摘要:

Although radio-wave propagation has been studied over a considerable period of time, there is a continuing and expanding need for new studies. The requirements for communication, and particularly for the transmission of data signals, necessitate studies in more detail than previously, if reliable statistics for the determination of system performance are to be established. New technologies open up the possibility for economic communication at higher frequencies, and new applications. Each application seeks to stretch the propagation performance to its limits. This paper outlines four key areas where new propagation data are urgently required. The mobile services are expanding extremely fast with the aim of providing personal communications to individuals on the move. Increased use of the radio spectrum for both terrestrial and space communications involves considerable frequency sharing with the need to plan and co-ordinate services effectively. Because of the nature of radio-wave propagation such co-ordination is international, and prediction methods are required for use by future World Administrative Radio Conferences. Developments in radio technology now allow communications at millimetric wavelengths to be considered, and detailed propagation information is still required. At the other end of the spectrum propagation via the ionosphere continues to offer a cheap and flexible means of communicating over long distances, but additional information is required to facilitate the design of automatic systems and digital modulation methods.

DOI:10.1049/jiere.1988.0050

出版商:IERE    

年代:1988

数据来源: IET

摘要:

Results obtained from a bandwidth study of multipath propagation at 55 GHz in a heavily built-up urban area are presented. A series of experiments in which two phase-correlated signals are transmitted at various frequency separations is described. Results indicate that 25 MHz is a good estimate for the coherence bandwidth in an urban multipath environment.

DOI:10.1049/jiere.1988.0051

出版商:IERE    

年代:1988

数据来源: IET

摘要:

The design of a wideband measuring system using a frequency stepping technique is presented. The system measures the amplitude and differential phase (group delay) variations of a pair of spaced frequencies over the bandwidth 850–960 MHz. The measurements are made when the vehicle carrying the receiver is stationary. Hence the Doppler shifts and spread of the signal observed by the moving receiver cannot be measured directly. Using the measuring system the complex frequency response of the UHF mobile radio channel has been measured in urban and suburban areas of the city of Leeds, UK. The presented results are classified into appropriate categories in terms of the building density and the natural environment. The preliminary analysis, based on derivations of the complex transfer function of the channel from measured data at a particular location and the corresponding frequency coherence function and power delay profile, is presented. A full discussion is given of the channel behaviour for different areas by interpreting frequency responses over the band 853-885 MHz and the corresponding frequency coherence function and power delay profile over the band 869–877 MHz.

DOI:10.1049/jiere.1988.0052

出版商:IERE    

年代:1988

数据来源: IET

摘要:

The large area characterization of the UHF mobile radio channel over the band 869–877 MHz for three different types of environment is presented. The results, representing the variations of the statistical parameters of the frequency coherence function and power delay profile, are particular to different locations in the city of Leeds, UK. The variations of the statistical parameters, which are coherence bandwidth, average delay, delay spread, excess delay, and number of discrete paths, are shown in their cumulative probability distribution forms. The worst and typical figures of these parameters are deduced from the corresponding distributions. The resulting figures indicate the limitation on maximum data rate for an optimum system performance, the required spacing for frequency diversity schemes, and the number of paths and their corresponding time delays for hardware and software simulation of the UHF mobile radio channel. Finally, variations of the shape of the power delay profiles and frequency coherence functions and their effects on the values of their corresponding statistical parameters over different blocks of frequencies are presented.

DOI:10.1049/jiere.1988.0054

出版商:IERE    

年代:1988

数据来源: IET

摘要:

Measurements have been undertaken as a part of the first phase of an investigation concerned with propagation into buildings. A series of trials has been conducted within the University of Liverpool precinct aiming to determine the building penetration loss of transmitted signals at 441, 900 and 1400 MHz. The tests were devised to study the first-order statistics of the signal inside buildings when the transmitter is outside. It has been found that the small-scale signal variation exhibits a Rayleigh distribution, while the large-scale signal variation is log- normally distributed with a standard deviation related to the area of the floor and the condition of transmission. The standard deviation was found to be 4 dB when no line-of-sight existed between the transmitter and the building where the receiver was located. If a line-of-sight path existed to part of or the whole of the building, the standard deviation increased to 6–9 dB. The penetration loss decreased at a rate of approximately 2dB per floor as a function of height within the building. The average penetration loss decreased at higher frequencies, the change being approximately 1 5 dB from 441 MHz to 896 MHz and 4 dB to 1400 MHz.

