Spatial Fading Channel Emulation for Over-the-air Testing of mmWave Radios: Concepts and Experimental Validations

Abstract Millimeter-wave (mmWave) communication is regarded as the key enabling component for fifth-generation (5G) cellular systems due to the large available spectrum bandwidth. To make mmWave new radio (NR) a reality, tremendous efforts have been exerted from the industry and academia. Performance evaluation of mmWave NR is a mandatory step and the key to ensuring the success of mmWave 5G deployment. Over-the-air (OTA) radiated method of testing mmWave NR in laboratory conditions is highly attractive, since it facilitates virtual field testing of mmWave devices in realistic propagation conditions. In this paper, we first discuss the need for and challenges in OTA measurement of mmWave 5G NR under fading channel conditions. After that, two promising candidate solutions, i.e., wireless cable and multi-probe anechoic chamber (MPAC), are detailed. Their principles, applicability for mmWave NR, and main challenges are discussed. Furthermore, preliminary experimental validation results in a frequency range 2 anechoic chamber are demonstrated for the wireless cable and MPAC methods at 28 GHz

Dynamic Sub-THz Radio Channel Emulation: Principle, Challenges, and Experimental Validation

Sub-terahertz (Sub-THz) technology, as one of the key candidates for the six generation (6G) systems, has attracted increasing attention from academia and industry, due to its promise to unleash vast amounts of new frequency spectrum. Sub-THz system designs pose unique and more challenging circumstances compared to traditional communication systems. These challenges arise from the demanding propagation conditions, limited availability of commercial radio frequency (RF) components, the need for high-gain and beam-steerable antennas that are highly integrated at both ends of the communication link, short-range communication scenarios, and the requirement for extreme data rates. Therefore, it is crucial to assess the performance of radio devices in realistic propagation channels in sub-THz communication systems. In this work, we present the concept, challenges, and enabling solutions for achieving sub-THz radio channel emulation. Moreover, we experimentally demonstrated the reconstruction of the measured propagation channels at 140 GHz with a commercial radio channel emulator in the laboratory. The developed dynamic fading channel replay concept and experimental validation procedure allows initial tests of future sub-THz communication devices

Feedback Mechanisms for Centralized and Distributed Mobile Systems

The wireless communication market is expected to witness considerable growth in the immediate future due to increasing smart device usage to access real-time data. Mobile devices become the predominant method of Internet access via cellular networks (4G/5G) and the onset of virtual reality (VR), ushering in the wide deployment of multiple bands, ranging from TVWhite Spaces to cellular/WiFi bands and on to mmWave. Multi-antenna techniques have been considered to be promising approaches in telecommunication to optimize the utilization of radio spectrum and minimize the cost of system construction. The performance of multiple antenna technology depends on the utilization of radio propagation properties and feedback of such information in a timely manner. However, when a signal is transmitted, it is usually dispersed over time coming over different paths of different lengths due to reflections from obstacles or affected by Doppler shift in mobile environments. This motivates the design of novel feedback mechanisms that improve the performance of multi-antenna systems. Accurate channel state information (CSI) is essential to increasing throughput in multiinput, multi-output (MIMO) systems with digital beamforming. Channel-state information for the operation of MIMO schemes (such as transmit diversity or spatial multiplexing) can be acquired by feedback of CSI reports in the downlink direction, or inferred from uplink measurements assuming perfect channel reciprocity (CR). However, most works make the assumption that channels are perfectly reciprocal. This assumption is often incorrect in practice due to poor channel estimation and imperfect channel feedback. Instead, experiments have demonstrated that channel reciprocity can be easily broken by multiple factors. Specifically, channel reciprocity error (CRE) introduced by transmitter-receiver imbalance have been widely studied by both simulations and experiments, and the impact of mobility and estimation error have been fully investigated in this thesis. In particular, unmanned aerial vehicles (UAVs) have asymmetric behavior when communicating with one another and to the ground, due to differences in altitude that frequently occur. Feedback mechanisms are also affected by channel differences caused by the user’s body. While there has been work to specifically quantify the losses in signal reception, there has been little work on how these channel differences affect feedback mechanisms. In this dissertation, we perform system-level simulations, implement design with a software defined radio platform, conduct in-field experiments for various wireless communication systems to analyze different channel feedback mechanisms. To explore the feedback mechanism, we then explore two specific real world scenarios, including UAV-based beamforming communications, and user-induced feedback systems

