CN101753500A - Method and system for efficiently restraining large peak-to-average power ratio (PAPR) of OFDM system based on companding - Google Patents

Abstract

The invention discloses a method and a system for efficiently restraining large PAPR of OFDM system based on companding, wherein the PAPR is debased and the error rate is reduced. The invention is characterized in that the invention provides a companding method for reducing the probability of generating large PAPR based on hyperbolic asymptote companding function by analyzing the fundamental reasons to the PAPR problem in the OFDM system and the factors of generating low probability of large PAPR, starting compressing time-domain large signal, enlarging time-domain dwarf signal and limiting super-large signal in combination with the advantages of amplitude limiting and companding. The invention is applied to OFDM system.

Description

A kind of method and system of the big peak-to-average power ratio of effective inhibition ofdm system based on companding

Technical field

The present invention relates to the peak-to-average power ratio problem in the orthogonal frequency division multiplex OFDM communication system, specifically relate to the non-linear companding method and the system of the big peak-to-average power ratio of a kind of effective inhibition ofdm system.

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:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k\exp \left(\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2008102072460E0000012.png,H2008102072460E0000032.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}}{N}\right)$ n＝0，1，......，N-1(1)

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:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10{\mathrm{<figure-callout\; id="10"\; label="log"\; filenames="H2008102072460E0000032.png,H2008102072460E0000041.png"\; state="\{\{state\}\}">log</figure-callout>}}_{10}\frac{\underset{n}{\max \left\{{\left|x_n\right|}^2\right\}}}{E\left\{{\left|x_n\right|}^2\right\}}---\left(2\right)$

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 suppressing the generation of big PAPR, is improving the OFDM symbol distribution and improve and be still waiting further improvement aspect the error rate.

Summary of the invention

The objective of the invention is to address the above problem, a kind of method of the big peak-to-average power ratio of effective inhibition ofdm system based on companding is provided, reduce peak-to-average power ratio PAPR and improve the error rate.

Another object of the present invention is to provide a kind of system of the big peak-to-average power ratio of effective inhibition ofdm system based on companding, reduced peak-to-average power ratio PAPR and improve the error rate.

Technical scheme of the present invention is: the present invention has disclosed a kind of method of the big peak-to-average power ratio of effective inhibition ofdm system based on companding, comprising:

Process at transmitting terminal companding transform ofdm signal further comprises:

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

(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 S shape companding function formula, this tanh S shape companding function formula is:

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

Wherein f () represents hyperbolic asymptote function, and 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, sign (x _n) represent x _nGet symbol;

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

The process of the ofdm signal behind receiving terminal reduction companding:

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

(6) 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 ';

(7) with the value of amplitude modulation coefficient α, companding coefficient k ofdm signal is carried out the companding inverse transformation with tanh S shape companding inverse transform function formula according to average amplitude V ', wherein tanh S shape companding inverse transform function formula is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol;

(8) restore primary signal.

The method of the above-mentioned big peak-to-average power ratio of effective inhibition ofdm system based on companding, wherein, three conditions that this companding transform in the step (3) satisfies are:

| f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

When | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

After α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

The present invention has also disclosed a kind of system of the big peak-to-average power ratio of effective inhibition ofdm system based on companding, comprising:

Emitter:

Modulator is modulated ofdm signal;

The first serial to parallel conversion unit transmits after ofdm modulation signal is converted to parallel signal;

The IFFT unit changes frequency-region signal into time-domain signal;

First calculates the average amplitude unit, and this time-domain signal of exporting by this IFFT unit calculates average amplitude V;

The companding transform unit carries out this time-domain signal is carried out companding transform with tanh S shape companding transform function formula according to companding coefficient k and this average amplitude V, amplitude modulation coefficient α;

The first parallel serial conversion unit is a serial signal with the conversion of signals behind the companding transform;

Digital to analog converter converts analog signal to this serial signal;

First low pass filter carries out being emitted to channel after the low-pass filtering to this analog signal;

Receiving system:

Second low pass filter receives the signal that comes to channel and carries out low-pass filtering;

Analog to digital converter becomes digital signal with analog signal conversion;

The second serial to parallel conversion unit transmits after this digital signal is converted to parallel signal;

