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. We show that larger capture effects and thus improved network performance can be achieved with proper choice of modulation. We also show that the use of simple error-correcting codes improves capture. The use of selection diversity also improves the capture effect both for fast and slow fading. 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, nonetheless, it helps to stabilize the system. Numerical results are presented for a slotted ALOHA system with 50 users. We have found that the maximum average throughput can be increased from about 36 percent to almost 60 percent by using channel coding and space diversity.
All Science Journal Classification (ASJC) codes
- Computer Networks and Communications
- Electrical and Electronic Engineering