Multiple-input And Multiple-output Technique Research Articles

ISOLATION ENHANCEMENT TECHNIQUES IN MIMO ANTENNA SYSTEMS: A SURVEY

In this survey paper, we discuss various techniques that can be employed to enhance isolation between multiple-input and multiple-output (MIMO) antennas. In this modern world, the MIMO antenna system is an important technique used in wireless technology. The channel capacity in a multipath environment can be improved by deploying multiple antenna elements, i.e., the MIMO technique at both the transmitter and receiver terminals. To have an efficient MIMO technique, the isolation between the multiple antenna elements must be as high as possible. In the past decade, many research works have proposed techniques to enhance isolation in MIMO antennas. In this survey, we examined various mutual coupling reduction techniques employed to improve isolation in multiple antenna elements and compared them based on various performance metrics. Isolation enhancement techniques such as stubs, filters, defected ground structure, decoupling networks, orientation of the radiating elements, parasitic elements, periodic structures, neutralization lines, metamaterials, etc., are discussed in this paper.

Enhancing NOMA’s Spectrum Efficiency in a 5G Network through Cooperative Spectrum Sharing

Non-orthogonal multiple access (NOMA) is one of the most effective techniques for meeting the spectrum efficiency (SE) requirements of 5G and beyond networks. This paper presents two novel methods for improving the SE of the downlink (DL) NOMA power domain (PD) integrated with a cooperative cognitive radio network (CCRN) in a 5G network using single-input and single-output (SISO), multiple-input and multiple-output (MIMO), and massive MIMO (M-MIMO) in the same network and in a single cell. In the first method, NOMA users compete for free channels in a competing channel (C-CH) on the CCRN. The second method provides NOMA users with a dedicated channel (D-CH) with high priority. The proposed methods are evaluated using the Matlab software program using the three scenarios with different distances, power location coefficients, and transmitting power. Four users are assumed to operate on 80 MHz bandwidths (BWs) and use the quadrature phase shift keying (QPSK) modulation technique in all three scenarios. Successive interference cancellation (SIC) and unstable channel conditions are also considered when evaluating the performance of the proposed system under the assumption of frequency selective Rayleigh fading. The best four-user SE performance obtained by user U4 was 3.9 bps/Hz/cell for SISO DL NOMA, 5.1 bps/Hz/cell for SISO DL NOMA with CCRN with C-CH, and 7.2 bps/Hz/cell for SISO DL NOMA with CCRN with D-CH at 40 dBm transmit power. While 64 × 64 MIMO DL NOMA improved SE performance of the best-use U4 by 51%, 64 × 64 MIMO DL NOMA with C-CH CCRN enhanced SE performance by 64%, and 64 × 64 MIMO DL NOMA with D-CH CCRN boosted performance by 65% SE compared to SISO DL NOMA at 40 dB transmit power. While 128 × 128 M-MIMO DL NOMA improved SE performance for the best U4 user by 79%, 128 × 128 M-MIMO DL NOMA with C-CH CCRN boosted SE performance by 85%, and 128 × 128 M-MIMO DL NOMA with D-CH CCRN enhanced SE performance by 86% when compared to SISO DL NOMA SE performance at 40 dB transmit power. We discovered that the second proposed method, when using D-CH with CCR-NOMA, produced the best SE performance for users. On the other hand, the spectral efficiency is significantly increased when applying MIMO and M-MIMO techniques.

MIMO to Enhance the Performance of VLC Systems

In general, visible light communication (VLC) systems run at low data rates. By introducing multiple input and multiple output (MIMO) techniques, service at enhanced data rates can be viable for VLC systems. This work proposes MIMO technique to attain VLC system with high data rates. To attain MIMO method this system includes a number of photodiodes with a narrow field of view (FOV), which highlights the benefit of using MIMO technology in improving the data rate. The results show that using MIMO technique leads to enhance the VLC system when it is compared with the traditional system (without using MIMO). The results show that an improvement in the signal-to-noise ratio (SNR) level, which is the most attempt to determine communication quality, increasing the channel bandwidth and reducing the delay spread are achieved when MIMO technique is used.

