CN101155168A - Method for reducing PAPR of OFDM system - Google Patents

Abstract

The present invention discloses a method for reducing PAPR of OFDM system. The method replaces traditional Mu law companding function by hyperbolic tangent function, to ensure the value obtained after companding the data of the original signal be within a certain range, the concrete process is that as follows: in transmission terminal, to calculate the time field OFDM signal after IFFT so as to obtain average amplitude, and confirm companding parameter k and amplitude modulation parameter Alpha based on the demand of OFDM system; according to the average amplitude and Alpha as well as k, to implement companding transformation to the OFDM signal with hyperbolic tangent function mode, then to transmit to the channel after parallel-serial conversion and filtering; in the receiving terminal, to calculate the received OFDM signal so as to obtain the average amplitude of the received signal, and to limit the amplitude of the OFDM signal based on threshold; according to average amplitude and alpha as well as k, to implement companding inverse transformation to the OFDM signal with hyperbolic tangent companding inverse transformation function mode, so as to resume the original signal. The present invention has the advantage of reducing PAPR well, and can be used to treat the PAPR in the fourth generation OFDM radio communication system.

Description

A kind of method that reduces ofdm system PAPR

Technical field

The invention belongs to communication technical field, relate to the peak-to-average power ratio PAPR problem in the orthogonal frequency division multiplex OFDM communication system, specifically a kind of non-linear companding method that effectively reduces the ofdm system peak-to-average power ratio.

Background technology

The orthogonal frequency division multiplex OFDM technology is with its availability of frequency spectrum, good anti-multipath decline performance and be considered to one of core technology of the 4th third-generation mobile communication 4G efficiently, and the OFDM technology has obtained extensive use in fields such as ADSL (Asymmetric Digital Subscriber Line) ADSL, digital audio broadcasting DAB and digital television broadcasting DVB, IEEE 802.11, IEEE 802.16 and power line broadband data communications at present.

The basic principle of OFDM is exactly that data flow is at a high speed passed through string and conversion, is assigned in the relatively low experimental process channel of transmission rate and transmits.Because the symbol period in each subchannel can increase relatively, therefore can alleviate the influence of the multidiameter expansion of wireless channel.And can between the OFDM symbol, insert protection at interval, the order protection greater than the maximum delay expansion of wireless channel, so just can be eliminated because the intersymbol interference ISI that multipath brings at interval to greatest extent.And, generally all adopt Cyclic Prefix at interval, thereby can avoid the interchannel interference ICI that brings by multipath as protection.

The ofdm communication system principle as shown in Figure 1.At the transmitting terminal of OFDM, be input as binary bit stream or image or random sequence a among Fig. 1 _nThen, adopt quadrature amplitude modulation QAM or phase shift keying modulation PSK to a _nCarry out premodulated one time, obtain frequency domain signal X (n), obtain time-domain signal x (n) again behind serial to parallel conversion and inverse fast fourier transform IFFT, this time-domain signal obtains actual transmission signal s (t) behind parallel serial conversion and digital-to-analogue conversion and low pass filter.At the receiving terminal of OFDM, what in fact carry out is the inverse process of above-mentioned transmitting terminal.

Time-domain signal x (n) in the ofdm communication system of Fig. 1 is carried out power normalization, obtain the time domain sample sequence { x of ofdm communication system _nAs follows:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k\exp \left(\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071001885900161.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}}{N}\right),n=\mathrm{0,1},......,N-1---\left(1\right)$

Wherein N is a sub-carrier number, X _kRepresent k the modulating data on the subcarrier, j represents

Compare with single-carrier system, because the OFDM symbol is independently to be formed through the sub-carrier signal addition of ovennodulation by a plurality of, such composite signal just might produce bigger peak power, can bring bigger peak-to-average power ratio PAPR thus.

This peak-to-average power ratio can be defined as:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10{\mathrm{<figure-callout\; id="10"\; label="log"\; filenames="A20071001885900141.png,A20071001885900161.png"\; state="\{\{state\}\}">log</figure-callout>}}_{10}\frac{\underset{n}{\max \left\{{\left|x_n\right|}^2\right\}}}{E\left\{{\left|x_n\right|}^2\right\}}---\left(2\right)$

Peak-to-average power ratio PAPR has proposed very high requirement to the linearity of amplifier in the transmitter, in ofdm system, change bigger signal and pass through non-linear components, when for example entering the amplifier nonlinearity zone, signal can produce nonlinear distortion and harmonic wave, cause significantly spread spectrum interference and inband signaling distortion, cause the whole system performance decrease; Also can increase the complexity of A/D and D/A converter simultaneously, reduce the accuracy of transducer.

