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Large-Scale Parameters of Spatio-Temporal Short-Range Indoor Backhaul Channels at 140 GHz
... In these models, the THz channel has been assumed to consist of a single deterministic LoS coefficient, which has been expressed as the sum of the free space and molecular absorption loss. Various LoS and NLoS indoor measurements are performed for wireless links operating at 28 GHz and 140 GHz 16,17 . Therein, based on the received signal strength of the multipath components of the links, the millimeter wave (mmWave) and THz channels have been deterministically modeled as the logarithmic scale sum of the exponential pathloss and lognormal shadowing. ...
... The indoor THz small-scale fading channel modeling has recently gained a momentum 7,16,17,20,[24][25][26][27][28][29][30][31] . Specifically, for the case of wireless backhaul THz links, the small-scale fading has been theoretically modeled by means of the α−µ distribution 24,26 . ...
... Subsequently, in order to eliminate the deterministic phenomenon of pathloss, by employing (1) to each link, the link pathgain measurements are normalized to unity as Incrementing a link channel realizations. The inherent high frequencies of the THz band lead to much higher propagation losses in comparison with the lower mmWave and ultra-high-frequency (UHF) bands 15,17,46 . The THz free space pathloss even at distances of a few meters and a low transmission frequency can be severe. ...
Terahertz (THz) band offers a vast amount of bandwidth and is envisioned to become a key enabler for a number of next generation wireless applications. In this direction, appropriate channel models, encapsulating the large and small-scale fading phenomena, need to be developed for both indoor and outdoor communications environments. The THz large-scale fading characteristics have been extensively investigated for both indoor and outdoor scenarios. The study of indoor THz small-scale fading has recently gained the momentum, while the small-scale fading of outdoor THz wireless channels has not yet been investigated. Motivated by this, this contribution introduces Gaussian mixture (GM) distribution as a suitable small-scale fading model for outdoor THz wireless links. In more detail, multiple outdoor THz wireless measurements recorded at different transceiver separation distance are fed to an expectation-maximization (EM) fitting algorithm, which returns the parameters of the GM probability density function. The fitting accuracy of the analytical GMs is evaluated in terms of the Kolmogorov-Smirnov, Kullback-Leibler (KL) and root-mean-square-error (RMSE) tests. The results reveal that as the number of mixtures increases the resulting analytical GMs perform a better fit to the empirical distributions. In addition, the KL and RMSE metrics indicate that the increase of mixtures beyond a particular number result to no significant improvement of the fitting accuracy. Finally, following the same approach as in the case of GM, we examine the suitability of mixture Gamma (MG) to capture the small-scale fading characteristics of the outdoor THz channels.
... Meanwhile, some agencies have measured the channel characteristics of D-band, but to our knowledge, few outdoor long-distance D-band channel characterization based on measurements have been reported [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. This paper presents the measurements of the D-band outdoor long-distance channels, explores the applicability of the FI and CI models at long distances in the D-band, and also fits the path loss index and shadow fading. ...
... In an urban microcell setting, the team also ran directionally resolved outdoor wideband measurement operations at 140 GHz [16]. In 2018, Aalto University reported a microcell directional channel at 140 GHz for a large indoor shopping mall environment, arguing that the spatiotemporal characteristics of the strong path are remarkably consistent between the 28 and 140 GHz channels, and they discovered that the channel's large-scale parameters are comparable at both frequencies [17]. Georgia Institute of Technology conducted a comprehensive analysis of the physical parameters of the terahertz indoor channel, including LOS path loss, power delay angle profile, temporal and spatial characteristics, and correlation between terahertz multipath characteristics [18]. ...
... The team analyzed the temporal and angular distribution of MPCs, as well as the correlation between channel parameters and their distribution [24,25]. Meanwhile, some agencies have measured the channel characteristics of D-band, but to our knowledge, few outdoor long-distance D-band channel characterization based on measurements have been reported [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. This paper presents the measurements of the Dband outdoor long-distance channels, explores the applicability of the FI and CI models at long distances in the D-band, and also fits the path loss index and shadow fading. ...
D-band (110–170 GHz) has received much attention in recent years due to its larger bandwidth. However, analyzing the loss characteristics of the wireless channel is very complicated at the millimeter-wave (MMW) band. Research on D-band wireless channels has been focused on indoor short-distance transmissions, with few studies looking at outdoor long-distance wireless channels. In this paper, we provide the design of the D-band outdoor long-distance transmission system, propose the outdoor line-of-sight (LOS) propagation measurements, and study the outdoor D-band propagation loss characteristics with distances up to 800 m. The path loss model uses the Floating Intercept (FI) and the Close-In (CI) model is established based on the least square method. In the CI model, the path loss exponent is greater than 2 and increases with frequency, while in the FI model, the path loss exponent has no apparent frequency dependence. The results show that D-band path loss in long-distance outdoor scenarios is greater than that in free space, indicating that the propagation condition is worse than in free space. The results show that both models have similar performance. Under this basis, the model with the smallest number of parameters would be the optimal choice. In addition, these results prospectively provide a theoretical model for designing and optimizing high frequency mm-wave propagation measurements at a distance of 200 m and beyond.
... In a similar way, Aalto University used a 200-m optical fiber between the Tx and the VNA to extend the straight-line measuring distance of a 140 GHz channel measurement system with Rx on a rotor [64], [65]. With the distance-extended measurement system, the team measured and analyzed the 140 GHz indoor channels in a shopping mall with measurement distance from 3 to 65 m and an airport check-in hall with measurement distance from 15 to 51 m) [65], [96]. ...
... Ray-tracing can be done based on those point clouds, with increased accuracy, though also typically significantly increased runtime of the simulation. Point-cloud ray-tracing has been applied to THz channels in [96], [183], [184]. ...
... We start with the analysis of the key channel characteristics, including the large-scale fading due to path loss and shadow fading as well as the small-scale fading due to multi-path effects, such as delay spread (DS), angular spread (AS), etc., for indoor and outdoor communications systems. The measurement setups, including the measurement distance range and the antenna configurations, of existing studies in both indoor and outdoor scenarios are summarized in Tables V and VI, from different groups including Shanghai Jiao Tong University collabrated with Huawei (SJTU & Huawei) [87], [89]- [92], University of Southern California (USC) [67], [86], [93]- [95], Technische Universität Braunschweig (TUBS) [83], [168], Georgia Institute of Technology (GIT) [77], [80], [264], [265], Beijing University of Post and Telecommunications (BUPT) [266], New York University (NYU) [102], [105], [106], [108], [109], [256], [267], Aalto University (AU) [65], [96], Technische Universität Ilmenau (TUL) [111], Türkiye Bilimsel ve Teknolojik Aratrma Kurumu (TÜBITAK) [268], Durham University (DU) [269], Ghent University (GU) [270], University Grenoble-Alpes (UGA) [271], Heinrich Hertz Institute (HHI) [112]. The channel characteristics established in these studies are discussed in the following parts. ...
