A satellite beacon receiver is designed for research and educational purposes. To provide data to investigate possible weather induced scattering processes, a complex valued dual branch architecture is chosen, operating in the Q-band. The construction is based on mostly readily available components and instruments at Aalborg University radio laboratory. The paper describes the beacon receiver and its features.

This article presents a massive multiple-input multiple-output (MMIMO) outdoor measurement campaign with bidirectional angular discrimination. Two dynamic user arrays of eight elements each are measured simultaneously. Multiuser consistency and spatial consistency are important for proper modeling and simulation of dynamic users in MMIMO channels. This article will investigate the common scatterers between two moving users by considering the power contribution from physical objects to each user. Interuser distance and user alignment in the direction of dominant scatterers are also considered. Paths are estimated from wideband dual-directional beam-scanning. A method is developed to group the paths based on delay and angular development along the measured tracks. The estimated delay and angle of each path, along with ray tracing simulations, are used to map the interactions of each path to surrounding walls or objects. The power contributions from objects are compared to determine common scatterers between users, which can cause larger correlation and a reduced MIMO capacity.

Geosynchronous satellite (GEO) communications are highly susceptible to interference from environments such as rain, clouds, and hail. This exhibits a technical challenge to accurately detect the status of the weak Q-band (39.4 GHz) satellite beacon signals, which is critical for ensuring reliable satellite pointing using the ground station antenna. This paper exploits recent advances in deep learning to cope with this challenge. The proposed approach based on deep neural networks (DNN) and filtering (Filter-DNN) classifies rare events such as cloud, mist, rain as Non-line of sight (NLOS) and ordinary clear skies as Line of sight (LOS). Beacon data from a GEO satellite (Alphasat) ground station under two different attenuation conditions is used for validation. The experimental results show that our method can detect the rare event with an accuracy score of 92% by using only 2000 data sample points, while conventional approaches such as MUSIC require about 100k sample points to maintain detection. These results indicate that the proposed technique could be a promising tool for achieving satisfactory results in space exploration and gain insights into GEO satellite communication problems.

Exploration of millimeter-wave (mmWave) bands has gained a significant interest in satellite communications. mmWave satellite communication link quality is highly sensitive to the pointing angle of the antenna in the ground station, due to its high directivity. For the multiantenna ground station design, it is also of importance to know pointing angles and angle difference of all antenna elements. However, it is challenging in the real-world setup. In this letter, we propose a novel calibration technique to estimate the electrical antenna pointing angle of the in situ ground station based on the received signal power pattern on the ground station, which is time-variant according to the satellite in-orbital motion. The proposed algorithm is numerically simulated and experimentally validated, demonstrating its effectiveness for the in situ antenna pointing angle calibration.

Obtaining down link (DL) channel state information (CSI) at the base station (BS) is challenging for frequencydivision-duplex (FDD) massive MIMO (MM) systems. Considerable overhead is required for DL training and feedback. Instead studies often assume highly correlated average spatial signal signatures (i.e. directional clusters) between FDD duplex links. These assumptions, however, only represent use of antennas with the same radiation pattern over the duplex band, leading to illumination of the same cluster. In this paper, we investigate pattern reciprocity, over the duplex band, for practical user handsets. We first show how a population of measured contemporary phones exhibits noticeable duplex pattern divergence. We then show measured complex pattern duplex divergence of a mock-up phone, where depolarization comes on top of gain differences. Thus we reveal a significant but overlooked brick in DL CSI assessment for FDD MM operation. Namely, in order for the FDD MM performance studies to be realistic, practical user handsets have to be considered.

Wind turbine blade deflection sensing system using ultrawideband radio links propagating along the blade is presented. Special focus is given to the challenges related to the multipath propagation along the blade. Results of electromagnetic modeling of the wireless link budget for deflected blades are presented. Some aspects of the sensing system that are different from a typical wireless communication link are discussed.

This letter analyzes the impact of interuser distance and angular separation on the channel correlation and achievable sum-rate for a massive multiple-input-multiple-output (MIMO) system in non-line-of-sight (NLOS) conditions. The investigation is based on outdoor measurements on a channel sounding system capturing the dynamic channel of two user arrays. The letter analyzes correlation and sum-rate with varying interuser distance and angular separation of dominant beams toward the users. A large span of correlation and sum-rate values are found across the range of distances and angular separation. The investigation shows a moderate link between interuser distance and correlation, but a strong impact on correlation is found only for low angular separation of the users. The results of this NLOS scenario suggest that a distance-based criteria alone is not sufficient to accurately model shared clusters and their correlation.

