Semi-deterministic channel model for multiple input multiple output systems. Part 1: Model development and validation

In this study a mathematical model, named `single interaction scattering reflecting (SISTER)`, to characterise wireless communication channel for outdoor and indoor environments is introduced which falls into semi-deterministic channel models. The aim of this study was to bridge the gap between the complicated theory of radio signal propagation and the idealised models using statistical channel properties for analysing multiple input multiple output (MIMO) systems. Therefore proposed model is developed based on the electromagnetic scattering and reflection and fundamental physics; however, it has been kept simple through appropriate assumptions. This model is validated by a three-dimensional ray-tracing tool. The numerical results obtained for different scenarios are presented and discussed in Part 2 of this paper.     

Simple correlated channel model for ultrawideband multiple-input multiple-output systems

A simple correlated channel model for ultrawideband (UWB) multiple-antenna systems is proposed. The authors show that a single numerical value of the spatial correlation coefficient is sufficient to accurately model the performance of UWB spatial multiplexing systems in an indoor environment. The appropriate value of the correlation coefficient is selected by ensuring a close match between the bit error rate results achieved on the proposed correlated channel and those on the measured indoor channel. The authors also experimentally confirm that the performance substantially degrades in the presence of high values of spatial correlation for a range of spatial multiplexing receivers, and quantify the relationship between this degradation and the value of the spatial correlation coefficient. Thus, a route for the development of the existing standards for single- antenna UWB channels to the multiple-antenna regime is provided here.     

Correlation-based double-directional stochastic channel model for multiple-antenna ultra-wideband systems

A correlation-based double-directional stochastic channel model for indoor multiple-input multiple-output (MIMO) ultra-wideband (UWB) propagation channels is proposed. The proposed model extends the IEEE 802.15.3a standard model to spatially correlated MIMO channels. Both angular and temporal statistics are taken into account in the modelling procedure. Spatial correlation is introduced into the multipath amplitude and time-of-arrival (ToA) matrices of the channel model. Each amplitude matrix consists of entries of correlated lognormal random variables, whereas each ToA matrix is obtained as the sum of a reference matrix and a difference matrix. The frequency-dependent spatial correlation function is derived to give an insight of model properties. Model parameters are determined based on well-known measurement campaigns. In addition, simulation-based analysis indicates that this model has desirable spatial correlation properties in both the time and frequency domains. The ToA correlation matrix was also found to have dominant effects on the correlation characteristics. This suggests that future research into spatial correlation properties of MIMO-UWB channels should focus on ToA correlation characteristics, rather than amplitude correlation characteristics, which are the current focus of narrowband and wideband MIMO channel research.     

Efficient MIMO channel estimation using complementary sequences

Low complexity channel estimation for single-carrier block transmission systems over multiple-input multiple-output time varying frequency-selective channels is investigated. A time slot structure that uses Golay complementary sequences with perfect periodic autocorrelations as two-sided pilot blocks is presented. Employing this structure, optimal least square estimate in the minimum mean square error (MMSE) sense is achieved. Furthermore, a computationally efficient algorithm which is named as fast periodic Golay correlation is proposed based on the specific generator and the properties related to circulant matrices. Finally, the simulation results show the MMSE performance of the proposed scheme and algorithm.     

一种适用于慢衰落信道OFDM系统的信道估计算法

针对慢衰落信道OFDM系统,提出了一种新的低复杂度的且能对抗定时误差的信道估计器.这种信道估计器是基于导频间隔I=2的特殊梳状导频结构设计的.基于工程实现的考虑,采用了最小平方(LS)算法进行导频信道估计,同时利用了线性内插对非导频信道进行估计.分析了定时误差对非导频子载波估计的影响,并提出了一种相当简单但十分有效的修正算法,仿真结果有力的证明了此算法能有效的抵抗定时误差对非导频信道插值估计的影响.     

提高MIMO系统容量的检测算法研究

为了满足通信容量的需求，在发射端和接收端设置多元素天线阵列构成多输入多输出系统，可以显著提高频谱的利用率，基于贝尔实验室提出的非线性迫零检测算法，提出了反向迫零检测算法．理论和仿真证明，在相同信噪比条件下，反向迫零检测算法获得的系统容量高于非线性迫零检测以及线性迫零检测算法．与奇异值分解算法相比，该算法虽然得到的系统容量有所减小，但是由于所需的运算量相对较小，因而易于实现．     

