The near/far effect in local ALOHA radio communications

Abstract

The ALOHA protocol allows many uncoordinated terminals to transmit data packets through a common channel. The application of ALOHA to short range (indoor or mobile) radio systems containing mobile terminals that send packets to a central base station is studied. In such systems, terminal-to-base distances can be vastly different and there can be pronounced shadowing. This gives rise to a capture effect at the receiver, where the packet arriving with the highest energy has a good chance of being detected accurately, even when other packets are present. It is well known that this capture effect improves the throughput and delay characteristics of the system as a whole. One of the principal findings is that even the user with the weakest signal shares in these improvements. This result is derived for the realistic case in which each terminal has a buffer to store packets that arrive while the terminal is waiting to transmit packets that were destroyed in earlier collisions.