Cross-layer Scheduling And Resource Allocation In Multiuser OFDM Systems

With the development of wireless mobile communication, the contradiction between the users' increasing business demand for quality of service(Qo S) and the limited spectrum becomes more prominent. In order to solve this contradiction, designers must start from the dimensions of the wireless network. Cross-layer scheduling and resource allocation combines the cross layer optimization design ideas and the traditional physical OFDM resource allocation algorithms, so as to improve overall system performance and ensure the service quality requirements for different types of multimedia services,resulting wider attentions in the future wireless communication systems.In this paper, the multiuser OFDM system of cross-layer scheduling and resource allocation are studied. Firstly,the subject of relevant theories is introduced, including the principle of OFDM technology, the multiuser OFDM system model, the classical scheduling algorithms, and the physical resource allocation algorithms, the dynamic resource allocation problems of Rate Adaptive model and Margin Adaptive model with the relevant solutions are also be analyzed.Secondly, in view of the optimization problem to maximize the total throughput with the limiting condition that different users have different Qo S restricted conditions when the total power is limited in the multiuser OFDM system, an improved resource allocation algorithm based on rate limits is proposed. This algorithm firstly using finite state markov chain to analyze queue state and Qo S of MAC layer, converting the limit the user's biggest packet loss to the lowest physical rate limits, then get rate limit conditions in the physical of subcarrier and power allocation. When making subcarrier and power allocation, give preference to users who need more power to achieve minimum speed, by miniming the consumed power to make more power remained to maximize the system throughput.Simulation results show that the improved algorithm not only enables users to rate eventually get promoted, thus improve the throughput, but also can reduce the interrupt probability.Finally, in view of the authorization of the OFDM system with multiple cognitive radio users and multiple cognitive users, in authorized user interference tolerance, cognitive users lowest rate and the system total transmission power constraint conditions to maximize total throughput of the cognitive users optimization problem is studied, a kind of approximate optimal resource allocation algorithm is proposed. The algorithm based on convex optimization theory, the original problem into the dual problem, iteration method is used to find the optimal solution of subcarrier and power. The simulation results show that the proposed algorithm can not only meet the minimum rate of different cognitive user limits, so as to satisfy the Qo S, but also can further improve throughput.