J.G. Gardiner

A new design of horizontally polarizedand dual-polarized uniplanar conical beam antennas for HIPERLAN

It is shown that a conical beam 5.2-GHz antenna suitable for HIPERLAN application, but working in horizontal polarization, can be realized as a group of microstrip patch radiators in a ring formation. Layouts with three and four patches are described, and radiation patterns are found to agree well with predictions from a simple array model. The three-patch form is smaller and gives a closer approximation to an azimuth-independent pattern. Patterns are very similar to those achieved in vertical polarization with previously reported disk antenna realizations, giving peak radiation at about 50/spl deg/ elevation. Two methods of impedance matching are found to give satisfactory results. A dual-polarized conical-beam microstrip antenna, with a strictly uniplanar conductor pattern, is also presented and realized as an array of three square patches whose corners meet a central feed point. For the second polarization, the antenna functions as a series fed array. Fairly good conical beam patterns have been obtained, though only moderate polarization purity appears to be obtainable from three-element arrays.

Measurement of the impulsive noise environment for satellite-mobile radio systems at 1.5 GHz

Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented.

Teletraffic analysis and simulation for nongeostationary mobile satellite systems

The teletraffic performance parameters of a nongeostationary satellite system are estimated through analytical and simulation methods. In order to reduce the number of assumptions, the simulation tool that was developed emulates a mobile satellite system that is closer to the real thing. Parameters of interest include blocking, handover failure, noncompletion, and forced-termination probabilities. These are analyzed in terms of variations in satellite spot cells coverage, overlapping between cells, and in terms of a mobility factor. Additionally, the effect on the grade of service of different channel assignment strategies, for handover purposes, are investigated. The results show that the analytical work is in good agreement with the simulation outcome.

Theoretical model to determine the blocking probability for SDMA systems

Antenna array technology has attracted the attention of the research community as a means to increase system capacity and improve the signal reception. Space division multiple access (SDMA) is a multi-access scheme based on the use of antenna arrays to separate users by exploiting their positions in space. Several works have been carried out to examine the improvement in the system capacity provided by SDMA. A theoretical model to determine the blocking probability for SDMA is derived. A closed-form linear system of equations is obtained whose numerical solution gives the blocking probability. The formulation is employed to assess the capacity gain improvement of a single-cell system under specific conditions. It is found from the results that SDMA is not efficient for low traffic loads, whereas it is so for high traffic.

Teletraffic analysis and simulation of mobile satellite systems

The teletraffic performance parameters of a mobile radio network based on a non-geostationary satellite system are estimated through analytical and simulation methods. Parameters of interest include blocking, handover failure and non-completion probabilities. Effects of different handover channel assignment strategies upon the grade of service are investigated. Results will show that the estimated parameters are in good agreement with the simulation results.

Delay-spread considerations of same-frequency repeaters in wideband channels

In current analog cellular systems, same-frequency repeaters are very often used as gap fillers. With digital wideband systems, the use of a repeater, with its inherent group delay added to the differential propagation delay, may yield a degradation in the performance in view of the resulting delay spread. An approach to estimate the statistics of the delay spread when each link is subjected to lognormal shadowing and each channels power-delay profile follows an exponential decay is presented. Expressions for the cumulative density function (CDF), mean value, mean-square value, and standard deviation for the RMS delay spread are derived, and their accuracy is verified through simulation.

Delay spread statistics in a two-path radio environment

This article focuses on the statistics of the RMS delay spread in an area illuminated by two signal sources, transmitting identical data on the same frequency. The considered channel consists of two delta impulses, separated by a differential propagation delay, each of them subjected to Nakagami or log normal fading. Analytical expressions for the PDF, mean value and standard deviation of the delay spread are presented, and the effects of each type of fading are compared.

Wideband characterisation of the high elevation orbit satellite-mobile channel, at L-band

An experiment to determine the wideband propagation statistics of the channel at L-band between a high-elevation orbit (HEO) satellite and a mobile unit is described. Channel sounding is accomplished by a spread spectrum beacon on board a light aircraft, together with a receiver located in a ground mobile unit employing a stepped cross-correlation measurement system. Some results of initial measurements are given.<<ETX>>

Communications service provision to land mobiles in northern Europe by satellites in high elevation orbits-propagation aspects

An experiment aimed at determining L-band fade statistics for future European land mobile satellite systems is described. During measurement trials, an aircraft was used to simulate a high-elevation orbit satellite whose transmissions were received by a land mobile unit. On the ground, signal-level statistics were measured as a function of two main variables: mobile environment and transmitter-to-receiver elevation angle. Results show that both factors greatly influence the dynamic and temporal nature of fading. Further, data gathered during experiments indicate clearly that, for Northern Europe, propagation problems would be alleviated considerably by using a constellation of highly elevated orbit satellites as opposed to a geostationary alternative.<<ETX>>

Interference analysis for ad hoc networking over UTRA-TDD air interface

Ad hoc networking over UTRA-TDD protocol (A. Barnawi and J. G. Gardiner, Aug. 2003) (ANOUP) was introduced by our research group as a protocol to combine ad hoc networking with the fixed wireless infrastructure. The aim of that combination is to improve the capacity and coverage of the cellular system. In this paper we model the interference due to ad hoc networking over the fixed UTRA-TDD networks and we quantify the impact of ANOUP on the system. It was shown that coverage improvement of 100% is quite achievable.