CN103391268B - Multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method - Google Patents

Abstract

The present invention is to provide a kind of multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method.OFDM symbol peak value probability of occurrence is reduced by mode transmission data being multiplied by scramble pattern, the pilot tone of different distributions pattern is utilized to carry scramble information, in conjunction with the sparse features of Shallow Water Acoustic Channels in the autonomous differentiation of receiving terminal to scramble pattern, the pattern selection peak-to-average ratio achieved without side information suppresses, and effectively improves efficiency and the reliability of communication system simultaneously.The pattern selection peak-to-average ratio Restrainable algorithms without side information transmission in the present invention can under the prerequisite of not losing PAPR rejection, and Exact Solutions calculates distribution pattern, realizes the reliable underwater sound communication without side information transmission.

Description

Multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method

Technical field

What the present invention relates to is a kind of method for restraining peak average power ratio of underwater sound communication, specifically a kind ofly inputs multi-output-orthogonal frequency division multiplexing based on MIMO-OFDM() method for restraining peak average power ratio of underwater sound communication.

Background technology

Bandwidth resources available in underwater sound communication are very limited, seriously limit quality and the speed of underwater sound communication.In this context, having the orthogonal frequency division multiplexi of high spectrum utilization to combine does not need increase available bandwidth or improve transmitting power and channel capacity can be made to obtain the MIMO technique of essence raising, becomes the new focus of high-speed underwater sound communication in recent years.Shallow Sea Acoustic Channel be usually looked at as one slow time become condition of sparse channel, can describe with constant filter when one.Compressed sensing limits the method for solving of the sparse solution of system as a kind of linear, accurately can recover sparse signal by a small amount of information, is therefore applicable to rebuilding the Shallow Sea Acoustic Channel with sparse property.Affecting MIMO-OFDM significant obstacle of extensive use in underwater sound communication is that it exists the defect of peak value average power ratio (Peak-to-average-power-ratio, PAPR).This defect not only can limit emission system efficiency, reduces the signal to noise ratio of Received signal strength, also can cause signal distortion, cause nonlinear distortion, destroys sub-carrier orthogonality, reduce systematic function.Enrich about the document of method for suppressing peak to average ratio in the research radio MIMO_OFDM communication technology both at home and abroad, but because underwater acoustic channel communications bandwidth resources is limited, low signal-to-noise ratio, slowly time-varying characteristics, the traditional method for suppressing peak to average ratio of simple employing obviously can reduce system communication speed.

Selected mapping method (SelectiveMapping, SLM) technology proposes at R.w.Bauml in 1996, and its general principle utilizes M scrambling phase sequence with input signal X=[X (0), X (1) ... X (N-1)] be multiplied, wherein n=0,1 ... N-1, m=1,2 ... M, after scrambling, data are X ^m=[X ^m(0), X ^m(1) ... X ^m(N-1)].To { X ^m(n) } M different OFDM symbol carry out independently IFFT conversion and obtain x ^m=[x ^m(0), x ^m(1) ... x ^m(N-1) OFDM symbol that wherein peak-to-average force ratio is minimum], is selected as transfer sequence.Wherein

Though the method suppresses PAPR effect a bit weaker compared to the method for direct amplitude limit but do not have performance of BER to lose, weak point is the IFFT conversion needing to carry out repeatedly, and computation complexity is higher.And in order to recover initial data accurately, need the supplementary adopted by transmitter to be delivered to receiver accurately.Once supplementary makes a mistake, the entrained whole mistake of information to be caused in a symbol, therefore needs to carry out special coding to this information, or repeatedly repeat to send so that ensure can restoring signal exactly at receiving terminal.So just need to transmit a large amount of side informations, cause the reduction of system communication efficiency and the waste of frequency band.

Summary of the invention

The object of the present invention is to provide a kind of scramble pattern that can realize high reliability to differentiate, the basis of not losing PAPR is effectively improved the multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method of band efficiency.

Answer to a riddle of the present invention is achieved in that

(1) at data sending terminal, by data X to be sent _dwith all M group scramble pattern P ^mbe multiplied, obtain the whole series of data after scrambling

(2) the different Comb Pilot position Po of M group is defined ^mas mark, corresponding different scramble pattern;

(3) by data sequence after scrambling with Comb Pilot sequence X _paccording to correspondence position Po ^mform candidate OFDM symbol X respectively ^m; Now carry scramble pattern serial number information in each candidate's OFDM symbol, be the side information in conventional method.

