Conventional Multiple-input Multiple-output Systems Research Articles

An Electromagnetic Information Theory Based Model for Efficient Characterization of MIMO Systems in Complex Space

It is the pursuit of a multiple-input-multiple-output (MIMO) system to approach and even break the limit of channel capacity. However, it is always a big challenge to efficiently characterize the MIMO systems in complex space and get better propagation performance than the conventional MIMO systems considering only free space, which is important for guiding the power and phase allocation of antenna units. In this manuscript, an Electromagnetic-Information-Theory (EMIT) based model is developed for efficient characterization of MIMO systems in complex space. The group-T-matrix-based multiple scattering fast algorithm, the mode-decomposition-based characterization method, and their joint theoretical framework in complex space are discussed. Firstly, key informatics parameters in free electromagnetic space based on a dyadic Green's function are derived. Next, a novel group-T-matrix-based multiple scattering fast algorithm is developed to describe a representative inhomogeneous electromagnetic space. All the analytical results are validated by simulations. In addition, the complete form of the EMIT-based model is proposed to derive the informatics parameters frequently used in electromagnetic propagation, through integrating the mode analysis method with the dyadic Green's function matrix. Finally, as a proof-or-concept, microwave anechoic chamber measurements of a cylindrical array is performed, demonstrating the effectiveness of the EMIT-based model. Meanwhile, a case of image transmission with limited power is presented to illustrate how to use this EMIT-based model to guide the power and phase allocation of antenna units for real MIMO applications.

Hybrid beamforming in Multiuser mmWave Massive MIMO System

Conventional MIMO systems typically use full digital processing for optimal performance while it requires an independent radio frequency (RF) chain for each antenna, which is not feasible for large-scale antenna arrays due to the high cost, high-power consumption and high complexity of RF chain components in high frequencies. Fortunately, in recent years, the Hybrid beamforming has been proposed as an efficient and auspicious technique for the practical implementation of millimeter-Wave (mmWave) multiple-input multiple-output (MIMO) wireless systems. In this paper we propose a novel HBF (Hybrid beamforming) algorithm and simulate the sum rate of the proposed approach, then compare it with other algorithms in the sum rates. Specifically, the HBF algorithm as well as the maximizing minimum phase difference algorithm are based on the MMSE (Minimum Mean Square Error). For the full-digital beamforming and the beam steering, the ZF (zero forcing) criterion is employed. Simulations demonstrate that the performance of the proposed algorithm is similar to the full digital algorithm, and its robustness is confirmed by comparisons with other existing algorithms under the same channel model.

Wireless Power Transfer by Beamspace Large-Scale MIMO With Lens Antenna Array

In this paper, we study wireless power transfer (WPT) using the discrete lens array-based beamspace large-scale multiple-input multiple-output (MIMO) system. The channel matrix of beamspace MIMO exhibits sparse property, which enables the transmitter to employ only a small number of active antennas while maintaining the full MIMO performance. Hence, the number of radio frequency (RF) chains can be significantly reduced, cutting the cost of hardware implementation and circuit power consumption. We consider two WPT design problems in the beamspace MIMO system with constraints on the number of RF chains: the sum power transfer and the max–min power transfer problems; and for each problem, we consider both multi-stream and uni-stream transmissions. For the sum power transfer problem, we show that the uni-stream power transfer achieves the same performance as the multi-stream case, and we propose two algorithms for the uni-stream transmission, namely, an eigendecomposition-based greedy algorithm and a truncated power iteration algorithm. For the max–min power transfer problem, we propose a semidefinite relaxation-based greedy algorithm for the multi-stream power transfer and a Riemannian conjugate gradient algorithm for the uni-stream case. The simulation results show that with a small number of RF chains, the beamspace MIMO system significantly outperforms the conventional MIMO system in terms of WPT efficiency.

