Multiple-input Multiple-output Propagation Research Articles

Estimating the Performance of MIMO SC-FDE Systems Using SISO Measurements

The demand for ubiquitous telecommunications services forces operators to have a special concern about signal quality and the coverage area they offer to their customers. This was usually checked by using suitable propagation models for Single Input Single Output (SISO) systems, which are no longer the case for new and future mobile generations, such as 5G and beyond. To guarantee good signal quality coverage, operators started to replace these models with Multiple Input Multiple Output (MIMO) ones. To achieve the best results, these models are usually calibrated with Drive Test (DT) measures; however, the DTs available for MIMO propagation models are sparse, in contrast to SISO ones. The main contribution presented in this paper is a methodology to extend the propagation models of SISO systems so they can be applied in MIMO sytems with Single-Carrier and Frequency-Domain Equalization (SC-FDE), while still using DTs acquired for SISO systems. This paper presents the impact on Bit Error Rate (BER) performance and its coverage area resulting from the application of our proposed method. We consider a MIMO SC-FDE system with an Iterative Block Decision Feedback Equalization (IB-DFE) receiver and we present the improvement expressions for the BER that we illustrate with some simulations.

Open area 2 × 2 MIMO channel model for 2 GHz low-elevation links with diversity and capacity applications

In civil surveillance applications, Unmanned Aerial Vehicles (UAV) are being increasingly used in floods, fires and law enforcement scenarios. In order to transfer large amounts of information from UAV-mounted cameras, relays, or sensors, large bandwidths are needed in comparison to those required for remotely commanding the UAV. This demands the use of higher frequency bands, in all probability in the vicinity of 2 or 5 GHz. Novel hardware developments need propagation channel models for the ample range of operational scenarios envisaged, including multiple input multiple output (MIMO) deployments. These configurations may enable a more robust transmission by increasing either the carrier-to-noise ratio (CNR) statistics or the achievable capacity. In this paper, a 2 × 2 MIMO propagation channel model for an open field environment capable of synthesizing a narrowband time-series at 2 GHz is described. Maximal ratio combining (MRC) diversity and capacity improvements are also evaluated through synthetic series and compared with measurement results. A simple flat, open scenario was evaluated based on which other, more complex environments can be modeled.

Statistical modeling of the high altitude platform dual-polarized MIMO propagation channel

In order to investigate the benefit of multiple-input multiple-output (MIMO) technique applying to the high altitude platform (HAP), a 2×2 MIMO statistical model, which can accurately describe the channel between HAP and high-speed train, is presented. And dual polarization diversity is particularly considered. Based on first-order three-state Markov chain, the single-input single-output (SISO) channel, a subset of the MIMO channel is first established. The ray tracing approach applied to the digital relief model (DRM) which covers the railway between Xi'an and Zhengzhou is used to obtain the state probability vector and matrix of the state transition probability. The proposed model considers both Doppler shift and temporal correlation, and the polarization correlation and spatial correlation statistical properties of large-scale fading and small-scale fading are analyzed. Moreover, useful numerical results on the MIMO HAP channel outage capacity are provided based on which, significant capacity gains with respect to the conventional SISO case are illustrated. Such statistical channel model can be applied to the future wireless communication system between HAP and high-speed train.

Keyholes in MIMO-OFDM: Train-to-Wayside Communications in Railway Tunnels

One of the key challenges in railway engineering is how to provide passengers an efficient, secure, and safe service. To achieve this, operators and stakeholders demand robust and high-capacity train-to-wayside broadband radio. Current radio technologies implement MIMO (Multiple-Input Multiple-Output) technology, whose use requires a good characterization of the propagation. In this paper, the results of an experimental campaign on MIMO propagation in subway tunnels are presented. The campaign makes use of an OFDM testbed at roughly 600 MHz, allowing the measurement of the 2×2 channel transfer matrix under different conditions regarding polarization, antenna separation, tunnel cross section, power allocation algorithm, and so forth. Particular attention is paid to the probability of appearance of keyholes, which imply a severe degradation of the MIMO performance even when transmitter and receiver antennas are uncorrelated. The measurements are carried out using a train that travels at the normal operative velocities. As a result of the measurements, it has been found that the use of vertical polarization at both terminals is advantageous and that, on average but for a narrow margin, λ-spaced antennas outperform λ/2-spaced ones (90% capacities of 7.00 and 6.76 bps/Hz, resp.), although the latter show a lower probability of keyholes. However, keyhole probabilities are always below 2%, so their influence on the performance of the whole system is limited.

