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Meta-surfaces intend to improve the performance of future wireless networks significantly by controlling the wireless propagation and shaping the radio waves according to the generalized Snell's law. A recent application of meta-surfaces are reconfigurable intelligent surfaces that are mainly proposed for the reflection and steering of the impinging signal. In this article, we introduce randomly reconfigurable surfaces (RRSs) aiming to diffuse the incoming wave and characterize the performance of an RRS-assisted communication network. To facilitate the performance analysis of an RRS-assisted network, first, we present novel closed-form expressions for the probability density function, the cumulative distribution function, the moments, and the characteristic function of the amplitude of the distribution of the sum of double-Nakagami- $m$ random vectors, whose amplitudes follow the double-Nakagami- $m$ distribution, and phases following the circular uniform distribution. We also consider a special case of this distribution, namely the distribution of the sum of Rayleigh-Nakagami-m random vectors. Then, we exploit the obtained expressions to investigate the RRS-assisted composite channel, assuming that the two links undergo Nakagami- $m$ fading. Specifically, closed-form expressions for the outage probability, the average received signal-to-noise ratio, the ergodic capacity, the bit error probability, the amount of fading, and the channel quality estimation index are provided to evaluate the performance of the considered system. Finally, these metrics are also derived for the practical special case where one of the two links undergoes Rayleigh fading, implying that this link is non-line-of-sight. [ABSTRACT FROM AUTHOR]

The fine timing measurement (FTM) protocol is designed to determine precise ranging between Wi-Fi devices using round-trip time (RTT) measurements. However, the multipath propagation of radio waves generates inaccurate timing information, degrading the ranging performance. In this study, we use a neural network (NN) to adaptively learn the unique measurement patterns observed at different indoor environments and produce enhanced ranging outputs from raw FTM measurements. Moreover, the NN is trained based on an unsupervised learning framework, using the naturally accumulated sensor data acquired from users accessing location services. Therefore, the effort involved in collecting training data is significantly minimized. The experimental results verified that the collection of unlabeled data for a short duration is sufficient to learn the pattern in raw FTM measurements and produce improved ranging results. The proposed method reduced the errors in raw distance measurements and well-calibrated ranging results requiring the collection of ground truth data by 47–50% and 17–29%, respectively. Consequently, positioning errors were reduced by 17–30% compared to the well-calibrated ranging scenario. [ABSTRACT FROM AUTHOR]

Vehicular Visible Light Communication (VVLC) is preferred as a vehicle to everything (V2X) communications scheme due to its highly secure, low complexity and radio frequency (RF) interference free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light emitting diodes (LEDs). Current VVLC channel models based on deterministic and stochastic methods provide limited accuracy for path loss prediction since deterministic methods heavily depend on site-specific geometry and stochastic models average out the model parameters without considering environmental effects. Moreover, there exists no wireless channel model that can be adopted for channel frequency response (CFR) prediction. In this paper, we propose a novel framework for the machine learning (ML) based channel modeling of the VVLC with the goal of improving the model accuracy for path loss and building the CFR model through the consideration of multiple input variables related to vehicle mobility and environmental effects. The proposed framework incorporates multiple measurable input variables, e.g., distance, ambient light, receiver inclination angle, and optical turbulence, with the exploitation of feed forward neural network based multilayer perceptron neural network (MLP-NN), radial basis function neural network (RBF-NN) and decision tree based Random Forest learning methods. The framework also includes data pre-processing step, with synthetic minority over sampling technique (SMOTE) data balancing, and hyper-parameter tuning based on iterative grid search, to further improve the accuracy. The accuracy of the proposed ML based channel modeling is demonstrated on the real world VVLC vehicle-to-vehicle (V2V) communication channel data. The proposed MLP-NN, RBF-NN and Random Forest based channel models generate highly accurate path loss predictions with 3.53 dB, 3.81 dB, 3.95 dB root mean square error (RMSE), whereas the best performing stochastic model based on two-term exponential fitting provides prediction accuracy of 7 dB RMSE. Moreover, MLP-NN and RBF-NN models are demonstrated to predict VVLC CFR with 3.78 dB and 3.60 dB RMSE, respectively. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RIS) is considered as a revolutionary technique to improve the wireless system performance by reconfiguring the radio wave propagation environment artificially. Motivated by the potential of RIS in vehicular networks, we analyze the secrecy outage performance of RIS-aided vehicular communications in this paper. More specifically, two vehicular communication scenarios are considered, i.e., a vehicular-to-vehicular (V2V) communication where the RIS acts as a relay and a vehicular-to-infrastructure (V2I) scenario where the RIS functions as the receiver. In both scenarios, a passive eavesdropper is present attempting to retrieve the transmitted information. Closed-form expressions for the secrecy outage probability (SOP) are derived and verified. The results demonstrate the potential of improving secrecy with the aid of RIS under both V2V and V2I communications. [ABSTRACT FROM AUTHOR]

