一种分布式多入多出(MIMO)信道的容量研究

分布式MIMO系统结合了点对点MIMO信道与分布式天线系统两者的特点，能改善链路的质量，提高覆盖面积。本文提出了一种包含路径损耗、阴影衰落与小尺度衰落的分布式MIMO信道模型，分析推导了采用该模型时的分布式MIMO信道容量。通过计算机仿真，研究分析了阴影衰落、Rice信道因子K等因素对分布式MIMO上行信道容量的影响，得出了分布式MIMO信道容量空间分布的特点。     

相关信道下MIMO信道容量优化算法的研究

该文研究MIMO系统收发端天线采用均匀线阵且放置空间有限,存在相关衰落时信道容量的优化方法。采用规范化信道模型,分析了信道相关性对平均信道容量和最优信号协方差矩阵的影响,推导了最优协方差矩阵的一阶条件;利用Jensen's不等式确定了信道容量的上界,给出了闭式解,并对相关信道下信号的传输模式进行了讨论。仿真结果表明,采用该优化方法,在各种SNR下,其平均容量接近Jensen's上界;得出信道相关程度对信道平均容量的影响依赖于信噪比的结论。     

On the Outage Capacity of Correlated Multiple-Path MIMO Channels

The use of multiple-antenna arrays can dramatically increase the throughput of wireless communication systems. Thus, it is important to characterize the statistics of the mutual information for realistic correlated channels. Here, a mathematical approach is presented, using the method of replicas, that provides analytic expressions not only for the average, but also for the higher moments of the distribution of the mutual information for the most general zero-mean Gaussian multiple-input multiple-output (MIMO) channels when the channel is known at the receiver. These channels include multitap delay paths, and channels with covariance matrices that cannot be written as a Kronecker product, such as general dual-polarized correlated antenna arrays. This approach is formally valid for large antenna numbers, in which case all cumulant moments of the distribution, other than the first two, scale to zero. In addition, it is shown that the replica-symmetric result is valid if the variance of the mutual information is positive and finite. In this case, it is shown that the distribution of the mutual information tends to a Gaussian, which enables the calculation of the outage capacity. These results are quite accurate even for few antennas, which makes this approach applicable to realistic situations.     

Frequency-Domain Bit-Flipping Equalizer for Wideband MIMO Channels

We propose a low-complexity equalizer whose performance approaches that of the optimal maximum-likelihood estimators in wideband multiple-input multiple-output (MIMO) channels. The proposed algorithm makes use of a bit-flipping refinement procedure preceded by a frequency-domain equalizer and is based on local-optima searching algorithms. Through performance evaluations, it is demonstrated that the proposed equalizer can perform well when a large number of diversity branches are available in severely dispersive fading channels.     

On the Ergodic Capacity of Rank-1 Ricean-Fading MIMO Channels

This paper investigates the ergodic capacity of Ricean-fading multiple-input-multiple-output (MIMO) channels with rank-1 mean matrices under the assumption that the channel is unknown at the transmitter and perfectly known at the receiver. After introducing the system model and the concept of ergodic capacity of MIMO channels, we derive the explicit expressions for the expected values of the determinant and log-determinant of complex noncentral Wishart matrices. Subsequently, we obtain new upper and lower bounds on the ergodic capacity of rank-1 Ricean-fading MIMO channels at any signal-to-noise ratio (SNR). We show that our bounds are tighter than previously reported analytical bounds, and discuss the impact of spatial fading correlation and Ricean K-factor with the help of these bounds. Furthermore, we extend the analysis of ergodic capacity to frequency selective spatially correlated Ricean-fading MIMO channels. We demonstrate that the calculation of ergodic capacity of frequency selective fading MIMO channels can be converted to the calculation of the one of equivalent frequency flat-fading MIMO channels. Finally, we present numerical results that confirm the theoretical analysis     

宽带相关信道下的MIMO-DFE自适应空时接收机

设计了基于RLS算法的宽带自适应判决反馈MIMO-DFE空时接收机,由于这种接收机不需要信道识别,从而降低了接收机的复杂度。通过蒙特卡罗仿真评估了接收机在宽带相关信道下的误码率性能。仿真结果表明,在宽带相关信道下,相关性越大,接收机的性能下降越严重。在相关系数为0.3、误码率为10~(-3)数量级时,由于信道相关使信噪比损失2dB左右。     

