REDUCTION OF THE ERROR FLOOR OF MSK BY SELECTION DIVERSITY

We examine the error floor of minimum shift keying (MSK) when the rece iver uses selection diversity, Both received signal strength indicatio n (RSSI)-driven diversity and bit error rate (BER)-driven diversity ar e analyzed. The considered channel is a two-delay Rayleigh-fading chan nel; detection is done by differential detectors with either fixed or adaptive determination of the sampling time. Analysis is based on the method of error regions, where the instantaneous impulse response is r epresented by phasors in the complex plane. We first compute the joint probability density function (pdf) of the phasors of the two diversit y branches. Depending on the selection criterion, the error probabilit y is then computed as an integral over certain functions of this pdf, In the limit of small delay spreads S, the integrals are evaluated ana lytically. For fixed sampling, the admissible delay spread for BER = 1 0(-3) is increased by about a factor of three (as compared to the no-d iversity case) for RSSI-driven diversity and a factor of four for BER- driven diversity. For adaptive sampling, RSSI-driven diversity gives l ittle improvement in the admissible S for BER = 10(-3) while BER-drive n diversity increases it by some 50%. Results are confirmed by compari son with Monte Carlo simulations and measurements.