CN101035105B - Method and device for reserving the sub-carrier to reduce the peak average power ratio of the OFDM system based on IFFT/FFT - Google Patents

Abstract

The invention discloses that based on open IFFT / FFT lower reserved subcarrier OFDM system PAPR methods and devices, and the system is using IFFT / FFT transform to a peak frequency domain Consumers sequence in the transmitter to reduce OFDM system ratio of power PAPR, the method described in steps including data distribution , IFFT transformation, realizing OFDM modulation, gained time-domain signal, judgment threshold and whether the number of iterations is to achieve settings, limited Consumers peak processing, extracted through FFT frequency domain reduce-peak sequence. The installations include the transmitter and receiver, the transmitter unit increased data distribution, data option modules, judgment unit, a unit reduce-peak sequence, sequence reduce-peak insert modules; Receiver increased information extraction unit. This invention in a process of elimination-series will not lead to the increase in bit error rate, the effect of significantly reducing the PAPR, the device is simple, running FFT / IFFT the iteration times is less.

Description

Reduce the method and apparatus of ofdm system peak-to-average power ratio based on the preserved sub-carrier of IFFT/FFT

Technical field

The invention belongs to communication technical field, relate to the reduction of the peak-to-average power ratio PAPR (Peak-to-Average Power Ratio) in orthogonal frequency division multiplex OFDM (the Orthogonal Frequency DivisionMultiplexing) communication system, specifically a kind of preserved sub-carrier TR based on IFFT/FFT (Tone Reservation) effectively reduces method and the device of ofdm system peak-to-average power ratio PAPR.

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 ADSL (Asymmetric Digital Subscriber Line) (ADSL), digital audio broadcasting (DAB) and fields such as digital television broadcasting (DVB), IEEE 802.11, IEEE 802.16 and power line broadband data communication 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.

Time domain sample sequence { the x of the OFDM of power normalization _nAs follows:

$x_n=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k\exp \left(\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H07117625920070425E000031.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;kn}}{N}\right),n=\mathrm{0,1},......,N-1---\left(1\right)$

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

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 (Peak Power), can bring bigger peak-to-average power ratio PAPR thus.Peak-to-average force ratio can be defined as:

$\mathrm{PAPR}\left(\mathrm{dB}\right)=10{\mathrm{<figure-callout\; id="10"\; label="log"\; filenames="H07117625920070425E000031.png,H07117625920070425E000051.png"\; state="\{\{state\}\}">log</figure-callout>}}_{10}\frac{\underset{n}{\max \left\{{\left|x_n\right|}^2\right\}}}{E\left\{{\left|x_n\right|}^2\right\}}---\left(2\right)$

Big peak-to-average power ratio PAPR has proposed very high requirement to the linearity of amplifier in the transmitter, the signal that this variation is bigger in ofdm system passes through non-linear components, when for example entering the amplifier nonlinearity zone, signal can produce nonlinear distortion, produce 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 their accuracy.For avoiding 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.For solving signal non-linear distortion problem in the ofdm communication system, the method that proposes mainly contains at present: signal predistortion technology comprises amplitude limit (Clipping), companding transform (Companding Transform) and preserved sub-carrier (Tone Reservation) 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 (Clipping) method that belongs to signal predistortion technology is the most a kind of method of easy realization.Its basic principle is that OFDM time-domain sampling signal and rectangular window function are multiplied each other, if the amplitude of OFDM time-domain signal less than threshold value, then the amplitude of this rectangular window function is 1; If signal amplitude is greater than threshold value, then the amplitude of this rectangular window function is less than 1.

Preserved sub-carrier Tone Reservation (TR) method that belongs to signal predistortion technology is the method for a kind of undistorted effective reduction ofdm system PAPR, its basic principle is that transmitting terminal keeps the special subcarrier (Tones) of a part, be used to produce the peak-to-peak signal that disappears that suppresses PAPR, receiver end ignores directly then that these are retained is used for suppressing data on the subcarrier of PAPR, and the useful signal that need to recover from other subcarrier that is used for transmit information data normally gets final product.

Particularly, be on L the subcarrier of reserving, to arrange suitable data, make data C on this L preserved sub-carrier _k(k=i ₁, i ₂..., i _Li ₁, i ₂..., i _LIndex for preserved sub-carrier) Dui Ying time-domain signal c (n) can suppress the peak value of original OFDM symbol just, be the poor of the amplitude of this peak point signal and threshold value just promptly also in the amplitude of the c of the peak value place of former OFDM symbol (n), then just in time the phase place with this peak point signal is opposite for phase place, and its principle as shown in Figure 1.As seen the TR scheme can not brought band interference without transmitted sideband information yet, and the receiver simplicity of design, does not need particular processing.

