A projected fast ISTA algorithm for joint beam forming and antenna selection in massive MIMO

Wireless Networks - The joint beam-forming and antenna selection problem encountered in modern multi-user massive multiple input multiple output (MIMO) communication systems is solved using the...     

一种基于分布式空时码的协作MIMO分集复用折衷新方案

协作MIMO通过多个单天线节点的相互协作构造多发射天线,以此形成一种虚拟MIMO多天线阵列获得空间分集增益。考虑到协作MIMO特点,天线间采用分布式空时编码进行编码协作。文章研究了协作MIMO中基于分布式空时码(DSTC)的分集复用折衷(DMT)新方案,该方案通过推导两种DSTC的中断概率与分集增益表达式,结合两类DSTC的DMT策略,根据改变复用增益阈值自适应获得最佳DMT与中断性能。数值仿真表明,所提的DMT策略可以逼近协作MIMO的DMT上限,协作节点采用该策略的中断性能仅次于上限的中断性能。在多节点构成协作MIMO网络分布式空时编码协作中,提出的DMT新方案可使系统高效地获得协作分集增益与中断性能。     

基于卷积神经网络自编码器结构的空时分组传输方案

为提高现有端到端通信系统的泛化能力和可靠性,提出了一种基于卷积神经网络的空时分组码（Space-Time Block Coding,STBC）多输入多输出通信系统物理层方案。该方案将通信系统物理层表述、调制和解调过程联合起来形成端到端自编码器系统,引入多层一维卷积层,分别构建发射机和接收机,并扩展为多天线模式。为进一步提高系统可靠性,合理规划网络结构和参数,联合信号的调制和编码方案,优化了系统模型。仿真实验表明,针对瑞利相关衰落下多输入多输出（Multiple-Input Multiple-Output,MIMO）信道应用场景,训练模型可以实现传统STBC系统的误码性能,两发两收系统在发送端相关系数为0和0.9时分别优于传统系统0.5 dB和1 dB。此外,经过优化后的系统可获得采用卷积编码的性能改善效果,其两发两收不同工作方式优于传统1/2码率卷积编码STBC系统1~3 dB。     

下一代无线通信系统的多用户MIMO技术

多输入多输出（MIMO）技术已成为下一代无线通信系统的关键技术之一.目前,MIMO系统的研究已经从点对点的单用户系统扩展到点对多点的多用户MIMO系统.介绍了多用户MIMO系统的模型,特别是下行链路的基于空分多址方式消除用户间干扰的预处理方法,并讨论了多用户分集和调度等相关问题.多用户MIMO系统是下一代无线通信系统的一种典型应用系统,因此研究其具有非常重要的意义.     

Multifunctional reconfigurable MEMS integrated antennas for adaptive MIMO systems

Multi-input multi-output systems with associated technologies such as smart antennas and adaptive coding and modulation techniques enhance channel capacity, diversity, and robustness of wireless communications as has been proven by many recent research results both in theory and experiments. This article focuses on the antenna aspect of MIMO systems. In particular, we emphasize the important role of the reconfigurable antenna and its links with space-time coding techniques that can be employed for further exploitation of the theoretical performance of MIMO wireless systems. The advantages of the reconfigurable antenna compared to the traditional smart antenna are discussed. Establishment of reconfigurable antennas requires novel radio frequency microelectromechanical systems technology, which has recently been developed in the authors' group. We briefly introduce this technology with emphasis on its distinct advantages over existing silicon-based MEMS technologies for reconfigurable antennas. A reconfigurable antenna design that can change its operating frequency and radiation/polarization characteristics is described. Finally, we present the experimental and theoretical results from impedance and radiation performance characterization for different antenna configurations.     

MIMO系统中的空时编码技术

下一代移动通信系统必须具有更高的传输速率和更好的传输性能,多输入多输出(MIMO)天线技术能够极大提高系统的信道容量从而满足要求.为了提高频率利用率和传输可靠性需要研究MIMO系统中的空时编码技术,文章介绍了目前主要的空时编码技术:空时格状编码和空时分组编码技术,同时指出MIMO系统在天线相关性、接收端复杂性、与单天线系统整合等方面仍存在问题.     

