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The rollout of the fifth-generation (5G) mobile network was completed in 2020. Now, the focus shifts towards exploring the new perspectives of Beyond 5G (B5G) and 6G. Despite being a key enabler of 5G, millimeter wave technology has not yet been fully implemented due to various deployment challenges. Over the past decade, numerous efforts have been dedicated to modeling the propagation channel across the spectrum from 0.5 to 100 GHz. Propagation models such as Close-In (CI), Floating Intercept (FI), and single frequency Alpha-Beta-Gamma (ABG) have been extensively utilized. However, a significant deviation between co- and cross-polarization models has been observed in many estimated models in the literature. In this paper, we propose an optimization of the classic CI model by considering both TX and RX antenna heights, along with a correction coefficient. Initially, we estimate the propagation channel using the classic CI model in indoor environments, revealing a notable deviation between co- and cross-polarization models. Subsequently, we introduce a new model aimed at reducing this deviation and optimizing the Path Loss Exponent (PLE). With our proposed model, the estimated channel depolarization in Line-of-Sight (LOS) conditions stands at 2.8 dB, 5.6 dB, and 2.9 dB for room, corridor, and stairwell environments, respectively. In contrast, utilizing the conventional model yields channel depolarization figures of 4.8 dB, 8.2 dB, and 7 dB for the same environments. This disparity in channel depolarization can have significant implications for millimeter wave propagation, particularly during meteorological events such as rainfall. [ABSTRACT FROM AUTHOR]

Wide bandwidth requirements for multi-Gbps communications have prompted the global telecommunications industry to consider new mid-band spectrum allocations in the 4–8 GHz FR1(C) and 7–24 GHz FR3 bands, above the crowded bands below 6 GHz. Allocations in the lower and upper mid-band aim to balance coverage and capacity, but there is limited knowledge about the radio propagation characteristics in the 4–24 GHz frequency bands. Here we present the world’s first comprehensive indoor propagation measurement and channel modeling study at 6.75 GHz and 16.95 GHz in mid-band spectrum conducted at the NYU WIRELESS Research Center spanning distances from 11–97 m using 31 dBm EIRP transmit power with 15 and 20 dBi gain rotatable horn antennas at 6.75 GHz and 16.95 GHz, respectively. Analysis of the omnidirectional and directional propagation path loss using the close-in free space model with 1 m reference distance reveals a familiar waveguiding effect in indoor environments for line-of-sight (LOS). Compared to mmWave frequencies, the omnidirectional LOS and non-LOS (NLOS) path loss exponents (PLE) are similar, when using a close-in 1 m free space path loss reference distance model. Observations of the omnidirectional and directional RMS delay spread (DS) at FR1(C) and FR3 as compared to mmWave and sub-THz frequencies indicate decreasing RMS DS as the carrier frequency is increased. The RMS angular spreads (AS) at 6.75 GHz are found to be wider compared to 16.95 GHz, showing greater number of multipath components from a broader set of directions in the azimuthal spatial plane when compared to higher frequencies. This work also presents results from extensive material penetration loss measurements at 6.75 GHz and 16.95 GHz using co and cross polarized antenna configurations for ten common construction materials found inside buildings and on building perimeters, including concrete walls, low-emissivity glass, wood, doors, drywall, and whiteboard. Our findings show penetration loss increases with frequency for all of the ten materials and partitions tested, and suggest further investigation of 3GPP material penetration loss models for at least infrared reflective (IRR) glass and concrete may be necessary. The empirical data and resulting models for radio propagation and penetration loss presented in this paper provide critical information for future 5G and 6G wireless communications.

Channel and delay coefficient are two essential parameters for the characterization of a multipath propagation environment. It is crucial to generate realistic channel and delay coefficient in order to study the channel characteristics that involves signals propagating through environments with severe multipath effects. While many deterministic channel models, such as ray-tracing (RT), face challenges like high computational complexity, data requirements for geometrical information, and inapplicability for space-ground links, and nongeometry-based stochastic channel models (NGSCMs) might lack spatial consistency and offer lower accuracy, we present a scalable tutorial for the channel modeling of dual mobile space-ground links in urban areas, utilizing the Quasi Deterministic Radio Channel Generator (QuaDRiGa), which adopts a geometry-based stochastic channel model (GSCM), in conjunction with an International Telecommunication Union (ITU) provided state duration model. This tutorial allows for the generation of realistic channel and delay coefficients in a multipath environment for dual mobile space-ground links. We validate the accuracy of the work by analyzing the generated channel and delay coefficient from several aspects, such as received signal power and amplitude, multipath delay distribution, delay spread and Doppler spectrum.

