Simulating Cooperative Diversity Protocols for Multi-hop Wireless and Sensor Networks

This paper discusses the simulation of Cooperative Diversity Protocols (CDP) which have emerged as a promising technique for improving reliability in a wireless environment. In CDP, neighboring node(s) cooperate with a transmitter to deliver multiple copies of a packet to a receiver, via independent fading channels. These multiple copies can be combined at the receiver to recover the original data. Researchers have proposed CDP at the physical and Medium Access Control (MAC) layers which exploit this behavior to improve reliability. This also improves the overall system energy efficiency by reducing the number of retransmissions required. However, the performance evaluation of such CDP has been limited to either analytical results or a simple three node scenario, comprising a single source-partnerdestination setup. This is because CDP requires cooperative functions such as partner selection, cooperative addressing, packet combining, and three-way handshaking between sourcepartner-destination which are absent in conventional simulation and hardware platforms. Our previous work has shown that performance of CDP in such three node setups nodes might not reflect the actual behavior of the protocols because factors such as channel contention and collisions are simply not present. In this paper, we identify the functions needed to simulate cooperative protocols at different layers of the communication protocol stack. We use OMNet++ with MiXiM as a reference framework as it very closely resembles the TCP model. Challenges arising from simulating large scale networks, redundant packet storage, and energy utilization are also discussed. Keywords—Cooperative Diversity; Simulation; OMNet++; MiXiM; Media Access Control; Reliability.