Dual antenna selection algorithms and feedback strategies with reduced complexity for multiple-input multiple-output systems

A simple antenna selection strategy for multiple-input multiple-output wireless systems with partial feedback is presented. In the proposed scheme, both transmit and receive antenna selection are done at the receiver, significantly reducing feedback information. In addition, this scheme uses row/column probability density function for antenna selection to reduce computational complexity without performance degradation. Unlike other schemes, two different antenna selection algorithms are used in high and low signal-to-noise ratio regimes, respectively, achieving additional performance gain in comparison to the single antenna selection algorithm. Simulation results show that the proposed scheme nearly approaches the optimal closedloop capacity (known as water-filling capacity) as random selection round for antenna selection increases.     

Cross-entropy optimisation of multiple-input multiple-output capacity by transmit antenna selection

Radio channel capacity can be increased dramatically using a multiple-input multiple-output (MIMO) scheme, but at the expense of hardware complexity. An efficient approach for complexity reduction is antenna subset selection at the transmitter and/or receiver. A novel transmit antenna selection algorithm is presented using the cross-entropy optimisation method to maximise channel capacity. In contrast with the existing work, the proposed algorithm guarantees a result to within 99% of the true optimum (i.e. the maximal capacity with selected transmit antennas) with substantially low complexity. The simulation results indicate that the proposed algorithm is independent of the relationship between the selected transmit array size and receive array size. The proposed scheme has the potential to make practical MIMO systems with high performance simpler to implement.     

Downlink transmission rate-control strategies for closed-loop multiple-input multiple-output systems

A novel downlink transmission rate-control and feedback reduction strategy for closed-loop multiple-input multiple-output (MIMO) multiple-input multiple-output wireless systems is presented. Unlike conventional systems that use signal to interference plus noise ratio at the receiver as an indicator of channel quality, we propose using instantaneous MIMO capacity as an indicator for the downlink transmission rate-control. A set of instantaneous capacity thresholds is first chosen such that the expected weighted capacity loss because of thresholding effects are minimised. While computing the thresholds, we also consider the quality of service and weight function to meet different traffics and user needs. Then a set of codebooks can be constructed minimising the overall capacity loss with given quality of service constraint. Simulation results show that, with only four data rate-control bits, our algorithm gives only 12% capacity loss in 4 times 4 MIMO systems and almost twice better than the current IS-856 standard in single-input single-output systems. In case of 5-bit feedback scenario, the proposed algorithm outperforms conventional systems by minimising instantaneous capacity loss.     

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.     

Three-dimensional channel modelling using spherical statistics for multiple-input multiple-output systems

Recently, the third generation partnership standards bodies (3GPP/3GPP2) have defined a two-dimensional channel model for multiple-input multiple-output (MIMO) systems, where the propagating plane waves are assumed to arrive only from the azimuthal direction and therefore not include the elevation domain. As a result of this assumption, the derived angle-of-arrival (AoA) distribution is characterised only by the azimuth direction of these waves. The AoA distribution of multipaths is implemented with a novel three-dimensional approach. The von Mises- Fisher (VMF) probability density function is used to describe their distribution within the propagation environment in both azimuth and co-latitude. More specifically, the proposed model uses a mixture of VMF distributions. A mixture can be composed of any number of clusters and this is clutter specific. The parameters of the individual cluster of scatterers within the mixture are derived and an estimation of those parameters is achieved using the spherical K-means algorithm and also the expectation maximisation algorithm. Statistical tests are provided to measure the goodness of fit of the proposed model. The results indicate that the proposed model fits well with MIMO experimental data obtained from a measurement campaign in Germany.     

Performance analysis of multiple-input multiple-output orthogonal frequency division multiplexing systems under the influence of antenna mutual coupling effect

The effect of antenna mutual coupling on signal correlation and bit error rate (BER) of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system has been modelled. A MIMOOFDM model with correlated channels is presented. The correlation matrices are determined with the antenna mutual coupling taken into account. The effect of antenna mutual coupling is characterised using the receiving and transmitting mutual impedances. A rigorous expression for the BER of the system employing quadrature phase-shift keying digital modulation is derived. A 2 x 2 MIMO-OFDM system using the Alamouti space?time block code for OFDM symbol transmission over 64 sub-channels spanning a 20 MHz band centred at 5.2 GHz is simulated. The simulated results show that the antenna mutual coupling has a significant effect on the BER performance, especially when the spacing between the antenna elements is small.     

