CN103441769B - PTS method for reducing PAPR of OFDM system - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a PTS method for reducing the PAPR of an OFDM system. After an OFDA signal is partitioned, autocorrelation with different autocorrelation coefficients is respectively added according to the plus or minus characteristic of a first data point real part of each piece, so that the aims that the PAPR of the OFDM signal is reduced and a receiving end detects the signal without sideband auxiliary information are achieved. The receiving end recovers a correlation coefficient according to the plus and minus characteristic of an autocorrelation value of each piece, a piece signal without autocorrelation and the autocorrelation coefficient corresponding to the piece signal are multiplied, and the phase rotation sequence timing the piece is judged according to the plus and minus characteristic of a product. The receiving end can recover an original signal without the sideband auxiliary information while the PAPR of the OFDM signal is effectively reduced through the self-correlation matching-PTS, so that band width is saved, and frequency spectrum utilization efficiency is effectively improved.

Description

A kind of PTS method reducing the PAPR of ofdm system

Technical field

The invention belongs to wireless communication technology field, be specifically related to a kind of PTS method reducing the PAPR of ofdm system.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing, OFDM) be a kind of multi-carrier modulation technology of superior performance, because it effectively can resist intersymbol interference (Inter-symbol Interference, ISI) and multidiameter delay and in widespread attention.There is multiple orthogonal subcarrier in ofdm system, its output signal is the superposition of multiple subsignal, thus there will be very high peak-to-average power ratio (Peak-to-average Power Ratio, PAPR).High PAPR can cause out-of-band power radiation, hardware nonlinearity distortion, and the mutual interference etc. between subcarrier makes systematic function severe exacerbation.Therefore, the PAPR reducing ofdm system has very important meaning.

The method of current reduction ofdm system PAPR is broadly divided into three classes: pre-distortion signal technology, coding class methods and probability class methods.Probability class methods are emphasis of research at present.The inreal peak power reducing ofdm signal of probability class methods, but by reaching to original OFDM signal enforcement linear partition or linear transformation the object reducing high-peak power probability of occurrence.Probability class methods comprise a lot of algorithm, as tone reservation (Tone Reservation, TR), selected mapping method (Selective Mapping, SLM), partial transmission sequence (Partial Transmit Sequence, PTS) etc.In order to recover primary signal at receiving terminal, PTS technology needs to transmit the secondary information of certain sideband, this reduces the spectrum utilization efficiency of system.In order to can at receiving terminal exactly by secondary for sideband Information recovering out, extra technology usually can be adopted if coding techniques is to process the secondary information of sideband, and this may cause the rising again of system PAPR, and reduce further again the availability of frequency spectrum of system.Autocorrelation matching-PTS method in this paper is while effective reduction system PAPR, in the middle of the Information Embedding of the rotatable phase factor to the autocorrelation of signal, transmission without the need to the secondary information of sideband just can realize signaling protein14-3-3, substantially increases spectrum utilization efficiency.

Summary of the invention

The object of the present invention is to provide a kind of PTS method reducing the PAPR of ofdm system, in the middle of the autocorrelation discriminant information of rotatable phase sequence being implanted to signal, just primary signal can be recovered without the need to transmitting the secondary information of sideband, improving spectrum utilization efficiency.

The object of the invention is to be achieved through the following technical solutions:

S1, set the frequency-region signal after serial to parallel conversion and baseband modulation as X, traditionally the division rule of PTS is divided into V sub-block X ^(m), wherein, m=1,2 ..., V, then passes through auto-correlation coefficient arbiter by all sub-blocks, judges coefficient correlation G (z);

S2, auto-correlation coefficient G (z) determined by S1 pass through autocorrelation signal generator together with sub-blocks all described in S1, obtain auto-correlation frequency domain sub-block signal;

S3, IFFT conversion is carried out to S2 gained auto-correlation frequency domain sub-block signal, frequency domain auto-correlation sub-block signal is transformed to time domain, all sub-block signals after conversion are multiplied by phase rotation coefficient b (m) respectively, b (m) ∈ (+1 ,-1), m=1,2,, V, supposes that time domain frequency domain sub-block signal is then by b (m) with be multiplied and can obtain alternate transmission sequence

