and setting subcarrier, make sub-carrier frequencies in frequency domain, show as continuous ascending single frequency, obtain the subcarrier binary code metadata of frequency orthogonal and gap variable;

S112, each subcarrier binary code metadata d by spreading code c (t) with frequency orthogonal and gap variable _i(t) cos (2 π f _cit+ θ) multiply each other, obtain the mutually orthogonal continually varying modulation signal of centre frequency of symbol data signal;

S113, by the binary element of modulation signal by following formula I) carry out spread processing and be added operation, thereby obtain spread-spectrum signal s (t):

$s\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_i{d}_i\left(t\right)c\left(t\right)\cos (2\mathrm{\&pi;}{f}_{c_i}t+\mathrm{\&theta;})---I)$

In likes I), the quantity that N is subcarrier, d _i(t) be t binary code metadata constantly in i channel, c (t) for the value producing with the shift register of linear feedback in band spectrum modulation unit be+1 or-1 t moment spread spectrum pseudo-random binary chip, f _cibe the subcarrier centre frequency in i channel, A _ibe the signal amplitude of i channel, θ is the initial phase of signal in this channel, d _i(t) cos (2 π f _cit+ θ) be the subcarrier binary code metadata of frequency orthogonal and gap variable.

6. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 4 changes, is characterized in that, in step S12, described carrier modulation unit is by Formula Il) adjust between line frequency difference, subcarrier frequency between frequency difference and subcarrier:

Line frequency difference: $\mathrm{\&Delta;}{f}_l=\frac{C}{2^n-1}$

Frequency difference between subcarrier: $\mathrm{\&Delta;f}=\frac{m}{N}\mathrm{\&Delta;}{f}_l=\frac{\mathrm{mC}}{(2^n-1)N}---\mathrm{II})$

Sub-carrier frequencies: $\{f_c-(\frac{N}{2}-1)\mathrm{\&Delta;f}\},\&CenterDot;\&CenterDot;\&CenterDot;,\{f_c-\mathrm{\&Delta;f}\},\left\{f_c\right\},\{f_c+\mathrm{\&Delta;f}\},\&CenterDot;\&CenterDot;\&CenterDot;,\{f_c+\left(\frac{N}{2}\right)\mathrm{\&Delta;f}\}$

, in, C is the spreading rate of spread spectrum pseudo-random binary chip likes II), 2 ⁿ-1 is the chip lengths of this chip, 2 ⁿin-1, n represents the progression of the feedback shift register in carrier modulation unit, △ f _lfor the line frequency difference of spread spectrum pseudo-random binary chip, △ f is frequency difference between each subcarrier, the quantity that N is subcarrier, f _ccentered by channel subcarrier centre frequency, m is more than or equal to 1 positive integer;

At parallel serial conversion unit, multicarrier spectrum-spread signal s (t) is carried out to wavelet inverse transformation and complete parallel-serial conversion; Wherein N is the quantity of subcarrier, supposes N=2 ⁱ, representing frequency change, L is time span, and the time that represents changes, and N parallel time frequency signal is together in series from low to high and forms following a plurality of series units by frequency:

s ₁(t ₁)...s ₁(t _L)，

s ₂(t ₁)...s ₂(t _L)，

s ₃(t ₁)...s ₃(t _L)s ₄(t ₁)...s ₄(t _L),

s ₅(t ₁)...s ₅(t _L)s ₆(t ₁)...s ₆(t _L)s ₇(t ₁)...s ₇(t _L)s ₈(t ₁)...s ₈(t _L)，

…

$s_{2^{i-1}+1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+1}\left(t_L\right)s_{2^{i-1}+2}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+2}\left(t_L\right)\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_L\right)s_{2^i}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i}\left(t_L\right).$

7. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 4 changes, is characterized in that, in step S21, obtains data symbols data-signal r (t) method and is:

