Cooperative connected automated mobility depends on sensing and wireless communication functions. With increasing carrier frequency both functions can be realized with the same hardware, however, the attenuation of radio signals increases quadratically with the carrier frequency. Hence, link setup becomes challenging in vehicular scenarios due to the required beam finding process. In this paper we investigate the multipath components of the vehicle-to-infrastructure (V2I) radio channel in three frequency bands with center frequencies of 3.2 GHz, 34.3 GHz and 62.35 GHz using measurement data with 155.5 MHz bandwidth and a sounding repetition rate of $31.25 \mu \mathrm{~s}$. The channel impulse responses are collected simultaneously at all three carrier frequencies. Using the high temporal sampling rate we apply the CLEAN algorithm, enabling the estimation of the weight, delay and Doppler frequency of multipath components. By analyzing the collinearity of the Doppler normalized scattering function between the frequency bands we found that the collinearity between the 3.2 GHz and 34.3 GHz band as well as between the 3.2 GHz and 62.35 GHz is smaller in the non-line of sight (NLOS) region but increases for the line-of-sight (LOS).

Reconfigurable intelligent surfaces (RISs) can provide a reliable and low-latency millimeter wave (mmWave) communication link in cases of a blocked line-of-sight (LoS) between the base station (BS) and the user equipment (UE). In such cases, the RIS mounted on a wall or ceiling can act as a bypass for the radio communication link. We present an active RIS with 127 patch antenna elements arranged in a hexagonal grid. The RIS operates at a center frequency of 23.8 GHz and each RIS element uses an orthogonal polarization transformation to enable amplification using a field-effect transistor (FET). The source and drain voltages of each FET are controlled using two bits. We consider that the RIS control unit is aware of the UE coordinates within the measurement area, relevant to the industrial control scenarios. We measure the received power on a 2D grid of $60 \mathrm{~cm} \times 90 \mathrm{~cm}$ using an $x y$-positioning table, with the RIS working in reflective and active mode. The results demonstrate the ability of the RIS to effectively focus the radio signal on the desired target points. We characterize the halfpower beam width in azimuth and radial directions with respect to the RIS position, enabling us to obtain a practical RIS configuration update criterion for a mobile UE. These results clearly show that RISs are prominent solutions for enabling reliable wireless communication in indoor industrial scenarios.

In an world shifting towards wireless communications, the already scarce electromagnetic spectrum within the unlicensed bands is becoming increasingly crowded. All wireless devices operating in those bands need to co-exist without interfering with each other. Frequency hopping spread spectrum (FHSS) is a communication technique especially resilient to interference due to its constant change of the carrier frequency and its narrowband transmission bandwidth. Furthermore, it produces minimal interference to other signals in the same frequency band using wider bandwidth. However, interference can also be harmful even for FHSS transmissions as a result of the loaded ISM bands. Intelligent spectrum sensing techniques can contribute to a more efficient spectral usage. In this paper, we propose a supervised learning algorithm which predicts the future time-frequency location of a FHSS signal. We design a convolutional neural network which is trained on a dataset, obtained from measurements of two FHSS sources. Based only on a small observation window of 50 ms, it predicts the signal appearance of the following 25 ms in a time-frequency representation. To show that we can accurately predict the signal, we introduce a special score measure. The mean score of about 0.9 with small standard deviation demonstrates the high fidelity prediction of the signal’s evolution.

In recent years, the amount of unmanned aerial vehicle (UAV) based applications has strongly increased. In order to fly the UAVs safely, their command and control link needs a reliable and robust communication channel. A line of sight (LOS) between the UAV operator and UAV is, at the moment, an essential requirement to guarantee an error-free communication. However, even in LOS conditions, the reception of a constant signal level is not assured. In this paper, we present the results of a measurement campaign with a UAV and a drone moving on the ground that were electronically tracked with simultaneous dedicated beams at 3.2 GHz coming from a 10 element antenna array. Small software-defined-radio modules were integrated in the drones to record the strength of the received signal when moving. The instantaneous GPS coordinates of the UAV were transmitted via a 4G link to a ground station that translated them into spherical coordinates used at the antenna array side. We show that the UAV itself and its flying inclination produce around 10 dB fluctuations in the received power, even in LOS conditions, and therefore shadowing cannot be ignored.

