CN100484116C - OFDM communication system and method for reducing peak uniform power ratio - Google Patents

Abstract

This invention relates to a method for reducing peak average power ration (PAPR) in OFDM communication system including: first of all determining the PAPR and its allowable error accepted by the communication system then to pre-judge it. If PAPR meets the preset requirement, then, the data is sent directly, if not the adaptive technology is adopted to automatically adjust the parameter, namely, to regulate the parameter value according to the difference between PAPR and preset PAPR to finish one circulation then to compute the PAPR changed parameter then repeat the process accordingly till the PAPR can meet the needs.

Description

The method of ofdm communication system and reduction peak-to-average power ratio

Technical field

The invention belongs to communication technical field, the method of peak-to-average power ratio in specifically a kind of reduction Orthodoxy Frequency Division Multiplex (OFDM:Orthogonal Frequency Division Multiplexing) communication system is to improve the performance of communication system.

Background technology

As far back as nineteen fifty-seven, OFDM just is used to multicarrier high frequency modulated demodulator, and Weinstein in 1971 and two scholars of Ebert have proposed to realize OFDM with fast Fourier transform (FFT:Fast FourierTransform).The main thought of OFDM is that the high speed serialization code stream is transformed into parallel low speed code stream, is modulated on equifrequent one group of mutually orthogonal subcarrier at interval.Its basic principle is that total channel width is divided into the subchannel that a plurality of bandwidth equate, each subchannel passes through the information symbol of subcarrier-modulated separately separately.In addition, the protection of introducing in the OFDM symbol can overcome the time delay expansion of multipath channel at interval effectively, eliminates intersymbol interference, has therefore eliminated the necessity that adopts complicated equalizer.Popular high-speed digital subscriber line HDSL, ADSL (Asymmetric Digital Subscriber Line) ADSL, very high speed digital subscriber lines VHDSL is the core transmission technology with OFDM at present.OFDM also is the standard modulation-demodulation technique of European digital audio broadcast, digital video broadcasting simultaneously.In addition, it still is the basis of WLAN (wireless local area network) physical layer, and it is core technology with OFDM that International Standards Organization in 1999 has passed through one, the WLAN standard 802.11a up to the 54Mbps transmission rate can be provided.

The basic communication system that adopts the OFDM technology is as shown in Figure 1: at the transmitting terminal of OFDM, be input as binary bit stream, image, or random sequence a _n, then, adopt quadrature amplitude modulation (QAM:Quadrature Amplitude Modulation) or phase-shift keying (PSK:Phase-Shift-Keying) to a _nCarry out premodulated one time, obtain X _n, the modulation system on each subchannel can be different, also can be identical.Load more bit modulation on the milder subchannel, loading bit loading seldom or not on the big subchannel that decline, this module can increase the transmission rate of system.X _nBehind serial to parallel conversion and invert fast fourier transformation (IFFT:Inverse Fast FourierTransform), obtain time-domain signal x _{L, n}, i.e. n sampled value in l symbol.Add protection at interval between the OFDM symbol, become cyclic prefix CP, it can eliminate the intersymbol interference that multipath fading causes, so just obtains signal s _{L, n}Signal s _{L, n}Through parallel serial conversion and digital-to-analogue conversion, just can obtain actual transmission signal s (t).At the receiving terminal of OFDM, what in fact carry out is the inverse process of above-mentioned transmitting terminal.

Though, adopt the communication system of OFDM technology to have lot of advantages, its major defect is exactly to have higher peak-to-average power ratio (PAPR:Peak-to-Average Power Ratio), and this peak-to-average power ratio can calculate with following formula:

$\mathrm{PAPR}=10{\log }_{10}[\underset{n}{\max }\left({\left|x_n\right|}^2\right)/\mathrm{mean}\left({\left|x_n\right|}^2\right)]---\left(1\right)$

Wherein,

The maximum power of expression OFDM symbol, mean (| x _n| ²) average power of expression OFDM symbol.

Usually ofdm signal can be regarded the summation of many independent same distribution signals as, when phase place is identical peak power be average power N doubly, wherein N is a sub-carrier number.High peak-to-average power ratio has a lot of disadvantageous aspects, for example, the linearity of pair amplifier has proposed very high requirement, if the dynamic range of linearity of amplifier part can not satisfy the variation of signal then received signal can produce distortion, destroy the orthogonality of each subcarrier of ofdm signal, make system performance degradation.

Problem at peak-to-average power ratio in the ofdm system has been carried out a large amount of research both at home and abroad, but existing method all is to do the reduction that exchanges peak-to-average power ratio for free of charge with other performance index of sacrificing communication system, for example, the error rate becomes the complexity increase of big, system etc.At present, the method for peak-to-average power ratio mainly contains in the reduction ofdm communication system that has proposed:

(1) signal predistortion technology

Signal predistortion technology mainly comprises amplitude limit, companding transform technology etc.

