CN101459648A - Method for lowering PAR of OFDM system based on virtual carrier preservation algorithm - Google Patents

Abstract

The invention discloses a method for lowering the OFDM system peak-to-average power ratio on the basis of virtual carrier reservation algorithms in the wireless communication technology field. The technical scheme comprises: obtaining respective time domain signals ci and x of a set special frequency domain signal Ci and a frequency domain signal which carries useful information through IFFT transformation, calculating the initial PAPR value of the x, recording the value as PAPRmin, setting an all-zero time domain signal cfinal, calculating the PAPR value of two values of x+cfinal+ci and x+cfinal-ci sequences, comparing with PAPRmin, storing the minimum PAPR value into PAPRmin, enabling a special time domain signal which satisfies the minimum PAPR value at present to be ctemp, modifying cfinal=cfinal+ctemp until i=L, and selecting a combination with the minimum PAPR to send. The method effectively lowers the complexity and bit error rate of peak-to-average power ratio calculation, and the system reliability is improved.

Description

Reduce the method for ofdm system peak-to-average force ratio based on the virtual carrier preservation algorithm

Technical field

The invention belongs to wireless communication technology field, relate in particular to a kind of method that reduces the ofdm system peak-to-average force ratio based on the virtual carrier preservation algorithm.

Background technology

Demand broadband to communicating by letter along with people, individualized and mobile is more and more higher, and OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology has obtained using widely at each wireless communication field.One big shortcoming of ofdm system is that higher peak-to-average power ratio is arranged, the transmission signal of ofdm system is superimposed the forming of transmission signal on a plurality of subcarriers, when these signals during with the addition of homophase phase place, the instantaneous power of gained signal is very big, the average power of signal head and shoulders above, cause system to produce higher PAPR (Peak-to-Average Power Ratio, peak-to-average power ratio).High PAPR has proposed very high requirement to the range of linearity of the power amplifier in the transmitter and receiver, and has increased the complexity of equipment such as A/D, D/A converter.If the range of linearity of amplifier can not satisfy the dynamic change scope of signal, then signal can produce nonlinear distortion, causes spectrum leakage, and the orthogonality between each subcarrier is destroyed, and produces inter-carrier interference, reduces the performance of system.So peak-to-average power is the major issue that ofdm system need solve than problem.

In the wireless OFDM system, the technology that reduces PAPR at present both at home and abroad mainly is divided into 3 classes: signal predistortion class technology, signal scrambling code class technology, coding class technology.The thought of signal predistortion class technology is that direct peak value to signal carries out nonlinear operation, and is the most direct, the simplest.Because what it adopted is nonlinear operation, produced outside in-band noise and the band and disturbed, so the error rate of system is than higher.The thought of coding class technology is only to send the code word that those have low PAPR characteristic, thereby has avoided sending the code word that those higher PAPR can occur.Such technology is a linear process, can not make signal produce distortion, does not therefore also have the shortcoming of amplitude limit class technology.But the computation complexity of coding class technology is very high, and encoding and decoding all bother very much, the more important thing is that the information rate of this class technology reduces very soon, therefore only are applicable to the situation that sub-carrier number is fewer.Signal scrambling code class technology, its core concept are to reduce the probability that big PAPR occurs, employing also be linear transformation, but such technical sophistication degree need carry out repeatedly IFFT computing and search procedure than higher.

Summary of the invention

The objective of the invention is to, at the ofdm system model under the frequency selective fading channels, reduce on the basis of peak-to-average power than (PAPR) at traditional virtual carrier preservation algorithm, propose a kind of method of reduction ofdm system peak-to-average force ratio of low complex degree, overcome the too high defective of method computation complexity of present existing reduction ofdm system peak-to-average force ratio.

