Decorrelating Detectors for a Dual Rate Synchronous DS/CDMA System

  • Authors:

  • Mohammad Saquib;Roy Yates;Narayan Mandayam

  • Affiliations:

  • Wireless Information Networks Laboratory (WINLAB), Rutgers University, PO Box 909, Piscataway, NJ 08855-0909, U.S.A. E-mail: saquib@winlab.rutgers.edu;Wireless Information Networks Laboratory (WINLAB), Rutgers University, PO Box 909, Piscataway, NJ 08855-0909, U.S.A. E-mail: saquib@winlab.rutgers.edu;Wireless Information Networks Laboratory (WINLAB), Rutgers University, PO Box 909, Piscataway, NJ 08855-0909, U.S.A. E-mail: saquib@winlab.rutgers.edu

  • Venue:
  • Wireless Personal Communications: An International Journal
  • Year:
  • 1999

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Abstract

This paper addresses the use of decorrelating detectors for a dual rateDS/CDMA system that serves both low bit rate and high bit rate users. Weassume that in an interval of duration T_0, a low rate usertransmits one bit while a high rate user transmits M bits.Applying a standard decorrelator to the interval of duration T_0 yields an M bit processing delay for high rateusers and a computational complexity that grows with M. Inthis paper, we propose a decorrelator that generates bit decisions for eachhigh rate user in every subinterval of duration T_0/M. Todecode a low rate user, a soft decoding rule applies maximal ratio combining on M separate decorrelated outputs of each low rate user. The soft decoding dual rate decorrelator eliminates the bit processing delay for high rate users and also reduces the computationalcomplexity of a standard decorrelator. Further, it is shown that theasymptotic efficiency of the standard decorrelator is greater than or equalto the proposed decorrelator. By evaluation, it is observed that when thesignature sequences have good correlation properties, the proposed softdecoding decorrelator is found to perform nearly as well as the standarddecorrelator. However, when the signature sequences have highcross-correlation, then the proposed decorrelator suffers in terms of biterror rate while retaining the near-far resistance property.