1) limiting technology

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.In our discussion, we will use normalized amplitude limit thresholding, i.e. amplitude limit rate CR, and amplitude limit thresholding A=CR* σ, and wherein, σ is the average power of ofdm signal.This shows, is that the baseband signal average power is under the condition of ofdm signal of N at carrier number $\mathrm{\σ}=\sqrt{N},$ The average power of bandpass signal is $\mathrm{\σ}=\sqrt{N/2}.$ Equal frequency domain phase convolution principle according to time domain multiplication, the frequency spectrum of the ofdm signal of process amplitude limit equals the convolution of the frequency spectrum and the window function frequency spectrum of original ofdm signal, therefore its out of band spectrum characteristic is mainly decided by the signal that spectrum width is bigger between the two, and just the frequency spectrum of rectangular window function decides

2) companding transform technology

Companding transform can be divided into the μ rule and A restrains two kinds.In the companding transform method, by the high-power compression that transmits, small-power transmitted amplify, thereby the average power that transmits is remained unchanged relatively.So not only can reduce the PAPR of system, and the small-signal anti-jamming capacity is strengthened.In the present invention, our usefulness be the mu-law companding conversion, so need the parameter of regulating companding coefficient μ just.

(2) high spped coding technology

The high spped coding technology mainly comprises: selectivity mapping SLM and part transfer sequence PTS.

1) selectivity mapping (SLM:Selective Mapping)

Signal in the transmitter of ofdm system can be expressed as:

x _k=IFFT[X _n], (n, k=0,1 ..., N-1), supposing to exist M different, length is the random phase sequence of vectors of N $P^{\left(\mathrm{\μ}\right)}=(P_0^{\left(\mathrm{\μ}\right)},P_0^{\left(\mathrm{\μ}\right)},,P_{N-1}^{\left(\mathrm{\μ}\right)}),$ Wherein (μ=1,2 ..., M),

[0,2 π) between evenly distribute.Can utilize this M phase vectors to carry out dot product with the list entries X of IFFT respectively, then can obtain M different output sequence X ^(μ)Then to a resulting M sequence X ^(μ)Implement discrete Fourier transform (DFT) IFFT respectively and calculate, the corresponding individual different output sequence of M that obtains $x^{\left(\mathrm{\μ}\right)}=(x_0^{\left(\mathrm{\μ}\right)},x_1^{\left(\mathrm{\μ}\right)},\·\·\·x_{N-1}^{\left(\mathrm{\μ}\right)});$ Last under the condition of given PAPR threshold value, in this M time-domain signal sequence, select best being used for of PAPR performance to transmit.

2) part transfer sequence (PTS:Partial Transmit Sequences)

At first utilize vector to come definition of data symbol X=[X ₀, X ₁..., X _N-1]; Then vectorial X is divided into the V group, respectively by { X _v, v=1,2 ..., V} represents, its dividing method can have multiple as: adjacent split plot design, the split plot design that interweaves, random division method, suppose that included number of subcarriers is identical in each grouping, then this M grouping is combined as follows: $X\′=\underset{v=1}{\overset{V}{\mathrm{\Σ}}}{b}_v{X}_v.$ { b wherein _v, v=1,2 ..., V} is a weight coefficient, and satisfies

And

This is called as supplementary; Then X ' is carried out inverse fast fourier transform IFFT, obtain x '=IFFT{X ' }.According to the linearity of IFFT, can utilize V independent inverse discrete fourier transform IDFT, each grouping is calculated: $x\′=\underset{v=1}{\overset{V}{\mathrm{\Σ}}}{b}_v\·\mathrm{IFFT}\left\{X_v\right\}=\underset{v=1}{\overset{V}{\mathrm{\Σ}}}{b}_v\·X_v,$ Wherein introduced V part transmission sequence PTS, X _v=IFFT{X _v.Select auxiliary weight coefficient b by using optimized Algorithm _v, make peak signal reach optimization.

(3) block encoding

Coding techniques commonly used mainly contains dagger-axe thunder Golay complementary series and Reed-Muller coding.The Reed-Muller coding is a kind of encoding scheme efficiently, and it can expand to binary system, the quaternary, octal system even higher system.It has guaranteed very little PAPR theoretically, and fine error-correcting performance also is provided, simultaneously also can be by the simple change of bit rate, PAPR and error-correcting performance being handled the situation of different channels.Relation is very closely arranged between Golay complementary series and the second order Reed-Muller sign indicating number, come the code word corresponding to big PAPR is separated by second order Reed-Muller sign indicating number being divided into some cosets, thereby play the purpose that reduces PAPR.

The above-mentioned method that these reduce PAPR all has the limitation of himself, mainly has the following disadvantages:

(1) adopts limiting technology that signal is carried out amplitude limit and can introduce clipped noise, when adopting filter to eliminate these noises, can cause peak value regeneration again, thereby can not satisfy the requirement of system design; Though adopt the companding transform technology can effectively reduce the PAPR of system, it can produce bigger influence to system again.

(2) adopting selectivity mapping, part transfer sequence and coding techniques is to be the reduction that cost has brought PAPR to increase redundancy, when sub-carrier number is big, this several method all needs bigger amount of calculation and complexity, and in practical at present ofdm communication system, sub-carrier number is generally all bigger, so its amount of calculation and complexity are difficult to accept.