Wideband MIMO Mobile-to-Mobile Channels: Geometry-Based Statistical Modeling With Experimental Verification

A 3-D reference model for wideband multiple-inputmultiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed along with its corresponding first- and second-order channel statistics. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles that travel along surface streets and expressways in a metropolitan area. To compare the first- and second-order channel statistics that were obtained from the reference model with those obtained from the empirical measurements, a new maximum-likelihood-based stochastic estimator is derived to extract the relevant model parameters from the measured data. The measured data is processed and compared with the analytical results. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model and the method for estimating the model parameters.      

Rayleigh环境下MIMO系统容量分析

研究了多输入多输出(MIMO)系统Rayleigh衰落信道矩阵的特征值以及天线空间相关性对信道容量的影响.Monte-Carlo数值仿真结果表明:MIMO系统能极大提高Rayleigh衰落环境中的系统容量,且容量随最小收发天线数目的增加而线性增加,但由于相关性对信道矩阵特征值及其统计分布的影响较大,因此可导致MIMO系统容量的损失.     

Outage Capacity of MIMO Poisson Fading Channels

The information outage probability of a shot-noise limited direct detection multiple-input–multiple-output (MIMO) optical channel subject to block fading is considered. Information is transmitted over this channel by modulating the intensity of a number of optical signals, one corresponding to each transmit aperture, and individual photon arrivals are observed at multiple receive photodetector apertures. The transmitted signals undergo multiplicative fading. The fading occurs in coherence intervals of fixed duration in each of which the channel fade matrix remains constant, and changes across successive such intervals in an independent and identically distributed fashion. The transmitter and the receiver are assumed to be provided with perfect channel state information (CSI). An optimization formulation for the outage probability problem is outlined and an exact characterization of the optimal average conditional duty cycles is provided.      

VBLAST在宽带空间相关信道下的性能分析

在宽带空间相关信道下,通过仿真分析、评估了VBLAST空时接收机的性能。仿真结果表明随着信道空间相关性的增大,系统的性能都有所下降;随着接收天线数的增加,信道相关性对系统的影响逐渐减小。     

The Throughput–Reliability Tradeoff in Block-Fading MIMO Channels

We build on Zheng and Tse's elegant formulation of diversity-multiplexing tradeoff (DMT) to provide a better understanding of the asymptotic interplay between transmission rate, error probability, and signal-to-noise ratio (SNR) in block-fading multiple-input multiple-output (MIMO) channels. In particular, we identify the limitation imposed by the notion of multiplexing gain and develop a new formulation called the throughput-reliability tradeoff (TRT), that avoids this limitation. The new characterization is then used to elucidate the asymptotic trends exhibited by the outage probability curves of block-fading MIMO channels     

MIMO Channels in the Low-SNR Regime: Communication Rate, Error Exponent, and Signal Peakiness

We consider multiple-input multiple-output (MIMO) fading channels and characterize the reliability function in the low signal-to-noise (SNR) regime as a function of the number of transmit and receive antennas. For the case when the fading matrix H has independent entries, we show that the number of transmit antennas plays a key role in reducing the peakiness in the input signal required to achieve the optimal error exponent for a given communication rate. Further, by considering a correlated channel model, we show that the maximum performance gain (in terms of the error exponent and communication rate) is achieved when the entries of the channel fading matrix are fully correlated. The results we presented in this work in the low-SNR regime can also be applied to the infinite bandwidth regime     

On the Derivation of the Exact, Closed-Form Capacity Formulas for Receiver-Sided Correlated MIMO Channels

This paper solves the problem of finding a closed-form expression for the average information-theoretic capacity of wireless systems with an arbitrary number of transmitter and receiver antennas. It is assumed that only the receivers have (perfect) knowledge of the channel state and that fading correlation is receiver-sided. The main purpose of the paper is accomplished by introducing a few very simple concepts and performing some clear-cut algebraic manipulations, making the presentation virtually self-contained. The results show a substantial capacity reduction in the presence of correlation between receiver antennas. It is also shown that employing linear arrays with nonuniform spacings may improve the system capacity, and a simple technique to exploit this possibility is presented. Isotropic and nonisotropic propagation scenarios are studied.      

