Multiple-input Multiple-output Channel Capacity Research Articles

Millimeter-Wave Dual-Band MIMO Channel Capacity Analysis Based on Climate Data: A Samsun Province Case Study

The analysis of multiple-input multiple-output (MIMO) channel capacity is important for developing and optimizing high-speed wireless communication systems that can meet the growing demand for data-intensive applications. This study aims to analyze the 4 × 4 MIMO channel capacity of outdoor urban and rural environments using the NYUSIM simulator. The channel models are designed for 28 GHz and 39 GHz frequencies for both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. Realistic channel models are simulated using annual climate data collected in Samsun province, Turkey in three different environments: urban microcell (UMi), urban macrocell (UMa), and rural macrocell (RMa) areas. According to the annual average channel capacity analysis, it is observed that there is a very small capacity difference between UMi and UMa areas at 28 GHz and 39 GHz frequencies in the LOS region, while the RMa area is found to have a very low capacity compared to the UMi and UMa areas. The channel capacity for RMa is found to be approximately eight times smaller than UMi and UMa. In the NLOS region, channel capacities decrease significantly (between 312 and 3953 times) compared to the LOS region, with the UMa area having the greatest capacity and the UMi area having the lowest capacity. Compared to the UMi channel capacity, the RMa channel capacity is 1.36 times higher for 28 GHz and 1.28 times higher for 39 GHz. When the monthly changes in channel capacity are examined, it is discovered that the amount of precipitation has the greatest impact on channel capacity, and the capacity decreases as the rain rate increases. The highest correlation between channel capacity and rain rate was −0.97 for RMa, with a 28 GHz frequency and LOS conditions. Additionally, it becomes clear that channel capacities increase in the summer months as the temperature rises and humidity and pressure fall.

UAV-Correlated MIMO Channels: 3-D Geometrical-Based Polarized Model and Capacity Analysis

The unmanned aerial vehicle (UAV) communication with the multiple-input–multiple-output (MIMO) system has attracted lots of attention to improve spectral efficiency and channel capacity. The large antenna spacing is often required to reduce the spatial correlation between subchannels. However, this requirement cannot be well satisfied in practical scenarios due to the limited dimension of UAV platforms. Therefore, polarization diversity is a promising approach for UAV MIMO systems. In this work, we propose a three-dimensional (3-D) geometrical-based polarized model for UAV-correlated MIMO channels. By utilizing the geometrical theory of polarization, we describe the channel depolarization caused by the terrestrial scattering environment based on the multicylinder geometrical model and then acquire the channel polarization function and polarized channel impulse response (CIR). Furthermore, we investigate the impact of the key factors, such as the UAV tilt rotation, cross-polarization, and limited antenna spacing on the UAV MIMO channel capacity. To validate the proposed UAV channel model, we compare the spatial correlations of the numerical simulation and UAV field measurement results for the co- and cross-polarized channels, and the close agreements between them are observed. This work can provide useful guidance and support for the design and performance evaluation of UAV communication networks.

Capacity Bounds for One-Bit MIMO Gaussian Channels With Analog Combining

The use of 1-bit analog-to-digital converters (ADCs) is seen as a promising approach to significantly reduce the power consumption and hardware cost of multiple-input multiple-output (MIMO) receivers. However, the nonlinear distortion due to 1-bit quantization fundamentally changes the optimal communication strategy and also imposes a capacity penalty to the system. In this paper, the capacity of a Gaussian MIMO channel in which the antenna outputs are processed by an analog linear combiner and then quantized by a set of zero threshold ADCs is studied. A new capacity upper bound for the zero threshold case is established that is tighter than the bounds available in the literature. In addition, we propose an achievability scheme which configures the analog combiner to create parallel Gaussian channels with phase quantization at the output. Under this class of analog combiners, an algorithm is presented that identifies the analog combiner and input distribution that maximize the achievable rate. Numerical results are provided showing that the rate of the achievability scheme is tight in the low signal-to-noise ratio (SNR) regime. Finally, a new 1-bit MIMO receiver architecture which employs analog temporal and spatial processing is proposed. The proposed receiver attains the capacity in the high SNR regime.

