Wi-Fi Goes to Town: Rapid Picocell Switching for Wireless Transit Networks

TLDR: This paper introduces new buffer management algorithms that allow participating APs to manage eachOthers' queues, rapidly quenching each others' transmissions and flushing each others', making the system effective at modern 802.11 bit rates that need frame aggregation to maintain high spectral efficiency.

Abstract: This paper presents the design and implementation of Wi-Fi Goes to Town, the first Wi-Fi based roadside hotspot network designed to operate at vehicular speeds with meter-sized picocells. Wi-Fi Goes to Town APs make delivery decisions to the vehicular clients they serve at millisecond-level granularities, exploiting path diversity in roadside networks. In order to accomplish this, we introduce new buffer management algorithms that allow participating APs to manage each others' queues, rapidly quenching each others' transmissions and flushing each others' queues. We furthermore integrate our fine-grained AP selection and queue management into 802.11's frame aggregation and block acknowledgement functions, making the system effective at modern 802.11 bit rates that need frame aggregation to maintain high spectral efficiency. We have implemented our system in an eight-AP network alongside a nearby road, and evaluate its performance with mobile clients moving at up to 35 mph. Depending on the clients' speed, Wi-Fi Goes to Town achieves a 2.4-4.7x TCP throughput improvement over a baseline fast handover protocol that captures the state of the art in Wi-Fi roaming, including the recent IEEE 802.11k and 802.11r standards.