CN1270462C - Partial transmission sequence method based on minimal non-linear noise for orthogonal frequency-division multiplexing system - Google Patents

Abstract

The present invention relates to a partial transmission sequence method based on minimal non-linear noise for an orthogonal frequency division multiplexing (OFDM) system, which belongs to the technical field of orthogonal frequency division multiplexing communication. The method comprises the following steps: dividing a frequency domain sequence to be sent into a plurality of parts, carrying out different kinds of phase rotation to each part, and using the power of non-linear noise as a basis for judging. Under the condition of not changing the average power of the system, the application of the method increases the bit error rate performance of the integral system.

Description

Ofdm system is based on the partial transmission sequence method of minimum nonlinear noise

Technical field

OFDM (OFDM) system belongs to the OFDM communications technical field based on the partial transmission sequence method of minimum nonlinear noise.

Background technology

(Orthogonal Frequency Division Multiplexing, OFDM) technology utilizes parallel data transmission and subchannel to overlap mutually to OFDM, when making full use of available bandwidth, avoids using equilibrium at a high speed, and the antagonism burst noise.It receives much attention in the communications field at present, at high bitrate digital subscriber line (HDSL), aspects such as digital audio broadcasting (DAB), digital video broadcasting (DVB) and wireless lan (wlan) have obtained extensive use, and IEEE 802.11a standard is also included with the OFDM technology.

But because the statistics between each subcarrier is independent, its corresponding time domain waveform shows serious random fluctuation, Gaussian distributed on the statistics.Therefore, transmitter power amplifier more easily enters the operate in saturation district, causes nonlinear distortion.

Proposed based on minimum peak-to-average power ratio (Peak to Average Power Ratio, partial transmission sequence algorithm PAPR) in " OFDMwith Reduced Peak-to-Average Power Ratio by Optimum Combination of Partial TransmitSequences " literary composition of on 1997 the 2nd phases " Electronics Letters " 368-369 page or leaf, delivering by S.H.Muller.

This method resolves into the individual frequency domain sub-vector of V (V 〉=2) with the N point frequency domain vectors that desire in the block of sub-carriers sends

$X={\mathrm{\Σ}}_{v=1}^V{X}^{\left(v\right)}$

The frequency domain sub-vector carries out laggard line phase rotation of IFFT computing and summation, obtains the time domain vector

$\tilde{x}={\mathrm{\Σ}}_{v=1}^V{b}^{\left(v\right)}\·\mathrm{IFFT}\left\{X^{\left(v\right)}\right\}$

B wherein ^(v)Be twiddle factor.To b ^(v)Various situations travel through, obtain corresponding to peak-to-average power ratio (ratio of peak power and average power) b hour ^(v)In General System, average power remains unchanged, peak power minimum under this condition.

But this method has only reduced the peak power of signal under the constant condition of system's average power, can't reflect the performance of BER of entire system.

Summary of the invention

The object of the present invention is to provide a kind of partial transmission sequence method that is used for OFDM (OFDM) system based on minimum nonlinear noise, this method can improve the performance of BER of entire system.

It is characterized in that: it contains following steps successively:

(1) the N point frequency domain vectors that desire in the block of sub-carriers is sent resolves into the individual sub-vector of V (V 〉=2)

$X={\mathrm{\Σ}}_{v=1}^V{X}^{\left(v\right)},$

Wherein, X: the frequency domain vectors that desire sends;

X ^(v): the frequency domain sub-vector that decomposites;

(2) the frequency domain sub-vector is carried out the IFFT computing, obtain the time domain sub-vector

a ^(v)＝IFFT{X ^(v)}(1≤v≤V)，

Wherein, IFFT{}: quick inverse-Fourier transform;

(3) above-mentioned sub-vector is carried out the phase place rotation, obtain the gyrator vector

x ^(v)＝b ^(v)·a ^(v)(1≤v≤V)，

Wherein, b ^(v): twiddle factor is the arbitrarily angled value of from 0 to 2 π;

(4) gyrator vector summation obtains the time domain vector

$\tilde{x}={\mathrm{\Σ}}_{v=1}^V{x}^{\left(v\right)},$

(5) the nonlinear noise power of calculating time domain vector

$N_{\mathrm{nl}}={\mathrm{\Σ}}_{n=0}^{N-1}[{f\left(\tilde{x}\left(n\right)\right)-\tilde{x}\left(n\right)]}^2,$

Wherein, Vector

In the n point;

F (): the transfer function of power amplifier;

(6) travel through all b ^(v)Value, and repeat (3), (4), (5) step obtains nonlinear noise power time domain vector hour

$x=\tilde{x}\left|\min \right\{N_{\mathrm{nl}}\left(\tilde{x}\right)\},$

The twiddle factor of this moment is b ^*, promptly

$b^{*}=b^{\left(v\right)}\left|\min \right\{N_{\mathrm{nl}}\left(\tilde{x}\right)\}$

(7) send x, and with b ^*Send as side information, be used for receiver and separate partial transmission sequence.

