Research On Joint Algorithm Of Suppression PAPR In CO-OFDM System Based On FHT

Orthogonal frequency division multiplexing(OFDM)is a multicarrier modulation(MCM)technology,which transmits serial high speed data information to parallel low speed subcarriers.Two basic advantages of OFDM are its ease of phase and channel estimation in time-varying environments and its robustness to channel dispersion.With the development of powerful digital signal processing(DSP)technology,OFDM has been widely used in digital audio broadcasting/digital video broadcasting(DAB/DVB),wireless local area network(WLAN)and other radio frequency fields due to its advantages of large capacity,long distance,anti-dispersion,high spectrum utilization.However,OFDM also has its inherent disadvantages,such as high peak to average power ratio(PAPR)and sensitivity to frequency and phase noise.In this thesis,PAPR reduction algorithms for coherent optical orthogonal frequency division multiplexing(CO-OFDM)systems of optical orthogonal frequency division multiplexing(OOFDM)are analyzed.1.The research background,advantages and disadvantages of CO-OFDM system and the key technologies of receiving and sending are introduced,the reasons for the high PAPR value of CO-OFDM system are analyzed,and the algorithms to reduce the PAPR value of the system briefly are summarized and analyzed.2.Fast Hadamard transform joint algorithm based on selective mapping(FHT-SLM),and fast Hadamard transform joint algorithm based on iterative partial transmission sequence(FHT-IPTS)algorithm are studied to suppress PAPR in CO-OFDM system.Hadamard algorithm has the disadvantage of very large amount of calculation.To solve this problem,a fast Hadamard transform(FHT)algorithm is proposed to reduce the complexity of 256-point Hadamard transform from 65536 times of addition and subtraction to 2048 addition and subtraction operations,which improves the calculation efficiency.The selective mapping(SLM)algorithm and partial transmit sequence(PTS)algorithm of probability algorithms do not bring signal distortion,but they have the disadvantage that the higher the number of blocks V is,the higher the computation cost is.The iterative partial transmission sequence(IPTS)algorithm is proposed to reduce the system PAPR.The simulation results show that when the complementary cumulative distribution function(CCDF)is10^-4,the PAPR0 values of FHT-SLM(V=8)and FHT-IPTS(V=8)are 7.63dB and 8.031dB respectively.Meanwhile,when the bit error rate(BER)is10^-3,the optical signal to noise ratio(OSNR)of FHT-SLM(V=8)algorithm is 21.2dB.The above research verifies the effectiveness of the proposed algorithm.3.Clipping joint algorithm based on FHT-SLM(FHT-SLM-Clipping)and FHT-SLM-?is studied to suppress PAPR in CO-OFDM system.In the pre-distortion algorithm,the clipping algorithm and?law companding algorithm have a good effect on PAPR reduction,but they have the problem of high bit error rate.However,the FHT-SLM algorithm has the deficiency that the higher the number of blocks,the higher the computational cost,so the pre-distortion algorithm and the low number of blocks FHT-SLM algorithm are combined.The simulation results show that when CCDF is 10^-4,V=4,clipping ratio(CR)is 4,the PAPR0 value of FHT-SLM-Clipping algorithm is6.149dB,and the PAPR0 value of FHT-SLM-?(V=4,?=1)is 5.288dB.When BER is 10^-3,the OSNR values of FHT-SLM-Clipping(V=4,CR=4)algorithm and FHT-SLM-?(V=4,?=1)algorithm are 20.59dB and 22.33dB respectively.The above research verifies the effectiveness of the proposed algorithm.4.FHT cascading modified two-piecewise linear companding(FHT-M-TPWC)algorithm are studied to suppress PAPR in CO-OFDM system.The two-piecewise linear companding(TPWC)algorithm of pre-distortion class has the problem of high BER.To solve this problem,an improved TPWC(M-TPWC)algorithm is proposed.Combining FHT algorithm with M-TPWC algorithm to further reduce the signal PAPR,the simulation results show that when CCDF is 10^4-,FHT-M-TPWC(?=1.6)algorithm reduces the PAPR0 value to 5.288dB for three iterations.When BER is 10^-3,the OSNR value of FHT-M-TPWC(?=1.6)algorithm for three iterations is 20.11dB.The above research verifies the effectiveness of the proposed algorithm.