Terahertz (0.1-10 THz) communications are envisioned as a key technology for sixth generation (6G) wireless systems. The study of underlying THz wireless propagation channels provides the foundations for the development of reliable THz communication systems and their applications. This article provides a comprehensive overview of the study of THz wireless channels. First, the three most popular THz channel measurement methodologies, namely, frequency-domain channel measurement based on a vector network analyzer (VNA), time-domain channel measurement based on sliding correlation, and time-domain channel measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are introduced and compared. Current channel measurement systems and measurement campaigns are reviewed. Then, existing channel modeling methodologies are categorized into deterministic, stochastic, and hybrid approaches. State-of-the-art THz channel models are analyzed, and the channel simulators that are based on them are introduced. Next, an in-depth review of channel characteristics in the THz band is presented. Finally, open problems and future research directions for research studies on THz wireless channels for 6G are elaborated.
... In a similar way, Aalto University used a 200-m optical fiber between the Tx and the VNA to extend the straight-line measuring distance of a 140 GHz channel measurement system with Rx on a rotor [36], [37]. With the distance-extended measurement system, the team measured and analyzed the 140 GHz indoor channels in a shopping mall with measurement distance from 3 to 65 m and an airport check-in hall with measurement distance from 15 to 51 m) [37], [64]. ...
... ray-tracing can be done based on those point clouds, with increased accuracy, though also typically significantly increased runtime of the simulation. Point-cloud ray-tracing has been applied to THz channels in [64], [143], [144]. ...
... We start with the analysis of the key channel characteristics, including the large-scale fading due to path loss and shadow fading as well as the small-scale fading due to multi-path effects, such as delay spread (DS), angular spread (AS), etc. for indoor and outdoor communications systems. The measurement setups, including the measurement distance range and the antenna configurations, of existing studies in both indoor and outdoor scenarios are summarized in Table V and VI, from different groups including Beijing Jiao Tong University (BJTU) [81]- [85], [224], Shanghai Jiao Tong University (SJTU) [58], [225], Georgia Institute of Techonology (GIT) [51], [226], [227], New York University (NYU) [70], [73], [75], [228], Technische Universität Braunschweig (TUBS) [54], [127], [229], University of Southern California (USC) [39], [57], [61]- [63], Aalto University (AU) [37], [64], Technische Universität Ilmenau (TUL) [77], Türkiye Bilimsel ve Teknolojik Araştırma Kurumu (TÜBITAK) [230], Durham University (DU) [231], Ghent University (GU) [232], University Grenoble-Alpes (UGA) [233], Heinrich Hertz Institute (HHI) [78]. The channel characteristics established in these studies are discussed in the following parts. ...
Terahertz (THz) communications are envisioned as a key technology for sixth generation (6G) wireless systems. The study of underlying THz wireless propagation channels provides the foundations for the development of reliable THz communication systems and their applications. This article provides a comprehensive overview of the study of THz wireless channels. First, the three most popular THz channel measurement methodologies, namely, frequency-domain channel measurement based on a vector network analyzer (VNA), time-domain channel measurement based on sliding correlation, and time-domain channel measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are introduced and compared. Current channel measurement systems and measurement campaigns are reviewed. Then, existing channel modeling methodologies are categorized into deterministic, stochastic, and hybrid approaches. State-of-the-art THz channel models are analyzed, and the channel simulators that are based on them are introduced. Next, an in-depth review of channel characteristics in the THz band is presented. Finally, open problems and future research directions for research studies on THz wireless channels for 6G are elaborated.
... In [5] and [6] a simplified line-of-sight (LoS) channel model for the range of 100-450 GHz and 200-450 GHz, respectively was presented. Meanwhile, the authors in [7] and [8], [9] performed LoS and non-line-ofsight (NLoS) wireless measurements at 90-200 GHz and 140-144 GHz, respectively. These works employed the common deterministic wireless communications pathloss model and by using their corresponding measurements, the pathloss exponent and lognormal shadowing parameters were extracted. ...
... The specifications of the THz channel sounding system utilized in this work can be found in [8], [9]. The RX and TX were fitted with a horn and a bicone antenna, respectively. ...
... From Table I the KL test values of the α-µ, Nakagami-m and Rice distributions are obtained from the KL α-µ , KL N and KL R columns, respectively. Based on the KL test values it is observed that the α-µ distribution provides a better fit than Rice and Nakagamim for the links 0, 3,7,9,10,11,13,14,18,19, and 20. Figures 2(a) and 2(b), serve as an illustrative example of the achieved fitting of the analytical distributions to the empirical ones for the links 7 and 20, respectively. ...
This contribution aims at experimentally validating the suitability of well known fading distributions in modeling the channel of indoor THz wireless systems. In particular the suitability of α-µ, Rice and Nakagami-m distributions is evaluated by fitting them to empirical channel measurements. The fitting performance is expressed in terms of the Kolmogorov-Smirnov (KS) and Kullback-Leibler (KL) divergence tests. The results show that the α-µ and Rice distributions achieve a good fit to the empirical data, wheras the Nakagami-m distribution fails to provide an adequate fit in the majority of the examined THz links.
... Due to the severe propagation losses in the THz band, the wireless communications in this frequency range rely heavily on the line-of-sight (LoS) component of the received signal 11,12,25 . Moreover, by taking this into account, the THz channel is commonly modeled by considering only the large-scale propagation phenomena, namely the shadowing and the deterministic pathloss [11][12][13][19][20][21][22][23][24] . The pathloss in the THz band is expressed as the product of the free space and molecular absorption loss 11 . ...
... Moreover, by employing these simplified models the THz channel was assumed to consist of a single coefficient in the LoS direction, which was obtained as the product of the free-space loss and the molecular absorption loss 11,19,20 . Meanwhile, LoS and non-line-of-sight (NLoS) channel measurements for various narrowband indoor wireless communications links operating at 28 GHz and 140 GHz were performed 12,13 . In these works, based on the measured received signal power of the multipath components of the different links, the respective millimeter www.nature.com/scientificreports/ ...
