Fifth-generation (5G) cellular networks will almost certainly operate in the high-bandwidth, underutilized millimeter-wave (mmWave) frequency spectrum, which offers the potentiality of high-capacity wireless transmission of multi-gigabit-per-second (Gbps) data rates. Despite the enormous available bandwidth potential, mmWave signal transmissions suffer from fundamental technical challenges like severe path loss, sensitivity to blockage, directivity, and narrow beamwidth, due to its short wavelengths. To effectively support system design and deployment, accurate channel modeling comprising several 5G technologies and scenarios is essential. This survey provides a comprehensive overview of several emerging technologies for 5G systems, such as massive multiple-input multiple-output (MIMO) technologies, multiple access technologies, hybrid analog-digital precoding and combining, non-orthogonal multiple access (NOMA), cell-free massive MIMO, and simultaneous wireless information and power transfer (SWIPT) technologies. These technologies induce distinct propagation characteristics and establish specific requirements on 5G channel modeling. To tackle these challenges, we first provide a survey of existing solutions and standards and discuss the radio-frequency (RF) spectrum and regulatory issues for mmWave communications. Second, we compared existing wireless communication techniques like sub-6-GHz WiFi and sub-6 GHz 4G LTE over mmWave communications which come with benefits comprising narrow beam, high signal quality, large capacity data transmission, and strong detection potential. Third, we describe the fundamental propagation characteristics of the mmWave band and survey the existing channel models for mmWave communications. Fourth, we track evolution and advancements in hybrid beamforming for massive MIMO systems in terms of system models of hybrid precoding architectures, hybrid analog and digital precoding/combining matrices, with the potential antenna configuration scenarios and mmWave channel estimation (CE) techniques. Fifth, we extend the scope of the discussion by including multiple access technologies for mmWave systems such as non-orthogonal multiple access (NOMA) and space-division multiple access (SDMA), with limited RF chains at the base station. Lastly, we explore the integration of SWIPT in mmWave massive MIMO systems, with limited RF chains, to realize spectrally and energy-efficient communications.

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A Comprehensive Survey on Millimeter Wave Communications for Fifth-Generation Wireless Networks: Feasibility and Challenges

This contribution provides experimental evidence for the two-wave with diffuse power (TWDP) fading model. We have conducted two indoor millimetre wave measurement campaigns with directive horn antennas at both link ends. One horn antenna is mounted in a corner of our laboratory, while the other is steerable and scans azimuth and elevation. Our first measurement campaign is based on scalar network analysis with 7 GHz of bandwidth. Our second measurement campaign obtains magnitude and phase information; it is additionally sampled directionally at several positions in space. We apply Akaike’s information criterion to decide whether Rician fading sufficiently explains the data or the generalised TWDP fading model is necessary. Our results indicate that the TWDP fading hypothesis is favoured over Rician fading in situations where the steerable antenna is pointing towards reflecting objects or is slightly misaligned at line-of-sight. We demonstrate TWDP fading in several different domains, namely, frequency, space, and time.

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Better than Rician: modelling millimetre wave channels as two-wave with diffuse power

We describe an extensive channel-measurement campaign, including 325 unique transmitter–receiver configurations, conducted in a lecture room with our 3-D double-directional 60 GHz channel sounder. The receiver was mounted on a mobile robot, with 40 cm spacing between channel acquisitions, enabling the tracking of clustered multipath components in the multidimensional delay-angle space. To mitigate against angle-estimation error and multipath blockage, we introduce a robust tracking algorithm based on the Assignment Problem. For the purpose of validation, the clusters were transformed from the delay-angle space onto a 2-D map of the environment and compared against the locations of cluster-generating reflectors, such as walls and tables. The location errors were typically within 30–50 cm. The clusters identified were then reduced to a stochastic map-based channel model, including reflection loss and dispersion characteristics such as the Ricean K-factor and angular spread. Given the 0.5 ns delay resolution of the channel sounder and angle-estimation error around 2°, the parameters were reported with high fidelity.