(3) no matter adopting who would have thought method in the past, when reducing peak-to-average power ratio, all can cause the deterioration of communication system performance, is a problem that needs solution at present so how to seek the compromise of the best between peak-to-average power ratio and systematic function.

The content of invention

One of purpose of the present invention provides a kind ofly can regulate the ofdm communication system that reduces peak-to-average power ratio automatically according to practical communication environment and index; Two of purpose provides a kind of method that reduces the ofdm communication system peak-to-average power ratio, to improve because of reducing the harmful effect that PAPR causes the ofdm communication system performance.

Realize that technical scheme of the present invention adopts pre-judgement technology and adaptive technique,, improve the flexibility and the adaptivity of ofdm communication system with the Automatic Optimal of realization parameter and automatic the trading off between peak-to-average power ratio and the systematic function.

Said pre-judgement technology is according to central-limit theorem, and the distribution of peak-to-average power ratio is along with the increase of sub-carrier number is tending towards Gaussian Profile gradually.Promptly when OFDM satisfy sub-carrier number greater than the time, it distributes very near Gaussian Profile, thereby its PAPR is bigger.But since usually ofdm communication system to be in the probability of big peak power very low, general ofdm signal power surpasses three times of average power, promptly when PAPR be that the probability of 9.6dB is about 0.1%, surpass its four times of average powers; When PAPR be the probability of 12dB less than 0.01%, signal is reduced without exception the processing of peak-to-average power ratio in order to satisfy the lower big peak power of probability of occurrence, can cause very big influence to the performance of system.Therefore, pre-judgement technology of the present invention is only handled the signal of big peak power, promptly earlier according to the range of linearity of power amplifier, determines acceptable peak-to-average power ratio PAPR ₀, and then judge that whether the peak-to-average power ratio of system meets the demands, if meet the demands, does not then handle and directly sends ofdm signal; If do not meet the demands, then adopt adaptive technique, till meeting the demands.

Said adaptive technique mainly refers to performance index and actual signal intelligence that basis is predetermined, adjusts parameter automatically according to adaptive algorithm, seeks optimization and finally realize compromise automatically between this a pair of contradiction of performance of PAPR and communication system.Because communication environment is ever-changing, particularly in wireless mobile communications, the main mode of radio wave propagation is direct wave, refracted wave, reflected wave and their composite wave, add the motion of travelling carriage itself, make that wireless channel between travelling carriage and the base station is changeable and be difficult to control, signal can suffer the influence of various declines during by channel, if adopt the method for the reduction PAPR of preset parameter, just can not adapt to the reality of changeable channel.The employing of adaptive technique mainly is to consider the reality that will adapt to changeable channel, to increase the flexibility and the adaptivity of communication system.

The present invention adopts described pre-judgement technology and adaptive technique, and the method step that reduces peak-to-average power ratio in the ofdm communication system is as follows:

At first, according to the range of linearity of power amplifier, make communication system acceptable peak-to-average power ratio PAPR in advance ₀With permissible error a;

Then, to through the signal behind inverse fast Fourier transform and the parallel serial conversion, judge in advance: if the peak-to-average power ratio PAPR just in the system satisfies predetermined PAPR ₀Requirement then directly sends data; If the PAPR of system does not satisfy predetermined PAPR ₀Requirement, then the parameter that reduces the PAPR method is carried out the self-adaptive processing of following process after, send data again:

(1) determines the parameter that ofdm signal is initial, for example companding coefficient μ or amplitude limit rate CR, recycle ratio λ, global cycle frequency n, permissible error α;

(2) earlier ofdm signal is handled, for example companding transform or amplitude limit, pass through general formula again:

${\mathrm{<figure-callout\; id="1"\; label="PAPR"\; filenames="C200410073081E00201.png,C200410073081E00211.png"\; state="\{\{state\}\}">PAPR</figure-callout>}}_1=10{\log }_{10}[\underset{n}{\max }\left({\left|x_n\right|}^2\right)/\mathrm{mean}\left({\left|x_n\right|}^2\right)]$

Calculate peak-to-average power ratio at that time, with PAPR ₁Represent, in the formula,

The maximum power of expression OFDM symbol, mean (| x _n| ²) average power of expression OFDM symbol;

(3) general peak-to-average power ratio PAPR at that time ₁With predetermined peak-to-average power ratio PAPR ₀Compare,, then directly data are sent if meet the demands;

(4) if peak-to-average power ratio PAPR at that time ₁Greater than the predetermined equal power P APR in peak ₀, then the difference according to the two increases companding coefficient μ or reduces amplitude limit rate CR, returns step (2);

(5) if peak-to-average power ratio PAPR at that time ₁Less than predetermined peak-to-average power ratio PAPR ₀, the difference of then judging the two again whether within the scope of permissible error α, if this difference in the scope of permissible error α, then loop ends sends data; If this difference not in the scope of permissible error α, then reduces companding coefficient μ or increases amplitude limit rate CR, and returns self adaptation step (2).

