Outdoor and indoor path loss modeling at the sub-THz band

In this letter, we present new measurement results to model large-scale path loss at the sub-THz (141-145 GHz) band, for both indoor and outdoor scenarios. Extensive measurement campaigns have been carried out, taking into account both line-of-sight (LoS) and non line-of-sight (NLoS) propagation. For all considered propagation scenarios, existing omni-directional and directional path loss model have been developed, based on the so-called close-in (CI) free-space reference distance model. Moreover, path loss modeling is applied for the 2nd and 3rd strongest multipath components (MPCs). Thus, path loss exponent and large-scale shadow fading estimates are provided. Moreover, power angular spread analysis is depicted, using power angular information up to the 3rd strongest MP

Towards versatile access networks (Chapter 3)

Compared to its previous generations, the 5th generation (5G) cellular network features an additional type of densification, i.e., a large number of active antennas per access point (AP) can be deployed. This technique is known as massive multipleinput multiple-output (mMIMO) [1]. Meanwhile, multiple-input multiple-output (MIMO) evolution, e.g., in channel state information (CSI) enhancement, and also on the study of a larger number of orthogonal demodulation reference signal (DMRS) ports for MU-MIMO, was one of the Release 18 of 3rd generation partnership project (3GPP Rel-18) work item. This release (3GPP Rel-18) package approval, in the fourth quarter of 2021, marked the start of the 5G Advanced evolution in 3GPP. The other items in 3GPP Rel-18 are to study and add functionality in the areas of network energy savings, coverage, mobility support, multicast broadcast services, and positionin

Analysis of Wave-interacting Objects in Indoor and Outdoor Environments at 142 GHz

| openaire: EC/H2020/871464/EU//ARIADNE | openaire: EC/H2020/101015956/EU//Hexa-XIn this paper, an analysis of wave-object interactions is presented for an entrance hall and on a street of a residential area at 142 GHz. Single-directional channel sounding and the resulting spatio-temporal propagation path estimates are fused with the detailed geometry of the environment through a ray-launcher. The improved ray-launcher accounts for higher-order reflections and realizes high correspondence of the measured paths on the geometry, allowing us to analyze wave-object interaction. In channels without line-of-sight, first and second-order reflections contribute about 60% of the total power. Large interior and exterior walls of buildings are found most influential to the multipath channel. About half of the total received power in some links can be attributed to the reflections on small objects such as pillars and staircases in indoor and lampposts in outdoor cases. While large objects produce most of the clusters to the channel, there are links where small objects generate up to four clusters. The obtained knowledge of wave-object interaction at 142 GHz serves as guidelines to set up site-specific and geometry-based channel modeling at the frequency.Peer reviewe

Uncertainty of millimeter-wave channel sounder due to integration of frequency converters

| openaire: EC/H2020/871464/EU//ARIADNEIn this study, we investigate the possible sources of measurement uncertainties with the integration of radio over fiber solution and frequency converters in millimeter-wave sounders. We examined analytically the effect of phase variations due to the disturbance of the optical fiber cable, the limited sideband suppression of the frequency converters, and the influence of the dispersion in rectangular waveguides to the response of the channel sounder. Characterization of the optical fiber cable confirms that disturbance of the cable leads only to phase variation. Back-to-back measurements of Aalto’s sounder operating at V- and D-bands also verify that disturbance of the cable supplying the local (LO) continuous-wave signals are most influential to the stability of frequency- and delay-domain responses of the sounder because the LO signals undergo frequency multiplication. We found that the V-band and D-band channel sounders, with at least 17 dB and 20 dB Image Rejection Ratio, have the maximum gain variation of 0.5 dB and 1.0 dB in the peak of channel impulse responses when subject to different fiber cable positions.Peer reviewe

Analyses of Beamspace MIMO Channels at 142GHz

| openaire: EC/H2020/101015956/EU//Hexa-X | openaire: EC/H2020/101095759/EU//Hexa-X-IIThis paper presents the analyses of a single-user beamspace MIMO on measured indoor and outdoor channels at 142 GHz. The rank is evaluated under different antenna sizes, number of beams, and thresholds. We assume a total power constraint at the transmitter which results in a decrease in signal-to-noise ratio as the link distance increases. When using spatial multiplexing, the indoor and outdoor sites demonstrate an average capacity gain of 2x and 1.5x at link distances below 60 m. Also, the rank for our measured 142 GHz channels is comparable to that at 60 GHz channels but significantly lower than the rank at 5 GHz channels reported in the literature. We also found that at 142 GHz, the indoor and outdoor sites have median ranks of 3.0 and 1.7 for the small antenna case, and 4.9 and 2.4 for the large antenna case assuming a rank threshold of 20 dB. The indoor site has a rank higher by 1.8 than the outdoor site, regardless of antenna size. The rank decreases by only 20% and 15% for indoor and outdoor scenarios when beam density is halved, allowing a significant reduction in implementation complexity of the beamspace MIMO without remarkably reducing the rank.Peer reviewe