Technical scheme of the present invention is that a kind of method based on virtual carrier preservation algorithm reduction ofdm system peak-to-average force ratio is characterized in that described method comprises the following steps:

Step 1: to L special frequency-region signal C that sets ⁱ(i=1,2 ..., L) carry out the IFFT conversion, with the time-domain signal c that obtains after the conversion ⁱ(i=1,2 ..., L) deposit in the memory; Wherein, L is for reducing the number of peak value carrier wave, reduce the selectable amplitude of peak value carrier wave get 0, ± 1};

Step 2: the frequency domain signal X that will carry useful information is carried out the IFFT computing, obtains time-domain signal, is designated as x;

Step 3: calculate the PAPR value of x, be designated as PAPR _MinInitialization i=1 sets complete zero time-domain signal c _Final, be used to store the special time-domain signal c that finally will send ⁱ

Step 4: calculate x+c _Final+ c ⁱAnd x+c _Final-c ⁱThe PAPR value of two sequences, and and PAPR _MinRelatively, the PAPR value with minimum deposits PAPR in _Min, and the special time-domain signal that makes satisfy minimum PAPR value this moment is c _Temp, and upgrade c _Final=c _Final+ c _Temp

Step 5: make i=i+1, repeat above-mentioned steps 4, until i=L;

Step 6: with time-domain signal x and c _FinalAddition obtains final x to be sent _Final, the PAPR of this moment _MinIt is exactly final peak-to-average force ratio.

Described special frequency-region signal C ⁱ(i=1,2 ..., be that i reduction peak value carrier position place value is 1 L), all the other carrier position place values are 0 sequence.

Effect of the present invention is, on the basis of virtual carrier preservation algorithm, reduce the ofdm system peak-to-average force ratio, reduced computation complexity effectively, the applicability of system and the equilibrium between the system complexity have been realized, guaranteed the practical application request of ofdm system, need not other transmitted sideband information simultaneously, and do not change the order and the phase relation of former sequence, thereby do not need to do any unnecessary processing at receiving terminal, can not exert an influence, thereby further improve the reliabilty and availability of system the error rate.

Description of drawings

Fig. 1 is suitable for ofdm system transmitting-receiving block diagram of the present invention.

Fig. 2 is the schematic diagram of virtual carrier preservation algorithm.

Fig. 3 the present invention is based on the method flow diagram that the virtual carrier preservation algorithm reduces the ofdm system peak-to-average force ratio.

Fig. 4 the present invention is based on the CCDF curve analogous diagram that the virtual carrier preservation algorithm reduces the method for ofdm system peak-to-average force ratio.

Embodiment

Below in conjunction with accompanying drawing, preferred embodiment is elaborated.Should be emphasized that following explanation only is exemplary, rather than in order to limit the scope of the invention and to use.

Fig. 1 is suitable for ofdm system transmitting-receiving block diagram of the present invention.Among Fig. 1, carry out the framing procedure of data, constitute by preface information and data message at transmitting terminal, carry out then QAM modulation, IFFT conversion, insert Cyclic Prefix after, carrying out parallel serial conversion, is intermediate-freuqncy signal by the OFDM time domain data that generates is flowed conversion of signals, sends.At receiving terminal, to carry out at first exactly synchronously and the work of channel estimating, carry out after the FFT conversion demodulating qam symbol according to the parameter of estimation, estimate the error rate.

Fig. 2 is the schematic diagram of virtual carrier preservation algorithm.Among Fig. 2, the basic thought that utilizes the virtual carrier preservation algorithm to reduce PAPR is: superpose with the frequency-region signal that carries useful information with a kind of frequency-region signal with special construction, resulting time-domain signal can reduce the peak value of the pairing time-domain signal of the latter effectively after making the former through the IFFT computing, thereby reaches the purpose of the PAPR of reduction system.

The subcarrier that defines nonzero value among the special frequency-region signal C is for reducing the peak value carrier wave, and the number that reduces the peak value carrier wave is designated as L.In theory, this L amplitude and the desirable arbitrary value of phase place that reduces the peak value carrier wave, but the set of value is larger like this, and the amount of calculation of system is very big.So in order to reduce amount of calculation, reduce the peak value carrier wave usually and only get particular range, by QAM, generally only get 0, ± 1, ± i}.