Two-Way Power Divider With Wide Tunable Power Ratio Range for Weighted-Polarization MIMO Antenna in BAN Radios at 2.45 GHz

This study presented an implementation of weighted-polarization multiple-input–multiple-output (MIMO) antenna for wireless body area networks at 2.45 GHz. The weight function determined by considering the variation in the cross-polarization power ratio <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(XPR)</i> and the antenna tilt angle was realized by a two-way power divider (PD), where tunable power ratio range of proposed PD could not only cross the boundary of equal power ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1), but also maintain a wide tunable range at the same time. The patch array antenna fed by the proposed PD consists of microstrip lines, capacitors, resistors, and varactor diodes can overcome the polarization mismatch in dynamic off-body channel due to the variation in radio-propagation environment and human movement by adjusting the bias voltages. The experiment of 2 × 2 MIMO channel capacity was conducted using a three-dimensional spatial fading emulator. The measured and simulated results are in good agreement. Under the considered condition of arm-swinging angle and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">XPR</i> , the tunable power ratio range of proposed PD can be realized from −1.25 dB to 20 dB; therefore, it is suitable for radio-frequency control antenna to obtaining high data transmission in future wearable MIMO applications.

3-D Deployment of UAV Swarm for Massive MIMO Communications

We consider the uplink transmission between a multi-antenna ground station and an unmanned aerial vehicle (UAV) swarm. The UAVs are assumed as intelligent agents, which can explore their optimal three dimensional (3-D) deployment to maximize the channel capacity of the multiple input multiple output (MIMO) system. Specifically, considering the limitations of each UAV in accessing the global information of the network, we focus on a decentralized control strategy by noting that each UAV in the swarm can only utilize the local information to achieve the optimal 3-D deployment. In this case, the optimization problem can be divided into several optimization sub-problems with respect to the rank function. Due to the non-convex nature of the rank function and the fact that the optimization sub-problems are coupled, the original problem is NP-hard and, thus, cannot be solved with standard convex optimization solvers. Interestingly, we can relax the constraint condition of each sub-problem and solve the optimization problem by a formulated UAVs channel capacity maximization game. We analyze such game according to the designed reward function and the potential function. Then, we discuss the existence of the pure Nash equilibrium in the game. To achieve the best Nash equilibrium of the MIMO system, we develop a decentralized learning algorithm, namely decentralized UAVs channel capacity learning. The details of the algorithm are provided, and then, the convergence, the effectiveness and the computational complexity are analyzed, respectively. Moreover, we give some insightful remarks based on the proofs and the theoretical analysis. Also, extensive simulations illustrate that the developed learning algorithm can achieve a high MIMO channel capacity by optimizing the 3-D UAV swarm deployment with the local information.

Channel modelling for vehicle‐to‐vehicle MIMO communications in geometrical rectangular tunnel scenarios

This study presents a multiple-input multiple-output (MIMO) statistical channel model for vehicle-to-vehicle (V2V) line-of-sight (LOS) and non-LOS mobile communication system in a rectangular tunnel environment. In order to improve the V2V communication system performance, the authors introduced the elevation and azimuth angles in three-dimensional modelling based on the original literature. In the proposed reference channel model, the single-bounced scattering propagation path of electromagnetic signals is considered and it is assumed that the scatterers are randomly distributed on the rectangular tunnel wall. Starting from the statistical physical channel model, the time-variant transfer functions are derived. Thereafter, the analytical expressions of the space–time–frequency cross-correlation function, the space cross-correlation function, the temporal autocorrelation function, the frequency correlation function, and MIMO channel capacity are derived. The influence of model parameters on the performance of the V2V communication system is also analysed. This work provides an innovative approach to channel modelling in a rectangular tunnel mobile communication environment.

Improving the Performance of HALE UAV Communication Link Through MIMO Cooperative Relay Strategy

High-altitude long endurance unmanned aerial vehicles (HALE UAVs) are military and strategic UAVs that fly above the ground in the stratosphere. The ability of stealth technology and long flight time, has led to use of these UAVs for various military missions such as interception and spying, control guidance, remote sensing, navigation, surveillance and others. In this paper, improving the performance of HALE UAVs communication through multiple input multiple output (MIMO) cooperative relay with amplitude-and-forward strategy is investigated. In clear sky (without rain), two-hop system with line of sight (LoS) channels from source to relay and relay to destination is considered. In LoS-MIMO channels, due to correlation between the sub-channels, neither high-rank MIMO channel nor maximum capacity are achieved. However, based on antennas optimum placement that provide orthogonally between the received signals, maximum capacity will be obtained. The proposed scheme in this paper dramatically increases capacity relative to LoS-SISO channel and dual-hop MIMO Rayleigh up to 6 b/s/Hz and 2 b/s/Hz respectively. Also, simulation results verify exactness analytical expressions. However, rain as one of the most important ambient conditions causes the signal to be scattered in different directions. Therefore, LoS channel is changed to fading (Rayleigh) channel by increasing rainfall. In this case, telecommunication range is proposed as a meaningful metric, and outage probability (Poutage) based on telecommunication range for N-hop channel is extracted. In rainy conditions, simulation results show, the telecommunication range dramatically increases by increasing the number of relay UAVs for specified outage probability so that in the long-range, the outage probability decreases up to 50% with the increasing number of relays.

