Matched filter-based RAKE combiner for wideband DS-CDMA mobile radio

A RAKE combiner based on a matched filter (MF) can be relatively easily implemented since the despread signal components that have propagated along different paths appear sequentially at the MF output. An important design problem is how to accurately select the paths having sufficiently large signal-to-noise power ratios (SNRs). This paper proposes a simple path selection algorithm that uses two selection thresholds. The first threshold is to select the paths that provide largest SNRs. However, as the total received signal power (sum of the signal powers of all paths) decreases, some of the selected paths become noisy. Therefore, we introduce a second threshold that discards the noisy or noise-only paths from among those selected by the first threshold. We apply the proposed path selection algorithm to a pilot symbol-assisted coherent RAKE combiner and find by computer simulations a near optimum set of the two thresholds in frequency selective multipath Rayleigh fading channels. Several power delay profile shapes are considered. The simulation results demonstrate that the MF-based RAKE combiner with the two selection thresholds can achieve a bit-error-rate (BER) performance close to the ideal case (i.e., the paths to be used for RAKE combining are selected for each power delay profile such that the required signal energy per information bitto-noise spectrum density ratio (E_b/N₀) is minimized).