Operating remotely piloted aircraft is not imaginable without a continuous data exchange between the air vehicle and the remote pilot. This data exchange requires reliable data links. One approach for such a data link discussed in the community is a terrestrial system deployed in C-band. A good knowledge of the physical conditions of the communication channel, in this case the air-ground/ground-air channel, is indispensable for the development of wireless data links. Therefore we carried out a 50 MHz bandwidth channel sounding campaign with a terrestrial transmitter and an airborne receiver. In this paper we give a detailed description of our campaign setup and the processing of the collected data. The campaign covered several flight scenarios, such as take-off, taxiing, and multiple en-route maneuvers. We furthermore present results on the received power and the amplitude distribution of the dominant component of the received signal for the different flight scenarios. We observed significant drops in reception power during certain maneuvers that need to be considered in the design process of a data link for unmanned aviation. Additionally, we show that the amplitude distribution follows the distributions commonly used in statistical channel modeling of wireless channels to some extent. We finally present parameter sets for multiple flight scenarios for scaling the amplitude distributions to allow a statistical channel modeling of the reception power of the first resolvable signal path. [ABSTRACT FROM AUTHOR]

The communications between two driving vehicles along a narrow street may be limited by the presence of a third vehicle blocking the transmission. In this work, we investigate radio wave propagation at 28 GHz in an urban street canyon scenario by conducting channel measurements, where the vehicle(s) occlude(s) the line-of-sight path. We quantify the impact of the car blockage and study the alternative propagation paths, which can be used for establishing a data link. Based on the obtained results, we report that besides the low-loss (3.4 dB) reflection from the wall, a radio link through the blocking car may potentially be established for data sharing. Specifically, the attenuation through clear windows is 2 dB, while the attenuation caused by sun protective film is 15 dB. Diffraction over the car and propagation in foliage reduce the multipath power drastically by 21–24 dB and 16–19 dB, respectively, and cannot be associated with reliable links. Finally, measurement results were compared with the ray-based simulation data, which demonstrate agreement to within ± 4.3 dB of measured losses. [ABSTRACT FROM AUTHOR]

In the fifth-generation (5G) system, millimeter-wave (mmWave) communication has been recognized as a candidate technique. To overcome the high transmission loss of mmWave, distributed antenna systems that consist of a base station (BS) connecting with multiple remote radio units (RRUs) were studied to improve the energy efficiency. In this letter, by utilizing the propagation characteristics of mmWave, we propose a cooperative multiuser beamforming method for energy-efficient transmissions in mmWave distributed antenna systems. The RRUs first decide the local serving group separately and the BS makes an optimization globally with limited data exchange. From simulation results, compared to the state-of-the-art method, it is shown that higher energy efficiency can be realized by the proposed method for the multiuser mmWave distributed system. [ABSTRACT FROM AUTHOR]

In this paper, we study the impact of obstacles (such as buildings) in the radio propagation in the urban vehicular network's environment. The impact has been realized not only by the network-level performance metrics, but also by the application-level performance metrics. A majority of the existing works consider perfect physical layer, which ignores the impact of path loss and shadowing effect in radio propagation caused by the urban canyon. First, we show that ignoring the impact of obstacles in radio propagation provides very high superficial network-level performance. Second, under obstacle shadowing, we perform analytical analysis and Ns-3 based realistic urban vehicular simulation of current dedicated short-range communication based safety message broadcasting to study the achievable performance of application-level performance metrics. This study reveals the answer of the key question, whether the achieved network-level performance metric is good enough for the safety-critical applications under the acute attenuation in radio propagation in urban environment. Third, we propose opportunistic vehicle-assisted or dedicated road side unit-assisted network coded relaying for improving reliability at road intersection. Simulation results show that the proposed approach improves more than 65% reliability for delay sensitive and around 25% reliability for less delay sensitive applications at intersections. [ABSTRACT FROM AUTHOR]

Information dissemination in VANETs mainly focuses on, e.g., the propagation of cooperative awareness messages and decentralized environmental notification messages on the control channel. As vehicles advance toward higher automation levels, VANETs should support more complex traffic services, which generates the demand for the propagation of Internet Protocol (IP)-based information and service data in multichannel environment as specified by IEEE Standard for Wireless Access in Vehicular Environments (WAVE). Multisource propagation in the multichannel environments will incur multisource relay confliction (MRC) which leads to higher latency and lower information propagation speed (IPS). However, the problem of how to mitigate the impact of MRC and maintain high IPS has not been studied sufficiently. In this paper, we propose success probability based relay contention algorithm (SPRCA) for mitigating the impact of MRC under WAVE channel environments. SPRCA presents a vital metric, success probability, for each vehicle to determine whether to join the relay candidate set of certain source and execute relay contention algorithm. SPRCA explores both real time location information of vehicles and stochastic properties of vehicular distribution. We construct a theoretical model for analyzing the performance of SPRCA with a stochastic geometry-based approach and derive the properties of the performance of SPRCA. We further demonstrate the network performance and the practicality in dynamic VANETs of SPRCA through simulations with realistic traffic flow data. [ABSTRACT FROM AUTHOR]