Design of Four-Port Integrated Monopole Antenna Using Refraction Effect of Dielectric Medium for Pattern Gain Enhancement

This article proposes a four-port integrated antenna structure with a dielectric medium, which can be used to increase the pattern gain. To enhance the multiple-input–multiple-output (MIMO) performance, a low correlation is required between antenna elements. First, the refraction effect of the proposed medium is explained, including a derivation of the phase variation. Second, a new four-port integrated monopole antenna is proposed, which operates at 2.4 GHz and is appropriate for supporting a beamforming technique with high gain and small size. The proposed antenna can be useful for reducing correlation with the use of a dielectric medium to increase the pattern gain. This allows the achievable MIMO channel capacity to be increased to the ideal MIMO gain by increasing the pattern gain.

High-Performance Multiple-Input Multiple-Output Antenna System For 5G Mobile Terminals

In this paper, the systematic design of a multiple antenna system for 5G smartphone operating at 3.5 GHz for multiple-input multiple-output (MIMO) operation in smartphones is proposed. The smartphone is preferred to be lightweight, thin, and attractive, and as a result metal casings have become popular. Using conventional antennas, such as a patch antenna, Inverted-F antennas, or monopole, in proximity to metal casing leads to decreasing its total efficiency and bandwidth. Therefore, a slot antenna embedded in the metal casing can be helpful, with good performance regarding bandwidth and total efficiency. The proposed multiple antenna system adopted the unit open-end slot antenna fed by Inverted-L microstrip with tuning stub. The measured S-parameters results agree fairly with the numerical results. It attains 200 MHz bandwidth at 3.5 GHz with ports isolation of (≤−13 dB) for any two antennas of the system. The influence of the customer’s hand for the proposed multiple antenna system is also considered, and the MIMO channel capacity is computed. The maximum achievable MIMO channel capacity based on the measured result is 31.25 bps/Hz and is about 2.7 times of 2 × 2 MIMO operation.

Spatial correlation analysis of imaging MIMO for underwater visible light communication

Absorption and scattering are the main problems affecting the transmission of large capacity information data in underwater visible light communication system(UVLC). To address these problems, we propose the imaging multiple input multiple output (MIMO) system for the underwater communication in this paper. Furthermore, the proposed system uses imaging lens to separate the light signal resulting in that decreasing disturbance of the proposed system is better than that of non-imaging MIMO. In this paper, the spatial correlation caused by imaging lens structure of underwater visible light imaging MIMO communication channel is analyzed. In addition, the influence of the spatial position for transmitting and receiving ends of the imaging system such as light-emitting diode (LED) light source array spacing, and the distance between LED and photodiode (PD) on spatial correlation are modeled. Moreover, the imaging MIMO channel capacities under different channel conditions are derived. The upper bounds of channel capacities under different spatial correlations are solved by equal power allocation method and water injection power allocation method. Finally, the simulation results show that the imaging MIMO system achieves a 12 dB gain at the same bit error rate (BER) compared to the non-imaging MIMO system. Furthermore, the capacity and BER performance of the proposed system are the best in the case of the weakest spatial correlation, and the performance is greatly improved as the spatial correlation becomes weaker.

Amplitude Constrained MIMO Channels: Properties of Optimal Input Distributions and Bounds on the Capacity.

In this work, the capacity of multiple-input multiple-output channels that are subject to constraints on the support of the input is studied. The paper consists of two parts. The first part focuses on the general structure of capacity-achieving input distributions. Known results are surveyed and several new results are provided. With regard to the latter, it is shown that the support of a capacity-achieving input distribution is a small set in both a topological and a measure theoretical sense. Moreover, explicit conditions on the channel input space and the channel matrix are found such that the support of a capacity-achieving input distribution is concentrated on the boundary of the input space only. The second part of this paper surveys known bounds on the capacity and provides several novel upper and lower bounds for channels with arbitrary constraints on the support of the channel input symbols. As an immediate practical application, the special case of multiple-input multiple-output channels with amplitude constraints is considered. The bounds are shown to be within a constant gap to the capacity if the channel matrix is invertible and are tight in the high amplitude regime for arbitrary channel matrices. Moreover, in the regime of high amplitudes, it is shown that the capacity scales linearly with the minimum between the number of transmit and receive antennas, similar to the case of average power-constrained inputs.

