CN102404039A - Multi-antenna diversity receiving method and device based on time inversion - Google Patents

Abstract

The invention discloses a multi-antenna diversity receiving method and device based on time inversion. The method comprises the following steps of: firstly, carrying out down-conversion treatment on radio frequency signals received by antennas respectively to obtain multiple unrelated compound baseband signals; next, carrying out channel evaluation respectively according to the obtained compound baseband signals to obtain independent transmission channel parameters of receiving antennas; then, working out time inversion conjugate formulae of channels according to the evaluated channel parameters; and then, carrying out convolution operation on the compound baseband signals received by the antennas and the time inversion conjugate formulae of corresponding transmission channels respectively; finally, processing the convolution result by an equal gain combination method to obtain a final multi-antenna diversity result. According to the method and device disclosed by the invention, the signal-to-noise ratio of the received signal can be increased, combination and balance strategies are simplified, and the performance of the wireless communication system is improved.

Description

A kind of multi-antenna diversity method of reseptance and device based on time reversal

Technical field

The invention belongs to wireless communication technology field, particularly a kind of multi-antenna diversity method of reseptance and device based on time reversal.

Background technology

Wireless communication system usually is operated in the complicated geographical environment, behind many different propagation paths such as the reflection of the electromagnetic wave signal of emission process, scattering, diffraction, arrives reception antenna.The signal component in different paths has different propagation delays, phase place and amplitude, and additionally has interchannel noise, their stack can make composite signal cancel out each other or strengthen, and forms multipath effect.The signal mutual superposition of out of phase and amplitude wherein, the amplitude of composite signal shows as fluctuations fast, forms rapid fading.For digit wireless communication system, when propagation delay was suitable with code-element period, the stack of the signal in different paths can produce very big intersymbol interference between different information code elements.The decline that multipath effect causes can reduce obtainable available signal power and increase the influence of disturbing; Make the reception signal of receiver produce distortion, waveform broadening, waveform is overlapping and distortion; Cause the communication system demodulator very big bit error rate to occur, so that can not communicate by letter fully.

Diversity reception is a kind of effective ways of antagonism multipath fading in the radio communication; It is at the signal of several decline situation that the receiving terminal dispersion receives different (mutual statistical is independent); In some way they are merged and concentrate, the signal to noise ratio of total reception signal is improved, the influence that reduces to decline.Multi-antenna diversity is claimed space diversity again, mainly is the independence of utilizing the received signal fadeout in different received place, realizes the anti fading function.The multi-antenna diversity basic comprising: the transmitting terminal common antenna sends, and receiving terminal receives with multiple antenna, and the distance between each reception antenna is half the greater than wavelength; Fading characteristic to guarantee reception antenna output signal is separate; That is to say that when the output signal of a certain secondary reception antenna was very low, the output of other reception antennas then not necessarily the low phenomenon of amplitude also occurred at this synchronization; Behind corresponding merging circuit; Obtain total reception antenna output signal that one tunnel signal amplitude is big, signal to noise ratio is best, so just reduced the influence of channel fading, improved the reliability of transmission.

Summary of the invention

Technical problem to be solved by this invention provides a kind of multi-antenna diversity method of reseptance and device based on time reversal, merges and balance policy to increase the signal to noise ratio that receives signal, to simplify, and improves performance in wireless communication systems.

For addressing the above problem, the present invention realizes through following technical scheme:

A kind of multi-antenna diversity method of reseptance based on time reversal may further comprise the steps:

(1) radiofrequency signal that each antenna is received is done down-converted respectively, obtains the incoherent complex baseband signal of multichannel;

(2) carry out channel estimating respectively according to the complex baseband signal that obtains, obtain independently transport channel parameters of each reception antenna;

(3) obtain conjugation-type time reversal of each channel according to the estimated channel parameter;

(4) complex baseband signal that each antenna is received carries out convolution algorithm with conjugation-type time reversal of corresponding transmission channel respectively;

(5) result with convolution adopts the equal gain combining method to obtain final multi-antenna diversity result.