Target localisation techniques and tools for multiple-input multiple-output radar

This study presents a comparative study of coherent and non-coherent target localisation techniques for multiple-input multiple-output (MIMO) radar systems with widely distributed elements. Performance is evaluated based on closed-form solutions developed for the best linear unbiased estimator (BLUE) for each of the localisation methods. These estimators afford insights into the relation between radar locations, target location and localisation accuracy. In particular, the means squared error of the BLUE is factored into a term dependent on signal and processing characteristics and a term dependent on sensor locations. The latter is referred to as geometric dilution of precision (GDOP). The best achievable accuracy for the coherent case is obtained, and a comparative study with the non-coherent case is presented. MIMO radar systems with coherent processing are shown to benefit from a gain because of coherent processing among sensors. This gain is referred to as coherent localisation gain, and it is proportional to the ratio of the signal carrier frequency to the effective bandwidth (a large ratio for typical signals). The footprint of multiple transmit/ receive sensors results in a gain, referred to as MIMO gain, for both processing techniques. The MIMO gain is proportional to the product of the number of transmitting and receiving sensors. Analysis of the MIMO gain through the use of GDOP contour maps demonstrate the achievable accuracy at various target locations for a given layout of sensors.     

Multilayered linear dispersion codes for flat fading multiple-input multiple-output channels

The authors investigate the design of linear dispersion (LD) codes, aiming at flexible encoding schemes that allow various rate-performance tradeoffs under a common coding structure. First, the capacity of LD codes is studied. It is shown that the maximum attainable multiplexing gain of a linear dispersion code is the number of symbols per channel use of the code (i.e. coding rate in symbols). In addition, conditions on the construction of linear dispersion matrices for various multiplexing gains are established. A general multilayered linear dispersion coding scheme that allows various multiplexing gains is then proposed. In the proposed scheme, coding rate can be adapted by employing different numbers of dispersion matrices. Furthermore, phase shifting among input symbols is applied to optimise the error performance without loss of multiplexing gain. The construction of dispersion matrices and the optimisation of the phase shifts together constitute a structured approach for the design of linear dispersion codes. Simulation results demonstrate that the new codes outperform conventional LD codes at various data rates.     

Non-adaptive multiple-input, multiple-output radar techniques for reducing clutter

Multiple-input, multiple-output (MIMO) radars enhance performance by transmitting and receiving coded waveforms from multiple locations. This paper describes MIMO techniques that can be used to improve radar performance, especially in airborne Ground Moving Target Indicator (GMTI) applications. The authors begin by showing how MIMO techniques can lower airborne radar clutter to noise ratios (CNRs). This results in smaller losses when observing stationary or low-velocity targets. Next, the authors consider the implementation of MIMO radar modes using electronically scanned arrays (ESAs). Specifically, the authors show how MIMO techniques, applied to subarray-based ESAs, can cause high grating lobes and/or reduced search rates. To address this problem, the authors describe new space ? time waveform coding techniques that can be used to improve performance. Two space ? time waveform encoding approaches are proposed: (i) an overlapped virtual transmit subarray approach, and (ii) a beamspace MIMO approach. A third approach, involving conventional MIMO waveforms and irregular subarrays, is also briefly considered.     

多业务蜂窝中继系统的接入控制算法

以多业务蜂窝中继系统已接入用户的服务质量(QoS)指标、中继负载大小为约束条件,在正交频分多址(OFDMA)方式下,将接入控制问题转化为最大化中继传输下所减少使用的子载波数的问题,并进一步考虑了用户对中继的选择、用户间竞争接入等情况,设计了几种改进的接入控制算法。同时,把这些算法推广到多业务的应用场景中,研究了不同速率业务比例对系统性能的影响。仿真结果表明,所提出的接入算法能支持更多接入用户、降低接入阻塞率和增加节省的子载波数,从而有效地提高了系统容量和资源利用率。     

Spatial frequency scheduling for long term evolution single carrier frequency division multiple access-based uplink multiple-input multiple-output systems

Mathematical expressions are derived for the received signal to interference plus noise ratio of uplink single carrier (SC) frequency division multiple access (FDMA) multi-user multiple-input multiple-output (MIMO) systems with spatial frequency domain packet scheduling. The scheduler is able to exploit the available multi-user diversity in time, frequency and spatial domains. Our analysis model is confined to 3GPP uplink SC-FDMA transmission in which we specifically investigate multi-user spatial division multiplexing MIMO schemes.     