Performance optimisation of indoor SVD‐based MIMO‐OFDM optical wireless communication systems

The performance of multiple-input and multiple-output (MIMO) flip-orthogonal frequency division multiplexing (flip-OFDM) for indoor optical wireless communications (OWCs) is studied here. To improve the system performance in terms of the bit error rate (BER), the singular value decomposition (SVD)-based MIMO technique is applied together with the bit loading technique. The authors, especially, focus on optimising the BER performance of SVD-based MIMO-OFDM OWC systems under the impact of the OFDM symbol design, the configuration of MIMO transmitters, the required data rates, the available bandwidth, and the angular diversity based on tilting receiver photo detectors (PDs). The system BER expressions are analytically derived and verified to be accurate through comparison with simulation results. The authors find that the 9 × 4-MIMO system is the optimal configuration in terms of a large coverage of low BER regions and low computational complexity for the 5 m × 5 m room. In addition, polar angle tilting of PDs can effectively improve the BER performance. Finally, in case of light dimming control with a low total transmit optical power, the system can benefit from a high multiplexing gain with a large tilting polar angle, as indicated by improved condition numbers of MIMO channel matrices.

Underwater cooperative MIMO communications using hybrid acoustic and magnetic induction technique

Future smart ocean applications require reliable communication networks connecting underwater sensors/robots and remote base stations, which is challenging to achieve due to the harsh and dynamic underwater channels. While Multiple-Input and Multiple-Output (MIMO) acoustic technique can address this problem, it is difficult to place multiple transducers on a single device due to the large wavelength. Although the cooperative MIMO technique could solve this issue, it was impossible to synchronize the distributed transmitters due to the extremely large and dynamic propagation delay of acoustic waves. In this paper, we propose an underwater cooperative MIMO communication mechanism, which is based on a hybrid acoustic and Magnetic Induction (MI) technique. The inter-node synchronization problem can be solved by using the MI technique so that the distributed transducers can cooperatively form narrow beams for long distance communications. The synchronization time and errors are significantly reduced since MI has negligible propagation delays. To quantitatively analyze the improvement, the closed-form of the synchronization error, signal-to-noise ratio (SNR), effective communication time, and throughput of the proposed system are rigorously derived. The proposed system is implemented in a software-defined testbed under the beamforming and space-time coding scheme. Through both numerical and experimental analysis, our hybrid cooperative MIMO mechanism can achieve much lower bit error rate and synchronization error than the conventional acoustic MIMO systems.

Subsurface MIMO: A Beamforming Design in Internet of Underground Things for Digital Agriculture Applications

In underground (UG) multiple-input and multiple-output (MIMO), transmit beamforming is used to focus energy in the desired direction. There are three different paths in the underground soil medium through which the waves propagate to reach the receiver. When the UG receiver receives a desired data stream only from the desired path, then the UG MIMO channel becomes a three-path (lateral, direct, and reflected) interference channel. Accordingly, the capacity region of the UG MIMO three-path interference channel, and the degrees of freedom (multiplexing gain of this MIMO channel) requires careful modeling. Therefore, expressions are required for the degrees of freedom of the UG MIMO interference channel. The underground receiver needs to perfectly cancel the interference from the three different components of the EM waves propagating in the soil medium. This concept is based upon reducing the interference of the undesired components to a minimum level at the UG receiver using the receive beamforming. In this paper, underground environment-aware MIMO using transmit and receive beamforming has been developed. The optimal transmit and receive beamforming, combining vectors under minimal intercomponent interference constraints, are derived. It is shown that UG MIMO performs best when all three components of the wireless UG channel are leveraged for beamforming. The environment-aware UG MIMO technique leads to three-fold performance improvements and paves the way for design and development of next-generation sensor-guided irrigation systems in the field of digital agriculture. Based on the analysis of underground radio-wave propagation in subsurface radio channels, a phased-array antenna design is presented that uses water content information and beam-steering mechanisms to improve efficiency and communication range of wireless underground communications. It is shown that the subsurface beamforming using phased-array antennas improves wireless underground communications by using the array element optimization and soil–air interface refraction adjustment schemes. This design is useful for subsurface communication system where sophisticated sensors and software systems are used as data collection tools that measure, record, and manage spatial and temporal data in the field of digital agriculture.

