Stability of Wireless Random Access Systems

Abstract

We characterize the stability, metastability, and the stationary regime of traffic dynamics in a single-cell uplink wireless system. The traffic is represented in terms of spatial birth-death processes, in which users arrive as a Poisson point process in time and space, each with a file to transmit to the base station. The service rate of each user is based on its signal to interference plus noise ratio, where the interference is from other active users in the cell. Once the file is fully transmitted, the user leaves the cell. We derive the necessary and sufficient condition for network stability, which is independent of the specific path loss function as long as it satisfies mild bound- edness conditions. A novel observation, shown through mean- field analysis and simulations, is that for a certain range of arrival rates, the network appears stable for possibly a long time, but can suddenly become unstable. This property is called metastability which is widely known in statistical physics but rarely observed in wireless communication. Finally, using mean- field analysis, we propose a heuristic characterization of the network steady-state regime when it exists, and demonstrate that it is tight for the whole range of arrival rates.