Cross-Layer Interaction Control And Utility-Based Bandwidth Allocation Research For Satellite-Terrestrial Links

With the widespread application of satellite communications, the number of users and types of traffic access to satellites increase, presenting new challenges to satellite communication systems. Using the scare bandwidth resource efficiently and providing satisfactory quality of service for the growing number of users are important problems to be addressed. However, because of the time-variation of feeder links, scarcity of bandwidth resource and the differences of users' traffic demands, bandwidth allocation is a complex problem in satellite networks. To solve these problems, this dissertation studies both issues of cross-layer interaction control and bandwidth allocation that is based on utility functions.To overcome the disadvantages of layered protocol in wireless networks, the coordination layer is introduced to increase the flexibility of protocol stack and to take advantages of layered structure. For four types of cross-layer interaction messages, we illustrate their application in bandwidth allocation scenario. Corresponding message formats are designed, and the working procedures are given for these cross-layer control messages. The advantages of the proposed cross-layer control mechanism are: 1) Channel state information can be acquired by users through cross-layer interactions, and users can request for bandwidth on this basis to avoid resource requesting in poor channel conditions. 2) When the bandwidth of feeder link changes significantly due to the occurrence of laser/microwave links switching event, users can be notified through the interaction of inter-node cross-layer event messages.This dissertation studies bandwidth allocation problem of satellite-terrestrial links based on utility functions. By using utility functions to describe user traffic features quantitatively, and setting the utility value of a system as the sum of all users' utilities, we establish a bandwidth allocation model aimed at maximizing the utility of a system. Different solutions are proposed to the models with different forms of utility functions. When using simple linear utility function, we solve the model directly, and the resulting bandwidth allocation scheme is equivalent to the priority-based scheme. When the utility function is sigmoid, which is more suitable to describe the traffic characteristics, an optimal bandwidth allocation scheme is given with the iteration method. By selecting an appropriate step, bandwidth adjustment is applied to user traffic that is insensitive to bandwidth changes. However, applying it to the computing capability-constrained satellite communication system is hard because of its high complexity. We thus propose an approximate method to solve this problem. By calculating the derivative of the utility function, an appropriate boundary value is selected according to the characteristics of the derivative function. We adjust the bandwidth of a particular type of traffic to this boundary value, and find a simpler bandwidth allocation scheme. When the satellite-terrestrial link switching event occurs, link capacity will change significantly in general, and bandwidth resource should be reallocated for users. We apply the proposed bandwidth allocation scheme to link switching scenario to reallocate bandwidth resource,which can make full use of bandwidth resource and provide better quality of service. Finally, the simulation program of proposed bandwidth allocation scheme is implemented to evaluate its performance. The result shows that the simplified bandwidth allocation scheme can make utility maximum approximately while reducing the complexity significantly.The model and solution proposed in this dissertation have some reference value for other utility-based resource allocation problems and simplify resource allocation schemes.