Atmospheric turbulence mitigation using spatial mode multiplexing and modified pulse position modulation in hybrid RF/FSO orbital-angular-momentum multiplexed based on MIMO wireless communications system

Abstract In this paper, the capacity of a free-space optical (FSO) communication over radio frequency (RF) could potentially be increased by the simultaneous transmission of multiple orbital angular momentum (OAM) based on spatial mode multiplexing (SMM) as an additional effective degree of freedom (EDOF) and quadrature amplitude modulation (QAM). This paper describes using hybrid RF/FSO-OAM based on multiple-input multiple-output (MIMO)/SMM using M-ary modified pulse position modulation (MPPM) and spatial PPM (SPPM) for potentially enhancing capacity in wireless communication systems. We present an analytical system design concerning OAM multiplexing and MIMO/SMM processing in free space communications channel under atmospheric turbulence (AT). Here, we assume a new architecture that closes the gap in speeds between millimeter-wave (mm-wave) wireless and optical links. In this study, we highlight recent advances in the use of OAM multiplexing for high-capacity FSO and mm-wave communications. We have developed the MPPM in FSO communication over RF using the source Gaussian model and SMM by proposing a new version of hybrid SPPM and MPPM. The novelty approach presents performance enhancement of the acquisition, pointing, tracking position and AT mitigation of link. We propose to use SMM combined with OAM-QAM based MIMO communications system to mitigate both weak and strong turbulence distortions. Simulation results show that the capacity of OAM-based MIMO system outperforms the capacity of the conventional MIMO system when the propagation distance is larger than a specific threshold. The use of transmitter lenses could enhance the OAM beams with a larger mode spacing (MS) of 2 (OAM l = + 1 , l = + 3 , l = + 5 , l = + 7 transmitted) shows a lower power penalty (PP) when the inter-channel crosstalk overwhelms a larger lateral displacement of about 2 mm. Using the lenses at the transmitter to focus OAM beams could reduce power loss and PP in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams and provide high power-efficiency. With a larger of the transmitter and receiver 8 cm, 10 cm aperture size respectively, the system with mode spacing of 2 (OAM l = + 1 , l = + 3 , l = + 5 , l = + 7 transmitted) and mode spacing of 3 (OAM l = + 1 , l = + 4 , l = + 7 , l = + 10 transmitted) of OAM beams based on MIMO should fulfill lower-power penalty of 2.2 dB, 3.4 dB, as respectively and could enhance system robustness under angular error but degrade tolerance of lateral displacement. The proposed system provides an excellent signal-to-noise ratio (SNR) for the capacity in the regime of strong atmospheric turbulence. In this way, the maximization of FSO communication and RF wide, the data capacity enhancement, and it is considered a massive solution in the bandwidth provision for future access networks. This work could be beneficial to the practical implementation of OAM-MIMO/SMM multiplexed RF/FSO links.

Information-Theoretic Treatment of Space Modulation MIMO Systems

In space modulation techniques (SMTs), data bits are transmitted through modulating spatial and signal symbols. Signal symbols are ordinary complex symbols drawn from an arbitrary constellation diagram, such as quadrature amplitude modulation. Yet, spatial symbols represent the different channel paths from multiple transmit antennas to all receive antennas in a multiple-input multiple-output (MIMO) system. At each particular time instant, one or more of these channel paths is used to transmit the signal symbol and all other paths remain inactive. The receiver jointly determines the transmitted symbol and the considered channel paths to retrieve the information bits. This is unlike any conventional wireless communication technique, and special information-theoretic treatment is needed. In this paper, the theoretical channel capacity of SMTs is deduced. The conditions under which such capacity can be achieved are derived and discussed. Mutual information results for space shift keying, spatial modulation, generalized spatial modulation, and quadrature spatial modulation, as illustrative examples of SMTs, over several fading channels are reported and thoroughly discussed. The obtained Monte Carlo simulation results validate the accuracy of the conducted analysis. It is demonstrated that SMTs can achieve substantial gains as compared to the conventional MIMO systems. Such gains are attainable with proper design of signal symbols for each specific fading channel.