Second calculates the average amplitude unit, the ofdm signal that receives is calculated the average amplitude V ' of received signal;

Amplitude limit unit relatively carries out amplitude limit to amplitude greater than the signal of α * V ', and the amplitude of guaranteeing to receive ofdm signal is less than α * V ', and wherein α is an amplitude modulation coefficient;

The companding inverse transformation block is carried out companding inverse transformation to ofdm signal with tanh S shape companding inverse transform function formula with the value of amplitude modulation coefficient α, companding coefficient k according to average amplitude V ';

The FFT unit changes time-domain signal into frequency-region signal;

The second parallel serial conversion unit is a serial signal with the conversion of signals after the companding inverse transformation;

Demodulator carries out demodulation process to signal.

The system of the above-mentioned big peak-to-average power ratio of effective inhibition ofdm system based on companding, wherein, this tanh S shape companding function formula of this companding transform unit institute foundation is:

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

Wherein f () represents hyperbolic asymptote function, and 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, sign (x _n) represent x _nGet symbol.

The system of the above-mentioned big peak-to-average power ratio of effective inhibition ofdm system based on companding, wherein, three conditions that this companding transform in this companding transform unit satisfies are:

| f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

When | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

After α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

The system of the above-mentioned big peak-to-average power ratio of effective inhibition ofdm system based on companding, wherein, the tanh S shape companding inverse transform function formula of this companding inverse transformation block institute foundation is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol.

The present invention contrasts prior art following beneficial effect: the present invention produces the little factor of probability by basic reason and the big PAPR that analyzes the generation of ofdm system PAPR problem, from compression time domain large-signal, expansion time domain small-signal and amplitude limit super large signal are started with, advantage in conjunction with amplitude limit and companding, proposed the big PAPR of a kind of reduction and produced the companding method of probability, thereby effectively reduced PAPR and improve the error rate based on hyperbolic asymptote companding function.Compared with prior art, the present invention has following advantage at least:

1, because 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 hyperbolic asymptote 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 hyperbolic asymptote companding function of the present invention has adopted amplitude modulation coefficient and two coefficients of companding coefficient, 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 preferred embodiment of the method for the big peak-to-average power ratio of effective inhibition ofdm system based on companding of the present invention.

Fig. 3 is the block diagram of preferred embodiment of the system of the big peak-to-average power ratio of effective inhibition ofdm system based on companding 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

The invention will be further described below in conjunction with drawings and Examples.

Embodiment based on the method for the big peak-to-average power ratio of effective inhibition ofdm system of companding

Fig. 3 shows the flow process of embodiment of the method for the big peak-to-average power ratio of effective inhibition ofdm system based on companding of the present invention.Seeing also Fig. 3, is the detailed description of each step in the method below.The method of present embodiment is included in the process (process of step S100～S103) and the ofdm signal behind receiving terminal reduction companding (the step S104～S108) of transmitting terminal companding transform ofdm signal.

Step S100: to the time domain sample sequence { x of ofdm system _nCalculate 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 it average after the delivery value, the average amplitude V of time domain can be obtained.

Step S101:, determine the value of companding coefficient k and amplitude modulation coefficient α according to the requirement of ofdm system.

For the companding coefficient k is the range of linearity according to power amplifier, makes maximum acceptable signal peak power P in advance _Gate, require the signal power behind the companding to be less than or equal to P _Gate, 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.Because usually to be in the probability of big peak power very low for ofdm communication system, general ofdm signal power surpasses three times of average power, promptly when PAPR be that the probability of 10dB is about 0.1%; Surpass its four times of average powers, promptly when PAPR be that the probability of 12dB is about 0.01%.Certainly because the probability that especially big signal occurs is minimum, and it is very little to improve income based on the error rate of this point, the back has also illustrated this point based on the emulation of MATLAB.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)

(5)

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

$E\left({s_n}^2\right)={\&Integral;}_{-\&infin;}^{\&infin;}{[\mathrm{\&alpha;}\&times;V\&times;\mathrm{sign}\left(x_n\right)\&times;\tan \mathrm{sig}\left(\frac{k\&times;\left|x_n\right|}{V}\right)]}^2{f}_{s_n}\left(x_n\right)d{x}_n---\left(6\right)$

Wherein

Be the probability density function of original signal, and the real part of original signal and imaginary part Gaussian distributed.

