OFDM自适应资源分配算法研究_

摘 要
正交频分复用(OFDM)技术能够有效抑制信号多径传播所造成的码间干扰、对抗多径衰落和提高系统的频谱利用率，是未来移动通信技术的热点，受到越来越广泛的关注。

OFDM系统的自适应资源分配技术，即自适应子信道、比特、功率分配技术，是根据各个子信道上实时的信道特性，动态地进行子信道、比特和功率分配，可以提高系统的性能，更加有效地利用频带资源。

OFDM系统的自适应资源分配技术是OFDM的关键技术之一，也是本文研究的重点。

本文首先分析无线信道的衰落特性，接着介绍OFDM技术的基本原理及系统实现。

本文基于单用户环境下详细论述自适应比特功率分配算法的原理和步骤，对现有的自适应OFDM算法，如Hughes-Hartogs算法、Chow算法、Fischer算法、以及Czylwik算法的优缺点进行分析比较。

在此基础上提出一种改进的比特分配算法并使用MATLAB进行仿真，结果表明该算法的性能与Hughes-Hartogs 算法接近，但是运算复杂度大大减小。

最后讨论了多用户OFDM系统中的子信道分配问题。

针对多用户OFDM系统，将其子信道分配问题和比特(功率)分配问题相结合，提出一种公平性更好的OFDM多用户自适应子信道分配算法。

算法在系统总的传输速率一定和满足传输质量的基础上，针对各个子信道对于不同用户的实时信道状况，动态地为各个用户进行子信道分配和比特(功率)分配，使系统所需要的发射功率尽可能降低到最小，同时尽可能保障用户之间的公平性。

通过对本文算法进行了理论分析和系统仿真，得到的结果证明:与现有的OFDM自适应算法相比，本文算法可以在保证一定服务质量的前提下，获得更优的系统性能。

关键词: 正交频分复用 自适应算法 资源分配 子信道分配 比特分配 功率分配 公平性
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ABSTRACT
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
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