Non-stationarity of vehicle-to-vehicle channels is one of the key elements that has to be taken into account for accurate channel modeling. The time-variance and its dual—the frequency selectivity—lead to non-stationarity. These can be assessed by both the temporal autocorrelation function and the Doppler spectrum, respectively. For fixed-to-mobile channels closed-form solutions for autocorrelation functions and Doppler spectra are well known. For vehicle-to-vehicle channels closed-form solutions exist, if uncorrelated double-bounce scattering is assumed. For time-variant, delay-dependent, correlated single-bounce scattering expressions are yet to be found. This contribution addresses the mentioned problem. Specifically, the proportionality between the Doppler probability density function (pdf) and Doppler power spectral density in time-varying scenarios for non-stationary, uncorrelated scattering is demonstrated. The latter also implies a proportionality between the characteristic function and the corresponding autocorrelation function; these functions are the Fourier transforms of the Doppler pdf and Doppler power spectral density, respectively. It is shown that time-varying characteristic functions and Doppler pdfs for general vehicle-to-vehicle scenarios can be derived in prolate spheroidal coordinates. The investigation of the Doppler frequency in these coordinates allows us to derive expressions of the maximum and minimum frequencies of the Doppler pdf in the vicinity of line-of-sight. Several vehicular scenarios of interest are investigated and closed-form solutions for the Doppler pdf and characteristic function are presented. An analysis of the results shows that the obtained expressions generalize well the known closed-form results for stationary channels. This further permits deriving some time-variant statistical channel parameters like the mean Doppler and Doppler spread. These parameters are particularly important when designing a Wiener filter or estimating propagation channel characteristics for highly time-variant vehicle-to-vehicle channels. [ABSTRACT FROM AUTHOR]

In ultra-dense small cell networks, spatial multiplexing gain is a challenge because of the different propagation conditions. The channels associated with different transmit–receive pairs can be highly correlated due to the: 1) high probability of line-of-sight (LOS) communication between user equipment (UE) and base station (BS) and 2) insufficient spacing between antenna elements at both UE and BS. In this paper, we propose a novel transmission technique titled Diversity Pulse Shaped Transmission (DPST), to enhance the throughput over the correlated multiple-input multiple-output (MIMO) channels in an ultra-dense small cell network. The fundamental of DPST is to shape transmit signals at adjacent antennas with distinct interpolating filters, introducing pulse shaping diversity. In DPST, each antenna transmits its own data stream with a relative deterministic time offset—which must be a fraction of the symbol period—with respect to the adjacent antenna. The delay is interpolated with the pulse shaped signal generating a virtual MIMO channel that benefits from increased diversity from the receiver perspective. To extract the diversity, the receiver must operate in an oversampled domain, and hence, a fractionally spaced equalizer (FSE) is proposed. The joint impact of DPST and FSE helps the receiver to sense a less correlated channel, eventually enhancing the UE's throughput. Moreover, in order to minimize the spatial correlation, we aim to optimize the deterministic fractional delay. Simulation results show that applying DPST to a correlated channel can approximately enhance the UE throughput by 1.93\times and 3.76\times in \text2\,\times\, \text2 and \text4\,\times \,\text4 MIMO systems, respectively. [ABSTRACT FROM AUTHOR]

With the aim of providing an overview of the propagation channels in a vehicle engine compartment, narrow-band (1–2 MHz) and broadband (500 MHz) channels in the frequency range from 2 GHz to 7.75 GHz were analyzed. To secure as much generality of analysis as possible, more than 500 propagation channels of seven types of automobiles were measured. The path loss and delay spread were analyzed in terms of distance and frequency. Models that take into account the interdependence of distance and frequency were used, considering that the object sizes in an engine compartment are comparable to the measurement wavelengths. The path-loss exponent for distance was about one below a break point of 450 mm and about three above the break point. The exponent for frequency was around one. The root-mean-square (RMS) delay spread increased as distance increased. Based on the obtained delay spread model, the propagation channel model was finally provided, which is a function of frequency and distance. Then, the channel model was validated by comparing delay spreads calculated from the generated channels and the measured channels. It is also noted that the channel dependence on the types of vehicle was not significant. [ABSTRACT FROM PUBLISHER]

With huge unlicensed bandwidth available in most parts of the world, millimeter-wave (mmWave) communications in the 60-GHz band has been considered as one of the most promising candidates to support multigigabit wireless services. Due to high propagation loss of mmWave channels, beamforming is likely to be adopted as an essential technique. Consequently, transmission in the 60-GHz band is inherently directional. Directivity enables concurrent transmissions (spatial reuse), which can be fully exploited to improve network capacity. In this paper, we propose a multipath multihop scheduling scheme, which is known as multipath multihop (MPMH), for mmWave wireless personal area networks (WPANs), where the traffic across links of low channel quality is transmitted through multiple paths of multiple hops to unleash the potential of spatial reuse. We formulate the problem of MPMH as a mixed-integer linear program (MILP), which is generally NP-hard. To enable the implementation of the multipath multihop transmission in practice, we propose a heuristic scheme including path selection, traffic distribution, and MPMH to efficiently solve the formulated problem. Finally, through extensive simulations, we demonstrate that MPMH achieves near-optimal network performance in terms of transmission delay and throughput and enhances network performance significantly, compared with existing protocols. [ABSTRACT FROM AUTHOR]

The effect of land cover is incorporated in the radio propagation prediction algorithm of Q-Rap. It is implemented by optimizing both the effective height of the land cover, hence affecting obstruction-loss calculations, and by adding terms to the basic transmission loss algorithm. A complete set of separate coefficients to these terms is determined for each land cover type. The optimization method improves the standard deviation of the error from 9.6 to 6.3 dB for measurements and predictions done at 390 MHz. This is an improvement of 3.3 dB over the original model that comprises the free-space loss equation with obstruction loss calculations for multiple knife edges. At this frequency, the correlation coefficient between the measured and predicted values improved from 79.5% to 85.6%. At 2145 MHz, the optimization method improves the standard deviation of the error from 16.2 to 8.6 dB, as well as the correlation coefficient between the measurements and predicted values from 56.2% to 70.5%. The use of the correlation coefficient between the measured and predicted signal values, in addition to the standard deviation of the error and mean error as criteria to be used when evaluating propagation prediction models, is also proposed in this paper. A basis for best practices in tuning propagation prediction algorithms in radio planning tools using semi-empirical models is presented. [ABSTRACT FROM PUBLISHER]

