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Human blockage and its dynamics are potential challenges for millimeter-wave (mm-wave) mobile communication. This article presents the results of wideband measurements at 27 GHz with one human blocker close by a dynamic mobile terminal (MT) as well as one or multiple dynamic human blockers further away from an MT. The measured human blockage loss is largest when the direct path (DP) in a line-of-sight (LOS) is blocked, but this loss is limited by other multipath components (MPCs). For nonline-of-sight (NLOS) channels, it is shown that human blockage loss is typically negligible. The presented measurement results show that human blockage loss in multipath channels is much smaller than that reported in diffraction-and measurement-based models, which neglect or minimize the contribution of all MPCs other than the DP. This suggests that the multipath nature of the indoor wireless channel highly limits the impact of human blockage.

A simple and effective body-centric localization algorithm has been proposed in this paper using UWB wearable technology. The algorithm has been validated through measurement campaigns with a human subject volunteer in an indoor environment. The algorithm takes into account statistical channel parameter analysis, machine learning (ML) algorithms and time-of-arrival (TOA) based range estimation/data fusion techniques. Two channel parameters namely path loss magnitude and rms delay spread are proposed as classification features to be applied to the ML algorithm to accurately classify the off-body channel links into LOS, PNLOS and NLOS scenarios. Multi-class support vector machine (MC-SVM) classifier along with SMOTE algorithm to take into account class imbalance is applied with the channel classification accuracy of 98.63 %. Threshold based range estimation algorithms are applied in order to mitigate NLOS scenarios caused mainly due to the presence of the human subject. Results report human localization accuracy in 0.5-3 cm range using TDOA data fusion technique for target estimation. Further validation is presented considering wide range of Tx-Rx distance, presence of another obstruction between the Tx-Rx links and performance in different environment which shows the suitability of the proposed methodology.

This article presents ultra-wideband (UWB) body-centric channel parameters for assessing the performance of the physical activities suitable for rehabilitation and physiotherapy purposes in the healthcare domain. Two channel parameters, path loss magnitude and rms delay spread, have been proposed to study the patterns/trends of various upper and lower limb activities for different positions. The channel for various activities has been distinguished into line of sight (LOS) and non-line of sight (NLOS) links. Three orientations of the wearable antenna have been considered for the placement on the wrist/ankle which are outer, inner, and front region, leading to significant differences in the channel parameters while performing physical exercises. The channel parameter values obtained are based on the orientation/placement of the wearable antenna, the distance between the two wearable nodes and the amount of obstruction caused by the human body, e.g., thigh/torso region. The proposed method enables effective monitoring capabilities and computes patterns of different exercises for all the limb positions measured, which in turn will aid in accurate human activity monitoring.

In order to realize the vision of “smart rail mobility,” a seamless high-data rate wireless connectivity with up to dozens of gigahertz bandwidth will be required. This forms a strong motivation for exploring the underutilized millimeter wave (mmWave) and sub-mmWave bands. In this article, the wireless channel in one “smart rail mobility” scenario—the intrawagon scenario—is characterized through ultrawideband (UWB) channel sounding and ray tracing (RT) at mmWave and sub-mmWave bands. To begin with, a series of horizontal directional scan-sounding measurements are performed inside a real high-speed train wagon at 60 and 300 GHz frequency bands with a bandwidth of 8 GHz. Correspondingly, the channel characteristics such as Rician $K$ -factor, root-mean-square (rms) delay spread (DS), azimuth spread of arrival, and azimuth spread of departure are extracted and analyzed. Based on the measurements, a self-developed RT simulator is validated through the reconstruction of the three-dimensional wagon model and the calibration of the electromagnetic (EM) properties of the main materials. This gives the chance to physically interpret the measurement results and characterize the intrawagon mmWave and sub-mmWave channels more comprehensively through extensive RT simulations.

In this article, the use of circularly polarized multiple-input–multiple-output (MIMO) antenna systems is proposed as a new solution for future body-to-body (B2B) applications. Four B2B channels have been characterized inside a mine. The statistical parameters of the B2B channels using co-positioned (CP) and 90° rotated (90R) antennas have been determined. Path loss (PL) exponent values varied between 2.33 and 1.26. The time dispersion parameters and channel capacities are computed for both CP and 90R scenarios. Moreover, channel correlation matrices and the Rician K-factor have been determined and discussed in terms of their effect on capacity and root mean square (rms) delay spread. Overall, the circularly polarized setup exhibits the best performance in terms of PL, rms delay spread, and channel capacity. The nonline-of-sight (NLOS) situation caused a significant drop in channel capacity due to the significant increase in PL, and an increase in the rms delay spread due to the multipath richness. The MIMO-NLOS scenario exhibits the highest throughput gain of 1.752 (at an SNR of 20 dB), due to its low branch correlation. A model of the B2B impulse response has been created based on a statistical–empirical approach to determine the optimal path amplitudes and time of arrival.

This communication presents foliage channel measurements at 28 GHz using a directional channel sounder. The measurements were conducted in vegetated areas of typical residential environments in Daejeon, South Korea. We first propose a pattern matching algorithm that allows us to overcome the angle resolution of a directional antenna and to estimate a more accurate receiving angle. Then propagation paths received from the vegetation and the surrounding buildings are classified and their power ratios are analyzed. Furthermore, foliage attenuation was determined from the measurement data according to the foliage depth, and appropriate models based on the modified exponential decay (MED) model and the maximum attenuation (MA) model are presented. In addition, the effect of foliage attenuation on seasonal variation is studied. These results will be useful for predicting path losses through the vegetated areas at 28 GHz by modeling the foliage loss as an additional path loss term. Finally, spatial–temporal channel characteristics in a vegetated environment were statistically analyzed including delay spread, coherence bandwidth, and angular spreads.

