Title :
Crest-factor study of MC-CDMA and OFDM
Author :
Choi, Byoung-Jo ; Kuan, Ee-Lin ; Hanzo, Lajos
Author_Institution :
Dept. of Electron. & Comput. Sci., Southampton Univ., UK
Abstract :
The crest-factor (CF) of M-ary PSK MC-CDMA systems is shown to be dependent upon the aperiodic cross-correlations as well as on the aperiodic autocorrelations of the spreading codes used. Based on this observation, the crest-factor distributions of BPSK MC-CDMA using two different binary orthogonal spreading sequences namely Walsh codes and orthogonal Gold codes-as well as two polyphase orthogonal sequences-Frank codes and Zadoff-Chu (1972) codes-are compared against that of BPSK OFDM. In a `lightly loaded´ system the polyphase sequences and the orthogonal Gold codes are shown to have better CF distributions. However, in a `fully loaded´ system, Walsh codes exhibit the best crest-factor distribution amongst the investigated codes. MC-CDMA using Walsh codes was found to exhibit a peak factor reduction of 1.5 over OFDM, when the number of subcarriers is 16 and a rate 15/16 CF reduction block code is used, while maintaining the same spectral efficiency. We found that Zadoff-Chu spread MC-CDMA showed the best BER performance amongst the considered systems in Rayleigh channels, when joint-detection was employed, despite its heavier clipping than that of the Walsh spread scheme. This is due to its low multiple user interference
Keywords :
OFDM modulation; Rayleigh channels; binary sequences; block codes; code division multiple access; error statistics; multiuser channels; phase shift keying; radiofrequency interference; signal detection; spread spectrum communication; BER performance; BPSK MC-CDMA; BPSK OFDM; DS-CDMA multiple user interference; Frank codes; M-ary PSK MC-CDMA systems; Rayleigh channels; Walsh codes; Zadoff-Chu codes; aperiodic autocorrelations; aperiodic cross-correlations; binary orthogonal spreading sequences; block code; crest-factor distributions; fully loaded system; joint-detection; lightly loaded system; orthogonal Gold codes; peak factor reduction; polyphase orthogonal sequences; spectral efficiency; spreading codes; subcarriers; Autocorrelation; Binary phase shift keying; Bit error rate; Block codes; Gold; Interference; Multicarrier code division multiple access; OFDM; Phase shift keying; Rayleigh channels;
Conference_Titel :
Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50th
Conference_Location :
Amsterdam
Print_ISBN :
0-7803-5435-4
DOI :
10.1109/VETECF.1999.797130
