Adaptive detection and channel estimation for dual-rate DS/CDMA networks in frequency-selective fading

摘要

In a Dual-Rate DS/CDMA system, a primary, "high rate" network coexists with a secondary one with a slower rate. Demultiplexing high-rate users typically entails, at the receiver end, a time-varying processing if Variable Spreading Length (VSL), Variable Chip Rate (VCR). or Variable Chip Rate with Frequency Shift (VCRFS) modulation formats are used. and Rake-Type demodulation schemes if the chip rate exceeds the channel coherence bandwidth. The realization of fully adaptive receivers thus requires the joint estimation of (a) the interference to be suppressed, whether from other users of the high-rate network or from the secondary network, and (b) the channel tap weights. The solution that we consider here assumes that, for each user, a pilot signal is transmitted along with the information-bearing signal. whether in a time-multiplexed or in a parallel-channel format. We consider both the uplink and the downlink channel and, based on a Minimum-Mean-Square-Error (MMSE) optimality criterion, we have come up with a fully adaptive system. capable on the one hand of tracking, through a cyclic Recursive-Least-Squares type algorithm, the periodically time-varying variations of the interference subspace and on the other of updating the channel tap weights estimates. A thorough performance assessment is presented, and the convergence dynamics of the system are derived through computer simulations in order to assess the impact of the prior uncertainty with regard to the other-users signatures and the channel tap weights realizations.