In the such scheme; The radiofrequency signal that each antenna receives is before carrying out down-converted; Need earlier radiofrequency signal to be carried out mixing and convert analog if signal to; Analog if signal is sent into AD conversion unit and is converted digital medium-frequency signal to through if sampling, and digital medium-frequency signal is sent into the Digital Down Convert unit and carried out Digital Down Convert.

In the such scheme, the result of convolution also included the time synchronized step before merging.

A kind of multi-antenna diversity receiving system based on time reversal comprises down-converter unit, channel estimating unit, time reversal processing unit and divide set and unit; Radiofrequency signal under wherein down-converter unit receives antenna is carried out Digital Down Convert and is converted digital complex baseband signal into; Complex baseband signal is sent into channel estimating unit and is estimated channel parameter; Channel parameter is sent into the time reversal processing unit and after getting its counter-rotating conjugation-type complex baseband signal is carried out process of convolution time, and the complex baseband signal after each antenna will be handled time reversal send branch set and unit to merge.

Above-mentioned multi-antenna diversity receiving system based on time reversal also further includes mixing unit and AD conversion unit; The mixing unit converts the radiofrequency signal that antenna receives to analog if signal after mixing; Analog if signal send AD conversion unit to convert digital medium-frequency signal to through if sampling, and digital medium-frequency signal is sent into down-converter unit.

Above-mentioned multi-antenna diversity receiving system based on time reversal also further includes clock unit, clock unit be channel estimating unit, time reversal processing unit and divide set and unit that clock is provided so that simultaneous operation is realized in above-mentioned each unit.

Compared with prior art, the present invention has following characteristics:

(1) strengthened the Signal-to-Noise after the merging: it is to select stronger in each an antenna receiving multipath signals path signal to merge respectively that present many antennas receive foldings; And the present invention is with each antenna receiving signal and its channel time reversible type convolution; Utilize the focus characteristics of time reversal; Can the signal in a plurality of paths be superimposed, realize rake, thereby strengthen the final signal to noise ratio that merges output;

(2) need not to carry out equilibrium: multipath transmisstion can produce intersymbol interference when code-element period is suitable with propagation delay; Need to adopt balancing technique to eliminate intersymbol interference; Adopt time reversal technology with the signal focus in a plurality of paths time together, also just eliminated the phase mutual interference between each path;

(3) simplified folding: equal gain combining need be adjusted the phase place of each antenna receiving signal, and after employing processing time reversal, the reception signal focus of each antenna is to identical phase place, and directly addition just can realize equal gain combining.

Description of drawings

Fig. 1 is the schematic diagram based on the multi-antenna diversity method of reseptance of time reversal;

Fig. 2 is the multi-antenna diversity reception bit error rate Vs SNR curve based on time reversal;

Fig. 3 is the multi-antenna diversity reception bit error rate Vs SIR curve based on time reversal;

Fig. 4 is the structure chart based on the multi-antenna diversity receiving system of time reversal.

Embodiment

Referring to Fig. 1, a kind of multi-antenna diversity method of reseptance based on time reversal of the present invention comprises the steps:

(1) for the signal of same information source emission, the radiofrequency signal expression formula of k antenna reception was during multi-antenna diversity received:

$y_k\left(t\right)=s_b\left(t\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\&CircleTimes;h_k\left(t\right)$ ①

In the formula: s _b(t) be the complex radical breath of taking a message of emission; f _cBe carrier frequency;

The expression convolution algorithm; h _k(t) be the impulse response of multidiameter fading channel, its expression formula is:

$h\left(t\right)=\underset{i=0}{\overset{L}{\mathrm{\&Sigma;}}}{a}_i\left(t\right)\mathrm{\&delta;}(t-{\mathrm{\&Delta;\&tau;}}_i)$ ②

In the formula: L is the multipath way, is reference path during i=0; a _i(t) be the multiple fading coefficients of i paths; Δ τ _iBe of the delay of i paths with respect to reference path.

