Algorithms for BER-Constrained Variable-Length Equalizers driven by Channel Response Knowledge over Frequency-Selective Radio Channel

In mobile radio systems, transmission conditions actually encounter large variations depending on the effective environmental configurations. Training sequences are periodically inserted into the transmitted messages so that the receiver can estimate the channel response. Based on this knowledge, we study the problem of adapting the equalizer filter length to a given channel impulse response under bit error rate constraint. In this paper, both linear equalizer (LE) and decision feedback equalizer (DFE) are studied. Accurate control of the equalizer length can improve the system´s performance while reducing the handset power consumption or reducing software load in a software radio context. Besides, in a multi-service system, it allows to manage variable quality of service requirements. Optimal and suboptimal criteria for determining the equalizer length are discussed in order to optimize the overall complexity of the receiver including training phase and decoding phases.