Kevin Paulson - Academia.edu (original) (raw)

Papers by Kevin Paulson

Radio Science, 2010

1] Studies have shown that climate change is leading to an increase in the incidence of heavy rai... more 1] Studies have shown that climate change is leading to an increase in the incidence of heavy rain in the United Kingdom, particularly over winter. The major interest has been on the hydrological impacts of this increase, and so studies have focused on rain accumulations over hours or days and for large catchments. The availability of fixed, microwave links is limited by the incidence of heavy rain with an integration time of a minute or less. This document introduces evidence of an increasing trend in rain rates associated with outages. High-resolution rain data, produced by 30 tipping bucket gauges sited in the south of England, have been analyzed to identify these trends. The data span up to 20 years at each site. Increasing trends in the incidence of rain rates exceeded at annual time percentages between 0.005% and 0.1% are demonstrated. Data suggest that the total annual outage would have doubled or tripled over each decade analyzed for the majority of fixed links operating at rain fade limited frequencies. It is plausible that this trend could continue.

Proceedings of the 11th International Conference on Telecommunications, 2011

1] Rainrate near the ground can be interpreted as a collection of random variables forming a rand... more 1] Rainrate near the ground can be interpreted as a collection of random variables forming a random field parameterized by three coordinates: two spatial coordinates and one temporal. Interest among the radio propagation community has been focused on the first order statistics of these random variables, principally on the average annual probability distribution of rainrate as a function of location. However, increasingly interest is turning to second order statistics describing high-resolution rainrate variation in both time and space. This information is important for the design of fade countermeasures and for efficient spectrum management. In this paper radar data from a widespread, slow moving and intense, stratiform rain event experienced by the southeastern UK on May 1, 2001, are used to calculate the second order, spectral, statistics of spatial-temporal log rainrate variation. It is demonstrated that log rainrate is self-similar in all three coordinates and that symmetry exists between the spatial and temporal variation. These data are used to develop an isotropic, spatial-temporal log rainrate model assuming that log rainrate is a homogeneous, Gaussian, random field. This model is developed further to yield closed form expressions for the mean and covariance of the random fields associated with rainrate, with specific attenuation and the logarithm of specific attenuation. Furthermore, expressions for the temporal covariance of the rain attenuation experienced by pairs of radio links are developed, and these expressions are tested against measured rain attenuation data from an experimental link.

Meas Sci Technol, 2012

ABSTRACT Microwave engineers and geomorphologists require rainfall data with a much greater tempo... more ABSTRACT Microwave engineers and geomorphologists require rainfall data with a much greater temporal resolution and a better representation of the numbers of large raindrops than is available from current commercial instruments. This paper describes an acoustic instrument that determines rain parameters from the sound of raindrops falling into a tank of water. There is a direct relationship between the kinetic energy (KE) of a raindrop and the acoustic energy that it creates upon impact. Rain KE flux density is estimated from measurements of the sound field in the tank, and these have been compared to measurements from a co-sited commercial disdrometer. Eight months of data have been collected in the eastern UK. Comparisons of rain KE estimated by the two instruments are presented and links between the KE and rainfall intensity are discussed. The sampling errors of the two instruments are analysed to show that the acoustic instrument can produce rain KE measurements with a 1 s integration time with sampling uncertainty of the same size as commercial instruments using a 1 min integration time.

2009 3rd European Conference on Antennas and Propagation, Mar 23, 2009

ABSTRACT To predict the quality of service (QoS) at a node in heterogeneous networks of line-of-s... more ABSTRACT To predict the quality of service (QoS) at a node in heterogeneous networks of line-of-sight, terrestrial, microwave links requires knowledge of the spatial and temporal statistics of rain over scales of a few meters to tens or hundreds of kilometres, and over temporal periods as short as one-second. Meteorological radar databases provide rainrate maps over areas with a spatial resolution as fine as a few hundred meters and a sampling period of 2 to 15 minutes. Such two-dimensional, rainrate map time-series would have wide application in the simulation of rain scatter and attenuation of arbitrary millimetre-wave radio networks, if the sampling period were considerably shorter i.e. of the order of 10 seconds or less, and the integration volumes smaller. This paper investigates a stochastic-numerical method to interpolate and downscale rainrate field time-series to shorter sampling periods and smaller spatial integration areas, while conserving the measured and expected statistics. A series of radar derived rain maps, with a 10 minute sample period, are interpolated to 10 seconds. The statistics of the interpolated-downscaled data are compared to fine scale rain data i.e. 10 seconds rain gauge data and radar data with a 300 metres resolution. The interpolated rain map time series is used to predict the fade duration statistics of a microwave link and these are compared to a published and ITUR model.

SEG Technical Program Expanded Abstracts

This paper describes the work undertaken by the Transport Group of the Environmental

Narrow bandwidth transducers used in existing ultrasonic data communication systems are known to ... more Narrow bandwidth transducers used in existing ultrasonic data communication systems are known to be devices with a high Q resonant response and low coupling to both the electrical drive and acoustic output interfaces. These features limit the speed of phase change when phase modulation (PM) is used. This paper studies the design of a Variable Structure Controller (VSC)-based transmitter with the aim of increasing the capacity of a PM-based communications system. Simulation results are presented to demonstrate the potential of this approach.

This chapter describes the challenge of MIMO-OFDM channel estimation when the number of antennas ... more This chapter describes the challenge of MIMO-OFDM channel estimation when the number of antennas is very large, for example, in multi-user systems. For downlink communications in multi-user systems, the number of transmit base station antennas may be large when compared to the number receiving antennas for a particular user due to size constraints on the mobile device. For uplink communications, the total number of transmitting antennas may be very large when compared to the receiving antennas at the base station. Following an introduction to the state-of-the-art estimators, we show that the vectorization of the flat fading channel model presents a preferable solution, where the CSI in the MIMO-OFDM system can be represented in a reduced parameter sense using an arbitrary basis.

A previous paper introduced an ultrasonic (US) transducer driven using Variable Structure Control... more A previous paper introduced an ultrasonic (US) transducer driven using Variable Structure Control (VSC) as part of a phase modulated communication system. This paper presents a receiver system also using VSC. The system aims to minimize transducer oscillation with the feedback control signal providing the output. Simulations show a receiver capable of responding within 50 µs to a phase reversal in the 40 kHz acoustic input.

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1992

ABSTRACT The understanding of the current density distribution on electrodes used in Electrical I... more ABSTRACT The understanding of the current density distribution on electrodes used in Electrical Impedance Tomography (ΕIΤ) is important in the application of image reconstruction algorithms. It is particularly important in iterative schemes where the forward problem of calculating the electric potential from boundary Dirichlet and Neumann data is solved many times. In this paper we present the results of some analytic calculations which have been made as a contribution to the understanding of this problem.

The 8th European Conference on Antennas and Propagation (EuCAP 2014), 2014

ABSTRACT It is known that the rain rate exceeded 0.01 % of the time has experienced an increasing... more ABSTRACT It is known that the rain rate exceeded 0.01 % of the time has experienced an increasing trend, in the UK, over the last twenty years. It is very likely that rain fade and outage experience a similar trend. This paper presents a method, applicably globally, to estimate these trends. The input data are parameters easily extracted from numerical weather prediction reanalysis data. The method is verified using rain gauge data from the UK.