Wireless channel properties in industrial environments can differ from residential or office settings due to the considerable impact of heavy machinery that triggers intricate multipath propagation effects and strong blockage effects. Previous investigations on wireless propagation in factories often consisted of empirical models, that is simple analytical formulas based on measurement data. Unfortunately, they usually lack in flexibility, since they seldom include geometrical parameters describing the industrial scenario and therefore turn out reliable only in industrial scenarios sharing the same propagation characteristics as those where the measurements were performed. In response to this limitation, this article harnesses the power of Machine Learning to model propagation markers like path loss, shadowing, and delay spread in the industrial environment. By employing Machine Learning techniques, the objective is to achieve flexibility and adaptability in modeling, enabling the system to effectively generalize across diverse industrial scenarios. The proposed model relies on a combination of predictive algorithms, including a linear regression model and a Multi-Layer Perceptron, working collaboratively to model the relationship between the considered propagation markers and input features like frequency and machine size, spacing, and density. Results are in fair overall agreement with previous studies and highlight some trends about the sensitivity of the propagation parameters to the considered input features.

Underwater acoustic (UWA) communication is an essential technology for networking underwater sensors and drones to support maritime activities. However, real-time data transfer among mobile nodes faces technical difficulties due to the severe nature of the UWA channel, which has large delay and Doppler spreads. Furthermore, the performance of UWA communication may be severely impaired by marked channel changes between line-of-sight (LoS) and non-line-of-sight (NLoS) environments. The goal of this work is to explore the UWA channel under LoS and NLoS conditions and evaluate their effect on UWA communication in terms of communication quality. Specifically, we measured the delay and Doppler spreads of the UWA channel by switching LoS/NLoS conditions. We also investigated the relationship between the signal-to-noise ratio (SNR) and bit error rate (BER) for UWA communication using Dopplerresilient orthogonal signal division multiplexing (D-OSDM). Experimental results showed that the delay spread of the UWA channel and received signal power markedly changes depending on LoS/NLoS conditions. Specifically, the delay spread in the LoS environment was about 10 ms, while that in the NLoS environment was much larger or difficult to observe owing to signal power attenuation. Furthermore, SNR in the NLoS environment was approximately 15 dB less than that in the LoS environment, resulting in increased BER. The obtained results suggest that adaptive signal power control is necessary to realize stable UWA communication in shallow water areas where there is a mixture of LoS and NLoS condition. [ABSTRACT FROM AUTHOR]

Quantification of uncertainties in the results of channel sounding measurements is important for their interpretation and further usage. In this paper, a novel uncertainty analysis methodology to quantify uncertainties of condensed parameters in measurements of dynamic millimeter-wave channels is presented. The bandwidth limitation and multipath threshold are identified as important impairments. Therefore, the methodology provides three uncertainty metrics for condensed parameters, namely a standard uncertainty to quantify the impact of random variations; a bias due to the multipath threshold; and a total bias including the impact of the bandwidth limitation. These uncertainty metrics are highly channel dependent. Therefore, the proposed methodology creates reference channels, which are representative of corresponding measured channels. Hardware and processing impairments are included in the analysis via a Monte Carlo simulation. This results in a general methodology that can quantify uncertainties in both static and dynamic channel measurements of any wideband channel sounder. The methodology is implemented, verified and demonstrated for the TU/e channel sounder, which exemplifies how it can be used. The proposed methodology can improve the analysis, interpretation and reporting of channel measurement results.

The multipath is unavoidable in radio frequency (RF) wireless communication, and affects almost every element of the communication systems. The impact of multipath on the received signal depends on whether the delay spread (i.e., spread of time delays associated with different multipath components) is large or small relative to the symbol period of the wireless communication system. In narrowband channels, the symbol period is set such that the delay spread is about one tenth (or less) of it. In broadband channels, it is set such that the delay spread is many times greater than the symbol period. In between these two extremes, there appears to exist an important, yet overlooked, class of channels whose delay spread is neither small nor large enough for them to fall into these two basic channel classes. In this paper, we study the effect of multipath on channels that fall in the transitional region between narrowband and broadband referred henceforth as “mediumband”. This paper shows that mediumband channels possess a distinct channel model, and pose both challenges and opportunities for reliable wireless communication. For instance, mediumband channels enable signalling at a significantly higher rate than that of narrowband channels, but on the flip side, as the degree of mediumband-ness increases, the quality of the channel deteriorates rapidly due to the excessive inter-symbol-interference (ISI). However, mediumband channels have an inherent ability to avoid deep fading, and if designed properly, mediumband wireless communication, which refers to wireless communication through mediumband channels, could be made to be significantly more reliable too.