On the Feasibility of Interference Alignment in Compounded MIMO Broadcast Channels With Antenna Correlation and Mixed User Classes

This paper presents a generalized closed-form beamforming technique that can achieve the maximum degrees of freedom in compounded multiple-input multiple-output (MIMO) broadcast channels with mixed classes of multiple-antenna users. The contribution is firstly described within the context of a three-cell network and later extended to the general multi-cell scenario where we also show how to determine the conditions required to align the interference in a subspace that is orthogonal to the one reserved for the desired signals. This is then followed by an analysis of the impact of antenna correlation for different channel state information acquisition models. The proposed scheme is examined under both conventional and Large-scale MIMO systems. It will be shown that the proposed technique enables networks with any combination of user classes to achieve superior performance even under significant antenna correlation, particularly in the case of the Large-scale MIMO systems.

Sparse-Aware Minimum Mean Square Error Detector for MIMO Systems

In this letter, we propose a novel detector, called the sparse-aware minimum mean square error (SA-MMSE) detector, to improve detection performance for multiple input multiple output (MIMO) systems. We first convert a conventional MIMO system into a sparse system via the symbol error vector obtained from a linear detector. Then, we develop a new sparse refining method, which has a similar structure as the linear MMSE detector, to improve the detection performance. The proposed SA-MMSE detector can be performed iteratively and has low complexity similar to that of the parallel interference cancellation (PIC). Simulation results show that the SA-MMSE detector outperforms the compressive-sensing-based detector and PIC with a similar complexity, especially when the numbers of users and antennas become large.

Capacity Evaluation of MIMO Channel With One Leaky Coaxial Cable Used as Two Antennas Over Linear-Cell Environments

Leaky coaxial (LCX) cable is widely used in wireless communication systems as an antenna, especially for a long and narrow area called the linear-cell environment. The general usage of LCX cable is that it can be treated as one antenna. To configure a multiple-input–multiple-output (MIMO) system, it requires more than one LCX cable. In this paper, we propose a simple design in which one single LCX cable can be used as two antennas. Therefore, the proposal reduces the cost and spacing requirement and releases the space requirement of MIMO deployment for wireless application over linear-cell environments. We will study the capacity of the proposed LCX–MIMO system using equal power (EP) allocation and water-filling power allocation and compare its capacity with the conventional MIMO system using monopole antennas. The capacity results over the 2.4 GHz band and the 5 GHz band show that the proposed LCX–MIMO channel has better capacity than that of using monopole antennas over linear-cell environments. In particular, it can achieve more capacity improvement than that of channel using monopole antennas with the simple EP allocation. The throughput experiments over 5 GHz also show that our proposal can achieve the higher and stable throughput over the radiation coverage of LCX cable.

Source Transmit Antenna Selection for Space Shift Keying With Cooperative Relays

In this letter, we propose a cooperative multiple-input multiple-output (MIMO) scheme combining transmit antenna selection (TAS) and space shift keying (SSK). In this scheme, source transmit antennas are selected and SSK is applied by using the selected antennas. Besides the direct link transmission, the relays, that decode the source signal correctly, take part in the transmission. Exact expressions and a considerably accurate approximate expression for the symbol error rate of the proposed SSK system are derived. It is shown that the proposed scheme outperforms the SSK system without TAS and also the conventional cooperative MIMO system, which employs source TAS, at practical signal-to-noise ratio values for especially high data rates and sufficient number of receive antennas at the destination.

Multiple-Beam Selection With Limited Feedback for Hybrid Beamforming in Massive MIMO Systems