DOI:10.1049/jiere.1988.0064

出版商:IERE    

年代:1988

数据来源: IET

摘要:

Easy access to computers, and the need to justify time spent on them, has encouraged research workers studying radio wave propagation to concentrate on those tasks which would be too complex or too time-consuming to undertake by hand. This paper attempts to show that there is still a place for the simpler approach. None of the studies mentioned in it has made use of anything more complicated than a programmable pocket calculator, yet, in some cases, the results have succeeded in challenging conventional theory. Patterns compress a great deal of information into visual images wherein absolute values are often irrelevant. The paper provides a selection of examples dealing with both isonospheric and tropospheric propagation.

DOI:10.1049/jiere.1988.0056

出版商:IERE    

年代:1988

数据来源: IET

摘要:

In considering the basic mechanism of heat exchange by convective circulation in the atmosphere it is apparent that the resultant thermal cell structure, as proposed by Bénard, may possess refractive index properties which will influence the cross-sectional shape of a narrow conical radio beam. A simplified classical toroidal cell is considered for the purpose of analysis to show that the core of such a cell in the atmosphere may act as a cylindrical concave lens. The resultant distortion of a narrow beam is discussed, and the concept is then developed further to show that trans-horizon propagation may result from an in-line array of thermal cells.

DOI:10.1049/jiere.1988.0058

出版商:IERE    

年代:1988

数据来源: IET

摘要:

Close to a high-power UK television station operating at frequencies around 800 MHz, reception difficulties were experienced by viewers owing to adverse height—gain characteristics up to 10 m above ground level, Most of the terrain between the station and the viewers was uncluttered and fully illuminated by the transmitting antenna within a radius of 4 km and so computer modelling of the soil scatter was undertaken by finite-element summation, avoiding any diffraction analysis, to predict the theoretical height—gain characteristics.The terrain was modelled as a two-dimensional cross-section between transmitter and receiver containing 40 000 soil elements each 0·25λ wide. The illumination from the highly-directional transmitting antenna, comprising 32 radiating elements in a 40 vertical stack, was modelled as an approximation to a true spherical wavefront emanating from each individual antenna element. Nearly 1·3 million phasor summations were required to illuminate the terrain at each frequency considered.Height-gain characteristics at any given receiving range were predicted by summing 40 000 scatter terms at each spot height. The predictions were compared with measurements to determine which parts of the terrain were contributing to the scatter. Further insight was obtained by plotting histograms of the individual contributions predicted from 160 facets of soil, each 25 m (65λ) wide, along the 4 km path profile.

DOI:10.1049/jiere.1988.0059

出版商:IERE    

年代:1988

数据来源: IET

摘要:

This paper is an exposition of the basic physics of the ionosphere, according to the present understanding. It concentrates on the large-scale ionospheric structure at heights above 100 km. Since the ionosphere depends greatly on the structure and dynamics of the neutral atmosphere from which it is formed, and on the geomagnetic field, brief descriptions of these are given. The paper then reviews the theoretical structure of the ionospheric layers and discusses the most important ionospheric phenomena. It concludes with a summary of recent progress and outstanding questions, and a bibliography for further reading.

DOI:10.1049/jiere.1988.0060

出版商:IERE    

年代:1988

数据来源: IET

摘要:

Power-generating wind turbines are becoming more widespread and of larger size. Evidence of distortion caused to terrestrial television broadcast services by some of these prompted the IBA into studying the problem, the results of which are given in this paper. These results should have some relevance to any form of radio wave service.Some references are given to existing literature, the theory is discussed and extended, experiments using microwaves and a model of a turbine are reported as well as measurements made round an actual turbine. Proposals are then made for a way in which the degree of damage caused to radio wave services may be predicted. Thus, the paper provides a way in which radio wave and wind turbine engineers may work together to find sites and other parameters which will allow harmonious co-existence.

DOI:10.1049/jiere.1988.0061

出版商:IERE    

年代:1988

数据来源: IET