CN103391268A - Multiple-input-multiple-output OFDM (orthogonal frequency division multiplexing) shallow sea underwater acoustic communication pattern selection PAR (peak-to-average ratio) restraining method - Google Patents

Abstract

The invention provides a multiple-input-multiple-output OFDM shallow sea underwater acoustic communication pattern selection PAR restraining method. By the aid of the manner of multiplying scrambling patterns by sent data, the occurrence probability of an OFDM symbol peak is reduced; and pilot frequency carrying scrambling information of different distribution patterns is used and combined with the sparsity characteristic of a shallow sea underwater acoustic channel, the scrambling patterns are distinguished independently at a receiving end, the pattern selection PAR restrain for sideband-free information is realized, and the efficiency and the reliability of a communication system are effectively improved at the same time. According to an endless information transmission pattern selection PAR restraining algorithm, on the premise that the restrain performance of the PAPR (peak to average power ratio) is not lost, the distribution patterns are calculated accurately, and the reliable underwater acoustic communication for the endless information is realized.

Description

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

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 of based on MIMO-OFDM(input multi-output-orthogonal frequency division multiplexing) method for restraining peak average power ratio of underwater sound communication.

Background technology

Bandwidth resources available in underwater sound communication are very limited, seriously limited quality and the speed of underwater sound communication.Under this background, the orthogonal frequency division multiplexi that high spectrum utilization arranged, in conjunction with not needing to increase available bandwidth or improving transmitting power and can make channel capacity obtain the MIMO technique that essence improves, becomes the new focus of high-speed underwater sound communication in recent years.Shallow Sea Acoustic Channel is looked at as thinning thin channel when slow usually, and in the time of can be with one, constant filter be described.Compressed sensing, as a kind of method for solving that limits the sparse solution of system for linearity, can accurately be recovered sparse signal with a small amount of information, therefore is fit to the Shallow Sea Acoustic Channel with sparse property is rebuild.Affecting MIMO-OFDM significant obstacle of extensive use in underwater sound communication is its defect that has 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 that receives signal, also can cause signal distortion, causes nonlinear distortion, destroy sub-carrier orthogonality, reduces systematic function.Abundant 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 due to underwater acoustic channel communication bandwidth resource-constrained, low signal-to-noise ratio, slow time-varying characteristics, simply adopt traditional method for suppressing peak to average ratio can obviously reduce system communication speed.

Selectivity mapping (Selective Mapping, SLM) technology proposes at R.w.Bauml in 1996, and its basic principle is to utilize M scrambling phase sequence

With input signal X=[X (0), X (1) ... X (N-1)] multiply each other, 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 symbols carry out independently IFFT conversion and obtain x ^m=[x ^m(0), x ^m(1) ... x ^m(N-1)], select the wherein OFDM symbol of peak-to-average force ratio minimum

As transfer sequence.Wherein

Though it is a bit weaker but there is no the performance of BER loss that the method suppresses the PAPR effect than the method for direct amplitude limit, weak point is to carry out IFFT conversion repeatedly, and computation complexity is higher.And in order to recover accurately initial data, the supplementary that transmitter need to be adopted is delivered to receiver accurately.In case supplementary makes a mistake, can cause the whole mistakes of information entrained in a symbol, therefore need to carry out special coding to this information, perhaps repeatedly repeat to send to guarantee at receiving terminal restoring signal exactly.So just need a large amount of side information of transmission, 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 scrambling pattern differentiation that can realize high reliability, effectively improve the multi-I/O OFDM shallow-sea underwater acoustic communication pattern of band efficiency and select method for suppressing peak to average ratio on the basis of not losing PAPR.

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

(1) at data sending terminal, with data X to be sent _DWith all M group scrambling pattern P ^mMultiply each other, obtain the whole series of data after scrambling

(2) the different Comb Pilot position Po of definition M group ^mServe as a mark, corresponding different scrambling patterns;

(3) with data sequence after scrambling

With the Comb Pilot sequence X _PAccording to correspondence position Po ^mForm respectively candidate OFDM symbol X ^mCarried scrambling pattern serial number information in each candidate OFDM symbol this moment, is the side information in conventional method.

