Level crossing rate and average fade duration for time diversity reception in Rayleigh fading conditions

Abstract

Time diversity, in which the same data are transmitted several times, is attractive in digital land mobile radio and is simple to implement because only one antenna is required. Expressions for the level crossing rate (LCR) and average fade duration (AFD) are derived in this paper for a system in which each data symbol is transmitted twice (two-branch diversity). As far as LCR is concerned, the expected diversity advantages can be obtained for a data repetition period, normalised by the maximum Doppler frequency, of about 0.2. For a large data repetition period, the AFD is halved. Measured values of LCR and AFD, obtained from 900 MHz signals received at a base station site, are in good agreement with the predicted values.