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. A 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.