Performance of spatially multiplexed MC-CDM with zero-forcing unified successive interference cancellation detection

Spatially multiplexed multicarrier code-division multiplexing (SM-MC-CDM) is a multiple-input multiple-output, orthogonal frequency division multiplexing (MIMO-OFDM) communication technique with multiple antennas used for spatial multiplexing and with frequency domain spreading on each antenna. Unified successive interference canceller (U-SIC) is an efficient detector recently introduced for SM-MC-CDM. This paper presents an analytical approach to the performance of zero-forcing (ZF) U-SIC for SM-MC-CDM communications. For a system with an equal number of transmit and receive antennas, an approximation for the probability density function of post-detection signal-to-noise ratio (SNR) is used to derive a closed-form analytical upper bound and approximations for the probability of error and ergodic capacity. It is shown that SM-MC-CDM with ZF U-SIC is able to achieve higher diversity order than that achieved by ZF and minimum mean squared error (MMSE) V-BLAST detectors used on each subcarrier of a MIMO-OFDM system with the same number of subcarriers. The diversity order obtained increases with the number of subcarriers. It is also shown that the ergodic capacity of the system decreases with increasing number of subcarriers.     

MIMO throughput optimisation via quantised rate control

The problem of throughput maximisation in a wireless multiple-input multiple-output (MIMO) system using a quantised feedback, which is an appropriate model for practical systems with limited feedback capacity, is considered. Unlike the ergodic capacity that can be achieved through power control only, maximising the throughput in the block fading channels is based on appropriate rate control strategy. The optimal quantised rate control design for general MIMO systems is formulated and a gradient descent search algorithm to find the optimal solution is employed. It is seen that the proposed quantised rate control scheme with only a few bits of feedback considerably improves the throughput of a MIMO system. With the same amount of feedback overhead, the proposed quantised rate control with constant power is compared with the optimal quantised power control strategy with an optimised constant rate, and the result demonstrates the importance of rate control in throughput maximisation. The effect of quantised rate control in MIMO systems employing different automatic repeat request schemes is also investigated     

MIMO-Terahertz in 6G Nano-Communications: Channel Modeling and Analysis

With the development of wireless mobile communication technology, the demand for wireless communication rate and frequency increases year by year. Existing wireless mobile communication frequency tends to be saturated, which demands for new solutions. Terahertz (THz) communication has great potential for the future mobile communications (Beyond 5G), and is also an important technique for the high data rate transmission in spatial information network. THz communication has great application prospects in military-civilian integration and coordinated development. In China, important breakthroughs have been achieved for the key techniques of THz high data rate communications, which is practically keeping up with the most advanced technological level in the world. Therefore, further intensifying efforts on the development of THz communication have the strategic importance for China in leading the development of future wireless communication techniques and the standardization process of Beyond 5G. This paper analyzes the performance of the MIMO channel in the Terahertz (THz) band and a discrete mathematical method is used to propose a novel channel model. Then, a channel capacity model is proposed by the combination of path loss and molecular absorption in the THz band based on the CSI at the receiver. Simulation results show that the integration of MIMO in the THz band gives better data rate and channel capacity as compared with a single channel.     

Fast antenna subset selection algorithms for multiple-input multiple-output relay systems

The antenna subset selection technique balances the performance and hardware cost in the multipleinput multiple-output (MIMO) systems, and the problems on the antenna selection in MIMO relay systems have not been fully solved. This paper considers antenna selection on amplify-and-forward (AF) and decode-andforward (DF) MIMO relay systems to maximise capacity. Since the optimal antenna selection algorithm has high complexity, two fast algorithms are proposed. The selection criterion of the algorithm for AF relay is to maximise a lower bound of the capacity, but not the exact capacity. This criterion reduces algorithmic complexity. The algorithm for DF relay is an extension of an existing antenna subset selection algorithm for one-hop MIMO systems. The authors show the derivations of the algorithms in detail, and analyse their complexity in terms of numbers of complex multiplications. Simulation results show that the proposed algorithms for both cases achieve comparable performance to the optimal algorithm under various conditions, and have decreased complexity.     

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.     