S4, calculate each alternate transmission sequence according to PAPR computing formula pAPR, and the signal selecting wherein minimum PAPR minimum for transmission;

S5, suppose that the signal received at receiving terminal is y, fFT operation is carried out to y, is transformed into frequency-region signal;

S6, carry out piecemeal according to partitioned mode described in S1 to y, be divided into V sub-block, each sub-block is expressed as Y ^(m), m=1,2 ..., V, to Y ^(m)carry out auto-correlation computation, recover the rotatable phase that auto-correlation coefficient is taken advantage of with each sub-block, the signal after the autocorrelation that is eliminated 1≤i≤V, described auto-correlation computation rule is, if the autocorrelation value of a sub-block is just, then the auto-correlation coefficient of this sub-block reverts to k (k > 0); If its autocorrelation value is negative, then the autocorrelation value of this sub-block reverts to-k (k > 0);

S7, by S6 gained with this corresponding rotatable phase 1≤i≤V is multiplied, and obtains the final each sub-block signal recovered, and by each sub-block signal plus of described final recovery, obtains the final data block Y recovered ^*,

S8, to S7 gained Y ^*carry out base band demodulating and parallel serial conversion, the signal finally recovered.

Further, described in S3, the number of alternate transmission sequence is n=2 ^v-1.

The invention has the beneficial effects as follows: be after ofdm signal piecemeal, add the different autocorrelation of auto-correlation coefficient respectively according to the positive and negative of each sub-block first data point real part, reach with this and reduce ofdm signal PAPR and the receiving terminal object without the need to the secondary infomation detection signal of sideband.Recover auto-correlation coefficient at receiving terminal according to the positive and negative of each sub-block autocorrelation value, and auto-correlation coefficient corresponding with it for the sub-block signal after eliminating autocorrelation is multiplied, judge according to the positive and negative of product the phase rotating sequence that this sub-block is taken advantage of.Autocorrelation matching-PTS, while effectively reducing ofdm signal PAPR, can recover primary signal at receiving terminal without the need to the secondary information of sideband, save bandwidth, effectively improve spectrum utilization efficiency.

Accompanying drawing explanation

Fig. 1 is the system block diagram of PTS-OFDM.

Fig. 2 is autocorrelation matching-PTS system block diagram.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described:

A typical ofdm signal can be expressed as follows:

wherein, N is the number of ofdm system sub-carriers, and X (n) is the frequency domain data through baseband modulation that the n-th subcarrier transmits, f _nbe the frequency of the n-th subcarrier, T is the cycle of an OFDM symbol.

The PAPR of signal is defined as the Instantaneous peak power of signal and the ratio of average power:

$\mathrm{PAPR}=\frac{\max \left\{{\left|x\left(t\right)\right|}^2\right\}}{E\left\{{\left|x\left(t\right)\right|}^2\right\}}$

Rewrite as follows time in units of dB:

wherein, | x (t) | ²represent the instantaneous power of signal, max [] represents maximizing, and E [] expression is averaged.

Use CCDF (Complementary Cumulative Distribution Function traditionally, CCDF) the PAPR distribution situation in ofdm system is weighed, the probability sum that the part sampled value being namely greater than threshold value in all PAPR sampled values occurs: P{PAPR>z}=1-P{PAPR≤z}=1-(1-e ^-z) ⁿ, wherein, z represents a threshold value of PAPR.Can find out, number of sub carrier wave N is larger, and P (PAPR > z) is larger.

As shown in Figure 1, the N number of subcarrier in an OFDM data is divided into V sub-block X to traditional PTS technology ^(m), m=1,2 ..., V.Division rule is as follows; The first, each sub-block vector length is equal; The second, for each sub-block, the position not being divided into the former OFDM symbol information in this block supplements 0.Each sub-block includes the data of different frequent points in N/V X.

