David G. Michelson

Moment-method estimation of the Ricean K-factor

In many radio propagation environments, the time-varying envelope of the received signal can be statistically described by a Ricean distribution. Traditional methods for estimating the Ricean K-factor from measured power versus time are relatively cumbersome and time consuming. We describe a simple and rapid approach wherein the K-factor is an exact function of moments estimated from time-series data. Comparisons with empirical distributions for fixed wireless paths validate the method.

Ricean

Fixed wireless channels in suburban macrocells are subject to fading due to scattering by moving objects such as windblown trees and foliage in the environment. When, as is often the case, the fading follows a Ricean distribution, the first-order statistics of fading are completely described by the corresponding average path gain and Ricean K-factor. Because such fading has important implications for the design of both narrow-band and wideband multipoint communication systems that are deployed in such environments, it must be well characterized. We conducted a set of 1.9-GHz experiments in suburban macrocell environments to generate a collective database from which we could construct a simple model for the probability distribution of K as experienced by fixed wireless users. Specifically, we find K to be lognormal, with the median being a simple function of season, antenna height, antenna beamwidth, and distance and with a standard deviation of 8 dB. We also present plausible physical arguments to explain these observations, elaborate on the variability of K with time, frequency, and location, and show the strong influence of wind conditions on K.

K

Mining and mineral exploration play important roles in the global economy. In mining operations, communication systems play vital roles in ensuring personnel safety, enhancing operational efficiency and process optimization. Over the period 1920-2012, this article surveys the evolution of wireless communications in underground mines, the developments of the underlying technology, and progress in understanding and modeling the underground wireless propagation channel. Current and future trends in technology, applications and propagation modeling are also identified. About ninety relevant references have been reviewed that consider: 1) the emergence of technology and applications, 2) analytical, numerical and measurement-based propagation modeling techniques, and 3) implications of the physical environment, antenna placement and radiation characteristics on wireless communication system design. Affected systems include narrowband, wideband/ultra-wideband (UWB) and multiple-antenna systems. The paper concludes by identifying open areas of research.

-Factors in Narrow-Band Fixed Wireless Channels: Theory, Experiments, and Statistical Models

Past efforts to develop measurement-based models of the UWB propagation channel have focused on residential, office, and industrial environments. However, with its confined volume and cylindrical structure, the geometry of the passenger cabin of a jet aircraft is fundamentally different from those environments considered previously. Here, we characterize large-scale aspects of UWB propagation within the passenger cabin of a typical mid-size airliner. Our measurement database consists of hundreds of frequency responses over the range 3.0 - 10.6 GHz that we collected aboard a Boeing 737-200 aircraft. The data were collected in a point-to-multipoint configuration in which a biconical UWB transmitting antenna was mounted at one of three locations near the cabin ceiling and an identical receiving antenna was mounted at headrest, armrest, and footrest level at over 50 locations throughout the cabin. We have accounted for the effects of human presence by collecting this data with the cabin empty, with passengers occupying half of the seats, and with passengers occupying virtually all of the seats. Our initial data reduction efforts have focused on the manner in which human presence and/or receiving antenna mounting location affects five large scale aspects of UWB propagation, i.e., those that affect coverage and reliability: (1) the distance dependence of path loss, (2) the frequency dependence of path loss, (3) the ratio of the energy in the line-of-sight component to the scattered components of the channel impulse response, (4) the RMS delay spread, and (5) the locations and distribution of the poles of the corresponding autoregressive frequency domain model.

A Survey of Wireless Communications and Propagation Modeling in Underground Mines

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.

UWB Radiowave Propagation within the Passenger Cabin of a Boeing 737-200 Aircraft

A conventional trihedral corner reflector can be modified to present either a twist-polarizing or a circularly polarizing response by adding conducting fins of rectangular corrugations of prescribed dimensions and orientation to one of its interior surfaces. Since the modified reflector retains most of the mechanical ruggedness and ease of manufacture of the original, it is suitable for deployment in the field for extended periods as required in radar navigation and remote sensing applications. For most directions of incidence the response of the reflector is dominated by triple-bounce reflections from the interior and is a function of the size and shape of the reflecting panels, the dimensions of the corrugations, and the orientation of the reflector with respect to the radar. Experimental results show that prototype twist-polarizing and circularly polarizing reflectors respond as predicted. >

Effect of Human Presence on UWB Radiowave Propagation Within the Passenger Cabin of a Midsize Airliner