On the capacity of orthogonalised correlated MIMO channels under different adaptive transmission techniques

Orthogonal space-time block codes (STBCs) are known to orthogonalise the multiple-input multiple-output (MIMO) wireless channel, thus reducing the space-time vector detection to a simpler scalar detection problem. The capacity of STBCs over correlated Rayleigh and Ricean flat-fading MIMO channels under different adaptive transmitting techniques is studied. Three adaptive schemes known as optimal power and rate allocation, total channel inversion with fixed rate policy and its truncated variant are studied. Taking into account the effect of channel correlation, closed-form expressions are obtained for the capacity of orthogonalised Rayleigh and Ricean MIMO channels under these adaptive transmission techniques in order to avoid Monte-Carlo simulations     

Efficient Gauss-Seidel Precoding with Parallel Calculation in Massive MIMO Systems

A number of requirements for 5G mobile communication are satisfied by adopting multiple input multiple output (MIMO) systems. The inter user interference (IUI) which is an inevitable problem in MIMO systems becomes controllable when the precoding scheme is used. In this paper, the horizontal Gauss-Seidel (HGS) method is proposed as precoding scheme in massive MIMO systems. In massive MIMO systems, the exact inversion of channel matrix is impractical due to the severe computational complexity. Therefore, the conventional Gauss-Seidel (GS) method is used to approximate the inversion of channel matrix. The GS has good performance by using previous calculation results as feedback. However, the required time for obtaining the precoding symbols is too long due to the sequential process of GS. Therefore, the HGS with parallel calculation is proposed in this paper to reduce the required time. The rows of channel matrix are eliminated for parallel calculation in HGS method. In addition, HGS uses the ordered channel matrix to prevent performance degradation which is occurred by parallel calculation. The HGS with proper number of parallelly computed symbols has better performance and reduced required time compared to the traditional GS.     

Performance analysis of free-space optical communication systems over atmospheric turbulence channels

Turbulence fading is one of the main impairments affecting the operation of free-space optical (FSO) communication systems. The authors study the performance of FSO communication systems, also known as wireless optical communication systems, over log-normal and gamma-gamma atmospheric turbulence-induced fading channels. These fading models describe the atmospheric turbulence because of its very good agreement with experimental measurement data. Closed-form expressions for the average (ergodic) capacity and the outage probability are derived for both statistical models. Another contribution of this work is a study of how the performance metrics are affected by the atmospheric conditions and other parameters such as the length of the link and the receiver's aperture diameter. The derived analytical expressions are verified by various numerical examples and can be used as an alternative to time-consuming Monte-Carlo simulations.     

Performance of the complex sphere decoder in spatially correlated MIMO channels

The use of multiple antennas at both transmitter and receiver is a promising technique for significantly increasing the capacity and spectral efficiency of wireless communication systems. In particular, spatial multiplexing techniques provide a means of increasing the data rate of the system without having to increase the transmitter power or the bandwidth. In recent years, special attention has been paid to the sphere decoder (SD) to detect spatially multiplexed signals. It provides optimal maximum likelihood (ML) performance with reduced complexity, compared to the maximum likelihood detector (MLD). An analysis of the performance of the SD in the presence of spatially correlated multiple-input multiple-output (MIMO) channels is presented. Analytical and simulation results show that, compared to suboptimal linear and nonlinear MIMO detectors, the SD suffers a complexity increase when correlation exists between the antennas at the transmitter or the receiver. In addition, a novel low-complexity channel ordering technique is introduced to reduce the complexity of the SD     

MIMO-OFDM radar for direction estimation

Multiple-input?multiple-output (MIMO) radar makes use of orthogonal signals to obtain the phase delay for each transmitting/receiving antenna pair, and thus increasing the accuracy of direction estimation. The previously proposed MIMO radar assumes narrowband signals that guarantee the waveform orthogonality during the signals? transmission, propagation and reception. However, a narrowband system is unstable in target localisation because of the fluctuation of the target?s radar cross section. An MIMO-OFDM radar is proposed for target localisation. It adopts the OFDM technique to simultaneously transmit and receive a set of multiple narrowband orthogonal signals at orthogonal frequencies. A practical model accommodating a physical target is presented to simulate the MIMO-OFDM radar. As an example, a composite target composed of five infinite dielectric cylinders is localised by a four-element uniform linear array. The performance of the MIMO-OFDM radar is investigated by examining the estimation error for different numbers of sub-bands, different signal-to-noise ratios and different target directions. It is demonstrated by simulation that the MIMO-OFDM radar gives more statistically stable estimation by spreading the signal power over a wider spectrum.     