This paper presents an experimental and analytical investigation of ultra-wideband (3–8 GHz) body-to-body (B-to-B) channel characterization. The channel parameters obtained are compared with off-body (off-B) and no-body (no-B) links. Measurements have been carried out considering different body positions and orientation of the Tx–Rx pair. The type of channel link and position of the wearable antenna lead to significant changes in the radio link channel. Path loss (PL) computed shows the increase in magnitude for non line of sight (NLOS) in comparison to line of sight (LOS), though the variation over a distance of 5 m is more significant for LOS (10 dB) than NLOS links (4–5 dB). For total NLOS links, B-to-B channels have slightly higher PL and delay spread parameters in comparison to off-B channel. The B-to-B LOS channels have least PL (44–56 dB), rms delay spread (0.5–4 ns), and multipath components (3–20) which can be attributed to the directional radiation pattern due to the presence of the human body for both Tx and Rx nodes. For back-to-back antenna orientation of the B-to-B channel, maximum signal strength degradation and multipath are observed. It can be concluded that for certain links, the B-to-B channel shows a significant change in channel behavior in comparison to off-B/no-B scenario.

Fixed performing antennas are ineffective in providing optimum performance in a changing multipath environment, such as underground mines where channel conditions quickly change as the antenna is moved. Hence, we investigated the performance of a pattern reconfigurable antenna (RA) in improving the wireless communications link in a hard rock underground mine. An RA and a dipole were characterized and compared in line-of-sight (LOS) and nonline-of-sight (NLOS) propagation scenarios. As a proof of concept, experiments were performed at the University of Queensland Experimental Mine using a 1 GHz frequency band centered at 2.45 GHz. Analysis of complex channel impulses captured through the frequency-domain channel sounding is presented. Also, the results show that reconfigurability in the rich multipath environment achieves a 20% and 34% improvement in path loss and delay spread, respectively, compared to a fixed-beam antenna in NLOS propagation. Furthermore, more than 34% improvement in coherence bandwidth is observed in LOS and NLOS. Therefore, reliable high-data-rate communication is achievable in underground mines by the effective management of multipath effects using the RA.

This paper presents the details and results of double-directional propagation measurements carried out in two indoor office environments: a semi-open, cubicle-type office space and a more traditional work environment with closed offices. The measurements cover seven frequency bands from 2.4 to 61 GHz, permitting the propagation characteristics to be compared over a wide range of candidate radio frequencies for next-generation mobile wireless systems, including ultra high frequency and millimeter-wave bands. A novel processing algorithm is introduced for the expansion of multiband measurement data into sets of discrete multipath components. Based on the resulting multipath parameter estimates, models are presented for frequency-dependent path loss, shadow fading, copolarization ratio, delay spread, and angular spreads, along with their interfrequency correlations. Our results indicate a remarkably strong consistency in multipath structure over the entire frequency range considered.

This paper presents an investigation of the wideband self-interference (SI) channel characteristics of a $2\times 2$ multi-input multi-output full-duplex transceiver using dual-polarized antennas. The measured SI channel power delay profiles at 2.45 GHz with 500 MHz span in various environments, anechoic chamber, laboratory room, and corridor, reveal that the SI channel can be represented by a multipath model consisting of two components: a quasi-static internal SI subchannel due to the specific Tx/Rx antenna structure and a time-varying external SI subchannel due to possible reflections from the surrounding environment. The quasi-static internal SI subchannel parameters can be derived from the Tx/Rx antenna structure specifications. The time-varying external SI channel exhibits cluster arrival features and can be represented by a modified Saleh–Valenzuela model with lognormal-distributed taps, and the cluster power exponentially decays with cluster arrival delay. However, the path power-versus-arrival-delay decay is exponential in a laboratory-room environment while it follows the power law in a corridor environment. The SI channel coherence bandwidth and delay spread in all three measurement environments follow normal and lognormal distributions, respectively.

Accurate and precise motion tracking of limbs and human subjects has technological importance in various healthcare applications. The use of impulse radio-ultra wideband technology (IR-UWB) technology due its inherent properties is of recent interest for high-accuracy localization. This paper presents experimental investigations and analysis of indoor human body localization and tracking of limb movements in 3-D based on IR-UWB technology using compact and cost-effective body-worn antennas. The body-centric wireless channel characterization has been analyzed in detail using parameters such as path loss magnitude, number of multipath components, rms delay spread, signal amplitude, and Kurtosis with the main focus to differentiate between line-of-sight (LOS) and non-LOS situations. Fidelity of the received signal is also calculated for different activities and antenna positions to study the pulse preserving nature of the UWB antenna, when it is placed on the human body. The results reported in this paper have high localization accuracy with 90% in the range from 0.5 to 2.5 cm using simple and cost-effective techniques which is comparable to the results obtained by the standard optical motion capture system.