无线通信系统的MIMO信道测量与建模

在多径信道中,使用多天线的M IMO(多输入多输出)无线系统能够比单天线系统提供更高的信道容量,而信道测量与建模是决定通信性能的一个重要因素。文中对目前国际范围内现有的M IMO信道测量和建模进行了研究,并进行了归纳和分类,同时分析了M IMO信道测量和建模的方法,指出了目前信道测量和建模中存在的问题,并给出了一些针对M IMO信道测量系统设计的建议。     

几种接收机在MIMO信道下的性能比较

多入多出（MIMO）无线信道具有空间复用增益和分集增益特性,因此MIMO系统和单入单出（SISO）无线系统相比能够获得更高的频谱效率。本文在不同天线组合下分析了几种MIMO空时信号处理算法的性能,仿真结果和理论分析表明：空间复用增益和分集增益不能同时获得最大,因此在设计MIMO通信系统时可根据实际情况选择天线数,即不仅考虑系统抵抗信道衰落的分集增益,还要考虑能够提供更高的数据传输速率,通过折衷考虑空间复杂增益和分集增益,从更全面的观点评估系统的性能。     

Implementable wireless access for B3G networks. II. MIMO receiver architectures [Topics in Radio Communications]

This article presents a comprehensive overview of the research conducted within Mobile VCE's Core Wireless Access Research Programme, a key focus of which has naturally been on MIMO transceivers. The article, the second of four, provides a follow on from the first article, which dealt with MIMO channels and comprises a compilation of material that has been presented in detail elsewhere (see references within the article). In Part I MIMO channel measurements, analysis, and modeling were presented, which were then utilized to develop compact and distributed antenna arrays. This article reports parallel activities into low-complexity MIMO single-user space-time coding techniques, as well as SISO and MIMO multi-user CDMA-based transceivers for B3G systems. Also, overall B3G system designs have been suggested for beamformed multilayer CDMA-based networks     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.     

B3G空中接口技术分析--MIMO信道测量

在多径信道中,使用多天线的MIMO无线系统能够比单天线系统提供更高的信道容量,而信道测量是决定通信性能的一个重要因素。对目前国际范围内现有的MIMO信道测量进行了研究,并做了归纳和分类。此外,对MIMO信道测量方法进行了分析,并给出了一些针对MIMO信道测量系统设计的建议,为B3G空中接口技术研究提供了技术支持。     

Limited feedback unitary precoding for spatial multiplexing systems

Multiple-input multiple-output (MIMO) wireless systems use antenna arrays at both the transmitter and receiver to provide communication links with substantial diversity and capacity. Spatial multiplexing is a common space-time modulation technique for MIMO communication systems where independent information streams are sent over different transmit antennas. Unfortunately, spatial multiplexing is sensitive to ill-conditioning of the channel matrix. Precoding can improve the resilience of spatial multiplexing at the expense of full channel knowledge at the transmitter-which is often not realistic. This correspondence proposes a quantized precoding system where the optimal precoder is chosen from a finite codebook known to both receiver and transmitter. The index of the optimal precoder is conveyed from the receiver to the transmitter over a low-delay feedback link. Criteria are presented for selecting the optimal precoding matrix based on the error rate and mutual information for different receiver designs. Codebook design criteria are proposed for each selection criterion by minimizing a bound on the average distortion assuming a Rayleigh-fading matrix channel. The design criteria are shown to be equivalent to packing subspaces in the Grassmann manifold using the projection two-norm and Fubini-Study distances. Simulation results show that the proposed system outperforms antenna subset selection and performs close to optimal unitary precoding with a minimal amount of feedback.     

全速率满分集准正交空时分组码的设计

在未来的第四代移动通信中,基于多输入多输出（MIMO）天线系统的空时编码技术是改善无线通信性能,提高带限系统数据传输速率的一种理想选择,但由于正交空时分组编码不能保证满分集和数据全速率传输,提出了一种利用星座图旋转可获得全速率满分集传输的旋转准正交空时分组码的设计方法。仿真结果表明,这种方法在不增加译码复杂度的情况下,其误比特率无论在低信噪比还是在高信噪比条件下都要优于已有的准正交空时分组码。     

多天线技术发展趋势探析

无线数据业务的爆炸式增长,特别是用户对高清晰度视频、手机电视等多媒体业务的需求越来越多,对无线通信系统的网络容量提出了更高的要求,多天线技术是满足第五代无线通信系统中网络容量需求的重要手段。分析了多天线技术的发展趋势,重点阐述了大规模天线阵列、协作多点传输、空间调制的技术原理、需要解决的关键问题及可能的解决手段。     

3G通信信号空时二维处理技术研究

多用户检测和阵列天线技术是3G通信的关键技术,文中提出了一种在码分多址移动通信系统中,将智能天线与多用户检测技术相结合的盲自适应空时多用户检测算法。该算法复杂度低,能够充分利用无线信道的空时结构特征,弥补了时域信号处理和空域信号处理二者的局限,进一步提高无线通信系统的用户容量、覆盖范围和传辕速率。     