(2) the radiofrequency signal y that above-mentioned each antenna is received _k(t) carry out mixing and convert analog if signal to; Analog if signal is sent into AD conversion unit and is converted digital medium-frequency signal to through if sampling; Digital medium-frequency signal is sent into the Digital Down Convert unit and is carried out the Digital Down Convert processing, obtains the incoherent complex baseband signal s of multichannel _k(t);

The radiofrequency signal that each antenna receives promptly 1. formula and local carrier carry out mixing and filtering, remove carrier information, and see that from frequency spectrum realizing moving the back obtains the complex radical breath of taking a message, its time domain expression formula is:

$s_k\left(t\right)=s_b\left(t\right)\&CircleTimes;h_k\left(t\right)$ ③

In the formula: s _b(t) be the complex radical breath of taking a message of emission; h _k(t) be the impulse response of multidiameter fading channel.

(3) according to the complex baseband signal s that obtains _k(t) carry out channel estimating respectively, obtain independently transport channel parameters of each reception antenna, estimate multipath channel h _k(t).

(4) obtain conjugation-type time reversal of each channel according to the estimated channel parameter, promptly get multipath channel h _k(t) conjugation-type h time reversal _k* (t) be:

$h_k*(-t)=\underset{i=0}{\overset{L}{\mathrm{\&Sigma;}}}{a}_{\mathrm{ki}}*(-t)\mathrm{\&delta;}(-t-{\mathrm{\&Delta;\&tau;}}_{\mathrm{ki}})$ ④

(5) the complex baseband signal s that each antenna is received _k(t) respectively with conjugation-type h time reversal of corresponding transmission channel _k* (t) carrying out convolution algorithm gets:

$\widehat{s_k}\left(t\right)=s_b\left(t\right)\&CircleTimes;h_k\left(t\right)\&CircleTimes;h_k*(-t)$ ⑤

With h _k(t) and h _k* (t) can be write as following form respectively:

h _k(t)＝a _k0(t)δ(t)+a _k1(t)δ(t-Δτ _k1)

+a _k2(t)δ(t-Δτ _k2)+…+a _kL(t)δ(t-Δτ _kL)

⑥

＝a _k0(0)δ(t)+a _k1(Δτ _k1)δ(t-Δτ _k1)

+a _k2(Δτ _k2)δ(t-Δτ _k2)+…+a _kL(Δτk _L)δ(t-Δτk _L)

h _k*(-t)＝a _k0*(0)δ(-t)+a _k1*(Δτ _k1)δ(-t-Δτ _k1)

+a _k2*(Δτ _k2)δ(-t-Δτ _k2)+…+a _kL*(Δτ _kL)δ(-t-Δτ _kL)

⑦

＝a _k0*(0)δ(t)+a _k1*(Δτ _k1)δ(t+Δτ _k1)

+a _k2*(Δτ _k2)δ(t+Δτ _k2)+…+a _kL*(Δτ _kL)δ(t+Δτ _kL)

By 6. 7. getting

$h_k\left(t\right)\&CircleTimes;h_k*(-t)=({\left|a_{k0}\left(0\right)\right|}^2+{\left|a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)\right|}^2+{\left|a_{k2}\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)\right|}^2+...+{\left|a_{\mathrm{kL}}\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)\right|}^2)\mathrm{\&delta;}\left(t\right)$

$+a_{k0}\left(0\right)a_{k1}*\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)\mathrm{\&delta;}(t+{\mathrm{\&Delta;\&tau;}}_{k1})+a_{k0}\left(0\right)a_{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">k</figure-callout>}2}*\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)\mathrm{\&delta;}(t+{\mathrm{\&Delta;\&tau;}}_{k2})+...+a_{k0}\left(0\right)a_{\mathrm{kL}}*\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)\mathrm{\&delta;}(t+{\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}})$ ⑧