基于ZF-DPC机制的多天线下行系统的自适应调制

以系统总速率最大化为目标,基于迫零污纸编码（ZF-DPC）机制提出了MIMO多用户下行系统的一种保障用户QoS的自适应调制方案。根据这一方案,基站应用空分多址接入（SDMA）同时支持多个用户;针对污纸编码（DPC）的极高复杂度,利用次优的ZF-DPC消除用户间的干扰;在理想信道信息情形下实现可变速率可变功率自适应调制。考虑到最优算法的高复杂度,提出了两种可应用到实际系统的低复杂度次优算法。仿真结果表明,次优算法在极大降低系统复杂度的同时,总速率比较接近最优算法的性能。     

大规模MIMO系统的全导频RZF预编码方法

研究了大规模多输入多输出(MIMO)系统的预编码。针对小区间干扰和导频污染会对预编码的有效性产生较大影响的问题,提出了一种改进的全导频正则化迫零(RZF)预编码方法。该方法通过将有限的正交导频信号分配给小区用户来对预编码矩阵中的信道向量进行优化,得到优化后的全导频正则化预编码矩阵,并依此推导出新的包含导频污染函数和用户干扰函数的和速率表达式。另外,综合考虑基站天线数、用户数以及导频重用因子,优化其配置关系,从而用较少的用户信息和更高的导频重用因子来抑制更多的小区间干扰,有效地提升系统性能。实验结果表明,这种改进的RZF预编码算法能够较好地提高系统容量,在完全已知信道状态信息(CSI)和未完全已知CSI两种情况下的频谱效率及和速率均优于传统的RZF方法。     

基于海面散射的莱斯MIMO信道容量研究

通过相关莱斯信道模型对海面散射水声多入多出(MIMO)信道容量进行了研究。从Helmholtz-Kirchhoff积分和Fresnel近似出发,得到海面散射信号的空间相关性,由于信道的协方差矩阵不可以表示成发射相关矩阵和接收相关矩阵的Kronecker积,通过Monte Carlo仿真研究了莱斯因子、接收信噪比和空间相关性对MIMO信道容量的影响。从对outage capacity和信道容量的CCDF(Complementary Cumulative Distribution Function)的仿真计算结果可以看出,莱斯衰落的MIMO信道容量并不总是小于瑞利衰落MIMO信道容量,当信道的空间相关性较大和接收信噪比较小时,由于信道的衰落作用将起主要作用,对于较小的收发阵元数,以非衰落的直达信号为主的莱斯MIMO信道容量将大于瑞利衰落的MIMO信道容量。     

MIMO-OFDM系统中一种新的信道估计方法

提出了多输入多输出-正交频分复用(MIMO-OFDM)系统中一种新的信道估计方法.根据最小均方误差的准则,推导出了求解信道频率响应的方程,方程求解的运算量主要集中在一个矩阵的求逆上.对每一个符号,此矩阵是固定的,所以矩阵的求逆仅需计算一次,整个求解过程的运算量较低.计算机仿真给出了这种方法的归一化均方误差和误码率性能.仿真结果表明,本文方法在多普勒频移为60Hz和360Hz下,其归一化的均方误差值相当,表明本文方法可以在不同的移动环境中良好工作.在不同的数据调制方式和不同的多普勒频移下,本文方法的误码率性能优于最小平方算法,略差于线性最小均方误差算法,但复杂度大大降低.     

适用于OFDM系统的改进的信道估计算法

针对实际系统中的信道冲激响应(CIR)泄漏问题,提出了一种适用于梳状导频正交频分复用(OFDM)系统的改进的最小二乘(LS)信道估计算法.该算法基于分数抽头延时信道近似(FTCA)的参数化信道模型,此信道模型采用一个抽头间隔为分数倍采样间隔的抽头延时线结构的有限冲激响应(FIR)滤波器表示.此算法首先通过FTCA信道模型来近似实际信道,然后再估计该信道模型中的某些参数来获取实际的信道信息;该算法利用了FTCA信道模型中所有的延时抽头,从而很好地抑制了CIR泄漏.仿真与分析表明,FTCA信道模型能够有效地近似实际信道,同时降低信道自相关矩阵的维数,从而提高信道估计的性能.     

基于无迹卡尔曼滤波的MIMO-OFDM系统信道估计算法

基于对现有MIMO-OFDM系统信道估计技术及其理论的分析,提出了一种基于无迹卡尔曼滤波（UKF）的信道估计算法。该算法不需要信道的任何先验统计信息,从频域出发,首先利用最小二乘（LS）算法得到导频处信道的粗略估计值,再在时域运用路径捕获法和UKF算法得到信道的精确估计值。仿真结果表明,与LS算法、最小均方（LMS）算法等相比,该算法在较低运算复杂度下可以获得信道估计性能的明显改善。     

Information theoretic capacity of Gaussian cellular multiple-access MIMO fading channel