(4) inverse fast Fourier transform is carried out to candidate's OFDM symbol and obtain time-domain signal x ^m, finally select wherein PAPR(papr) and the minimum symbol of value as transmission symbol;

(5) Fourier transform is carried out to received signal at receiving terminal, frequency domain data Y (k) obtained;

(6) frequency domain extracted respectively corresponding to M group pilot frequency locations receives information, obtains channel strip frequency domain response estimation information after channel estimating

(7) by match tracing method match channels, M group channel time domain impulse response is recovered

(8) normalization obtain M group channel time domain impulse response calculate auto-correlation coefficient, in M coefficient correlation of acquisition corresponding to minimum value the channel time domain impulse response being the reality of channel is estimated corresponding m value is the sequence number of scramble pattern;

(9) utilize the scramble pattern obtained in previous step to reception frequency-region signal descrambling code, and to its demapping, channel-decoding, recover to send data.

Pilot frequency sequence X in described step (3) _p, select the sequence of PAPR inhibition without negative effect, avoid the peak regeneration after adding pilot tone.

The present invention reduces the peak-to-average power ratio of OFDM symbol at transmitting terminal by scrambling phase sequence, utilize Comb Pilot to carry scramble sequence in the distribution pattern of frequency domain and select information, at receiving terminal by carrying out match tracing to the pilot tones domain response received, the scramble pattern achieving high reliability differentiates, under the prerequisite of not losing PAPR rejection, achieve the pattern system of selection without side information transmission, decrease the probability causing whole symbol all wrong because of sideband supplementary mistake, also improve communication efficiency and the band efficiency of system simultaneously.

Invention provides the SLM method of the MIMO-OFDM under a kind of applicable sparse underwater acoustic channel environment without side information, and the method is based on selected mapping method technology, and the sparse feature of Bound moisture Acoustic channel is improved method.The Comb Pilot that the method improved utilizes Different Weight to distribute carries phase rotating sequence information, by carrying out match tracing to the pilot tones domain response received, the scramble pattern achieving high reliability differentiates, on the basis of not losing conventional method PAPR, effectively improve band efficiency.

Major advantage of the present invention is:

1) for the feature of OFDM symbol peak value average power ratio, the multiple scramble pattern of employing dot product, the mode therefrom selecting the less symbol of PAPR value to carry out transmitting avoid the appearance of peak value, reduce the PAPR value of symbol, improve the efficiency of transmitting transducer.

2) improving one's methods of the present invention's proposition utilizes Comb Pilot to carry scramble sequence selection information in the distribution pattern of frequency domain, avoid and take this hard up band resource in underwater sound communication, the band efficiency of raising system, detecting scramble pattern sequence number by detecting channel simultaneously, also ensure that the real-time of communication system.

3) improvement pattern system of selection proposed by the invention is based on compressive sensing theory, utilize the sparse property of Shallow Water Acoustic Channels, information is selected by finding scramble pattern to channel matched, save the necessary side information of conventional pattern system of selection, reduced the error code disaster risk caused because of side information reading mistake, reduced system transmitting terminal energy ezpenditure, improve band system band utilization ratio.

Accompanying drawing explanation

Select to suppress peak-to-average power ratio method system block diagram without side information pattern in Fig. 1 MIMO-OFDM system.

Fig. 2 is based on the pattern detector arrangement block diagram of compressive sensing theory.

Fig. 3 simulated channel impulse response.

Fig. 4 the present invention and conventional pattern selection mode and non-scrambled signals CCDF curve comparison figure.

The system BER performance comparison figure of the present invention and traditional approach and the known pattern selection mode of side information under Fig. 5 white Gaussian noise.

The system BER performance comparison figure of the present invention and conventional pattern selection mode and the known pattern selection mode of side information under the burst noise environment of Fig. 6 Alpha Stable distritation.

Embodiment

Below in conjunction with accompanying drawing and example, patent of the present invention is further illustrated.

The pattern selection peak-to-average ratio suppressing method improved needs to define the different Comb Pilot position of M group corresponding M group different scrambling pattern P ^m=[P ^m(0), P ^m(1) ..., P ^m(N-1)], 0≤m≤M, selects one group not have the pilot frequency sequence X of negative effect to PAPR inhibition simultaneously _p=[X _p(0), X _p(1) ..., X _p(N-1)].