In this study, an investigation into the small-scale and multipath fading of radio wave propagation in a complex building environment has been conducted by using Afe Babalola University Ado-Ekiti Nigeria, College of Engineering building as a case study. The study utilizes sliding correlator channel sounding measurement techniques, implemented on NI USRP 2920 modules by using GNU radio software. Moreover, single-input and single-output configurations have been employed by setting one module as a transmitter and the other one as a receiver, propagating at a carrier frequency of 1.2 GHz. Five scenarios within the first floor of the building have been considered and various cases in each one of the scenarios are either outdoor-to-indoor, indoor-to-outdoor, indoor or outdoor measurement. The analysis of the scatter plot of the maximum delay spread against the distance of experiments for the line-of-sight and non-line-ofsight cases show that analytical expression cannot be obtained due to the complexity of the building structure. The result obtained also shows that the maximum delay spread values are between 575 µs and 1023 µs, which points to the existence of a frequency selective fading condition that causes intersymbol interference and data rate reduction. [ABSTRACT FROM AUTHOR]

New specific scenarios are expected for 5G systems in various environments, such as stadiums, subway platforms, factories, livestock barns. On the other hand, the applicability of conventional propagation models to new specific environments has not been clarified. In this paper, we report path loss and spatiotemporal characteristics such as delay spread (DS) and azimuth and zenith angular spread of arrival (ASA and ZSA) in the 28 GHz-band in various environments. By comparing the degree of fit to the conventional models, we considered whether the models for conventional scenarios assumed by previous mobile systems can be applied to the propagation characteristics in each specific environment. As a result, we clarify that the following points should be considered when applying the conventional model. The measured path loss characteristics were mostly close to those of the conventional models. However, the path loss in the non-line-of-sight with propagation to another room was larger than the conventional model, assuming there was a hall space environment with some blockers. Regarding the DS, we obtained the results that the characteristics were mainly affected by existence of long-distance delayed wave caused by a long narrow space and materials of the internal walls and ceiling. Larger ASA characteristics were obtained in the subway platform environment and the factory environment because of metallic obstacles and walls. Regarding the ZSA, a larger ZSA was obtained in the stadium due to scattering from spectator seats, and a smaller ZSA was obtained in the subway platform due to the low ceiling height and long propagation distance.

In-band full duplex (IBFD) communications are a potential solution to spectrum scarcity. IBFD communications offer greater spectral efficiency than traditional half-duplex communications by transmitting and receiving on the same frequency channel. However, IBFD operation requires overcoming the challenge of eliminating the self-interference coupled from the transmit antenna to the receive subsystem. Knowledge of the characteristics of the loopback propagation channel makes it easier to cancel out the self-interference. Nevertheless, complex field trials are required to adequately characterize loopback channels, which is still lacking in the recent literature. This paper proposes a measurement campaign in a real and ongoing broadcast transmission center to characterize the main characteristics of loopback channels. The work proposes a set of loopback channels based on field trials and an empirical analysis of the most relevant parameters of the channel model, such as the Doppler spectrum, the delay spread, and the K-factor. • A new methodology for measuring and characterizing broadcast loopback channels. • Characterizing the loopback channel in terms of the amplitude and the delay of the paths. • An analysis of the obtained delay spread and K-factor values. • Characterizing the Doppler spectrum of the loopback channel in broadcast transmitters. • Performance evaluation of the proposed channel models under an ATSC 3.0 compliant transceiver chain. [ABSTRACT FROM AUTHOR]

The need for wireless communication appears everywhere, and with as few interruptions as possible. An extensive and in-depth study has been conducted on the limitations of wireless communication in pedestrian tunnels. Using an analytical mathematical ray tracing model, and performing tunnel measurements, with an autonomous measuring setup, the model was validated. An extraordinary wide band was used for the experiments, which also featured optical systems to ensure accurate results. Since the tunnel is narrow, the differences between the different paths are small, and in order to distinguish them a resolution of 0.2 ns was used. The RMS delay spread, σ τ , decreases throughout the tunnel, and at no point exceeds 1 ns. [ABSTRACT FROM AUTHOR]

One of the challenges in underwater acoustic positioning is the occurrence of missing measurements and large errors in multipath environments, such as shallow water and harbor areas. In this paper, we propose a new underwater positioning method for multipath environments by using direct wave arrival time groups and database matching. The proposed method accurately measures baseline length from the impulse response of the underwater channel by calculating time window groups that cover the propagation time from the sound source to each hydrophone in advance and then extracting only the impulse response around the propagation time of the direct waves when the sound source exists in a certain region of the measurement space. The performance of the proposed method was experimentally evaluated in a static environment. The results showed that the proposed method achieved an accuracy of 0.03 m and a precision of 0.02 m in a test tank. [ABSTRACT FROM AUTHOR]