General Capacity Bounds for Spatially Correlated Rician MIMO Channels

This paper considers the capacity of spatially correlated Rician multiple-input multiple-output (MIMO) channels. We consider the general case with double-sided correlation and arbitrary rank channel means. We derive tight upper and lower bounds on the ergodic capacity. In the particular cases when the numbers of transmit and receive antennas are equal, or when the correlation is single sided, we derive more specific bounds which are computationally efficient. The bounds are shown to reduce to known results in cases of independent and identically distributed (i.i.d.) and correlated Rayleigh MIMO channels. We also analyze the outage characteristics of the correlated Rician MIMO channels at high signal-to-noise ratio (SNR). We derive the mean and variance of the mutual information and show that it is well approximated by a Gaussian distribution. Finally, we present numerical results which show the effect of the antenna configuration, correlation level (angle spreads), Rician$K$-factor, and the geometry of the dominant Rician paths.     

Capacity Analysis for Continuous Alphabet Channels With Side Information, Part II: MIMO Channels

In this second part of our two-part paper, we consider the capacity analysis for wireless mobile systems with multiple-antenna architectures. We apply the results of the first part to a commonly known baseband, discrete-time multiple-antenna system where both the transmitter and receiver know the channel's statistical law. We analyze the capacity for additive white Gaussian noise (AWGN) channels, fading channels with full channel state information (CSI) at the receiver, fading channels with no CSI, and fading channels with partial CSI at the receiver. For each type of channels, we study the capacity value as well as issues such as the existence, uniqueness, and characterization of the capacity-achieving measures for different types of moment constraints. The results are applicable to both Rayleigh and Rician fading channels in the presence of arbitrary line-of-sight and correlation profiles.     

基于天线选择的低秩信道MIMO系统容量研究

最近的研究表明,在衰落信道多天线MIMO系统的容量随发射天线数线性增加.而对于低散射环境,即使信号经历独立的衰落,信道秩的降低也会严重影响系统容量的增加.对于这种低秩环境,选择天线发射或接收可以有效地降低系统的成本.本文研究了天线选择对低秩信道MIMO系统容量的影响.仿真结果表明,对不同的信道条件,适当选择天线发射不仅可以增加信道容量,而且可以降低系统的复杂度和射频成本.适当选择天线接收,在不严重降低系统容量的前提下,也达到了降低系统成本的目的.     

Noncoherent MIMO Communication: Grassmannian Constellations and Efficient Detection

This paper considers the design of both a transmitter and a receiver for noncoherent communication over a frequency-flat, richly scattered multiple-input multiple-output (MIMO) channel. The design is guided by the fact that at high signal-to-noise ratios (SNRs), the ergodic capacity of the channel can be achieved by input signals that are isotropically distributed on the (compact) Grassmann manifold. The first part of the paper considers the design of Grassmannian constellations that mimic the isotropic distribution. A subspace perturbation analysis is used to determine an appropriate metric for the distance between Grassmannian constellation points, and using this metric, greedy, direct and rotation-based techniques for designing constellations are proposed. These techniques offer different tradeoffs between the minimum distance of the constellation and the design complexity. In addition, the rotation-based technique results in constellations that have lower storage requirements and admit a natural “quasi-set-partitioning” binary labeling.      

Capacity Analysis of MIMO Group-Broadcast Channels with Time-Division Scheduling

This paper investigates the ergodic sum capacity for a MIMO group-broadcast channel with time-division scheduling (TDS). In this scheme, the overall user set is divided into subgroups, among which a single user subgroup which maximizes the instantaneous sum capacity will be scheduled at a time. In order to characterize the TDS performance, we first derived an asymptotic bound to the full capacity obtained by dirty paper coding (DPC). This bound is a closed-form expression and performs well for different system configurations. Further concerning practical precoding techniques, we studied its achievable sum capacity by using block-diagonalization (BD) and zero-forcing (ZF) precoding. Based on these results, the achieved scheduling gain by TDS over random scheduling is analyzed. We also compared the scheduling gains under different transmission strategies including DPC, BD, and ZF precoding. The results reveal that TDS provides the largest scheduling gain for the system with ZF precoding. Finally, we also discussed the effect of the group cardinality on the performance of TDS. Numerical results show the tightness of derived capacity bounds and verify the correctness of our analysis.