Methodology for Multipath-Component Tracking in Millimeter-Wave Channel Modeling

Clustering of multipath components (MPCs) is an important aspect of propagation channel modeling. When a time series of measurements, based on movement of transmitter and/or receiver, is available, the temporal evolution of MPCs can be used as a basis for clustering. We present an algorithm that bases clustering not only on distance of MPCs in the delay/angle space, but also how similar the temporal evolution of their parameters are. Sample results obtained from a vehicle-to-vehicle measurement campaign show good performance of the proposed algorithm.

Trajectory-Joint Clustering Algorithm for Time-Varying Channel Modeling

The increasing requirement for the mobile data traffic accelerates the research of millimeter-wave (mm-wave) for future wireless systems. Accurate characterization of the mm-wave propagation channel is fundamental and essential for the system design and performance evaluation. In this paper, we conducted measurement campaigns in various indoor scenarios, including classroom, office, and hall scenarios, at the frequency bands of 27–29 GHz. The spatial channel characteristics were recorded by using a large-scale uniform circular array. A high-resolution parameter estimation algorithm was applied to estimate the mm-wave spherical propagation parameters, i.e., the azimuth angle, elevation angle, delay, source distance, and complex amplitude of multipath components. With the same measurement system, the channel parameters including decay factor, delay spread, angular spread, and line of sight power ratio are investigated thoroughly in individual indoor scenarios and compared in different indoor scenarios. Furthermore, the impact of the furniture richness level and indoor geometry on the propagation parameters are also investigated.

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Experimental Characterization of Millimeter-Wave Indoor Propagation Channels at 28 GHz

This paper presents a clustering and tracking method that exploits the geometry of the scattering points (SPs) obtained from the measurement-based ray tracer. The multipath components (MPCs) were categorized into clusters by applying the KPowerMeans (KPM) framework to those SPs. The clusters were tracked by comparing the cluster-centroid SPs of the adjacent snapshots. The clusters were estimated based on the indoor environment geometry at 11 GHz, and their physical mechanisms were interpreted. The complexity and performance of this method was assessed and compared with that of conventional KPM by comparing the number of floating point operations (FLOPS) and the channel eigenvalues obtained from the reconstructed channel matrices, which were calculated by superposing the MPCs randomly generated from intracluster parameters. The verification of this method showed that most clusters were estimated and tracked according to the physical location of the scatterers in the environment with acceptable error. Moreover, the eigenvalues reconstructed from the proposed method were closer to the measured ones with less number of FLOPS, which indicates both accuracy and complexity improvement. The results also imply that multiple-input multiple-output performance is highly dependent on the radio propagation channel; therefore, it is imperative that clusters in the channel be determined accurately.

Multipath Clustering and Cluster Tracking for Geometry-Based Stochastic Channel Modeling

Double Directional Millimeter Wave Propagation Channel Measurement and Polarimetric Cluster Properties in Outdoor Urban Pico-cell Environment

This paper presents an analysis of geometry-based cluster frequency dependency at super-high-frequency bands, including 3, 10, and 28 GHz. First, multipath components were extracted from the measured data by using the space-alternating generalized expectation-maximization algorithm. Then, geometry-based clusters were estimated by using the enhanced scattering point-based KPowerMeans (SPKPM) algorithm. Finally, the frequency dependencies of their scattering intensities were discussed with the assistance of physical optics. The analysis results showed that the SPKPM could also be applied to obtain reasonable scattering locations at multiple frequencies in most cases. In addition, reflection on smooth surfaces was the dominant mechanism of clustering where there was no frequency dependence, whereas diffraction, scattering, and shadowing were significant causes of frequency dependence. Assuming that the line-of-sight is obstructed, diffraction, scattering, and shadowing accounted for 30–40% of the entire channel in terms of power, which was not negligible and thus the channel was largely frequency-dependent. The analysis results are expected to provide crucial insights for multiple-frequency channel modeling for fifth-generation wireless systems.

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Panawit Hanpinitsak

Papers

Experimental Characterization of Millimeter-Wave Indoor Propagation Channels at 28 GHz

Multipath Clustering and Cluster Tracking for Geometry-Based Stochastic Channel Modeling

Double Directional Millimeter Wave Propagation Channel Measurement and Polarimetric Cluster Properties in Outdoor Urban Pico-cell Environment

Frequency Characteristics of Geometry-Based Clusters in Indoor Hall Environment at SHF Bands

2D Interleaver Design for Image Transmission over Severe Burst-Error Environment