Ofdm communication system of the present invention comprises: transmitting element, judge that unit, self adaptation reduce the peak-to-average power ratio unit, reduce inverse process unit, the receiving element of peak-to-average power ratio in advance.Wherein:

Transmitting element is used to receive the signal behind 4-QAM modulation and the serial to parallel conversion, and through invert fast fourier transformation, add Cyclic Prefix and parallel serial conversion, form OFDM transmission signal, send into pre-judgement unit;

Pre-judgement unit, be used for that OFDM is sent signal and judge processing in advance, respectively by two-way output, promptly one tunnel signal that will need not to reduce peak-to-average power ratio is directly delivered to D/A conversion unit, another road will need to reduce the signal of peak-to-average power ratio, deliver to self adaptation and reduce the peak-to-average power ratio unit;

Self adaptation reduces the peak-to-average power ratio unit, be used for signal to the output of pre-judgement unit, automatically regulate companding coefficient μ or amplitude limit rate CR according to (1)～(5) adaptive process in the method for peak-to-average power ratio in the described reduction ofdm communication system, deliver to D/A conversion unit;

Parameter by automatic adjusting reduction peak-to-average power ratio method is met the peak-to-average power ratio of requirement and the signal of systematic function, delivers to D/A conversion unit;

Reduce the inverse process unit of peak-to-average power ratio, be used for anticipation had no progeny and adopted the signal that reduces the peak-to-average power ratio method to carry out inverse process to recover, send into the serial to parallel conversion unit then;

Receiving element is used to receive the signal through serial to parallel conversion, and by going Cyclic Prefix, fast fourier transform, outputs to the parallel serial conversion unit, through the signal that needing to obtain after the 4-QAM demodulation.

Above-mentioned predetermined peak-to-average power ratio PAPR ₀Determine by the linear dynamic range of power amplifier that mainly peak power is not more than the input power that power amplifier allows.

The permissible error α of above-mentioned scheduled communication system requires to determine that degree of regulation is high more that according to the degree of regulation of communication system the value of α is more little.

The principle of above-mentioned circulation is to make the PAPR of system as much as possible near predetermined value, so the global cycle number of times is the bigger the better in theory, so just can reach the minimum that influences to systematic function, can satisfy the requirement of PAPR simultaneously again.If excessively can influence efficiency of transmission again but obtain, so choose according to actual conditions in actual applications, in emulation of the present invention, getting the global cycle number of times is 5, can reach pre-provisioning request, as shown in Table 1 and Table 2.

The present invention compares with the method for existing reduction peak-to-average power ratio, has following advantage:

1. owing to the present invention is based on the less fact of probability that peak-to-average power ratio high in practical communication occurs, so adopting pre-judgement technology is of great use, can be only the signal of the high PAPR of small probability be handled accordingly by adopting pre-judgement technology, thereby avoided all will carrying out unnecessary processing to all signals, improved efficiency of transmission, and to the whole communication system Effect on Performance is not very big, the flexibility that has improved communication system;

2. owing to the present invention adopts based on adaptive technique, according to expectation index and practical communication channel circumstance, regulate messaging parameter automatically, make it satisfy the expection requirement as much as possible, therefore, can make peak-to-average power ratio satisfy our requirement as much as possible, and realize compromise between PAPR and the systematic function automatically, improve the adaptivity of communication system and intelligent.

Description of drawings

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

Fig. 2 is the ofdm communication system theory diagram that adopts the inventive method

Fig. 3 is a first embodiment of the present invention principle flow chart

Fig. 4 is a second embodiment of the present invention principle flow chart

Fig. 5 is the CCDF CCDF comparison diagram of the first embodiment of the present invention

Fig. 6 is the error rate comparison diagram of the first embodiment of the present invention and the variation diagram of companding coefficient μ

Fig. 7 is the CCDF CCDF comparison diagram of the second embodiment of the present invention

Fig. 8 is the error rate comparison diagram of the second embodiment of the present invention and the variation diagram of amplitude limit rate CR

Embodiment

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

With reference to Fig. 2, the radiating portion of ofdm communication system mainly comprises: 4-QAM modulator, invert fast fourier transformation IFFT digital signal processor 6, parallel serial conversion 8, self adaptation reduce peak-to-average power ratio unit 13, digital to analog converter 15, low pass filter 16, receiving unit is actually the inverse process that sends part, mainly comprises: low pass filter 20, analog-to-digital conversion 22, fast fourier transform FFT digital signal processor 29,4-QAM demodulator 32.

The transmission of ofdm communication system, receiving course are distinguished as follows:

During transmission, the data symbol stream 2 of the information of carrying that information source 1 produces is delivered to modulator 3, carries out the quadrature amplitude modulation first time, adopts the 4-QAM modulation here.Binary data stream just is mapped as binary data on each parallel channel the point on the signal constellation which after modulating through 4-QAM, promptly forms the data sequence of plural form.These data are delivered to the transmitting terminal of OFDM through the data 5 behind the serial to parallel conversion 4.Should the parallel sequence of plural number carry out the modulation second time by 6 pairs of invert fast fourier transformation IFFT digital signal processors, promptly original signal is carried out frequency modulation(FM) with one group of orthogonal sine and cosine signal, parallel complex data after obtaining modulating is in order to keep adding synchronously Cyclic Prefix 7 in complex data.This complex data is merged into serial data stream 9 by parallel serial conversion 8 with the data flow of each passage, and promptly the OFDM symbol is sent to pre-judgement unit 10.

