MAC Protocols for Wireless Sensor Networks: Tackling the Problem of Unidirectional Links
Experiments have shown that unidirectional links are quite common in wireless sensor networks. Still, many MAC protocols ignore their existence, even though they have a tremendous impact on the performance of both TDMA- and contention based protocols. In contention based protocols the medium may be assumed free when it is indeed busy. In TDMA based protocols two neighboring nodes might get assigned the same slot even though there is an unidirectional link between them. In this paper, the authors discuss the influence of unidirectional links on communication protocols in wireless sensor networks, focusing on MAC protocols. They also present two protocols that do not only eliminate the negative side effects of unidirectional links, but use them for message transmission as well.