Exploitation of Time-Variations in Wireless Channels using Two Different CDMA Systems

The time-varying nature of radio channels deteriorates the performance of a wireless system. However, there are two code division multiple access (CDMA) based transmission systems which are capable of adapting to these variations efficiently. In one of these systems, information symbols are transmitted simultaneously and in the other system, information symbols are chip-interleaved before transmission. Both systems exploit temporal variations in the channels so efficiently that using the estimated channel coefficients they are capable of outperforming the conventional system with perfect channel state information (CSI) at the receiver. In this paper, we analyze the relative performance behavior of these two promising fade-resistant CDMA systems. We show that both fade-resistant transmission systems exhibit identical performance when the system load is high. However, when the system load is light, the chip-interleaved system slightly outperforms the system that transmits information symbols simultaneously due to higher self-interference in the latter.