With the next generation of mobile communication being trialled across the world, 5G New Radio (NR) promises to provide a flexible radio interface that fits a diverse range of use cases. As trials and pilots progress, propagation studies are required that evaluate electromagnetic (EM) propagation effects for 5G NR signals. In this article, 5G NR signals are used to evaluate the over-the-air (OTA) error vector magnitude (EVM) within a line-of-sight (LoS) rural/urban environment. For the same receiver locations, time dispersion and propagation loss were measured via the root mean square (RMS) delay spread and path loss. The transmitter-receiver distance investigated ranged from 60 m to 450 m. From the measurement campaign, the path loss exponent (PLE) using a directional antenna at the receiver was 1.98, and 1.82 with an omnidirectional antenna. The root mean square error (RMSE) of the floating intercept/close-in (FI/CI) models for the path loss was 4.96/4.74 and 3.84/3.23 for directional and omnidirectional receivers. The delay spread using a cross polar configuration showed significant increase and a dependency of the delay spread on the path loss was observed. For the measurement route, the mean delay spread was 24 ns and 35 ns for directional and omnidirectional measurements. With regards to the EVM, 16 and 64-QAM transmissions were robust along the entire route for directional and omnidirectional antennas, whereas 256-QAM worked in locations where there was minimal obstruction to the propagation path. The average EVM (%) for 16, 64 and 256-QAM measured along the route was 4.5/5.3/3.9 and 3.4/4.3/3.6 for omnidirectional and directional antennas. The OTA results also show that using a directional antenna (as the receiver) significantly improves the obtainable signal quality of 5G NR signals and also reduces outages for higher modulation schemes. With the measurement results presented, system designers can design efficient receivers, estimate coverage and adequately provision services using 5G NR on the sub-6 GHz frequency band.

A compact-range wireless access system in the 60-GHz band has been proposed for multi-Gb/s data transfer. A prototype Gigabit Access Transponder Equipment (GATE) was built to evaluate the system performance in terms of received signal strength, signal-to-noise ratio (SNR), and bit error rate (BER). The proposed system operates in the near-field regions of large array antennas adopted in the transmitter (Tx). The time delays due to the signals transmitted from different array elements to the receiver (Rx), or/and those due to the multiple reflections between Tx and Rx antennas become comparable with the symbol lengths in our gigabit wireless access system. In that sense, this system would be susceptible to intersymbol interference (ISI). In this study, the concept of ISI is introduced in the antenna field for the first time. An equivalent baseband communication system is newly proposed to evaluate the wireless channel, including Tx and Rx antennas. The analysis procedures and equations are provided for the calculation of ISI. The ISIs due to three potential contributions are analyzed in detail. It is verified that our proposed ISI analysis has succeeded in relating the antenna characteristic to the system performance observed in the baseband.

Accurate propagation characteristics are essential for future indoor millimeter-wave (mmWave) small cell network planning. This paper presents propagation measurements at 26 GHz and 38 GHz which are important candidate bands for fifth generation mmWave communication. Measurements are conducted in an indoor corridor, as well as a stairwell whose mmWave channel is seldom investigated before. In these measurements, an omnidirectional biconical antenna is used as transmitter and a steerable directional horn antenna is used as receiver. The directional and omnidirectional path loss exponents, shadow factors, cross-polarization discrimination ratios and root-mean-square delay spreads are analyzed for both line-of-sight and non-line-of-sight scenarios in both co-polarization and cross-polarization, and these characteristics are compared for different frequencies and environments. It is found obvious depolarization phenomenon in non-line-of-sight scenario for higher frequency. Compared to the corridor, the stairwell has larger path loss exponents and root-mean-square delay spreads, and the depolarization is also more evident in stairwell. The results in this paper are beneficial to building efficient and robust indoor mmWave communication systems.

The millimeter-wave (mm-wave) frequency band is projected to play a critical role in next-generation wireless networks owing to its large available bandwidth. Despite the theoretical potential for high data throughput, the mm-wave frequency faces numerous challenges—including severe path loss and high penetration loss. Therefore, a reliable understanding of channel propagation characteristics is required for the development of accurate and simple indoor communication systems. In this study, we conducted measurement campaigns with unique transmitter- receiver combinations using horn and tracking antennas, at 3.7 and 28 GHz in an indoor corridor environment on the $10^{th}$ floor of an IT building and the $3^{rd}$ floor of the main building of Chosun University, Gwangju, South Korea, and the details are presented herein. In both line-of-sight and non-line-of-sight scenarios, the large-scale path losses, and small-scale channel statistics, such as root mean square delay spread, and number of clusters, were obtained using the measurement results in a waveguide structure indoor corridor environment. We have proposed alternate methodologies beyond classical channel modeling to improve path loss models using artificial neural network (ANN) techniques—to alleviate channel complexity and avoid the time-consuming measurement process. The presented regression successfully assists the prediction of the path loss model in a new operating environment using measurement data from a specific scenario. The validated results suggest that the ANN large-scale path loss model used in this study outperforms the close-in reference distance and floating-intercept (alpha-beta) models. Additionally, our result shows that the number of time clusters follows an Erlang distribution.