Hybrid multiple-input multiple-output (MIMO) systems have been thought as a promising technology in future 5G. Compared with conventional digital MIMO systems, such a structure is equipped with fewer RF chains, which would reduce the computational complexity and hardware cost, and meanwhile additional analog beamforming is introduced to maintain the performance. However, scarce RF chains make channel state information acquisition difficult for analog beamforming. In this paper, we consider a practical hybrid beamforming, which includes zero-forcing (ZF) precoding in digital beamforming, and beam selection for analog beamforming. First, the statistic information of users (e.g., angle and distance) is utilized to construct an approximate channel for each user. Second, users individually evaluate the codebook and feedback the results, by which base station (BS) makes optimization and selects the final beams for analog beamforming. Finally, BS performs the digital baseband ZF precoding with the equivalent channel. In the process, we give two limited feedback methods for users, and two corresponding beam selection methods for BS. These methods are evaluated in the Rayleigh fading channels and mmWave channels. Simulation results show that our hybrid beamforming could approach performance of conventional digital precoding, and more RF chains could provide better performance. Moreover, proposed methods only require once feedback and effectively reduce the delay, and two feedback methods achieve a good tradeoff between performance and feedback cost.

Effective Interference Nulling Virtual MIMO Broadcasting Transceiver for Multiple Relaying

In multi-hop relay networks, the improving end-to-end sum rate is a challenging issue. Although a new cooperative beamforming called virtual multiple-input multiple-output (MIMO) has been introduced as a possible solution, conventional virtual MIMO systems have severe signaling overhead among master and source nodes when the number of hops increases. To resolve this problem, a broadcast virtual MIMO system and a virtual MIMO broadcasting transceiver (VMBT) have been proposed to reduce the computational complexity and improve the end-to-end sum rate. However, the application of such methods is limited to environments wherein interference from other links and networks is not considered. Thus, it is difficult to apply them to practical multi-hop relay networks. In this paper, we propose a generalized version of the VMBT in which intra- and inter-network interferences are simultaneously caused by multiple transmission of clusters in the same network and each network’s usage of the same frequency band, respectively. To achieve this goal, we propose an effective interference nulling VMBT scheme. Simulation results show that the proposed scheme has efficient performance in terms of average end-to-end sum rate compared with conventional schemes.

Capacity Analysis of Orbital Angular Momentum Wireless Channels

The orbital angular momentum (OAM) technology is able to provide a new degree of freedom for wireless communication systems. The energy of OAM waves is focused within a circle region surrounding the beam axis, which makes the propagation gains inside and outside the circle region different. However, in the existing literature, the propagation gains inside and outside the circle region are assumed to be the same. Therefore, the impact of OAM waves’ spatial energy distribution on the capacity of OAM wireless communication systems has not been fully investigated. Considering the spatial energy distribution characteristics of OAM waves, in this paper, an OAM wireless channel model is proposed. Based on the proposed OAM wireless channel model, the capacity of OAM-based multiple-input multiple-output (MIMO) communication system is analytically derived. Simulation results indicate that the capacity of OAM-based MIMO system outperforms the capacity of conventional MIMO system when the transmission distance is larger than a specific threshold. Our results provide a basic capacity model for OAM-based MIMO communication systems.

Element-by-Element Full-Rank Optical Wireless MIMO Systems Using Narrow-Window Angular Filter Designed Based on One-Dimensional Photonic Crystal

In the field of radio-frequency (RF) communications, the multiple-input multiple-output (MIMO) strategy allows us to attain a higher rate of data transfer due to the multipath-rich environment. In contrast, it is challenging to achieve the same rate in a highly correlated channel that is specific to optical wireless communications. In this paper, we propose the novel concept of an element-by-element optical MIMO system that enables the interference-free reception of parallel symbol streams; it achieves this by using an angular filter (AF) with a narrow transparent window. The AF consists of a one-dimensional photonic crystal, and the angular selectivity is obtained by using the extremely small wave vector regime. We demonstrate that the capacity of the proposed system increases linearly with the minimum number of transmit source elements and receive detectors, which is similar to conventional RF MIMO systems.