... Despite the heavy rely on the existence of the LoS component in THz wireless communications, there are aerosols in the atmospheric medium, as well as objects laid in the propagation environment that can act as scatterers 12,13,29 . Hence, there can be THz multipath components with significant power capable of being detected by the RX even if they arrive from NLoS directions 4,12,21 . ...
As the wireless world moves towards the sixth generation (6G) era, the demand for 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 to the terahertz (THz) band, where more than 20 GHz of contiguous bandwidth can be exploited. As a result, novel wireless systems 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, α-µ 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 for developing the theoretical and optimization frameworks for such systems and networks.
... The channel measurements on the D band were conducted by Aalto university in various locations in Helsinki region, Finland [29]- [31]. Several datasets from these measurements are openly available in [32]. ...
... The exact measurement setups have been detailed in various previous works, such as in [29] for the Aalto University entrance hall, [30] for the shopping mall, and [31] for the airport and shopping mall. The shopping mall and airport measurements were conducted at 143.1 GHz center frequency, while the remaining ones were conducted in the 142 GHz frequency with 4 GHz bandwidth. ...
Millimeter-Wave (mmWave) (30-300 GHz) and D band (110-170 GHz) frequencies are poised to play a pivotal role in the advancement of sixth-generation (6G) systems and beyond with increased demand for greater bandwidth and capacity. This paper focuses on deriving a generalized channel impulse response for mmWave communications, considering both outdoor and indoor locations for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. The analysis is based on statistical insights obtained from measurements conducted at distinct locations with a center frequency of 142 GHz, examining parameters such as path gain, delay, number of paths (NoP), and angle distributions. Whereas different distributions serve as candidate models for the gain of LOS communications, only specific distributions accurately describe the NLOS gain, LOS and NLOS delay, LOS and NLOS NoP, and LOS and NLOS angular distributions. The channel is modeled based on geometry-based stochastic channel modeling (GBSM) with parameters derived from the statistical analysis. The maximum excess delay is used as a metric to evaluate the performance of the proposed model against empirical data.
... Path loss, delay and angular spread statistics in large cubic office scenarios at 159 GHz, and conference room scenarios at 190 GHz, were also assessed in [25] and [26], respectively. Finally, larger indoor areas were examined in [27]- [30] including entrance halls, shopping malls, and airport halls. ...
... Therefore, strong MPCs arrive around the Rx from various directions resulting in increased the azimuth spreads. In spacious environments, such as shopping malls, airport halls, and entrance halls [27]- [30], smaller angular spreads are encountered as the scattering surfaces are distantly separated and far from the Rx, thus facilitating a sparser channel. It also worth commenting the difference between m τ and σ τ . ...
Next generation wireless networks will necessitate new and wide spectrum swaths able to accommodate and support Tb/s applications and services. In this regard, frequencies above 100 GHz are anticipated to be allocated, which requires a thorough analysis of the propagation characteristics at those segments. This article presents a detailed analysis of the indoor channel at sub-THz frequencies, modeling its temporal and spatial characteristics for line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, relying on extensive deterministic simulations. According to the results, frequency selective characteristics are revealed. The obtained root-mean-square delay spread is in the range of 4.4–10.3 ns for LOS, and 6.9–18.8 ns for NLOS scenarios, respectively. A high spatial degree of freedom is also observed based on the increased azimuth spreads with a mean value of 57.4for LOS, and 88.1for NLOS locations, which is associated with the environment geometry. All the large-scale features of the channel exhibit a linear variation with distance, whereas according to the Gini Index and K-factor analysis, a channel with limited sparsity is encountered, especially in NLOS scenarios. Furthermore, the spatial coherence of the channels’ attributes is also assessed and modeled using an exponential decaying sinusoid relationship. A faster channel decoherence is observed in NLOS locations. Finally, the temporal and spatial properties of the channel are modeled statistically, delivering its related features that include the ray and cluster decaying rates, the inter-arrival delays, the azimuth and elevation angle-of-arrivals, and the cluster and ray occurrence.
... In Europe, numerous multiorganisational projects have been conducted including ref. [34]. Nguyen et al. [35] provide analyses of 140 GHz shopping mall and airport check-in hall measurements to compare with the 3GPP model, and conclude that their 140 GHz measurements agree with the 3GPP path loss model. Larsson et al. [36] provide a comparison of propagation coverage maps among 28, 58, and 143 GHz. ...
... According to ref. [1], the 3GPP office refers to an office building comprising various rooms including open-space cubicles, traditional small office, corridors etc, in which cases the NLoS clutter source can be a cement wall so that NLoS paths can be determined more explicitly. Note also that the authors in ref. [35] reported that its sub-THz measurements, collected in a shopping mall and an air-port check-in hall at 140 GHz, have path loss characteristics similar to those of the 3GPP office. ...
For 5G beyond and/or 6G mobile services, a new spectrum at frequencies above 100 GHz has received great attention lately. To characterise the similarities and the differences between frequencies below 100 GHz and above 100 GHz, this paper provides analyses of multi‐frequency propagation characteristics based on wideband measurements at 28, 38, 71, 82, and 159 GHz, with an emphasis on the sub‐THz (i.e. the 159 GHz) propagation characteristics. All the frequency measurements were conducted in the same cubicle office room environment by locating the transmitter and the receiver at the same positions. The measurement results show that the path loss and the shadow fading characteristics do not exhibit significant differences depending on the frequency range from 28 to 159 GHz. However, the delay spread shows a generally decreasing trend as the frequency increases. Additionally, angular domain analyses were conducted with the 159 GHz measurements.
... In [5] and [6] the authors provided a simplified deterministic channel model for LoS THz wireless links operating in the ranges of 100-450 GHz and 200-450 GHz, respectively. In [7] and [8], [9] wireless link measurements in the range of 90-200 GHz and at 140 GHz were performed, respectively. In both of these works LoS and non-line-of-sight paths were measured. ...
... A THz frequency-domain channel sounding system, which is also elaborated in [8], [9], was utilized to study spatio-temporal multipath characteristics. The RX and TX were equipped with a 19 dBi horn and a 0 dBi bicone antenna, respectively. ...
This 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.
... With the increasing interest in this frequency range, several studies have been conducted to better understand wave propagation and develop channel models at the sub-THz band based on measurements. The large-scale parameters (LSP) of the propagation channel such as path loss, delay, and angular spreads are extracted based on sub-THz measurements performed in an empty room [2], indoor corridor [3], airport and shopping mall [4], industrial setting [5]- [7], train wagon and station [8], and urban scenario [9]. Deterministic and stochastic channel models have also been developed at the sub-THz band. ...