There has been an increasing interest in the millimeter wave (mmW) frequency regime in the design of next-generation wireless systems. The focus of this work is on understanding mmW channel properties that have an important bearing on the feasibility of mmW systems in practice and have a significant impact on physical (PHY) layer design. In this direction, simultaneous channel sounding measurements at 2.9, 29 and 61 GHz are performed at a number of transmit-receive location pairs in indoor office, shopping mall and outdoor environments. Based on these measurements, this paper first studies large-scale properties such as path loss and delay spread across different carrier frequencies in these scenarios. Towards the goal of understanding the feasibility of outdoor-to-indoor coverage, material measurements corresponding to mmW reflection and penetration are studied and significant notches in signal reception spread over a few GHz are reported. Finally, implications of these measurements on system design are discussed and multiple solutions are proposed to overcome these impairments., 13 pages, 8 figures, Accepted for publication at the IEEE Transactions on Antennas and Propagation

In this paper, we present novel ultrawideband (UWB) off-body channel measurement campaigns in indoor environments aiming the characterization of the delay and the angular properties of the channel. Measurements were performed by using isolated UWB antenna and body-mounted antennas on different positions. Multipath and cluster parameters are estimated by means of space alternating generalized expectation-maximization (SAGE) and a clustering algorithm. These estimates allow an analysis of the variations of the channel properties due to the presence of the body. Notably, we observe strong modifications of the spatial characteristics of the channel. The delay spread is characterized as a function of the body orientation and the antenna position on the body. In addition, a modeling of the angles-of-arrival based on a Laplacian distribution is given. A cluster modeling is provided along with parameters. Finally, the part of diffuse multipath components not detected by SAGE algorithm is analyzed in function of the communication scenario.

Deterministic field prediction has been widely used to provide channel data for coverage analysis. Among these prediction tools, point cloud-based methods have been developed for millimeter-wave frequencies in order to characterize the environment with higher precision, but they have not taken into account all the necessary propagation mechanisms. In this paper, we present the implementation for predicting both specular reflections and diffraction as well as the total channel, including the aforementioned mechanisms along with scattering and shadowing. Both line-of-sight (LOS) and non-LOS channels are predicted and validated against measurements in a cafeteria. The result shows excellent agreement between prediction and measurement in terms of power delay profiles, power angular spectra, path loss, mean delay, delay spread, and azimuth spread.

This paper presents experimental investigations and analysis of ultra-wideband localization of body-worn antennas in an indoor environment. Three-dimensional (3-D) tracking of wearable antennas placed on the upper human body is achieved using a compact and cost-effective antenna and time of arrival (TOA) localization techniques. Various features such as rms delay spread, kurtosis, and signal amplitude have been used to classify the channel type between each antenna location and base station. Non-line-of-sight identification and mitigation techniques have been used to enhance the accuracy of the localization technique applied. Geometric dilution of precision of the base-station configuration and numerical analysis on the radiation patterns for different locations of the body-worn antenna has been studied in terms of variation in localization accuracy. High-accuracy 3-D localization results in the range of 1–2 cm are obtained with the antennas placed on the limbs and 1–3 cm for the torso region. The accuracy achieved is 3 times better than commercially available UWB localization and tracking systems. The significantly high-accuracy results obtained for all antenna locations demonstrate the reliability and suitability of UWB technology for various indoor tracking and localization applications in the fields of healthcare, sports, and well-being.

A site-specific convex pyramidal beam tracing model of ultrawideband (UWB) indoor propagation channels is described in detail. The model is fast and accurate, since it does not need to apply nontrivial and costly tests to determine all the existing rays between the transmitter and receiver. Predictions from the model are compared with those from corresponding measurements, performed under line-of-sight (LOS) and nonline-of-sight (NLOS) conditions. A good agreement is displayed between predicted and measured impulse responses, as well as of some derived parameters (average power, mean delay, and delay spread), as they vary with the distance between the transmitter and the receiver.

Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower atmosphere, can trap the propagating signals. The trapping effects of the atmospheric ducts can be utilized as a communication medium for beyond-line-of-sight (b-LoS) links. Although the wave propagation and the refractivity estimation techniques for the atmospheric ducts are well studied, there is no work that provides a channel model for the atmospheric ducts. Therefore, we develop a large-scale path-loss model for the surface ducts based on the parabolic equation (PE) methods for the first time in the literature. In addition, we develop a ray-optics (RO) method to analyze the delay spread and angle-of-arrival (AOA) of the ducting channel with the surface ducts. Using the developed RO method, we derive an analytical expression for the effective trapping beamwidth of the transmitter to predict the ranges of the beamwidth that can be trapped by the surface ducts according to the refractivity and the channel parameters., NA

Millimeter-wave radios operating at unlicensed 60 GHz and licensed 70 GHz bands are attractive solutions to realize short-range backhaul links for flexible wireless network deployment. We present a measurement-based spatio-temporal statistical channel model for short-range millimeter-wave links in large office rooms, shopping mall, and station scenarios. Channel sounding in these scenarios at 60 and 70 GHz revealed that spatio-temporal channel characteristics of the two frequencies are similar, making it possible to use an identical channel model framework to cover the radio frequencies and scenarios. The sounding also revealed dominance of a line-of-sight and specular propagation paths over diffuse scattering because of weak reverberation of propagating energy in the scenarios. The main difference between 60 and 70 GHz channels lies in power levels of the specular propagation paths and diffuse scattering which affect their visibility over the noise level in the measurements, and the speed of power decay as the propagation delay increases. Having defined the channel model framework, a set of model parameters has been derived for each scenario at the two radio frequencies. After specifying the implementation recipe of the proposed channel model, channel model outputs are compared with the measurements to show validity of the channel model framework and implementation. Validity was demonstrated through objective parameters, i.e., pathloss and root-mean-square delay spread, which were not used as defining parameters of the channel model.