This paper analyzes the performance of well-known precoding schemes for massive multiple-input multiple-output (MMIMO) systems. The investigations are based on extensive measurements made with a sounding system capable of capturing the dynamic channels towards users moving in many different outdoor scenarios. Assuming ideal channel state information (CSI), results show that the mean sum-rate of the maximum ratio transmission (MRT) precoder varies considerably with the scenario, e.g., from 6.5 to 14.5 bit/s/Hz (10%- and 90%-percentiles) for a 64 element uniform linear array (ULA) at the base station (BS), while the zero-forcing (ZF) and signal to leakage and noise ratio (SLNR) precoders are more robust and higher performing with variation from 13.4 to 16.3 bit/s/Hz in the same conditions. However, when the CSI is non-ideal the performance drops. With the CSI delayed corresponding to movement of about 1/5 of a wavelength, the ZF and SLNR mean sum-rate is 60-92% of that achieved with ideal CSI (10%- and 90%-percentiles). More statistics for different massive array sizes with both delay and frequency offset CSI are given in the paper.

Ultra-Reliable Low Latency Communication (URLLC) is one of the distinctive features of the upcoming 5G wireless communication, going down to packet error rates (PER) of 10^-9. In this paper we discuss the statistical properties of the wireless channel models that are relevant for characterization of the lower tail of the Cumulative Distribution Function (CDF). We show that, for a wide range of channel models, the outage probability at URLLC levels can be approximated by a simple power law expression, whose exponent and offset depend on the actual channel model. The main insights from the analysis can be summarized as follows: (1) the two-wave model and the impact of shadowing in combined models lead to pessimistic predictions of the fading in the URLLC region; (2) the CDFs of models that contain single cluster diffuse components have slopes that correspond to the slope of a Rayleigh fading, and (3) multi-cluster diffuse components can result in different slopes. We apply our power law approximation results to analyze the performance of receiver diversity schemes for URLLC-relevant statistics and obtain a new simplified expression for Maximum Ratio Combining (MRC) in channels with power law tail statistics.

Full-wave numerical analysis of an ultrawideband wireless link in frequency band 3-5 GHz along a 37.3 m long wind turbine blade is presented. The method used for the analysis is the well-established finite-difference time-domain (FDTD) method with staggered Yee mesh. Simulated results are compared to data obtained from measurement on a real blade, in two experiments involving antennas transmitting both from outside near the blade tip and from inside the blade. In the first experiment, when the wave is propagated along the entire blade and received near the blade root, the differences between the simulation and the measurement are found in pulse magnitudes within 3 dB and in delay within 1.5 ns. In the second experiment, the emitted waves are studied at only 10 m distance, but at higher elevations, and the error reaches 6 dB in magnitude and 1.9 ns in delay. Possible reasons for observed discrepancies between the simulations and the measurements are briefly discussed. Despite the long distances involved and challenges connected to the numerical dispersion and anisotropy, the FDTD method turns out to be a feasible choice for full-wave numerical modeling of problems of this type, albeit with slightly high sensitivity to the underlying model.

This paper describes propagation measurements of an Ultra Wide Band (UWB) pulse along a full-scale wind turbine blade. The aim is to use the UWB channel characteristics to determine the deflection of the wind turbine blade under different wind loads. The frequency response is measured from 1 to 20 GHz and by use of Fast Fourier Transform (FFT) studied the delay domain. It has been found challenging to determine the deflection of the blade only by looking at the delay difference between the Line-Of-Sight (LOS) pulse and a pulse reflected from the blade. To determine from which area of the blade the reflection originates a ray-tracing study incorporating a model of the curvature of the blade have been conducted. This showed the area causing the reflections depended highly on the placement of the antenna on the wind turbine blade.

Both massive multiple-input multiple-output (MIMO) technology and use of frequencies in the range 24-100 GHz are considered essential for upcoming 5G systems. Measurements of the new type of channels are needed, but this is challenging due to the large number of channels in massive MIMO and the short wavelength in the 24-100 GHz channels (so-called mmWave channels). This article describes a sounder system capable of measurements in both types of channels. While the same sounder system supports simultaneous massive MIMO and mmWave channels, the number of channels in each band and in total is in practice limited. For massive MIMO in the 300-6000 MHz band alone, arrays with up to 128 receiver (Rx) elements are possible, receiving from 16 independent mobile transmitter (Tx) antennas, where all channels are measured within 1.3 ms and in a 200 MHz bandwidth. To the authors' knowledge, this is the first sounding system with this number of channels and a speed necessary for measuring the dynamic channels in typical application scenarios. For mmWave channels, the sounder operates in the range 18-40 GHz. For these bands up to 2 Tx elements and 16 Rx elements can be measured. In addition, the article describes some measurements in both a massive MIMO setup in an indoor sports arena and an mmWave setup with a handheld device containing a 7-element array.