Statistical Modeling of Ultrawideband MIMO Propagation Channel in a Warehouse Environment

This paper describes an extensive propagation channel measurement campaign in a warehouse environment for line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios. The measurement setup employs a vector network analyzer operating in the 2–8-GHz frequency band combined with an $8 \times 8$ virtual multiple-input multiple-output (MIMO) antenna array. We develop a comprehensive statistical propagation channel model based on high-resolution extraction of multipath components and subsequent spatiotemporal clustering analysis. The intracluster direction of departure (DoD), direction of arrival (DoA), and the time of arrival (ToA) are independent, both for the LOS and NLOS scenarios. The intracluster DoD and DoA can be approximated by the Laplace distribution, and the intracluster ToA can be approximated by an exponential mixture distribution. The intercluster analysis, however, shows a dependency between the cluster DoD, DoA, and ToA. To capture this dependency, we separately model the clusters caused by single and multiple bounce scattering along the aisles in the warehouse. The intercluster DoD distribution follows a Laplace distribution, while the cluster DoA conditioned on the DoD is approximated by a Gaussian mixture distribution. The model was validated using the capacity and delay-spread values.

A Statistical Model of the In-Home MIMO PLC Channel Based on European Field Measurements

The multiple-input multiple-output (MIMO) technique is well known in the field of wireless communications, and has recently been proposed to increase the capacity of in-home power line communication (PLC) networks. MIMO PLC employs the protective earth in addition to the classical line and neutral wires to form a multi-sensor transmission channel. By considering the additional reception of common-mode signals, up to two simultaneous transmit ports and four receive ports can be considered. In order to develop new signal processing strategies optimally exploiting the MIMO propagation characteristics and to evaluate their performance, the accurate modeling of the transmission channel is necessary. This paper presents a comprehensive statistical model of the in-home MIMO PLC channel based on an extensive measurement data base collected in six European countries. The paper first analyzes the main MIMO PLC channel parameters, including path loss parameters and wideband parameters, such as the delay spread, coherence bandwidth, and small-scale statistics. A focus is then made on the MIMO correlation matrix, and its modeling using empirical statistical distributions. A fully parameterized channel model is then developed, with a particular emphasis on both the frequency fading structure of the transfer function and the correlation matrix between sub-channels. As a result, the proposed model generates random MIMO PLC channel realizations, statistically representative of the experimental observations.

8K Terrestrial Transmission Field Tests Using Dual-Polarized MIMO and Higher-Order Modulation OFDM

Japan Broadcasting Corporation (NHK) is conducting research on the next-generation of digital terrestrial broadcasting that will enable ultrahigh definition television such as 8K. Multiple-input multiple-output (MIMO) technology should be able to expand the single-input single-output channel capacity. $2 {\times }2$ MIMO is adopted in ATSC3.0 as an optional method. In order to construct a next-generation terrestrial network using MIMO technology and to ensure an adequate link budget especially as regards the MIMO propagation parameters, two experimental stations have been installed in Hitoyoshi city, Kumamoto, Japan. This system is an extension of the conventional DTV system in Japan, called ISDB-T. NHK conducted $2 {\times }2$ MIMO field tests using one station and $4 {\times }2$ MIMO field tests using two stations composing a single frequency network (SFN). For the $4 {\times }2$ MIMO test, an advanced SFN using space time coding was developed. The $2 {\times }2$ MIMO field tests involved terrestrial 8K transmissions (91 Mb/s) over a single UHF band channel (6 MHz bandwidth). The degradation of required carrier to noise ratio compared to laboratory measurements in dual-polarized MIMO propagation was under 3 dB even in non-line-of-sight conditions. The $4 {\times }2$ MIMO field tests indicated that the required received power of the SFN was up to 3 dB better than that of the conventional SFN.

Benefits of Rich Scattering in MIMO Channels: A Graph-Theoretical Perspective

In this letter, the impact of scattering on a multiple-input multiple-output (MIMO) propagation environment is studied based on a recently-proposed graph-theoretical channel model. An old result that rich scattering in MIMO propagation environments is a requisite for the channel matrix to have full rank (equivalently for the channel capacity to scale linearly with the number of antennas) is verified. Then, novel insights on the importance of scattering in MIMO channels from a graph-theoretical perspective are provided. By showing that the adjacency matrix of the whole propagation channel has same spectrum (eigenvalues) as the sub-graph inter-connecting the scatterers, it is inferred that all graph-theoretical properties of the propagation graph are contained in the scattering fraction of the channel. In particular, it is inferred that the channel model can be almost-surely reconstructed from the sole knowledge of the spectrum of the sub-graph interconnecting the scatterers. These results may find application in MIMO channel modeling in settings where full pilot-based channel estimation is infeasible or impractical, as in high-mobility scenarios.

