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The lower THz bands are foreseen as candidates to achieve the data-rates demanded in the sixth generation (6G) of wireless communications. Hence, multiple measurements for characterization of propagation at these frequencies in different scenarios are being conducted all around the world. This also impulses activities on standardization of measurement equipment and methodologies to define common practices and make measurements from different actors comparable. Therefore, in the present paper we investigate the accuracy of a dual-polarized ultra-wideband channel sounder in the time, angular, and polarization domains by means of a verification methodology based on interferometry.

Hybrid, mixed analogue/digital beam-forming architectures are a central research topic for the development of mm-wave communication for fifth generation. Most approaches are based on phase shifters in the analogue part, which are inherently narrowband. In this study, the authors evaluate the effects and performance of narrowband beam-steering on wideband signals using two different modelling approaches: spatial-narrowband model, in which the inter-antenna element delays are neglected, and spatial-wideband model, in which the inter-antenna element delays are considered. They show that neglecting the spatial-wideband effects on channel models overestimates the focusing of beam-forming, the expected delay spread reduction, and achievable data-rate with an increasing number of antennas and bandwidth. These effects are quantised by simulations using a realistic ray-tracing scenario at 60 GHz.

Industry 4.0 is the scenario in which the 5G and beyond networks are expected to show all their potential. However, while propagation at sub-6 GHz has been widely investigated in industry environments, mm-waves propagation and channel modelling in those scenarios is still under early research. Therefore, we introduce novel simultaneous multiband ultra-wideband measurements at 6.75 GHz and 30 GHz in LOS and NLOS with RX below and above clutter level. This unique set-up allows a direct comparison between the sub-6 GHz and mm-wave channel. Results have shown larger specular to dense multi-path components power ratio and shorter large-scale parameters at mm-waves.

This contribution presents propagation measurements at 60 GHz in indoor non-line of sight scenarios. Besides analysing the measurements, the authors have considered several system aspects, such as bandwidth and directivity in order to investigate the small-scale behaviour of the radio channel after beam-forming. The results show that due to the high resolution in the angular and time domain achievable by large antenna arrays and wideband signals, the fading is significantly reduced and the equivalent transmission channel becomes more sparse and deterministic. These insights represent an essential source of information for future systems design and the ongoing channel modelling activities for systems operating at mm-waves.

The World Radiocommunication Conference 2015 (WRC-15) identified a number of frequency bands between 24 and 86 GHz as candidate frequencies for future cellular networks. In this article, an extensive review of propagation characteristics and challenges related to the use of millimeter wave (mm-wave) in future wireless systems is presented. Reference to existing path-loss models including atmospheric and material attenuation in recommendations of the International Telecommunication Union (ITU) in Geneva, Switzerland, is given, and the need for new multidimensional models and measurements is identified. A description of state-of-the-art mm-wave channel sounders for single and multiple antenna measurements is followed by a discussion of the most recent deterministic, semideterministic, and stochastic propagation and channel models. Finally, standardization issues are outlined with recommendations for future research.

Our goal is to identify if limited channel-state information is sufficient to mitigate interferences between the stations of a wireless mobile backhaul network, which is especially of great importance if the network employs full-duplex operation or terrestrial and satellite links sharing the same spectrum. We analyze and compare the signal-to-interference-and-noise ratio of plain beam steering and zero-forcing beam steering for a millimeter-wave backhaul network with limited channel-state information where only the positions of the stations are known, while buildings and other possible sources of multipath components are unknown. Numerical analyses based on raytracing in a realistic urban scenario reveal that zero-forcing beam steering outperforms plain beam steering by about 12 dB. Furthermore, we compare the steering approaches to block diagonalization with full channel-state information as a reference. For situations with low signal-to-noise ratio as in wide-band communications, zero-forcing beam steering can achieve a similar signal-to-noise-and-interference ratio to block diagonalization. We conclude that knowing the positions of wireless backhaul stations obviates the need for expensive channel estimation.

In the present paper we analyse small-scale fading of reflections at 60 GHz using different antennas and bandwidths. The aim is to investigate the deterministic property of the channel in view of modelling and deployment of systems with larger bandwidths and higher directivity. We have investigated the scattering effect of a reflection on a wall emulating a beam-former in a NLOS condition. The results show that the distribution of the amplitudes fit better with a Rician than a Rayleigh distribution. Furthermore, we show that an increasing bandwidth and directivity increases the k-factor, supporting the idea of deterministic paths apart from the LOS.

A wireless channel is always composed of both deterministic and stochastic multi-path components. A high Rician K-factor increases the contribution of deterministic channel components, thereby reducing the significance of stochastic parts of a channel. This paper focus at the investigative analysis of K-factor and fading depth to analyze the deterministic behavior of a channel under a certain bandwidth. In this paper, 4 different propagation setups have been studied including a LOS, reflections from black board and wall are considered due to their different surface roughness and double bounce reflections from both surfaces. It has been observed that in all propagation cases, small scale fading depth asymptotically converges towards zero dB whereby K-factor increases with bandwidth. Results also show that the de-polarization of a signal increases its amplitude fading. This effect is much more significant at lower bandwidths but an increase in bandwidth reduces the difference in fade depths between polarized and depolarized signals. These observations lead to a conclusion that channel tend to be more deterministic at higher bandwidths.

