Research Of Key Technologies For Multicarrier And Multicarrier Code Division Multiple Access Systems

Multicarrier and multicarrier CDMA systems are the candidates with a greatapplied foreground for future mobile communications system.Some keytechniques in the two kinds of systems,including the reduction of peak-averagepower ratio and so on,are studied in this dissertation.The main contents ofthe dissertation are as following: (1) The way to constitute a multicarrier signal by using any onecomplementary code from multiphase complementary code pair is proposed,andthe upper bound on crest factor for a multicarrier signal is studied.A wayto synthesize multiphase complementary code pairs is analyzed based on thecomplementary autocorrelations function matrix.For a given kernel length,anumber of multiphase complementary code pairs can be obtained by changingrelated parameters.The simulation results and theoretic analysis show thatthe crest factors of the multicarrier signals formed from multiphasecomplementary codes are less than or equal to 6dB,regardless of the numberof subcarriers. (2) Upper and lower bounds on peak-to-average power ratio (PAPR) in OFDMsystems are analysed and derived.The selective mapping (SLM) technique usedto reduce PAPR is studied with the help of the upper bound.For a 16-subcarrierBPSK-OFDM system,the effect of the SLM technique on reducing the PAPR in thesystem is proved by calculating simulation.By utilizing the relationshipsbetween Golay complementary sequences and Reed-Muller codes,a block encodingalgorithm with which input information sequences are encoded into Golaycomplementary sequences is investigated.In order to increase the code rate,theencoding algorithm with which input information sequences are encoded intosub-Golay sequences is proposed based on the encoding algorithm of the Golaysequence.The simulation and comparison of the PAPR characteristics for a 16subcarriers 8PSK-OFDM system are proceeded by using the two encodingalgorithms.For the Golay encoding scheme,an efficient decoding algorithmbased on fast Hadamard transform (FHT) is also analyzed. (3) The new upper bound on complementary cumulative distribution function(CCDF) of the PAPR of a band-limited OFDM signal is derived based on thelevel-crossing rate theory,and the Monte Carlo simulation of the PAPRdistribution of a 16QAM-OFDM system with different subcarriers is carried outto test the tightness of the new upper bound.The simulation results show thatthe new upper bound matches the simulation results well when the subcarriernumber is greater than or equal to 64.The investigation shows that when thesubcarrier number is large,the probability that the PAPR is greater than agiven value is directly proportional to the subcarrier number and the dominanteffect is the stochastic behavior of the OFDM signal. (4) The relations between the signal envelope power of MPSK MC-CDMA(basedon the frequency domain spreading)and the aperiodic autocorrelation and theaperiodic cross-correlation functions of the spreading code sequences areanalysed.The effects of the different orthogonal spreading code sequences onthe signal envelope power and the connection between PAPR and the user numberare studied by simulation.The model of the MC-CDMA system using SLM is proposedand the upper bound on PAPR for the system is derived.The effects of thedifferent phase sequences in SLM on the PAPR distribution and the connectionbetween PAPR and the user number are compared by simulation.The resultsindicate that when random sequences,Shapiro-Rudin sequences or Golaycomplementary sequences are chosen as the phase sequences in SLM,SLM hasobvious effect on the PAPR reduction in MC-CDMA systems and the system PAPRnearly maintains constant as the number of users changes. (5) For partially coherent(the local subcarriers contain the random phaseerrors)multicarrier DS-CDMA system(which is based on the time domainspreading),operating over a slow-variable frequency-selective Rayleighfading channels,a analytic method of the BER upper bound for the system isproposed based on the Tikhonov density distribution of stochastic phase error.The simulation results show that the...