Deploying wireless systems in vehicles is an area of current interest. Often, it is implicitly assumed that the electromagnetic environment in vehicle cavities is analogous to that in reverberation chambers, it is therefore important to assess to what extent this analogy is valid. Specifically, the cavity time constant, electromagnetic isolation and electric field uniformity are investigated for typical vehicle and vehicle-like cavities. It is found that the time constant is a global property of the cavity (i.e., it is the same for all links). This is important, as it means that the root-mean-square delay spread for any link is also a property of the cavity, and thus so is the coherence bandwidth. These properties could be exploited by wireless systems deployed in vehicles. It is also found that the field distribution is not homogeneous (and is therefore not uniform), but can be isotropic. For situations where the field distribution is isotropic, the spatial coherence is well defined, and therefore multiple-input-multiple-output antenna arrays can be used to improve performance of wireless systems. For situations where the field distribution is not isotropic, the angular spread is not uniform, and therefore beamforming can be used to improve performance of wireless systems.

The satellite-to-helicopter radio channel is measured, characterized, analyzed, and modelled. We used a sweep time delay cross correlation sounder operating at 14.25 GHz and actual helicopters for the experiment. From the measurements, signal fading, delay and Doppler spread are estimated. Wideband radio channel results show that the signal delay spread is small enough, so 32 MHz satellite transponders could be used with no need of equalization. We also observed two important propagation impairments on the received signal envelope, both of them caused by the main rotor blades. The first one is the power attenuation produced when the LoS is obstructed by the blades. We demonstrate that this effect could be mitigated by using spatial or polarization diversity technique in the receiver end. The second one is the presence of multipath propagation leading to a power level oscillation dependent on the amplitude of the received multipath components. An UTD-based 3-D ray tracing model was used to conclude that the main multipath components are generated by diffraction on the rotor blade edges.

Channel models are important tools to evaluate the performance of new concepts in mobile communications. However, there is a tradeoff between complexity and accuracy. In this paper, we extend the popular Wireless World Initiative for New Radio (WINNER) channel model with new features to make it as realistic as possible. Our approach enables more realistic evaluation results at an early stage of algorithm development. The new model supports 3-D propagation, 3-D antenna patterns, time evolving channel traces of arbitrary length, scenario transitions and variable terminal speeds. We validated the model by measurements in a coherent LTE advanced testbed in downtown Berlin, Germany. We then reproduced the same scenario in the model and compared several channel parameters (delay spread, path gain, K-factor, geometry factor and capacity). The results match very well and we can accurately predict the performance for an urban macro-cell setup with commercial high-gain antennas. At the same time, the computational complexity does not increase significantly and we can use all existing WINNER parameter tables. These artificial channels, having equivalent characteristics as measured data, enable virtual field trials long before prototypes are available.

This paper presents the large scale parameters of wideband multipath channels based on extensive measurement campaigns in various indoor environments. The measurements were conducted with a wideband multiple-input multiple-output (MIMO) channel sounder having a bandwidth of 400 MHz at 11 GHz which is a challenging frequency for future mobile systems. In particular, polarization characteristics of path-loss, shadowing, cross-polarization power ratio (XPR), delay spread and coherence bandwidth are characterized. The measurement results show that the path-loss exponents range between 2.0 and 3.0 for none-line-of-sight (NLoS), 0.36 and 1.5 for LoS, respectively. Vertically and horizontally polarized transmissions have almost same path-gain, but in some corridor-room NLoS environments, the path-loss for HH is significantly large. In most cases, the RMS delay spreads are less than 20 and 50 ns for NLoS and LoS, respectively, and the average coherence bandwidth is less than 30 MHz. The Rician K-factors range between 2 and 3 dB for cross-polarization, and in large Hall environments, those for co-polarization are greater than 6.0 dB with 10% probability. Finally, some dominant propagation mechanism and site-specific behaviors are illustrated using the double-directional measurement results.

A good modeling of the radio propagation channel is essential to the design of high-performance wireless systems; therefore, the proper interpretation of the data acquired from the sounding process is a task of major importance in the construction of such models. The relevance vector machine (RVM) constitutes a learning algorithm, based on Bayesian Statistics, used in regression and classification problems. Recently, RVM was employed to filter the channel multipath components of simulated power delay profiles embedded with noise, enabling the determination of the paths arriving at the reception antenna, their arrival times and complex amplitudes. In this paper, the RVM algorithm is further studied, regarding its detection capabilities, but the power delay profiles were obtained from measurements carried out in an indoor channel. A comparison with the constant false alarm rate (CFAR) multipath identification scheme, based on computational simulation and real channel measurements, evidences the behavior of both detection schemes. Simulations also present the detection limits of the method, such as maximum multipath magnitude ratio and minimum interarrival time. Finally, the characterization of important parameters of a real wideband multipath indoor channel is presented, in terms of confidence intervals and probability distribution fittings.

The main concern of this paper is to study the presence of a cascaded Butler network in diversity antenna systems. The advantages of a cascaded Butler network in 2-D multipath environments have been already shown. These advantages are limited to either correlated or nonuniform multipath environments with a line-of-sight component. In the frame of this paper, for the first time, we show a further advantage of a cascaded Butler network in 3-D multipath environments, including the effects of coupling. This advantage is associated with an improved convergence in received signals' covariance matrix in a multipath environment wherein the number of independent incoming waves is limited, i.e., nonrich multipath environment. For this purpose, we use a simulation tool in which a multipath scenario with certain number of incoming waves is emulated and some selected multiport antennas are exposed to it. Afterwards, the simulated random received signals are used to yield different performance metrics like spatial correlation. This advantage achieves considerable practical interest since a typical actual multipath scenario is most likely a nonrich multipath environment.