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

As transmission symbol;

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

(6) extract respectively the corresponding frequency domain of M group pilot frequency locations and receive information, obtain channel strip frequency domain response estimation information after channel estimating

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

(8) normalization Obtain M group channel time domain impulse response Calculate Auto-correlation coefficient, in the M of an acquisition coefficient correlation, minimum value is corresponding

The channel time domain impulse response that is the reality of channel is estimated Corresponding m value is the sequence number of scrambling pattern;

(9) utilize the scrambling pattern that obtains in previous step to receiving the frequency-region signal descrambling code, and it is separated mapping, 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 adding the peak value regeneration after pilot tone.

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

Invention provides a kind of and has been fit to MIMO-OFDM under sparse underwater acoustic channel environment without the SLM method of side information, and the method, take the selectivity mapping techniques as basis, is improved method in conjunction with the sparse characteristics of underwater acoustic channel.The Comb Pilot that improved method utilizes Different Weight to distribute is carried the phase rotating sequence information, carry out match tracing by the pilot tones domain response to receiving, realized the scrambling pattern differentiation of high reliability, on the basis of not losing the conventional method PAPR, effectively improved band efficiency.

Major advantage of the present invention is:

1) for the characteristics of OFDM symbol peak value average power ratio, adopt a plurality of scrambling patterns of dot product, therefrom select mode that the less symbol of PAPR value transmits to avoid the appearance of peak value, reduce the PAPR value of symbol, the efficiency of raising transmitting transducer.

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

3) improvement pattern system of selection proposed by the invention is take compressive sensing theory as basis, utilize the sparse property of Shallow Water Acoustic Channels, by being found the scrambling pattern, channel matched selects information, saved the necessary side information of conventional pattern system of selection, reduced the error code disaster risk that causes because of the side information reading mistake, reduced the consumption of system transmitting terminal energy, improved the band system band utilization ratio.

Description of drawings

Select to suppress peak-to-average power ratio method system block diagram without the 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 scrambled signals CCDF curve comparison figure not.

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

The system BER performance comparison figure of the pattern selection mode that under the stable burst noise environment that distributes of Fig. 6 Alpha, the present invention and conventional pattern selection mode and side information are known.

Embodiment

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

Improved pattern selects method for suppressing peak to average ratio need 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, select one group of pilot frequency sequence X that the PAPR inhibition be there is no negative effect 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 transmitting terminal scrambling this moment, 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=1 k∈Po ^m

The M that obtains after all scramblings is organized the defined formula of time-domain signal according to peak-to-average power ratio:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10{\mathrm{<figure-callout\; id="10"\; label="log"\; filenames="HDA00003538975900014.png,HDA00003538975900022.png"\; state="\{\{state\}\}">log</figure-callout>}}_{10}\frac{\max {\left|x\right|}^2}{E\left({\left|x\right|}^2\right)}---\left(4\right)$

Calculate respectively its PAPR value, select the sequence of peak-to-average force ratio minimum

As transfer sequence.

At the pattern detector of receiving terminal utilization based on compressive sensing theory, determine by detecting the pilot tone pattern scrambling phase sequence of selecting, this is the core that pattern of the present invention is selected method for restraining peak average power ratio.

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

Y(k)=X(k)H(k)+W(k) （5）

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

Definition

For the estimated value of channel H (k), corresponding m group pilot frequency locations Po ^mThe frequency domain reception information of extracting is Y _P ^m, pilot frequency information Obtain M group channel strip frequency domain response estimation information this moment

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

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

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

F wherein _MP() expression match tracing.

Normalization

Obtain M group channel time domain impulse response

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

The M group

There is and only have one group to be that the channel time domain impulse response is estimated

Actual value, calculate

Auto-correlation coefficient,

In M the coefficient correlation that obtains, minimum value is corresponding

The channel time domain impulse response that is the reality of channel is estimated

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

Can utilize and select

Actual value and corresponding scrambling pattern, realize receiving the signal frequency domain response go disturb and balanced.

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

Following emulation experiment is example of the present invention, by this example, can verify performance of the present invention.