Though the Clipping method is simple, can bring relevant problem for ofdm system.At first, the OFDM symbol amplitude is distorted, can cause system and self disturb, thereby cause the error rate BER performance of system to reduce.Secondly the nonlinear distortion of ofdm signal can cause the increase of out-of-band radiation performance number, and then also can cause the increase of error rate of system.

Traditional waveform TR algorithm that prestores generates the data sequence at a series of preserved sub-carriers place at random, after the IFFT conversion, stores as the time domain peak-to-peak signal that disappears.Peak-to-peak signal and the preserved sub-carrier place data of then these being disappeared are time-domain signal (obtaining through the IFFT conversion) addition respectively of the OFDM symbol of " 0 ", find that sequence that wherein can make composite signal have minimum PAPR value, be inserted into the preserved sub-carrier place, with information sequence, again after the IFFT conversion, as transmission signals.Therefore, traditional waveform TR algorithm that prestores can be thought state algorithm, can not find the suitable peak data that disappears at dynamic information sequence.

The content of invention

The object of the invention is to avoid the deficiency of above-mentioned prior art, by analyzing the basic reason that ofdm system PAPR problem produces, peak value from subdue the OFDM time-domain signal is started with, in conjunction with the advantage of Clipping and TR scheme, a kind of method and device of the TR scheme based on the IFFT/FFT transfer pair proposed.This scheme realizes easy, and only needs less iterations just can obtain good PAPR inhibition effect.

The main points of preserved sub-carrier TR method are to place suitable data on L preserved sub-carrier, make these data after the FFT conversion, obtain the suitable peak-to-peak signal that disappears.

A certain OFDM frequency domain information sequence X is in the TR algorithm:

$X=\left\{\begin{array}{cc}{X}_k,& k\&NotElement;\{i_1,i_2,...,i_L\}\\ 0,& k\&Element;\{i_1,i_2,...{,i}_L\}\end{array}\right.---\left(3\right)$

I wherein ₁, i ₂..., i _LCall number for preserved sub-carrier.X is carried out the IFFT conversion obtains time-domain signal x (n):

x(n)＝IFFT(X) (4)

According to a certain threshold value x (n) is carried out amplitude limit and disappear behind the peak, the signal x (n) behind the peak that obtains disappearing, the peak value part that then surpasses threshold value among the x (n) can be regarded time domain ideal peak eliminating signal c (n) as:

c(n)＝x(n)-x(n) (5)

In addition, to a certain frequency domain peak data sequence C that disappears:

$C=\left\{\begin{array}{cc}{C}_k,& k\&Element;\{i_1,i_2,...,i_L\}\\ 0,& k\&NotElement;\{i_1,i_2,...,i_L\}\end{array}\right.---\left(6\right)$

If C is after the IFFT conversion, it is similar to time domain ideal peak eliminating signal c (n) to obtain the time domain peak-to-peak signal c (n) that disappears, and then the signal x ' PAPR value (n) that obtains after c (n) disappears the peak of x (n) also can have substantial degradation.

x′(n)＝x(n)-c(n)＝IFFT(X)-IFFT(C)＝IFFT(X-C) (7)

C can be expressed as:

C＝FFT(c(n))＝FFT(x(n)-x′(n))＝FFT′(x(n))-FFT(x′(n)) (8)

By formula (3), (6) and (7) as can be known, the peak sequence C that disappears and information sequence X can not cause interference to the data in the information sequence, so the BER that this method causes are 0 after merging.

So the PAPR process of inhibition of TR is to select suitable c or corresponding C, make the following formula minimum:

$\mathrm{PAPR}\left(x^{\&prime;}\left(n\right)\right)=\frac{{\underset{n}{\max }|x\left(n\right)-c\left(n\right)|}^2}{E\left\{{\left|x\left(n\right)\right|}^2\right\}}---\left(9\right)$

Formula (9) be need to prove, PAPR definition herein is different from general PAPR definition slightly, difference be denominator be not to x ' (n)=x (n)-c (n) asks average power, but only x (n) is asked average power content, why doing like this is to cause PAPR to reduce for fear of the rising owing to x ' average power (n), and does not reach the purpose of real reduction peak signal.And new PAPR formula (also being formula (9)) just can guarantee to guarantee when PAPR reduces that the peak power of original relatively OFDM symbol has decline.

