Error performance of narrowband and spread-spectrum modulation with diversity in frequency-selective channel

Abstract

Abstract The analysis of irreducible average bit error of narrowband and direct sequence spread-spectrum modulation using BPSK, QPSK, DPSK and DQPSK in Rayleigh and Rician frequency-selective channels is presented. The analysis for narrowband modulation shows a substantial improvement in irreducible BER at moderate normalized delay spread when a specular component (K) is present in the channel. This improvement decreases rapidly as normalized delay spread increases. However, with the use of direct sequence spread-sprectrum, this improvement can be maintained even at high values of normalized delay spread. With selection diversity, the irreducible BER in Rayleigh fading is less than 10−5with normalized delay spread of up to 0-7 and 0-2 for DPSK and DQPSK, respectively. When equal-gain combining is used, BER of less than 10−4 is obtained under Rayleigh fading with normalized delay spread of up to 1.0 for DPSK, whereas BER of less than 10−4is obtained with normalized delay spread of up to 0-4 for DQPSK.