Models and performance evaluation for multiple-input multiple-output space-time adaptive processing radar

Signal and clutter modelling and optimum performance evaluation for multiple-input multiple-output (MIMO)-based space?time adaptive processing radar is addressed. A signal model is developed to account for both code diverse MIMO (c-MIMO) and frequency diverse MIMO (f-MIMO), and a general framework on performance evaluation is presented to take into account various waveform configurations including phased array (PA), partially correlated MIMO and ideally orthogonal MIMO. The proposed framework evaluates the system performance through optimum processing (OP) gain and transmit array (TA) gain. The OP gain is in turn evaluated by the number of available space?time measurements (ASMs) that depends on the number of clutter degrees of freedom (clutter NDoF) relative to the system degrees of freedom (system NDoF). The waveform diversity introduced by MIMO, especially f-MIMO, could significantly enhance the OP gain by increasing the number of ASMs. Hence, in OP-gain-limited scenarios, where the overall performance significantly degrades despite the TA gains, the preferable configuration in terms of optimum performance would be ordered as f-MIMO, c-MIMO, and last, PA, that is, no MIMO.     

放大转发中的最优功率分配与最佳中继选择

用最优功率分配与最佳中继选择相结合的方法实现了放大转发系统的误比特率最小化。为了使单中继非协作放大转发系统的误比特率最小,通过分析媒体接入控制(MAC)层的请求发送/允许发送(RTS/CTS)信息,获得候选中继前向信道和后向信道的增益,以信道增益为变量,得到最佳功率分配的闭合表达式。同时,以误比特率作为中继选择准则,实现分布式最佳中继选择。仿真结果表明,与同类算法相比,该功率分配与中继选择策略使系统的误比特率达到最小。     

单天线中继辅助视距MIMO系统渐近容量及中继策略的研究

研究了视距环境下单天线中继节点辅助MIMO系统的信道模型及容量。针对系统容量与众多因素相关和表达式复杂的问题,根据天线阵列波束相关性及MIMO信道的特点,得出了具有简洁结构的系统渐近容量表达式,进而基于该表达式提出了中继节点最佳位置选择的方法,并与加入中继节点前的系统容量进行了比较,得到了中继选择策略。数值计算与分析结果表明,系统渐近容量具有很好的渐近特性,基于渐近容量的中继策略性能优异并具有很好的鲁棒性。同时渐近容量和中继策略运算复杂度低,适合工程应用。     

Reduced complexity detection technique for layered space time block coded multiple-input multiple-output orthogonal frequency division multiplexing

The combination of vertical Bell Labs layered space time (V-BLAST) and space time block coding (STBC), known as a Layered STBC (LSTBC) system, offers high spectral efficiency with a higher order of diversity. The system structure, computational complexity and error performance of the V-BLAST and LSTBC multiple-input multiple-output orthogonal frequency division multiplexing systems are analysed and compared. It is shown that, compared with V-BLAST, the overall diversity order of LSTBC increases two fold. This diversity gain is achieved at the expense of a four?fold increase in the computational complexity of the QR decomposition (QRD) algorithm, required at the receiver of both LSTBC and V-BLAST. The authors propose a modified QRD algorithm which reduces this four-fold complexity to two fold.     

The performance and efficiency of envelope elimination and restoration transmitters for future multiple-input multiple-output wireless local area networks

The inefficiency of contemporary power amplifiers (PAs), when operating in their linear region, is a major obstacle to mobile operation of wireless local area networks (WLANs) based on IEEE 802.11n. Therefore the use of more efficient envelope elimination and restoration (EER) transmitter architectures is considered. In addition to high efficiency it is also necessary to satisfy the spectral mask and achieve satisfactory link-level performance. Link-level simulations of a contemporary WLAN PA show that, at the power back-offs necessary to achieve sufficient linearity, the power added efficiency (PAE) is only ~1% for a system with four transmit antennas. In contrast, simulations of a phase feedback EER PA architecture show that it is possible to achieve an average PAE of 70%, while satisfying the spectral mask, with only a small degradation in link-level performance.     