With the development of various wireless communication networks, Wi-Fi Router positioning and deployment systems have become widely popular in recent years to improve coverage in various environments. In this paper, we present an appropriate mechanism for defining the deployment of Wi-Fi Routers to improve coverage in the Oxford Languages Institute (OLI) environment. In addition, the institute's environment was simulated using the Wireless InSite (WI) Package. In this work, two types of Wi-Fi Routers are used. The first is the TP-Link, while the second is the Rocket. These two devices operate at 2.4 and 5 GHz frequencies. There are two objectives in this work. The first aim is to determine the best location to cover the simulated scene environment in a better way. The second aim is to compare Wi-Fi Routers to find out which Wi-Fi Router is better and find out how many Wi-Fi Routers we need to cover the institute's environment. The comparison between Wi-Fi Routers was based on basic parameters to measure the performance of wireless networks, the most important of which are Coverage Rate (CR) Percentage, Signal Quality Rate (SQR), and Received Power Rate (RPR). According to the results that were shown on the Graphical User Interface (GUI) using MATLAB Software. We noticed that the CR, SQR, and RPR of the Rocket are 83.9080%, 97.0082%, and -35.2337 dBm respectively, and these results are better than the results provided by the TP-Link, as it gave the CR, SQR, and RPR are 32.1839%, 77.8690%, and -58.1685 dBm, respectively. Finally, we conclude that CR using the Rocket is good and we need one device to cover the institute's environment. While CR using the TP-Link is bad and we need five devices to reach the coverage provided by the Rocket because the Rocket has high transmitted power and gain capacity. [ABSTRACT FROM AUTHOR]

Owing to its several advantages over other wireless schemes, visible light communication (VLC) shall be at the forefront of optical wireless communication technology. However, due to multipath reflections and spatial distribution of light-emitting diode (LED) transmitters, there is an inherent delay spread in the VLC channels. We perform a comprehensive quantitative study on the effect of several practical factors like LED semi-angle, wall reflectivity, number of reflections, number of LED panels, room size, and user locations on the channel delay parameters, namely RMS delay spread and coherence bandwidth of the channel. We present the detailed derivation of the multipath VLC channel model and incorporate the effect of inter-symbol interference in bit error rate (BER) performance of the multipath VLC system. We analyze the average BER of the system under different practical scenarios and determine the penalty in signal to noise ratio entailed by a change in the system parameters mentioned above. We conclude that it is sufficient to model up to three reflections in the VLC channel to emulate the effect of multipath propagation on the channel characterization and BER analysis of the system. The results and analyses presented herein provide critical insights into the effect of multipath reflections in indoor VLC links, particularly the BER performance and channel delay characteristics. We also provide some key recommendations for the design of practical VLC systems by outlining the data rates that can be served under different system configurations.

