Research On Adaptive Resource Allocation Algorithms For OFDM Systems

With the rapid growing of wireless applications, the conflict between the limited wireless resource and the increasing Quality of Service (QoS) requirement of multi-media traffics becomes more and more urgent. It involves various technologies from different layers of wireless systems to reconcile the conflict. At the physical layer, Orthogonal Frequency Division Multiplexing (OFDM) is an efficient capacity approaching technique for broadband wireless systems; At the data link layer, resource optimization is a vital way to increase the system throughput and the utilization of wireless resource while providing the QoS requirement of multimedia traffics. In this dissertation, under the guidance of multiuser information theory, the resource optimization techniques in OFDM systems are intensively studied.Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique with high spectral efficiency. It divides wireless channel into N orthogonal subchannels, then converts high speed serial bits stream to parallel and transmit through lower speed subchannels. So it can support high speed data service, and has strong capacity of combating with multipath interference. Simultaneously,OFDM can dynamically allocate system resources (such as bit, power,etc.) according to subchannel's fading and multipath delay characteristics, and every subcarrier can carry on self-adaptation modulation. Thus, it has much strong flexibility, and can not only improve the utilization efficiency of system resources, but also meet user's different capacity demands.Dynamic allocation of resources in OFDM system primarily adjusts transmission power subcarriers and bits amount according to real-time channel status information .The methods of dynamic resource allocation are researched in this paper. First, the development, advantages and disadvantages , basic principle of OFDM are given. Second, the idea and superiority of dynamic resource allocation is introduced.Then much more researches are made on the power and bit allocation algorithms for single-user OFDM systems and a simplifying algorithm is presented . Finally , the dynamic resource allocation in multi-user OFDM systems is discussed greatly. Several sub-optimal algorithms are researched. The main results of this thesis are:①.A better simplifying greedy algorithm is presented for power and bit allocation in single-user OFDM systems. Simulations and the problem analysis are done.②. An improved allocation algorithm possessing equity is introduced because of the disadvantage of existing algorithm .Simulation has done to prove that our algorithm has the performance close to the multi-user waterfilling algorithm which is a joint allocation algorithm and has the lower computational complexity than it. Our algorithm also can be used in actual systems.③.This paper also presents a new subchannel allocation method, simulation results show that the algorithm also have good performance.