Multiple-antenna communication systems: an emerging technology

A recent development in wireless communications is the application of multiple-input multiple-output (MIMO) systems to radio communications via use of multiple antennas. In order to investigate the technologys potential, an experimental MIMO system containing two four-element antenna arrays (4x4) has been developed at the University of Alberta. The system is used to obtain MIMO channel measurements in a typical indoor office environment in the ISM band (902-928 MHz). Measurement campaigns have been performed using different antenna spacings and two different types of antenna: half-wavelength (lambda/2) centre-fed dipoles and dual-polarized patches. The measurements are used to calculate channel capacities for an indoor 4x4 MIMO system. The measurements confirm the high capacity potential of a MIMO channel, with ergodic capacity of approximately 21 bits per channel use available with either antenna type at a signal-to-noise ratio of 20 dB if the antenna element separation is lambda/2 or larger. An introduction to basic MIMO theory, a discussion of the University of Alberta wireless MIMO testbed, and observations regarding the measured indoor MIMO channel are presented in the paper.     

Space-time codes in wireless communications

The need to provide reliable high data rate communication over the wireless channel has led to the development of efficient modulation and coding schemes. Diversity (time, frequency, space, polarization, angle) is an effective method to combat fading and improve the link reliability of the wireless channel. Time and frequency diversity lead to loss in bandwidth efficiency. However, by employing multiple antennas at the transmitter and/or at the receiver, spatial diversity mitigates fading without sacrificing the precious bandwidth resource. It is difficult to implement receive diversity in the downlink because of size and power limitations on the portable/mobile terminal. This has motivated the use of transmit diversity schemes wherein multiple antennas are used at the transmitter for the downlink transmission from the base station to the portable terminal. In space-time coding, intelligent coding of symbols across space and time can be done to reap the advantages due to coding and diversity. The coding in space is obtained by using multiple antennas at the transmitter. The article discusses aspects of space-time coding. This is an important research topic in the design of emerging wireless systems. Deployment of wireless systems using space-time codes is expected in the near future.     

基于LS码的分布式MIMO-CDMA系统研究

研究了基于LS码的分布式MIMO-CDMA系统结构,提出了广义的分布式MIMO系统的信道模型,给出了采用MIMO技术时发射机和接收机的结构.最后以单小区双天线的三基站收发端分布式网络为例,仿真了不同的扩频序列、基站收发端的数目和多天线与系统性能的相互关系.结果表明使用LS码扩频的分布式MIMO-CDMA系统性能比使用Walsh码扩频的MIMO-CDMA系统性能优越,基站收发端或移动台采用多天线时的性能优于单天线.     

MIMO ARQ无线通信系统中发送天线选择的联合优化

为了获得MIMO系统的巨大容量,同时降低系统的实现代价,人们越来越重视天线选择技术.文章基于MIMO ARQ无线通信系统,针对发送天线选择和预编码技术的联合使用,依照系统容量,提出了一种次优的联合优化算法.这一算法把天线选择和预编码分成2个部分完成：在重发数据时,首先利用先前发送时的相关信息和当前的信道信息来选择发送天线;在完成天线选择后,再采用注水算法来优化预编码矩阵.仿真表明,这一算法所获得的信道容量十分接近穷举法所得到的最大信道容量.     

Analysis of maximal-ratio of transmitting/receiving antenna selection with perfect and partial channel information

To improve system performance and reduce the complexity and cost of receiver hardware, we investigated a new multiple-input multiple-output (MIMO) scheme combining maximal-ratio transmitting and receiver antenna selection (MRT/RAS). In this scheme, a single receiving antenna, which maximizes the signalto-noise ratio (SNR) at the receiver, is selected for demodulation. The closed-form outage probability and the bit error rate (BER) of the MRT/RAS system are both presented. The simulation demonstrates that the MRT/RAS scheme can achieve a full diversity order as if all the receiving antennas were used. It is shown that the MRT/RAS scheme outperforms some more complex space-time codes of the same spectral efficiency. The analytical results are verified by simulation. In the end, we also analyze the MRT/RAS system based on partial channel information.     