For fear of described nonlinear distortion, traditional method is to adopt the linear amplifier of great dynamic range, perhaps the nonlinear amplifier working point is compensated, but the efficient of power amplifier is reduced greatly, and the cost of whole system increases greatly.Solve signal non-linear distortion problem in the ofdm communication system, the PAPR of signal in will the reduction system, at present the method for the reduction PAPR that proposes mainly contains: three kinds of signal predistortion technology, high spped coding technology, block encoding, and wherein signal predistortion technology comprises amplitude limit, companding transform and preserved sub-carrier etc.; The high spped coding technology comprises selectivity mapping SLM and part transfer sequence PTS; Block encoding comprises Golay complementary series and Reed-Muller coding etc.Wherein amplitude limit is simple effective method, and it is to reduce PAPR by subduing peak signal, but this method has been owing to introduced in-band noise and out-of-band radiation, thereby will cause the increase of the ofdm system error rate.Companding transform is similar to amplitude limit, also is to reach the purpose that reduces peak-to-average power ratio by changing signal amplitude.Represent companding transform with C{}, this companding transform should satisfy following two conditions:

(1) when | x|≤m, | C{x}| 〉=| x|; Otherwise, | C (x) |≤| x|, wherein m represents the breakover point of companding transform;

(2) when satisfying E{|x| ²≈ E{|C{x}| ², can guarantee conversion front and back average power about equally.For satisfying above-mentioned condition, companding transform can adopt following mu-law companding formula to describe:

$s_n=C\left\{x_n\right\}=\frac{{\mathrm{Vx}}_n}{\ln (1+\mathrm{\&mu;})\left|x_n\right|}\ln (1+\frac{\mathrm{\&mu;}}{V}|x_n\left|\right)---\left(3\right)$

S wherein _nSignal behind the expression companding,

V represents OFDM symbol x _nAverage amplitude, the breakover point of companding transform just,

μ is the companding coefficient.

Can implement the inverse transformation of companding transform to received signal at receiving terminal, that is:

$y_n=C^{-1}\left\{r_n\right\}=\frac{V^{\&prime;}{r}_n}{\mathrm{\&mu;}\left|r_n\right|}\left\{\exp \right[\frac{\left|r_n\right|\ln (1+\mathrm{\&mu;})}{V^{\&prime;}}]-1\}---\left(4\right)$

Y wherein _nSignal behind the expression companding transform, r _nThe expression received signal, V ' is the average amplitude of received signal.

Original relatively OFDM symbol, because companding transform compresses the signal significantly in the original OFDM symbol, small amplitude signal is enlarged, so the distribution through the data symbol behind the companding transform is more tight, the symbol quantity that big amplitude occurs reduces to some extent, has promptly reduced PAPR.Increase along with μ, this improvement is also more and more obvious, but because the companding curve characteristic of traditional companding transform function, it is not enough to especially big Signal Compression and the expansion of special small-signal, therefore can not present evenly through the data symbol behind the companding transform to distribute closely.Though the companding transform inverse transformation also can be reduced received signal substantially, because the average power of OFDM symbol can be variant slightly, thereby also can there be some differences in the signal after the companding transform inverse transformation and primary signal, and promptly companding transform can cause certain error rate.

As seen, though companding transform has more flexibility than amplitude limit, companding transform is reducing PAPR, is improving the OFDM symbol distribution and improve and be still waiting further improvement aspect the error rate.

The content of invention

The objective of the invention is to avoid the deficiency of prior art, by analyzing the basic reason that ofdm system PAPR problem produces, large-signal from the compression time domain, small-signal is started with in the expansion time domain, advantage in conjunction with amplitude limit and companding, the method of a kind of PAPR of reduction has been proposed, with effective reduction PAPR with improve the error rate.

