Sensor Network Media Access Design

Wireless Sensor Networks impose additional challenges on Media Access Control mechanisms. Many schemes have been proposed that use either CSMA or TDMA protocols; however design of a CSMA protocol for WSNs must be more than a general purpose mechanism. In this work, we analyze the parameters of a CSMA layer and their affect on performance. We examine how to use upcalls to notify applications of the underlying channel utilization to enable an application to change its sampling phase, sampling interval, or aggregation methods. To increase performance, an effective carrier sense algorithm is presented for collision avoidance (CA). Using these principles, we implemented a CSMA-CA scheme called B-MAC on the UC Berkeley mica2 platform. B-MAC raises the maximum theoretical bandwidth of the mica2 from 42 packets/sec to 53 packets/sec, outperforms the default 802.11-style TinyOS MAC layer by over 100% (in terms of packet throughput) and achieves 85% channel utilization. B-MAC shows the need for application coordination in wireless sensor network media access layers.