虚拟Massive MIMO信道测量系统的研制

设计并研制了一种低成本的虚拟大规模多天线(以下简称Massive MIMO)无线信道的系统,用于提取无线信道特性。系统由激励信号源、双锥全向天线、时钟同步单元、射频接收单元和数据采集存储单元等模块组成,并通过上位机控制软件控制。文章先介绍了系统实现原理和各部分功能模块的作用,进而通过实验室校准验证所设计的系统能够准确的提取出无线信道传播特性,例如,在多径的测试中可以准确的得到多径数目、多径时延以及多径损耗。另外在角度域的测量中,可以以最大平均误差不大于0.6°得到1×2MIMO的到达角度。     

Active integrated antennas

Even with microwave techniques, however, signal losses in materials and decreased gain and power from solid-state devices become significant obstacles to creating low-cost, high-frequency wireless systems. Perhaps the most dramatic effect occurs when a circuit component becomes a significant fraction of a wavelength. At this point it may begin to function well as an antenna. For microwave and mm-wave signals, this can occur with circuits that are only centimetres in size. With conventional circuit techniques, this radiation may cause drastic signal losses, spurious coupling between circuit elements, and radio interference with other. However, with new techniques, it is possible to create circuits that use these effects to advantage. Known as active integrated antennas, these circuits have sparked interest as possible solutions to problems in designing the next-generation wireless systems. Active integrated antennas are a combination of solid-state devices and circuits with printed antenna structures. They comprise integrated radio-system elements that are fabricated using inexpensive printed-circuit techniques     

Simulation of Multi-Element Antenna Systems for Navigation Applications

The application of user terminals with multiple antenna inputs for use with the global navigation satellite systems like Global Positioning System (GPS) and Galileo has attracted more and more attention in the past years. Multiple antennas may be spread over the user platform and provide signals required for the platform attitude estimation or may be arranged in an antenna array to be used together with array processing algorithms for improving signal reception, e.g., for multi-path and interference mitigation. In order to generate signals for testing of receivers with multiple antenna inputs and corresponding receiver algorithms in a laboratory environment, a unique hardware signal simulation tool for wavefront simulation has been developed. The signals for a number of antenna elements are first generated in a flexible user defined geometry as digital signals in baseband and then mixed up to individual RF-outputs. This paper describes the principle functionality of the system and addresses some calibration issues. Measurement setups and results of data processing with simulated signals for different applications are shown and discussed.     

基于S参数的共轭匹配MIMO系统注水容量研究

大规模MIMO系统需要在有限的空间里采用多副天线,这将不可避免的引入耦合,耦合会影响MIMO系统性能。研究基于S参数的匹配网络MIMO系统注水容量。通过S参数网络模型,在传输端功率分配上引入注水定理,推导分析不同匹配条件下的容量闭合公式,通过Matlab对不同的接收端匹配条件下的容量进行仿真,包括：无耦合、自阻抗匹配和最优匹配几种情况。结果表明引入注水定理最大化传输端功率并且在接收端最佳共轭匹配的情况下,系统性能得到很大的改善和提高。     

Linear-complexity detection with iterative processing for space-time coded systems

This paper considers wireless data transmission over multi-input, multi-output (MIMO) channels when only the receiver has perfect channel state information. A linear-complexity space-time detector is derived in the context of a turbo-code-based space-time transmitter and iterative processing (turbo detection, demodulation and decoding). Simulation results illustrate that the proposed receivers, suitable for uplink transmission, perform at a level within 2 to 3 dB of the ergodic channel capacity on MIMO channels affected by uncorrelated and correlated Rayleigh flat fading.     