$\begin{array}{c}r\left(t\right)=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}[D\left(t\right)+R\left(t\right)]+n\left(t\right)\\ =\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}[A_i{d}_i(t-T_d)c(t-T_d)\cos (2\mathrm{\&pi;}{f}_{\mathrm{ci}}t-{\mathrm{\&phi;}}_0)+\\ \mathrm{\&alpha;}{A}_i{d}_i(t-T_d-\mathrm{\&Delta;}{T}_d)c(t-T_d-\mathrm{\&Delta;}{T}_d)\cos (2\mathrm{\&pi;}{f}_{\mathrm{ci}}t-{\mathrm{\&phi;}}_0-\mathrm{\&Delta;}{\mathrm{\&phi;}}_0)]+n\left(t\right)\end{array}---\mathrm{III})$

Formula III) in, D (t) is direct signal, and R (t) is reflected signal, and n (t) is noise, T _dfor propagation delay, φ ₀for sub-carrier phase, α be reflected signal compared to the relative propagation loss of direct signal, 0< α≤1 wherein, △ T _dfor relative propagation delay, △ φ ₀for relative phase difference;

Then, adopt following formula I V) r (t) is transformed into plural form,

$\begin{array}{c}r\left(t\right)=h\left(t\right)*y\left(t\right)=h\left(t\right)*[s\left(t\right)+n\left(t\right)]=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}h(\mathrm{\&tau;},t)y(t-\mathrm{\&tau;})=\\ \underset{i=1}{\overset{N_p}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i\exp \left[j{\mathrm{\&phi;}}_i\left(t\right)\right]y(t-\mathrm{\&tau;})\end{array}---\mathrm{IV})$

In likes IV), the impulse response that h (t) is receive channel, y (t) is for transmitting, and τ is time delay, φ _i(t) be phase place, * is convolution sign, N _pquantity for the y that transmits (t); The time selectivity characteristic of channel can be showed by the impulse response h (t) of channel, and the frequency selectivity characteristic of channel can be showed by the frequency response H (f) of channel.

8. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 4 changes, is characterized in that, in step S22, carries out as follows the operation of wavelet transformation:

$W_{j,k}={\left|2^j\right|}^{-\frac{1}{2}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}r\left(t\right)\stackrel{-}{\mathrm{\&psi;}}\left(\frac{t-k{2}^j}{2^j}\right)\mathrm{dt}$

, in, upper line represents conjugate function likes V); In order to realize wavelet inverse transformation, the time-frequency diagram data of input can be regarded as to serial wavelet coefficient w _j,k(s ₂(t ₁) ... s ₂(t _l), s ₃(t ₁) ... s ₃(t _l) s ₄(t ₁) ... s ₄(t _l), s ₅(t ₁) ... s ₅(t _l) s ₆(t ₁) ... s ₆(t _l) s ₇(t ₁) ... s ₇(t _l) s ₈(t ₁) ... s ₈(t _l) ..., $s_{2^{i-1}+1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+1}\left(t_L\right)s_{2^{i-1}+2}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^{i-1}+2}\left(t_L\right)\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i-1}\left(t_L\right)s_{2^i}\left(t_1\right)\&CenterDot;\&CenterDot;\&CenterDot;s_{2^i}\left(t_L\right))$ With approximation coefficient a _j,k(s ₁(t ₁) ... s ₁(t _l)), while carrying out multi-carrier modulation, carrier wave will be respectively small echo Ψ _j,k(t)=2 ^-j/2Ψ (2 ^-jt-k) and scaling Equations through parallel serial conversion unit, can obtain output signal y (t).

9. the method for the small echo multi-carrier spread spectrum communication system that time-frequency according to claim 8 changes, is characterized in that, the expression formula of output signal y (t) is:

For adaptive channel time-frequency changes, the value of adjustable parameters N and L; According to the T/F selectivity characrerisitic of channel, if frequency selectivity is strong, N value is optional larger, and L value is optional smaller; If time selectivity is strong, N value is optional smaller, and L value is optional larger; After wavelet inverse transformation, the data-signal y (t) that time-frequency diagram data will convert series connection to is sent to receiving terminal through wireless channel.

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