The principle of time-frequency duality of DS-CDMA and MC-CDMA

Direct sequence (DS) and Multi-carrier (MC) code division multiple access (CDMA) are competing schemes for wireless multiple access systems. They have been studied and compared by many researchers. Time and frequency domains have long been used to represent linear systems in dual forms. In this paper it is shown, using time-frequency duality, that DS and MC can be considered dual CDMA systems or dual representations of a unique CDMA system, depending on the relationship between the spreading waveforms. The effects of transmission over a time-variant, frequency-selective channel on these dual systems are also considered. It is shown that frequency selectivity produces the same effect in MC-CDMA as time variation in DS-CDMA and vice-versa. Detection strategies for DS and MC CDMA are interrelated and their performance is compared by simulation.