A novel stochastic technique is presented to directly model singular vectors and singular values of a multiple input multiple output channel. Thus the component smodeled directly in the eigen domain can be adapted to exhibit realistic physical domain behavior when assembled. The model exploites natural paths of eigenmodes, such that a simple Doppler filter generator process can be used. Furthermore it is possible to directly manipulate the singular vector dynamics in a way that an unrealistic "stress channel" can be modeled in the eigen domain. This is particularly useful for testing the eigenmode channel tracking ability internal to a communication device such as a modem, where impairments in tracking will cause interference between eigenmodes. The model can also facilitate mode tracking testing as it directly produces tracked ungtangled eigenmodes, providing the narrowest possible singular vector Doppler spectra and consequently lowest required update rates of each eigenmode. The singular vector based model targets testing of the eigen domain functionality of MIMO modems/devices, an apparatus focus, without the need for including the decomposition stages.

This paper presents a Massive-MIMO measurement campaign with bi-directional angular discrimination. Aspects like non-stationarity, spatial consistency and spherical wavefronts become important for proper modeling of such channels. This campaign is designed to measure and investigate these aspects of the channel. The paper includes analyses of the angular statistics and the dual directional power angular spectrum for a few locations. Next, the paths/clusters are mapped to a 2D map for visualisation of clusters. Finally, non-stationarity across the large array aperture is investigated in terms of angular statistics and power.

A postprocessing method to compensate for the numerical dispersion of the Yee-FDTD scheme is presented. The method makes use of frequency domain deconvolution of the erroneous phase shift from the obtained results and can be applied on certain specific conditions, such as for simulations on elongated computational domains. Validation of the method is performed by comparing to analytical solution in a simplified empty-space scenario. Application to simulation of an UWB deflection sensing system is demonstrated, with good match between numerical and measured results.

A postprocessing method to compensate for the numerical dispersion of the Yee-FDTD scheme is presented. The method makes use of frequency domain deconvolution of the erroneous phase shift from the obtained results and can be applied on certain specific conditions, such as for simulations on elongated computational domains. Validation of the method is performed by comparing to analytical solution in a simplified empty-space scenario. Application to simulation of an UWB deflection sensing system is demonstrated, with good match between numerical and measured results.

The deflection of a wind turbine blade can be monitored with an ultra-wideband (UWB) deflection sensing system, which consists of one transmitting antenna at the blade tip and two receiving antennas at the blade root. The blade deflection is calculated by two estimated tip-root antenna distances. Applying the tip antenna inside a blade is highly preferred in practice, but it leads to strong multipath. The multipath may cause interference and cancellation to the direct pulse and affect the accuracy of tip-root distance estimations. In this paper, a method of utilizing an absorber inside the blade to suppress the multipath is proposed for the in-blade tip antenna. The physical mechanism of the proposed idea is described with a simplified multipath model. Simulations are performed with a 2.5-m-long blade tip section to investigate the tendencies of how the absorber affects pulse waveforms. More accurate verifications of the proposed method are carried out with different full-blade measurements. From all the results, it is found that the proposed technique can efficiently suppress multipath for the in-blade tip antenna, and improve the pulse wave front fidelity, so that the UWB sensing system can also be utilized in a much longer blade. Finally, some other conclusions are also addressed.

An ultra-wideband (UWB) blade deflection sensing system with a tip antenna inside a blade is investigated in this paper. The lower UWB band of 3.1-5.3 GHz is utilized. This system composes of two UWB radio links between one antenna inside the blade tip and two antennas outside the blade root. Blade deflections are tracked via two radio links using delay-based distance estimation and triangulation. In order to build reliable radio links, time-domain pulse field distributions are simulated to optimize the in-blade tip antenna polarization and the locations of the two root antennas around the root surface. Full-blade time-domain measurements are proposed to verify the simulations and realize the blade deflection sensing with an in-blade tip antenna. With the optimized in-blade tip antenna polarization and two root antenna locations, an accuracy of 2 cm is achieved for the tip-root antenna distance estimation, and the sensing system can realize the deflection tracking with a maximum deviation of 0.21 m and a root mean squared error of 0.11 m.