Routing performance in the presence of unidirectional links in multihop wireless networks

We examine two aspects concerning the influence of unidirectional links on routing performance in multihop wireless networks. In the first part of the paper, we evaluate the benefit from utilizing unidirectional links for routing, as opposed to using only bidirectional links. Our evaluations are based on three transmit power assignment models that reflect some realistic network scenarios with unidirectional links. Our results indicate that the marginal benefit of using a high-overhead routing protocol to utilize unidirectional links is questionable. Most common routing protocols, however, simply assume that all network links are bidirectional, and thus may need additional protocol actions to remove unidirectional links from route computations. In the second part of the paper, we investigate this issue using a well known on-demand routing protocol, Ad hoc On-demand Distance Vector (AODV), as a case study. We study the performance of three techniques for AODV for efficient operation in presence of unidirectional links, viz., BlackListing, Hello, and ReversePathSearch. While BlackListing and Hello techniques explicitly eliminate unidirectional links, the ReversePathSearch technique exploits the greater network connectivity offered by the existence of multiple paths between nodes. Performance results using ns-2 simulations, under varying number of unidirectional links and node speeds, show that all three techniques improve performance by avoiding unidirectional links, the ReversePathSearch technique being the most effective.