Evaluation of metrics for characterising the dispersion of the mobile channel

This paper analyses the suitability of the RMS delay spread and coherence bandwidth when characterising system quality-of-service of QPSK operating in a variety of wideband mobile channels. It is demonstrated that the RMS delay spread is unduly affected by the presence of relatively weak signals with large excess delay, limiting it´s effectiveness when characterising the time dispersion. The coherence bandwidth is shown to offer a more general dispersion metric. Furthermore it is indicated that the instantaneous system performance is poorly characterised by the dispersion parameters calculated from the discrete power delay profile (such as the RMS delay spread). The instantaneous delay spread incorporates the effects of pulse shaping and the vector summation which occurs in the instantaneous channel impulse response. Consequently, the instantaneous delay spread is demonstrated to provide a better indication of the instantaneous performance than the RMS delay spread