Interaction Engineering: Achieving Perfect CSMA Handshakes in Wireless Networks

摘要

Carrier Sense Multiple Access (CSMA) protocols are unable to effectively arbitrate the medium in wireless networks; problems such as hidden and exposed terminals occur frequently leading to collisions, poor performance and unfairness. CSMA networks can be optimized by careful tuning of transceiver parameters, such as transmission power and carrier sensing threshold, to maximize spatial reuse of wireless channel while minimizing collisions. However, existing studies fail to jointly optimize these parameters to eliminate collisions and maximize spatial reuse. Our approach leverages on the observation that links under CSMA interfere in one of the few discrete interaction modes; each mode leads to different behavior in terms of performance and fairness. The proposed methodology controls the transceiver parameters to convert destructive interaction modes (such as various types of hidden terminals) into constructive ones; we call this approach Interaction Engineering (IE). In this paper, we first formulate a model and centralized algorithm that computes the parameters based on one-to-one interaction between the links. We then develop a distributed IE protocol. We evaluate the protocols under Wireless LAN and multi-hop wireless networks using both simulation and testbed. We show that IE eliminates a vast majority of the collisions and significantly boosts spatial reuse. For example, in the WLAN scenarios, we observed a median improvement of $4times$ in throughput and more than $2.5times$ improvement in fairness, and orders of magnitude improvement in connection delay and jitter. IE also shows significant improvements in multi-hop networks, and under different forms of traffic such as video and TCP.