The problem of blind data rate detection for a variable rate Direct-Sequence Code- ||Division Multiple-Access system is addressed. The system model is based on the time-division duplex mode of the UMTS standard. Two multi-rate access strategies, namely Variable Spreading Gain (VSG) and Variable Chipping Rate (VCR), are considered. A host of blind algorithms based on or inspired by maximum likelihood principles are investigated. Rate detectors with implicit or explicit multiple access interference (MAI) suppression are considered. Based on the MA1 suppression filter, additional rate detectors are devised. Comparison of the devised algorithms in terms of complexity and performance is presented. Performance bounds for maximum likelihood principle based algorithms are also developed. It is seen through simulation results that the best complexity and performance tradeoff is achieved by evaluating the average "power" at the output of the MA1 suppression filters associated with the candidate rate.
Keywords: DS-CDMA, UMTS-TDD, multirate, variable rate, VSG, VCR, maximum likelihood, MA1 suppression.