一种改进的准正交空时分组码设计方案

基于MIMO天线系统的空时编码技术是改善无线通信性能、提高带限系统数据速率的一种理想选择。但是由于正交空时分组码不能保证数据全速率传输,为此提出一种改进的准正交空时分组码设计方案。该编码方法利用准正交准则,能够保证数据以全速率传输。并在此基础上具体讨论和分析了编码的编、译码算法和误码性能。该编码方法既不降低分集增益也不增加译码复杂度,并且可以获得一定的编码增益。仿真结果表明,这种方法的误比特率无论在低信噪比还是在高信噪比条件下都要优于已有的准正交空时分组码——Jafarkhani码。     

Iterative Joint Channel Estimation and Multi-User Detection for Multiple-Antenna Aided OFDM Systems

Multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to single-input-single-output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell layered space-time architecture (BLAST) or space division multiple access (SDMA) multi-user MIMO OFDM systems, none of the known channel estimation techniques allows the number of users to be higher than the number of receiver antennas, which is often referred to as a "rank-deficient" scenario, owing to the constraint imposed by the rank of the MIMO channel matrix. Against this background, in this paper we propose a new genetic algorithm (GA) assisted iterative joint channel estimation and multi-user detection (GA-JCEMUD) approach for multi-user MIMO SDMA-OFDM systems, which provides an effective solution to the multi-user MIMO channel estimation problem in the above-mentioned rank-deficient scenario. Furthermore, the GAs invoked in the data detection literature can only provide a hard-decision output for the forward error correction (FEC) or channel decoder, which inevitably limits the system's achievable performance. By contrast, our proposed GA is capable of providing "soft" outputs and hence it becomes capable of achieving an improved performance with the aid of FEC decoders. A range of simulation results are provided to demonstrate the superiority of the proposed scheme.     

空时编码在单天线UWB通信系统中的应用

超宽带(UWB)适用于基带多用户通信、战场无线通信和高数据率多媒体业务等通信系统,其数据传输速率高、功耗低、多径分辨能力强。但超宽带脉冲信号时域支撑区极窄,信道为密集多径,将空时编码技术引入超宽带通信系统,能够提升无线通信系统的信道容量与抗误比特率性能。在对UWB空时分组编码系统模型性能理论分析的基础上,对空时分组码在单天线UWB系统应用方案与UWB空时分层码方案进进行了简要介绍,利用Matlab对IEEEUWB信道模型进行仿真,提出了空时编码在UWB通讯技术中应用后提升短距高速率无线通信的性能的结论 。     

TCP performance over wireless MIMO channels with ARQ and packet combining

Multiple-input multiple-output (MIMO) wireless communication systems that employ multiple transmit and receive antennas can provide very high-rate data transmissions without increase in bandwidth or transmit power. For this reason, MIMO technologies are considered as a key ingredient in the next generation wireless systems, where provision of reliable data services for TCP/IP applications such as wireless multimedia or Internet is of extreme importance. However, while the performance of TCP has been extensively studied over different wireless links, little attention has been paid to the impact of MIMO systems on TCP. This paper provides an investigation on the performance of modern TCP systems when used over wireless channels that employ MIMO technologies. In particular, we focus on two representative categories of MIMO systems, namely, the BLAST systems and the space-time block coding (STBC) systems, and how the ARQ and packet combining techniques impact on the overall TCP performance. We show that, from the TCP throughput standpoint, a more reliable channel may be preferred over a higher spectral efficient but less reliable channel, especially under low SNR conditions. We also study the effect of antenna correlation on the TCP throughput under various conditions.     

一种基于特定干扰图样的下行多用户MIMO预编码方法

本文在研究线性迫零类下行多用户MIMO预编码方法的基础上,提出了一种适用于单天线用户的预编码矩阵生成方法.利用信道补矩阵的奇异值分解,可以将下行多用户MIMO信道分解为多个带有基于干扰图样产生的多用户干扰的并行单用户信道.同时本文给出了一种特殊的干扰图样以及相应的显式参数优化方法,包括波束成型和功率分配.通过计算机仿真,重点在4天线场景下分析了该预编码器的系统性能.结果显示,相对于线性迫零类算法,本文提出的预编码方法可以有效的提高系统性能.在Pout等于0.1时,相对于单天线的BD方法,PBIF-Rp将损耗信道容量提高了超过45%,而PBIF-Op提高了100%以上.仿真结果和分析都证明了本方法的进一步研究的潜力.