주파수 분할 방식의 거대 다중 안테나 시스템을 위한 빔형성 기반의 채널상태정보 기준신호 전송기술

기존 MIMO 시스템 대비 수십 또는 수백 배 많은 송신 안테나들이 설치되어 있는 주파수 분할(frequency division duplex, FDD) 방식의 거대 다중 안테나(massive multiple-input mulitple-output, Massive MIMO)에선 송신 안테나 별 CSI-RS(channel state information reference signal) 전송을 위해 기존 MIMO 시스템 대비 너무 많은 하향 및 상향링크 자원 요소가 필요하다는 한계를 갖는다. 이러한 단점들을 극복하기 위해 본 논문에선 주파수 분할 방식의 거대 다중 안테나 시스템에서 많은 송신 안테나를 사용하더라도 자원요소(resource element, RE)를 재사용함으로써 송신 안테나 수에 비례하지 않는 제한된 양의 하향링크 자원만을 사용하여 CSI-RS를 효과적으로 전송하는 기술 및 자원격자 구조를 제안하였다. Since FDD massive MIMO (multiple-input multiple-output) system deploys hundreds of transmit antennas at base station (BS) compared to conventional MIMO system, the overhead of transmitting channel state information reference signal (CSI-RS) increases proportionally to the number of transmit-antennas. To overcome these disadvantages, we proposed beamforming based CSI-RS transmission technique for FDD massive MIMO system which transmit CSI-RS by limited amount of downlink resources.

A Review of Compressive Sensing Detection for Spatial Modulation in Massive MIMO System

Multiple Input Multiple Output (MIMO) low complexity receiver which utilizes the compressive sensing detection for Spatial Modulation in large scale MIMO system in order to reduce the system complexity. In conventional MIMO system; huge amount of antennas is used at both ends to exploit the multipath propagation. This system maximizes the throughput performance and data rates are increased but only at the cost of high hardware complexity and increased power-consumption. Spatial Modulation Matching Pursuit (SMMP) is the proposed enhanced CS technique used for the improvement of detection performance. Hence, this paper reviews recent research findings concerning normalized Compressive Sensing (CS) detection algorithm, used for Spatial Modulation (SM) in massive MIMO, to lowers the signal processing complexity, which in result improves the energy efficiency of system against that of conventional MIMO system.This strategy is achieved by involving additional structures and sparsity in which a single transmitter antenna or a subset of it is turned on at each case to transmit a certain data. The subset of antenna which is turned on for transmission depends on approaching data bits. Therefore, the total increase in the spectral efficiency of the system is given as base-two logarithm of whole antennas at the transmitter. It reduces the signal processing load at base station and doesn’t depend upon any synchronization between transmitters. The Spatial Modulation Matching Pursuit used prevents the Inter Channel Interference (ICI) of the system which in result improves the Bit Error Rate (BER) performance than the typical MIMO system.

Novel Single-RF MIMO System Based on Repetitive Pulse Width Modulation

Many alternative systems have been studied based on compact single-RFs for multiple-input multiple-output (MIMO) systems. However, the implementation of such systems has been limited by a lack of robustness in relation to system environment. In this letter, we propose a novel MIMO system based on a repetitive pulse width modulation, which requires a single-RF and switches only, without the need for a phase shifter. The mathematical formulations for the proposed system are derived and the signal difference between our proposed system and a conventional MIMO system is shown mathematically. The performance of the proposed system is verified by comparing its channel capacity with that of a conventional MIMO system.

Robust RF Beamforming for Millimeter Wave MIMO–OFDM Systems

In conventional multiple-input multiple-output systems, each antenna is connected to a radio-frequency (RF) chain. Due to the tiny wavelength of millimeter waves (mmWave), tens of antennas can be packed into a small area in mmWave transceivers. However, implementing an RF chain for each antenna is impractical due to the high cost and power of mixed-signal devices. In order to reduce the cost and get benefit from the antennas, an analog RF beamformer is implemented using variable gain amplifiers and analog phase shifters. In this paper, we propose a novel spatial diversity scheme for mmWave RF beamforming. The transmitter is assumed to have partial knowledge of the channel to the receiver. We formulate the spatial diversity problem as maximizing the geometric mean of the projections of the RF precoder on the transmit steering vectors and the geometric mean of the projections of the RF combiner on the receive steering vectors. To solve the optimization problem of the RF beamformers, we propose two solution algorithms. The first algorithm is based on semidefinite relaxation (SDR). Due to the high computational complexity of the SDR algorithm, we propose a simpler second algorithm, which is gradient ascent algorithm. Simulation results show that the proposed spatial diversity scheme outperforms the conventional spatial diversity schemes in case of no blockage and in case of blockage to any propagation path regardless of the number of propagation paths.

