Optimal forwarding in wireless networks: opportunistic network coding

In wireless networks, unintended nodes in the vicinity of the sender and receiver, potentially causing interference to their own communications, can generally overhear transmissions. Much of the related research has considered this as a nuisance and resulted in various proposals for overcoming the interference using scheduling, channel assignment, and many other mechanisms. In recent years, there has been growing attention to methods that aim to take advantage of the broadcast nature of the wireless medium and the ability of nodes to overhear their neighbors’ transmissions. Two of the most important such methods are opportunistic routing (OR) and wireless network coding (NC), exemplified by the ExOR and COPE protocols, respectively. This thesis presents study of jointly optimizing packet delivery (in terms of reducing transmissions) of forwarding schemes in wireless network that combine elements from both the OR and NC approaches. The key problem is that OR and NC perform best at contrasting scenarios; while OR is beneficial when link delivery ratios are low, NC performs better where link delivery ratios are high. To find an optimal solution by combining both schemes, the problem is restricted to a 2-hop network, where multiple common neighbors relay traffic on a bidirectional unicast connection between two nodes. A dynamic programming algorithm has been presented to find the optimal forwarding scheme as a function of link error probabilities, and demonstrated that it can achieve significant reduction in the number of transmissions compared to either OR or NC employed alone, even in a simple scenario of two common neighbors between the connection endpoints. Numerical results and simulation results are used to analyze the benefits of proposed scheme