Development of Millimeter-Wave Mobile Camera and Performance Improvement in Outdoor LOS Environment

The Millimeter-wave Mobile Camera (MiMoCam) developed by NHK STRL uses millimeter-wave band (42GHz/55GHz) to transmit Hi-Vision TV picture with high quality and low latency. Multiple-input multiple-output (MIMO) technology which uses a number of antennas at both the transmitter and receiver can be adapted to use to transmit higher quality Hi-Vision TV picture. The camera was intended to be used in a studio environment where there is a high degree of multi-path, however there are also many requests for the MiMoCam to be used outdoor. This will present a different channel statistics where the camera will be operating in a near line-of-sight (LOS) environment without much reflected waves. We have conducted an outdoor transmission test and measured the outdoors transmission performance of the proposed MIMO system to clarify the possibility of using the MiMoCam in outdoor environment. This paper introduces the features of the MiMoCam system and the MIMO transmission technique used in the MiMoCam and presents the findings of this outdoor test. It was also confirmed that channel correlation of the MIMO propagation channels were suppressed by using orthogonally polarized waves and bit error rate (BER) characteristics with respect to the average receiving carrier-to-noise ratio (CNR) was improved. Finally, we could find the feasibility of the MiMoCam outdoor operation from these results.

Spatial correlation and capacity measurements for wideband MIMO channels in indoor office environment

This paper describes a broadband multiple input, multiple output (MIMO) channel characterization platform and capacity measurement results in indoor office environment. The MIMO testbed has been designed for broadband MIMO channel sounding, capacity measurements and for characterizing the directional-multipaths of the radio propagation channel. The MIMO channel data have been collected in 5 GHz band inside a modern office environment. Capacity results from these experiments are discussed for different propagation conditions, including non line-of-sight (NLOS) and LOS propagations with various spacings between array elements. Spatial correlations are analyzed from the measured data and a frequency selective MIMO channel model based on the correlation statistics is validated. Post-processing of the measured data with a sequential ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) algorithm is utilized to extract the directions of departures and arrivals of multipath components at the transmitting and receiving arrays, respectively. A method of obtaining broadband MIMO capacity, indirectly, from a single directional measurement of MIMO propagation channel is also proposed and verified from the measurement results.

Lateral Position Dependence of MIMO Capacity in a Hallway at 2.4 GHz

We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 times 4 multiple-input multiple-output (MIMO) system in which both ends of the wireless link are located in a hallway. This scenario is of interest due to the increasing mobility of wireless devices, and because hallways have previously been reported to create difficulties for MIMO propagation. In this paper we focus on the variation in capacity as a function of position as one side of the wireless link is moved laterally (i.e., vertically and horizontally) in the hallway. We find not only significant degradation in MIMO capacity due to rank collapse, but also identify considerable variability due to changes in the signal strength. The capacity along a vertical cut is found to be relatively constant about 7.5 plusmn 1 bps/Hz for a reference signal-to-noise ratio (SNR) of 10 dB at a range of 12 m, which is significantly less than the ideal maximum of 11.5 bps/Hz. The capacity along a horizontal cut is found to be about 6.7 plusmn 3 bps/Hz under the same conditions, dominated by a large-scale signal strength variation which can be attributed to identifiable propagation mechanisms. We also consider the performance relative to simpler rank-1 (diversity/beamforming) schemes, with and without channel state information.

Impact of Clustering in Indoor MIMO Propagation Using a Hybrid Channel Model

The clustering of propagating signals in indoor environments can influence the performance of multiple-input multiple-output (MIMO) systems that employ multiple-element antennas at the transmitter and receiver. In order to clarify the effect of clustering propagation on the performance of indoor MIMO systems, we propose a simple and efficient indoor MIMO channel model. The proposed model, which is validated with on-site measurements, combines the statistical characteristics of signal clusters with deterministic ray tracing approach. Using the proposed model, the effect of signal clusters and the presence of the line-of-sight component in indoor Ricean channels are studied. Simulation results on channel efficiency and the angular sensitivity for different antenna array topologies inside a specified indoor scenario are also provided. Our investigations confirm that the clustering of signals significantly affects the spatial correlation, and hence, the achievable indoor MIMO capacity.

Models for MIMO propagation channels: a review

AbstractThis paper reviews recently published results on multiple input multiple output (MIMO) channel modeling. Both narrowband and wideband models are considered. We distinguish between two main approaches to MIMO channel modeling, that is, physically based and nonphysically based modeling. The nonphysical models primarily rely on the statistical characteristics of the MIMO channels obtained from the measured data, while the physical models describe the MIMO channel (or its distribution) via some physical parameters. We briefly review different MIMO channel models and discuss their relationships. Some interesting aspects will be described in more detail and we note areas in which few results are available. Copyright © 2002 John Wiley & Sons, Ltd.