Multiuser Receivers for Coded CDMA Systems
Abstract
In this dissertation, the asynchronous direct sequence code division multiple access (CDMA) communication system is described and a number of multiuser detection approaches are proposed that improve upon the performance of the conventional base station. Both coded and uncoded systems are studied for nondispersive, additive white Gaussian noise (AWGN) channels. For the uncoded system case, the multiuser detection techniques that have already been proposed are first reviewed. Then, two decision feedback equalizers (DFE's) that have been proposed are combined to form a new hybrid DFE which outperforms the others in situations where the multiuser interference in the system is high. Next, the case where each user in the system employs a convolutional code to improve its performance is studied. First, the optimal multiuser sequence estimator is formulated, and it is shown that this receiver may be implemented using a Viterbi algorithm which operates on a time varying trellis with a number of states which is exponential in the product of the number of users in the system and the constraint length of the codes used (for the rate 1/2 code case). Because this optimal receiver has a very high complexity, a variety of suboptimum receivers are proposed which have a performance level near that of the optimal receiver's but have a more manageable complexity. All of the approaches are compared on the basis of their performance (through analysis and simulation), their complexity and their decoding delay.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1994
- Accession Number
- ADA356730
Entities
People
- Thomas R. Giallorenzi
Organizations
- University of Virginia