The present invention utilizes the IFFT/FFT transfer pair to seek the frequency domain peak sequence C that disappears at transmitting terminal _L, to reduce the PAPR of ofdm system transmission signals, its detailed process is as follows:

(1) data allocations, at N in the carrier wave, data " 0 " are placed in the position of L good according to the rules preserved sub-carrier on L subcarrier, the normal information data after the constellation mapping were carried out in the position placement of other N-L data subcarrier;

(2) carry out the IFFT conversion, realize the OFDM modulation, obtain x (n);

(3) if the PAPR of x (n) meets the demands or iterations has reached the maximum of setting, then x (n) is exported as final output signal; Otherwise, changeed for (4) step;

(4) according to the threshold value of setting, x (n) is carried out the amplitude limit peak that disappears, obtain disappear signal x (n) behind the peak of amplitude limit;

(5) disappear time-domain signal x (n) before the peak of amplitude limit deducts disappear time-domain signal x (n) behind the peak of amplitude limit, obtains time domain ideal peak eliminating signal c (n);

(6) c (n) is carried out N point FFT conversion and obtain frequency domain ideal peak eliminating sequence C;

(7) C is extracted L subcarrier data of corresponding positions of reservation and obtain sequence C _L

(8) to C _LThe amplitude of carrying out adjustment obtains C _L, make C _LCorresponding time domain consistent that amplitude and the amplitude of step (5) resulting ideal peak eliminating signal c (n) of peak-to-peak signal c (n) try one's best that disappear;

(9) with C _LMerge with the information data on N-L the data subcarrier; Changeing for (2) step handles.

The device of realizing said method of the present invention comprises transmitting terminal and receiving terminal, the characteristics of transmitting terminal be on the basis of traditional ofdm system, increased data allocations unit, data selection unit, judging unit, the peak sequence generation unit that disappears, the peak sequence that disappears insert the unit; The characteristics of receiving terminal are to have increased information extraction unit;

The data allocations unit of transmitting terminal: be used for placing data " 0 ", on remaining subcarrier, place and want information transmitted the L that reserves in advance preserved sub-carrier position;

The data selection unit of transmitting terminal: being used to select is that the peak-to-peak signal that still will disappear inserts the input of the output of unit as the IFFT unit with the input as the IFFT unit of the signal of data allocations unit output; When an OFDM symbol was for the first time processed, the data-signal that data selection unit selection data allocations unit transmits was as the input of IFFT unit; Otherwise the peak sequence of selecting to disappear is inserted the input of the data sequence of unit output as the IFFT unit;

The peak sequence of disappearing of transmitting terminal is inserted the unit: be used for the disappear data merging at peak data and information subcarrier place of preserved sub-carrier place;

The peak sequence generation unit that disappears of transmitting terminal: be used for the output signal of IFFT conversion is carried out amplitude limiting processing, make signal amplitude behind the amplitude limit less than the amplitude threshold value of setting; With signal before the amplitude limit and the signal subtraction behind the amplitude limit, extract the time domain ideal peak eliminating signal that peak value surpasses the amplitude threshold value, time domain ideal peak eliminating signal is transformed into frequency domain ideal peak eliminating sequence through the FFT conversion; Extract the data at preserved sub-carrier place in the frequency domain ideal peak eliminating sequence, the data at other subcarrier place are made as " 0 "; The peak data that disappears to the preserved sub-carrier place that extracts is amplified certain multiple;

The judging unit of transmitting terminal: the PAPR value that is used to calculate the time-domain signal that obtains through the IFFT conversion, the record iterations, described PAPR value and iterations are compared with the PAPR threshold value and the maximum iteration time of setting signal respectively, if the PAPR value of signal is smaller or equal to the PAPR threshold value of setting, or iterations judges then that more than or equal to the maximum iteration time of setting the output of IFFT is transferred to parallel serial conversion unit; If less than the maximum iteration time of setting, the output of judgement IFFT is transferred to the peak sequence generation unit that disappears greater than the PAPR threshold value of setting and iterations for the PAPR value of signal.

The information extraction unit of receiving terminal: be used to extract the data at receiving terminal N-L information subcarrier place, the data at L preserved sub-carrier place are directly abandoned.

