【作者】 朱雪梅；

【导师】 袁东风；

【作者基本信息】 山东大学 ， 通信与信息系统， 2009， 博士

【摘要】 未来无线通信网络不仅要具有更大的系统容量,还要支持高速率的无线通信传输业务,同时满足不同业务的服务质量(QoS,Quality of Service)要求。然而,随着人们对业务多样性需求的不断增长,无线频谱资源日益匮乏,已经成为遏制无线通信网络发展的瓶颈。因此,如何提高频谱利用率成为了当前无线通信研究的热点问题。基于多天线技术的跨层自适应机制可以有效地解决这个问题。一方面,跨层自适应机制允许网络各层共享与其它层相关的信息,对无线网络进行整体设计,使得在无线信道具有明显的资源受限和时变衰落的特性下,提高频谱利用率,保证用户的服务质量(QoS)。另一方面,多天线技术可以在不增加系统带宽和天线发射功率的情况下,使频谱利用率成倍增加并能够保证可靠的传输。本论文围绕频谱利用率的提高、无线链路传输性能的改进,分别针对物理层MIMO自适应方案和单用户MIMO、多用户MIMO跨层自适应方案展开了深入地研究。本论文的研究成果可为下一代无线通信系统的标准化提供参考依据。具体来说,论文的主要创新之处在于:1.针对物理层自适应MIMO系统,提出了两种改善系统性能的自适应方案。第一,在深入研究空时编码正交矩阵设计的基础上,提出了基于格拉斯曼流形构造的高率正交空时码的自适应方案,该方案对收发天线的数目没有限制,而且译码简单。第二,在DSTTD(Double Space-Time Transmit Diversity)系统中,利用信道反转思想提出了一种次优的非对称调制自适应功率分配算法,该算法对系统的性能改善明显。2.针对单用户MIMO系统的相关信道环境,在数据链路层丢包率和时延两个QoS约束下,利用跨层信息分析了AMC_OSTBC_T-ARQ系统中天线衰落相关性对频谱利用率的影响,给出了相关Nakagami-m信道下AMC_OSTBC_T-ARQ系统的频谱利用率、误包率、中断概率的闭合表达式;研究表明,相比Nakagami-2分布,相关性对Rayleigh分布下的跨层系统频谱利用率影响更严重。3.针对单用户MIMO系统中多天线带来的射频成本的限制,提出了一种基于发送天线选择结合正交空时码(TAS/OSTBC)的单用户跨层自适应方案,推导出了任意发射天线数目的TAS/OSTBC接收信噪比的概率分布函数和跨层系统频谱利用率的闭合表达式。4.针对多用户MIMO系统中空间分集与多用户分集的矛盾,提出了综合考虑物理层信道状态变化,联合自适应调制、TAS/OSTBC技术及多用户分集技术,对用户进行跨层自适应调度。以目标BER(Bit Error Rate)为QoS约束,分别推导出最大化SNR调度和归一化最大SNR调度算法在用户信道衰落不同分布时的多用户跨层系统频谱利用率的表达式,并与OSTBC传输技术比较得出:基于TAS/OSTBC技术的多用户跨层自适应调度方案可以很好的弥补OSTBC引起的多用户分集性能下降,提升系统的频谱利用率。更多还原

【Abstract】 Future wireless communication aims not only to provide larger system capacity and support higher data rates communication services, but also satisfy the quality of service (QoS) requirements of different services. However, with the continuous growth of diverse wireless service demands, radio resources such as frequency spectrum would be far from adequate and has become a bottleneck in restraining the development of wireless communication networks. Thus how to improve the spectral efficiency has become a hot research topic of the current wireless communications network. An attractive technique known as adaptive cross-layer mechanism based on multiple antennas has been identified as one of the most promising techniques to solve this problem. On one hand, adaptive cross-layer mechanism allows information sharing and information exchange among different layers and optimizes them under limited radio resources and harsh wireless channel conditions in order to achieve both higher system spectral efficiency and better QoS. On the other hand, multiple antennas technology can double spectral efficiency and guarantee the transmission reliability without increasing system bandwidth and antenna transmit power.In this dissertation, adaptive MIMO schemes at physical layer and adaptivecross-layer schemes based on single-user MIMO system and multi-user MIMO systemare intensively studied, respectively, in order to improve the spectral efficiency and thetransmission performance of wireless link. The research results could potentially workas the standardization reference for the next generation wireless communicationnetworks. The main novelty contributions of my work are as follows:1. We proposed two novel adaptive schemes for the physical layer adaptive MIMOsystem to make the system performance better. Firstly, based on the extensiveinvestigation of orthogonal matrix design of space-time coding, an adaptivehigh-rate orthogonal space-time coding scheme from the Grassmann manifold wasproposed. This scheme has no limitation on the number of transmitter and receiverantennas, and has a simple decoding algorithm. Secondly, driven by the idea of channel inversion, we proposed a sub-optimal adaptive power allocation algorithm combined with asymmetric adaptive modulation in double space-time transmit diversity (DSTTD) system. It can enhance the system performance significantly.2. Considering the correlated channel conditions of single-user MIMO system, under the constraint of QoS of packet loss probability and time delay at data link layer, we analyzed the effect that antenna fading correlation has on the spectral efficiency in AMC_OSTBC_T-ARQ system, combining of adaptive modulation and coding (AMC) and truncated automatic repeat request (T-ARQ) in the presence of orthogonal space-time block coding (OSTBC) transmit diversity by using the cross-layer information analysis. We deduced the closed-form expressions for the spectral efficiency, packet error rate, and outage probability of this AMC_OSTBC_T-ARQ system under correlated Nakagami-m channels. Results showed that correlation reduced spectral efficiency of the cross-layer system under Rayleigh channel more than that under Nakagami-2 channel.3. Considering the problem that the multiple transmit antenna deployment with multiple RF-chains may result in increasing complexity, size, and cost, we proposed that transmit antenna selection / orthogonal space-time block coding(TAS/OSTBC) scheme was extended to be in adaptive single-user cross-layer scheme that combines AMC with hybrid ARQ techniques. We derived the analytical closed-form expression for probability density function (PDF) of the receiver signal-to-noise ration (SNR) and the overall average spectral efficiency under adaptive cross-layer TAS/OSTBC transmission scheme with the arbitrary number of transmitter antennas.4. In order to resolve the problem between the spatial diversity and the multi-user diversity in multi-user MIMO system, we proposed an adaptive multi-user cross-layer scheduling strategy that incorporated the AM, TAS/OSTBC technologies of physical layer into the multi-user selection diversity. Based on the constraint of QoS of target bits error rate, we derived the closed-form analytical expressions for the overall spectral efficiency based on maximum SNR scheduling and maximum normalized SNR scheduling when users have non-identical channel conditions. Results showed that the adaptive multi-user cross-layer scheduling strategy based on TAS/OSTBC can dramatically enhance the spectral efficiency of the system and offset the multi-user diversity performance degradation caused by OSTBC.更多还原