Filter bank multi-carrier (FBMC) is an emerging 5G technology due to its finer spectral characteristics than its counterpart orthogonal frequency-division multiplexing (OFDM). In most cases, FBMC is united with an Offset Quadrature Amplitude modulation (OQAM) for individual sub-carrier to maximize the spectrum efficiency and Nyquist rate. But it is achieved at the cost of an inherent accumulative imaginary interference called intrinsic interference. When a channel is highly selective, the FBMC system undergoes inter-symbol-interference (ISI) and co-channel interference (CCI). In this research, we consider FBMC QAM as a solution to intrinsic interference and mitigates both ISI and CCI by incorporating ML equivalent signal detection. In this paper, some of the prominent issues related to the existing FBMC–OQAM are explored and its potential integrity constraints with existing MIMO and signal detection techniques are studied. In addition to that, a lightweight optimized ML which constitutes parallel sub-detectors with the least hardware complexity overhead is proposed. It also achieved a near-optimal performance that matches the CP-OFDM system. In this research, the experimental results proved that the proposed suboptimal ML detector offered significant complexity reduction with improved quality of services. Thus evidently shows the proposed system is attractive from both BER performance and hardware complexity reduction perspectives for 5G communications. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the impact of small receiver displacement on a signal propagation in a typical conference room environment at a millimeter wave frequency of 60 GHz. While channel measurements provide insights on the propagation phenomena, their use for the wireless system performance evaluation is challenging. Whereas, carefully executed three-dimensional ray tracing (RT) simulations represent a more flexible option. Nevertheless, a careful validation of simulation methodology is needed. The first target of this article is to highlight the benefits of an in-house built three-dimensional RT tool at 60 GHz and shows the effectiveness of simulations in predicting different characteristics of the channel. To validate the simulation results against the measurements, two different transmitter (Tx) positions and antenna types along with ten receiver (Rx) positions are considered in a typical conference room. In first system configuration, an omnidirectional antenna is placed in the middle of the table, while in the second system configuration a directed horn antenna is located in the corner of the meeting room. After validating the simulation results with the measurement data, in the second part of this work, the impact of a small change, i.e., 20 cm in the receiver position, is studied. To characterize the impact, we apply as performance indicators the received power level, root mean square delay spread (RMS-DS) and RMS angular spread (RMS-AS) in azimuth plane. The channel characteristics are considered with respect to the direct orientation (DO), i.e., the Rx antenna is directed toward the strongest incoming path. Different antenna configurations at the Tx and Rx side are applied to highlight the role of antenna properties on the considered channel characteristics. Especially, in the second system configuration the impact of different antenna half power beamwidth on different considered channel characteristics is highlighted through acquired simulation results. The validation of results shows the RMS error of only 2–3 dB between the measured and simulated received power levels for different Tx configurations in the direction of DO. Results indicate that only a small change of the Rx position may result a large difference in the received power level even in the presence of line-of-sight between the Tx and Rx. It is found that the STD of received power level across the room increases with the decrease in HPBW of the antenna. As can be expected, directed antennas offer lower value of RMS-DS and RMS-AS compared with isotropic antenna. [ABSTRACT FROM AUTHOR]

This paper presents a measurement-based analysis of wideband 39 GHz millimeter wave (mm-wave) dual-polarized propagation channel under the impact of foliage presence between a transmitter (Tx) and a receiver (Rx). The measurements were conducted in a rich-vegetation area, and the so-called direction-scan-sounding (DSS) method which rotates a horn antenna in angular domains was applied, aiming at investigating the direction-of-arrival (DoA)-dependent characteristics of polarimetric channels. Four Tx-to-Rx polarization configurations were considered, including co-polarization scenarios with vertical Tx-polarization to vertical Rx-polarization (VV) and horizontal to horizontal (HH), as well as cross-polarization with vertical to horizontal (VH) and horizontal to vertical (HV), which allow scrutinizing the differences in delay-direction dispersion for usually-encountered scenarios. A foliage loss model for various vegetation depths in VV polarization configuration, was also presented in this paper. The results show that the foliage-loss DoA spectra for VH and HV are similar, while the spectra exhibit less penetration loss in most directions for VV than for the HH. Furthermore, the presence of vegetation between the Tx and the Rx leads to larger dispersion in delay compared to the clear line-of-sight (LoS) scenario, particularly for vertical polarization in the Tx side, and additionally, the foliage presence also results in evident DoA dispersion, specially in the HV scenario. Selectivity in directions caused by foliage is more significant in vertically-polarized Tx scenarios than in the horizontally-polarized Tx scenarios. A statistical model is established summarizing these comparison details.

This paper introduces a measurement campaign to investigate the characteristics of massive multiple-input multiple-output (MIMO) channels in both line-of-sight (LoS) and obstructed LoS suburban outdoor environments. The measurements are conducted at the center frequency of 3.5 GHz with a bandwidth of 160 MHz. The transmitter is equipped with a 4 × 8 planar patch antenna array and the receiver is equipped with a 4 × 8 cylindrical patch antenna array. Each patch consists of two antenna ports which have main polarizations of +45° and -45°, respectively, resulting in a total of 64 × 64 sub-channels. We examined the influence of different polarization combinations on channel characteristics such as power delay profile (PDP), K-factor and delay spread for both LoS and obstructed LoS scenarios. Results show that the characteristics are more dependent on the Rx antennas rather than the Tx antennas. When the Rx antennas are facing the Tx antenna array, the received power is higher, the K-factor is lower and the delay spread is lower in cross-polarization cases with respect to the co-polarization ones in general. When the Rx antennas are back-facing the Tx antenna array, lower powers, higher K-factors and higher delay spreads can be observed in cross-polarization cases with respect to the co-polarization cases. In conclusion, the polarimetric influence on the channel characteristics depends on the antenna structure as well as the environment.

