Virtual overhearing: An effective way to increase network coding opportunities in wireless ad-hoc networks

Overhearing is of great importance to wireless network coding in that it can be exploited to obtain the side information needed for packet decoding. Recently, a new technique called virtual overhearing (VOH) was proposed to allow a node to obtain the packet sent by another node that is multiple hops away for free. This can overcome the limitation of overhearing and be used to discover more coding opportunities. In this paper, we take advantage of VOH and propose two modes of exploiting VOH to increase coding opportunities in wireless ad-hoc networks. First, we make use of VOH to increase the chance of finding a route with coding opportunities for a new incoming flow. Second, and more importantly, we make use of VOH to create coding opportunities between two established flows which are currently unmixable. Note that most previous studies only attempt to find coding opportunities rather than create them. Based on these two modes of VOH usage, we design two routing protocols: distributed coding-aware routing with virtual overhearing (DCAR-VOH), and its enhanced version DCAR-VOH+. DCAR-VOH implements only the first mode of usage, whereas DCAR-VOH+ incorporates both modes of usage. Our extensive simulations indicate that VOH provides an effective way to discover coding opportunities, resulting in improved network performance. The positive effect of the second mode of usage stands out especially.