Simulated conditions:

In the Matlab emulation platform, build 22 and receive the MIMO-OFDM underwater sound communication system, FFT length 8192, number of sub carrier wave 1025, communication band 6～12kHz, generate 10 at random ³Individual OFDM symbol, QPSK mapping, adopt Space Time Coding and convolution coding, the 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 characteristics than traditional SLM method PAPR rejection, Fig. 4 has provided the present invention and traditional SLM mode and scrambled signals CCDF curve comparison figure not, 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 that a kind of pattern without side information is selected method for suppressing peak to average ratio, improving band efficiency, reduce the transmitting power loss, and reduce factors such as being subjected to noise due to communication system and affect and fail correctly to understand side information and cause the aspects such as risk of error code disaster to have greater advantage.Traditional pattern is selected method for suppressing peak to average ratio need to increase phase sequence in transmitted signal and is selected information, and each data symbol needs

The side information of bit, be used for determining the sequence number of selected scrambling phase sequence, wherein

Expression be maximum integer less than x, M is the sum of the scramble sequence that adopts.And need interpolation bulk redundancy (normally coding redundancy) can correctly understand this information to guarantee system receiving terminal, to avoid the whole symbolic information demodulation mistake disaster that causes due to side information demodulation mistake.For the system of multiple-input and multiple-output, the shared amount of information of this redundancy is huge.Than the conventional pattern system of selection, the inventive method need not the sequence number of selected scrambling phase sequence is transferred to receiving terminal 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 the pilot tone pattern, realize selecting information effectively to understand to the scrambling pattern.The inventive method has been saved data volume, data transmission efficiency and band efficiency have been improved, the probability that cause the whole mistakes of whole symbol because of sideband supplementary mistake have been reduced, also improved simultaneously the communication efficiency of system, guaranteed the real-time of communication, the cost of paying is 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, thereby raising entire system efficiency and stability are very suitable.

Fig. 5, Fig. 6 have provided respectively the system performance of BER contrast under white Gaussian noise and the stable burst noise environment that distributes of Alpha of the known pattern selection mode of the present invention and conventional pattern selection mode and side information, as can be seen from the figure the inventive method is better than traditional SLM method, the method performance of BER known with side information is substantially suitable, can prove absolutely that the inventive method can correctly 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 be estimated channel frequency domain response more accurately, and BER performance that equally can elevator system, make it reach the requirement of reliable communication.The inventive method can guarantee when 6dB underwater sound communication normally, reliably carry out, be better than the 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 scrambling drawing information in the environment of burst noise, be suitable for existing the underwater sound communication of burst noise situation.

In sum, the inventive method is a kind of improvement pattern system of selection of inhibition peak-to-average power ratio of suitable shallow-sea underwater acoustic communication.The inventive method has been improved transmission and the judgment mode of side information, has overcome the dependence of traditional SLM method to side information, under the prerequisite of not losing the PAPR rejection, has improved the BER performance of system.Guarantee correctly resolving of receiving terminal scrambling pattern sequence number by the mode that detects channel, improved communication efficiency and the band efficiency of system, guaranteed real-time and the reliability of MIMO-OFDM underwater sound communication system.

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

Claims (2)

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

(1) at data sending terminal, with data X to be sent _DWith all M group scrambling pattern P ^mMultiply each other, obtain the whole series of data after scrambling

(2) the different Comb Pilot position Po of definition M group ^mServe as a mark, corresponding different scrambling patterns;

(3) with data sequence after scrambling

With the Comb Pilot sequence X _PAccording to correspondence position Po ^mForm respectively candidate OFDM symbol X ^m

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

As transmission symbol;

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

(6) extract respectively the corresponding frequency domain of M group pilot frequency locations and receive information, obtain channel strip frequency domain response estimation information after channel estimating

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

(8) normalization

Obtain M group channel time domain impulse response

Calculate

Auto-correlation coefficient, in the M of an acquisition coefficient correlation, minimum value is corresponding

The channel time domain impulse response that is the reality of channel is estimated

Corresponding m value is the sequence number of scrambling pattern;

(9) utilize the scrambling pattern that obtains in previous step to receiving the frequency-region signal descrambling code, and it is separated mapping, channel-decoding, recover to send data.

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

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