Data to be sent are X _d, after scrambling, the signal of data subcarrier position can be expressed as:

$X_D^m=P^{\mathrm{mT}}{X}_D---\left(1\right)$

After now transmitting terminal scrambling, signal can be expressed as at frequency domain:

$X^m\left(k\right)=a{X}_D^m\left(k\right)+b{\mathrm{XD}}_P\left(k\right)---\left(2\right)$

Wherein:

$a=1,b=0,k\∉{\mathrm{Po}}^m---\left(3\right)$

a=0,b=1k∈Po ^m

To the M group time-domain signal obtained after all scramblings according to the defined formula of peak-to-average power ratio:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10{\log }_{10}\frac{\max {\left|x\right|}^2}{E\left({\left|x\right|}^2\right)}---\left(4\right)$

Calculate its PAPR value respectively, select the sequence that peak-to-average force ratio is minimum as transfer sequence.

Utilize the pattern detector based on compressive sensing theory at receiving terminal, by detecting the scrambling phase sequence that pilot tone pattern is determined to select, this is the core that method for restraining peak average power ratio selected by pattern of the present invention.

Suppose that frequency domain Y (k) data obtained after Fourier transform at receiving terminal meet formula (5):

Y(k)=X(k)H(k)+W(k)（5）

Wherein H (k) is the response of frequency domain kth sub-channels, and W (k) is the noise on frequency domain kth sub-channels.

Definition for the estimated value of channel H (k), corresponding m group pilot frequency locations Po ^mit is Y that the frequency domain extracted receives information _p ^m, pilot frequency information now obtain M group channel strip frequency domain response estimation information

${\hat{H}}_P^m=\frac{Y_P}{X_P^m}---\left(6\right)$

By match tracing method match channels, recover M group channel time domain impulse response

${\hat{h}}_P^m=f_{\mathrm{MP}}\left({\hat{H}}_P^m\right)---\left(7\right)$

Wherein f _mP() represents match tracing.

Normalization obtain M group channel time domain impulse response

${\hat{h}}_P^{\′m}=\mathrm{Normlize}\left({\hat{h}}_P^m\right)---\left(8\right)$

M group have and only have one group to be that channel time domain impulse response is estimated actual value, calculate auto-correlation coefficient,

In M the coefficient correlation obtained corresponding to minimum value the channel time domain impulse response being the reality of channel is estimated

$\hat{h}=\underset{m=1,...,M}{\min }\left(\mathrm{xcorr}\left({\hat{h}}_P^{\′m}\right)\right)---\left(9\right)$

Can utilize and select actual value and the scramble pattern of correspondence, realize Received signal strength frequency domain response go to disturb and balanced.

Based on compressive sensing theory pattern detector arrangement as shown in Figure 2.

Emulation experiment is below example of the present invention, can be verified by this example to performance of the present invention.

Simulated conditions:

In Matlab emulation platform, build 22 and receive MIMO-OFDM underwater sound communication system, FFT length 8192, number of sub carrier wave 1025, communication band 6 ~ 12kHz, stochastic generation 10 ³individual OFDM symbol, QPSK maps, and adopts Space Time Coding and convolution coding, simulated channel impulse response as shown in Figure 3,4 times of over-samplings.

In order to illustrate that the inventive method does not have lossy feature compared to traditional SLM method PAPR rejection, Fig. 4 gives the present invention and traditional SLM mode and non-scrambled signals CCDF curve comparison figure, as can be seen from the figure, the inventive method overlaps substantially with the CCDF curve of traditional SLM method, shows that its PAPR rejection does not lose.