M分布模型下多跳相干OFDM FSO系统的性能研究

本文在涵盖了从弱湍流到强湍流的所有信道条件,能够表征现有大多数湍流信道的M分布模型下,采用QPSK调制方式研究了多跳相干OFDM FSO系统的性能。系统在中继辅助链路的发射机和接收机之间使用DF中继协议。考虑大气湍流、路径损耗以及瞄准误差对大气信道衰落模型的联合作用,分别推导出系统的中断概率和误符号率的Meijer G形式的闭合表达式。通过仿真分析了中继链路长度、中继节点数以及子载波个数等关键因素对系统的中断性能和误符号率性能的影响。本研究为中继系统的实际应用奠定了理论基础。     

Detailed characterisation of an indoor MIMO channel in the double directional spatial domain

The spatial domain characteristics of an indoor multiple-input multiple-output (MIMO) communication system are examined in detail. Using a high-resolution algorithm, the authors were able to effectively estimate multipath parameters on the joint azimuth of arrival/azimuth of departure (AoA/AoD) domain. The analysis showed dense clustering phenomena at the vast majority of considered locations and a strong correlation between the azimuth spreads of the two angular domains with the presence of line-of-sight (Los) specular components or when the distance between the transmitter (Tx) and the receiver (Rx) is low. The authors also noticed higher azimuth dispersions, compared with those reported in the literature, which can be attributed to low antenna heights and local scattering interactions in the vicinity of both the transmit and receive arrays. Finally, the impact of the spatial global parameters on the ergodic MIMO capacity was tested revealing a direct relation between them.     

Time jitter influence on the performance of gamma–gamma turbulence FSO links with various modulation schemes

ABSTRACT

The research area of optical wireless communication links has attracted significant interest over the last years due to the significant advantages offered by this kind of technology. However, the performance of FSO communication systems depends strongly on the effects, which are related to the atmosphere along the propagation path such FSO links are using. More specifically, the weather conditions and atmospheric turbulence effects can deteriorate considerably the performance characteristics. In this work, we are studying the joint influence of atmospheric turbulence and time jitter effects on the average BER of an FSO link by presenting a new approach for various modulation schemes. Thus new closed-form mathematical expressions are derived for accurate estimation of the BER performance of the optical wireless communication systems. Finally, using the obtained expressions and typical parameter values for FSO links, the numerical results are presented and then verified through Monte Carlo simulations.     

A Low-Cost Open-Hardware Wideband Multiple-Input–Multiple-Output (MIMO) Wireless Channel Sounder

Due to the complexity of multiple-input–multiple-output (MIMO) wireless channels, direct measurement is the main viable option for accurate characterization. Details on a new low-cost wideband channel sounder are presented, which was mainly constructed from conventional instruments and components. This switched architecture system is similar to commercial channel sounders and has modest cost ($≪$ US$ 50 000). The sounder operates in the 2- to 8-GHz range with up to 100 MHz of instantaneous bandwidth and supports eight transmitters and receivers, which are sufficient to support the development and assessment of current and future MIMO wireless systems. In this “open-hardware” project, the hardware design and software components are openly available to other researchers interested in developing or enhancing the MIMO measurement capability. The actual systems built at the University of Pretoria, Pretoria, South Africa, and Brigham Young University, Provo, UT, are presented, as are some example studies.      

On modeling and performance analysis of non-cooperative multi-antenna multi-user MIMO systems

This work presents modeling and performance analysis of beamforming in non-cooperative multi-user multiple-input multiple-output (MU-MIMO) cellular systems using stochastic geometry based abstraction models. Particularly, a downlink MU-MIMO system is investigated in which an array of antenna elements at the base stations (BS) serves several user devices. We derive the closed-form expression of the complimentary cumulative distribution function (CCDF) of signal-to-interference-plus-noise ratio (SINR) representing the coverage probability for orthogonal pilot sequences and thereby characterize a number of related special cases. Moreover, closed-form expressions are also obtained for the CCDF of signal-to-interference ratio (SIR) for non-orthogonal pilot sequences and we also derive useful special cases of it and identify the support region of our analysis. Lastly, we define the numerical expression of ergodic capacity and utilize a partial fraction expansion to solve a simple form. Our contribution in this work is twofold, we not only provide a pedagogical tutorial-like exposition of stochastic geometry technique to model terrestrial networks, but also augment the existing literature in the field with aspects of frequency reuse factor, an indicator function for pilot usage, and the effect of pilot contamination. Simulation results are presented to support the theoretical part.     

