Low complexity PAPR suppression method in FRFT-OFDM system

摘要

The invention relates to a method that low complexity suppression of PAPR in FRFT-OFDM system, which belongs to the field of broadband wireless digital communications technology and can be used to reduce the PAPR in FRFT-OFDM system. The method is based on fractional random phase sequence and fractional circular convolution theorem, which can effectively reduce the PAPR of system. The method of the invention has the advantages of simple system implementation and low computational complexity. In this method, the PAPR of the system can be effectively reduced while keeping the system reliability. When the number of candidate signals is the same, the PAPR performance of the proposed method was found to be almost the same as that of SLM and better than that of PTS. More importantly, the proposed method has lower computational complexity than that of SLM and PTS.

主权项

1. A method that low complexity suppression of PAPR in FRFT-OFDM system, characterized in that the steps of the method are follows:
1) carry out N-point IDFRFT of the complex data X after digital modulation which length is N at sending end of communication system; after the process of subcarrier modulation, FRFT-OFDM symbols x(n) in time domain can be obtained; 2) according to periodic of chirp, making out p-order periodic extension of the x(n) in time domain of chirp and obtaining extended sequence which is represented as x((n))P,N; p-order discrete fractional Fourier converted into the formula of periodic extension in time domain of chirp is:x(n-N)j12cotα(n-N)2Δt2=x(n)-j12cotαn2Δt2(9) 3) move x((n))P,N to the right with the iM (i=1, 2, . . . L) point, take the main value range of x((n))P,N and obtain chirp circumferential displacement of FRFT-OFDM signals in time domain—x((n−iM))P,NRN(n); 4) Multiply x((n−iM))P,NRN(n) andη(n,i)=j12cotα[-2Mn+(M)2]Δt2by point, get φ(n,i) is:
φ(n,i)=x((n−iM))P,NRN(n)η(n,i),i=0,1 . . . L−1,n=0,1, . . . ,N−1  (10) 5) weighted stacking of φ(n,i) by r(l)(i) in step (4), get candidate signals {tilde over (x)}(l)(n) of FRFT-OFDM in time domain is:x~(l)(n)=∑i=0L-1r(l)(i)ϕ(n,i),n=0,1…N-1,l=1,2,…S(11) 6) select the minimum candidate signals {tilde over (x)}(l)(n) of PAPR in time domain as transmission signals. The weighting factor r(i)opt which can make PAPR of candidate signals minimum in time domain is used as sideband information, and send it to receiving end. According to sideband information r(i)opt, the receiving end recovers sending-information;r(i)opt=argminPARP{r(1)(i),…,r(S)}{x~(l)(n)}(12) Wherein, FRFT is fractional Fourier transform; OFDM is an orthogonal frequency division multiplexing; FRFT-OFDM is orthogonal frequency division system which is based on Fractional Fourier Transform; N is the number of subcarriers; X is the complex data after digital modulation which length is N; IDFRFT is inverse discrete fractional Fourier transform; x (n) is the symbol of the time-domain FRFT-OFDM; chirp is a linear FM; p is the order of Fractional Fourier Transform; x((n))P,N is the extended sequence which is obtained by p-order periodic extension of chirp in time domain; N is the cycle length of chirp (in the present invention, the cycle length of chirp is equal to the number of sub carriers); α=pπ/2, dt is the sampling interval of continuous signals; L is the length of the random phase sequence; M=N/L,RN(n)={11≤n≤N-10Otheris the value of the primary value range; r(l)(i) is the weighting factor with L-length, S is the number of alternative Fractional random phase sequence, PAPR is the peak to average power ratio.