G. Auer

Mobile channel estimation for decision directed RAKE receivers operating in fast fading radio channels

The authors describe a robust channel prediction technique for a direct sequence spread spectrum (DS-SS) system in a fast fading environment. For improved performance the RAKE filter taps are coherently combined, hence accurate channel estimation is required. An FIR type linear prediction filter for each RAKE filter tap is used to estimate the channel response. In order to do this, the data decisions are fed back to the prediction filter. The stability of the proposed system is achieved through differential encoding of the data bits. It is demonstrated through simulations that the performance of the proposed decision directed receiver is better than that of an idealised receiver where channel estimation is not corrupted by decision feedback errors (e.g. by means of employing a pilot signal). The channel estimate can be significantly improved by employing a second stage channel estimation filter.

Per-survivor processing applied to decision directed channel estimation for a coherent diversity receiver

The problem of coherent detection for a diversity receiver to combat the severe penalty of transmitting over a Rayleigh fast fading channel is addressed. The principle of per-survivor processing is employed to estimate the channel response for BPSK modulated signals. To achieve this, a symbol aided plus decision directed transmission scheme is used. Simulation results demonstrate that the proposed algorithm can track the fading fluctuations.

Hybrid filtering for per-survivor processing in flat fading channels

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.