A model based on experimental observations of the delay power spectrum in closed rooms is proposed. The model includes the distance between the transmitter and the receiver as a parameter which makes it suitable for range based radio localization. The experimental observations motivate the proposed model of the delay power spectrum with a primary (early) component and a reverberant component (tail). The primary component is modeled as a Dirac delta function weighted according to an inverse distance power law (d-n). The reverberant component is an exponentially decaying function with onset equal to the propagation time between transmitter and receiver. Its power decays exponentially with distance. The proposed model allows for the prediction of, e.g., the path loss, mean delay, root mean squared (rms) delay spread, and kurtosis versus the distance. The model predictions are validated by measurements: they show good agreement with respect to distance dependent trends. A model based on experimental observations of the delay power spectrum in closed rooms is proposed. The model includes the distance between the transmitter and the receiver as a parameter which makes it suitable for range based radio localization. The experimental observations motivate the proposed model of the delay power spectrum with a primary (early) component and a reverberant component (tail). The primary component is modeled as a Dirac delta function weighted according to an inverse distance power law (d-n). The reverberant component is an exponentially decaying function with onset equal to the propagation time between transmitter and receiver. Its power decays exponentially with distance. The proposed model allows for the prediction of e.g. the path loss, mean delay, root mean squared (rms) delay spread, and kurtosis versus the distance. The model predictions are validated by measurements: they show good agreement with respect to distance dependent trends.

The performance of multiple-input-multiple-output (MIMO) system operating at the 60 GHz band is investigated based on experimental data in a real underground mine gallery. However, the millimeter wave (mmW) channels face some challenges such as high propagation loss. In order to overcome this issue, a planar microstrip antenna array has been designed, and fabricated. Moreover, the effect of miners' activity in the vicinity of the short-range wireless link is studied. Statistical parameters of the propagation channel, such as RMS delay spread, path loss, K-factor, channel correlation and capacity are extracted and analyzed. Results suggest that miners presence substantially affects both received power and time dispersion parameters and should therefore be considered when developing underground mine wireless networks in the unlicensed 60-GHz band.

The results of a wideband measurement campaign carried out at L-band in order to characterize the receiver end of the radio link between satellites with elevations lower than 5 $^{\circ}$ and mobile receivers are summarized in this paper. A swept time-delay cross-correlation (STDCC) channel sounder with 1.675-GHz carrier frequency and 12.5-ns delay resolution was used to obtain complex low-pass impulse responses of the propagation channel in urban, suburban, rural, lightly wooded, and heavily wooded environments. Delay spreads and coherence bandwidths have been obtained and studied according to three different propagation conditions. Results show how shadowing and blockage together with the propagation environment impact on the delay spread and the coherence bandwidth.

The spectrum crunch currently experienced by mobile cellular carriers makes the underutilized millimeter-wave frequency spectrum a sensible choice for next-generation cellular communications, particularly when considering the recent advances in low cost sub-terahertz/millimeter-wave complementary metal–oxide semiconductor circuitry. To date, however, little is known on how to design or deploy practical millimeter-wave cellular systems. In this paper, measurements for outdoor cellular channels at 38 GHz were made in an urban environment with a broadband (800-MHz RF passband bandwidth) sliding correlator channel sounder. Extensive angle of arrival, path loss, and multipath time delay spread measurements were conducted for steerable beam antennas of differing gains and beamwidths for a wide variety of transmitter and receiver locations. Coverage outages and the likelihood of outage with steerable antennas were also measured to determine how random receiver locations with differing antenna gains and link budgets could perform in future cellular systems. This paper provides measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks and gives insight into antenna beam steering algorithms for these systems.

An experimental study of the time reversal (TR) technique is presented in a single-input-single-output configuration over the frequency range of 2-12 GHz. A special emphasis of this work is to investigate and compare impulse response (IR) and TR characteristics for omnidirectional biconical and directional spiral antennas over realistic indoor ultrawideband (UWB) channels in both line-of-sight (LOS) and non-line-of-sight (NLOS) environments. We discuss the effects of channel multipath dispersion and antenna frequency-dependant delay distortions on the received responses in both time and frequency domains. The effectiveness of TR for waveform compression is characterized by computing root mean square delay spread and peak-to-average power ratio. Our study suggests that the effectiveness of time reversal is subject to a tradeoff between competing effects-namely, compensation of spectral phase variation (which leads to compression) and aggravation of spectral amplitude structure (which opposes compression). Although TR is a powerful technique for compensation of phase distortions associated with broadband frequency-independent antennas (as shown in LOS experiments with spiral antennas), it shows only modest performance in compressing time spread associated with multipath delays.

The ultrawideband (UWB) propagation channel is analyzed by means of measurements carried out in the 2-5 GHz frequency band in an office environment for different scenarios. Measurements were performed for different polarizations on the transmitting and receiving arrays so the effect of the signal polarization can be also taken into account in the analysis. The main contribution of this paper is not only the analysis of path loss and RMS delay spread in a bandwidth of 3 GHz, but also the influence of frequency on such parameters. The relationship between the path loss for copolar configurations and the cross-polarization discrimination (XPD), both in space and frequency domain, is also addressed.