General run-to-run (R2R) control framework using self-tuning control for multiple-input multiple-output (MIMO) processes

During recent years, run-to-run (R2R) control techniques have been developed and used to control various semiconductor manufacturing processes. The R2R control methodology combines response surface modelling, engineering process control, and statistical process control. The main objective of such control is to manipulate the recipe to maintain the process output of each run as close to the nominal target as possible. The primary focus of this research is on the multiple-input multiple-output self-tuning control of R2R processes. A general control scheme is presented that can compensate for a variety of noise disturbances frequently encountered in semiconductor manufacturing. The controller can also compensate for various system dynamics, including autocorrelated responses, deterministic drifts, and varying process gains and offsets. Self-tuning controllers are developed to provide on-line parameter estimation and control. A recursive least squares algorithm is normally used to provide on-line parameter estimation to the controller. This type of control strategy used in the proposed self-tuning controller applies the principle of minimizing total cost (in the form of an expected off-target and controllable factors adjustment) to obtain a recipe for the next run. It is shown through the simulation study that even if the control model is non-linear, the self-tuning controller offers satisfactory control performance for R2R applications as compared with those of the control actions provided by the optimizing adaptive quality controller module. At last, a relevant application to chemical mechanical planarization in semiconductor manufacturing, a critical fabrication step involving two quality characteristics (removal rate and within-wafer non-uniformity), is used to illustrate the proposed controller. In this case study, a multivariate statistical process control technique via the Hotelling T?² statistic is also used as a dead-band for further investigation.     

Development of Run-To-Run (R2R) controller for the multiple-input multiple-output (MIMO) system using fuzzy control theories

Run-to-Run (R2R) control has been extensively applied in semiconductor manufacturing. In particular, del Castillo, E. and Rajagopal, R., A multivariate double EWMA process adjustment scheme for drifting processes. IIE Trans., 2002, 34, 1055–1068, investigated double multivariate exponentially weighted moving average (MEWMA) controller for the multiple-input multiple-output (MIMO) system in an attempt to adjust and maintain the linear dynamic process outputs on target. Multivariate fuzzy control, inherently different from conventional MEWMA-based control, is another promising alternative that consists of fuzzy logic and set concept. Providing the fuzzy control can structure an appropriate membership function for the R2R MIMO system, thus it can be shown a practically useful control tool in comparison to MEWMA control. In this paper, fuzzy logic is utilized to design the multivariate fuzzy controller for the type of R2R applications based primarily on the min-max-gravity method advocated by Gupta, M.M., Kiszka, J.B. and Trojan, G.M., Multivariable structure of fuzzy control systems. IEEE Trans. Sys., Man Cybern., 1986, 16, 638–656. Under a variety of disturbance models, the proposed multivariate fuzzy controller can produce quite competitive control performance when compared to MEWMA control.     

结合天线选择和索引组合映射调制的MIMO系统研究

空间调制是一种高数据速率、低复杂度的多输入多输出无线传输技术,因其发射天线被信息序列随机激活,若被激活的信道状态不佳将导致系统误码性能下降.于是,提出一种结合天线选择和索引组合映射调制的传输方案.该方案将传统空间调制的激活天线索引比特和星座符号索引比特组合映射为一个新的调制符号,结合天线选择算法确定最佳发射天线子集,将新的调制符号通过最佳信道进行传输.在算法实现过程中采用了奇异值分解和硬限制检测等方法降低计算复杂度.实验分别仿真了两种天线选择算法下的系统性能.结果表明,提出的方案比传统的空间调制系统具有更好的误比特率特性.     

Fast algorithms for data reduction in modern optical three-dimensional profile measurement systems with MMX technology

Confocal microscopy and white-light interferometry are two promising methods for the three-dimensional microstructure analysis of technical and biologic specimens. For both methods the specimen is scanned through the focus position by means of an actuator. A large series of intensity frames is acquired. These data are used for the final calculation of the topography. We demonstrate that the multimedia extended (MMX) instruction set, which is implemented in modern Intel microprocessors, can be used for effective real-time preprocessing and for fast evaluation algorithms. So this new technique enables the implementation of more-complex algorithms with acceptable run times even on standard computer technology. The possibilities of the MMX instruction set are discussed for confocal microscopy and for white-light interferometry.