Research On Cooperative Routing In Multi-hop Wireless Networks

Due to complicated network environment,multi-hop wireless network faces strong multipath fading effect which seriously influences the wireless transmission,and it’s necessary to adopt effective method to mitigate fading to enhance the quality of wireless network.Cooperative communication(CC)has gain a lot of rencent interests and aplications.CC can allievate channel fading,increase wireless transmission capacity and reliability,enlarge wireless transmission range,and save transmission energy.CC exploits the broadcasting characteristic of wireless channel and organizes the single antenna terminator in multiple users’ environment to form a virtual antenna array.The device participating in CC can mutually forwarding message,and multiple copies of the same message can arrive the receiver via different wireless channels,and the cooperative diversity gain.The advantage of CC has been comprehensively in single-hop wireless network.However,its performance decreases significantly in multi-hop wireless network due to co-channel interference.This dissertation combines multi-radio multi-channel technique and studies the problem of cooperative routing and channel assignment by considering the fairly resource allocation.The main contribution is as following:(1)Existing cooperative routing algorithms don’t consider fairness of allocating network resource and make some flows’ throughput too small,resulting in that users under these flows treated unfairly.To solve this problem,the problem of fair cooperative routing is studied,and a distributed Fair Cooperative Routing algorithm in Multi-Gates wireless mesh network(FCRMG)is proposed.Firstly,the algorithm divides the network into multiple overlapped clusters,and models the problem of fair cooperative routing as a convex optimization,whose objective function is maximizing the sum of logarithm of flows’ throughput to pursue the fairness.Then,a distributed dual decomposition and subgradient method is used to deterimine the cooperative route and transmission rate.The simulation results shows that FCRMG can largely improve the throughput of the minimum flow without decreasing the total network throughput,which make flows use network resources more fairly.(2)For multi-radio multi-channel wireless network,recent cooperative routing algorithms don’t consider channel assignment under limted number of radios on the node.To take advantage of cooperative diversity gain as well as reducing co-channel interference,the problem of joint cooperative routing and channel assignment is studied.At first,by considering the transmission characteristic of many-to-one,a cooperative module virtualization method is designed.Based on the method,the problem of joint cooperative routing and channel assignment is simplified as the problem of joint direct routing and channel assignment,and it is proved as NP-hard.Then,a relaxed joint cooperative routing and channel assignment algorithm(L-JCRCA)is proposed.The algorithm loosen the constraint condition and relax the model to a linear programming problem.After obtain the primary solution,the number of channels for some nodes may be more than the number of their radios and a local channel adjustment procedure will be operated.The simulation result shows that L-JCRCA can effectively improve network throughput.(3)The centralized algorithm needs to obtain the global network information.Although it can achieve the optimal solution,it’s not practical to implement it in a real network.Hence,a distributed algorithm of joint cooperative routin and channel assignment is proposed.The algorithm is consist of two steps.In the first step,a routing metrice of RATC(Reminder Available Transmission Capacity)is designed.Based on the metric,a distributed cooperative routing algorithm is presented to make flows pass through network more evenly and share nodes as few as possible.In the second step,by considering the characteristic of the cooperative link,a distributed channel assignment based on graph coloring is proposed to reduce co-channel interference.Compared with traditional channel assignment algorithms,the proposed method is suitable for both direct links and cooperative links.The simulation result shows that our algorithm can effective improve network throughput under different network environment.(4)In order to save the power consumption of the wireless network under guaranteeing the minimal bandwidth for some important application,a power-bandwidth cooperative routing metric is designed.Based on the metric,a distributed cooperative routing algorithm for multi-radio multi-channel wireless network with limited energy.The algorithm is consist of three part: cooperative route selection,links’ channel adjustment and nodes’ power adjustment.The cooperative route selection is used for finding a reasonable cooperative route for new arrival flow.The links’ channel assignment is used for adjusting channels of forwarding links of new arrival flow.When the transmission rate of some links can’t meet the requirement of its minimal bandwidth,the nodes’ power adjustment procedure will be called to improve transmission power of these links.The simulation result shows that the algorithm can effectively save the network energy under guaranteeing the requirement of minimal bandwidth.In summary,this dissertation studies the fairness problem of cooperative routing.And by combining multi-radio multi-channel technique,several cooperative routing and assignment algorithms are proposed for different network environment to satisfy the users’ requirement of QoS and energy consumption.