Research On Adaptive Resource Allocation Algorithm For OFDM Cooperative Relaying System

In recent years, wireless communication technology develops rapidly. However,multipath fading characteristics of wireless channel led to severe inter symbol interference(ISI), and has a serious influence on service quality and data transmission rate ofcommunication system. Orthogonal Frequency Division Multiplexing (OFDM) is a specialkind of multi-carrier modulation scheme, OFDM technology has the advantages of highspectrum efficiency, strong ability to resist multipath time delay, capability to eliminate theISI, it is regarded the preferred modulation technology of wireless communication system.Diversity is also a way to resist multipath fading and enhance the reliability of transmissioneffectively. Multiple Input Multiple Output (MIMO) technology is a typical example ofdiversity, it can achieve space diversity, resist wireless fading channel, and increase thechannel capacity through the antennas installed in the transmitter and the receiver. On thecondition of wireless spectrum resources are scarce and expensive, the advantages ofMIMO technology has been widely recognized. However, MIMO technology has a highdemand of system transmission power, antenna distance and mobile terminal size, so it ishard for MIMO technology to apply in the actual system.Cooperative communication technology is a special kind of space diversity, it canmake full use of the radio characteristics of radio waves. The wireless nodes in the networkcooperate mutually to form a virtual antenna array to obtain space diversity gain oftraditional MIMO technology. Cooperative communication technology combines theadvantages of diversity technology and relay transmission technology, it can solve theproblems of the sender and the receiver antenna technical without any increase of hardware,and provide a new way for the application of MIMO technology. Cooperativecommunication technology not only can effectively improve the system capacity, reducenetwork overhead, expand the coverage area, but also can be combined with other keywireless communication technology flexibly.Wireless resource management and optimization has always been concerned by people.Adaptive resource allocation algorithms of the system dynamically allocate subcarrier andpower, according to the requests of different business, different quality of service and theinstantaneous channel state information. When combining OFDM technology andcooperative relay technology, it not only can effectively resist multipath fading and improvespectrum efficiency, but also can improve system capacity and expanding coverage. Thesetwo technologies give full play to the advantages. There will be more and more users andneeds of the communication business in future communication system, as a result, adaptiveresource allocation problem in cooperative relay OFDM system has become a hot spot ofresearch in the next generation wireless communication system. At present, the research on resource allocation problem in cooperative relay OFDMsystems most based on different QoS (Quality of Service) guarantee. In the actualcommunication system, different users have different requests of QoS. In order to meet therequirements of users better, this paper puts forward an adaptive resource allocationalgorithm based on different time delay business for half duplex amplifying cooperativecommunication system. There are both delay-constrained (DC) and non-delay-constrained(NDC) traffic in this algorithm. The DC users are at constant rates and NDC users are atvariable rates. In the process of subcarrier allocation, considering the differences of channelcharacteristic between the two-hop relay links, two algorithms on subcarrier matching andno-matching are proposed. In the process of power allocation, an optimal power allocationalgorithm is obtained based on the Lagrange multiplier method and the KKT(Karush-Kuhn-Tucker) conditions, considering the high calculation complexity of theoptimal solution and inappropriate application in actual system. Therefore, this paperpresents a heuristic power allocation algorithm, this algorithm reduces the computationalcomplexity and more suitable for system implementation.Simulation results show that the proposed algorithms in this paper can guarantee DCusers to achieve the target data rate and reduce the required transmission power. At thesame time, the proposed algorithms can maximize the sum rate of the NDC users, and it cansatisfy the QoS requirements of different time delay in the system.