CDMA

DS-CDMA

ABSTRACT (BY  SHANTHI PRIYA)
Direct sequence code division multiple-access (DS-CDMA) has been selected as the fundamental signalling technique for third generation (3G) wireless communication systems, due to its advantages of soft user capacity limit and inherent frequency diversity. However, it suffers from multiple-access interference (MAI) caused by the non-orthogonality of spreading codes, particularly for heavily loaded systems. Therefore, techniques for mitigating the MAI, namely multiuser detection, have been the subject of an intensive research effort over the past two decades.
This paper examines the performance of decision feedback based iterative channel estimation and multiuser detection in channel coded aperiodic DS-CDMA systems operating over multipath fading channels. First, explicit expressions describing the performance of channel estimation and parallel interference cancellation based multiuser detection are developed. These results are then combined to characterize the evolution of the performance of a system that iterates among channel estimation, multiuser detection and channel decoding. Sufficient conditions for convergence of this system to a unique fixed point are developed.