A DS spread spectrum RAKE receiver with narrowband interference rejection capability: operation in fading channels

The authors analyze the performance of a modified noncoherent direct-sequence differential-phase-shift-keying (DS/DPSK) spread-spectrum RAKE receiver which operates under the conditions of a frequency-selective fading channel with narrowband tone interference. Interference rejection capability is added to a basic noncoherent RAKE receiver by including a front-end prewhitening filter. For the case of N Rayleigh fading signal paths with tone interference the BER (bit-error rate) is quite good and is shown, in some cases, to approach single-path nonfading DPSK performance. With multipath and a tone interferer the system is much less sensitive to an increase in the number of prewhitening filter coefficients. In the example shown the performance of the receiver with a six-tap prewhitening filter is almost identical to that of a three-tap version