The described peak sequence generation unit that disappears comprises: amplitude limit unit, time domain ideal peak eliminating signal generation unit, FFT unit, preserved sub-carrier place peak data extraction unit and the preserved sub-carrier place peak data amplifying unit that disappears that disappears, wherein:

The amplitude limit unit: be used for the signal of IFFT conversion is carried out amplitude limiting processing, the amplitude that makes signal behind the amplitude limit is less than setting threshold value;

Time domain ideal peak eliminating signal generation unit: be used for signal subtraction behind signal before the amplitude limit and the amplitude limit, extract the part that peak value surpasses threshold value, i.e. time domain ideal peak eliminating signal;

FFT unit: be used for the signal transformation of time domain ideal peak eliminating is become frequency domain ideal peak eliminating sequence;

The preserved sub-carrier place peak data extraction unit that disappears: be used for extracting the data at frequency domain ideal peak eliminating sequence preserved sub-carrier place, the data at other subcarrier place are made as " 0 ";

The preserved sub-carrier place peak data amplifying unit that disappears: be used for the peak data that disappears at the preserved sub-carrier place that extracts is amplified certain multiple.

Described judging unit comprises PAPR calculator, iterations counter and decision device, wherein:

PAPR calculator: the PAPR value that is used to calculate the time-domain signal that obtains through the IFFT conversion;

Iterations counter: be used for the number of times that an OFDM symbol of recording processing iteration is crossed;

Decision device: according to PAPR calculator calculated value and iteration count record value, described PAPR value and iterations are compared with the PAPR threshold value and the maximum iteration time of setting signal respectively, if the PAPR value of signal is smaller or equal to the PAPR threshold value of setting, or iterations judges then that more than or equal to the maximum iteration time of setting the output of IFFT is transferred to parallel serial conversion unit; If less than the maximum iteration time of setting, the output of judgement IFFT is transferred to the peak sequence generation unit that disappears greater than the PAPR threshold value of setting and iterations for the PAPR value of signal.

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

One. compare with the Clipping method

1.Clipping method directly distorts to the OFDM symbol amplitude, can cause system and self disturb, thereby cause the error rate BER performance of system to reduce; And the present invention is based on the IFFT/FFT transfer pair, and effectively seek the peak data that disappears, utilize the peak data that disappears directly to make the time-domain signal after the IFFT conversion have lower PAPR, thereby can not bring the reduction of error rate BER performance;

2, the Clipping method can be regarded the product of OFDM sampled signal and rectangular window function as, therefore can bring band interference, causes the increase of out-of-band radiation power; And therefore the present invention can not bring these problems owing to different with the principle of Clipping method reduction PAPR.

Two. compare with the TR algorithm of the waveform that prestores

1, the prestore TR algorithm of waveform can only be selected the conduct peak sequence that disappears in limited several sequences, and optional scope is very little, can not effectively reduce the PAPR of information sequence; The present invention is based on the IFFT/FFT transfer pair and dynamically seek the peak sequence that disappears that is suitable for the specifying information sequence, therefore can effectively reduce systematically PAPR;

2, the tradition waveform TR algorithm that prestores needs more preserved sub-carrier, just can obtain certain PAPR and reduce effect; And the present invention program can obtain better PAPR reduction effect under identical condition;

3, embodiment of the present invention is simple, and each module all is some common modules, does not have complicated structure, and it is less to carry out the iterations of FFT/IFFT, and l-G simulation test shows, only needs iteration three times, just can obtain good PAPR inhibition effect.

Description of drawings

Fig. 1 is that the TR algorithm reduces the PAPR schematic diagram

Fig. 2 is the iterative process flow chart of the TR scheme based on the IFFT/FFT transfer pair of the present invention

Fig. 3 is the ofdm system block diagram of the TR scheme based on the IFFT/FFT transfer pair of the present invention

Fig. 4 is that the peak sequence generation unit that disappears of the present invention constitutes block diagram

Fig. 5 is that judging unit of the present invention constitutes block diagram

Fig. 6 is the TR scheme based on the IFFT/FFT transfer pair of the present invention and the complementary cumulative distribution function C CDF comparison diagram of the waveform TR scheme that prestores

Fig. 7 is the complementary cumulative distribution function C CDF comparison diagram that the present invention is based on the different threshold values of TR scheme of IFFT/FFT transfer pair

Embodiment

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

With reference to Fig. 2, the present invention is used for the TR scheme based on the IFFT/FFT transfer pair at ofdm system, carries out as follows:

The first step according to the parameter request of ofdm system, is set the number L of preserved sub-carrier number in the N of a system subcarrier, and the position of definite preserved sub-carrier, determines the PAPR threshold value D and the maximum iteration time M of signal.