In this paper, a novel empirical propagation model for mobile radio links in a container terminal environment is presented. Measurement propagation research carried out in the Deepwater Container Terminal (DCT) in Gdańsk, Poland is described, and the investigated environment is characterized. The results of the statistical evaluation of the new model are discussed. In addition, statistical tuning of the Walfisch–Ikegami model for the investigated environment is presented. [ABSTRACT FROM PUBLISHER]

This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) in time-variant wireless propagation channels. We particularly consider the challenges of the IEEE 802.11p standard, which is the worldwide dominant system for vehicular communications. For historic reasons, 802.11p uses a pilot pattern that is identical to the pattern used in 802.11a, which was initially designed for the estimation of indoor channels with little or no time variations. Therefore, this pilot pattern violates the sampling theorem for channels with both large delay spread and large Doppler spread, as often occurs in vehicular communications. To remedy this problem, we design a robust iterative channel estimator based on a 2-D subspace spanned by generalized discrete prolate spheroidal sequences. Due to the tight subspace design, the iterative receiver is able to converge to the same bit error rate (BER) as a receiver with perfect channel knowledge. Furthermore, we propose a backward compatible modification of the 802.11p pilot pattern such that the number of iterations sufficient for convergence can be reduced by a factor of 2–3, strongly reducing implementation complexity. [ABSTRACT FROM PUBLISHER]

As small-scale fading is a spatial phenomenon, the movement of objects in the environment around static sensor nodes can induce significant fades. However, there have not been many works characterizing small-scale fading due to environmental factors for ground-surface wireless communications. We first measure the temporal fading characteristics experienced by antennas located just 1.5 cm above the surface of the ground due to wind-blown foliage or human movement in the environment for a narrowband channel in the 400-MHz frequency band. We then compare the extracted data to existing distributions and show that fading due to wind-blown foliage can be modeled as a Nakagami-m distribution, with wind speed and excess path-loss-dependent m shape factors. The \alpha-\mu distribution best characterizes the small-scale fading of a single human pedestrian, which is shown to have a repeatable pattern and can be up to 40 dB below the no-fading mean, whereas the Rician distribution, with an excess path-loss-dependent K-factor, can be used to characterize fading from multiple human pedestrians. We also report the second-order statistics of the average fade duration and the level crossing rate for fading caused by wind-blown foliage and multiple human pedestrians. Finally, we discuss the significance of the results on wireless sensor network protocol design and applications. [ABSTRACT FROM PUBLISHER]

Among the various approaches recently proposed for blind estimation of wideband multiple-input-multiple-output (MIMO) wireless channels, subspace-based algorithms are particularly attractive due to their good performance and simple structure. These algorithms primarily exploit the orthogonality of the noise and signal subspaces of the correlation matrix of the received signals to estimate the unknown channel coefficients. In practice, the correlation matrix is unknown and must be estimated through time averaging over multiple received samples. To this end, the unknown channel must remain time invariant through the averaging process, which may pose a serious problem in practical applications. In this paper, to relax this requirement, we propose a novel subspace-based blind channel-estimation algorithm with reduced time averaging, as obtained by exploiting the frequency correlation among adjacent subcarriers in MIMO orthogonal frequency-division multiplexing (OFDM) systems. Simulation results show that the proposed approach outperforms other previously proposed methods within a reasonable averaging time over a Third-Generation Partnership Project (3GPP) spatial channel model. [ABSTRACT FROM AUTHOR]

Land mobile satellite (LMS) channels at the L (1/2 GHz) and S (2/4 GHz) frequency bands are mainly affected by propagation effects due to the local environment of a mobile terminal, such as multipath, shadowing, and blockage. Future systems for mobile satellite services (MSS) will operate at higher frequency bands, such as Ku (12/14 GHz) and Ka (20/30 GHz), where the tropospheric propagation effects also play an important role. Experimental campaigns conducted so far for Ku/Ka-band LMS channels have not considered any possible correlation between the tropospheric and local environment propagation effects. However, recent experimental work has indicated that these fading effects are not independent. As a first analytical approach to this open problem, a novel statistical analysis is presented in this paper. Emphasis is put on Ku/Ka-band LMS channels whose fading events can be modeled by the Ricean distribution with a relatively high K-factor. A novel analytical relationship between the Ricean K-factor and the rain attenuation effects is derived, and based on them, an analytical statistical prediction model for the distribution of the Ricean K-factor is derived. Particular attention is paid to the rainfall spatial inhomogeneity, as well as to the different effects of the climatic area of interest (temperate versus tropical) on the Ricean K-factor statistics. Thus, the presented analysis considers both spatially correlated bivariate lognormal and gamma statistics for the accurate characterization of rain attenuation. The proposed models are flexible and incorporate the impact of several critical operational, climatic, and geometrical parameters of an LMS channel on its multipath behavior under rainfall conditions. Useful numerical results are provided, specific future planned work is outlined, and the need for further experimental verification data is also pointed out. [ABSTRACT FROM AUTHOR]