The inventive method is a kind of pattern selection peak-to-average ratio suppressing method without side information, at raising band efficiency, reduce transmitting power loss, and reduce and fail correctly to understand side information because communication system affects by factors such as noises and cause the aspects such as the risk of error code disaster to have greater advantage.Traditional pattern selection peak-to-average ratio suppressing method needs to increase phase sequence in transmission signal and selects information, and each data symbol needs the side information of bit, is used for determining the sequence number of selected scrambling phase sequence, wherein what represent is the maximum integer being less than x, and M is the sum of adopted scramble sequence.And need to add bulk redundancy (normally coding redundancy) to ensure that system receiving terminal can correctly understand this information, to avoid the whole symbolic information demodulation mistake disaster caused due to side information demodulation mistake.For the system of multiple-input and multiple-output, the amount of information shared by this redundancy is huge.Compared to conventional pattern system of selection, the inventive method is without the need to being transferred to receiving terminal using the sequence number of selected scrambling phase sequence as side information, utilize Comb Pilot to carry scramble sequence in the distribution pattern of frequency domain and select information, by in the effective identification of receiving terminal to pilot tone pattern, realize selecting information effectively to understand to scramble pattern.The inventive method has saved data volume, improve data transmission efficiency and band efficiency, decrease the probability causing whole symbol all wrong because of sideband supplementary mistake, also improve the communication efficiency of system simultaneously, ensure that the real-time of communication, the cost paid is then the increase of amount of calculation.But due to underwater sound communication, improve the complexity of system receiving terminal to reduce the consumption of transmitting terminal, thus raising entire system efficiency and stability are very suitable.

Fig. 5, Fig. 6 sets forth the known pattern selection mode of the present invention and conventional pattern selection mode and side information system performance of BER under the burst noise environment of white Gaussian noise and Alpha Stable distritation and contrast, as can be seen from the figure the inventive method is better than traditional SLM method, substantially suitable with the method performance of BER that side information is known, can absolutely prove that the inventive method correctly can judge the sequence number of selected phase bit sequence, for receiver provides reliable side information.And due to the sparse characteristic of shallow sea channel, compression sensing method can estimate channel frequency domain response more accurately, equally can the BER performance of elevator system, make it reach the requirement of reliable communication.The inventive method can ensure when 6dB underwater sound communication normal, reliably carry out, be better than conventional pattern system of selection.It can also be seen that from Fig. 6, the inventive method has certain anti-burst noise ability, also can reliable and effective deciphering scramble pattern information in the environment of burst noise, is suitable for the underwater sound communication that there is burst noise situation.

In sum, the inventive method is a kind of improvement pattern system of selection of suppression peak-to-average power ratio of applicable shallow-sea underwater acoustic communication.The inventive method improves transmission and the judgment mode of side information, overcomes traditional SLM method to the dependence of side information, under the prerequisite of not losing PAPR rejection, improves the BER performance of system.Ensure that correctly resolving of receiving terminal scramble pattern sequence number by the mode detecting channel, improve communication efficiency and the band efficiency of system, ensure that real-time and the reliability of MIMO-OFDM underwater sound communication system.

Above example is only an example of the present invention's application; content of the present invention should not only be confined in MIMO-OFDM system; enter to have more for single-input single-output, singly and enter in the ofdm system that singly goes out to suppress peak-to-average power ratio all to use more, be therefore all subject to the protection of patent of the present invention.

Claims (2)

1. a multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method, is characterized in that comprising the steps:

(1) at data sending terminal, by data X to be sent _dwith all M group scramble pattern P ^mbe multiplied, obtain the whole series of data after scrambling

(2) the different Comb Pilot position Po of M group is defined ^mas mark, corresponding different scramble pattern;

(3) by data sequence after scrambling with Comb Pilot sequence X _paccording to correspondence position Po ^mform candidate OFDM symbol X respectively ^m;

(4) inverse fast Fourier transform is carried out to candidate's OFDM symbol and obtain time-domain signal x ^m, finally select the symbol that wherein papr value is minimum as transmission symbol;

(5) carry out Fourier transform to received signal at receiving terminal, obtain frequency domain data Y (k);

(6) frequency domain extracted respectively corresponding to M group pilot frequency locations receives information, obtains channel strip frequency domain response estimation information after channel estimating

(7) by match tracing method match channels, M group channel time domain impulse response is recovered

(8) normalization obtain M group channel time domain impulse response calculate auto-correlation coefficient, in M auto-correlation coefficient of acquisition corresponding to minimum value the channel time domain impulse response being the reality of channel is estimated corresponding m value is the sequence number of scramble pattern;

(9) utilize the scramble pattern obtained in previous step to the decoding of reception frequency-region signal, and to its demapping, channel-decoding, recover to send data.

2. multi-I/O OFDM shallow-sea underwater acoustic communication pattern selection peak-to-average ratio suppressing method according to claim 1, is characterized in that the pilot frequency sequence X in step (3) _p, select the sequence of papr inhibition without negative effect.