【作者】 李晓辉；

【导师】 易克初；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2007， 博士

【摘要】 为了提高频谱效率、支持多业务的高速数据的传输,人们公认必将采用两种关键技术:一是正交频分复用(OFDM),二是多入多出(MIMO)。无线资源的综合利用是未来移动通信的重要支撑技术,对提高系统频谱效率、保证用户服务质量(QoS)起着至关重要的作用。在基于MIMO OFDM的未来移动通信系统中,可用的无线资源从一维空间扩大到多维空间,从一收一发的可变速率、可变调制、可变功率、可变系统带宽,到多发多收下的可变天线数目、天线的联合使用方式,再到结合媒体接入控制(MAC)层和物理层的交叉层资源调度,使得无线资源管理变得非常复杂。本文在分析MIMO OFDM系统模型和改进无线局域网MAC协议的基础上,研究了结合物理层与MAC层的MIMO OFDM系统交叉层无线资源管理技术。主要工作概括如下:1.研究了IEEE 802.11无线局域网(WLAN)及其QoS增强MAC协议,提出了一种基于时延的退避算法,使竞争窗口(CW)随着不同业务需求和当前时延动态变化,因而可在保证高优先级用户QoS(时延和吞吐量)的前提下,避免低优先级用户饥饿的问题。2.研究了OFDM系统中的物理层功率分配和比特加载技术,在比例公平算法的基础上,根据不同业务的QoS需求,提出了结合MAC层与物理层的多用户OFDM系统交叉层无线资源管理算法。该算法不仅考虑了用户信道状态信息,而且考虑了业务优先级及其QoS特性。此外还提出了使用容量区域估计可接入用户数的接入控制算法。通过对各用户带宽、时延等特性的分析与仿真表明,所提算法能够保证用户所需的QoS。3.研究了MIMO系统中的物理层功率分配和比特加载技术。在块对角算法的基础上,针对块对角算法用户数不能大于基站发送天线数的限制,提出一种空域和时域相结合的无线资源管理算法。算法结合空域的多用户天线选择和时域上的时隙分配,把资源管理扩展到空时二维,使得各用户带宽、时延等QoS需求在某个给定大小的周期内得到有效保证。4.在充分研究OFDM和MIMO系统资源分配算法的基础上,研究了空间相关性对MIMO系统的影响,给出了一种MIMO OFDM系统中的空-时-频三维资源分配算法,其中通过频域分离可能存在空间高度相关的用户,为他们分配不同子载波来避免空间多用户干扰;同时还根据用户请求带宽进行空域天线选择和频域子载波分配。此外,在时域采用速率补偿机制,提高吞吐量,并保证用户间的公平性。这种补偿机制的原理是:当某个或某几个用户的信道质量过差时,将其带宽暂时分配给其他用户使用,以便提高总的频谱效率,而当这些信道质量变好时,则给予速率补偿,以满足其带宽需求。更多还原

【Abstract】 OFDM (Orthogonal Frequency Division Multiplexing) and MIMO (Multi-Input and Multi-Output) are believed to be two necessary techniques for the intending mobile wireless communication since they can provide high specturm efficiency and high data rate in mutli-path envieronment.The integrated utility of radio resource is an important support for the future mobile communication systems, which play a crucial role in resaining the frequency efficiency and QoS(quality of service) guarenttee. In the mobile communicationsystem based on MIMO and OFDM, the radio resource manegment is extended from one dimension to multiple dimensions, and from variable rate, variable modulation mode, variable power and bandwidth under single input single output, to the variable number and the different mode of the antennas as well as their working cooperatively, moreover, involving the cross-layer resource management in MAC and PHY. All in all, the issue of radio resource allocation becomes more and more complicated.On the basis of the models for MIMO OFDM systems and the MAC protocol of WLAN (Wireless Local Area Networks), this dissertation researches on the resource management of combining PHY and MAC layer for MIMO OFDM systems. The author’s main research contents and contributions are summarized as follows:1. After investigation of the MAC protocol for IEEE 802.11 WLAN, a delay based back-off scheme is proposed, through which the CW (Contention Windows) can be dynamically adjusted according to the requirements of users and the current delay, so that the starvation of the users with low priorities can be avoided under the condition of guaranteeing QoS for the users of high priorities. Its performance has been validated by theoretical analysis and computer simulation.2. Through researching the power allocation, bit loading and sub-carrier allocation techniques, as well as the proportional fairness algorithm, the dissertation proposes a MAC and PHY resource allocation algorithm for multi-user OFDM systems. The algorithm allocates the resource by combining the QoS requirements and the characteristics of OFDM. Furthermore, the number of the acceptable users is estimated by the limitation of the capacity region. This characteristic of the proposed algorithm has been verified by theoretical analysis and the results of simulation to demonstrate the performance in bandwidth and delay for every user. 3. The resource allocation of multi-user MIMO systems is analyzed. Aiming to the limitation of the traditional block diagonal (BD) algorithm that the number of the users must be less than the number of the antennas of the base station, we propose a space-time domain resource allocation algorithm. The resource management is extended to the space-time 2-dimensional domain by combining the selection of the antennas for users in the space dimension with the time slot allocation in the time domain, which makes the users’ QoS requirement in average bandwidth and delay can be guaranteed in a given size of time period.4. Based on the study of the resource allocation algorithm of OFDM and MIMO systems, the research is extended to the space-time-frequency 3-dimensional domain for multi-user MIMO OFDM systems, where the interference between some users caused by their high correlation in space domain is avoided by separating them in frequency domain, i.e. allocating them with different sub-carrier, and where the antenna selection and sub-carrier allocation are performed according to the users’ bandwidth request and the correlation between different users. Besides, the rate compensation mechanism is adopted in the time domain so as to satisfy the fairness. The principle of the compensation mechanism is that if some user channels appear to be too poor in some duration, its bandwidth is temporarily allocated to other users so as to obtain higher spectrum efficiency; when any one of the channels is getting better, some rate compensation is given to satisfy its band width requirement.更多还原