In this paper we present dual-band massive multiple-input multiple-output (MIMO) channel measurements for a railway station scenario. The massive MIMO link shall provide an ultra-reliable low-latency communication link from the control center to the locomotive. In the measurement campaign the locomotive moves from line-of-sight (LOS) to non line-of-sight. We present dual frequency band measurements, where the massive MIMO array at the base station has 24 receive antenna elements at 1890 MHz and 8 receive antenna elements at 748 MHz. The measurement bandwidth is 20 MHz and we use a repetition rate of 1 ms to acquire the time-variant channel frequency response from the locomotive to all 32 antenna elements in parallel. We provide a first analysis of the root mean square (RMS) delay spread, the path loss coefficients and the channel hardening in both frequency bands. The measurements show that the RMS delay spread at lower frequencies is slightly smaller compared to higher frequencies, due to a stronger LOS component at lower frequencies. Furthermore, the results indicate that increasing the number of receive antennas in vertical domain, does not allow for better channel hardening and that lower frequencies allow for better channel hardening with the same amount of antennas.

This paper discusses a freely available and open dataset containing vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-pedestrian (V2P) OFDM-based wireless channel measurement data including synchronised sensor data such as radar, LiDAR and high precision GPS. The wireless channel measurement is conducted at the carrier frequencies of 3.2 GHz and 5.81 GHz which are the most promising frequency bands in which future V2X communication systems will operate. The dataset contains the wireless channel measurement data of various V2X scenarios along with synchronized sensor information from a vehicle. In addition to the wireless channel measurement data, the dataset also includes frame error rate measurements from a IEEE 802.11p based communication system, synchronized to the other measurement data.

In this paper we present and discuss results of a wireless vehicle-to-vehicle (V2V) dualband channel measurement campaign at center frequencies of 3.2 GHz and 34.3 GHz in an urban street scenario. The measurement is conducted using a bandwidth of 155.5 MHz and a sounding repetition rate of 62.5 $\mu \mathrm{s}$ for both bands. At the transmitter side we use omni-directional antennas and at the receiver side directional antennas with 17° opening angles. With this setup, we present the first comparison of simultaneous and dynamic multiband V2V measurements using the time-variant power delay profile (PDP) and the Doppler spectral density (DSD). We find close similarities for the line-of-sight, specular as well as diffuse reflections in both frequency bands, enabling future work for out-of-band beam finding in vehicular mmWave systems.

In this paper we present a software defined radio (SDR) based measurement framework that allows for simultaneous measurements of wireless communication channels over multiple bands. We present and discuss results of a wireless vehicular-to-infrastructure multiband channel measurement campaign at center frequencies of 3.2 GHz, 34.3 GHz and 62.35 GHz in a street crossing scenario. The measurement is conducted using a bandwidth of 155.5 MHz and a sounding repetition rate of 31.25 μs. We compare the measurements using the time-variant power delay profile (PDP) and the Doppler spectral density (DSD).

In this paper we adopt and modify a well-known locality-aware hashing scheme to the problem of active stochastic scatterer selection in vehicular non-stationary geometry-based stochastic channel models (GSCM). We show, how under relaxed assumptions on the query set an efficient selection of active stochastic scatterers during simulation is computationally feasible. The proposed approach enables real-time simulation and emulation of large-scale GSCMs by restricting the active stochastic scatterer set to meet given resource constraints. We showcase our approach by introducing a GSCM that is boot-strapped via OpenStreetMap data. The stochastic scatterers are placed automatically along buildings, traffic signs and vegetation. We validate and investigate the impact of the proposed approach on the accuracy of a GSCM by means of second order statistics of the time- and frequency-varying fading process. For validation and performance evaluation we parameterize our GSCM using a vehicular wireless channel measurement campaign conducted in the inner city of Vienna. The impact of selecting only a subset of scatterers is then evaluated using the calibrated GSCM.

We present a mobile fronthaul methodology for the analogue optical transmission of native radio signals with integrated photonic true-time delay for the beam steering of phased-array antennas. Laser-based coherent homodyne detectors and the delay dissemination through ultra-dense wavelength division multiplexing ensure a low complexity at the optical layer. We experimentally demonstrate beamsteering for a linear phased-array antenna with a 1×3 configuration at 3.5 GHz carrier frequency and prove native radio signal transmission over the 14.3-km reach coherent optical fronthaul at a low end-to-end error vector magnitude of 3.3%. Experimental results are found to stand in good agreement with theoretical predictions.

We present a strategy to overcome channel aging and to enable massive multiple-input multiple-output (MIMO) in highly time-varying scenarios. Given the self-contained 5G slot structure, we introduce channel prediction methods for the down-link utilizing up-link reference symbols and investigate the prediction quality for synthetic and empirical high mobility channel measurement data. Further, we combine channel prediction with orthogonal precoding to decrease the bit error rate (BER) and allow longer prediction horizons. We show through link-level simulations that this framework exhibits a performance drop of only 1 dB compared to perfectly known channel state information for a velocity of 160 km/h at 3.5 GHz. We conclude the paper with a parametric BER study in dependence of the prediction/precoding horizon length.