Development of radio frequency transmitters including on‐chip antenna for intelligent human sensing systems

This paper presents the essentials of the development of an integrated smart microsensor system that has been developed to monitor the motion and vital signs of humans in various environments. Integration of RF transmitter technology with complementary metal‐oxide‐semiconductor/micro electro mechanical systems (CMOS/MEMS) microsensors is required to realize wireless smart microsensors for the monitoring system. Sensors for the measurement of body temperature, perspiration, heart rate (pressure sensor), and motion (accelerometers) are candidates for integration on the wireless smart microsensor system. In this paper, the development of radio frequency transmitter (RF) that will be integrated on wireless smart microsensors is presented. A voltage controlled RF‐CMOS oscillator (VCO) has been fabricated for the 300‐MHz frequency band applications. Also, spiral inductors for an LC resonator and an integrated antenna have been realized with a CMOS‐compatible metallization process. The essential RF components have been fabricated and evaluated experimentally. The fabricated CMOS VCO showed a conversion factor from voltage to frequency of about 81 MHz/V. After matching the characteristic impedance (50 Ω) of the on‐chip integrated antenna and the VCO output, more than 5 m signal transmission from the microchip antenna has been observed. The transmitter showed remarkable improvement in transmission power efficiency by correct matching with the microchip antenna. Essential technologies of the RF transmitter for the wireless smart microsensors have been successfully developed. Also, for the 300‐MHz band application, the integrated RF transmitter, with the CMOS oscillator and the on‐chip antenna, has been successfully demonstrated for the first time. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

室内多径信道的三维宽带多极化测量方法

针对室内多径信道的特点,提出了一种可对室内多径信道进行三维宽带多极化测量的方法,并设计制作了三维宽带多极化测量系统,利用该系统对典型室内环境的多径信道进行了测量。测量系统的发射端和接收端天线阵列各由一组虚拟的多极化天线阵列构成,多径信道的频域响应由矢量网络分析仪测量得到。利用此系统对典型室内环境中多径信道进行的三维多极化测量结果表明,不同极化方式的电磁波在相同多径环境中的传播特性有明显差异。在不同的测量位置,包括直射和非直射的多径条件下,不同极化的多径信道之间相关系数都很低,证明可以利用不同极化方式多径信道的不相关在室内环境中构建极化分集的MIMO系统。     

Use of low-cost patch antennas in modern wireless technology

In this article, an overview of a special type of antenna called patch antennas is presented. Patch antennas are used in several wireless applications like global positioning system (GPS) receivers and radar systems. A patch antenna is constructed by having a conductive patch on a dielectric substrate above a conductive ground plane. A patch antenna can be constructed and integrated on a PCB or within a chip along with other circuit components. The excitation of the patch is via a feed line. This feed will supply the patch with the electrical signal to be converted to an electromagnetic wave. Several feed types exist based on the patch type and application. This article gives an overview of the construction of this type of antenna, its major characteristics, and design parameters along with the technologies in which it is being used.     

On the outage probability‐constrained solutions for MIMO‐based cognitive radio systems: Achievable and tight Ergodic capacity bound

Two closed‐form solutions for the approximation bound in relation to resource allocation for multiple‐input multiple‐output (MIMO) ‐based cognitive radio systems are provided. The design problem is actualized in the underlay scenario for a single‐user strategy. The concentration is mainly on the Ergodic capacity constrained by an outage probability at the secondary receiver, regarding our imperfect knowledge of the interference channel at the transmitter. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Microwave exposure and safety associated with personal wireless telecommunication base stations

There are considerable public concerns regarding the biological effects and safety of microwave exposure from wireless base stations. There have been repeated calls for measures and tools that would reduce the exposure to microwave radiation from cellular mobile telephone operations. The radiated power from a base station antenna can vary from less than 1 to as high as 500 W per channel (or transmitter), depending on the location and type of the antenna used for a cellular communication system. The level of public exposure to microwave energy from any base station varies depending on antenna type, location, and distance from the base station. The microwave exposure a person receives from a base station thus depends on both the distances from the antenna, and the angle below the direction of the main beam.     

