There is strong impetus by the Telecom Infra Project to exploit the 60 GHz unlicensed band for public Wi-Fi in urban environments, by installing access points on light poles. Although many 60 GHz urban channel measurements have been recorded to date, they have resulted only in path loss models or root-mean-square (RMS) delay spreads. What is needed at millimeter-wave is a spatially consistent channel model for beamtracking that embodies the characteristics of these short wavelengths—sparsity and rough surface scattering—such as the Quasi-Deterministic model. In this letter, we fit the model to channel measurements we recorded in an urban environment. The measurements were recorded at 4, 6, and 9 m antenna heights to investigate the tradeoffs between light pole heights. The large-scale channel metrics between the model and the measurements were shown to match very well.

Quasi-Deterministic Channel Propagation Model for 60 GHz Urban Wi-Fi Access From Light Poles

Rapid growth in wireless communication technologies and the introduction of smart phones has resulted in an unprecedented increase in the demand for data. Present systems operating at sub-6 GHz frequencies are not capable of addressing this increased data demand from future wireless communication systems, owing to the limited bandwidth available and spectral congestion at these frequencies. The potential for using largely unallocated frequency spectrum available at millimetre wave frequencies to address this increased data demand has been studied recently. To overcome the increased propagation and penetration losses at millimetre wave frequencies, integrated circuit technologies and signal processing techniques are being developed in order to make millimetre wave communication a reality. In wireless system deployment, the system planner must deploy base station antennas at the most appropriate locations to maximize system performance. In this research, the effect of transmitting antenna deployments on system performance in single room office environments at millimetre wave frequencies is investigated using a three-dimensional implementation of Geometrical Optics and the Uniform Theory of Diffraction (GO/UTD). Multiple antenna deployments and artificial environmental modifications (such as planar and non-planar reflectors, hemispherical array reflectors and reflectarrays) are also investigated in order to quantify how such techniques could improve system performance. A quantitative estimate of shadowing inside the office volume indicated that there are significant shadow regions that cannot be eliminated by simply increasing the transmitted power. It is shown that such regions can be significantly reduced in size if an appropriate deployment of multiple antennas or passive reflectors is adopted.

Deploying Millimetre Wave Indoor Wireless Systems

A 60 GHz swept-tone channel sounder with 1 GHz measurement bandwidth has been developed. The sounder has been used to analyse millimetre-wave propagation in a compact indoor office environment. Profiles of the power angle-of-arrival have been measured for a number of different transmitter and receiver configurations to identify the dominant propagation paths. It was found that the power carried on specular single-and double-bounce reflections from objects in the office (e.g., door frames and whiteboards) are typically 15–20 dB below that carried on the line-of-sight (LOS) path. A further experiment with an absorber phantom (representing the human body) showed the LOS path can be readily shadowed at 60 GHz. However, the attenuation introduced by an internal wall consisting of drywall mounted on timber frames was measured to be between 11– 22 dB, leading to the conclusion that internal walls may be insufficient to isolate co-channel systems if the LOS path is otherwise occluded.

60 GHz Millimetre-Wave Channel Characterisation for Indoor Office Environments

This article presents a novel and cost-effective vector network analyzer (VNA)-based phase-compensated channel sounder operating in the frequency range of 10–50 GHz using radio-over-fiber (RoF) techniques, which can support multilink/channel long-range phase-coherent measurements. The optical cable enables long-range channel measurements with a dynamic range of 115.7 dB at 30 GHz (for the back-to-back connection). The phase compensation scheme is utilized for stabilizing the inherent phase variations introduced by the optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. A novel optical delay line and combiner scheme is proposed and implemented to separate the signals, thereby saving the port resource on the VNA for multilink/channel measurements. The proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with the presence of thermal changes and mechanical stress. The phase change could be maintained within 3° at 10–30 GHz and 7° in 30–50 GHz compared to the over 80° phase variation introduced by the cable effects at 10–50 GHz, demonstrating the robustness and effectiveness of the developed channel sounder in practice. With the proposed optical delay line and combiner scheme, multiple channels can be measured simultaneously with minimal VNA ports, significantly reducing the measurement cost and time for multilink channel measurements. Two multilink indoor channel measurements are conducted and analyzed using a virtual uniform rectangular array (URA) at 28-GHz bands. The results demonstrate the capability of the proposed channel sounder to perform high-fidelity long-range ultrawideband multilink channel measurements.