Operation on the COSSAP of work station communication simulation platform proves: the present invention has improved the performance of BER of entire system, has reached intended purposes.

Description of drawings

Fig. 1 theory diagram of the present invention.

The FB(flow block) of Fig. 2 embodiment of the invention 1.

The FB(flow block) of Fig. 3 embodiment of the invention 2.

The performance comparison diagram of Fig. 4 embodiment 1 and prior art.

The performance comparison diagram of Fig. 5 embodiment 2 and prior art.

Embodiment

Embodiment 1: ask for an interview Fig. 2

The first step: the N point frequency domain vectors that desire in the block of sub-carriers is sent evenly resolves into the individual sub-vector of V (V 〉=2) according to the mode of adjoining

$X={\mathrm{\Σ}}_{v=1}^V{X}^{\left(v\right)},$

Also be

X (l) wherein: l the point of vector X

X ^v(l): sub-vector X ^vL point

The mode of adjoining means as far as possible adjacent subcarrier is divided in the same part.For example adopt N=512 subcarrier when system, and when being divided into the V=2 part, then the 0th～255 subcarrier is in first, the 256th～511 subcarrier is in second portion

Second step: the frequency domain sub-vector is carried out the IFFT computing, obtain the time domain sub-vector

a ^(v)＝IFFT{X ^(v)}(1≤v≤V)，

It is expressed as with matrix form

a ^(v)＝IF·X ^(v)，

X wherein ^(v)And a ^(v)Be N * 1 column vector,

IF is the IFFT transformation matrix of N * N

$\mathrm{IF}(m,n)=\frac{1}{N}{e}^{j\frac{2\mathrm{\πmn}}{N}},$ (0≤m≤N-1，0≤n≤N-1)

The 3rd step: above-mentioned sub-vector is carried out the phase place rotation, obtain the gyrator vector

x ^(v)＝b ^(v)·a ^(v)(1≤v≤V)，

For making things convenient for computing, b ^(v)Between 0～2 π, do not travel through, get usually ± 1 or ± j.This moment only need be to real, the imaginary part negate or the transposition of vector, and does not need complicated complex multiplication operation.

The 4th step: the summation of gyrator vector obtains the time domain vector

$\tilde{x}={\mathrm{\Σ}}_{v=1}^V{x}^{\left(v\right)},$

The 5th step: the nonlinear noise power that calculates the time domain vector

$N_{\mathrm{nl}}={\mathrm{\Σ}}_{n=0}^{N-1}[{f\left(\tilde{x}\left(n\right)\right)-\tilde{x}\left(n\right)]}^2,$

The 6th step: travel through all b ^(v)± 1 with ± j value, and repetition (3), (4), (5) step obtain nonlinear noise power time domain vector hour

$x=\tilde{x}\left|\min \right\{N_{\mathrm{nl}}\left(\tilde{x}\right)\},$

The twiddle factor of this moment is b ^*

The 7th step: send x, and with b ^*Send as side information, be used for receiver and separate partial transmission sequence.

Embodiment 2: ask for an interview Fig. 3

Step and example 1 are basic identical, and difference is:

(1) step was evenly resolved into the individual sub-vector of V (V 〉=2) randomly with the N point frequency domain vectors that desire in the block of sub-carriers sends

$X={\mathrm{\Σ}}_{v=1}^V{X}^{\left(v\right)}.$

Concrete enforcement in the following way: for example adopt N=512 subcarrier when system, and when being divided into the V=2 part, it is the independent same distribution Gaussian random variable t of average with 0 that elder generation generates 512 at random ₀～t ₅₁₁, and successively i=0～511 are done as judging

0≤i≤511

Divide to carry out part, and guarantee the randomness and the uniformity of division.