A novel coverage-prediction method for outdoor radio propagation based on the inversion theory is proposed here. Coverage prediction in a wireless cellular network is treated as an inverse problem instead of using high-precision geometric modeling. More precisely, the problem is solved by an inversion of the measured data under some a priori constraints, and the complicated propagation-prediction problem is reduced to solving a system of large-scale ill-condition equations. The effectiveness of the proposed method is demonstrated by using experiments under various radio environments in Guangdong, China. The prediction results are approximately consistent with independent checking samples, and the proposed strategy is compared with other existing approaches. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach to estimating multipath parameters such as time delays and attenuation factors for channel measurements using a vector network analyzer. In the proposed scheme, we introduce a coarse-and-fine time-delay-estimation scheme and attenuation-factor-estimation schemes. The coarse time-delay estimation employs a superresolution technique based on the generalized eigenvalues utilizing signal subspace eigenvectors (GEESE) algorithm, and the fine time-delay estimation is derived to exploit real-valued attenuation factors. For attenuation-factor estimation, we focus on the least squares estimator (LSE) and the simplified estimator (SE). Numerical results show that the proposed time-delay-estimation scheme outperforms the multiple-signal classification (MUSIC)-based time-delay-estimation scheme. Theoretical analysis and computer simulations are used in the comparisons of the LSE and the SE. [ABSTRACT FROM AUTHOR]

This paper presents a path-shadowing model for indoor populated environments that has been developed based on computer simulations. The propagation paths between the transmitting and receiving points in an empty rectangular space are determined using the ray-tracing method, in which moving quasi-human bodies that are modeled as cylinders with a finite height are generated in the space, and intersections of the paths with the bodies are counted. From the results, the shadowing probabilities, durations, and intervals are evaluated for each propagation path, and this shadowing process is characterized as a Markov process. This paper proposes a method that individually generates the shadowing effects on each propagation path. The measurement results of the path-shadowing characteristics using a 5.2-GHz high-resolution channel sounder are presented, and the validity of this model is confirmed. Similar measurement results using a photoelectric sensor are also presented to reinforce the channel-sounding measurement results. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic property of a tropical forested channel due to the weather effect on very high frequency (VHF) and ultrahigh frequency (UHF) radio-wave propagation. In this paper, continuous-wave (CW) envelope fading waveforms are recorded over a period of 59 s with static antennas. This paper focuses on the analysis of the combined effect of wind and rain, which is often encountered in a tropical forest. The induced temporal effects are discussed and compared with theoretical models. It is found that the distribution of temporal fading components resembles a Rician distribution function. Its Rician K factor gradually decreases as the strength of either wind or rain increases due to the movement of the forest components. [ABSTRACT FROM AUTHOR]

This paper presents a class of routing protocols called road-based using vehicular traffic (RBVT) routing, which outperforms existing routing protocols in city-based vehicular ad hoc networks (VANETs). RBVT protocols leverage real-time vehicular traffic information to create road-based paths consisting of successions of road intersections that have, with high probability, network connectivity among them. Geographical forwarding is used to transfer packets between intersections on the path, reducing the path's sensitivity to individual node movements. For dense networks with high contention, we optimize the forwarding using a distributed receiver-based election of next hops based on a multicriterion prioritization function that takes nonuniform radio propagation into account. We designed and implemented a reactive protocol RBVT-R and a proactive protocol RBVT-P and compared them with protocols representative of mobile ad hoc networks and VANETs. Simulation results in urban settings show that RBVT-R performs best in terms of average delivery rate, with up to a 40% increase compared with some existing protocols. In terms of average delay, RB VT-P performs best, with as much as an 85% decrease compared with the other protocols. [ABSTRACT FROM AUTHOR]

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input-multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area. [ABSTRACT FROM AUTHOR]

This paper proposes a stochastic multipath model that is useful for generating multiple-input-multiple-output (MIMO) channel matrices in time-variant environments. The multipath model is developed by first extracting the relevant multipath cluster characteristics from measured indoor channel data and subsequently capturing these characteristics in an autoregressive stochastic model. This model is then used to generate channel matrices whose space-time characteristics closely match those of realistic scenarios, particularly when birth and death of multipath clusters-are included in the stochastic representation. Computational examples reveal the applicability and the accuracy of the approach. While the current implementation is based on data taken assuming that propagation is confined to the horizontal plane, this paper also discusses the extension of the model to describe 3-D propagation, enabling its application to a wide range of physical scenarios and antenna characteristics. [ABSTRACT FROM AUTHOR]

Non-line-of-sight (NLOS) propagation degrades the performance of wireless location systems. Thus, developing algorithms that are robust to NLOS considerations is of great importance. Based on time-of-arrival (TOA) and angle-of-arrival (AOA) measurements, this paper introduces a new approach, which consists of incorporating the coordinates of dominant scatterers as unknowns in the location algorithm. It is assumed that the first arriving path signal at each base station (BS) experiences a single dominant scatterer, but the BSs are allowed to have different dominant scatterers. Locating the mobile station is accomplished by means of a nonlinear optimization procedure under nonlinear constraints. Two algorithms are proposed: The first algorithm assumes that hybrid TOA/AOA measurements are available at three BSs. In the second algorithm, the AOA is assumed to be available at the serving BS only. The performance of the proposed algorithms is assessed and compared with that of existing algorithms through extensive simulations. [ABSTRACT FROM AUTHOR]