In this paper we introduce the AIT ray tracer (RT) that is able to accurately simulate propagation effects of wireless communication channels. It covers the classical propagation mechanisms such as specular reflections, transmission and edge-diffraction. The novelty of our RT is that it allows to obtain correlated diffuse scattering and, thus, provides a time-variant Doppler spectral density. This is achieved by introducing a lattice-based surface tiling, which does not alter the position of the scattering points during simulation but provides high resolution diffuse scattering. The selection of the basis vectors for the finite lattice ensures that each ray falls into a separate delay bin (at least for first-order scattering). We implement our RT using the NVIDIA OptiX ray tracing engine, this enables us to trace a vast amount of rays in a single pass. We compare our RT simulations to a measurement conducted in a non-stationary urban intersection scenario achieving a near perfect match in terms of second order statistics.

Repeatable system-level test methods for vehicle-to-everything communication (V2X) are crucial in improving road safety and supporting connected autonomous driving. They rely on geometrical channel models that provide realistic signal propagation delays, Doppler shifts and path loss. In this work we focus on the validation of an OpenStreetMap (OSM) geometry based stochastic channel model (GSCM) that has a high degree of automation and low computational complexity. In an urban intersection scenario we compare the time-variant power delay profile (PDP) and Doppler spectral density (DSD) obtained from a measurement campaign to the ones obtained by the OSM-GSCM. Furthermore, we measure packet error rates (PER) of commercial modem hardware by connecting a transmitter and a receiver to the AIT channel emulator, i.e. using a hardware-in-the-loop (HiL) setup. We compare the PER obtained when the channel emulator uses the OSM-GSCM as input and when it uses the measured impulse responses. The OSM-GSCM path loss shows minor differences to the measurements due to the 2D structure of the OSM-GSCM, while the PER, PDP and DSD exhibit a good match between OSM-GSCM and empirical measurement data.

The advantages of measuring multiple wireless links simultaneously has been gaining attention due to the growing complexity of wireless communication systems. Analyzing vehicular communication systems presents a particular challenge due to their rapid time-varying nature. Therefore multi-node channel sounding is crucial for such endeavors. In this paper, we present the architecture and practical implementation of a scalable mobile multi-node channel sounder, optimized for use in vehicular scenarios. We perform a measurement campaign with three moving nodes, which includes a line of sight (LoS) connection on two links and non LoS(NLoS) conditions on the third link. We present the results on the obtained channel delay and Doppler characteristics, followed by the assessment of the degree of correlation of the analyzed channels and time-variant channel rates, hence investigating the suitability of the channel's physical attributes for relaying. The results show low cross-correlation between the transfer functions of the direct and the relaying link, while a higher rate is calculated for the relaying link.

This paper reports on a power-delay profile measurement campaign emulating a mobile vehicle-to-infrastructure urban-highway environment. The measured location is in the city of Brno, Czech Republic. Utilizing a correlative 50 GS/s time-domain channel sounder with a center frequency of 59.6 GHz and 8 GHz bandwidth and with open-ended WR15 waveguide antennas, we characterize the representative millimeter wave radio channels in terms of the RMS delay spread and its variability caused by mobile scatterers (i.e., vehicles). The RMS delay spread exhibits notable heteroscedasticity as its standard deviation can decrease by 40%. The measured high resolution power-delay profiles exhibit clustering behavior, where a typical number of reflected multipath components is four to five.

Ultra-reliable wireless communication links require the utilization of all diversity sources of a wireless communication channel. Hadani et al. propose a two dimensional discrete symplectic Fourier transform (DSFT) as orthogonal pre-coder for a time-frequency modulation scheme. In this paper we explore general orthogonal precoding (OP) and its performance in time- and frequency-selective channels. We show that iterative parallel interference cancellation (PIC) and iterative channel estimation methods can be used for the detection of OP. A scalar signal model for OP transmission is obtained by PIC. Based on this signal model, we can prove that all constant modulus sequences, e.g. the DSFT basis functions or Walsh-Hadamard sequences, lead to the same performance for OP. We validate our receiver structure by numerical link level simulations of a vehicle-to-vehicle communication link with a relative velocity of 0... 200 km/h, We demonstrate that OP achieves a gain of about 4.8 dB if compared to orthogonal frequency division multiplexing at a bit error rate of 10-4. Our performance results for coded OP are the best results for a fully documented receiver architecture, published so far.

The performance of wireless communication systems is fundamentally determined by wireless communication channel properties. Wireless vehicular communication channels exhibit multipath propagation and non-stationary channel statistics. Methods and tools for the repeatable test of wireless communication systems and signal processing algorithms in such environments are urgently needed to enable the development of reliable communication links with low-latency. In this paper we present the measurement and validation of a real time channel emulation method for non-stationary vehicular scenarios based on a geometry-based stochastic channel model.