【作者】 贾勇；

【导师】 王林；

【作者基本信息】 西安理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 OFDM(正交频分复用)最突出的优点是频谱利用率高、抗多径时延能力强,适合未来高速宽带无线通信的应用。在宽带移动OFDM系统中,不同的子信道经受不同的信道衰落,具有不同的传输能力。需要研究更加有效的无线资源分配及管理策略,以便在有限的带宽上达到更高频谱效率、更高的发射功率利用率以及更好的系统性能。因此自适应资源分配得到广泛关注,是当前OFDM研究热点问题之一。在多径频率选择性衰落信道中,不同的子信道受到不同的衰落,具有不同的传输能力,在多用户OFDM系统中,由于传输路径不同,各用户的信道衰落是相互独立的。各个子信道的衰落情况不一样,对于一个用户呈现出深衰落的子载波不一定对其他用户也呈现深衰落。因此可以考虑一种根据瞬时信道特性来为每一个用户分配子载波的多用户子载波分配方法。这样只有当一个子载波在所有的用户中都处于深衰落时才会被弃用,从而更有效地利用信道资源。目前,对于多用户系统中的资源分配问题有许多研究方法,这些方法大体上可以分为两类:静态分配方法和动态分配方法。静态分配方法有两种典型的分配策略:OFDM-TDMA和OFDM-FDMA。静态分配算法中,子载波和比特的分配是预先设定的,没有充分地利用瞬时信道增益信息。本文主要分析动态分配算法,从给定总数据速率条件下的总体发射功率最小化问题和给定总发射功率限制条件下的数据速率最大化问题两个角度研究了OFDM系统的资源分配问题。本文在已有算法的基础上研究了一种改进的多用户OFDM系统子载波和比特分配算法。本算法采用分步的思想对系统资源进行动态分配,在给定误码率和用户最小传输速率要求的条件下,使系统总的发送功率最小。仿真结果表明,该算法计算简单,优化效率高。更多还原

【Abstract】 OFDM (Orthogonal Frequency Division Multiplexing) has outstanding advantages because that it could utilize frequency resource sufficiently and robust against channel delay spread. It’s suitable for high speed and broadband wireless communication. In broadband OFDM system over mobile fading channels, each individual sub channel has its own attenuation. So each sub channel has different channel capacity. A more efficient radio resource allocation and management scheme should be proved to transmit with higher spectrum and power efficiency and higher system performance. Adaptive allocation of resource gains more and more attention and becomes one of the focuses in OFDM research.In multiuser environment, the so-called ’mutiuser diversity’ by dynamically allocating subcarriers among the users can be used. Since the subcarriers that appear to be in deep fade for one user may not be in deep fades for others, spectral efficiency can be improved, and equivalently, transmit power can be reduced.Now, there are many ways to solve how to allocate the resources. Generally, they can be divided into two classes: fixed resource allocation and dynamic resource allocation. Fixed resource allocation schemes, such as time division access (TDMA) and frequency division multiple access (FDMA), assign an independent dimension, e.g. time slot or sub channel, to each user. A fixed resource allocation scheme is rigid regardless of the current channel condition. This paper mostly analyzes dynamic allocation algorithm. From the total data rate to be under the conditions of the overall transmission power to minimize the problems and limitations of transmission power under the condition of maximum data rate of two angles on the issue of OFDM system resource allocation problem. This paper studies on an improved algorithm for subcarrier and bit allocation in multiuser OFDM systems. The algorithm uses the idea of step-by-step for dynamic allocation of resources and tries to minimize the total transmission power with given BER and each user’s requirement on minimum rate. Simulation result shows that the proposed algorithm is simple in calculation and high in efficiency.更多还原