Wireless networks are the preferred future access networks for both defense and civilian deployments as part of telecommunication networks. The successful implementation of long term evolution (LTE) networks and applications such as the Internet of Things (IoT) in the telecommunication infrastructure has guaranteed rates of up to 100 Mbps while supporting ultra-dense wireless access network. With the incorporation of LTE-Advanced and fifth-generation wireless protocols, the data rates are expected to reach upto 1 Gbps. Hence, there is a pertinent requirement to carry out channel measurements at sub 1 GHz, 2 GHz, and 3 GHz bands to enable the design and implementation of optimum transceivers for pico-cells of LTE and future wireless networks. For the first time measurements and comparison with standard models of channel impulse response models have also been carried out in five different terrains namely Urban, Semi-Urban, Forest, Rural, and Desert terrains in the Indian sub-continent to effectively cover a variety of deployments of future wireless access networks for defense wireless networks. [ABSTRACT FROM AUTHOR]

This study proposes a new strategy of extracting parameters for tapped delay line (TDL) channel models from vehicle to infrastructure channel measurements. The proposed approach is based on an already existing method to derive parameters for a non‐stationary model using first‐order Markov chains. It will be shown that with the proposed method, the number of taps necessary to regenerate the delay spread of a channel can be significantly reduced. An approach will be discussed to evaluate the performance of the model. The feasibility of the method will be confirmed using channel sounding measurements. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel underwater acoustic (UWA) communication scheme that achieves energy and spectrum efficiency simultaneously by combining Doppler-resilient orthogonal signal division multiplexing (D-OSDM) and multiple-input–multiple-output (MIMO) signaling. We present both the transmitter processing and the receiver processing for MIMO D-OSDM. We evaluate the performance of MIMO D-OSDM in simulations with a large intersymbol interference of 25 symbols and a Doppler spread with a maximum Doppler shift of 8 Hz. In addition, the sea trial is performed in Suruga Bay, where the receiver is mounted on a barge and a research vessel with the transmitter makes round trips along a line with a speed of 4 kn. In the experiments, we obtain an intersymbol interference of 3.6–29.7 symbols and a Doppler spread of several Hertz (leading to a spread of over two to three subcarrier spacings). The simulation results suggest that MIMO D-OSDM has an advantage over normal D-OSDM, Doppler-resilient MIMO orthogonal frequency division multiplexing (MIMO D-OFDM), and classical OFDM with MIMO signaling (MIMO OFDM)—MIMO D-OSDM achieves better bit error rate performance than the benchmarks. The sea trial results also support the advantage of MIMO D-OSDM—it achieves a coded block error rate of 3.2% while normal D-OSDM and MIMO D-OFDM achieve a coded block error rate of 9.7% and 9.3%, respectively. We conclude that MIMO D-OSDM can become a viable technique that achieves reliable and effective UWA communication. [ABSTRACT FROM AUTHOR]

The increasing requirement for the mobile data traffic accelerates the research of millimeterwave (mm-wave) for future wireless systems. Accurate characterization of the mm-wave propagation channel is fundamental and essential for the system design and performance evaluation. In this paper, we conducted measurement campaigns in various indoor scenarios, including classroom, office, and hall scenarios, at the frequency bands of 27-29 GHz. The spatial channel characteristics were recorded by using a large-scale uniform circular array. A high-resolution parameter estimation algorithm was applied to estimate the mm-wave spherical propagation parameters, i.e., the azimuth angle, elevation angle, delay, source distance, and complex amplitude of multipath components. With the same measurement system, the channel parameters including decay factor, delay spread, angular spread, and line of sight power ratio are investigated thoroughly in individual indoor scenarios and compared in different indoor scenarios. Furthermore, the impact of the furniture richness level and indoor geometry on the propagation parameters are also investigated.

This paper presents 3–4 and 38–40 GHz wideband channel characteristics for industrial internet‐of‐things (IIoT) scenario based on measurements. The channel measurement equipment applied in the measurements consists of a programmable vector network analyzer and necessary auxiliaries. An extensive amount of data in line‐of‐sight (LoS) and non‐line‐of‐sight (NLoS) scenarios is collected with omnidirectional antennas in both transmitter and receiver ends. With the Space‐Alternating Generalized Expectation‐maximization (SAGE) algorithm, the multipath components (MPCs) of the received signals are extracted to calculate the channel model parameters, for example, channel gain coefficient, delay spread, and Ricean K factor. By studying the statistical characteristics of these parameters, a stochastic channel model in IIoT scenario is initially established and compared with the existing indoor channel models. Moreover, the distinctive characteristics of channel parameters in the millimeter wave band and sub‐6 GHz band in the IIoT scenario are demonstrated. Plain Language Summary: Usually, the industrial environments are complicated and variable, which makes the communications in factory more difficult than those in general indoor scenarios. Hence, more information about the characteristics of the radio propagation in industrial scenarios is needed. This work presents 3–4 and 38–40 GHz wideband channel characteristics for industrial internet‐of‐things (IIoT) scenarios based on measurements, which is helpful to the design of the communication systems and the installation of low‐latency, high‐speed, high‐stability communication facilities on automation production equipment in industrial environments. Key Points: The 3–4 and 38–40 GHz wideband channel models in an industrial internet‐of‐things (IIoT) scenario are presentedThe variance of shadow fading in the IIoT scenario is larger than that in general indoor scenariosThe values of K factors in the IIoT scenario demonstrate significant dependence on the premises of the Rx [ABSTRACT FROM AUTHOR]

