Impact of spreading bandwidth on RAKE reception in dense multipathchannels

摘要

Spread spectrum (SS) multiple access techniques have been proposednfor third generation broadband wireless access. We develop an analyticalnframework to quantify the effects of spreading bandwidth on SS systemsnoperating in dense multipath environments in terms of the receivernperformance, receiver complexity, and multipath channel parameters. Innparticular, we consider wide-sense stationary uncorrelated scatteringn(WSSUS) Gaussian channels with frequency-selective fading. The focus ofnthe paper is to characterize the combined signal of the RAKE receivernfingers tracking the strongest multipath components. Closed formnexpressions for the mean and the variance of the total RAKE receivernoutput signal-to-noise ratio (SNR) are derived in terms of the number ofnRAKE fingers, spreading bandwidth, and multipath spread of the channel.nThe proposed problem is made analytically tractable by transforming thenphysical RAKE paths into the virtual path domain. A representativenresult indicates that for SS systems with 5 MHz signal bandwidthnoperating in a channel with constant power delay profile having 5 Μsnspread, the average SNR gain from increasing the number of RAKE fingersnfrom one to three is 3.8 dB and from three to five is 1.5 dB.nFurthermore, the reduction in the variation of SNR is 1.1 dB and 0.4 dBnfor the same increments in the number of fingers