Definition R ^N=0,1,2 ..., N-1} is the position sequence of all N subcarrier in the ofdm system.Definition R ^c={ i ₀, i ₁..., i _L-1Be to reduce peak value carrier wave residing position sequence in all N subcarrier and 0≤i in the ofdm system ₀＜i ₁＜...＜i _L-1＜N.Then defining R is R ^NIn remove R ^cAfter set, i.e. R ^cSupplementary set: R=R ^N-R ^cIt is on the sub-carrier positions of non-zero that frequency domain signal X and C satisfy original frequency domain signal X value, and frequency-region signal C value is zero; Be that frequency-region signal C value is a non-zero on zero the sub-carrier positions in original frequency domain signal X value.That is:

$\begin{array}{cc}{X}_k=\left\{\begin{array}{cc}{X}_k& k\∈R\\ 0& k\∈R^c\end{array}\right.& C_k=\left\{\begin{array}{cc}0& k\∈R\\ C_k& k\∈R^c\end{array}\right.\end{array}---\left(1\right)$

Virtual carrier in the ofdm system of definition employing virtual carrier preservation algorithm is reserved than (ToneReservation Ratio is TRR) for reducing the ratio of peak value carrier number L and carrier number N, i.e. TRR=L/N.

The frequency-region signal C that will have a special construction is added on the useful frequency domain signal X, is used to reduce the PAPR of ofdm system, the time-domain signal x that the stack back is produced _TCan be expressed as:

x _T＝Q(X+C)＝Q(X)+Q(C)＝x+c (2)

Wherein Q is the mathematical description of discrete Fourier transform (DFT) IFFT.X, c represent that respectively frequency domain signal X, C are through the resulting time-domain signal of discrete Fourier transform (DFT) IFFT.The Q matrix description is as follows:

Peak-to-average force ratio definition based on the ofdm system of virtual carrier preservation algorithm can change into like this:

$\mathrm{PAPR}\left(x_T\right)=\frac{\underset{n}{\max }\left\{{|x+c|}^2\right\}}{E\left\{{|x+c|}^2\right\}}---\left(4\right)$

And because in the ofdm system that adopts the virtual carrier preservation algorithm, it is generally more less than (TRR) that virtual carrier is reserved, so E{|x+c| ²≈ E{|x| ², then following formula can be reduced to:

$\mathrm{PAPR}\left(x_T\right)=\frac{\underset{n}{\max }\left\{{|x+c|}^2\right\}}{E\left\{{\left|x\right|}^2\right\}}---\left(5\right)$

So can make time-domain signal x by choosing signal C _TThe peak value minimum, thereby reduce PAPR.As seen the core of this algorithm is how to seek the frequency-region signal C that can effectively reduce PAPR in the ofdm system.Bring in from reception, it is as follows that the burst that is received carries out obtaining data sequence after the FFT computing:

$H_k(X_k+C_k)+N_k=\left\{\begin{array}{cc}{H}_k{X}_k+N_k& k\∈R\\ H_k{C}_k+N_k& k\∈R^c\end{array}\right.---\left(6\right)$

In view of traditional virtual carrier preservation algorithm complexity is bigger, at this virtual carrier preservation algorithm that proposes a kind of low complex degree, the starting point is to reduce the complexity of system.In ofdm system, number of sub carrier wave N is known and generally can become that the shared carrier position of data message and pilot frequency information is also fixed substantially.Can propose to improve to traditional algorithm in view of the above, the present invention the amplitude-phase range of choice that reduces the peak value carrier wave is defined as 0, ± 1}, i.e. K=3.