According to the restriction of (5) formula and (6) formula, when k was chosen, α also can be determined simultaneously.Be chosen as 0.3,0.4 such as work as k in the ofdm system of 1024 subcarriers, 0.45 o'clock, α was approximately equal to 3.5,2.7,2.5 respectively.

Step S102:, ofdm signal is carried out companding transform with tanh S shape companding function formula according to the value of average amplitude V and companding coefficient k, amplitude modulation coefficient α.

Of the present invention one big characteristics are exactly to replace traditional mu-law companding function with tanh S shape companding function, make the data of original signal be within certain scope in the value that obtains behind the companding.

Tanh sigmoid function formula is:

$\tan \mathrm{sig}\left(x\right)=\frac{2}{1+e^{-2x}}-1---\left(7\right)$

To the expansion of (7) formula, definition tanh S shape companding function formula is:

$s_n=\mathrm{\&alpha;}\&times;V\&times;\mathrm{sign}\left(x_n\right)\&times;\tan \mathrm{sig}\left(\frac{k\&times;\left|x_n\right|}{V}\right)---\left(8\right)$

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, | x _n| expression is to x _nTake absolute value; 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 (8) formula as can be seen | s _n| less than α * V, and because tanh S shape 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.

Companding transform in this step need satisfy three conditions:

(1) | f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

(2) as | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

(3) after α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

Step S103: the signal behind the companding transform carried out and go here and there sending to channel after conversion and the filtering.

Step S104: receive data.

Step S105: the average amplitude V ' that the ofdm signal that receives is calculated received signal.

Step S106: the ofdm signal that receives is carried out amplitude limit by setting thresholding.

Because in theory | R _n' | less than α * V ', it is 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.

Step S107: with the value of amplitude modulation coefficient α, companding coefficient k ofdm signal is carried out the companding inverse transformation with tanh S shape companding inverse transform function formula according to average amplitude V '.

Wherein tanh S shape companding inverse transform function formula is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol.

Above-mentioned formula also can be expressed as:

$R_n=0.5\&times;\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;\frac{V^{\&prime;}}{k}\&times;\ln \{1+\frac{2\&times;\left|{R_n}^{\&prime;}\right|}{\mathrm{\&alpha;}\&times;V^{\&prime;}-\left|{R_n}^{\&prime;}\right|}\}---\left(9\right)$

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

Step S108: restore primary signal.

Embodiment based on the system of the big peak-to-average power ratio of effective inhibition ofdm system of companding

Fig. 3 shows the principle of the embodiment of the applied ofdm communication system of the present invention.See also Fig. 3, the ofdm communication system of present embodiment comprises emitter and receiving system.Wherein emitter comprises modulator 3, serial to parallel conversion unit 5, IFFT unit, calculates average amplitude unit 13, IFFT unit 7, companding transform unit 9, parallel serial conversion unit 11, digital to analog converter 16 and low pass filter 18.Companding transform unit 9 is used for ofdm signal is carried out companding transform with tanh S shape companding function formula (8), and other unit of emitter are conventional the connection.Receiving system comprises low pass filter 22, analog to digital converter 24, serial to parallel conversion unit 26, calculates average amplitude unit 40, compares amplitude limit unit 28, companding inverse transformation block 30, FFT unit 32, parallel serial conversion unit 34 and demodulator 36.Companding inverse transformation block 30 is used for ofdm signal is carried out the companding inverse transformation with tanh S shape inverse transform function formula (9).Between deserializer 26 and companding inverse transformation block 30, connect relatively amplitude limit unit 28, 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 ', the amplitude of guaranteeing the ofdm signal that receives is less than α * V ', and other unit of receiving system are conventional the connection.

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

Emitter for ofdm system, the random data symbols streams 2 that information source 1 produces is as ofdm signal, through modulator 3 (for example being baseband modulator) modulation, modulation can be adopted QAM or QPSK, ofdm signal is mapped as the signal 4 of plural form, through serial to parallel conversion unit 5 ofdm modulation signal is converted into parallel input signal 6 then, 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, signal 12 calculates average amplitude 14 by calculating average amplitude unit 13, and average amplitude 14 and time-domain signal 8 are sent into companding transform unit 9.