The technical scheme that realizes the object of the invention is: utilize hyperbolic tangent function to replace traditional mu-law companding function, make the data of original signal be within certain scope in the value that obtains behind the companding.Detailed process is as follows

A. reduce the method for ofdm system PAPR at transmitting terminal, comprise following process:

(1) to the time domain sample sequence { x of ofdm communication system _nCalculate its average amplitude V;

(2), determine the value of companding coefficient k and amplitude modulation coefficient α according to the requirement of ofdm system;

(3) according to the value of average amplitude V and companding coefficient k, amplitude modulation coefficient α, to ofdm signal with

Tanh companding formula carries out companding transform, and this tanh companding functional expression is;

$s_n=\frac{\mathrm{\&alpha;}\&times;x_n\&times;V}{\left|x_n\right|}\tanh \left(\frac{k\&times;\left|x_n\right|}{V}\right)$

Wherein, the companding coefficient k is used to control the degree to the signal companding, and it is constant that amplitude modulation coefficient α is used to keep signal average power before and after companding transform;

(4) signal behind the companding is carried out and go here and there the conversion and filtering after send to channel.

B. reduce the method for ofdm system PAPR at receiving terminal, comprise following process:

(1) ofdm signal that receives is calculated the average amplitude V ' of received signal;

(2) ofdm signal that receives is carried out amplitude limit by setting thresholding, promptly amplitude is carried out amplitude limit greater than the signal of α * V ', the amplitude of guaranteeing the ofdm signal that receives is less than α * V ';

(3) with the value of amplitude modulation coefficient α, companding coefficient k ofdm signal is carried out the companding inverse transformation with tanh companding inverse transformation formula according to average amplitude V ', this tanh companding inverse transform function formula is;

$R_n=0.5\&times;\frac{V^{\&prime;}\&times;{R_n}^{\&prime;}}{k\&times;\left|{R_n}^{\&prime;}\right|}\&times;\ln \left\{\frac{\mathrm{\&alpha;}\&times;V^{\&prime;}+\left|{R_n}^{\&prime;}\right|}{\mathrm{\&alpha;}\&times;V^{\&prime;}-\left|{R_n}^{\&prime;}\right|}\right\}$

R ' wherein _nThe expression received signal,

(4) restore primary signal.

The present invention compares with art methods, has the following advantages:

1, because tanh companding function of the present invention is asymptotic hyperbola, it all is better than traditional companding transform to the compression effectiveness of peak signal with to the expansion effect of small-signal, therefore it can more effectively be limited in ofdm signal within certain scope, thereby reduces PAPR better.

2, because the present invention adopts tanh companding function that small-signal is enlarged, strengthened the resistance of small-signal to noise.

3, because the present invention sets thresholding the signal that exceeds limited range is carried out amplitude limit, limited the influence of big noise to signal to a certain extent, therefore the error rate of system of the present invention is better than traditional companding transform a little.

4, because tanh companding function of the present invention has adopted amplitude modulation coefficient α and two coefficients of companding coefficient k, be respectively applied for and adjust average amplitude and companding degree, make when the companding function is adjusted, to have more flexibility.

5, simulation result shows, the present invention can carry out more efficient compression and expansion to peak signal and small-signal, and the ofdm signal amplitude more is distributed within certain scope in the concentrated area, has reduced the requirement of the signal pair amplifier range of linearity, improved the efficient of linear amplifier.

Description of drawings

Fig. 1 is the theory diagram of existing ofdm communication system;

Fig. 2 is the flow chart of the inventive method;

Fig. 3 realizes system block diagram of the present invention;

Fig. 4 is simulation result figure of the present invention;

Fig. 5 is the complementary cumulative distribution function C CDF comparison diagram of different companding coefficient k among the present invention;

Fig. 6 is the error rate Ber comparison diagram of different companding coefficient k among the present invention.

Embodiment

Followingly the present invention is described in further detail with reference to accompanying drawing.

With reference to Fig. 3, it is as follows that the present invention reduces ofdm system PAPR process:

Be used for companding transform method of the present invention at ofdm system, by carrying out:

The first step is with calculating the average amplitude V of ofdm signal in time domain;

With the time domain sample sequence { x of conventional method to ofdm communication system _nAsk average after the delivery value, can obtain the average amplitude V of time domain.

Second step, the tanh companding functional expression in the structure ofdm system;

Replace traditional mu-law companding function with hyperbolic tangent function, make the data of original signal be within certain scope in the value that obtains behind the companding.