This letter presents coherence bandwidth values at 1945 MHz over 50 MHz using mobile channel data from 107 small areas in an urban environment with transmit ranges up to 4 km. Empirical relationships between coherence bandwidth for correlation levels 0.9 and 0.5 and root mean square (rms) delay spread are derived and compared with those from the literature. In contrast to previous modeling attempts, this letter investigates whether the additional knowledge of distance and path-loss improves predictions for coherence bandwidth; significant improvement for 0.5 correlation level was found. [ABSTRACT FROM AUTHOR]

The 5th generation (5G), the next generation mobile communication, has more requirements than the previous generation 4th generation (4G). For example, Spectral efficiency, peak data rate and mobility it is. Of these requirements, Orthogonal Time Frequency Space (OTFS) has been proposed as a waveform design study to support mobility. OFDM used in 5G and 4G has a weak point in high speed environment. When the frequency shift occurs due to the Doppler effect, orthogonality between subcarriers of OFDM is broken and performance is degraded. To compensate for this, a complex Doppler compensation algorithm is required, which leads to an increase in complexity. OTFS processes signals in two dimensions in the delay-Doppler domain through the Symplectic Finite Fourier Transform (SFFT). It is compatible with conventional OFDM and can be used as pre-coder and post-coder to effectively handle Doppler without complicative compensation algorithms. This paper evaluates and compares the performance of OFDM and OTFS in high Doppler and time delay environments. As a receiver, we used MP detector proposed for OTFS. The performance is similar to OFDM at low SNR, and the performance is noticeably better than OFDM at high SNR. [ABSTRACT FROM AUTHOR]

We evaluate channel hardening for a large scale antenna system by means of indoor channel measurements over four frequency bands, 1.472 GHz , 2.6 GHz , 3.82 GHz and 4.16 GHz . NTNU's Reconfigurable Radio Network Platform has been used to record the channel estimates for 40 radio links to a 64 element array with wideband antennas in a rich scattering environment. We examine metrics for channel hardening, namely, the coherence bandwidth, the rms delay spread and the normalized effective subcarrier power, for the effective channel perceived by a single user after precoding and superposition in the downlink. We describe these metrics analytically and demonstrate them with measured data in order to characterize the rate of hardening of the effective channel as the number of antenna elements at the base station increases. The metrics allow for direct insight into the benefits of channel hardening with respect to radio system requirements. [ABSTRACT FROM AUTHOR]

Starting from outdoor transmission, crossing vegetation, the wideband and narrowband characterization of the indoor mobile radio channel in the 700 MHz band is obtained from experiments carried out in the indoor environment of the Engineering building at Fluminense Federal University, and from the processed data, respectively, the power-delay profiles obtained permitted to calculate the time dispersion parameters and the envelope of the signal permitted to adjust probability density functions to the signal variability, concluding about the influence of vegetation on those characteristics. [ABSTRACT FROM AUTHOR]

Reverberation chambers (RVCs) are used to provide an efficient and reliable testbed for emulating the wireless channel effects in the laboratory environment. In the literature, various techniques have been studied to enrich the channel emulation capabilities of RVCs. However, insufficient control of some of the emulated channel characteristics (such as time and frequency dispersions) still leaves an open problem for RVC-based channel emulators. In this paper, novel channel emulation techniques by using RVC are introduced to enhance the flexibility in controlling the emulated time and frequency dispersions of the channels. Surface acoustic wave delay lines and power controllers (i.e., amplifiers and attenuators) are used to add degrees of freedom for manipulating the power delay profile during delay spread emulation. This technique also overcomes the challenge of achieving higher delay spread values with benchtop-sized RVC. The second technique is aimed to control the Doppler spectrum shape emulated in the chamber by judiciously placing radio frequency absorbers around the mechanical stirrer. Experimental and mathematical analyses are conducted to evaluate the proposed techniques, and the results show that the proposed methods can improve the channel emulation in the RVCs. [ABSTRACT FROM AUTHOR]