Calculate the time domain sample sequence { x of average amplitude unit 13 usefulness conventional methods to ofdm communication system _nAsk it average after the delivery value, the average amplitude V of time domain can be obtained.Companding transform unit 9 carries out this time-domain signal is carried out companding transform with tanh S shape companding transform function formula according to companding coefficient k and this average amplitude V, amplitude modulation coefficient α, the signal 10 behind the output companding transform.

This tanh S shape companding function formula of 9 foundations in companding transform unit is:

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

Wherein f () represents hyperbolic asymptote function, and 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, sign (x _n) represent x _nGet symbol.

Three conditions that companding transform in the companding transform unit 9 satisfies are:

| f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

When | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

After α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

Signal 10 behind the companding transform is converted to serial signal 15 through parallel serial conversion unit 11 earlier, is converted to analog signal 17 through digital to analog converter 16 again, after low pass filter 18 exports channel 20 to after being processed into signal 19.

Receiving system for ofdm system, the signal 21 of channel 20 outputs is processed into signal 23 through low pass filter 22, convert digital signal 25 to through analog to digital converter 24 again, be converted to parallel signal through serial to parallel conversion unit 26 then, obtain signal 27 and 39, wherein signal 27 is sent into comparison amplitude limit unit 28, and signal 39 is sent into and calculated average amplitude unit 40.Calculate the average amplitude V ' that the 40 pairs of ofdm signals that receive in average amplitude unit calculate received signal, be divided into two paths of signals output, one road signal 41 exports comparison amplitude limit unit 28 to, and another road signal 42 exports companding inverse transformation block 30 to.

Relatively the 28 pairs of amplitudes in amplitude limit unit are carried out amplitude limit greater than the signal of α * V ', and the amplitude of guaranteeing to receive ofdm signal is less than α * V ', and wherein α is an amplitude modulation coefficient.

Relatively the signal 29 of amplitude limit unit 28 outputs is sent into companding inverse transformation block 30, and companding inverse transformation block 30 is carried out companding inverse transformation to ofdm signal with tanh S shape companding inverse transform function formula with the value of amplitude modulation coefficient α, companding coefficient k according to average amplitude V '.Wherein tanh S shape companding inverse transform function formula is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol.

Above-mentioned formula also can be expressed as:

$R_n=0.5\&times;\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;\frac{V^{\&prime;}}{k}\&times;\ln \{1+\frac{2\&times;\left|{R_n}^{\&prime;}\right|}{\mathrm{\&alpha;}\&times;V^{\&prime;}-\left|{R_n}^{\&prime;}\right|}\}---\left(9\right)$

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

Companding inverse transformation block 30 is handled the processing of signal 31 through FFT unit 32 that obtains and is obtained frequency-region signal 33, is converted to serial signal 35 through parallel serial conversion unit 34, exports the stay of two nights 38 again after demodulator 36 is demodulated to signal 37 to, 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 S shape 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.

Imitative straight 2

In order to illustrate that the companding transform that the present invention is based on tanh S shape companding function has the effect of better reduction ofdm system signal PAPR than traditional companding scheme, Fig. 5 has provided these two kinds of scheme CCDF CCDF (comparison diagram of simulation curve of CCDF=Pr{PAPR＞PAPR0}).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 0.35,0.65 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 0.5～1.5dB to improve, visible companding method of the present invention is to suppressing the better effects if of big 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 0.35,0.65 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 slight improvements than traditional companding method on bit error rate performance.

The foregoing description provides to those of ordinary skills and realizes or use of the present invention; those of ordinary skills can be under the situation that does not break away from invention thought of the present invention; the foregoing description is made various modifications or variation; thereby protection scope of the present invention do not limit by the foregoing description, and should be the maximum magnitude that meets the inventive features that claims mention.