Dedicated model for the efficient assessment of wireless power transfer in the radiative near‐field

In this paper, a novel method to efficiently calculate the power transfer efficiency of a wireless power transfer system in the radiative near‐field is proposed. The technique allows repositioning of the antennas without large additional cost. It relies on a single simulation (or measurement) of the radiation pattern of the antennas used. Thanks to its high computational efficiency, it can be used in multi‐transmitter and multi‐receiver scenarios when there is no coupling between devices via the reactive near‐field. Our method is applied to the latter to demonstrate its accuracy and computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

An efficient medium access control protocol for mobile ad hoc networks using antenna arrays

In recent years, the use of directional antennas in wireless networks has been widely studied. Since the medium access control (MAC) protocol of the IEEE 802.11 standard was initially designed for systems with omnidirectional antennas, it cannot perform efficiently when directional antennas are used. In this paper, an efficient two-channel MAC protocol is designed for ad hoc networks that are equipped with directional antennas. The proposed protocol utilizes the large throughput offered by directional antennas using two frequency-division multiplexed channels. The first channel is used for control information, and the second for user-data transmission. The proposed MAC protocol operates in two main modes: the omnidirectional mode, in which one antenna is used for the transmission of users? control frames, and the directional mode, in which antenna arrays are used for the transmission of data frames. The proposed protocol is assessed by means of computer simulations based on randomly generated network topologies reflecting the random movement of nodes in the network. Based on these topologies, performance comparisons with the existing MAC protocols are presented for different system parameters. In all cases, the proposed MAC protocol is shown to offer a significant throughput improvement relative to the existing protocols.     

虚拟接收天线MIMO系统及其检测

分层空时接收机的空时复用MIMO可以获得容量的线性增长,但是分层空时处理过程需要接收天线的数量必须至少等于或大于发送天线的数量,对于体积很小的移动手机来说设计多根天线是很困难的,从而阻碍了其广泛的发展。提出了空间复用系统中虚拟接收天线的新概念。每个子数据流都进行一定的时间偏移再传输,同时对接收端输出信号过采样,虚拟接收天线就产生了,物理接收天线的数量相应得到减少。     

基于射线跟踪的MIMO信道容量分析

随着无线通信的发展,MIMO已经成为无线通信领域中的研究热点,场强和信道容量的分布预测是通信系统进行网络规划、管理和维护通信网的基础,对无线网络的优化有着十分重要的意义.选用确定性模型射线跟踪模型,采用镜像法来建立室内MIMO信道模型,并使用MATLAB软件对所建立的模型进行仿真.首先建立特定的室内场景,对其路径损耗进行预测,并与实际测量值进行对比,验证了该模型的正确性及有效性;然后,在理论上对MIMO容量进行分析;最后,仿真分析信噪比(SNR)以及天线数目对MIMO信道容量的影响.     

Rapid prototyping of MIMO‐OFDM based on parity bit selected and permutation spreading

In this paper, a novel MIMO‐OFDM transmission scheme is developed to effectively enable multi‐access by joint code design across multiple antennas, subcarriers, OFDM frames, and users. It achieves better spectrum efficiency while improving bit error rate performance. The proposed scheme uses either parity bit selected or permutation techniques to assign spreading codes at the transmitter side. As a result, the detection at the receiver is greatly improved because of the fact that identifying the spreading code(s) directly yields the transmitted data symbols. The paper also investigates the field‐programmable gate array implementation of the proposed algorithms; optimization techniques are proposed to reduce area, power, and time. These techniques include a pipelined architecture for inverse FFT/FFT blocks, an efficient low complexity algorithm for despreading based on counters and comparators and an optimized architecture for complex matrix inversion using Gauss–Jordan elimination (GJ‐elimination). Finally, the fixed‐point optimized field‐programmable gate array architecture for MIMO‐OFDM transceiver is developed, where the maximum allowed performance loss because of quantization is defined, the tradeoffs between BER performance and area reduction are investigated. Copyright © 2015 John Wiley & Sons, Ltd.