There are two paths of data output line 11 and 12 in pre-judgement unit 10, judges that in advance the process that the unit is judged in advance is: the peak-to-average power ratio PAPR that obtains OFDM symbol 9 earlier ₁, then with acceptable PAPR ₀Compare, if the PAPR of this moment ₁Satisfy PAPR ₀Requirement, then symbol 9 directly enters digital to analog converter 15 by output line 11; If the PAPR of this moment ₁Greater than PAPR ₀, then symbol 9 enters self adaptation reduction peak-to-average power ratio unit 13 by output line 12 and reduces PAPR ₁

The main effect that self adaptation reduces peak-to-average power ratio unit 13 is: by adopting adaptive algorithm, regulate companding coefficient μ or amplitude limit rate CR automatically, so that the peak-to-average power ratio of communication system meets the demands as much as possible.Its course of work is: the data that anticipation is had no progeny are by after reducing peak-to-average power ratio and handling, again by adopting the adaptive algorithm part, by obtaining the best parameter value after the iteration cycle process, for companding transform is exactly companding coefficient μ, for amplitude limit method then is amplitude limit rate CR, at this moment just obtained the As soon as possible Promising Policy requirement peak-to-average power ratio.

Add supplementary by the data after the self-adapting compressing conversion and obtain serial complex data 14, be sent to digital to analog converter 15, carry out filtering through delivering to low pass filter 16 after the digital-to-analogue conversion, the data 17 that obtain after the filtering are sent to channel 18 and launch.The low pass filter here is also referred to as formed filter, can be raised cosine filter, FIR filter, iir filter, it also can be the low pass filter of other types, its main effect is the bandwidth that restriction sends signal, improve sideband, the spectral characteristic of signal, make to have decay preferably, so that reduce aliasing effect.So at this moment the design of low pass filter 16 is very crucial, should consider during specific design that message transmission rate, bandwidth, the characteristic of channel etc. are all multifactor.The channel here can be various channels, both can be that wire message way also can be a wireless channel, if wireless channel needs that also data 17 are carried out upper side frequency and handles, adopt additive white Gaussian noise (AWGN:Additive White GaussianNoise) channel here for the sake of simplicity.

During reception, the signal demand by channel 18 obtains analog signal 21 through low pass filter 20, and this filter is also referred to as matched filter.This analog signal becomes digital signal after by analog to digital converter 22.This analog to digital converter 22 has the two ways of digital signals output line, pre-judgement situation in the corresponding process of transmitting of difference, do not adopt the method that reduces peak-to-average power ratio if anticipation is had no progeny, then the signal after the analog-to-digital conversion 22 is not carried out any processing, directly enter serial-parallel converter 27 by transmission line 23; Adopt the method that reduces peak-to-average power ratio if anticipation is had no progeny, then the digital signal of analog to digital converter 22 outputs enters the inverse process 25 of corresponding reduction peak-to-average power ratio by transmission line 24, and then sends into serial to parallel conversion 27; Before being carried out demodulation, the parallel complex data flow behind the serial to parallel conversion also needs to remove Cyclic Prefix 28, undertaken obtaining signal 30 after the demodulation by 29 pairs of these data flow of fast fourier transform FFT digital signal processor then, this signal is again through recovering and raw information 2 essentially identical reception information 33 after parallel serial conversion 31 and the 4-QAM demodulation 32, to satisfy the requirement of the stay of two nights 34.

Because communication environment is ever-changing, particularly in wireless mobile communications, the main mode of radio wave propagation is a space wave, i.e. direct wave, refracted wave, reflected wave and their composite wave.Add the motion of travelling carriage itself, make that wireless channel between travelling carriage and the base station is changeable and be difficult to control, signal can suffer the influence of various declines during by channel, so if adopt the method for the reduction PAPR of preset parameter, just can not adapt to the reality of changeable channel.So the present invention has introduced adaptive technique, the adaptive technique here mainly refers to according to predetermined performance index and actual signal intelligence, according to adaptive algorithm, adjust parameter automatically, between this a pair of contradiction of performance that reduces PAPR and communication system, seek optimization and finally realize compromise automatically.Therefore when ofdm communication system was worked, the signal after pre-judgement adopted adaptive technique if desired, will utilize the self-adapting compressing conversion to carry out the iteration of parameter.Can adopt diverse ways for the self-adapting compressing conversion, for example: companding, amplitude limit, part transfer sequence, selectivity mapping, coding etc.The present invention has provided two kinds of embodiment.