1. the hyperbolic tangent function formula is:

$\tanh \left(x\right)=\frac{e^x-e^{-x}}{e^x+e^{-x}}---\left(5\right)$

2. to the expansion of (5) formula, definition tanh companding functional expression is:

$s_n=\frac{\mathrm{\&alpha;}\&times;x_n\&times;V}{\left|x_n\right|}\tanh \left(\frac{k\&times;\left|x_n\right|}{V}\right)---\left(6\right)$

Wherein, x _nN symbol representing original OFDM symbol sebolic addressing, V represent to calculate the average amplitude of ofdm signal in time domain, and k is the companding coefficient, and α is an amplitude modulation coefficient; This companding coefficient k is used to control the degree to the signal companding, and it is constant that this amplitude modulation coefficient α is used to keep signal average power before and after companding transform.

From (6) formula as can be seen | s _n| less than α * V, and because tanh companding function is asymptotic hyperbola, so it all is better than traditional companding transform to the compression effectiveness of peak signal with to the expansion effect of small-signal.

In the 3rd step,, determine the value of companding coefficient k and amplitude modulation coefficient α according to the requirement of ofdm system linear amplification scope;

For the companding coefficient k is the range of linearity according to power amplifier, makes maximum acceptable signal peak power P in advance _Max, require the signal power behind the companding to be less than or equal to P _Max, promptly k is used for the PAPR of control signal.After k was selected, the value of α was in order to keep before and after the companding transform average power of OFDM symbol constant.And the average power of inhibit signal can improve the efficient of linear transmitter amplifier, can avoid the expansion of Gaussian noise AWGN at receiving terminal simultaneously, thereby increases the signal to noise ratio snr of receiving end signal.Here the average power of inhibit signal must satisfy following formula:

E(x _n ²)＝E(s _n ²)(7)

E (s wherein _n ²) power of the signal of expression behind the companding, its formula is as follows:

$E\left(s_n^{\&prime;2}\right)={\&Integral;}_{-\&infin;}^{\&infin;}{\left[\frac{\mathrm{\&alpha;}\&times;x_n\&times;V}{\left|x_n\right|}\tanh \left(\frac{k\&times;\left|x_n\right|}{V}\right)\right]}^2{f}_{s_n}\left(x_n\right){\mathrm{dx}}_n---\left(8\right)$

F wherein _Sn(x _n) be the probability density function of original signal, and the real part of original signal and imaginary part Gaussian distributed.

According to (7) formula and the restriction of (8) formula ground, when k was chosen, α also can be determined simultaneously.Such as in the ofdm system of 1024 subcarriers when k is chosen as 0.4, α is approximately equal to 2.733.

In the 4th step,, ofdm signal is carried out companding transform with tanh companding function formula (6) according to average amplitude V that sends signal and the value of α, k;

The 5th step, the signal behind the companding carried out and go here and there change and filtering after send to channel;

The 6th step, the ofdm signal R ' that channel is received _n/ calculate, draw the average amplitude V of received signal;

In the 7th step, carry out amplitude limit to received signal;

Because in theory | R ' _n| less than α * V ', it is 0.99 * α * V ' that the present invention establishes a thresholding for received signal, and amplitude is carried out amplitude limit greater than the signal of α * V ', and the amplitude of guaranteeing the ofdm signal that receives is less than α * V ', thereby reduces Gaussian noise influence to received signal.

The 8th goes on foot, and draws the inverse transformation formula of corresponding transmitting terminal companding function;

To the tanh companding function function s that inverts _n, the inverse transformation formula that can draw received signal is:

$R_n=0.5\&times;\frac{V^{\&prime;}\&times;{R_n}^{\&prime;}}{k\&times;\left|{R_n}^{\&prime;}\right|}\&times;\ln \left\{\frac{\mathrm{\&alpha;}\&times;V^{\&prime;}+\left|{R_n}^{\&prime;}\right|}{\mathrm{\&alpha;}\&times;V^{\&prime;}-\left|{R_n}^{\&prime;}\right|}\right\}---\left(9\right)$

R ' wherein _nThe expression received signal, the average amplitude of V ' expression received signal.

The 9th step, according to the value of average amplitude V ' He α, the k of received signal, ofdm signal is carried out the companding inverse transformation with the inverse transformation formula (9) of tanh companding transform, restore primary signal.

