Helper initiated distributed cooperative medium access control protocol for wireless networks

Abstract

Cooperative data transmission is one of the most significant techniques to mitigate fading induced errors in wireless networks. The key idea in cooperative data transmission is that of resource sharing among multiple nodes in a network. This idea enables to design technologies using efficient spectrum utilizations. Although multiple input multiple output system provides a single node to be equipped with multiple antennas, relative higher cost in implementing this system is a barrier. Spatial diversity for wireless transmission requires more than one antenna at the transmitter. However, mobile devices are usually limited by size, so installation of multiple antennas increases the hardware complexity significantly. Due to the omnidirectional nature of wireless signal, a data transmission between a source node and a destination node can be overheard by many other neighbor nodes. By exploiting this characteristic, a number of recent research activities on cooperative Medium Access Control (MAC) have been devised where low data rate stations are assisted by the high data rate stations in forwarding data traffics. Therefore, wireless devices with a single antenna can effectively form a virtual array of antennas by sharing each other’s antennas in a multiuser environment. In this thesis a mathematical model is derived for the performance analysis of the legacy IEEE 802.11 DCF MAC using markov chain. This thesis proposes a new distributed cooperative MAC protocol and evaluates the proposed protocol’s performances using mathematical modeling. In the proposed protocol a potential relay node initiates itself to participate in the cooperation by calculating supported data transmission rate between source to relay and relay to destination links. Mathematical analysis of the proposed protocol in error prone channel and flat fading Rayleigh environment is presented in this thesis. Performance of the proposed scheme is compared with that of the existing IEEE 802.11 DCF MAC. Numerical results show that the proposed scheme can increase throughput and decrease average frame delay of any IEEE 802.11 Wireless LAN’s low data rate station comprehensively.