By the linear characteristic of inverse fourier transform as can be known, can respectively X, C be carried out addition again behind the IFFT earlier, effect is carried out IFFT after being equal to addition again.The improvement basic idea is: fixing frequency-region signal C ⁱ, i=1,2 ..., L, wherein C ⁱBeing i, to reduce peak value carrier position place value be 1, all the other carrier waves be the N point sequence that is extended under 0 situation (herein the phase place range of choice be 0, ± 1}), store each fixedly frequency-region signal C then ⁱ, i=1,2 ..., pairing time-domain signal c after the L process IFFT computing ⁱ, i=1,2 ..., L is expanded into frequency domain signal X on request with the useful signal that will transmit simultaneously, and it is carried out the IFFT computing, will obtain time-domain signal and be designated as x, again with time-domain signal x and fixing time-domain signal c ⁱBe combined into the row iteration addition, the time-domain signal combination that therefrom obtains the PAPR minimum sends.

Fig. 3 the present invention is based on the method flow diagram that the virtual carrier preservation algorithm reduces the ofdm system peak-to-average force ratio.Among Fig. 3, step 301: earlier with L special frequency-region signal C ⁱ(i=1,2 ..., L) through the time-domain signal c after the IFFT conversion ⁱ(i=1,2 ..., L) deposit in the memory.Wherein, reduce the selectable amplitude of peak value carrier wave get 0, ± 1}, L is for reducing the number of peak value carrier wave.

Step 302: the frequency domain signal X that will carry useful information is carried out the IFFT computing, and the time-domain signal that obtains is designated as x.

As the positional information R that determines special frequency-region signal C ^cAfter, just can determine the special frequency-region signal C that the L kind is fixing earlier ⁱ, obtain special frequency-region signal and useful frequency-region signal separately time-domain signal after the IFFT conversion according to linear characteristic IFFT (X+C)=IFFT (the X)+IFFT (C) of IFFT conversion then.

Step 303: calculate the PAPR value of x, be designated as PAPR _MinInitialization i=1 sets complete zero time-domain signal c _Final, be used to store the special time-domain signal c that finally will send ⁱ

Step 304: calculate x+c _Final+ c ⁱAnd x+c _Final-c ⁱThe PAPR value of two sequences, and and PAPR _MinRelatively, the PAPR value with minimum deposits PAPR in _Min, and the special time-domain signal that makes satisfy minimum PAPR value this moment is c _Temp, and upgrade c _Final=c _Final+ c _Temp

Step 305: make i=i+1, repeat above-mentioned steps 4, until i=L.

In the ofdm system of traditional employing virtual carrier preservation algorithm, the frequency-region signal C of special construction chooses according to the traversal search mode.Basic thought is: in N subcarrier, have L to reduce the peak value carrier wave, each amplitude-phase that reduces the peak value carrier wave has K (comprising zero) to plant possible value, by L K that reduces all amplitude-phases of peak value carrier wave of search ^LA kind of optimum combination is therefrom selected in kind of combination at last, makes the PAPR minimum.

Mend L control data that is used to reduce PAPR long for direct behind the former useful frequency-region signal data X of N-L, thereby form the superposed signal X+C that can produce low PAPR.For former useful frequency domain signal X, has the alternative frequency-region signal C of special construction earlier with itself and each ⁱAddition obtains data splitting X+C ⁱ, obtain time-domain signal x after this data splitting process IFFT computing ⁱ _T, at last again from this K ^LPlant the combination x that chooses the PAPR minimum in the combination ⁱ _T, and it is transmitted as last OFDM symbol.As seen, this traditional subcarrier preservation algorithm need carry out K altogether ^LInferior IFFT computing, and along with the increase of sub-carrier number N, the number of times that perhaps reduces the required IFFT computing of carrying out of increase of peak value carrier number L also can obviously increase, and therefore traditional subcarrier preservation algorithm complexity is bigger.