With reference to Fig. 3, the applied ofdm communication system of the present invention comprises and transmitting and receiving.Wherein radiating portion comprises: modulator 3, deserializer 5, IFFT unit 7, average amplitude computing unit 9, companding transform unit 13, parallel-to-serial converter 11, digital to analog converter 16 and low pass filter 18.This companding transform unit 13 is used for ofdm signal is carried out companding transform with tanh companding function (6) formula; Other unit of this radiating portion are conventional the connection.Receiving unit comprises: low pass filter 22, analog to digital converter 24, deserializer 26, companding inverse transformation block 30, FFT unit 32, average amplitude computing unit 41, parallel-to-serial converter 34 and demodulator 36.This companding inverse transformation block 30 is used for ofdm signal is carried out the companding inverse transformation with tanh companding inverse transform function (9) formula; Be connected with comparison amplitude limit unit 28 between this deserializer 26 and the companding inverse transformation block 30, the ofdm signal that is used for receiving passes through thresholding, amplitude is carried out amplitude limiting processing greater than the signal of α * V ', and the amplitude of guaranteeing the ofdm signal that receives is less than α * V '; Other unit of receiving unit are conventional the connection.

The course of work of whole OFDM system is as follows:

One, the transmitting terminal of ofdm communication system

The random data symbols streams 2 that information source 1 produces is as ofdm signal, and through baseband modulator 3 modulation, modulation can be adopted QAM or QPSK, ofdm signal is mapped as the signal 4 of plural form; Through deserializer 5 ofdm modulation signal is converted into parallel input signal 6 then, promptly is assigned in the relatively low N of the transmission rate channel and transmits; Through IFFT unit 7 conversion, change frequency-region signal into time- domain signal 8 and 12, this signal 12 calculates average amplitude 14 by average amplitude computing unit 13, and average amplitude 14 and time-domain signal 8 are sent into companding transform unit 9; The signal 10 that the companding transform unit carries out after companding transform obtains handling according to companding coefficient and 14 pairs of time-domain signals of average amplitude 8; Signal 10 is sent into channel through after the processing of serial-parallel converter 11, digital to analog converter 16 and low pass filter 18.

Two, the receiving terminal of ofdm communication system

The signal 21 of channel output obtains signal 25 after low pass filter 22 and analog to digital converter 24 processing, signal 25 is handled through serial-parallel converter 26 and is obtained signal 39 and 27, wherein 27 send into comparison amplitude limit unit 28, relatively the amplitude limit unit carries out amplitude limit to amplitude greater than the signal of α * V ', and the amplitude of guaranteeing the ofdm signal that receives is less than α * V '; Signal 39 is sent into average amplitude computing unit 40 and is calculated average amplitude, and this mean value is divided into two- way 41 and 42, sends into comparison amplitude limit unit 28 and companding inverse transformation block 30 respectively; Relatively the signal 29 of amplitude limit unit 28 outputs is handled through companding inverse transformation block 30 and is obtained signal 31, the processing of signal 31 through FFT unit 32 obtains frequency-region signal 33, signal 33 place 38 of delivering letters after the processing of parallel serial conversion unit 34 and demodulator 36 recovers original signal.

Effect of the present invention can further specify by following emulation.

Emulation 1

This ofdm system simulated conditions is as follows:

Ofdm signal is produced by random signal source, the 16QAM modulation, and sub-carrier number is 1024, adopts 4096 IFFT, i.e. 4 times of over-samplings.Value according to the average amplitude V under this condition and companding coefficient k, amplitude modulation coefficient α is carried out companding transform to ofdm signal with tanh companding formula, and the curve of this companding and traditional companding curve are compared, as shown in Figure 4.From Fig. 4 as seen, when the original amplitude of signal was big, the amplitude behind the companding of the present invention was less, so it can more effectively be limited in ofdm signal within certain scope, thereby reduced PAPR better, had improved the utilance of linear amplifier; Effective expansion has also reduced the range of linearity requirement of system to the linear amplifier of signal to effective amplification of small-signal with to large-signal simultaneously, has also improved the utilance of linear amplifier.

