Asynchronous CDMA systems with random spreading-part II: design criteria

  • Authors:
  • Laura Cottatellucci;Ralf R. Müller;Mérouane Debbah

  • Affiliations:
  • Eurecom, Sophia Antipolis, France and Institute of Telecommunications Research, University of South Australia, Adelaide, SA, Australia;Norwegian University of Science and Technology, Trondheim, Norway;SUPELEC, Gif-sur-Yvette, France and Eurecom, Sophia Antipolis, France

  • Venue:
  • IEEE Transactions on Information Theory
  • Year:
  • 2010

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Abstract

Totally asynchronous code-division multiple-access (CDMA) systems are addressed. In Part I, the fundamental limits of asynchronous CDMA systems are analyzed in terms of spectral efficiency and SINR at the output of the optimum linear detector. The focus of Part II is the design of low-complexity implementations of linear multiuser detectors in systems with many users that admit a multistage representation, e.g., reduced rank multistage Wiener filters, polynomial expansion detectors, weighted linear parallel interference cancellers. The effects of excess bandwidth, chip-pulse shaping, and time delay distribution on CDMA with suboptimum linear receiver structures are investigated. Recursive expressions for universal weight design are given. The performance in terms of SINR is derived in the large-system limit and the performance improvement over synchronous systems is quantified. The considerations distinguish between two ways of forming discrete-time statistics: chip-matched filtering and oversampling.