Research On The Opportunistic Communication Protocols In IEEE 802.11 Based Mesh Networks

IEEE 802.11 based wireless mesh networks are designed to provide extendable,convenient and cheap Internet access.However,due to the limitation of bandwidths and unpredictable random packet losses in wireless networks,mesh networks can't fully satisfy the increasing demands for throughput from applications such as online high definition videos and file sharing.Motivated by these problems,in this thesis,we propose new protocols on opportunistically exploiting the diversity in wireless networks to significantly improve the throughput and stability of wireless mesh networks.The main characteristic of wireless networks is the uncertainty:randomness in users' locations,behaviors and environments interacting with complicated signal attenuations,leads to random independent link statuses.These random independent signal attenuation processes,which are usually defined as diversity,can be utilized through multiple antennas or multiple users.In this thesis,we propose new architectures to exploit the multi-user diversity of wireless mesh networks in an opportunistic way with small synchronization and control overhead by jointly utilizing the randomness in intra-flow network coding and the dynamic nature of the 802.11 MAC.The main contents of this dissertion are as following:A new opportunistic patch protocol is designed.The protocol performs error recovery at intermediate nodes using multi-user diversity by allowing nodes opportunistically broadcast the corrupted packets for one hop.The nodes which can help to recover the corrupted packet opportunistically generate patches for the packet,route the patch to help the nodes to eliminate noises.A network coding based opportunistic retransmission protocol is proposed.We design a new online network coding for multiple senders with incomplete knowledge to a receiver.Simulation results show that the new algorithm can select intermediate nodes closer to the destination to relay packets in an efficient way.A new algorithm to coordinate the forwarding nodes in opportunistic routing is proposed.We present a reliable opportunistic data link layer exploiting the multiuser diversity by jointly utilizing the diversity of random access feature in 802.11 MAC and the randomness of intra-flow network coding.Simulation results show that the algorithm can reduce the retransmission count and achive high throughput gains.We give an analysis model to characterize the short term unfairness of IEEE 802.11 and its impact to the route stablebility of multihop wireless networks.Unlike former scheduling algorithms work precisely on separated links and only allow one link to transmit at a time,however,the link scheduled to transmit may still wait for packets from its upstream links and is not ready to send,we leverages this constraint by opportunistically selecting a group of links to transmit and utilizes 802.11 DCF to coordinate the links.Simulation results show that the algorithm can reduce end-to-end delay and achieve high throughput gains.