Preserved sub-carrier is many more, and the effect that the present invention program reduces PAPR is just good more, but because the preserved sub-carrier place does not propagate useful information, and preserved sub-carrier is many more, the band efficiency of system is also just low more.Therefore, when implementing the solution of the present invention, the effect that the number of preserved sub-carrier and the PAPR of system the reduce consideration of will compromising, generally, the number L of preserved sub-carrier is advisable to be no more than total sub-carrier number purpose 1/5.

The selection of preserved sub-carrier position better promptly in total N subcarrier, is selected L position at random, and is fixed up selecting at random, and the data that receiving terminal receives are through after the processing necessarily, the data at this L subcarrier place is abandoned get final product.

In second step, data allocations is distributed data " 0 " at L preserved sub-carrier place, distributes the normal information data after carrying out constellation mapping successively at N-L remaining subcarrier place.

The 3rd step, carry out the IFFT conversion, realize the OFDM modulation, obtain time-domain signal x (n).

The 4th step, decision process, the time-domain signal x (n) that obtains is carried out the detection of PAPR calculating and iterations m after the IFFT conversion, and compare with the PAPR threshold value D and the maximum iteration time M that set respectively, if the PAPR of signal is smaller or equal to the threshold value D that sets, or iterations m is more than or equal to the number of times M that sets, and then this signal is just exported as final transmission signals; If the PAPR of signal less than set point M, then carries out subsequent treatment to x (n) greater than threshold value D and iterations.

In the 5th step, the threshold value D according to setting carries out amplitude limiting processing to time-domain signal x (n), obtains limitation signal x (n).

Amplitude limit operation can be counted as the OFDM sampled signal and rectangular window function multiplies each other, if the amplitude of ofdm signal during less than threshold value, then the amplitude of this rectangular window function is 1, otherwise the amplitude of this rectangular window function is less than 1.

The 6th step deducted signal x (n) behind the amplitude limit with the signal x (n) before the amplitude limit, can obtain the part c (n) that signal peak among the x (n) surpasses thresholding, with c (n) as the desirable peak-to-peak signal that disappears of time domain.

The 7th step, ideal peak eliminating signal c (n) is carried out the FFT conversion, obtain the ideal frequency domain peak sequence C that disappears.

The 8th step, take out the data at preserved sub-carrier place among the C, the data that are about to information subcarrier place among the C are changed to " 0 ", obtain the frequency domain peak sequence C that disappears _L

This offsets sequence for desirable peak value C, if the data and the C at original N subcarrier place are subtracted each other, after signal after subtracting each other carried out the IFFT conversion, then obtain satisfied fully the condition of PAPR of time-domain signal less than the PAPR threshold value of setting, but so also just the data at each information subcarrier place have been disturbed, receiving terminal can't recover information sequence.Therefore, the data that preserved sub-carrier among the C can only be gone out remain, and the data at information subcarrier place are changed to " 0 ", progressively reduce the PAPR of signal according to preserved sub-carrier.

The 9th step is to C _LThe amplitude of carrying out adjustment obtains C _L, make C _LCorresponding time domain consistent that amplitude and the amplitude of the 5th resulting ideal peak eliminating signal c of step (n) of peak-to-peak signal c (n) try one's best that disappear.

The tenth step is with C _LMerge with N-L information subcarrier, obtain the sequence after the Data Update at preserved sub-carrier place.Jump to the 3rd step continuation Signal Processing.

With reference to Fig. 3, realize that the system and device of the inventive method comprises transmitting terminal and receiving terminal.The characteristics of transmitting terminal be on the basis of original ofdm system, increased data allocations unit 4, data selection unit 5, judging unit 7, disappear peak sequence generation unit 8 and the peak sequence of disappearing insert unit 9; The characteristics of receiving terminal are to have increased information extraction unit 20.

As shown in Figure 4, the peak sequence generation unit 8 that disappears of transmitting terminal is made up of amplitude limit unit 23, time domain ideal peak eliminating signal generation unit 24, FFT unit 25, preserved sub-carrier place peak data extraction unit 26, the preserved sub-carrier place peak data amplifying unit 27 that disappears that disappears.

As shown in Figure 5, the judging unit 7 of transmitting terminal is made up of PAPR calculator 28, iterations counter 29 and decision device 30.

