A unidirectional link exists in an ad-hoc network when a node B is within the transmission range of another node A while node A cannot directly hear node B. However, a reverse route from B to A might exist, by going through multiple nodes. Unidirectional links may exist in an ad hoc network due to variation in transmission power of different nodes, noise or other signal propagation phenomena, and heterogeneity in transmission hardware of nodes in the network In this paper, we statistically analyze the connectivity of ad hoc networks in the presence of unidirectional links. We generate several random topologies employing two models and study the connectivity of the sub-graphs formed by including unidirectional links of different reverse-route lengths. We observe from this analysis that the connectivity has a heavy-tail distribution and that using only bidirectional links could cause partitions in the network. This analysis also shows that the inclusion of unidirectional links with short reverse-routes (2-3 hops) is often sufficient to restore good connectivity in unidirectional networks.
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