基于MIMO异构Ad Hoc网络节点调度优化算法

多输入多输出(MIMO)技术在很大程度上提升无线网络的传输可靠性与频谱利用率。异构Ad Hoc网络中的节点不需要有线连接就能够直接通信，从而弥补了固定网络基础设施通信的缺陷。因此，异构Ad Hoc网络结合MIMO技术成为了学术界的一个研究热点。然而，在基于MIMO异构Ad Hoc网络中，不同的发送–接收对之间是通过不同的链路传输数据流，而链路与链路之间会存在共信道干扰的现象。好的节点调度方法对减少链路之间的干扰起很重要的作用。针对异构Ad Hoc网络传输链路特点，本文提出的分布式节点调度优化方法，根据每一条链路与其他链路之间的竞争情况，得到每一条链路的资源分配(rate)。在进行节点调度的过程中，根据不同链路的rate值，发送节点可以选择最优的接受节点传输数据流。实验仿真结果表示，分布式节点调度优化算法能够明显减少共信道干扰现象，从而提升系统的吞吐量。 Multiple-input and multiple-output (MIMO) can obviously improve transmission reliability and bandwidth efficiency in wireless networks. The nodes in heterogeneous Ad Hoc networks enable to communicate directly without wired connections, making up the lack of communication with fixed network infrastructures. Therefore, heterogeneous Ad Hoc networks combined with MIMO techniques becomes one of the research hotspots in academia. However, in heterogeneous Ad Hoc networks based on MIMO, different transmitter-receiver pairs transmit data streams by different links which have the effect of co-channel interference. A good scheduling algorithm plays an important part in reducing the co-channel interference. According to the characteristics of heterogeneous Ad Hoc networks and the contention regions between links, we propose node scheduling optimization algorithm to obtain resource allocation (rate). Based on different rate of different links, transmitters can choose the optimum receivers to transmit data streams via node scheduling. The results of the experience proof that node scheduling optimization algorithm can highly improve the system throughput with reducing the effect of co-channel interference.

Mobility-Aware Video Streaming in MIMO-Capable Heterogeneous Wireless Networks

Multiple input and multiple output (MIMO) is a well-known technique for the exploitation of the spatial multiplexing (MUX) and spatial diversity (DIV) gains that improve transmission quality and reliability. In this paper, we propose a quality-adaptive scheme for handover and forwarding that supports mobile-video-streaming services in MIMO-capable, heterogeneous wireless-access networks such as those for Wi-Fi and LTE. Unlike previous handover schemes, we propose an appropriate metric for the selection of the wireless technology and the MIMO mode, whereby a new address availability and the wireless-channel quality, both of which are in a new wireless-access network so that the handover and video-playing delays are reduced, are considered. While an MN maintains its original care-of address (oCoA), the video packets destined for the MN are forwarded with the MIMO technique (MUX mode or DIV mode) on top of a specific wireless technology from the previous Access Router (pAR) to the new Access Router (nAR) until they finally reach the MN; however, to guarantee a high video-streaming quality and to limit the video-packet-forwarding hops between the pAR and the nAR, the MN creates a new CoA (nCOA) within the delay threshold of the QoS/quality of experience (QoE) satisfaction result, and then, as much as possible, the video packet is forwarded with the MUX. Through extensive simulations, we show that the proposed scheme is a significant improvement upon the other schemes.

Analysis of Multistatic Pixel Correlation in SAR

The field of wireless communications has benefited from multiple-input and multiple-output (MIMO) techniques. As researchers seek to apply MIMO (multistatic) techniques to radar and specifically to synthetic aperture radar (SAR), a key factor in determining MIMO application and performance is the level of correlation of signals from different receiver/transmitter pairs. The level of correlation determines whether a MIMO array falls into the category of a collocated array or a distributed array. The type of array dramatically affects which MIMO techniques may be performed and what advantages MIMO offers from conventional techniques. This paper presents models for calculating geometric correlation of multistatic SAR pixels using a ground-plane image formation. The models' results are compared to previous correlation models found in literature. A key result is that correlation depends on pixel resolution and not the number of individual scatterers. This paper concludes that most MIMO arrays operating on a single platform operate in the collocated regime.

