Rate-Control and Queueing of Backhaul Downstream Traffic for Mobile Wireless Systems

A backhaul network in mobile wireless systems consists of lower-level base stations (BSs) and upper-level access routers (ARs). While the legacy model considers only a queue at a BS for downstream traffic, we focus on queues at both the BS and the AR, hence calling it the split two-level queueing (S-2Q) model. The transmission rate of the backhaul link between a BS and an AR can be adjusted to stablize the BS queue. We develop a queue-aware rate control algorithm for the backhaul link such that BS queues will suffer neither buffer overflow nor underflow due to drastic short-term variations in wireless channel condition. We then derive the stability conditions of BS queues and propose two strategies, each applicable to handoff and normal (non-handoff) users separately. For handoff users, it is desirable that the BS queue buffers as few packets as possible to improve handoff performance. For normal users, it is desirable that the BS queue buffers as many packets as possible to exploit multiuser diversity of opportunistic scheduling. Our in-depth simulation results have shown that the proposed algorithm stabilizes the BS queue for normal users and reduces handoff latency to 0.8 second from 3 seconds for handoff users.