ALOHA WITH CAPTURE OVER RAYLEIGH FADING LOCAL RADIO CHANNELS.

The effects of capture on the average system throughput and delay performance of slotted Aloha have been analyzed for slow and fast Rayleigh fading radio channels. A short-range multipoint-to-base-station packet radio network is considered. Several different definitions of capture are considered where the bit error probability is used as a criterion. The authors show that larger capture effects and thus improved network performance can be achieved with proper choice of modulation and that the use of space diversity and/or simple error-correcting codes improves capture. It is concluded that the inverse distance variability of the received signal is the main reason for the capture effect. The Rayleigh fading alone yields a very small contribution in terms of throughput. Numerical results are presented for a slotted Aloha system with 50 users. It is found that the maximum average throughput can be increased from about 36% to almost 60% by using coding and diversity.