The 3GPP channel model for new radios, described in 3GPP TR 38.901, is one of the most widely used channel models in the cellular wireless community. Originally established at below-6GHz radio frequencies and gradually expanded to cover new frequencies, its applicability to the new frequencies has always been an interest of the community. Our comparison of the radio channel responses from the measurements and the original 3GPP channel model, along with their variants adapted to sub-Terahertz frequency at 142 GHz in indoor and outdoor environments, sheds light on the possible improvement of the model. The original model defines cluster azimuth angles such that stronger clusters are always concentrated around a reference direction. Meanwhile, the measured azimuth power spectrum indicates that strong clusters randomly come from any direction. An alternative approach to iteratively generate cluster angles is therefore proposed, which provides improved agreement of the angular spread and eigenvalue statistics between measured and generated channels, at the expense of increased computational complexity in generating clusters. Moreover, the number of rays has no significant impact on the eigenvalue statistics. Setting the number of clusters fixed results in inaccurate statistics of the number of eigenmodes in generated sparse multipath channels.
... Several measurement campaigns have been undertaken to explore the propagation characteristics and establish a channel model [8] [9]. Numerous sub-THz channel measurements have been conducted across a wide range of indoor hotspot scenarios (InH), encompassing train-to-infrastructure [10], vehicular communications [11], shopping malls, airport check-in halls [12], data centers [13], motherboards [14], aircraft cabins [15], factory buildings [16], lecture rooms [17], meeting rooms [18] [19], office rooms [19], corridors [20], and indoor short-range scenarios [21] [24]. ...
Sub-Terahertz communication has broad application prospects for realizing ultra-broadband sixth generation (6G) system. One fundamental challenge when moving to new spectrum is to understand the science of radio propagation and propose an accurate and effective channel prediction method. In this paper, we first conduct extensive vector network analyzer-based radio propagation measurements at 140 GHz and 220 GHz in indoor hallway and lobby environments and at 280 GHz in an indoor laboratory environment. Omnidirectional and best directional path loss are modeled by empirical single-band and multi-band path loss models. Numerical results demonstrate that large-scale close-in model in this paper is simpler and more physically-based compared to floating-intercept model. In particular, a path loss prediction method based on environment features is proposed, which can predict path loss directly by utilizing random forest method, and the propagation environment are defined and extracted by scatterer features and related features of the transmitter and receiver. The performance of the proposed method is better than that of empirical path loss models. The measured results not only enrich the datasets of indoor sub-THz channel propagation, also can guide communication systems, network planning and deployment for 6G and beyond.
... Thus far, several measurement campaigns have been undertaken to explore the propagation characteristics and establish a channel model [8] [9]. Numerous THz channel measurements have been conducted across a wide range of indoor hotspot scenarios (InH), encompassing train-to-infrastructure [10], vehicular communications [11], shopping malls, airport check-in halls [12], data centers [13], motherboards [14], aircraft cabins [15], factory buildings [16], lecture rooms [17], meeting rooms [18] [19], office rooms [19], corridors [20], and indoor shortrange scenarios [21] [24]. ...
Terahertz (THz) communications are envisioned as one of the promising technologies to enable ultra-broadband 6G systems. One fundamental challenge when moving to new spectrum is to understand the science of radio propagation and propose an accurate and effective channel prediction method for predicting the signal coverage. In this paper, we first conduct extensive VNA-based wideband radio propagation measurements at 220 GHz in indoor hallway and lobby environments and at 280 GHz in an indoor laboratory environment. Omnidirectional and best directional path loss are analyzed and modeled by empirical single-band and multi-band path loss models. Besides, propagation statistics such as Rician K-factor (KF) and root mean square (RMS) delay spread (DS) are modeled by Weibull distribution and lognormal distribution, respectively, and two-slope model is proposed to analyze the relationship of the KF, RMS DS and distance in various scenarios. Numerical results demonstrate that large-scale close-in model in this paper is simpler and more physically-based compared to floating-intercept model. In particular, path loss prediction method based on environment features is proposed, which can predict path loss directly by utilizing random forest method, and the propagation environment are defined and extracted by scatterer features and related features of Tx and Rx. The performance of the proposed model is better than that of empirical path loss models. The measured results not only enrich the datasets of indoor THz channel propagation, also can guide communication systems, network planning and deployment for 6G and beyond.
... In this context, a plethora of works in literature can be found investigating the band of frequencies from 100 GHz to 250 GHz using different types of channel sounders. In the earlier mentioned spectrum, measurement campaigns have been conducted in various common indoor and outdoor places of usage such as on laboratory desktop [7], [8], in office room [9]- [12], in factory building [13], in airport check-in hall [14], in urban microcell [15]- [17] and in urban street [18]. ...
In this paper, a newly developed 300 GHz channel sounder is presented followed by a detailed description of test measurements and the subsequent results obtained to validate its working. An elucidation of the high-resolution double-directional channel measurement in a typical conference room scenario precedes the comparison of the results obtained for the current campaign to that obtained from an earlier campaign at 60 GHz for a similar setup. It is observed that a similar number of clusters for both the bands under investigation for all the transmitter (Tx) and receiver (Rx) positions are obtained from the generated power spectra. Any deviation is theorized to be caused either due to the usage of lower measurement bandwidth in the 60 GHz campaign or due to limited elevation expanse in the 300 GHz measurement. To identify the interacting objects (IOs) causing the clusters, environment-embedded angular power spectra (APS) and ray tracing simulations are used. The large-scale parameters (LSPs) are also evaluated for both campaigns. It is observed that signal propagation in the terahertz (THz) band is dominated more by the line-of-sight (LoS) path compared to the millimeter wave (mm-wave) band (below 100 GHz). The results are also compared with other similar results from the literature.