Embodiment 1

The first embodiment of the present invention is discussed in conjunction with companding transform, and it implements flow chart such as Fig. 3

Shown in: the first step, at first determine acceptable peak-to-average power ratio PAPR ₀

Whether second step calculated the peak-to-average power ratio PAPR of primary signal, and it is disconnected to carry out anticipation, need to adopt companding transform to reduce peak-to-average power ratio with decision; If the peak-to-average power ratio PAPR of primary signal is greater than PAPR ₀, then need to carry out the 3rd step process and carry out self adaptation reduction peak-to-average power ratio; If the peak-to-average power ratio PAPR of primary signal is less than PAPR ₀, then jumped to for the 4th step;

In the 3rd step, self adaptation reduces the peak-to-average power ratio process:

(1) determines companding coefficient μ, iteration coefficient lambda, total iterations n, permissible error a;

(2) the input data are carried out the mu-law companding conversion that the companding coefficient is μ, and calculate the peak-to-average power ratio PAPR after the companding transform ₁Promptly

${\mathrm{<figure-callout\; id="1"\; label="PAPR"\; filenames="C200410073081E00201.png,C200410073081E00211.png"\; state="\{\{state\}\}">PAPR</figure-callout>}}_1=10{\log }_{10}[\underset{n}{\max }\left({\left|x_n\right|}^2\right)/\mathrm{mean}\left({\left|x_n\right|}^2\right)]$

In the formula,

The maximum power of expression OFDM symbol, mean (| x _n| ²) average power of expression OFDM symbol;

(3) the companding coefficient is carried out iteration optimization and handle, promptly earlier judge whether iterations has arrived, iteration finishes if iterations has arrived; If iterations does not arrive, judge PAPR again ₁Whether greater than PAPR ₀If, PAPR ₁Greater than PAPR ₀, then the difference according to the two strengthens companding coefficient μ, and promptly according to μ=(1+ α) μ, wherein α=(PAPR1-PAPR0) * λ adjusts parameter μ, returns the beginning in the 3rd step then; If PAPR ₁Less than PAPR ₀, the difference that at this moment also needs to judge the two whether in allowed limits, if in allowed band, then iteration finishes, and gets back to for the 4th step; If not in allowed band, then the difference according to the two reduces companding coefficient μ, and promptly according to μ=(1+ α) μ, wherein the * λ of α=(PAPR1-PAPR0) adjusts parameter μ, returns the beginning in the 3rd step then, till iteration meets the demands.

In the 4th step, iterative process finishes, and data are sent.

As seen, the principle of iteration of the present invention is to make the peak-to-average power ratio of system as much as possible near predetermined value, both to the minimum that influences of systematic function, can satisfy the requirement of peak-to-average power ratio with realization simultaneously again.

Embodiment 2

The second embodiment of the present invention is discussed in conjunction with amplitude limit, its implementation process such as Fig. 4:

The first step is at first determined acceptable peak-to-average power ratio PAPR ₀

Whether second step calculated the peak-to-average power ratio PAPR of primary signal, and it is disconnected to carry out anticipation, need to adopt amplitude limit method to reduce peak-to-average power ratio with decision; If the peak-to-average power ratio PAPR of primary signal is greater than PAPR ₀, then need to carry out the 3rd step process and carry out self adaptation reduction peak-to-average power ratio; If the peak-to-average power ratio PAPR of primary signal is less than PAPR ₀, then jumped to for the 4th step;

In the 3rd step, self adaptation reduces the peak-to-average power ratio process:

(1) makes amplitude limit rate CR, iteration coefficient lambda, total iterations n, permissible error a;

(2) the input data are carried out the amplitude limit that the amplitude limit rate is CR, and calculate the employing amplitude limit by general formula

Peak-to-average power ratio PAPR after the method ₁, promptly

${\mathrm{<figure-callout\; id="1"\; label="PAPR"\; filenames="C200410073081E00201.png,C200410073081E00211.png"\; state="\{\{state\}\}">PAPR</figure-callout>}}_1=10{\log }_{10}[\underset{n}{\max }\left({\left|x_n\right|}^2\right)/\mathrm{mean}\left({\left|x_n\right|}^2\right)]$

In the formula,

The maximum power of expression OFDM symbol, mean (| x _n| ²) average power of expression OFDM symbol;

(3) amplitude limit rate CR is carried out iteration optimization and handle, promptly earlier judge whether iterations has arrived, iteration finishes if iterations has arrived; If iterations does not arrive, judge PAPR again ₁Whether greater than PAPR ₀If, PAPR ₁Greater than PAPR ₀, then the difference according to the two reduces amplitude limit rate CR, and promptly according to CR=(1-α) CR, wherein α=(PAPR1-PAPR0) * λ adjusts amplitude limit rate CR, returns the beginning in the 3rd step then; If PAPR ₁Less than PAPR ₀, the difference that at this moment also needs to judge the two whether in allowed limits, if in allowed band, then iteration finishes, and gets back to for the 4th step; If not in allowed band, then the difference according to the two strengthens amplitude limit rate CR, and promptly according to CR=(1-α) CR, wherein the * λ of α=(PAPR1-PAPR0) adjusts parameter amplitude limit rate CR, returns the beginning in the 3rd step then, till iteration meets the demands;

In the 4th step, iterative process finishes, and data are sent.