Higher spectral efficiency can be achieved by exploiting the space dimension inherent to any wireless communication system using multiple receiver and multiple transmitter antennas (MIMO). There are several results that provide closed form solutions for acellular system with a single antenna at each base station and each user terminal. Results are also available for the single cell case with MIMO. A cellular system with multiple antennas at the transmitter and the receiver nodes has not been investigated to obtain a closed form solution for the capacity limit. The main information theoretic theorems are not directly applicable to this system because of the form of the channel matrix of such a system. In this paper we extend the well known Wyner's model to a MIMO cellular system. It is observed that the achievable rate is bound by an upper limit and lower limit corresponding to two extreme fading conditions: channel with Rayleigh fading and with no fading. The analytical results are verified using Monte Carlo simulations. The analysis provides the insight that for a cellular system, increasing the number of transmitting antennas is not beneficial to increase the achievable rate, and this is reflected in the results obtained.     

相关MIMO信道下一种特征波束成型方案的性能研究

提出了相关多输入多输出信道下的一种空时分组码、空分复用与波束成型相结合的新方案．该方案利用了发射分集和空分复用所带来的分集和复用增益，并基于接收机反馈的信道相关矩阵设计了一种波束成型器．仿真结果表明，这种方案的性能较传统的方案在高信噪比时能获得较大的改善．     

Indoor body-area channel model for narrowband communications

Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described.     

Power allocation in SVD- and GMD-assisted MIMO systems

Singular-value decomposition (SVD)-based multiple-input multiple-output (MIMO) systems have attracted a lot of attention in the wireless community where the whole MIMO channel is decomposed into a number of unequally weighted independent single-input single-output (SISO) channels. The unequal weighting of the SISO channels has led to intensive research on bit- and power allocation even in MIMO channel situations with poor scattering conditions identified as the antenna correlation effect. In this situation, the unequal weighting of the SISO channels becomes even much stronger. In comparison to the SVD-assisted MIMO transmission, geometric mean decomposition (GMD)-based MIMO systems are able to compensate for the drawback of weighted SISO channels when using SVD at the cost of remaining interferences which can be easily removed by using dirty paper precoding. Together with different QAM constellation sizes per layer, bit loading and power allocation can be helpful to balance the bit-error probabilities in the activated number of MIMO layers. The novel contribution of this paper is that optimal and suboptimal power allocation solutions are investigated under the assumption of unequal SISO channels as well as different QAM constellation sizes per MIMO layer. Our results show that GMD-based MIMO transmission has the potential to significantly simplify the process of bit and power loading and outperforms the SVD-based MIMO transmission as long as the same QAM-constellation size is used on all equally-weighted SISO channels.     

Dual-monopole array backed by a reflector for antenna diversity/MIMO systems

A dual-monopole array backed by a plane reflector is designed and rigorously analysed to provide information on the installations and applications of monopole arrays mounted on a wall or ceiling for antenna diversity/multiple-input and multiple-output (MIMO) operations. The optimum design of the array is determined through computer simulation. On the basis of the experimental measurements and theoretical investigations in a typical rich multipath environment, the authors found that both the diversity gain and the average MIMO capacity of the array are almost unaffected by the distance of the array from the reflector if the distance is greater than ~0.16lambda. On the other hand, both the diversity gain and the average MIMO capacity are significantly reduced once the separation between the monopoles is less than ~0.2lambda. The findings have reference values for the design of monopole arrays in diversity/MlMO systems     

上行虚拟MIMO系统的双比例公平用户配对算法

在分析上行虚拟多输入多输出(V-MIMO)系统的传统正交用户配对算法的基础上,提出了一种先按比例公平准则选取第一个用户,然后基于一种改进的比例公平准则选取其配对用户的新的双比例公平(D-PF)用户配对算法,并基于不同的接收机结构分析评估了该算法的吞吐量性能以及用户之间的公平度.仿真结果表明,与传统的正交用户配对算法相比,所提D-PF算法能够取得更好的吞吐量和用户公平度性能.     

毫米波大规模MIMO系统波束选择方案的设计

针对毫米波大规模MIMO系统采用全数字预编码时,所需射频链路数量过多而导致能量消耗高的问题,提出了一种基于透镜的波束选择方案。该方案首先通过分析用户受干扰的可能性,将所有的用户分为干扰用户组和非干扰用户组,然后对于非干扰用户,直接利用最大功率准则进行波束选取,而对于干扰用户,则通过低复杂度增量算法选择合适的波束使系统和速率最大化。仿真结果表明,在有效减少系统所需射频链路数量和降低计算复杂度的基础上,该方案的系统和速率能够达到接近全数字预编码方案的水平,并且能够获得更高的能量效率。