Research On Analysis Of Adaptive Resource Allocation Algorithms For OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) technique is capable of suppressing inter-symbol interference (ISI) caused by multipath propagation, confronting multipath fading and improving the efficiently of spectrum resource. As the hotspot of future mobile technologies, OFDM has been widely and deeply researched. It is considered to be the most promising technology of the next generation wireless communication system. The Adaptive OFDM is a very important researching field at present. The algorithm that determines how many subcarriers to occupy for each user and how many bits to transmit in each subcarrier to maximize system performance is called Adaptive Resource Allocation algorithm or Adaptive Subcarrier, Bit and Power Allocation algorithm. It is one of the key technologies in OFDM system, also it is the article's key point.Firstly, this dissertation analyzes characteristics of wireless channel fading, then simply introduces the principle of OFDM scheme and the implement of OFDM system. The principle and the steps of bit allocation algorithm based on single user OFDM system is introduced in detail, Performances of some classic bit allocation algorithms such as Hughes-Hartogs algorithm,Chow algorithm,Fischer algorithm,and Czylwik algorithm are analyzed and compared. An improved algorithm of minimum transmit power is proposed. According to the result of MATLAB simulation, The performance of the algorithm is close to H-H algorithm but the complexity of computing is reduced. Finally, we mainly discuss the algorithms of subcarriers allocation used in Multiuser OFDM system. The problem of assigning subcarriers and power to different users in OFDM System has recently been an area of active research. Combining the subcarrier allocation and bit loading, the dissertation proposes an improved multi-user algorithm of adaptive OFDM for better proportion. The aim of the algorithm is to reduce the total power needed by the system and improve the efficiency of frequency resource with the assurance of transmission QoS While maintaining proportional fairness. Compared to the traditional algorithm, The proposed algorithm has significantly lower complexity, and in simulation, yields better performance. The sum capacity is distributed more fairly and flexiby among users than traditional algorithms. .