Joint carrier phase tracking and multi-user demodulation of narrow-band signals

Coherent joint detection of cochannel signals is an effective method for improving quality and system capacity for narrow-band TDMA systems in the presence of interference. Accurate estimation of signal parameters is thus required in order to separate the signals for different users. This paper proposes an accurate method for estimating phase and frequency errors that are present in the received signal. Combined with multi-user sequence estimation, an approach is developed that uses a cross-coupled, digital phase-locked loop (DPLL) to track the phase and frequency estimates during demodulation. Additionally, the frequency estimates are smoothed across multiple data slots to improve the performance. Simulation results are presented showing the efficacy of this approach to compensate for phase and frequency errors present in single-antenna ANSI-136 handsets.