About this Book

CSMA-based wireless mesh networks are vulnerable to collisions. Even a single unicast flow can exhibit excessive collisions from hidden terminals. Furthermore, fairness objectives for single-hop networks can cause undesirable behaviors for mesh networks. Mesh networks of wireless sensors suffer from undesirable protocol interactions due to these challenges. Inter-protocol collisions and unfair channel usage between protocols cause the behavior of one protocol to change depending on other protocols. These inter-protocol interactions complicate the design of large sensor network systems. Motivated by these problems, this dissertation presents grant-to-send, a novel collision avoidance mechanism for wireless mesh networks. Rather than announce packets it intends to send, a node using grant-to-send announces packets it expects to hear others send. This dissertation provides evidence that inverting collision avoidance in this way greatly improves wireless mesh performance without significant overhead. Grant-to-send is simple to implement, and is compatible with existing hardware. Grant-to-send is also general enough to replace protocol-specific collision avoidance mechanisms common to sensor network protocols. While these individual mechanisms only avoid intra-protocol collisions, grant-to-send provides a MAC mechanism which can address both intra- and inter-protocol collisions. This dissertation also proposes a fairness scheme for mesh networks, which can be applied to protocol fairness. The fairness scheme combines and modifies traditional flow-based fairness techniques such as fair queueing and fair scheduling. However, the complexities of wireless make these mechanisms insufficient by themselves. This dissertation therefore proposes two new mechanisms that address these limitations, channel decay and fair cancellation, and shows that the fairness scheme can significantly improve protocol fairness. Together, this dissertation shows that achieving collision avoidance and fairness can make mesh networks perform better, more reliable, and thus easier to design.