... In this context, a plethora of works in literature can be found investigating the band of frequencies from 100 GHz to 250 GHz using different types of channel sounders. In the earlier mentioned spectrum, measurement campaigns have been conducted in various common indoor and outdoor places of usage such as on laboratory desktop [7], [8], in office room [9]- [12], in factory building [13], in airport check-in hall [14], in urban microcell [15]- [17] and in urban street [18]. ...
p>In this paper, a newly developed 300 GHz channel sounder is presented followed by a detailed description of test measurements and the subsequent results obtained to validate its working. An elucidation of the high-resolution double-directional channel measurement in a typical conference room scenario precedes the comparison of the results obtained for the current campaign to that obtained from an earlier campaign at 60 GHz for a similar setup. It is observed that a similar number of clusters for both the bands under investigation for all the transmitter (Tx) and receiver (Rx) positions are obtained from the generated power spectra. Any deviation is theorized to be caused either due to the usage of lower measurement bandwidth in the 60 GHz campaign or due to limited elevation expanse in the 300 GHz measurement. To identify the interacting objects (IOs) causing the clusters, environment-embedded angular power spectra (APS) and ray tracing simulations are used. The large-scale parameters (LSPs) are also evaluated for both campaigns. It is observed that signal propagation in the terahertz (THz) band is dominated more by the line-of-sight (LoS) path compared to the millimeter wave (mm-wave) band (below 100 GHz). The results are also compared with other similar results from the literature.</p
... In this context, a plethora of works in literature can be found investigating the band of frequencies from 100 GHz to 250 GHz using different types of channel sounders. In the earlier mentioned spectrum, measurement campaigns have been conducted in various common indoor and outdoor places of usage such as on laboratory desktop [7], [8], in office room [9]- [12], in factory building [13], in airport check-in hall [14], in urban microcell [15]- [17] and in urban street [18]. ...
p>In this paper, a newly developed 300 GHz channel sounder is presented followed by a detailed description of test measurements and the subsequent results obtained to validate its working. An elucidation of the high-resolution double-directional channel measurement in a typical conference room scenario precedes the comparison of the results obtained for the current campaign to that obtained from an earlier campaign at 60 GHz for a similar setup. It is observed that a similar number of clusters for both the bands under investigation for all the transmitter (Tx) and receiver (Rx) positions are obtained from the generated power spectra. Any deviation is theorized to be caused either due to the usage of lower measurement bandwidth in the 60 GHz campaign or due to limited elevation expanse in the 300 GHz measurement. To identify the interacting objects (IOs) causing the clusters, environment-embedded angular power spectra (APS) and ray tracing simulations are used. The large-scale parameters (LSPs) are also evaluated for both campaigns. It is observed that signal propagation in the terahertz (THz) band is dominated more by the line-of-sight (LoS) path compared to the millimeter wave (mm-wave) band (below 100 GHz). The results are also compared with other similar results from the literature.</p
... The two-slope path loss model for the shortrange THz propagation is given in [6], which demonstrates the joint effect of the transmitter-receiver separation and the frequency on the received power. The large-scale parameters of the spatio-temporal channel for 140 GHz at the shopping mall and airport hall are investigated in [7]. By combining ray-tracing and statistical methods, an indoor communication hybrid cluster-based channel modeling is proposed for 130 GHz -143 GHz in [8]. ...
In this work, extensive propagation characteristics of short range 240 to 300 GHz terahertz (THz) channels are mapped based on a measurement campaign conducted utilizing a novel, task specific measurement system. The measurement system allows collecting measurements from different distances and orientations in a very fine grained resolution, which is a particular issue in achieving realistic THz channel estimation. After the accurate measurement results are obtained, they are investigated in terms of channel impulse and channel frequency response. Furthermore, the fading channel amplitude histograms are modeled with the Gamma mixture model (GMM). The expectation-maximization (EM) algorithm is utilized to determine the corresponding mixture parameters. Also, to demonstrate the flexibility of the GMM, the Dirichlet process Gamma mixture model (DPGMM) is utilized in cases where the EM algorithm fails to represent histograms. Moreover, the suitability of the GMM is evaluated utilizing Kolmogorov Smirnov tests. Results verify that the GMMs can simulate the fading channel of micro-scale THz wireless communication in a realistic way, providing important implications regarding the achievable capacity in these channels. Finally, the average channel capacity of each link is evaluated using the probability density function of GMMs to gain deeper insight into the potential of micro-scale THz communications.
... The telecommunications industry is one of the key sectors undergoing rapid and continuous evolution of different multimedia and cellular-based broadband communication technologies, such as high-speed packet access (HSPA) [56], long-term evolution (LTE) [57,58], new radio (NR) [2,59,60], among others. Continuous measurement-based data facilitate monitoring, performance evaluation, and optimization of the wireless network [35,[61][62][63]. ...
Considering the ever-growing demand for an efficient method of deductive mining and extrapolative analysis of large-scale dimensional datasets, it is very critical to explore advanced machine learning models and algorithms that can reliably meet the demands of modern cellular networks, satisfying computational efficiency and high precision requirements. One non-parametric supervised machine learning model that finds useful applications in cellular networks is the Gaussian process regression (GPR). The GPR model holds a key controlling kernel function whose hyperparameters can be tuned to enhance its supervised predictive learning and adaptive modeling capabilities. In this paper, the limited-memory Broyden–Fletcher–Goldfarb–Shanno (LBFGS) with kernel parameters selection (KPS) algorithm is employed to tune the GPR model kernel hyperparameters rather than using the standard Bayesian optimization (BOP), which is computationally expensive and does not guarantee substantive precision accuracy in the extrapolative analysis of a large-scale dimensional dataset. In particular, the hybrid GPR–LBFGS is exploited for adaptive optimal extrapolative learning and estimation of throughput data obtained from an operational 5G new radio network. The extrapolative learning accuracy of the proposed GPR–LBFGS with the KPS algorithm was analyzed and compared using standard performance metrics such as the mean absolute error, mean percentage error, root mean square error and correlation coefficient. Generally, results revealed that the GPR model combined with the LBFGS kernel hyperparameter selection is superior to the Bayesian hyperparameter selection method. Specifically, at a 25 m distance, the proposed GPR–LBFGS with the KPS method attained 0.16 MAE accuracy in throughput data prediction. In contrast, the other methods attained 46.06 and 53.68 MAE accuracies. Similarly, at 50 m, 75 m, 100 m, and 160 m measurement distances, the proposed method attained 0.24, 0.18, 0.25, and 0.11 MAE accuracies, respectively, in throughput data prediction, while the two standard methods attained 47.46, 49.93, 29.80, 53.92 and 47.61, 52.54, 53.43, 54.97, respectively. Overall, the GPR–LBFGS with the KPS method would find valuable applications in 5G and beyond 5 G wireless communication systems.
... The measurement campaigns performed in the shopping mall and airport check-in hall are described in [10]. The third indoor site, which is further described in [20], is in the entrance arXiv:2209.11324v1 ...
In this paper, 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 lineof- 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 derived using up to the 3rd strongest MPC.
... Outdoor urban environment measurements at 140 GHz were performed in [18], where the Power Angular spectrum (PAS) was explored. In [20] long-range measurements in a shopping mall and airport with distances of up to 60 m were performed, large-scale parameters, e.g. path loss were investigated. ...