How many beams does sub-THz channel support

| openaire: EC/H2020/101015956/EU//Hexa-XAntenna, radio frequency (RF) circuit, algorithm, and system researchers on sub-THz RF are interested in knowing characteristics of corresponding radio channels. Among other things, a relevant question is the number of beams supported by the channel. From wideband directional propagation measurements one can estimate how many significant paths are present in a measurement location, but interpreting that to separable beams is not trivial. In this letter, we introduce three methods to approximate the number of beams that a measured power angular delay profile can support. We show also example evaluations and distribution functions of beam numbers, estimated from indoor D-band measurement data.Peer reviewe

How many beams does sub-THz channel support

| openaire: EC/H2020/101015956/EU//Hexa-XAntenna, radio frequency (RF) circuit, algorithm, and system researchers on sub-THz RF are interested in knowing characteristics of corresponding radio channels. Among other things, a relevant question is the number of beams supported by the channel. From wideband directional propagation measurements one can estimate how many significant paths are present in a measurement location, but interpreting that to separable beams is not trivial. In this letter, we introduce three methods to approximate the number of beams that a measured power angular delay profile can support. We show also example evaluations and distribution functions of beam numbers, estimated from indoor D-band measurement data.Peer reviewe

An experimentally validated fading model for THz wireless systems

| openaire: EC/H2020/871464/EU//ARIADNEAs the wireless world moves towards the sixth generation (6G) era, the demand of supporting bandwidth-hungry applications in ultra-dense deployments becomes more and more imperative. Driven by this requirement, both the research and development communities have turned their attention into the tera hertz (THz) band, where more than 20 GHz of contiguous bandwidth can be exploited. As a result, novel wireless system and network architectures have been reported promising excellence in terms of reliability, massive connectivity, and data-rates. To assess their feasibility and efficiency, it is necessary to develop stochastic channel models that account for the small-scale fading. However, to the best of our knowledge, only initial steps have been so far performed. Motivated by this, this contribution is devoted to take a new look to fading in THz wireless systems, based on three sets of experimental measurements. In more detail, measurements, which have been conducted in a shopping mall, an airport check-in area, and an entrance hall of a university towards different time periods, are used to accurately model the fading distribution. Interestingly, our analysis shows that conventional distributions, such as Rayleigh, Rice, and Nakagami-m, lack fitting accuracy, whereas, the more general, yet tractable, alpha-mu distribution has an almost-excellent fit. In order to quantify their fitting efficiency, we used two well-defined and widely-accepted tests, namely the Kolmogorov-Smirnov and the Kullback-Leibler tests. By accurately modeling the THz wireless channel, this work creates the fundamental tools of developing the theoretical and optimization frameworks for such systems and networks.Peer reviewe

Analyses of beamspace MIMO channels at 142GHz

Abstract This paper presents the analyses of a single-user beamspace MIMO on measured indoor and outdoor channels at 142 GHz. The rank is evaluated under different antenna sizes, number of beams, and thresholds. We assume a total power constraint at the transmitter which results in a decrease in signal-to-noise ratio as the link distance increases. When using spatial multiplexing, the indoor and outdoor sites demonstrate an average capacity gain of 2x and 1.5x at link distances below 60 m. Also, the rank for our measured 142 GHz channels is comparable to that at 60 GHz channels but significantly lower than the rank at 5 GHz channels reported in the literature. We also found that at 142 GHz, the indoor and outdoor sites have median ranks of 3.0 and 1.7 for the small antenna case, and 4.9 and 2.4 for the large antenna case assuming a rank threshold of 20 dB. The indoor site has a rank higher by 1.8 than the outdoor site, regardless of antenna size. The rank decreases by only 20% and 15% for indoor and outdoor scenarios when beam density is halved, allowing a significant reduction in implementation complexity of the beamspace MIMO without remarkably reducing the rank

A New Look to THz Wireless Links: Fading Modeling and Capacity Assessment

| openaire: EC/H2020/871464/EU//ARIADNEThis work investigates the suitability of α–µ distribution to model line-of-sight (LoS) and non-line-of-sight (NLoS) multi-path fading in terahertz (THz) wireless systems. The goodness of fit of α–µ to the small-scale fading of the measured channels is evaluated in terms of the Kolmogorov-Smirnov (KS) test. The KS test revealed the capability of α–µ distribution to capture the fading characteristics of THz wireless channels. To highlight the importance of this study and the applicability to the theoretical analysis of THz wireless systems, for indicative values of α and µ, the ergodic capacity of THz wireless systems is assessed.Peer reviewe