Experimental Evaluation of the Tri-Polarized MIMO Channel Properties Based on a Compact Multimode Antenna

Based on a planar and compact antenna, extensive measurements are conducted to investigate the behavior of the colocated tri-polarized multiple-input multiple-output (MIMO) system working at 3.5 GHz. Several scenarios with different multipath distributions have been considered, including a reverberation chamber (RC) and also some line-of-sight (LOS) and obstructed LOS (OLOS) real-world indoor environments. Many channel parameters of the MIMO system are analyzed based on the measured data, including cross-polarization discrimination (XPD), Ricean K-factor, correlation coefficient (CC), MIMO channel capacity gain (CG), channel eigenvalues, and ellipticity statistic (ES). The results show that for a multi-polarized MIMO system, the effects of polarization coupling and transition depend strongly on the polarimetric scattering characteristic of the environments. Furthermore, in all the scenarios tested, three non-zero eigenvalues of the MIMO channel matrix are obtained, which indicates that three independent subchannels can be supported by the tri-polarized MIMO system.

Optimal Transmission in MIMO Channels With Multiuser Interference

Cochannel interference is one of the inevitable deleterious components in designing and analyzing of a wireless network. The use of multiple antennas at both transmitting and receiving nodes is a promising technique to suppress and/or alleviate the effect of cochannel interference on capacity. In this paper, we assess the effects of both antenna correlation and cochannel interference on the ergodic capacity of multiple-input multiple-output channels with covariance feedback. In particular, we consider a general family of spatial fading correlation model-called unitary-independent-unitary -which encompasses most of zero-mean channels with arbitrary fading profiles including the popular separable correlation channel models. We derive the average minimum mean-square error and signal-to-interference-plus-noise ratio of the parallel spatial streams using Berezin’s supermathematics. We then put forth the structure of optimal input covariance matrix maximizing the mutual information connected with the necessary and sufficient conditions as a generalization of the noise-limited case, which is tested by a simple iterative algorithm. Together with the powerful supermathematical framework, the result in the paper enables us to quantify the multiuser MIMO interference effects on the capacity in terms of spatial correlation and interference power heterogeneity.

Channel Diagonalization for Cloud Radio Access

The diagonalization of a conventional multiple-input multiple-output (MIMO) channel into parallel and independent subchannels via singular value decomposition (SVD) is a fundamental strategy that allows the MIMO channel capacity to be achieved using scalar channel codes. This letter establishes a similar channel diagonalization result for the uplink and the downlink of a cloud radio access network (C-RAN), in which a central processor is connected to a remote radio head (RRH) serving a single user via rate-limit digital fronthaul carrying the compressed baseband signal. Specifically, we show that the diagonalization of the MIMO channel between the RRH and the user via SVD and the subsequent independent and parallel quantization of scalar signals and channel coding in each of the subchannels is optimal. This letter establishes this fact using the majorization theory. Further, an uplink-downlink duality for the multiple-antenna C-RAN is identified for this single-user case.

MIMO Channel Capacity and Configuration Selection for Switched Parasitic Antennas

Multiple-input multiple-output (MIMO) systems offer significant enhancements in terms of their data rate and channel capacity compared to traditional systems. However, correlation degrades the system performance and imposes practical limits on the number of antennas that can be incorporated into portable wireless devices. The use of switched parasitic antennas (SPAs) is a possible solution, especially where it is difficult to obtain sufficient signal decorrelation by conventional means. The covariance matrix represents the correlation present in the propagation channel, and has significant impact on the MIMO channel capacity. The results of this work demonstrate a significant improvement in the MIMO channel capacity by using SPA with the knowledge of the covariance matrix for all pattern configurations. By employing the “water-pouring algorithm” to modify the covariance matrix, the channel capacity is significantly improved compared to traditional systems, which spread transmit power uniformly across all the antennas. A condition number is also proposed as a selection metric to select the optimal pattern configuration for MIMO-SPAs.

Interference-Free Criterion for Interference-Unaware Receive Transform in MIMO Co-Channel Interference

In this letter, we derive the upper bound and the lower bound of the achievable rate for the interference-unaware receive transformation (IURT), which does not require interference knowledge or precoding, to obtain the criterion for making IURT become interference free in multiple-input–multiple-output (MIMO) systems under co-channel interference. We prove that if the receive-antenna number is larger than or equal to the interference-free threshold, which is equal to the summation of the transmit-antenna number and the interference’s covariance-matrix rank, then the derived upper bound reaches the interference-free MIMO channel capacity. Furthermore, we prove that by increasing both the transmit-antenna number and the receive-antenna number the derived lower bound can come closer to the interference-free MIMO channel capacity. Simulation results show that if the receive-antenna number is larger than the interference-free threshold, then the achievable rate of IURT can achieve the interference-free MIMO channel capacity.