With the increasing demand for high bandwidth wireless communication systems, and with a congested spectrum in the sub-6 GHz frequency bands, researchers have been looking into exploration of millimeter wave (mmWave) and sub-terahertz (sub-THz) frequency bands. Channel modeling is essential for system design and performance evaluation of new wireless communication systems. Accurate channel modeling relies on reliable measured channel data, which is collected by high-fidelity channel sounders. Furthermore, it is of importance to understand to which extent channel parameters are frequency dependent in typical deployment scenario (including both indoor short-range and outdoor long-range scenarios). To achieve this purpose, this paper presents a state-of-art long-range 28 GHz and 300 GHz VNA-based channel sounder using optical cable solutions, which can support a measurement range up to 300 m and 600 m in principle, respectively. The design, development and validation of the long-range channel sounders at mmWave and sub-THz bands are reported, with a focus on their system principle, link budget, and back-to-back measurements. Furthermore, a measurement campaign in an indoor corridor is performed using the developed 300 GHz system and 28 GHz channel sounding systems. Both measured channels at the 28 GHz and 300 GHz channels are shown to be highly sparse and specular. A higher number of Multi Path Components (MPC) are observed for the 28 GHz system, while the same main MPC are observed for both systems.
... Even though diffraction coefficients are smaller as the RF increases, reflections on concrete walls, metal lampposts and tinted glasses can deliver power from one link end to another, making the link connectivity in NLoS feasible through one or multiple reflections even for upper mmWave. The finding of pathloss exponents does not differ from available insights for lower mmWave RF according to the comparison of indoor hotspot channels [17]. The number of multipaths or clusters is an important degree of freedom. ...
... Even though diffraction coefficients are smaller as the RF increases, reflections on concrete walls, metal lampposts and tinted glasses can deliver power from one link end to another, making the link connectivity in NLoS feasible through one or multiple reflections even for upper mmWave. The finding of pathloss exponents does not differ from available insights for lower mmWave RF according to the comparison of indoor hotspot channels [17]. The number of multipaths or clusters is an important degree of freedom. ...
6G will be characterized by extreme use cases, not only for communication, but also for localization, and sensing. The use cases can be directly mapped to requirements in terms of standard key performance indicators (KPIs), such as data rate, latency, or localization accuracy. The goal of this paper is to go one step further and map these standard KPIs to requirements on signals, on hardware architectures, and on deployments. Based on this, system solutions can be identified that can support several use cases simultaneously. Since there are several ways to meet the KPIs, there is no unique solution and preferable configurations will be discussed.
This paper investigates the potential transformation to be ushered in by 6G technology in telecommunications, enabling huge data rates, low latencies, high-reliability connectivity, and broadened connections based on its heterogeneous cellular architecture. It is a complex work dealing with an analysis of the evolution toward 6G while using heterogeneous networks (HetNets) that take advantage of various technologies, such as small cells, macro cells, non-terrestrial networks (NTNs), and ultra-dense networks (UDNs). It discusses the architectural progress, such as spectrum efficiency, advanced beamforming, and application of AI and ML toward network optimization for 6G HetNets. The deployment challenge for the 6G HetNets: spectrum allocation, energy efficiency, interoperability, security, with solutions such as cognitive radio networks, energy harvesting, and blockchain for improved security. It also delves into the far-reaching impacts of 6G HetNets in sectors like smart cities, autonomous driving, IoT, telemedicine, and AR/VR experiences. The importance of 6G is further expounded in achieving seamless connectivity, superior mobile broadband, and supporting massive machine-type communications, therefore reshaping our digital interactions. The paper concludes on the significance of collaborative research, policy development, and standardization efforts in 6G deployment complexity management and exploitation of the full potential of 6G toward technological and societal development. It presents a holistic view of 6G’s heterogeneous cellular architecture, emphasizing its architectural innovations, challenges, and the promising future it portends for wireless communication systems.
Technology research and standardization work of sixth generation (6G) has been carried out worldwide. Channel research is the prerequisite of 6G technology evaluation and optimization. This paper presents a survey and tutorial on channel measurement, modeling, and simulation for 6G. We first highlight the challenges of channel for 6G systems, including higher frequency band, extremely large antenna array, new technology combinations, and diverse application scenarios. A review of channel measurement and modeling for four possible 6G enabling technologies is then presented, i.e., terahertz communication, massive multiple-input multiple-output communication, joint communication and sensing, and reconfigurable intelligent surface. Finally, we introduce a 6G channel simulation platform and provide examples of its implementation. The goal of this paper is to help both professionals and non-professionals know the progress of 6G channel research, understand the 6G channel model, and use it for 6G simulation.
As the world warms up to the idea of millimeter wave (mmWave) communication and fifth generation (5G) mobile networks, realization slowly dawns that the data rate, latency, throughput, and other performance metrics that are used to assess a new wireless communication technology will not be enough to support the demands of envisioned futuristic applications. Thus there is an eagerness to further climb up the frequency ladder to use the large swathes of available spectrum in the 0.1 - 10 THz band which is expected to act as the key technology enabler to fulfill the requirements of the sixth generation (6G) wireless communication and possibly even beyond. Channel measurement and modeling are crucial to the design and deployment of future wireless communication systems and researchers across the world are putting their best foot forward to accelerate the process. The present article presents comprehensive assimilation of research efforts in the context of THz channel sounding. A detailed overview of the current channel sounding techniques is first introduced followed by their relevance to THz band channel measurement. An in-house novel channel sounder developed for THz band measurement is also briefly introduced in this context. The paper next provides elaborate dissemination of various measurement campaigns in the band of interest followed by the modeling techniques that are available in the literature and are being adopted for the THz band. Post the description of different challenges and future research directions in the context of sounding, measurement, and modeling the article is concluded.
The Terahertz (THz) band (0.1-10~THz), which supports Terabit-per-second (Tbps) data rates, has been envisioned as one of the promising spectrum bands for sixth-generation (6G) and beyond communications. In this paper, an angular-resolvable wideband channel measurement campaign in an indoor L-shaped hallway at 306-321~GHz is presented, by using a frequency-domain vector network analyzer (VNA)-based channel sounder. Four line-of-sight (LoS), six quasi-line-of-sight (QLoS) and eight non-line-of-sight (NLoS) receiver points are measured. However, measured data spreads due to the rich scattering environment and the antenna pattern, which puzzles traditional clustering algorithms. To solve this problem, a simulation-assisted Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering algorithm is proposed, where the deterministic simulation result is extracted to adapt the conventional DBSCAN algorithm. The proposed algorithm outperforms conventional clustering algorithms like DBSCAN, K-means, and K-power-means in terms of Silhouette, Calinski-Harabasz and Davies-Bouldin indices. Furthermore, the THz multi-path propagation in the L-shaped hallway is elaborated, and channel characteristics of multipath and clusters are analyzed in depth.