This paper presents and analyzes the results of millimeter-wave 60-GHz frequency range propagation channel measurements that are performed in various indoor environments for continuous-route and direction-of-arrival (DOA) measurement campaigns. The statistical parameters of the propagation channel, such as the number of paths, the RMS delay spread, the path loss, and the shadowing, are inspected. Moreover, the interdependencies of different characteristics of the multipath channel are also investigated. A linear relationship between the number of paths and the delay spread is found, negative cross correlation between the shadow fading and the delay spread can be established, and an upper bound exponential model of the delay spread and the path loss is developed to estimate the worst case of the RMS delay spread at given path loss. Based on the DOA measurements that are carried out in a room [line of sight (LOS)] and in a corridor with both LOS and nonline-of-sight (NLOS) scenarios, radio-wave propagation mechanisms are studied. It is found that considering the direct wave and the first-order reflected waves from smooth surfaces is sufficient in the LOS cases. Transmission loss is very high; however, diffraction is found to be a significant propagation mechanism in NLOS propagation environments. The results can be used for the design of 60-GHz radio systems in short-range wireless applications [ABSTRACT FROM AUTHOR]

Inspired by recent promotions of wireless location services and applications, this paper develops a simple model for detecting a mobile caller location with low implementation complexity and promising accuracy. The model that is described in this paper employs the geometrical transformation method with single propagation delay measurement. Depending on the number of available surrounding base transceiver stations (BTS5), a set of the pseudodistances and pseudodistance differences is provided through the geometrical distances between the home and multiple foreign BTSs, which is called the geometrical transformation method. Accordingly, the mobile caller location can be detected using the circular location technique and the hyperbolic location technique. The major benefit of the proposed model is that during a call to detect the mobile caller's location, the use of geometrical transformation allows us to overcome the location handover problem. A forcing handover in a Global System for Mobile Communications (GSM) network or a three-way soft handover in a Universal Mobile Telecommunications System (UMTS) network, for example, occurs when detecting the location when a standard model that is based on the measurement of the propagation delay is utilized. Comparing the standard model with the proposed model, the former needs at least three propagation delays that were simultaneously measured from at least three BTSs, whereas the latter needs only a single propagation delay that was measured from the home BTS. Moreover, in the case where we do not have a priori information of a non-line-of-sight (NLOS) error, a deterministic parameter that is related to the propagation delay is defined. This parameter is shown as limited a priori information for calibrating the coarse resolution in the proposed location model, which is caused by the NLOS error. To have significant findings, we conduct a practical experiment in an urban environment based on a 1.8-GHz commercial cellular network. In the five-BTS case where the location error is less than 300 m, the probability of location error that the proposed model with a bit period of 1/2 achieved is greater than 0.85. Although the performance of the proposed location model does not satisfy the U.S. Federal Communications Commission Enhanced 911 (FCC E-911) requirements, it is a good solution for the deployment of wireless location services and applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of a measurement campaign conducted in the winter of 2002 around the city of Munich in southern Germany. The primary goal was to evaluate the link performance of the land mobile satellite channel at Ku-band and to characterize the temporal behavior of the channel to help in the evaluation of different fade mitigation techniques for future mobile satellite systems that aim at employing this frequency band. To achieve this objective, first- and second-order channel statistics will be presented, the outage probability of the channel analyzed, and a Markov-chain-based narrowband channel model proposed. [ABSTRACT FROM AUTHOR]

Tests for the wide-sense stationarity (WSS) of multivariate random processes are developed and applied to measured multiple-input--multiple-output (MIMO) radio channel responses. Evolutionary spectral density functions are used to estimate the time-dependent power spectral density, and analysis of variance procedures are applied to determine whether the first and second moments of the data series exhibit statistically significant changes over short intervals. It is found that while the assumption of WSS is met in 40%-70% of half-second intervals for a single element at the transmitter and receiver, only 2%-12% of intervals with two elements at the transmitter and receiver are jointly WSS; furthermore, the occurrence of non-WSS intervals is not dependent on the antenna separation. The analyses also show that WSS intervals are interspersed with long non-WSS intervals. [ABSTRACT FROM AUTHOR]

Propagation path losses affecting intervehicle communication (IVC) at 60 GHz are presented. In order to examine the radio-propagation characteristics in the IVC system, in the first stage of our investigation, we have carried out propagation tests between two vehicles communicating in a line-of-sight (LOS) situation at fixed positions on a smooth surface paved with asphalt, which is the normal communication condition. Furthermore, the non-LOS (NLOS) situation with up to three intermediate vehicles, which can cause an obstruction, has been conducted. To construct path-loss models in NLOS cases, the uniform theory of diffraction technique was applied to the calculation of waves propagating through the intermediate vehicles. The propagation path models were derived from the measured results. In the second stage, a path-loss prediction formula was derived by statistically processing the data that had been calculated using the propagation path model. The propagation tests between the vehicles in motion confirm that the path-loss prediction formula is very useful when the communicating vehicles are moving, and it is therefore suitable for designing the cells that form the IVC. [ABSTRACT FROM AUTHOR]

In this paper, the validity of Recommendation ITU-R P.1546 in a short-range terrestrial environment is analyzed. Its three versions (P.1546, P.1546-1, and P.1546-2) are compared against simple models and evaluated using measurement results that were obtained by utilizing the pilot signal of a commercial code-division multiple-access mobile telephone network. Measurement results show that P.1546-2, on average, underestimates the field strength by more than 10 dB for typical Australian rural areas. However, it improves the error standard deviation compared to previous versions. The causes of these effects and the suggestions for further development of the Recommendation are discussed and evaluated. [ABSTRACT FROM AUTHOR]

