179,936 research outputs found
A Tractable Product Channel Model for Line-of-Sight Scenarios
We present a general and tractable fading model for line-of-sight (LOS)
scenarios, which is based on the product of two independent and non-identically
distributed - shadowed random variables. Simple closed-form
expressions for the probability density function, cumulative distribution
function and moment-generating function are derived, which are as tractable as
the corresponding expressions derived from a product of Nakagami- random
variables. This model simplifies the challenging characterization of LOS
product channels, as well as combinations of LOS channels with non-LOS ones. We
leverage these results to analyze performance measures of interest in the
contexts of wireless powered and backscatter communications, where both forward
and reverse links are inherently of LOS nature, as well as in device-to-device
communications subject to composite fading. In these contexts, the model shows
a higher flexibility when fitting field measurements with respect to
conventional approaches based on product distributions with deterministic LOS,
together with a more complete physical interpretation of the underlying
propagation characteristics.Comment: This work has been submitted to the IEEE for possible publication.
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Energy efficiency of some non-cooperative, cooperative and hybrid communication schemes in multi-relay WSNs
In this paper we analyze the energy efficiency of single-hop, multi-hop, cooperative selective decode-and-forward, cooperative incremental decode-and-forward, and even the combination of cooperative and non-cooperative schemes, in wireless sensor networks composed of several nodes. We assume that, as the sensor nodes can experience either non line-of-sight or some line-of-sight conditions, the Nakagami-m fading distribution is used to model the wireless environment. The energy efficiency analysis is constrained by a target outage probability and an end-to-end throughput. Our results show that in most scenarios cooperative incremental schemes are more energy efficient than the other methods
Indoor off-body wireless communication: static beamforming versus space-time coding
The performance of beamforming versus space-time coding using a body-worn textile antenna array is experimentally evaluated for an indoor environment, where a walking rescue worker transmits data in the 2.45 GHz ISM band, relying on a vertical textile four-antenna array integrated into his garment. The two transmission scenarios considered are static beamforming at low-elevation angles and space-time code based transmit diversity. Signals are received by a base station equipped with a horizontal array of four dipole antennas providing spatial receive diversity through maximum-ratio combining. Signal-to-noise ratios, bit error rate characteristics, and signal correlation properties are assessed for both off-body transmission scenarios. Without receiver diversity, the performance of space-time coding is generally better. In case of fourth-order receiver diversity, beamforming is superior in line-of-sight conditions. For non-line-of-sight propagation, the space-time codes perform better as soon as bit error rates are low enough for a reliable data link
Passive Scene Reconstruction in Non-line-of-sight Scenarios
Locating and identifying hidden objects can prove critical in applications ranging from military reconnaissance to emergency rescue. Although non-line-of-sight (NLOS) reconstruction and imaging have received much attention recently, state-of-the-art methods often use coherent sources (lasers) or require control of the scene. This dissertation focuses on passive NLOS scene reconstruction using the light reflected off a diffusive wall. No control over the light illuminating the scene is assumed, and the method is compatible with the partially coherent fields ubiquitous in both indoor and outdoor environments. In order to counteract the detrimental effects of the wall, rather than measuring the 2-dimensional intensity of the reflected light, we exploit the full 4-dimensional spatial coherence function to reconstruct the scene. As a step towards the NLOS problem, we first consider the line-of-sight (LOS) problem. Numerical simulations using Fresnel propagation operators show that our forward model has good agreement with experimental results. We show that numerically back-propagating the measured coherence function enables a visual estimation of the objects\u27 sizes and locations. To facilitate efficient, systematic and explicit detection of object parameters in the inverse problem, we propose a closed-form approximation of the propagated coherence function. Using this analytic solution we formulate a minimum residue optimization problem which is solved using a gradient descent algorithm. Then, for the NLOS problem, we derive an analytic model based on experimentally-verified scattering models. This model is used to study the information retained in the coherence function after the field interacts with the wall, and this insight is used to classify and estimate simple objects. Finally, we consider imaging in more complicated settings with larger objects. We formulate a multi-criteria convex optimization problem, which fuses the reflected field\u27s intensity and spatial coherence information at different scales, along with an algorithm to efficiently solve the proposed problem
Antenna and Propagation Considerations for Amateur UAV Monitoring
The broad application spectrum of unmanned aerial vehicles is making them one of the most promising technologies of Internet of Things era. Proactive prevention for public safety threats is one of the key areas with vast potential of surveillance and monitoring drones. Antennas play a vital role in such applications to establish reliable communication in these scenarios. This paper considers line-of-sight and non-line-of-sight threat scenarios with the perspective of antennas and electromagnetic wave propagation
A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations
The vehicle-to-vehicle (V2V) propagation channel has significant implications
on the design and performance of novel communication protocols for vehicular ad
hoc networks (VANETs). Extensive research efforts have been made to develop V2V
channel models to be implemented in advanced VANET system simulators for
performance evaluation. The impact of shadowing caused by other vehicles has,
however, largely been neglected in most of the models, as well as in the system
simulations. In this paper we present a shadow fading model targeting system
simulations based on real measurements performed in urban and highway
scenarios. The measurement data is separated into three categories,
line-of-sight (LOS), obstructed line-of-sight (OLOS) by vehicles, and non
line-of-sight due to buildings, with the help of video information recorded
during the measurements. It is observed that vehicles obstructing the LOS
induce an additional average attenuation of about 10 dB in the received signal
power. An approach to incorporate the LOS/OLOS model into existing VANET
simulators is also provided. Finally, system level VANET simulation results are
presented, showing the difference between the LOS/OLOS model and a channel
model based on Nakagami-m fading.Comment: 10 pages, 12 figures, submitted to Hindawi International Journal of
Antennas and Propagatio
Directional analysis of measured 60 GHz indoor radio channels using SAGE
Abstract in Undetermined Directional properties of the radio channel are of high importance for the development of reliable wireless systems operating in the 60 GHz frequency band. Using transfer functions measured from 61 to 65 GHz in a conference room we have extracted estimates of the multi-path component parameters using the SAGE algorithm. In the paper we compare results for line-of-sight (LOS) scenarios and the corresponding non-line-of-sight (NLOS) scenarios and present values of the direction spread at the Tx and the Rx
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