Public Safety Communications above 6 GHz: Challenges and Opportunities

Advanced public safety communication (PSC) services call for fast, reliable and low-latency communication technologies, capable of supporting diverse communication modes (aerial, unmanned, vehicular, and peer-to-peer), fast channel dynamics, and ad hoc or mesh structures. For this reason, PSC has been identified as one of the key potential uses cases for the next generation of communication systems, the so-called 5G. In this scenario, the millimeter wave (mmWave) bands and other frequencies above 6 GHz are particularly interesting, since they are largely untapped and offer vastly more spectrum than current cellular allocations in the highly congested bands below 6 GHz, thus enabling orders of magnitude greater data rates and reduced latency. For example, new PSC networks in the mmWave bands could support high-definition video, virtual reality, and other broadband data to large numbers of first responders. Surveillance drones or ambulances could also be provided high-speed connectivity along with machine-type communication for remotely controlled robotic devices entering dangerous areas. However, the way towards this ambitious goal is hindered by a number of open research challenges. In this paper, after a brief introduction to PSC services and requirements, we illustrate the potential of the frequencies above 6 GHz for PSC and discuss the open problems that need to be solved in order to pave this way. Finally, we describe the main components of a test platform for mmWave systems that is functional to the study of such complex scenarios and that we plan to develop as an invaluable tool for realizing mmWave PSC networks

Statistical analysis and channel modeling in next generation wireless communication systems

In this thesis, statistical analysis and channel modeling in next generation wireless communication systems is presented in detail. The primary focus of this thesis is on the statistical modeling of interference temperature (IT) in cognitive radio systems, and empirical study of wireless channel characterization of unmanned aerial vehicle (UAV)-assisted communications at ultra-wideband (UWB) and at millimeter wave (mmWave) frequencies.Firstly, in the cognitive radio system, a novel idea to statistically model the dynamic interference threshold (IT) from user traffic demand is presented in detail. It is shown that the cognitive radio system with dynamic IT will have high capacity performance with less outage probability over a system that does not utilize dynamic IT. The detailed theoretical analysis with expressions for mean capacity and outage probability in general operation region, and in high power region are derived and subsequently, validated with the simulations results. In addition, the effect of secondary user interference on primary user is also examined in this part.In the second part, wireless channel characterisation for unmanned aerial vehicle-to-wearables (UAV2W) at UWB frequency is analysed, and studied empirically in an indoor warehouse environment. The frequency and distance dependent path gain analysis at different bandwidths for a corresponding carrier frequency with time dispersion characteristics is presented in detail. Furthermore, from statistical modeling, it was shown that the Log-normal distribution is the best fit distribution model to characterize fading in these UAV2W systems.Finally, a novel emulation method for UAV motion by a robotic arm is presented to study the mmWave channel characteristics (Doppler spreading and path loss) at 28 GHz. In addition to that, empirical study is carried out to analyze the propeller modulation effect caused by the propellers in UAVs with an actual UAV setup. These important statistical analysis, and channel modeling discussed in this thesis are very critical in designing, analysing, and in implementation of fifth generation (5G) and beyond 5G (B5G) communication for the future. This thesis is a stepping stone in that direction

A portable 28-GHz channel sounder platform and measurement results from close-to-ground field tests

This article describes a novel, bespoke, and low-cost 28-GHz RF TX and RX front end design that has been combined with a commercial Software-Defined Radio and Raspberry Pi controller to realize a portable propagation measurement system for the 28-GHz band. The complete sounder system can resolve an impulse from RX powers down to −107 dBm (3-dB impulse SNR) and the sounder TX can generate a signal of −8 dBm. Therefore, using 20-dBi antennas supports path-loss (PL) measurements of 139 dB. The sounder can resolve time-domain reflections to 33 ns in a channel measurement bandwidth of 60 MHz, producing both time-domain and frequency-domain results. The complete sounding system has been used to perform close-to-ground RF channel measurements, with propagation loss models and time-domain impulses extracted. Close-to-ground measurement is an underreported area of propagation research that is relevant for novel use-cases, such as in military applications or for mobile device-to-device communications. A key initial finding from the trials is that the PLs for 28-GHz indoor and outdoor links at circa 70 cm above ground seem close to that of free space, with very few strong reflections with delays exceeding 33 ns