Design and performance assessment of THz communications systems, which will form an essential part of 6G, require an understanding of the propagation channels the systems will operate in. This paper presents investigations of the channel characteristics in various scenarios at 145 GHz, which is the band currently envisioned for the first round of deployments. In particular, we review several extensive measurement campaigns performed by the University of Southern California in both outdoor and indoor environments. We present the measurement and evaluation methodology and sample results that illustrate the dominant propagation effects in different environments. We then summarize the parameters of the statistical channel models for path loss, delay dispersion, and angular dispersion. Based on these results, we find that even in NLoS (non-line-of-sight) situations, Gbit/s communications can be sustained over a 100 m distance; that (for an antenna gain of 20 dB), there is considerable delay dispersion, requiring tens of equalizer taps, and that angular dispersion is significant in both LoS and NLoS situations. The channel parameters can be thus used as a basis for system design and evaluation under realistic operating conditions.
Antenna, 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.
Terahertz (THz)-band communications are a key enabler for future-generation wireless communication systems that promise to integrate a wide range of data-demanding applications. Recent advances in photonic, electronic, and plasmonic technologies are closing the gap in THz transceiver design. Consequently, prospect THz signal generation, modulation, and radiation methods are converging, and corresponding channel model, noise, and hardware-impairment notions are emerging. Such progress establishes a foundation for well-grounded research into THz-specific signal processing techniques for wireless communications. This tutorial overviews these techniques, emphasizing ultramassive multiple-input-multiple-output (UM-MIMO) systems and reconfigurable intelligent surfaces, vital for overcoming the distance problem at very high frequencies. We focus on the classical problems of waveform design and modulation, beamforming and precoding, index modulation, channel estimation, channel coding, and data detection. We also motivate signal processing techniques for THz sensing and localization.
The field of wireless communication networks has witnessed a dramatic change over the last decade due to sophisticated technologies deployed to satisfy various demands peculiar to different data-intensive wireless applications. Consequently, this has led to the aggressive use of the available propagation channels to fulfill the minimum quality of service (QoS) requirement. A major barometer used to gauge the performance of a wireless communication system is the spectral efficiency (SE) of its communication channels. A key technology used to improve SE substantially is the multiple input multiple output (MIMO) technique. This article presents a detailed survey of MIMO channel models in wireless communication systems. First, we present the general MIMO channel model and identified three major MIMO channel models, viz., the physical, analytical, and
standardized models. The physical models describe the MIMO channel using physical parameters. The analytical models show the statistical features of the MIMO channel with respect to the measured data. The standardized models provide a unified framework for modern radio propagation architecture, advanced signal processing, and cutting-edge multiple access techniques. Additionally, we examined the strengths and limitations of the existing channel models and discussed model design, development, parameterization, implementation, and validation. Finally, we present the recent 3GPP-based 3D channel model, the transitioning from 2D to 3D channel modeling, discuss open issues, and highlight vital lessons learned for future research exploration in MIMO communication systems.
Frequencies from 100 GHz to 3 THz are promising bands for the next generation of wireless communication systems because of the wide swaths of unused and unexplored spectrum. These frequencies also offer the potential for revolutionary applications that will be made possible by new thinking, and advances in devices, circuits, software, signal processing, and systems. This paper describes many of the technical challenges and opportunities for wireless communication and sensing applications above 100 GHz, and presents a number of promising discoveries, novel approaches, and recent results that will aid in the development and implementation of the sixth generation (6G) of wireless networks, and beyond. This paper shows recent regulatory and standard body rulings that are anticipating wireless products and services above 100 GHz and illustrates the viability of wireless cognition, hyper-accurate position location, sensing, and imaging. This paper also presents approaches and results that show how long distance mobile communications will be supported to above 800 GHz since the antenna gains are able to overcome air-induced attenuation, and present methods that reduce the computational complexity and simplify the signal processing used in adaptive antenna arrays, by exploiting the Special Theory of Relativity to create a cone of silence in over-sampled antenna arrays that improve performance for digital phased array antennas. Also, new results that give insights into power efficient beam steering algorithms, and new propagation and partition loss models above 100 GHz are given, and promising imaging, array processing, and position location results are presented. The implementation of spatial consistency at THz frequencies, an important component of channel modeling that considers minute changes and correlations over space, is also discussed. This paper offers the first in-depth look at the vast applications of THz wireless products and applications and provides approaches for how to reduce power and increase performance across several problem domains, giving early evidence that THz techniques are compelling and available for future wireless communications.
Terahertz (THz) wireless data centers can provide low-latency networks and dynamic scalability that are vital for the next-generation cloud computing infrastructure. The knowledge of THz propagation characteristics in a data center environment is essential to the development of novel THz communication systems. However, a comprehensive characterization and modeling of THz propagation channels, which includes various obstructions in a data center is not available. This paper presents results from a THz channel measurement campaign conducted in a data center environment. Various propagation scenarios such as line-of-sight (LoS) link, non-LoS (NLoS) link using existing materials in a data center to redirect the beam, and obstructed-LoS (OLoS), -NLoS (ONLoS) links with common objects in data centers (cables and server racks’ mesh doors) serving as obstruction were investigated. Propagation channel parameters such as pathloss and root-mean-squared (RMS) delay spread were analyzed in the aforementioned scenarios while cluster-based modeling was implemented for some scenarios. The proposed model for THz propagation in a data center environment was validated with the measured data. The average inter-arrival time of clusters (1/Λ) and rays (1/λ) are estimated as 4.4 ns and 0.24 ns, respectively. We find that local scattering objects such as server-rack frames/pillars can be used to assist the NLoS type of link, and that cooling airflow in the data center has a negligible impact on THz propagation. Power cables and mesh doors of the server racks can cause additional attenuation of about 20 dB and 6 dB, respectively. Cluster model and other characterization results provided in this work are pertinent to THz wireless system design for data center environments.