In traditional PTS method, it is X=[X (0), X (1) that X is expressed as vector form, X (N-1)], X can be divided into V sub-block according to random, adjacent, the three kinds of division rules that interweave, and each sub-block is expressed as X ^(m), m=1,2 ..., V, then X can be expressed as: then be multiplied by suitable phase rotation coefficient before each sub-block, and select one group and make to transmit there is the phase factor of minimum peak-to-average power ratio wherein, b (m), m=1,2 ..., V is phase rotation coefficient, b (m)=exp (j φ (m)) m=1,2 ..., V.Especially, when the rotatable phase factor is restricted to b (m) ∈ (+1 ,-1), m=1,2 ..., during V, can U=2 be obtained ^v-1individual alternate transmission sequence, and need the ratio number of the secondary information of the sideband of transmission specially for log ₂u=log ₂2 ^v-1=V-1.

Time-domain signal is obtained through inverse fast fourier transform (Inverse Fast Fourier Transform, IFFT) by frequency-region signal: $\hat{x}=\mathrm{IFFT}\left(\underset{m=1}{\overset{v}{\mathrm{\Σ}}}b\left(m\right)X^{\left(m\right)}\right)=\underset{m=1}{\overset{v}{\mathrm{\Σ}}}b\left(m\right)*\mathrm{IFFT}\left(X^{\left(m\right)}\right)=\underset{m=1}{\overset{v}{\mathrm{\Σ}}}b\left(m\right)x^{\left(m\right)}$ According to $\mathrm{PAPR}\left(\mathrm{dB}\right)=10\log 10\frac{\max \left\{{\left|x\left(t\right)\right|}^2\right\}}{E\left\{\right|{x\left(t\right)|}^2\}}$ Calculate the PAPR of each alternative signal respectively, the signal selecting wherein PAPR minimum is for transmission, and transmission simultaneously identifies the secondary information of the sideband of phase rotating sequence.

The system block diagram of autocorrelation matching-PTS method that the present invention proposes as shown in Figure 2.Suppose that the frequency-region signal after serial to parallel conversion and baseband modulation is X, traditionally the division rule of PTS is divided into V sub-block, X ^(m), m=1,2 ..., V.Then all sub-blocks are passed through auto-correlation coefficient arbiter.Auto-correlation coefficient arbiter is according to the positive and negative auto-correlation coefficient determining this sub-block of first data point real part in each sub-block, if its real part is just, then the auto-correlation coefficient of this sub-block is judged to be α=k, (k > 0), otherwise, the auto-correlation coefficient of this sub-block is determined as α=-k, (k > 0).

The transfer function of autocorrelation signal generator used in the present invention is: G (z)=1+ α ^*z ^-1, wherein, z ^-1transfer operation backward, as z ^-1s (t)=s (t-1).By autocorrelation signal generator together with the coefficient correlation judge all sub-blocks and auto-correlation coefficient arbiter, obtain autocorrelative frequency domain sub-block signal.Then we process autocorrelative frequency domain sub-block signal by the subsequent treatment after conventional P TS method piecemeal.First, by IFFT conversion, frequency domain auto-correlation sub-block signal is transformed to time domain, then each sub-block is multiplied by phase rotation coefficient respectively.Now we limit b (m) ∈ (+1 ,-1), m=1, and 2 ..., V, so according to the analysis to conventional P TS method, we can obtain U=2 ^v-1individual alternate transmission signal.Foundation | x (t) | ²represent the instantaneous power of signal, max [] represents maximizing, and E [] expression is averaged, and the PAPR of signal is defined as the Instantaneous peak power of signal and the ratio of average power:

$\mathrm{PAPR}=\frac{\max \left\{{\left|x\left(t\right)\right|}^2\right\}}{E\left\{{\left|x\left(t\right)\right|}^2\right\}}$

Rewrite as follows time in units of dB:

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

Calculate the PAPR of each alternate transmission signal respectively, and the signal selecting wherein PAPR minimum for transmission.The information of rotatable phase sequence has implicitly been implanted in the middle of the autocorrelation of signal by we, therefore does not need the secondary information of transmission sideband, saves bandwidth, improves spectrum utilization efficiency.

Suppose that the signal received at receiving terminal is y, it can be expressed as received signal strength, after FFT operation, is transformed into frequency-region signal.

