Spread-time CDMA resistance in fading channels

Spread-time code division multiple access (ST-CDMA) was proposed as an alternative CDMA scheme to spread spectrum (SS) (see Crespo, P.M. et al., Proc. IEEE Globecom, p.836-40, 1991; US Patents No. 5177768, 5175744, 5175743, 5173923; IEEE Trans. Commun., vol.43, no.6, p.2139-48, 1995). ST-CDMA can be considered as the time-frequency dual of SS-CDMA. In ST-CDMA, pseudorandom (PN) sequences are assigned to each user, and the Fourier transform of the transmitted pulse for a given user is determined by modulating the amplitude of the desired spectrum by the user´s PN sequence. The main advantage of ST-CDMA is the flexibility with which power-limited pulses can be designed. We examine the effect of fading channels on the performance of spread-time. We compute the average signal-to-interference-plus-noise ratio in two different fading channels both for ST-CDMA and SS-CDMA. We show that ST-CDMA has 2.1 dB better performance than SS-CDMA with a rectangular pulse chip