Trace-Orthogonal PPM-Space Time Block Coding Under Rate Constraints for Visible Light Communication

Visible light communications (VLC) represents a new frontier of communications allowing high data-rate Internet access, specially in indoor environments, where the use of light emitting diodes (LEDs) is growing as a viable alternative to traditional illumination. As a result, LED output intensity can be varied faster than human eye can perceive, thus guaranteeing simultaneous wireless communications and illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically around several MHz. The use of multiple input and multiple output (MIMO) techniques in optical wireless system helps to increase the capacity of the system and thus improve the system performance. In this paper, we investigate the use of an optical MIMO technique jointly with pulse position modulation (PPM) in order to improve the data rates without reducing the reliability of the link. PPM is known to be signal-to-noise ratio efficient modulation format, while it is bandwidth inefficient so the use of MIMO can compensate that drawback with reasonable complexity. Furthermore, an offline tool for VLC system planning, including error probability and transmission rate, has been proposed in order to solve the tradeoff between transmission rate and error rate. Finally, several numerical results and performance comparisons are reported.

Review of wideband MIMO channel measurement and modeling for IMT-Advanced systems

In October 2005, the next generation mobile communication system was officially named as the International Mobile Telecommunications-Advanced (IMT-Advanced) by the ITU Radiocommunication Sector (ITU-R). Wideband multiple input and multiple output (MIMO) channel models in multiple propagation environments are fundamental for IMT-Advanced systems and such research has been initiated since 2003. The research challenges come from the fact that the wider bandwidth (20–100 MHz) and the advanced multiple antenna technology have been proposed for the IMT-Advanced system, thus leading to higher sampling rates and multiple spatial propagation channels. In this review, four aspects of wideband MIMO channel measurement and modeling are discussed: (1) radio channel measurement procedure and equipment; (2) large scale fading models; (3) small scale fading models; and (4) MIMO channel models. In particular, the large scale fading affected by the carrier frequency is investigated for urban macrocells and it shows that the higher carrier frequency results in greater loss for non-line-of-sight (NLoS) conditions in the cities of China, for which the frequency dependent factor is 32.1. Moreover, the dense and the obviously higher buildings also lead to a larger angle spread (AS) of both the angle of arrival and angle of departure in urban macrocell scenarios. The results indicate that there is the potential to explore the MIMO technique for an IMT-Advanced system with larger ASs, which would lead to the high system capacity. The progress on MIMO models is described and some methods for simplifying geometry-based stochastic channel models (GBSM) are proposed. Finally future research topics on channel measurement and modeling are identified.

D-BLAST OFDM with Channel Estimation

Multiple-input and multiple-output (MIMO) systems formed by multiple transmit and receive antennas can improve performance and increase capacity of wireless communication systems. Diagonal Bell Laboratories Layered Space-Time (D-BLAST) structure offers a low-complexity solution for realizing the attractive capacity of MIMO systems. However, for broadband wireless communications, channel is frequency-selective and orthogonal frequency division multiplexing (OFDM) has to be used with MIMO techniques to reduce system complexity. In this paper, we investigate D-BLAST for MIMO-OFDM systems. We develop a layerwise channel estimation algorithm which is robust to channel variation by exploiting the characteristic of the D-BLAST structure. Further improvement is made by subspace tracking to considerably reduce the error floor. Simulation results show that the layerwise estimators require 1 dB less signal-to-noise ratio (SNR) than the traditional blockwise estimator for a word error rate (WER) of when Doppler frequency is 40 Hz. Among the layerwise estimators, the subspace-tracking estimator provides a 0.8 dB gain for WER with 200 Hz Doppler frequency compared with the DFT-based estimator.