The present invention utilizes the confirmability of special frequency-region signal to store its corresponding time-domain signal to reduce the complexity of system.Adopting method of the present invention to reduce the ofdm system of peak-to-average force ratio,, only need do once IFFT computing, and not need all K to frequency domain signal X for each frequency domain signal X ^LPlant combination and all carry out the IFFT computing, thereby greatly reduced the operation times of IFFT, it only needs memory of extra use to store as calculated good time-domain signal c ⁱ, i=1,2 ..., L has reduced the complexity of system.In asking the process of PAPR, adopt iteration to ask the method for suboptimal solution, only need K * L iteration, much smaller than the K of traversal search method ^LInferior iteration has further reduced the complexity of system.This algorithm does not need to transmit side information, does not need inverse operation, and does not change the order and the phase relation of former sequence, thereby does not need to do any unnecessary processing at receiving terminal, can not produce a very large impact the error rate, is an outstanding feature of this algorithm yet.

Step 6: with time-domain signal x and c _FinalAddition obtains final x to be sent _Final, the PAPR of this moment _MinIt is exactly final peak-to-average force ratio.

Fig. 4 the present invention is based on the CCDF curve analogous diagram that the virtual carrier preservation algorithm reduces the method for ofdm system peak-to-average force ratio.Among Fig. 4, simulated conditions is: sub-carrier number N=512, modulation system QAM, the amplitude-phase scope be 0, ± 1}, i.e. K=3, reduce peak value carrier number L=16, L=32 and do not pass through complementary cumulative distribution function (CCDF) curve under three kinds of situations of any processing (primary signal).CCDF curve from Fig. 4 has some improvement through the PAPR characteristic that reduces the more undressed ofdm system of PAPR characteristic of the ofdm system that the method for ofdm system peak-to-average force ratio handles based on the virtual carrier preservation algorithm of the present invention as can be seen, is 10 at CCDF ^-3The place, adopting the PAPR value of the system that reduces peak value carrier number L=32 is 8.2dB, and the PAPR value of primary signal is 11.2dB, and increase along with L, it is good more to improve effect, increases but the complexity of system is also just corresponding, needs to send more power, need to sacrifice certain availability of frequency spectrum, make the availability of frequency spectrum reduce.As seen this improvement algorithm can effectively reduce the PAPR value of ofdm system, this simulating, verifying this algorithm have the effect that improves PAPR, and need not transmitted sideband information, complexity is very low.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (2)

1, a kind of method based on virtual carrier preservation algorithm reduction ofdm system peak-to-average force ratio is characterized in that described method comprises the following steps:

Step 1: to L special frequency-region signal C that sets ⁱ(i=1,2 ..., L) carry out the IFFT conversion, with the time-domain signal c that obtains after the conversion ⁱ(i=1,2 ..., L) deposit in the memory; Wherein, L is for reducing the number of peak value carrier wave, reduce the selectable amplitude of peak value carrier wave get 0, ± 1};

Step 2: the frequency domain signal X that will carry useful information is carried out the IFFT computing, obtains time-domain signal, is designated as x;

Step 3: calculate the PAPR value of x, be designated as PAPR _MinInitialization i=1 sets complete zero time-domain signal c _Final, be used to store the special time-domain signal c that finally will send _i

Step 4: calculate x+c _Final+ c ⁱAnd x+c _Final-c ⁱThe PAPR value of two sequences, and and PAPR _MinRelatively, the PAPR value with minimum deposits PAPR in _Min, and the special time-domain signal that makes satisfy minimum PAPR value this moment is c _Temp, and upgrade c _Final=c _Final+ c _Temp

Step 5: make i=i+1, repeat above-mentioned steps 4, until i=L;

Step 6: with time-domain signal x and c _FinalAddition obtains final x to be sent _Final, the PAPR of this moment _MinIt is exactly final peak-to-average force ratio.

2, a kind of method based on virtual carrier preservation algorithm reduction ofdm system peak-to-average force ratio according to claim 1 is characterized in that described special frequency-region signal C ⁱ(i=1,2 ..., be that i reduction peak value carrier position place value is 1 L), all the other carrier position place values are 0 sequence.

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