Slotted Aloha for Networked Base Stations

TL;DR

This paper analyzes the performance of slotted Aloha in networks with multiple base stations, showing how cooperation among stations significantly improves throughput and decoding success rates.

Contribution

It introduces a model for multi-base station slotted Aloha, quantifies the benefits of cooperation, and provides formulas and simulations demonstrating performance gains.

Findings

Peak throughput scales linearly with the number of base stations

Cooperative decoding significantly outperforms non-cooperative methods

Heuristic formulas accurately predict cooperative decoding success

Abstract

We study multiple base station, multi-access systems in which the user-base station adjacency is induced by geographical proximity. At each slot, each user transmits (is active) with a certain probability, independently of other users, and is heard by all base stations within the distance $r$. Both the users and base stations are placed uniformly at random over the (unit) area. We first consider a non-cooperative decoding where base stations work in isolation, but a user is decoded as soon as one of its nearby base stations reads a clean signal from it. We find the decoding probability and quantify the gains introduced by multiple base stations. Specifically, the peak throughput increases linearly with the number of base stations $m$ and is roughly $m/4$ larger than the throughput of a single-base station that uses standard slotted Aloha. Next, we propose a cooperative decoding, where the mutually close base stations inform each other whenever they decode a user inside their coverage overlap. At each base station, the messages received from the nearby stations help resolve collisions by the interference cancellation mechanism. Building from our exact formulas for the non-cooperative case, we provide a heuristic formula for the cooperative decoding probability that reflects well the actual performance. Finally, we demonstrate by simulation significant gains of cooperation with respect to the non-cooperative decoding.