In ultra-wideband (UWB) wireless propagation channels, each multipath component (MPC) can exhibit delay dispersion or, equivalently, frequency dependence; even more, this dispersion can be different for different MPCs. While this effect is understood to have important implications for UWB system design, extraction of the frequency-dependence parameters from measurements has been lacking. This paper will provide both the theoretical tools for the parameter extraction, and provide experimental results of such parameters in UWB indoor channels. We first develop a method that extracts a single MPC. Based on the image principle, the method identifies locations and intensity of radio sources including both original and image sources (corresponding to MPCs) by a distributed antenna array. We show that the method provides spatial resolution better than 0.5 m and is robust against possible measurement errors. Having applied the method to the measured channels in indoor line-of-sight scenarios, we track the detected image sources over (partially overlapping) frequency subbands to obtain frequency dependent properties of their intensity and location. The variation of the source intensity over the frequency was found to be significant. Furthermore, the locations of the image sources can vary as the frequency changes. Comparison of the results with models that do not describe varying per-path frequency dependence revealed noticeable difference in the shape of the CIRs, and as a result, in the delay spread and the number of significant delay bins for Rake reception.

The wireless channel of backscatter radio systems is a two-way pinhole channel, created by the concatenation of two standard wireless channels. We present a method to calculate wideband channel parameters of backscatter channels based on the parameters of the constituent one-way channels. The focus is on characteristics that are vital for narrowband and wideband ranging, such as the K-factor w.r.t. the direct (line-of-sight) path and the RMS delay spread. The presented analyses include uncorrelated as well as correlated channel pairs and are thus valid for bistatic and monostatic antenna setups. We also show that the uncorrelated scattering (US) assumption holds for the backscatter channel provided that the constituent channels are US.

Radio channel models for 60 GHz very-high-speed radio systems in hospital environments are presented. Two possible applications of those systems have been considered: real-time video streaming for angiography and ultrasonic imaging. Channel modeling was performed for delay domain multipath characteristics based on extensive radio channel measurement campaigns in angiography and ultrasonic inspection rooms. The measurement results revealed that the shapes of the power delay profiles in the angiography and ultrasonic imaging rooms were significantly different from that reported in the IEEE802.15 TG3c and IEEE802.11 TGad channel models. For this reason, novel model structures were developed to model radio channels in these hospital scenarios accurately. Statistical descriptions of the channel model parameters are given based on the measurements, and, finally, implementation guidelines of the channel models are provided. The channel model validation results show a good agreement of root-mean-square delay spread between channel model outputs and channel measurements. The channel model is useful for the performance evaluation of the wireless systems in hospital environments.

Using a similar approach to that applied in acoustics and in microwave reverberation chambers, a theory of wideband propagation in a closed environment is discussed. Here, a room environment is viewed as a lossy cavity, characterized by diffuse scattering from walls and internal obstacles. For experimental results, measurements from 3 to 8 GHz were performed in a 24 passenger section of an aircraft cabin. This UWB system has the transmitter at ceiling height and the receivers at armrest and headrest positions. The measurements were performed for the cabin being unoccupied and fully occupied. In the theoretical model, the closed room environment is characterized by the reverberation time and volume, and these parameters allow derivation of the the remaining parameters such as path loss and average passenger absorption. The RMS delay spread and mean excess delay are also studied. For the mean power the agreement between the theory and measurements is good to within 1-2 dB, indicating the excellent accuracy of the method, which extends to estimating body absorption in real world environments. The total absorption from the seated passengers is dominated by the few who are near the transmitter. In general, this absorbed power is relatively small, so the effect of passengers is marginal for this configuration of a cabin communication system.

Dynamic changes in the propagation environment affect transmissions from/to static wireless communication devices. In indoor situations, people moving near transmitting/receiving antennas may alter the propagation channel. To characterize these changing conditions, low-mobility time-domain measurements were taken in three office environments, covering the band from 3.5 GHz to 10.5 GHz. In this paper, we analyze three propagation aspects for bands with different center frequencies and bandwidths ranging from 50 MHz to 5.7 GHz, as follows: the channel diversity (rank); static-to-dynamic changes in received power; and the number of resolvable multipath components. Initial analysis shows that the t location-scale distribution gives the best fit for the dynamic RMS delay spread. Further investigations indicate that channel diversity changes significantly with the environment. Such diversity also depends linearly on the channel perturbation and centre frequency, but its increment due to bandwidth expansion is relatively small.

We report on measurements that characterize multipath conditions that affect broadband wireless communications in building penetration scenarios. Measurements carried out in various large structures quantify both radio-signal attenuation and distortion (multipath) in the radio propagation channel. Our study includes measurements of the complex, wideband channel transfer function and bandpass measurements of a 20 MHz-wide, digitally modulated signal. From these, we derive the more compact metrics of time delay spread, total received power and error vector magnitude that summarize channel characteristics with a single number. We describe the experimental set-up and the measurement results for data collected in representative structures. Finally, we discuss how the combination of propagation metrics may be used to classify different propagation channel types appropriate for public-safety applications.