$+a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)a_{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">k</figure-callout>}2}*\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)\mathrm{\&delta;}(t+{\mathrm{\&Delta;\&tau;}}_{k2}-{\mathrm{\&Delta;\&tau;}}_{k1})+...+a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)a_{\mathrm{kL}}*\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)\mathrm{\&delta;}(t+{\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}-{\mathrm{\&Delta;\&tau;}}_{k1})+...$

Then 5. formula becomes

$\widehat{s_k}\left(t\right)=({\left|a_{k0}\left(0\right)\right|}^2+{\left|a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)\right|}^2+{\left|a_{k2}\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)\right|}^2+...+{\left|a_{\mathrm{kL}}\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)\right|}^2)s_b\left(t\right)$

$+a_{k0}\left(0\right)a_{k1}*\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)s_b(t+{\mathrm{\&Delta;\&tau;}}_{k1})+a_{k0}\left(0\right)a_{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">k</figure-callout>}2}*\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)s_b(t+{\mathrm{\&Delta;\&tau;}}_{k2})+...+a_{k0}\left(0\right)a_{\mathrm{kL}}*\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)s_b(t+{\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}})$ ⑨

$+a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)a_{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">k</figure-callout>}2}*\left({\mathrm{\&Delta;\&tau;}}_{k2}\right)s_b(t+{\mathrm{\&Delta;\&tau;}}_{k2}-{\mathrm{\&Delta;\&tau;}}_{k1})+...+a_{k1}\left({\mathrm{\&Delta;\&tau;}}_{k1}\right)a_{\mathrm{kL}}*\left({\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}\right)s_b(t+{\mathrm{\&Delta;\&tau;}}_{\mathrm{kL}}-{\mathrm{\&Delta;\&tau;}}_{k1})+...$

By 9. be prone to knowing, back main lobe (formula 9. in the 1st) is by force handled in the reception signal elapsed time counter-rotating of k antenna, wherein | and a _Ki(0) | ²Be the energy of i paths, visible each paths all has contribution to main lobe, and is big or small irrelevant with the path delay of time, shows to handle time reversal to have the rake effect, can be with the energy focusing on all paths in reference path.From the treatment effect to multipath, processing time reversal is similar with the RAKE processing, but treatment effect and structure and different.At first, RAKE handles can only be applied to cdma system, handles time reversal and then only is applied to any wireless communication system.Secondly, RAKE handles and can only the multipath energy branch collection of time-delay greater than a chip be got up, and handles time reversal and can all multipath energies be gathered together, and irrelevant with time delay, promptly time delay also can gather together less than the multipath energy of a code-element period.

(6) result with convolution adopts the equal gain combining method to obtain final multi-antenna diversity result;

The multipath energy of handling each antenna through time reversal focuses in the reference path; For many antennas receiving system; Therefore etc. the reference path under the condition of clock synchronization of each reception antenna is consistent, and promptly the reference path signal time delay phase place of each antenna is consistent, and gain just need not to adjust the phase place that respectively receives signal in closing; Directly addition can realize multi-antenna diversity, promptly has:

$\hat{s}\left(t\right)=\widehat{s_1}\left(t\right)+\hat{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="HDA0000124159300000012.png"\; state="\{\{state\}\}">s</figure-callout>}}_2}\left(t\right)+...+\widehat{s_N}\left(t\right)$ ⑩

Fig. 2 and Fig. 3 have provided the performance of BER comparison curves based on the multi-antenna diversity system of time reversal and single antenna reception; Simulate 5 diversity antennas, 4 paths situation; At signal interference ratio (SIR) is the 20dB condition, and the noise robustness based on the multi-antenna diversity receiving system of time reversal during errored bit property 10-3 is superior to the about 12dB of single antenna receiving system; At signal to noise ratio (snr) is the 20dB condition, and the interference free performance based on the multi-antenna diversity receiving system of time reversal during errored bit property 10-3 is superior to the about 6dB of single antenna receiving system.