The fading and correlation characteristics of virtual, yet realistic, Line-of-Sight (LOS) 4 × 2500 millimetric (mmW) massive MIMO channels are investigated at 94 GHz in an indoor office environment for three different Tx-Rx distance scenarios. The capability of the mmW massive MIMO channel to spatially decorrelate the users is evaluated with the computation of the channel correlation and other channel metrics such as power to interference ratio and condition number. In particular, the correlation between channel vectors for a given user and its influence on receiving correlation is discussed. The results clearly demonstrate the capability of mmW massive MIMO systems to reach orthogonal Tx-Rx streams even for a small 7 × 7 antenna array subset with correlation between users <0.2. Moreover, strong phase variations at Tx side at this frequency range are highlighted through channel phase correlation studies and were shown to contribute to the decorrelation at Rx side between close users paving the way for further massive MIMO system enhancements.
Modeling propagation channels for future pico-cellular indoor THz communication systems requires the knowledge of the reflective properties of building materials. The reflectivity of smooth, optically thick materials can be modeled with Fresnel equations. In case of materials with a rough surface, diffuse scattering reduces the power reflected in the specular direction. Kirchhoff scattering theory can be employed to derive modified Fresnel equations which account for these losses by introducing a Rayleigh roughness factor calculated from the measured surface height distribution of the sample under observation. Using the resulting, analytically derived reflection coefficient based on material parameter and surface measurements in propagation models enables the simulation of arbitrary configurations. We present a set of calculated and measured reflection coefficients for a selection of common indoor building materials which are in good agreement, thus verifying our modeling approach. Furthermore, we illustrate by ray-tracing simulations the effect of wall and ceiling roughness on propagation in future indoor scenarios. Both, absolute power levels and propagation patterns are shown to be strongly influenced by scattering. In some cases, reflected transmissions with longer propagation paths can be more efficient than the shorter ones in terms of incurred losses.
This paper presents details about an extensive channel measurement campaign and subsequent statistical channel models for the characterization of 300 GHz channels for wireless rack-to-rack (R2R) and blade-to-blade (B2B) communications in a data center-like environment. Measurements were conducted in various scenarios such as R2R line-of-sight (LoS), R2R obstructed-LoS (OLoS), R2R reflected-non-LoS (RNLoS), R2R obstructed-RNLoS (ORNLoS), B2B RNLoS, B2B ORNLoS, and B2B LoS scenarios. In the aforementioned scenarios, we explored the impact of transmitter (Tx)/receiver (Rx) misalignment and obstructions such as cables, metal cabinets, and mesh structures on THz propagation, as well as possibility of using existing metal objects as reflectors that guide waves for NLoS type of links that are prevalent in data centers. For the R2R LoS scenario, an optical lens was used to extend the Tx-Rx separation distance. This led to a waveguide effect in the channels measured thereby resulting into a path loss exponent (PLE) of 1.48 with a shadowing gain of 0.7 dB. When obstructions of cables are present, ORNLoS link performs better than OLoS link with 2.5 dB lower shadowing gain and weaker multipath. Reflector in the RNLoS link has reflection coefficients very close to 1 for all incident angles. For the B2B scenario, a dual-reflector THz transceiver rack system is proposed to enable wireless links across vertically stacked servers and allow easy maintenance and repair of servers. The measured path loss closely follows the Friis values in the LoS link and in the RNLoS link with hollow vertical ground plane. When obstructions of cables are present, the ORNLoS link experiences 5-10 dB higher path loss and on average 0.25 GHz lower coherence bandwidth than the RNLoS link. Measured statistical channel properties show that the shadowing gain caused by cable clusters follows the log-normal distribution.
In this paper, we measure, simulate, and characterize the train-to-infrastructure (T2I) inside-station channel at the terahertz (THz) band for the first time. To begin with, a series of channel measurements is performed in a train test center at 304.2 GHz with 8 GHz bandwidth. Rician
K
-factor and root-mean-square (RMS) delay spread are extracted from the measured power-delay profile. With the aid of an in-house-developed ray-tracing (RT) simulator, the multipath constitution is physically interpreted. This provides the first hand information of how the communicating train itself and the other train on site influence the channel. Using this measurement-validated RT simulator, we extend the measurement campaign to more realistic T2I inside-station channel through extensive simulations with various combinations of transmitter deployments and train conditions. Based on RT results, all cases of the target channel are characterized in terms of path loss, shadow fading, RMS delay spread, Rician
K
-factor, azimuth/elevation angular spread of arrival/departure, cross-polarization ratio, and their cross correlations. All parameters are fed into and verified by the 3GPP-like quasi-deterministic radio channel generator. This can provide the foundation for future work that aims to add the T2I inside-station scenario into the standard channel model families, and furthermore, provides a baseline for system design and evaluation of THz communications.
In this study, the authors present a measurement-based analysis of the indoor radio channel characteristics of both the specular and dense multipath components [specular part of the channel (SMC) and diffuse part of the channel] at 94 GHz within a 3 GHz bandwidth. On the basis of an investigation of the frequency stationarity of this band, they have selected multiple sub-bands to perform their evaluation. A method is developed that allowed for the estimation of the specular propagation paths, after which the remainder is regarded as the diffuse spectrum. Radio channel characteristics such as the path loss, root-meansquare delay spread, and the SMC ratio have been calculated as a function of transmitter-receiver distance, and in the different sub-bands. On the basis of the diffuse spectrum, the behaviour of the reverberation time is analysed for the first time in the 94 GHz band.
Results on penetration loss measurements in the THz frequencies between 0.1-2 THz are reported. The measurements were conducted with time domain spectroscopy using the TeraView TeraPulse 4000 measurement equipment. We concentrate on the frequency-dependent penetration characteristics of various materials typical for indoor environments, providing both qualitative and quantitative assessment. The results show that the lower end of the THz band (< 0.5 THz) suffers only modest loss in comparison to the higher frequencies. For the materials considered in this paper, plastic, glass and hardboard , the exact penetration properties are both frequency-and material-dependent. The incident angle to the material increases the penetration loss through increased path length inside the material. The exact values of these losses are provided.
Ultrabroadband Terahertz communication systems are expected to help satisfy the ever-growing need for unoccupied bandwidth. Here, we present ultra broadband channel measurements at 300 GHz for two distinct indoor scenarios, a point-to-point link of devices on a desktop and the connection of a laptop to an access point in the middle of an office room. In the first setup, measurements are taken with regard to distance, different antenna types and device displacements. Additionally, an interference constellation according to the two-ray model is examined. In the second setup, the focus is on the detection and characterization of the LOS- and the NLOS-paths in an indoor environment, including a maximum of two reflections. Temporal channel characteristics are examined with regard to maximum achievable symbol rates. Furthermore, ray obstruction due to objects in the transmission path is investigated.
Channel model characteristics in D-band for NLOS indoor scenarios
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