According to the partitioned mode identical with transmitting terminal, Received signal strength is divided into V sub-block and each sub-block is expressed as Y ^(m), m=1,2 ..., V then Y can be expressed as: then, by each sub-block by autocorrelation signal adaptation, respectively auto-correlation computation is done to each sub-block signal, to recover the rotatable phase that auto-correlation coefficient and each sub-block are taken advantage of.The recovery rule of auto-correlation coefficient is as follows: if the autocorrelation value of a sub-block is just, then the auto-correlation coefficient of this sub-block reverts to k (k > 0); If its autocorrelation value is negative, then the autocorrelation value of this sub-block reverts to-k (k > 0).Then each the sub-block signal Y will recovered _i, 1≤i≤V and the auto-correlation coefficient of its correspondence recovered 1≤i≤V is in the lump by autocorrelation signal inverse transformation generator, and passable arrives the signal eliminated after autocorrelation 1≤i≤V.

And then, eliminate autocorrelation after each sub-block signal the auto-correlation coefficient of 1≤i≤V and its correspondence 1≤i≤V is simultaneously by rotatable phase arbiter.Rotatable phase decision rule corresponding to each sub-block is as follows: by the auto-correlation coefficient of each sub-block 1≤i≤V and this sub-block signal the real part of first data point in 1≤i≤V is multiplied, if product is greater than 0, then and the rotatable phase sequence that this sub-block is corresponding 1≤i≤V is+1; Otherwise 1≤i≤V is-1.

Afterwards, each sub-block signal of autocorrelation will be eliminated the rotatable phase that 1≤i≤V is corresponding with it 1≤i≤V is multiplied, and can obtain the final each sub-block signal recovered, and then by each sub-block signal plus, just obtains the final data block Y recovered ^*, namely again through base band demodulating and parallel serial conversion, the signal that just can finally be recovered.

Claims (2)

1. reduce a PTS method of the PAPR of ofdm system, it is characterized in that: its step is as described below:

S1, set the frequency-region signal after serial to parallel conversion and baseband modulation as X, traditionally the division rule of PTS is divided into V sub-block X ^(m), wherein, m=1,2 ..., V, then passes through auto-correlation coefficient arbiter by all sub-blocks, judges coefficient correlation G (z);

S2, auto-correlation coefficient G (z) determined by S1 pass through autocorrelation signal generator together with sub-blocks all described in S1, obtain auto-correlation frequency domain sub-block signal;

S3, IFFT conversion is carried out to S2 gained auto-correlation frequency domain sub-block signal, frequency domain auto-correlation sub-block signal is transformed to time domain, all sub-block signals after conversion are multiplied by phase rotation coefficient b (m) respectively, b (m) ∈ (+1 ,-1), m=1,2,, V, supposes that time domain frequency domain sub-block signal is then by b (m) with be multiplied and can obtain alternate transmission sequence

S4, calculate each alternate transmission sequence according to PAPR computing formula pAPR, and the signal selecting wherein minimum PAPR minimum for transmission;

S5, suppose that the signal received at receiving terminal is y, fFT operation is carried out to y, is transformed into frequency-region signal;

S6, carry out piecemeal according to the division rule of conventional P TS described in S1 to y, be divided into V sub-block, each sub-block is expressed as Y ^(m), m=1,2 ..., V, to Y ^(m)carry out auto-correlation computation, recover the rotatable phase that auto-correlation coefficient is taken advantage of with each sub-block, the signal after the autocorrelation that is eliminated described auto-correlation computation rule is, if the autocorrelation value of a sub-block is just, then the auto-correlation coefficient of this sub-block reverts to k (k > 0); If its autocorrelation value is negative, then the autocorrelation value of this sub-block reverts to-k (k > 0);

S7, by S6 gained with this corresponding rotatable phase be multiplied, obtain the final each sub-block signal recovered, by each sub-block signal plus of described final recovery, obtain the final data block Y recovered ^*,

S8, to S7 gained Y ^*carry out base band demodulating and parallel serial conversion, the signal finally recovered.

2. a kind of PTS method reducing the PAPR of ofdm system according to claim 1, is characterized in that: described in S3, the number of alternate transmission sequence is n=2 ^v-1.