According to Fig. 3, Fig. 4 and shown in Figure 5, the course of work that device of the present invention is implemented reduction ofdm communication system PAPR is as follows:

One, the transmitting terminal of ofdm communication system

As shown in Figure 3, the random data symbols streams that produces from system's random signal generating unit 1 is as ofdm signal, after baseband modulation unit 2 adopts QAM or QPSK modulation, the mapped signal of ofdm signal for N-L plural form, through string and converting unit 3 N-L serial complex data is converted into N-L complex data, the suitable position of L is selected in data allocations unit 4 between N-L parallel complex data then, and L position slotting " 0 ", make it to become N parallel data-signal, and with the input of this signal as data selection unit 5; Another input of data selection unit 5 is the data sequence of peak sequence insertion unit 9 outputs that disappears, data selection unit 5 selects to import the data of IFFT unit 6, when an OFDM symbol is for the first time processed (L preserved sub-carrier place also do not load the peak sequence that disappears), the data-signal that data selection unit 5 selection data allocations unit 4 transmit is as the input of IFFT unit 6, otherwise the peak sequence of selecting to disappear is inserted the input of the data sequence of unit 9 outputs as IFFT unit 6; Signal has been transformed into time-domain signal x (n) after IFFT unit 6 is handled, realized the modulation of OFDM; This time-domain signal is fed to judging unit 7 then, and judging unit 7 is selected to transfer signals to parallel serial conversion unit 10 or disappear peak sequence generation unit 8 according to decision rule; If signal is introduced to the peak sequence generation unit 8 that disappears, the frequency domain that the peak sequence generation unit 8 that then disappears generates the preserved sub-carrier place according to the signal of the input peak data C that disappears _LDisappeared then peak sequence of these data is inserted unit 9 and has been inserted into L preserved sub-carrier place, realized the merging of the disappear peak data and N-L the information subcarrier data of L preserved sub-carrier, this signal that includes the peak data that disappears has been fed to data selection unit 5 then, carries out iterative processing; If the signal of IFFT unit 6 outputs is behind judging unit 7; be admitted to parallel serial conversion unit 10; then will the walk abreast conversion of signals of input of parallel serial conversion unit 10 is serial output; in order to eliminate intersymbol interference ISI to greatest extent, also to insert unit 11 at interval and between each OFDM symbol, insert protection at interval by protection.Protection is the data flow process D/A conversion unit 12 of unit 11 outputs at interval; digital signal is converted to analog signal; pass through low pass filter 13 filtering again; the signal of output sends to channel 14; this channel can be that wire message way also can be a wireless channel; if wireless channel then needs the data of low pass filter 13 outputs are carried out upconversion process, for example adopt additive white Gaussian noise (AWGN) channel 14.

As shown in Figure 4, in the peak sequence generation unit 8 that disappears, amplitude limit unit 23 carries out amplitude limiting processing according to the amplitude threshold value of setting to the signal of input, makes the amplitude of the signal behind the amplitude limit be not more than threshold value; Time domain ideal peak eliminating signal generation unit 24 goes out the desirable time domain peak-to-peak signal c (n) that disappears according to signal before the amplitude limit and the signal extraction behind the amplitude limit then, specific implementation is for deducting the signal before the amplitude limit signal behind the amplitude limit, and the difference of gained is exactly the desirable time domain peak-to-peak signal that disappears; Then, FFT unit 25 is transformed to the ideal frequency domain peak sequence C that disappears with the desirable time domain peak-to-peak signal that disappears _LThen, the preserved sub-carrier place disappears peak data extraction unit 26 from the ideal frequency domain peak sequence C that disappears _LIn extract the peak data that disappears at preserved sub-carrier place, disappear after peak data amplifying unit 27 amplifies through the preserved sub-carrier place, be transferred to the peak sequence that disappears and insert unit 9.

As shown in Figure 5, in judging unit 7, PAPR calculator 28 calculates the PAPR value of input signal, iterations counter 29 is write down and is handled the OFDM symbol number of times crossed of iteration, decision device 30 is compared the PAPR value of PAPR calculator 28 outputs and the value of iterations counter 29 respectively with the PAPR threshold value and the maximum iteration time of setting signal, if the PAPR of signal is smaller or equal to the threshold value of setting, or iterations is more than or equal to the number of times of setting, then the input signal with judging unit 7 is transferred to parallel serial conversion unit 10, if less than set point, then the input signal with judging unit 7 is transferred to the peak sequence generation unit 8 that disappears greater than threshold value and iterations for the PAPR of signal.

