Coding, Decoding and Multiuser Detection for Wireless CommunicationsCoding, Decoding and Multiuser Detection for Wireless Communications

Licentiatavhandling, 1997

In the strive for making the Universal Mobile Telecommunication System (UMTS) a reality, concepts and techniques are to be developed which can provide both high system capacity and sufficient quality for the increasing number of mobile users. To obtain these objectives, powerful and flexible error control coding is needed, as well as efficient means for many users to share the same commmication medium. This thesis contributes by presenting new optimum convolutional channel codes, outperforming those previously reported. These new and improved codes are then used as a basis for deriving flexible and powerful families of codes with many code rates. The various wireless services require different levels of error protection as well as a means for matching different data rates to the rate of the channel. Rate matching in multirate direct-sequence code-division multiple-access (DS-CDMA) systems is described and the performance is evaluated in terms of efficiency. Furthermore an error control scheme capable of providing extremely low error rates is proposed and shown to be a good candidate for some services in wireless mobile systems. A wireless system using DS-CDMA as its multiple access technique is normally severely interference limited. Joint detection of many users as well as interference cancellation techniques have in recent years been proposed to reduce the impact of the interference. The performance of a number of detectors is compared and shown to be very sensitive to errors in the time and phase estimates.