Optimal Design of Uniform Circular Antenna Array in mmWave LOS MIMO Channel

The capacity of millimeter-wave (mmWave) line-of-sight (LOS) multiple-input multiple-output (MIMO) channel can be reduced due to the absence of rich scattering. However, the optimization of antenna array deployment can enable the maximum spatial multiplexing gain in the mmWave LOS MIMO channel, which can be applied to the long distance airborne data transmission. In this paper, we first establish the channel model of mmWave LOS MIMO based on a uniform circular antenna array (UCA) and derive the upper/lower bound of channel capacity. Aiming at achieving the maximum capacity of mmWave LOS MIMO channel, we propose the Newton-iterative method to obtain the optimal parameters of UCA. To simplify the optimization algorithm, the 2-D search can be transformed into 1-D search. Then, the analysis of bit error rate (BER) of the mmWave LOS MIMO system based on the UCA has been provided to quantify the mmWave LOS MIMO channel. Finally, numerical results demonstrate that the optimal parameters of UCA can be obtained by the Newton-iterative method and the BER of mmWave LOS MIMO communication system based on the corresponding optimized UCA can be minimized.

A Novel MIMO Channel Model for Vehicle-to-Vehicle Communication System on Narrow Curved-Road Environment

This paper presents a generalized statistical multiple-input multiple-output (MIMO) fading channel model for a vehicle-to-vehicle (V2V) non-line of sight mobile communication system on narrow curved-road environments. The MIMO channel model captures the propagation effect that occurs when vehicles move towards a junction with a side road and corner scatterings. In this paper, both single- and double-bounced scattering mechanisms are considered and it is assumed that the scatterers are uniformly distributed in the form of narrow arcs outside the annular road. Our geometry-based channel model takes the exact relationship between the angle-of-arrival and the angle-of-departure into account. Thereafter, the statistical properties of the model are studied under the assumption of non-isotropic scattering. Analytical expressions of different parameters, such as the space---time-frequency cross-correlation function, Doppler power spectral density, and MIMO channel capacity are provided. Furthermore, the influence of model parameters on the performance of V2V communication system has been analyzed. The study provides a design layout of MIMO V2V communication systems with a wide-band spatial channel model enabling the performance analysis of new high-data-rate transmission schemes for narrow curved-road propagations.

Contribution of non-uniform EBG antenna arrays to the enhancement of MIMO channel capacity

The work proposes novel multiband and of low profile antenna arrays with hybrid type elements, for the realization of a MIMO (Multiple Input–Multiple Output) wireless communication system with great capacity. Each element is composed of a linear dipole integrated with a non-uniform Electromagnetic Band Gap (EBG) lattice. This EBG type, influences the system by two ways, the strong reduction of the Mutual Coupling (MC) among the closely positioned array's elements and the high radiation gain values of each element, inside wide space areas. Both of them make the antenna element capable of enhancing the MIMO channel capacity. It was ascertained by the results which were received taking into account globally, the MC and the radiation patterns of the antenna elements. The Spatial Channel Model (SCM) scenario for Urban Micro and Urban Macro environments was applied and the capacity calculation was made in one step which incorporates both the channel and the antenna characteristics. Results for the capacity at all three bands of operation are presented, for 10dB SNR level, along with respective ones received from dipole arrays in front of Perfect Electric Conductor (PEC). The comparison shows clearly the superiority of the proposed hybrid type array and its robust performance in wireless propagation scenarios.

Experimental study on the statistic characteristics of a 3x3 RF MIMO channel over a single conventional multimode fiber.

Based on the observed random fluctuation phenomenon of speckle pattern across multimode fiber (MMF) facet and received optical power distribution across three output ports, we experimentally investigate the statistic characteristics of a 3×3 radio frequency multiple-input multiple-output (MIMO) channel enabled by mode division multiplexing in a conventional 50µm MMF using non-mode-selective three-dimensional waveguide photonic lanterns as mode multiplexer and demultiplexer. The impacts of mode coupling on the MIMO channel coefficients, channel matrix, and channel capacity have been analyzed over different fiber lengths. The results indicate that spatial multiplexing benefits from the greater fiber length with stronger mode coupling, despite a higher optical loss.