Two, the receiving terminal of ofdm communication system

At the ofdm communication system receiving terminal; at first will carry out filtering by low pass filter 15 through the signal that receives after the Channel Transmission; be digital signal through AD conversion unit 16 with analog signal conversion again; again after unit 17 removal protections are at interval removed in overprotection at interval; data are sent into string and converting unit 18; after FFT unit 19 conversion; time-domain signal is converted to frequency-region signal; extract by the data message of information extraction unit 20 again information subcarrier place; the data at preserved sub-carrier place are abandoned; by parallel serial conversion unit 21 parallel data stream is converted to serial data stream then, through base band demodulator 22 serial data stream is demodulated into the ofdm signal that will receive at last and sends.

Effect of the present invention can further specify by Fig. 6 and Fig. 7.

Fig. 6 has provided the CCDF CCDF emulation correlation curve of the ofdm system that the present invention is based on IFFT/FFT transfer pair TR scheme and traditional TR scheme.Fig. 7 has provided based on the CCDF simulation curve under the different threshold values of IFFT/FFT transfer pair TR scheme.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 (10)

PAPR0＞0

Simulated conditions is as follows: ofdm signal is produced by random signal source, the QPSK modulation, and sub-carrier number is 256, simulation times is 20000.

Emulation 1

In order to illustrate that the TR scheme that the present invention is based on the IFFT/FFT transfer pair has the effect of better reduction ofdm system signal PAPR than traditional TR scheme, Fig. 6 has provided the comparison diagram of these two kinds of scheme CCDF simulation curves.The PAPR threshold value that wherein the present invention is based on the TR scheme of IFFT/FFT transfer pair is 7dB, and iterations is 3, and the tradition waveform TR scheme that prestores prestores 16 waveforms.As can be seen from Figure 6, the PAPR of scheme of the present invention is significantly improved than the tradition waveform TR scheme that prestores, and is 10 at CCDF ^-4The time, PAPR has approximately reduced 3dB.

Emulation 2

Fig. 7 is that the TR scheme that the present invention is based on the IFFT/FFT transfer pair is reserved 16 subcarriers, iteration 3 times, the CCDF simulation curve figure that the PAPR threshold value is different.From figure, can find out intuitively, this scheme has the performance of good restraining PAPR under the thresholding condition with higher, be under the situation of 8dB and 9dB for example at thresholding, can make the PAPR that handles the back signal drop in the thresholding fully, explanation is when threshold value is big, and the TR scheme that the present invention is based on the IFFT/FFT transfer pair has identical effect with Clipping in the PAPR reduction.

Claims (4)

1. reduce the method for ofdm system peak-to-average power ratio based on the preserved sub-carrier of IFFT/FFT, it is characterized in that: utilize the IFFT/FFT transfer pair to produce the frequency domain peak sequence C that disappears at the transmitting terminal of system _L, to reduce ofdm system peak-to-average power ratio PAPR, its detailed process is as follows:

(1) data allocations on the position of L preserved sub-carrier of the N of system subcarrier defined, is placed data " 0 ", the normal information data after the position placement constellation mapping of other a N-L subcarrier;

(2) carry out the IFFT conversion, realize the OFDM modulation, obtain time-domain signal x (n);

(3) if the PAPR of x (n) meets the demands or iterations has reached the maximum of setting, then x (n) is exported as final output signal; Otherwise, changeed for (4) step;

(4) according to the threshold value of setting, x (n) is carried out the amplitude limit peak that disappears, obtain disappear signal x (n) behind the peak of amplitude limit;

(5) deduct disappear time-domain signal x (n) behind the peak of amplitude limit with disappear time-domain signal x (n) before the peak of amplitude limit, obtain ideal peak eliminating signal c (n);

(6) c (n) is carried out N point FFT conversion and obtain frequency domain sequence C;

(7) C is extracted L subcarrier data of corresponding positions of reservation, obtain sequence C _L

(8) to C _LThe amplitude of carrying out adjustment obtains C _L, make C _LCorresponding time domain consistent that amplitude and the amplitude of step (5) resulting ideal peak eliminating signal c (n) of peak-to-peak signal c (n) try one's best that disappear;

(9) with C _LMerge with the information data on N-L the data subcarrier; Changeing for (2) step handles.

