Performance evaluation of adaptive suppression schemes for asynchronous CDMA systems in frequency-selective multipath fading

Includes bibliographical references (pages [104]-106)The thesis objective is to examine various adaptive schemes for asynchronous Code Division Multiple Access (CDMA) in frequency-selective multipath fading environments. Three schemes are considered here in detail; (i) N-tap adaptive detector, (ii) D-tap cyclically shifted filter bank (CSFB) scheme and (iii) Blind equalization scheme. The normalized Least Mean Square (NLMS) algorithm is used for tap adaptation in the first two methods. The gradient descent algorithm is used for the blind equalization scheme. The system considered has 10 users of which 8 are synchronous (v^ =0) with a relative power level of 5dB. It has one asynchronous user (vj =40Tc) with a relative power level of lOdB with respect to the desired user. The chip length was considered to be of length 63 and an input AWGN of variance 0.01. The users are provided with a pseudo-random sequence generated by the Gold code generator, which is preferred over regular shift register code generators due to its relatively better code properties. The results show that all three schemes perform well even in the presence of a multipath fading channel. The N-tap MMSE detector exhibits better initial convergence, while the CSFB scheme performs better after the initial convergence is achieved. Blind equalization gives improved results as compared to the matched filter receiver, although the earlier two schemes perform better than blind equalization.M.S. (Master of Science