Performance Analysis of Spreading Sequences in Radio Channels

Abstract: In this thesis, we have studied direct sequence spread spectrum based CDMA communication system. We have analyzed CDMA based transmitter and receiver structures operating in Rayleigh fading and additive white Gaussian noise (AWGN) channel characteristics, in which data is transmitted and received. We next focused on spreading sequences used in such systems and analyzed the system performance in the presence of various sequences. We have studied the sequence properties, analyzed their bit error rate (BER) and compared traditional Walsh Hadamard sequences with uni¯ed complex Hadamard transform (UCHT) sequences, modi¯ed UCHT sequences and complex Oppermann sequences. We concluded that complex Oppermann se- quences and some UCHT sequences outperform Walsh Hadamard sequences in asynchronous CDMA systems because of their polyphase characteristics and better correlation properties. Next, we considered the problem of optimization among the sequence sets and showed that optimized subsets perform significantly better as compared to random selection of sequences within a sequence set.