Spectral shaping for optimum RAKE receiver performance

This paper describes work carried out on examining the effects of spectral shaping on the performance of the RAKE receivers, in the presence of multipath propagation. Modelling techniques are used to simulate frequency-selective fading on DS modulated spread spectrum signals. RAKE receiver performance is examined with several pulse shaping filters. The filters range from ideal rectangular to Gaussian, covering the extreme performance bounds. The effect of pulse shaping is studied for several different signalling bandwidths, examining the benefits of frequency diversity and increased path diversity resolution on the filter performance. To enable the pass-band study of such systems, a static frequency-sensitive geometrical propagation channel model is used. The channel model provides information such as frequency and impulse response, delay power spectrum and the spaced-frequency correlation function of the channel. Based on the channel model output, signalling bandwidth and pulse shape, the output of RAKE receivers are categorised in terms of fade-depth statistics. The results indicate that pulse shape influence the RAKE receiver performance considerably. Depending on the filter type, there can be up to 7 dB improvement on the fade-depth at the receiver output. Results show that trade-off between the pulse width and side-lobe interference, favours the later. So filters such as Chebyshev, that result in pulses with narrow main-lobe but high side-lobes provide better performance than filters with larger main lobe, but low and rapidly decaying side-lobes, such as raised-cosine and Gaussian