A new filtering strategy to combat delay spread

A class of nonlinear-phase intersymbol-interference (ISI)-free filters, that lead to asymmetrical pulse shapes and provide a more robust performance in a delay spread controlled mobile environment without increasing signaling bandwidth, is proposed. A piecewise linear-phase filter with cosine roll-off is designed. Coherent QPSK (quadrature phase shift keying) and the two-ray Rayleigh fading model are assumed in the analyses. When the delay power is 10 dB lower than the first path, the performance is improved. It is also found that increasing the excess bandwidth leads to reduction of error floors for both linear- and nonlinear-phase filters. The reduction of error floors could lead to the use of low-overhead forward error-control coding, increasing the overall capacity