We have characterized the effect of human presence on path gain and time dispersion over ultrawideband (UWB) channels within the passenger cabin of a typical midsize airliner. We measured a few hundred channel frequency responses over the range 3.1-6.1 GHz between various locations within a Boeing 737-200 aircraft, with and without volunteers occupying the passenger seats. The links were deployed in a point-to-multipoint configuration with the transmitting antenna along the centre-line of the forward part of the cabin at either the ceiling or headrest level and the receiving antenna at the headrest or armrest level at selected locations throughout the rest of the cabin. As the density of occupancy increased from empty to full, path gain dropped by no more than a few dB on the ceiling-to-headrest paths but dropped by up to 10 dB on the ceiling-to-armrest and headrest-to-armrest paths. The gain reduction reached its maximum at the mid-point of the cabin and decreased thereafter. In all cases, increasing the density of occupancy caused the distance dependence of the rms delay spread to decrease greatly, the decay rate of the scattered components in the power delay profile (PDP) to almost double and the number of significant paths to drop by almost half. The results suggest that human presence substantially affects both path gain and time dispersion within the aircraft and should therefore be considered when assessing the performance of in-cabin wireless systems.

A generalized definition is presented of multipath angular spread, used to study the spatial correlation of the signal envelope in a three-dimensional wireless channel, both in the cases of a three-dimensional and a horizontal travel direction. Previous results from two-dimensional modeling are shown to be a special case of this general analysis when the multipath power and the travel direction are confined to a single plane in space. The results show that the main lobe of the spatial correlation of the signal envelope at a given distance has an approximately Gaussian dependence on the three-dimensional multipath directivity metric proposed in this paper, for both cases for the travel direction.

A statistical model for ultrawideband (UWB) off-body communication channels is proposed. The presented results are the outcome of extensive real-body measurements carried out in the frequency range between 3.5 and 6.5 GHz in typical indoor environments. The signal power gain is modeled by a log-linear dual-breakpoint model, the parameters of which depend on both the body orientation as well as the distance between the transmitter and the on-body sensor. The general trend implies that in large distances, the received signal strength is less sensitive to changes in the body orientation angle, especially if propagation occurs in dense multipath environments. Furthermore, the small-scale channel variations of the total received signal strength are found to follow a normal distribution. This fact was verified by means of the central limit theorem (CLT), since correlation between multipath components is found to be negligible. Moreover, time dispersion analysis is provided by means of RMS delay spread. Finally, based on the newly estimated parameters, a model implementation for wideband power is proposed and several comparisons between the empirical data and the simulation results are presented.

A wideband directional measurement campaign was managed inside an arched highway tunnel to analyze the radio propagation channel inside such tunnel for future cellular systems in terms of coverage, delay spread and dominant scatterers. Measurements were performed in 3 rounds with different transmitter positions. Using a wideband channel sounder equipped with a cylindrical dual polarized array at the receiver, the spatio-temporal characteristics of the received propagation paths could be estimated by means of a super-resolution estimation algorithm. The extracted paths using this super-resolution algorithm constitute 88% of the total received power. It was also observed that the line-of-sight component (53%) plus single-bounce scattering (26%) comprise up to 79% of the total received power. In other words, more than 90% (i.e. 79% in 88%) of the extracted paths consists of the line-of-sight component and single-bounce scatterings. The strong contribution from single-bounce scattering paths causes the path gain exponent along the tunnel to be larger than -2 which is the value for free space. This validates that there is wave guiding effect in the tunnel and coverage is extended relative to open space. The rms delay spreads are generally less than 20 ns and increase when influenced by scattering objects such as jetfans. The dominant scatterers are identified and classified into 6 classes based on the structure of the tunnel and existing objects such as ground, wall, light-frame, ceiling, jetfan and cleaner-parking. It was observed that scattering from ground was dominant among all classified scatterers in all scenarios.

In this paper, a 4 times 4 indoor multiple-input multiple-output (MIMO) measurement campaign at a frequency of 2.45 GHz is presented. The main contribution of this work is the analysis of the impact of radio-wave polarization in MIMO systems operating at a typical indoor scenario through the calculation-from the measurements carried out-of a great deal of parameters such as the mean path loss, the cross polarization discrimination (XPD), and the RMS delay spread, which are all essential to estimate the performance of real MIMO systems. In this sense, some path loss models-which have been adjusted according to the measurements-are given, taking into account polarization, attenuation through walls, and the effect of T-junctions existing in the considered indoor scenario. Moreover, additional parameters such as the K-factor and statistical distribution, as well as spatial parameters, are discussed.

A high-resolution channel sounding technique has been used to investigate the cross-polarization of electromagnetic waves in the 5-6 GHz band. Experiments were performed in two non-line-of-sight indoor locations, and it was found that there is a strong dependency of the cross-polarization of multipath components on the elevation angle-of-arrival. For a vertically polarized transmitting antenna, clusters of co-polarized multipath components were confined predominantly to the region around the horizontal plane that contains the virtual line-of-sight between transmitter and receiver. In contrast, cross-polarized signals were detected for a variety of elevation angles with considerable power levels. The surroundings of the receiver were identified as the principal source of depolarized signals. In addition, time dispersion analysis of the multipath signals led to the determination of the AoAs where there is a strong correspondence between co- and cross-polarized signals as a consequence of the partial depolarization of MPCs. This work supports the exploitation of the joint space and polarization diversities in indoor propagation scenarios to improve the system performance.

The radiation characteristics of ultrawideband (UWB) antennas vary with frequency, introducing directionally asymmetric bandwidth reduction and waveform dispersion. In this paper, we develop a simple technique to alleviate the distortion due to nonisotropically dispersive antennas, and use indoor channel measurements to verify its performance. The approach is based on multipath direction estimation and therefore involves antenna arrays. We show that antenna distortion can enhance sensor localization ambiguity and introduce errors in its estimate. Antenna compensation mitigates this effect, significantly improving the location estimation accuracy. We further demonstrate that antenna compensation helps reduce the small-scale fading artifacts that arise due to the antennas, thus reducing the channel spatial variability and delay spread. Our technique can also aid empirical channel characterization by providing antenna-independent propagation data. © 2008 IEEE.