Emulation 2

In order to illustrate that the companding transform that the present invention is based on tanh companding function has the effect of better reduction ofdm system signal PAPR than traditional companding scheme, Fig. 5 has provided the comparison diagram of these two kinds of scheme CCDF CCDF simulation curves.This CCDF promptly calculates the probability that peak-to-average power ratio surpasses a certain threshold value, and its mathematic(al) representation is:

Pr{PAPR＞PAPR0}＝1-(1-e ^-PAPR0) ^N

PAPR0＞0

Wherein, PAPR0 represents the threshold value of peak-to-average power ratio, and PAPR represents the equal power in actual peak of ofdm signal.

As can be seen from Figure 5, along with the increase of the value of k, the present invention reduces the effect of PAPR and becomes better and better; Other two kinds of companding methods are with respect to original ofdm signal, and its PAPR has bigger improvement; And companding method of the present invention gets 0.3,0.4 and at 0.45 o'clock at k, get 0.3,0.8 with traditional companding transform μ and compare with 1.0, and when the CCDF of two kinds of methods curve initial drop point is identical, be 10 at CCDF ^-4The position, companding transform method of the present invention has the PAPR about 0.5dB to improve, visible companding method of the present invention is to suppressing the better effects if of PAPR.

Emulation 3

This simulated conditions is as follows:

Ofdm signal is produced by random signal source, the 16QAM modulation, and awgn channel, sub-carrier number are 1024, adopt 4096 IFFT, i.e. 4 times of over-samplings; Companding method of the present invention gets 0.3,0.4 and 0.45 at k, and traditional companding transform μ gets 0.3,0.8 and 1.0.

Ber curve such as Fig. 6 with companding method of the present invention and the emulation of traditional companding transform method.From Fig. 6 as seen, under identical SNR, BER is the smaller the better; Though two kinds of companding methods have all caused bit error rate performance to a certain degree to descend, companding method of the present invention has slightly improvement than traditional companding method on bit error rate performance.

Claims (4)

1. one kind is reduced the method for ofdm system PAPR at transmitting terminal, comprises following process:

(1) to the time domain sample sequence { x of ofdm communication system _nCalculate, draw the average amplitude V that sends signal;

(2), determine the value of companding coefficient k and amplitude modulation coefficient α according to the requirement of ofdm system;

(3) according to the value of average amplitude V and companding coefficient k, amplitude modulation coefficient α ofdm signal is carried out companding transform with tanh companding formula, this tanh companding functional expression is;

$s_n=\frac{\mathrm{\&alpha;}\&times;x_n\&times;V}{\left|x_n\right|}\tanh \left(\frac{k\&times;\left|x_n\right|}{V}\right)$

Wherein, the companding coefficient k is used to control the degree to the signal companding, and it is constant that amplitude modulation coefficient α is used to keep signal average power before and after companding transform;

(4) signal behind the companding is carried out and go here and there the conversion and filtering after send to channel.

, a kind ofly reduce the method for ofdm system PAPR at receiving terminal, comprise following process:

(1) ofdm signal that receives is calculated, draw the average amplitude V ' of received signal;

(2) ofdm signal that receives is carried out amplitude limit by setting thresholding, promptly amplitude is carried out amplitude limit greater than the signal of α * V ', the amplitude of guaranteeing the ofdm signal that receives is less than α * V ';

(3) according to the value of the average amplitude V ' of received signal and amplitude modulation coefficient α, companding coefficient k to ofdm signal, carry out the companding inverse transformation with tanh companding inverse transformation formula, this tanh companding inverse transform function formula is;

$R_n=0.5\&times;\frac{V^{\&prime;}\&times;{R_n}^{\&prime;}}{k\&times;\left|{R_n}^{\&prime;}\right|}\&times;\ln \left\{\frac{\mathrm{\&alpha;}{\&times;V}^{\&prime;}+\left|{R_n}^{\&prime;}\right|}{\mathrm{\&alpha;}\&times;V^{\&prime;}-\left|{R_n}^{\&prime;}\right|}\right\}$

R wherein _n' expression received signal,

(4) restore primary signal.

, according to claim 1,2 described methods, it is characterized in that the companding coefficient k is the range of linearity according to power amplifier, make maximum acceptable signal peak power P in advance _Max, require the signal power behind the companding to be less than or equal to P _Max

4. method according to claim 2, the value that it is characterized in that setting thresholding is α * V ' of 0.99 times, i.e. 0.99 * α * V '.

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