With its confined volume, cylindrical structure and high density of seating, the passenger cabin of a typical midsize airliner is significantly different from the residential, office, outdoor and industrial environments previously considered by IEEE 802.15.4a. We have characterized the shape of the ultrawideband (UWB) channel impulse response (CIR) and the fading statistics experienced by individual multipath components (MPCs) within that environment based upon 3300 complex frequency responses that we measured over the range 3.1-10.6 GHz at various locations aboard a Boeing 737-200 aircraft. We found that: (1) the shape of the CIR generally follows IEEE 802.15.4as dense single-cluster model, but with negligible rise time if the link is line-of-sight, (2) both the mean and variance of the exponential decay constant tend to increase with transmitter-receiver separation and also as the receiving antenna drops from the headrest to the footrest of the passenger seats, and (3) small-scale fading of individual MPCs at each measurement location within the aircraft tends to follow a Nakagami distribution with a lognormally-distributed m-parameter that has a mean value of 0.2 dB and a standard deviation of 1.1 dB. We have modified IEEE 802.15.4as CIR simulator to generate responses similar to those seen in the cabin.

Depolarizing trihedral corner reflectors for radar navigation and remote sensing

In this paper, we propose a received signal strength indication-based distributed Bayesian localization algorithm based on message passing to solve the approximate inference problem. The algorithm is designed for precision agriculture applications, such as pest management and pH sensing in large farms, where greater power efficiency besides communication and computational scalability is needed but location accuracy requirements are less demanding. Communication overhead, which is a key limitation of popular non-Bayesian and Bayesian distributed techniques, is avoided by a message passing schedule, in which outgoing message by each node does not depend on the destination node, and therefore is a fixed size. Fast convergence is achieved by: 1) eliminating the setup phase linked with spanning tree construction, which is frequent in belief propagation schemes and 2) the parallel nature of the updates, since no message needs to be exchanged among nodes during each update, which is called the coupled variables phenomenon in non-Bayesian techniques and accounts for a significant amount of communication overhead. These features make the proposed algorithm highly compatible with realistic wireless sensor network (WSN) deployments, e.g., ZigBee, that are based upon the ad hoc on-demand distance vector, where route request and route reply packets are flooded in the network during route discovery phase.

Characterization of UWB Channel Impulse Responses Within the Passenger Cabin of a Boeing 737-200 Aircraft

In this article, we give an overview of recent research on propagation properties in high-speed railways (HSRs). The channel fading in HSRs is a big challenge for wireless access. It is essential to understand the channel-fading behavior before the system design. The novel results of propagation and channel models are presented. The details of channel characteristics, such as path loss, shadow fading, and Ricean K- factor, are discussed in each scenario. A comprehensive picture of propagation and channel-modeling research in railways is shown.

RSSI-Based Distributed Self-Localization for Wireless Sensor Networks Used in Precision Agriculture

The tendency for the multipath components (MPCs) in wideband channel impulse responses (CIRs) to appear in clusters that are characterized by their own arrival and decay rates was first observed over twenty years ago by Saleh and Valenzuela. Cluster identification is thus an obvious and essential first step in the channel modeling process. However, despite the tremendous effort that has been applied to ultra wideband (UWB) channel modeling by groups such as IEEE 802.15.3a and 802.15.4a in recent years, clusters are still usually identified through time-consuming manual techniques that rely on subjective assessment by the analyst. This presents a significant limitation to development of channel models applicable to new environments. Our algorithm for automated identification of clusters in UWB CIRs seeks to overcome these limitations by making cluster identification less subjective and less time consuming. The starting point for the algorithm is expression of the UWB power delay profile (PDP) on a semi-logarithmic scale so that exponential decay profiles will be displayed as straight lines with constant slopes. After the most significant MPCs have been identified by searching for local maxima within the PDP, an iterative procedure is used to determine the combination of straight lines that best fit these MPCs and thereby not exceed a threshold for RMS error. The number of clusters that are required is defined by number of straight lines while the slopes of the lines define the cluster decay rate. By assuming that incrementing the number of clusters used to represent a CIR will always involve subdividing an existing cluster, we reduce the number of combinations dramatically (and make the algorithm tractable). Cluster identification trials conducted using UWB CIRs generated using a simulation code developed by the IEEE 802.15.4a channel modeling committee have confirmed the validity of our approach.