Research On Resource Allocation In OFDMA Based Cooperative Networks

Nowadays, people are more concerned about the quality of service (QoS) and data transmission rate of communication system. High data rate and High capacity rely on frequency spectrum, which is really rare in mobile telecommunication system.How to use these limited resources to satify different users with different QoS requirements becomes an important issue in future wireless telecommunication researches.OFDM has been selected as the core technology in physical layer of future wireless telecommunication system due to its ablity to conquer multipath fading and high utilization rate of frequency spectrum. Diversity technology is also quite useful to conquer fading. However,the traditional diversity technology is realized by antenna array,which is not applicable to the user equipment due to its limited size and costs. So the cooperative diversity technology becomes a new solution,which is based on the theory of relay channel. With the help of the relay station,it can form a virtual MIMO system to make the communication more reliable.The data rate and reliability of the communication will be dramatically improved if OFDM and cooperative technology are combined together.In this dissertation, we mainly focus on the impact of the positon and work mode of relay stations to the capacity of OFDMA networks. Meanwhile, we also proposed an algorithm of resource allocation in multi-hop cooperative OFDMA networks.Firstly, we give some background information of OFDM technology as well as some current researches in the resource allocation of OFDM networks.Then basic cooperative communication theory is introduced and by using three node model and two work mode of relay station:Decoded and Forward, Amplified and Forward are mainly discussed.Secondly, the impact of position and work mode of relay station to the capacity of single cell networks is analyzed. According to the simulation results, the optimal relay position is given.And DF mode outperforms AF mode under the same conditions.Lastly, a cross-layer design based on AU function is proposed to measure the users' satisfaction of the QoS and working as the QoS optimization objective. Due to the complexity of the optimization objective and mixed constrains,the total relay selection combined with resource allocation algorithm is divided in to two subproblems:the optimal relay-subcarrier selection and a heuristic power allocation among users and relays on each subcarrier. According to the simulation results, the AU function seems to be efficient and the proportion of different QoS factors can be adjusted so as to satisfy various requirements of services.