629 research outputs found
The Distribution of Minimum of Ratios of Two Random Variables and Its Application in Analysis of Multi-hop Systems
The distributions of random variables are of interest in many areas of science. In this paper, ascertaining on the importance of multi-hop transmission in contemporary wireless communications systems operating over fading channels in the presence of cochannel interference, the probability density functions (PDFs) of minimum of arbitrary number of ratios of Rayleigh, Rician, Nakagami-m, Weibull and α-µ random variables are derived. These expressions can be used to study the outage probability as an important multi-hop system performance measure. Various numerical results complement the proposed mathematical analysis
Experimental characterisation of the off-body wireless channel at 2.4 GHz for dairy cows in barns and pastures
status: publishe
In-vehicle channel sounding in the 5.8-GHz band
The article reports vehicular channel measurements in the frequency band of 5.8 GHz for IEEE 802.11p standard. Experiments for both intra-vehicle and out-of-vehicle environments were carried out. It was observed that the large-scale variations (LSVs) of the power delay profiles (PDPs) can be best described through a two-term exponential decay model, in contrast to the linear models which are suitable for popular ultra-wideband (UWB) systems operating in the 3- to 11-GHz band. The small-scale variations (SSVs) are separated from the PDP by subtracting the LSV and characterized utilizing logistic, generalized extreme value (GEV), and normal distributions. Two sample Kolmogorov-Smirnov (K-S) tests validated that the logistic distribution is optimal for in-car, whereas the GEV distribution serves better for out-of-car measurements. For each measurement, the LSV trend was used to construct the respective channel impulse response (CIR), i.e., tap gains at different delays. Next, the CIR information is fed to an 802.11p simulation testbed to evaluate the bit error rate (BER) performance, following a Rician model. The BER results strongly vouch for the suitability of the protocol for in-car as well as out-of-car wireless applications in stationary environments.The article reports vehicular channel measurements in the frequency band of 5.8 GHz for IEEE 802.11p standard. Experiments for both intra-vehicle and out-of-vehicle environments were carried out. It was observed that the large-scale variations (LSVs) of the power delay profiles (PDPs) can be best described through a two-term exponential decay model, in contrast to the linear models which are suitable for popular ultra-wideband (UWB) systems operating in the 3- to 11-GHz band. The small-scale variations (SSVs) are separated from the PDP by subtracting the LSV and characterized utilizing logistic, generalized extreme value (GEV), and normal distributions. Two sample Kolmogorov-Smirnov (K-S) tests validated that the logistic distribution is optimal for in-car, whereas the GEV distribution serves better for out-of-car measurements. For each measurement, the LSV trend was used to construct the respective channel impulse response (CIR), i.e., tap gains at different delays. Next, the CIR information is fed to an 802.11p simulation testbed to evaluate the bit error rate (BER) performance, following a Rician model. The BER results strongly vouch for the suitability of the protocol for in-car as well as out-of-car wireless applications in stationary environments
MGF Approach to the Analysis of Generalized Two-Ray Fading Models
We analyze a class of Generalized Two-Ray (GTR) fading channels that consist
of two line of sight (LOS) components with random phase plus a diffuse
component. We derive a closed form expression for the moment generating
function (MGF) of the signal-to-noise ratio (SNR) for this model, which greatly
simplifies its analysis. This expression arises from the observation that the
GTR fading model can be expressed in terms of a conditional underlying Rician
distribution. We illustrate the approach to derive simple expressions for
statistics and performance metrics of interest such as the amount of fading,
the level crossing rate, the symbol error rate, and the ergodic capacity in GTR
fading channels. We also show that the effect of considering a more general
distribution for the phase difference between the LOS components has an impact
on the average SNR.Comment: 14 pages, 8 Figures and 2 Tables. This work has been accepted for
publication at IEEE Transactions on Wireless Communications. Copyright (c)
2014 IEEE. Personal use of this material is permitted. However, permission to
use this material for any other purposes must be obtained from the IEEE by
sending a request to [email protected]
Ultra Reliable UAV Communication Using Altitude and Cooperation Diversity
The use of unmanned aerial vehicles (UAVs) that serve as aerial base stations
is expected to become predominant in the next decade. However, in order for
this technology to unfold its full potential it is necessary to develop a
fundamental understanding of the distinctive features of air-to-ground (A2G)
links. As a contribution in this direction, this paper proposes a generic
framework for the analysis and optimization of the A2G systems. In contrast to
the existing literature, this framework incorporates both height-dependent path
loss exponent and small-scale fading, and unifies a widely used
ground-to-ground channel model with that of A2G for analysis of large-scale
wireless networks. We derive analytical expressions for the optimal UAV height
that minimizes the outage probability of a given A2G link. Moreover, our
framework allows us to derive a height-dependent closed-form expression and a
tight lower bound for the outage probability of an \textit{A2G cooperative
communication} network. Our results suggest that the optimal location of the
UAVs with respect to the ground nodes does not change by the inclusion of
ground relays. This enables interesting insights in the deployment of future
A2G networks, as the system reliability could be adjusted dynamically by adding
relaying nodes without requiring changes in the position of the corresponding
UAVs
A Deterministic Equivalent for the Analysis of Non-Gaussian Correlated MIMO Multiple Access Channels
Large dimensional random matrix theory (RMT) has provided an efficient
analytical tool to understand multiple-input multiple-output (MIMO) channels
and to aid the design of MIMO wireless communication systems. However, previous
studies based on large dimensional RMT rely on the assumption that the transmit
correlation matrix is diagonal or the propagation channel matrix is Gaussian.
There is an increasing interest in the channels where the transmit correlation
matrices are generally nonnegative definite and the channel entries are
non-Gaussian. This class of channel models appears in several applications in
MIMO multiple access systems, such as small cell networks (SCNs). To address
these problems, we use the generalized Lindeberg principle to show that the
Stieltjes transforms of this class of random matrices with Gaussian or
non-Gaussian independent entries coincide in the large dimensional regime. This
result permits to derive the deterministic equivalents (e.g., the Stieltjes
transform and the ergodic mutual information) for non-Gaussian MIMO channels
from the known results developed for Gaussian MIMO channels, and is of great
importance in characterizing the spectral efficiency of SCNs.Comment: This paper is the revision of the original manuscript titled "A
Deterministic Equivalent for the Analysis of Small Cell Networks". We have
revised the original manuscript and reworked on the organization to improve
the presentation as well as readabilit
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