A propagation model is needed to evaluate the performance of handover in mobile-communication systems. Generally, the received signal level from base stations (BSs) is calculated assuming path loss, and a lognormal (shadow)-fading model is used for evaluating intercell handover. The lognormal fading was assumed to be uncorrelated between cells. However, since the correlation between sectors is not clarified, an appropriate shadow-fading model to evaluate intersector handover has not yet been proposed. To obtain shadow-fading characteristics between neighboring sectors, the change in signal level and the direction of arrival of incoming waves at a BS must be clarified. This paper proposes a simple model of incoming waves to evaluate the performance of intersector handover. The validity of the proposed model is confirmed by comparing the difference between signal levels in BS sectors that are calculated using the proposed model and the measured power azimuth spectrum. [ABSTRACT FROM AUTHOR]

This paper covers some of the work carried out in the planning of the Global System for Mobile Communication for Railway (GSM-R) of the tunnels on the new high-speed trains in Spain. Solutions based on distributed antenna systems have been tested by installing several 900-MHz transmitters inside and outside of a 4000-m tunnel and measuring the propagation indifferent conditions. The measurements have been used to model the effects of tunnel propagation, including curves, trains passing from the outside to the inside, and the effect of two trains passing inside the tunnel. All cases have been tested by comparing solutions using isofrequency and multifrequency distributed transmitters inside the tunnel. The improvements of signal-to-noise ratio and the reduction of the blocking effects of two trains passing have demonstrated the advantages of using isofrequency distributed antenna systems in tunnels. Finally, a complete propagation model combining both modal analysis and ray tracing has been applied to predict the propagation loss inside and outside these tunnels, and results have been compared with the measurements. The model has proven to be very useful for radio planning in new railway networks. [ABSTRACT FROM AUTHOR]

Fast full-wave computation of fields is the main reason for a radio system planner to apply the parabolic-equation method (PEM) for radio-coverage prediction. In this paper, the capability of PEM for the determination of backward electromagnetic-field scattering by single and multiple knife edges is investigated. For the wave equation, a suitable solution is considered. Contrary to the available formulations for the PEM, the proposed method includes a backward-propagating term. For both the forward and backward terms, the split-step algorithm is employed. Similar to the terrain-masking method, the effect of edges is exerted by the Fresnel-Kirchhof approximation into the forward-propagating wave. For the backward field, a similar algorithm is derived. Then, an iterative marching algorithm is developed for modeling radio wave propagation over multiple knife edges. Numerical results are compared with those of Uniform Theory of Diffraction (UTD) and finite-difference time-domain methods for the single-knife-edge problem. In addition, the effect of the backward-propagating field on radio wave propagation is investigated. The effect of edge locations and heights on the backward scattered field and number of computational iterations is studied. It is seen that, for the single knife edge, the backward scattered field depends on the height and location of the edge. The intensity of the backscattered field is a monotonic increasing function of the edge height. In addition, by increasing the edge height, the beam width of the backward scattered field increases. In ranges far from the knife edge in front of it, the field spreads, and its amplitude decreases. For multiple knife edges, it is seen that, in addition to the single back- ward scattered field, radio-wave-propagation modeling requires multiple forward-backward terms between successive edges. The geometry of the problem determines the required number of terms for sufficient accuracy. [ABSTRACT FROM AUTHOR]

A simplified analytical model is presented to predict the specific attenuation for propagation through a tree canopy in a residential environment for frequencies of up to 2 GHz. In this approach, the canopy of a tree is modeled as an ensemble of leaves and branches all having prescribed location and orientation statistics. The Foldy-Lax discrete scattering theory is used to find the specific attenuation of a tree associated with the mean field. Explicit formulas are presented to calculate the specific attenuation of a tree canopy. It is shown that the specific attenuation of a tree canopy depends on the frequency, polarization, electrical and geometrical characteristics of branches and leaves, biophysical parameters of a tree, and statistical distribution of branches and leaves in reference to the angle of incidence of the plane wave. It is also shown that for deciduous trees, as opposed to coniferous trees, the inclination angle distribution of the branches is more vertical, producing a higher specific attenuation for the vertical-polarization incident wave than for the horizontal-polarization incident wave. [ABSTRACT FROM AUTHOR]

In this paper, we address methods of mitigating one of the major issues affecting wireless location accuracy in land mobile terrestrial environments: nonline-of-sight (NLOS) propagation. In order to improve location accuracy under such conditions, we propose a novel methodology for NLOS environments based on the use of scattering models to classify propagation environments. The scattering models allow modeling of the NLOS error so that the NLOS effect can be incorporated into a location algorithm. Through the use of the scattering models, we develop three novel location techniques based on the statistics of measured ranges via moment matching, the expectation maximization algorithm, and a Bayesian algorithm. Simulation results and discussion are given to illustrate the performance in typical NLOS environments. The results show that the algorithms provide improvement over traditional location algorithms. [ABSTRACT FROM AUTHOR]

This paper concerns the measurement-based comparison of urban microcellular mobile radio channel characteristics at 1.9 GHz and a higher frequency, i.e., 5.8 GHz, where future wireless systems could operate. Characteristics that are reported include transmission loss, root-mean-square delay spread, frequency correlation, and envelope fading statistics. Conclusions are drawn concerning whether significant differences in the performance of mobile radio links operating under the same signal-to-noise ratio conditions in the two bands would be expected in the area where the measurements were made. [ABSTRACT FROM AUTHOR]