PERFORMANCE ANALYSIS OF SPATIAL MODULATION IN MIMO- A SURVEY

Spatial modulation (SM) is a recently developed transmission technique that uses index of antenna in a multiple input multiple output (MIMO) antenna system, as additional means of data transmissions. The use of index of the active antennas at any time instant is the main idea behind spatial modulation. The information bits to be transmitted are divided into two parts. The first part is mapped to a symbol chosen from the signaling constellation, where depending on modulation scheme the number of bits per symbol varies. The second part determines the antenna index to be selected from a set of antennas available for data transmission. Thereby increases the spectral efficiency and decreases the complexity at receiver section. The rate of data transmission can much more increased by mapping into subsets of antennas in MIMO. The paper summarizes some of the recent works and issues of SM MIMO. The antenna selection in spatial modulation mainly depends on the incoming information data which is unlike the antenna selection in conventional MIMO system which depends on the channel state information (CSI) and the received signal strength.

Modulation-Mode and Power Assignment in SVD-Assisted Broadband MIMO Systems using Polynomial Matrix Factorization

Singular-value decomposition (SVD)-based multiple-input multiple-output (MIMO) systems have attracted a lot of attention in the wireless community. However, applying SVD to frequency-selective MIMO channels results in unequally weighted single-input single-output (SISO) channels requiring complex resource allocation techniques for optimizing the channel performance. Therefore, a different approach utilizing polynomial matrix factorization for removing the MIMO interference is analyzed, outperforming conventional SVD-based MIMO systems in the analyzed channel scenario.

빔공간 MIMO 시스템에 기반한 OFDM 전송방법

Beamspace Multiple-Input Multiple Output(MIMO) system can transmit multiple data by using Electronically Steerable Parasitic Array Radiator(ESPAR) antenna which has single Radio Frequency(RF)-chain. Beamspace MIMO system can reduce complexity of the system and size of antenna in comparison with the conventional MIMO system because of characteristic of ESPAR antenna using the single antenna and the RF-chain. Heretofore, only the research of transmitting single-carrier has been conducted by the use of beamspace MIMO system. Therefore, in this paper, we propose beamspace MIMO system based on Orthogonal Frequency Division Multiplexing(OFDM) for transmitting the multi-carrier and analysis the performance of this system. We find a proper reactance value which has good performance because proposed system changes the performance by the reactance values of parasitic elements. and we confirm that performance of the proposed system is similar to conventional MIMO system based on OFDM. 논문 15-40-03-02 The Journal of Korean Institute of Communications and Information Sciences '15-03 Vol.40 No.03 http://dx.doi.org/10.7840/kics.2015.40.3.425 425 ※ 이 논문은 2012년도 정부(교육과학기술부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(No. 2012017339) 그리 고 이 논문은 2013년도 정부(교육과학기술부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(No.2013R1A2A2A01 005849) 그리고 본 연구는 미래창조과학부 및 정보통신기술진흥센터의 정보통신·방송 연구개발 사업의 일환으로 수행하였음(14-000 -04-001, 고집적 Compact MIMO 안테나 개발). First Author : Smart Radio Research Team, Electronics and Telecommunications Research Institute, jkchoi@etri.re.kr, 정회원 ° Corresponding Author : Department of electronics engineering, Chungbuk National University, ecomm@cbu.ac.kr, 정회원 * Department of electronics engineering, Chungbuk National University, acy890217@naver.com, 학생회원 논문번호:KICS2014-10-438, Received October 30, 2014; Revised March 2, 2015; Accepted March 2, 2015 The Journal of Korean Institute of Communications and Information Sciences '15-03 Vol.40 No.03