Hybrid filtering for per-survivor processing in flat fading channels

Abstract

Receiver designs for maximum likelihood sequence estimation (MLSE) of BPSK modulated signals transmitted through a flat fading channel are described. This results in a receiver which jointly estimates the channel impulse response and detects the received data sequence. The receiver uses data as well as pilot symbols, embedded in the Viterbi algorithm (VA), referred to as per-survivor processing (PSP). It is demonstrated through simulations that the performance of PSP is very sensitive to the choice of the channel estimation filter. PSP employing a FIR filter to estimate the channel impulse response (CIR) is well examined for fast fading conditions. For modest fading rates however, stability problems due to pilot aided channel estimation occur. When channel estimation is performed using an IIR filter, the receiver shows superior performance for slow fading, while it is not suitable for fast fading. In this paper a hybrid realisation of PSP is proposed, using both a FIR and IIR filter, yielding a receiver suitable for slow and fast fading channels.