Efficient And Fair Communication Protocols For Wireless Mesh Network

Our life has been changed by the developing wireless communication technologies,from which we can enjoy the convenient services and easy accessing to Internet.Widely used in Wireless Local Area Network(WLAN),IEEE 802.11 provides cheap wireless connection to Internet.However,most WLANs used today are designed in Infrastructure mode.All the clients get to the Access Point by one hop wireless connection which is connected to Internet by wired cable lines.Therefore, the coverage of WLAN is relatively smaller compared to the wired network.In addition,since the coverage of wireless network depends on the availability of cable lines,it increases the cost of building multiple WLANs to cover a larger area completely.Thus,in order to expand the coverage of wireless signals,and to reduce the cost,a new concept "Wireless Mesh Network" is proposed.It has been deployed in areas including medical care system,oil and coal industry,as well as public safety.In wireless mesh network,data packet is forwarded to the destination node by multiple hops before it arrives at the destination or the gateway node.Conventional communication protocols in layers of the protocol stack cannot fully adapt to this new feature,which makes the end-to-end transmissions inefficient and unfair.Aiming to improve efficiency and fairness of data transmissions in wireless mesh network,we focus on the following three issues,"distributed multi-hop transmission mode","unstability and asymmetry of wireless links",and "Interference between wireless links in shared spectrum" in this dissertation.We investigate the reasons why traditional communication protocols are inefficient and unfair for multi-hop transmissions.By optimizing and re-designing the protocols in transport layer,network layer,and media access control protocols,efficiency and fairness of communication protocols are well improved,and a series of fantastic solutions are presented.First of all,in order to find the reasons why transport layer protocols are inefficient in mesh network,we model the TCP fairness problem in wireless mesh network.It is found that fairness of TCP protocols in wireless mesh network is affected by the hop count from the source to the destination,number of neighbors of a node,traffic load on each node,and the retransmission counter.Then,a MAC error warning method for SCTP over high bit error rate wireless network is designed using cross layer design method,which improves the performance of transport layer protocols by keeping the size of congestion window.Secondly,we design a new routing metric for multi-radio and multi-channel wireless mesh network,which considers the transmission interference and load balance between neighbor links.Then,taking the asymmetry of wireless link into account,we propose a directional double metric routing metric,and design an AODV-based routing protocol.Two different routing paths can be created between source node and destination node by only one route discovery process.Furthermore, we design and implement multi-radio mesh nodes to investigate the performance of routing protocols on multi-radio mesh network.Transmission performances of single-radio and multi-radio mesh network are compared from experiment results of different experiment scenarios.Thirdly,we consider how multi-radio multi-channel techniques affect opportunistic routing in mesh network.By numerical analysis and simulation results, we explain why multi-radio multi-channel can improve the performance of opportunistic routing,and propose a new channel assignment method to improve the efficiency of system.In order to achieve better efficiency as the size of mesh network grows,we design a dynamical distributed spectrum sharing algorithm to ensure the coexistence of different wireless systems on unlicensed band.It enhances the system capacity by reducing the interference between neighbor transmission pairs.Additionally,a fixed channel assignment method is proposed for 2.4GHz wireless mesh network. Transmission efficiency of UDP and TCP are highly improved by interference cancellation algorithms and multi-user mode of MIMO.At last,to ensure the heterogeneous mesh nodes fairly share the wireless resource in mobile mesh network,we design an adaptive packet size adjusting algorithm to guarantee fairness among flows in mobile wireless mesh network.