Fig. 4 is the performance of BER and the prior art performance comparison diagram of the embodiment of the invention 1.Be without loss of generality, ofdm system is got N=512 subcarrier, QPSK (Quarter Phase Shift Keying is adopted in the frequency domain symbol mapping, four phase place phase-shift keyings), adopt the white Gaussian noise channel circumstance, input rollback rate (Input Backoff, the ratio of power amplifier input saturation power and average power signal) is 2dB.Can find out that from Fig. 4 and Fig. 5 the embodiment of the invention has obviously improved the performance of BER of system.

Curve 1 is not for using the performance of BER of partial transmission sequence among Fig. 4, curve 2 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 2 parts, curve 3 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 3 parts, curve 4 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 4 parts, curve 5 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 2 parts, curve 6 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 3 parts, and curve 7 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 4 parts.

As seen from Figure 4, no matter adopt the partial transmission sequence that also is based on the equal power ratio of smallest peaks based on the partial transmission sequence of minimum nonlinear noise power, when the part number of dividing (V) was big more, system's regulating power was strong more, performance is good more, but needed amount of calculation is also big more.When employing was divided into two-part partial transmission sequence based on minimum nonlinear noise power, systematic function was suitable with the partial transmission sequence based on minimum peak-to-average power ratio that is divided into three parts; Employing be divided into three parts based on the partial transmission sequence of minimum nonlinear noise power the time, systematic function even be better than being divided into tetrameric partial transmission sequence based on minimum peak-to-average power ratio.

As seen by using the criterion of minimum nonlinear noise power as partial transmission sequence, consider every possible angle of the influence of interior all sampling points of whole OFDM code-element period to systematic function, can under the condition of identical operation complexity, obtain better system performance, perhaps under the condition that obtains given systematic function, reduce computational complexity.

Sub-vector adopts the pseudorandom dividing mode among Fig. 5, and other condition and Fig. 4 are identical.And systematic function slightly is better than adjoining dividing mode.

Curve 1 is not for using the performance of BER of partial transmission sequence among Fig. 5, curve 2 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 2 parts, curve 3 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 3 parts, curve 4 is for being divided into the performance of BER based on the partial transmission sequence of minimum peak-to-average power ratio of 4 parts, curve 5 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 2 parts, curve 6 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 3 parts, and curve 7 is for being divided into the performance of BER based on the partial transmission sequence of minimum nonlinear noise of 4 parts.

Claims (3)

1, a kind of ofdm system is characterized in that based on the partial transmission sequence method of minimum nonlinear noise: it contains following steps successively:

(1) the N point frequency domain vectors that desire in the block of sub-carriers is sent resolves into the individual sub-vector of V (V 〉=2)

$X={\mathrm{\Σ}}_{v=1}^V{X}^{\left(v\right)},$

Wherein, X: the frequency domain vectors that desire sends;

X ^(v): the frequency domain sub-vector that decomposites;

(2) the frequency domain sub-vector is carried out the IFFT computing, obtain the time domain sub-vector

a ^(v)＝IFFT{X ^(v)}(1≤v≤V)，

Wherein, IFFT{}: quick inverse-Fourier transform;

(3) above-mentioned sub-vector is carried out the phase place rotation, obtain the gyrator vector

x ^(v)(n)＝b ^(v)·a ^(v)(1≤v≤V)，

Wherein, b ^(v): twiddle factor;

(4) gyrator vector summation obtains the time domain vector

$\tilde{x}={\mathrm{\Σ}}_{v=1}^V{x}^{\left(v\right)},$

(5) the nonlinear noise power of calculating time domain vector

$N_{\mathrm{nl}}={\mathrm{\Σ}}_{n=0}^{N-1}{[f\left(\tilde{x}\left(n\right)\right)-\tilde{x}\left(n\right)]}^2,$

Wherein, Vector In the n point;

F (): the transfer function of power amplifier;

(6) select different b repeatedly ^(v)Value, and repeat (3), (4), (5) step obtains nonlinear noise power time domain vector hour

$x=\tilde{x}\left|\min \right\{N_{\mathrm{nl}}\left(\tilde{x}\right)\},$

The twiddle factor of this moment is b ^*

(7) send x, and with b ^*Send as side information, be used for receiver and separate partial transmission sequence.

2, transmission sequence method according to claim 1 is characterized in that: the frequency domain vectors that desire is sent evenly resolves into the individual sub-vector of V (V 〉=2) according to the mode of adjoining.

3, transmission sequence method according to claim 1 is characterized in that: the frequency domain vectors that desire is sent evenly resolves into the individual sub-vector of V (V 〉=2) randomly.

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