2. be used to realize the device of the described method of claim 1, comprise transmitting terminal and receiving terminal, it is characterized in that: transmitting terminal has increased data allocations unit, data selection unit, judging unit, the peak sequence generation unit that disappears, the peak sequence of disappearing insert the unit; Receiving terminal has increased information extraction unit;

Transmitting terminal

Data allocations unit: be used for placing data " 0 ", on remaining subcarrier, place and want information transmitted the L that reserves in advance preserved sub-carrier position;

Data selection unit: when an OFDM symbol was for the first time processed, the data-signal that data selection unit selection data allocations unit transmits was as the input of IFFT unit; Otherwise the peak sequence of selecting to disappear is inserted the input of the data sequence of unit output as the IFFT unit;

The peak sequence of disappearing of transmitting terminal is inserted the unit: be used for the disappear data merging at peak data and information subcarrier place of preserved sub-carrier place;

Peak sequence generation unit disappears: be used for the output signal of IFFT conversion is carried out amplitude limiting processing, make signal amplitude behind the amplitude limit less than the amplitude threshold value of setting; With signal before the amplitude limit and the signal subtraction behind the amplitude limit, extract the time domain ideal peak eliminating signal that peak value surpasses the amplitude threshold value, time domain ideal peak eliminating signal is transformed into frequency domain ideal peak eliminating sequence through the FFT conversion; Extract the data at preserved sub-carrier place in the frequency domain ideal peak eliminating sequence, the data at other subcarrier place are made as " 0 "; The peak data that disappears to the preserved sub-carrier place that extracts is amplified certain multiple;

Judging unit: the PAPR value, the record iterations that are used to calculate the time-domain signal that obtains through the IFFT conversion, described PAPR value and iterations are compared with the PAPR threshold value and the maximum iteration time of setting signal respectively, if the PAPR value of signal is smaller or equal to the PAPR threshold value of setting, or iterations judges then that more than or equal to the maximum iteration time of setting the output of IFFT is transferred to parallel serial conversion unit; If less than the maximum iteration time of setting, the output of judgement IFFT is transferred to the peak sequence generation unit that disappears greater than the PAPR threshold value of setting and iterations for the PAPR value of signal;

The information extraction unit of receiving terminal is used to extract the data at receiving terminal N-L information subcarrier place, and the data at L preserved sub-carrier place are directly abandoned.

3. the device that reduces the ofdm system peak-to-average power ratio based on the preserved sub-carrier of IFFT/FFT according to claim 2, it is characterized in that: the described peak sequence generation unit that disappears comprises: amplitude limit unit, time domain ideal peak eliminating signal generation unit, FFT unit, preserved sub-carrier place peak data extraction unit and the preserved sub-carrier place peak data amplifying unit that disappears that disappears, wherein:

The amplitude limit unit: be used for the signal of IFFT conversion is carried out amplitude limiting processing, the amplitude that makes signal behind the amplitude limit is less than setting threshold value;

Time domain ideal peak eliminating signal generation unit: be used for signal subtraction behind signal before the amplitude limit and the amplitude limit, extract the time domain ideal peak eliminating signal that peak value surpasses threshold value;

FFT unit: be used for the signal transformation of time domain ideal peak eliminating is become frequency domain ideal peak eliminating sequence;

The preserved sub-carrier place peak data extraction unit that disappears: be used for extracting the data at frequency domain ideal peak eliminating sequence preserved sub-carrier place, the data at other subcarrier place are made as " 0 ";

The preserved sub-carrier place peak data amplifying unit that disappears: be used for the peak data that disappears at the preserved sub-carrier place that extracts is amplified certain multiple.

4. the preserved sub-carrier based on IFFT/FFT according to claim 2 reduces the device of ofdm system peak-to-average power ratio, and it is characterized in that: described judging unit comprises PAPR calculator, iterations counter and decision device, wherein:

PAPR calculator: the PAPR value that is used to calculate the time-domain signal that obtains through the IFFT conversion;

Iterations counter: be used for the number of times that an OFDM symbol of recording processing iteration is crossed;

Decision device: according to PAPR calculator calculated value and iteration count record value, described PAPR value and iterations are compared with the PAPR threshold value and the maximum iteration time of setting signal respectively, if the PAPR value of signal is smaller or equal to the PAPR threshold value of setting, or iterations judges then that more than or equal to the maximum iteration time of setting the output of IFFT is transferred to parallel serial conversion unit; If less than the maximum iteration time of setting, the output of judgement IFFT is transferred to the peak sequence generation unit that disappears greater than the PAPR threshold value of setting and iterations for the PAPR value of signal.

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