Error rate considerations for a high bit rate DS-SS BPSK dual space diversity RAKE

In high bit rate DS-SS BPSK mobile radio reverse links with RAKE demodulators the frequency selective channel causes intersymbol interference. For many years the standard Gaussian approximation error rate has been used and for high bit rates its accuracy is not known. We compare the Gaussian approximation to error rate derived using total probability theorem, Chernoff and Prabhu bounds with true statistics of intersymbol interference. For signal-to-noise ratio´s (SNR´s) greater than 6 dB (cases of interest), we show that the Gaussian approximation is a much looser upper bound than our bounds. The Prabhu bound which can be tailored to different intersymbol interference conditions is the tightest bound. We show that the RAKE combats incoherent intersymbol interference while the immunity it offers decreases for SNR´s greater than 10 dB. Finally, a dual space diversity RAKE provides an 8 dB space diversity gain.