A comprehensive and integrative overview (excluding ultrawideband measurements) is given of all the empirical data available from the open literature on various temporal properties of the indoor radiowave communication channel. The concerned frequency range spans over 0.8-8 GHz. Originally, these data were presented in about 70 papers in various journals, at diverse conferences, and in different books. Herein overviewed are the multipaths' amplitude versus arrival delay, the probability of multipath arrival versus arrival delay, the multipath amplitude's temporal correlation, the power delay profile and associated time dispersion parameters (e.g., the RMS delay spread and the mean delay), the coherence bandwidth, and empirically ldquotunedrdquo tapped-delay-line models. Supported by the present authors' new analysis, this paper discusses how these channel-fading metrics depend on the indoor radiowave propagation channel's various properties, (e.g., the physical environment, the floor layout, the construction materials, the furnishing's locations and electromagnetic properties) as well as the transmitted signal's carrier-frequency, the transmitting-antenna's location, the receiving-antenna's location, and the receiver's detection amplitude threshold.

A multidimensional analysis of multipath propagation in urban micro- and macro-cellular environment has been carried out. Multidimensional measurement data, including path-loss, delay spread and direction-of-arrival are compared with simulations performed with a 3D ray tracing model which takes diffuse scattering into account. The results are analyzed highlighting the dominant propagation mechanisms in the different cases and model performance/shortcomings. In particular, the results show that diffuse scattering plays a key role in urban propagation, with an impact on both narrowband and wideband parameters in most cases. Also, the accuracy and the characteristics of environment representation can have a significant impact on prediction even in simple topologies.

The polarization characteristics of the indoor ultrawideband channel are investigated using dual-polar 3.1-10.6 GHz channel measurements. Under the generalized elliptical polarization framework, the channel cross-polar discrimination (XPD) statistics are evaluated. Lognormal and triangular distributions are shown to well model the XPD and ellipticity angle. Considerable spectral and small-scale spatial variability is observed in the XPD. Asymptotic convergence of XPD to its mean with increasing bandwidth is established. An analysis of the variation of tap XPD with excess delay indicates that the XPD is highest for the initial paths. It is shown that increased scattering leads to greater depolarization. The dependence of XPD on the channel's rms delay spread is modelled using a linear regression with -0.5 dB/ns slope. This characterization will aid the analysis of polarization-dependent loss and the design of polarized multiple-antenna systems.

Results are presented on wideband radio propagation measurements and statistical modeling at 2.4 GHz and 5.8 GHz in real underground mine tunnels. This peculiar type of confined environment is characterized by very rough surfaces and a frequent absence of a line-of-sight between transmitting and receiving antennas. The resulting propagation characteristics differ from those frequently encountered in more typical indoor environments such as offices and corridors. Indeed, the rms delay spread shows little or no correlation with respect to transmitter-receiver distance and, in addition, no impulse response path arrival clustering effect is observed. However, the path amplitude distribution does tend to follow a Rice distribution in the line-of-sight case, and a Rayleigh distribution otherwise.

Ultrawideband (UWB) is a promising technology for wireless body area networks (WBANs). This paper studied the impacts of 3.1–10.6 GHz on-human-body UWB channel on the impulse radio WBAN system. A performance evaluation method is presented for the realistic UWB WBAN systems, which observes the waveform distortion along the signal path. The measurement and characterization of the 3.1–10.6 GHz on-human-body UWB channel are devised to generate the radiographs of path loss and delay spread for the first time. The performance of the UWB impulse radio WBAN transceiver in terms of bit error rate (BER) is evaluated based on the waveform distortion and on-human-body channel measurement, which shows the human body effect is more significant than the environment effect, especially when the propagation channel contains no line-of-sight path. Various candidate pulse shapes and modulation schemes forUWBWBAN are studied and their performances with the measured WBAN channel are evaluated and compared. Published version

Three-dimensional (3-D) ray tracing has advanced to such a degree that it can provide channel parameters like delay spread, Doppler spread, angular spread, and distribution functions of long- and short-term fading with high accuracy for fixed to mobile and mobile to mobile communications. These parameters are absolutely required during the specification phase of future mobile communications systems in order to define the air interface and a variety of other relevant system parameters. This paper describes state-of-the-art ray tracing capabilities. A 3-D ray tracing model developed at the Universitaumlt Karlsruhe is presented. Important characteristic channel parameters are briefly discussed. Based on these parameters the model is verified by wideband nondirectional and directional measurements at 2 and 5.2 GHz, respectively, showing a good agreement. The proposed 3-D ray tracing model can therefore be used in order to extract parameter sets for the specification of future mobile communications systems and to optimize existing ones

Impulse response radiowave propagation measurements from an urban area of Denver, CO, are described. The basic transmission loss and delay spread are used to characterize the mobile communications environment. These metrics are quantified using path loss slope and delay spread statistics. By analyzing the results versus carrier frequency, the relative propagation impairments at 430, 1350, 2260, and 5750 MHz are compared. It was found that the path loss slope increased on average by 11 dB/dec and the median delay spread decreased from 0.7 to 0.3 /spl mu/s over the decade of frequencies measured.