دانلود رایگان مقاله استراق سمع مجازی: راه موثر برای افزایش فرصت برنامه نویسی شبکه در شبکه های بی سیم ادهاک

Abstract

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.

7. Conclusions and areas for future improvement

In this paper, we took advantage of a recently proposed new technique called virtual overhearing (VOH) to benefit the routing performance in multi-hop wireless ad-hoc networks. We presented two modes of utilizing VOH and designed two network codingaware routing protocols in this paper. The first protocol, DCARVOH, makes a new incoming flow aware of existing VOH during the route discovery and allows it to find a route with coding opportunities. The second protocol, DCAR-VOH+, makes further use of VOH to create coding opportunities between two established flows which are currently unmixable. As a result, there are many more coding opportunities in DCAR-VOH+ compared with DCARVOH. Furthermore, we proposed an adaptive encoding mechanism for the two routing protocols to ensure all coded packets could be decoded. Extensive simulation results showed that in different network scenarios both DCAR-VOH and DCAR-VOH+ can discover or create extra coding opportunities compared with the two well-known network coding schemes, DCAR and COPE, resulting in improved network performance. In particular, a network with either the inter-cluster traffic or the three-node cyclic traffic favors both DCAR-VOH+ and DCAR-VOH, and with the two modes of VOH usage implemented, DCAR-VOH+ generally outperforms DCAR-VOH. To further improve DCAR-VOH and DCAR-VOH+, the future work can be as follows.