Claims (6)

1. method based on the big peak-to-average power ratio of effective inhibition ofdm system of companding comprises:

Process at transmitting terminal companding transform ofdm signal further comprises:

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

(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 S shape companding function formula, this tanh S shape companding function formula is:

$S_n=\mathrm{\&alpha;}\&times;V\&times;\mathrm{sign}\left(x_n\right)\&times;f\left(\frac{k\&times;\left|x_n\right|}{V}\right)$

Wherein f () represents hyperbolic asymptote function, and 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, sign (x _n) represent x _nGet symbol;

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

The process of the ofdm signal behind receiving terminal reduction companding:

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

(6) 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 ';

(7) with the value of amplitude modulation coefficient α, companding coefficient k ofdm signal is carried out the companding inverse transformation with tanh S shape companding inverse transform function formula according to average amplitude V ', wherein tanh S shape companding inverse transform function formula is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol;

(8) restore primary signal.

2. the method for the big peak-to-average power ratio of effective inhibition ofdm system based on companding according to claim 1 is characterized in that, three conditions that this companding transform in the step (3) satisfies are:

| f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

When | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

After α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

3. system based on the big peak-to-average power ratio of effective inhibition ofdm system of companding comprises:

Emitter:

Modulator is modulated ofdm signal;

The first serial to parallel conversion unit transmits after ofdm modulation signal is converted to parallel signal;

The IFFT unit changes frequency-region signal into time-domain signal;

First calculates the average amplitude unit, and this time-domain signal of exporting by this IFFT unit calculates average amplitude V;

The companding transform unit carries out this time-domain signal is carried out companding transform with tanh S shape companding transform function formula according to companding coefficient k and this average amplitude V, amplitude modulation coefficient α;

The first parallel serial conversion unit is a serial signal with the conversion of signals behind the companding transform;

Digital to analog converter converts analog signal to this serial signal;

First low pass filter carries out being emitted to channel after the low-pass filtering to this analog signal;

Receiving system:

Second low pass filter receives the signal that comes to channel and carries out low-pass filtering;

Analog to digital converter becomes digital signal with analog signal conversion;

The second serial to parallel conversion unit transmits after this digital signal is converted to parallel signal;

Second calculates the average amplitude unit, the ofdm signal that receives is calculated the average amplitude V ' of received signal;

Amplitude limit unit relatively carries out amplitude limit to amplitude greater than the signal of α * V ', and the amplitude of guaranteeing to receive ofdm signal is less than α * V ', and wherein α is an amplitude modulation coefficient;

The companding inverse transformation block is carried out companding inverse transformation to ofdm signal with tanh S shape companding inverse transform function formula with the value of amplitude modulation coefficient α, companding coefficient k according to average amplitude V ';

The FFT unit changes time-domain signal into frequency-region signal;

The second parallel serial conversion unit is a serial signal with the conversion of signals after the companding inverse transformation;

Demodulator carries out demodulation process to signal.

4. the system of the big peak-to-average power ratio of effective inhibition ofdm system based on companding according to claim 3 is characterized in that this tanh S shape companding function formula of this companding transform unit institute foundation is:

$S_n=\mathrm{\&alpha;}\&times;V\&times;\mathrm{sign}\left(x_n\right)\&times;f\left(\frac{k\&times;\left|x_n\right|}{V}\right)$

Wherein f () represents hyperbolic asymptote function, and 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, sign (x _n) represent x _nGet symbol.

5. the system of the big peak-to-average power ratio of effective ofdm system based on companding according to claim 4 is characterized in that, three conditions that this companding transform in this companding transform unit satisfies are:

| f (∞) |≤P _Gate, f (x)=-f (x), wherein is the threshold value of determining according to real system;

When | x _n| during≤m, | s _n| 〉=| x _n|, otherwise, | s _n|≤| x _n|, wherein m represents the breakover point of companding transform;

After α and k are selected, satisfy E{|x _n| ²≈ E{|s _n| ², can guarantee conversion front and back average power about equally.

6. the system of the big peak-to-average power ratio of effective ofdm system based on companding according to claim 5 is characterized in that the tanh S shape companding inverse transform function formula of this companding inverse transformation block institute foundation is:

$R_n=\mathrm{sign}\left(R_n^{\&prime;}\right)\&times;V^{\&prime;}/k\&times;f^{-1}\left(\frac{R^{\&prime;}}{\mathrm{\&alpha;}\&times;V^{\&prime;}}\right)$

F wherein ^-1The inverse function of () expression hyperbolic asymptote function, R _n' expression received signal, sign (R _n') represent R _n' get symbol.

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