This paper introduces a fading model, which explores the nonlinearity of the propagation medium. It derives the corresponding fading distribution—the α-μ distribution-which is in fact a rewritten form of the Stacy (generalized Gamma) distribution. This distribution includes several others such as Gamma (and its discrete versions Erlang and central Chi-squared), Nakagami-m (and its discrete version Chi), exponential, Weibull, one-sided Gaussian, and Rayleigh. Based on the fading model proposed here, higher order statistics are obtained in closed-form formulas. More specifically, level-crossing rate, average fade duration, and joint statistics (joint probability density function, general joint moments, and general correlation coefficient) of correlated α-μ variates are obtained, and they are directly related to the physical fading parameters. [ABSTRACT FROM AUTHOR]

In this paper, an effective technique is proposed for locating a mobile station's position when the range measurements are corrupted by non-line-of-sight (NLOS) errors. By linearizing the inequality of range models incorporating NLOS errors and adding loose variables, the method first acquires a preliminary estimation that relies on an initial value. After addressing the effect of linearization error and analyzing the preliminary estimation, a noniterative estimator that does not need an initial value is deduced. The method does not require knowledge of NLOS error statistics. Simulation results indicate that the proposed algorithm can restrain the NLOS errors and improve location accuracy. [ABSTRACT FROM AUTHOR]

Stochastic properties of the binary channel that describe the successes and failures of the transmission of a modulated signal over a time-correlated flat-fading channel are considered for investigation. This analysis is employed to develop κth-order Markov models for such a bunt channel. The order of the Markov model that generates accurate analytical models is estimated for a broad range of fading environments. The parameterization and accuracy of an important class of hidden Markov models, known as the Gilbert-Elliott channel (GEC), are also investigated. Fading rates are identified in which the κth-order Markov model and the GEC model approximate the fading channel with similar accuracy. The latter model is useful for approximating slowly fading processes, since it provides a more compact parameterization. [ABSTRACT FROM AUTHOR]

This paper describes measurements of the outdoor-to-indoor channel conducted in the Seattle, WA, and San Francisco Bay, CA, areas at 2.5 GHz. With broad-band wireless access, in mind, an empirical model similar to the COST 231 model is built from the measured data. The impacts of wall material, angle of incidence, and receive height are noted and introduced in the modeling approach. [ABSTRACT FROM AUTHOR]

This paper presents a model for the scattering of radiowaves from the canopy of a single tree. The canopy is modeled as a cylindrical volume containing randomly distributed and oriented cylinders, representing the branches, and thin disks, representing the leaves. A simple expression for the incoherent scattered field outside the canopy is obtained using Twersky's multiple scattering theory. This expression is shown to agree well with results of scattering measurements on a live tree typical of those found in urban environments. The scattering model can be readily incorporated in ray-based propagation prediction tools that assist the planning of microcellular radio networks. This involves the use of so-called tree-scattered rays, which interact at the tree centers. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in prediction accuracy that can be achieved in realistic urban microcellular scenarios by taking into account the scatter from trees. [ABSTRACT FROM AUTHOR]

When constructing a propagation channel model, a substitute is often created by giving an arbitrary shape or form to scatterer distributions based on its intuitive appeal for a certain radio environment. However, such models do not necessarily represent the actual propagation process and may yield inaccurate results. The main objective of this paper is to provide an insight into the underlying relationship between geometric models and the particular physical propagation process they represent. The workhorse is the semi-geometrically based statistical (SGBS) model and the two heuristic rules. The SGBS model defines the distribution of dominant scatterers contributing to the last reradiation of multipath components to the base station. The earlier multiple-reflection process is modeled using the composite Nakagami/log-normal probability density function. Two parameters are then introduced; namely, the effective path length and the normalized space-dependent intensity measure. Using these two metrics, two heuristic rules are subsequently proposed to provide the missing Link between the canonical models and the physical channel. The rules are then applied to revisit several widely used geometric models in macro- and microcellular environments. As a working example, the Gaussian scatterer density model is further extended using such an approach. Important channel parameters such as power azimuthal spectrum, power delay spectrum, and azimuthal and delay spreads are then calculated and compared with simulation results. [ABSTRACT FROM AUTHOR]

Presents an effective location algorithm, which considers non-line-of-sight propagation. Comparison of the algorithm with other methods; Importance of location algorithm in land cellular wireless location systems; Use of a number of receivers distributed separately.

Proposes a model from observations that propagation in urban environments may occur owing to different mechanisms. Overview on the statistical behavior of received field strength in the vicinity of the transmitter; Description on the two-plane model of urban propagation.

Proposes a novel technique for measuring the angular distribution and cross-polarization ratio of the incident power at the mobile station in different types of propagation environments. Calculation of the mean effective gain (MEG) of an antenna; Description on the experiments; Discussion on the statistical distribution of incident waves; MEG comparison of handset antennas.

Investigates the correlation properties of shadow fading as a function of angle between two personal communication services-based stations over urban, light urban and suburban terrain. Analysis of interference; Relationship between shadow fading and angles; Information on distance correlation instruments.

Studies the possible application of adaptive antennas in microcellular operational environments with the help of a site-specific ray-tracing propagation model. Explanation on the radio channel propagation model, adaptive antenna model and the employed algorithms; Results for the radio channel characteristics in small-cell environments; Discussion on the performance of an adaptive antenna for the scenarios of one and two desired users.