Mobility

Inverting Wireless Collision Avoidance

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Executive Summary

The authors describe grant-to-send, a novel collision avoidance algorithm 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. They present evidence that inverting collision avoidance in this way greatly improves wireless mesh performance. Evaluating four protocols from 802.11 meshes and 802.15.4 sensor networks, they find that grant-to-send matches or outperforms CSMA and RTS/CTS in all cases. For example, in a 4-hop UDP flow, grant-to-send can achieve 96% of the theoretical maximum throughput while maintaining a 99.9% packet delivery ratio. They also find that grant-to-send is general enough to replace protocol-specific collision avoidance mechanisms common to sensor network protocols.

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