Coding, Modulation and Multiuser Decoding for DS-CDMA Systems
Abstract
The general trend both in wireless and fixed network communication systems is flexibility in services, data rates, desired delay and performance. Future systems should not be designed for specific services but be more general and allow for a multitude of services, both now existing and those not yet invented. Considered in this thesis is the design of a flexible direct-sequence code-division (DS-CDMA) system, supporting many services, and using advanced receiver structures and coding techniques. The first part focus on modulation methods to achieve multiple data rates in a DS-CDMA system. Considered are the multi-processing-gain, the multi-modulation, and the multicode schemes. It is shown that the multicode and multi-processing-gain schemes have about the same performance, while the multi-modulation scheme performs significantly worse for high-rate users. Disadvantages are: for the multi-processing-gain the low suppression of external interference for the high-rate users; and for the multicode scheme the high variations in the envelope for high-rate users which results in decreased spectral efficiency, increased bit error rate, and less power efficient amplifiers. The envelope variations can, however, be significantly reduced by the introduction of a high-rate non-linear block code --- a precoder. To further increase the the number of possible source data rates, a rate matching scheme using a family of rate-compatible convolutional codes is presented. The codes are variable…
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