Linearly Polarized Millimeter Wave Reflectarray with Mutual Coupling Optimization

This work provides the design and analysis of a single layer, linearly polarized millimeter wave reflectarray antenna with mutual coupling optimization. Detailed analysis was carried out at 26 GHz design frequency using the simulations of the reflectarray unit cells as well as the periodic reflectarray antenna. The simulated results were verified by the scattering parameter and far-field measurements of the unit cell and periodic arrays, respectively. A close agreement between the simulated and measured results was observed in all the cases. Apart from the unit cells and reflectarray, the waveguide and horn antenna were also fabricated to be used in the measurements. The measured scattering parameter results of the proposed circular ring unit cells provided a maximum reflection loss of 2.8 dB with phase errors below 10°. On the other hand, the measured far-field results of the 20 × 20 reflectarray antenna provided a maximum gain of 26.45 dB with a maximum 3 dB beam width of 12° and 1 dB gain drop bandwidth of 13.1%. The performance demonstrated by the proposed reflectarray antenna makes it a potential candidate to be used in modern-day applications such as 5^th Generation (5G) and 6^th Generation (6G) communication systems.     

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.     

Th-Shaped Tunable Multi-Band Antenna for Modern Wireless Applications

A compact, reconfigurable antenna supporting multiple wireless services with a minimum number of switches is found lacking in literature and the same became the focus and outcome of this work. It was achieved by designing a Th-Shaped frequency reconfigurable multi-band microstrip planar antenna, based on use of a single switch within the radiating structure of the antenna. Three frequency bands (i.e., 2007–2501 MHz, 3660–3983 MHz and 9341–1046 MHz) can be operated with the switch in the ON switch state. In the OFF state of the switch, the antenna operates within the 2577–3280 MHz and 9379–1033 MHz Bands. The proposed antenna shows an acceptable input impedance match with Voltage Standing Wave Ratio (VSWR) less than 1.2. The peak radiation efficiency of the antenna is 82%. A reasonable gain is obtained from 1.22 to 3.31 dB within the operating bands is achieved. The proposed antenna supports Universal Mobile Telecommunication System (UMTS)-1920 to 2170 MHz, Worldwide Interoperability and Microwave Access (WiMAX)/Wireless Broadband/(Long Term Evolution) LTE2500–2500 to 2690 MHz, Fifth Generation (5G)-2500/3500 MHz, Wireless Fidelity (Wi-Fi)/ Bluetooth-2400 to 2480 MHz, and Satellite communication applications in X-Band-8000 to 12000 MHz. The overall planar dimension of the proposed antenna is 40 × 20 mm². The antenna was designed, along with the parametric study, using Electromagnetic (EM) simulation tool. The antenna prototype is fabricated for experimental validation with the simulated results. The proposed antenna is low profile, tunable, lightweight, cheap to fabricate and highly efficient and hence is deemed suitable for use in modern wireless communication electronic devices.     

A demonstrator for a low-cost, cordless, multi-carrier spread-spectrum system

Because of the need for spectrally efficient systems for wireless communication, many research activities have been carried out in the area of spread-spectrum techniques. Multi-carrier spread-spectrum (MC-SS) is a new modulation technique with better spectral properties than direct-sequence spread-spectrum (DS-SS). In this paper, a new MC-SS system is introduced. A customized surface acoustic wave (SAW) filter has been designed as a fast analog correlator. A demonstrator testbed has been developed for the 2.4-GHz industrial, scientific, and medical (ISM) band. Experimental measurements of the intermediate frequency (IF) and baseband correlation are presented.     

预编码室内MIMO可见光通信系统空间相关性分析

为了解决多用户MIMO(MU-MIMO)室内可见光通信中存在用户间干扰问题及对角化(BD)算法所产生的子信道强弱的问题,利用子流选择BD算法,对室内MU-MIMO可见光通信系统的误码率进行优化。建立了MU-MIMO室内可见光通信的信道模型,利用控制变量法并采用不同LED与PD距离的参数,对比了在4×4 MIMO与8×8 MIMO两种不同的室内系统布局方式下的信道空间相关性,分析对比子流选择BD算法及BD算法的系统容量及误码率性能。结果表明,随着空间相关的不断增强,误码率性能下降,子流选择BD算法相对于BD算法可以带来4 dB以上的增益。