The present invention reduces the method for PAPR and compares with the method for the reduction PAPR that has proposed at present, its outstanding advantage is exactly by adopting pre-judgement technology and adaptive technique, the flexibility and the adaptivity of ofdm communication system have been increased, and every performance index of communication system can both be met the demands as much as possible, nor can increase too big system complexity.

Effect of the present invention can further verify that the CCDF CCDF that uses is meant that PAPR surpasses a certain value by following The simulation experiment result in emulation, for example, and PAPR _cProbability, can be expressed as with the mathematics formula: Prob{PAPR〉PAPR _c.

Emulation experiment 1

Get total iterations n and be 5, permissible error a is 0.1dB, PAPR ₀Be 6.8dB; Get 1024 subcarriers and adopt the 4-QAM modulation system, adopt additive white Gaussian noise channel, the self adaptation companding method is carried out emulation experiment.

When SNR=14dB, the CCDF of its peak-to-average power ratio contrasts as shown in Figure 5.As seen from Figure 5, the peak-to-average power ratio of original OFDM symbol is the highest, adopts the peak-to-average power ratio of pre-judgement technology and adaptive technique minimum, and the peak-to-average power ratio that adopts original companding transform method (μ=1) is between the two.

When SNR=14, the self-regulating process of error rate comparison diagram and companding coefficient μ as shown in Figure 6.

When SNR=14, situation of change such as the table 1 of companding coefficient μ.

The companding coefficient μ situation of change of table 1:SNR=14dB

Simulation times	The situation of change of companding coefficient μ
		1	1.0→0.7149→0.6141→0.6248
2	1.0→0.691→0.577
		... ...	... ... ... ... ...
100	1.0→0.6407→0.4985→0.4353
		... ...	... ... ... ... ...
9900	1.0→0.73
		9901	1.0
... ...	... ... ... ... ...
		10000	1.0→0.6805→0.5596

Companding coefficient μ is can be self-regulating as can be seen from Table 1, and for the emulation first time, companding coefficient μ changes to 0.7149 by initial 1.0, be adjusted to 0.6141, when being adjusted to 0.6248, PAPR at this moment satisfies our requirement at last, so iteration finishes; For the emulation second time and later emulation, situation of change is similar.

As seen from Figure 6: the error rate minimum that signal is handled not, but its PAPR is excessive, and maximum can be 12.2845dB; And the error rate of the error rate that the adopts adaptive technique traditional companding transform more fixing than companding coefficient μ is little.Here emulation 10000 times, adopting the average of the error rate of adaptive technique is 2.613 * 10 ^-4, the error rate of traditional companding transform (companding coefficient μ fixes) is 4.318 * 10 ^-4And it also is minimum adopting the PAPR of adaptive technique, and at this moment its PAPR maximum is 6.8dB, and the PAPR maximum of traditional companding transform that companding coefficient μ fixes is 7.7563dB.As seen, adopt the performance of method of the present invention best, and realized trading off between the RAPR and the error rate automatically.In addition as can be seen from Figure 6, by adopting pre-judgement technology and adaptive technique also less to the influence of systematic function when reducing PAPR.

Emulation experiment 2

Get total iterations n and be 5, permissible error a is 0.1dB, PAPR ₀Be 6.9dB, get 1024 subcarriers and adopt the 4-QAM modulation system, adopt additive white Gaussian noise channel, the adaptive amplitude-limiting method is carried out emulation experiment.

When SNR=14dB, the CCDF of peak-to-average power ratio is to such as Fig. 7.As seen from Figure 7: the peak-to-average power ratio of original OFDM symbol is the highest, adopts the peak-to-average power ratio of pre-judgement technology and adaptive technique minimum, and the peak-to-average power ratio of employing raw sliced method (CR=2.2) is between the two.

When SNR=14dB, self-regulating process such as Fig. 8 of error rate contrast and thresholding coefficient CR.

When SNR=14dB, situation of change such as the table 2 of amplitude gate limit value CR.

The amplitude gate limit value CR situation of change of table 2:SNR=14dB

Simulation times	The situation of change of amplitude limit parameters C R
		1	2.2→2.1215→2.1796→2.1328
2	2.2→2.1193→0.577
		... ...	... ... ... ... ...
100	2.2→2.1229→2.1808→2.1341
		... ...	... ... ... ... ...
9990	2.2→2.2758
		9991	2.2→2.1238→2.1812→2.1350
... ...	... ... ... ... ...
		10000	2.2→2.1168

Table 2 shows: amplitude limit rate CR can regulate automatically according to adaptive algorithm, up to the satisfied requirement of PAPR.

Adopt the amplitude limit method of adaptive technique better equally as can be seen from Fig. 7 and Fig. 8 than traditional amplitude limit method.In addition as can be seen from Figure 8, by adopting pre-judgement technology and adaptive technique also less to the influence of systematic function when reducing PAPR.