If a channel is frequency dependent then Uncorrelated Scattering (US) (a narrow-band assumption) don't hold. This has a significant impact at the considered channel modeling methodology as delay and angular dispersion of waves can no longer be studied independently because the small scale fading of individual multipath components become correlated. In this paper, we investigate the frequency dependence of the 30 GHz millimeter-Wave (mmWave) Ultra-Wide band (UWB) channel. Our indoor small lecture room measured channel results show that both delay and angular spreads vary significantly for different frequencies within a measured UWB channel. This is due to different interactions with objects in the environment due to significant difference in the comparative wavelengths. Therefore, we stress that mmWave-UWB channel modeling methodology must take into account the frequency dependence of channel parameters. In order to support its significance, we have also provided an evidence from mmWave system architecture point of view.

In the present paper we introduce the architecture of a hybrid digital / analog beam-forming with polarization compensation. To evaluate the performance of this architecture we use double-directional, ultra wideband dual-polarized channel measurements at 70 GHz that have been carried out in a small-office environment scenario at the TU Ilmenau. Different positions of Tx and Rx have been measured using horn antennas. The channel impulse responses (CIR) have been processed to emulate a communication system with analog beam-forming capabilities. A single data stream adopting single beam and multi-beam beam-forming strategies has been tested with the measured data, showing an improvement in performance achieved by adopting such an architecture.

The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter wave (mm-Wave) frequencies for increasing bandwidth. As a consequence, new technologies have to be deployed to tackle the drawbacks of higher frequency bands, e.g. increased path loss. Development and verification of those novel technologies required an understanding of the propagation effects at mm-Wave which enabled by channel sounding measurements and analysis. Due to the variety of considered frequency bands and the necessity of spatial resolved measurements for e.g. testing of beamforming approaches, measurement duration and comparability becomes problematic. This paper presents multi-band channel sounder architectures, usable to measure up to four frequency bands simultaneously. Furthermore, we present a measurement campaign, featuring full polarimetric and directional resolved dual-band measurements, which comprises the microwave band at 10 GHz and the mm-Wave band at 30 GHz. Preliminary analysis results are presented.

Double-directional, ultra wideband dual-polarized channel measurements at 70 GHz have been carried out in a small-office environment. The aim of these measurements is to study the temporal, directional, and polarization properties of the channel for modelling purposes of the future wireless communication systems at mm-waves. A highly deterministic behaviour of the channel and the environment has been identified, as well as the limitations of only parameterizing channel models as WINNER for the new mm-wave channel models.

Owing to the limitation in bandwidth of currently used frequency bands, future fifth generation (5G) mobile networks will need to operate at higher frequencies. However, one important step in the research activities for the next generation of mobile networks is the broadband fully polarimetric analysis of the multipath propagation in dynamic single and multiuser scenarios under time-variant shadowing environments in millimetre- wave (mm-wave) channels. This paper presents a channel sounding campaign at 70 GHz in an urban outdoor scenario focusing on broadband channel characteristic at mmwave. For the measurements a novel dual-polarized (DP) ultrawideband (UWB) multi-channel sounder (DP-UMCS) architecture, developed at the TU Ilmenau for propagation measurements in cellular networks, was used to study the directional and polarization properties of the channel in view of the future wireless communication systems.

Increasing data rates in mobile networks require new technologies for the next generation of mobile communication systems such as massive MIMO, device-centric architectures, smarter devices, machine-2-machine communication etc. However, one important step to reach the goal of 100 GBit/s will be use of higher bandwidth. Owing to the limitation in bandwidth of currently used frequency bands, future fifth generation (5G) mobile networks will need to operate at higher frequencies. Analysis of the multipath propagation in dynamic single and multi-user scenarios under time-variant shadowing environments with high bandwidth requires a millimetre-wave (mm-wave) channel sounder (CS). It must provide ultra-wideband (UWB) real-time operation with multiple antennas and a high dynamic range. In addition, polarimetric information is needed to fully characterise the wireless channel, e.g. for cases of polarisation misalignment at the mobile device. This paper presents a novel UWB dual-polarised (DP) mm-wave channel sounder architecture for real time measurements in 5G mobile networks to overcome these requirements. We also show measurement data to motivate the need for polarimetric double-directional measurements.

Owing to the increasing data rates, future 5G mobile networks will need to operate at higher frequencies and bandwidths. To investigate new techniques for those networks, channel sounding is essential for measuring and analysing the multipath propagation in single and multi-user situations under time-variant shadowing environments. This requires a challenging design of the millimeter-wave (mm-wave) channel sounder (CS) - it must provide ultra-wideband (UWB) real-time operation with multiple antennas and a high dynamic range. In addition, polarimetric information is needed to fully characterise the wireless channel, e.g. for cases of polarisation misalignment at the mobile device. This paper presents a novel UWB dual-polarised mm-wave channel sounder architecture for real time measurements in 5G mobile networks and motivates the need for polarimetric measurements with experimental data collected at 60 GHz.