A kind of multi-antenna diversity receiving system based on time reversal that can realize above-mentioned multi-antenna diversity method of reseptance based on time reversal is as shown in Figure 4, its mainly by mixing unit, AD conversion unit, down-converter unit, channel estimating unit, time reversal processing unit, divide set and unit and clock unit to form.The mixing unit converts the radiofrequency signal that antenna receives to analog if signal after mixing; Analog if signal send AD conversion unit to convert digital medium-frequency signal to through if sampling; Digital medium-frequency signal send down-converter unit; Down-converter unit is carried out Digital Down Convert with digital medium-frequency signal and is converted digital complex baseband signal into; Complex baseband signal is sent into channel estimating unit and is estimated channel parameter, and channel parameter is sent into the time reversal processing unit and after getting its counter-rotating conjugation-type complex baseband signal carried out process of convolution time, and the complex baseband signal after each antenna will be handled time reversal send branch set and unit to merge; Clock unit be channel estimating unit, time reversal processing unit and divide set and unit that clock is provided so that simultaneous operation is realized in above-mentioned each unit.

The present invention can through above-mentioned each independently functional module make up and to form; Also can realize down-converter unit, time reversal processing unit, and, realize channel estimating unit and divide set and unit via FPGA by DSP to the control of AD conversion unit; Even can directly computer be sent in each antenna receiving signal digitlization, realize down-converter unit, channel estimating unit, time reversal processing unit and divide set and unit with the mode of software.

Claims (6)

1. multi-antenna diversity method of reseptance based on time reversal is characterized in that may further comprise the steps:

(1) radiofrequency signal that each antenna is received is done down-converted respectively, obtains the incoherent complex baseband signal of multichannel;

(2) carry out channel estimating respectively according to the complex baseband signal that obtains, obtain independently transport channel parameters of each reception antenna;

(3) obtain conjugation-type time reversal of each channel according to the estimated channel parameter;

(4) complex baseband signal that each antenna is received carries out convolution algorithm with conjugation-type time reversal of corresponding transmission channel respectively;

(5) result with convolution adopts the equal gain combining method to obtain final multi-antenna diversity result.

2. a kind of multi-antenna diversity method of reseptance according to claim 1 based on time reversal; It is characterized in that: the radiofrequency signal that each antenna receives is before carrying out down-converted; Need earlier radiofrequency signal to be carried out mixing and convert analog if signal to; Analog if signal is sent into AD conversion unit and is converted digital medium-frequency signal to through if sampling, and digital medium-frequency signal is sent into the Digital Down Convert unit and carried out Digital Down Convert.

3. a kind of multi-antenna diversity method of reseptance based on time reversal according to claim 1 is characterized in that: the result of convolution also included the time synchronized step before merging.

4. multi-antenna diversity receiving system based on time reversal is characterized in that: comprise down-converter unit, channel estimating unit, time reversal processing unit and divide set and unit; Radiofrequency signal under wherein down-converter unit receives antenna is carried out Digital Down Convert and is converted digital complex baseband signal into; Complex baseband signal is sent into channel estimating unit and is estimated channel parameter; Channel parameter is sent into the time reversal processing unit and after getting its counter-rotating conjugation-type complex baseband signal is carried out process of convolution time, and the complex baseband signal after each antenna will be handled time reversal send branch set and unit to merge.

5. a kind of multi-antenna diversity receiving system according to claim 4 based on time reversal; It is characterized in that: also further include mixing unit and AD conversion unit; The mixing unit converts the radiofrequency signal that antenna receives to analog if signal after mixing; Analog if signal send AD conversion unit to convert digital medium-frequency signal to through if sampling, and digital medium-frequency signal is sent into down-converter unit.

6. a kind of multi-antenna diversity receiving system according to claim 4 based on time reversal; It is characterized in that: also further include clock unit; Clock unit be channel estimating unit, time reversal processing unit and divide set and unit that clock is provided so that simultaneous operation is realized in above-mentioned each unit.

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