Design and Validation of a Multilink Phase- Compensated Long-Range Ultrawideband VNA-Based Channel Sounder

A significant number of propagation models have been proposed for 5G communication systems in recent years. Among the different environments studied, indoor propagation environments have emerged in importance. The present paper reviews current research in indoor propagation modelling at different frequencies relevant to 5G signal propagation. The paper goes on to present a model for attenuation of 5G signals in the X band. The model takes into account the variation of signal attenuation due to varying number of human bodies and other obstacles present in the indoor environment at different times of a day, leading to time-dependent difference in signal to noise ratio (SNR). A non-linear polynomial based machine learning technique is then used to obtain a least-squares (LS) estimate of SNR from the model.

Attenuation Modelling and Machine Learning Based SNR Estimation for 5G Indoor Link

Millimeter-wave (mmWave) communications promise Gigabit/s data rates thanks to the availability of large swaths of bandwidth between 10–100 GHz. Although cellular operators prefer the lower portions of the spectrum due to popular belief that propagation there is more favorable, the measurement campaigns to confirm this – conducted by ten organizations thus far – report conflicting results. Yet it is not clear whether the conflict can be attributed to the channel itself – measured in different environments and at different center frequencies – or to the differences in the organizations’ channel sounders and sounding techniques. In this paper, we propose a methodology to measure mmWave frequency dependence, using the 26.5–40 GHz band as an example. The methodology emphasizes calibration of the equipment so that the measurement results represent the channel alone (and not the channel coupled with the channel sounder). Our results confirm that free-space propagation is indeed frequency invariant – a well understood phenomena but to our knowledge reported nowhere else at mmWave to date. More interestingly, we found that specular paths – the strongest after the line-of-sight path and so pivotal to maintaining connectivity during blockage – are the least invariant compared to weaker diffracted and diffuse paths.

/pdf/methodology-for-measuring-the-frequency-dependence-of-2soyyejf.pdf

Methodology for Measuring the Frequency Dependence of Multipath Channels Across the Millimeter-Wave Spectrum

A hardware testbed to characterise propagation for wideband indoor millimetre-wave channels in the 57–60 GHz band is described. The testbed is based on a direct conversion architecture and uses commercial-off-the-shelf components to transmit and receive the millimetre-wave signals and generate/capture the corresponding baseband waveforms. Tone-test measurements have been used to quantify the impact of hardware impairments in the testbed, and indicate that compensation for the IQ-imbalance arising from the mixers is required. The attenuation introduced by common building materials has also been experimentally investigated using a vector network analyser over the 33–50 GHz millimetre-wave bands. Pine wood was found to introduce approximately 25 dB attenuation, while the attenuation due to drywall was approximately 1.4 dB. These results suggest that internal partitions made from drywall may not be sufficient to isolate co-channel systems in a building. Measurements using sponge material also indicate materials with high water content experience increased attenuation.

Indoor millimetre wave channel measurements for 5G wireless systems

This paper describes a wideband synthetic-aperture system and the associated Fourier processing for generating high-resolution spatial and temporal estimates of the signal propagation environment in wireless communication channels at millimeter-wave frequencies. We describe how to configure the synthetic aperture system for high angular resolution by sampling the progression of signal phase across a large planar area in space. We also show how to synthesize discrete measurements of the channel frequency response taken sequentially over a wide bandwidth to create power delay profiles (PDPs) in specified angular directions with high delay resolution. We provide a rigorous uncertainty analysis that can be made metrologically traceable to fundamental physical standards. This uncertainty framework can propagate the errors inherent in the measured signals through to the final channel estimates and derived parameters such as root-mean-square delay or angular spread. We illustrate use of the system in conjunction with two different analysis tools to extract both narrowband and wideband parameter estimates from the synthetic aperture, allowing its use as a stand-alone channel sounder or as a tool for verifying the performance of wireless devices.

https://ieeexplore.ieee.org/ielx7/8782711/8889399/10025561.pdf

Damla Guven

Papers

Methodology for Measuring the Frequency Dependence of Multipath Channels Across the Millimeter-Wave Spectrum

60 GHz Millimetre-Wave Channel Characterisation for Indoor Office Environments

Indoor millimetre wave channel measurements for 5G wireless systems

Wideband Synthetic-Aperture Millimeter-Wave Spatial-Channel Reference System With Traceable Uncertainty Framework