During the SNR=14dB that has been emulation of the present invention more than, adopt the situation of companding transform and amplitude limit method.Lower the analysis of PAPR method and other state of signal-to-noise and emulation similarly for other.

Discuss with emulation at the ofdm communication system in the multicarrier although reduce the method for PAPR among the present invention and be, but it is equally applicable to other multi-carrier communications systems with higher PAPR, for example, fields such as mobile communication, digital broadcasting, Digital Television and optical fiber communication.The present invention illustrates disconnected technology of anticipation and adaptive technique in conjunction with companding transform and amplitude limit in addition, but the present invention is applicable to that equally also other reduces the method for PAPR, for example: selectivity mapping, part transfer sequence, coding method etc.Its parameter difference of diverse ways, for example, for the companding transform method, its parameter is exactly that finger pressure expands coefficient μ; For amplitude limit method, its parameter is meant amplitude limit rate CR; For the PTS method, its parameter then is meant packet count V; For the SLM method, its parameter then refers to the number M of random phase sequence of vectors, adopts in the method for the present invention and just can determine the parameter that these are different.

Claims (4)

1. peak-to-average power ratio method that reduces in the ofdm communication system, step is as follows:

Make communication system acceptable peak-to-average power ratio PAPR at first, in advance ₀With permissible error a;

Then, to judging in advance through the signal behind inverse fast Fourier transform IFFT and the parallel serial conversion; If the peak-to-average power ratio PAPR in the system satisfies predetermined PAPR ₀Requirement then directly sends data; If the peak-to-average power ratio PAPR of system does not satisfy predetermined PAPR ₀Requirement, then the parameter of PAPR is carried out the self-adaptive processing of following process after, send data again:

(1) determines companding coefficient μ or amplitude limit rate CR, iteration coefficient lambda and total iterations n of ofdm signal;

(2) ofdm signal is carried out companding transform or amplitude limit according to (1), utilize general formula to calculate at that time peak-to-average power ratio PAPR again ₁, promptly

${\mathrm{PAPR}}_1=10{\log }_{10}[\underset{n}{\max }\left({\left|x_n\right|}^2\right)/\mathrm{mean}\left({\left|x_n\right|}^2\right)]$

In the formula,

The maximum power of expression ofdm signal, mean (| x _n| ²) expression ofdm signal average power;

(3) incite somebody to action peak-to-average power ratio PAPR at that time ₁With predetermined peak-to-average power ratio PAPR ₀Compare, judge at first whether iterations has arrived, iteration finishes if iterations has arrived, directly data is sent; If iterations does not arrive, again with PAPR ₁With PAPR ₀Compare;

(4) if peak-to-average power ratio PAPR at that time ₁Greater than predetermined peak-to-average power ratio PAPR ₀, then the difference according to the two increases companding coefficient μ or reduces amplitude limit rate CR, returns self adaptation step (2);

(5) if peak-to-average power ratio PAPR at that time ₁Less than predetermined peak-to-average power ratio PAPR ₀, the difference of then judging earlier the two whether within the scope of permissible error a, if this difference in the scope of permissible error a, then iteration finishes, the transmission data; If this difference not in the scope of permissible error a, then reduces companding coefficient μ or increases amplitude limit rate CR, and returns self adaptation step (2).

2. method according to claim 1, wherein scheduled communication system acceptable peak-to-average power ratio PAPR ₀Determine according to the linear dynamic range of communication system power amplifier that mainly promptly peak power is less than or equal to the input power that power amplifier allows.

3. method according to claim 1, wherein the permissible error a of scheduled communication system determines that according to the degree of regulation requirement of communication system degree of regulation is high more, the value of a is more little.

4. ofdm communication system comprises:

Transmitting element is used to receive the signal behind 4-QAM modulation and the serial to parallel conversion, and through invert fast fourier transformation, add Cyclic Prefix and parallel serial conversion, form OFDM transmission signal, send into pre-judgement unit;

Pre-judgement unit, be used for that OFDM is sent signal and judge processing in advance, respectively by two-way output, promptly one tunnel signal that will need not to reduce peak-to-average power ratio is directly delivered to D/A conversion unit, another road will need to reduce the signal of peak-to-average power ratio, deliver to self adaptation and reduce the peak-to-average power ratio unit;

Self adaptation reduces the peak-to-average power ratio unit, be used for signal to the output of pre-judgement unit, automatically regulate companding coefficient μ or amplitude limit rate CR according to the described step of claim 1 (1)～(5) adaptive process, be met the peak-to-average power ratio of requirement and the signal of systematic function, deliver to D/A conversion unit;

Reduce the inverse process unit of peak-to-average power ratio, be used for anticipation had no progeny and adopted the signal that reduces the peak-to-average power ratio method to carry out inverse process to recover, send into the serial to parallel conversion unit then;

Receiving element is used to receive the signal through serial to parallel conversion, and by going Cyclic Prefix, fast fourier transform, outputs to the parallel serial conversion unit, through the signal that needing to obtain after the 4-QAM demodulation.

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