Terrestrial Radio Links Research Articles

Simple rain-attenuation-prediction technique for terrestrial radio links

It is shown that the simple technique called the ‘path reduction coefficient’ can be widely used to predict rain attenuation on terrestrial radio links due to the good agreement obtained between measured and calculated attenuation, mainly for low percentages of time. Comparisons between the presented method and the method adopted by the CCIR are given.

Analysis of long‐term rain attenuation statistics

An experimental verification of Lin's prediction model for rain attenuation statistics, with data taken from a terrestrial radio link in Athens, is presented. It provides an encouraging indication that this model could be the appropriate one for radio paths in the Greek airspace.

Rainfall scatter interference between terrestrial and satellite radio-links

The effect of scattering by rain on the interference between terrestrial and satellite radio links is examined. The important role played by rain attenuation inside and outside the common volume is evident from the comparison between experimental and theoretical results. For higher rain intensities, the experimental results are in good agreement with those calculated, but for lower intensities the calculated results underestimate the phenomena.

Synchronization of atomic clocks through the ‘Symphonie’ satellite

The intercomparison of time and frequency standards is restricted by the inadequacy of terrestrial radio time transfer links in terms either of accuracy or of geographical coverage. The use of artificial satellites can improve this situation. (Blair, 1974; Chi and Byron, 1975; Markowitz et al., 1966; Ramasastry et al., 1973; Saburi et al., 1976; Steele et al., 1964; Yamamoto et al., 1976). Two experiments are described in which the geostationary telecommunications satellite Symphonie is used. A two‐way simultaneous link is employed in order to eliminate the need to know the propagation delays. Details of a test carried out in December 1976 between Raisting (West Germany) and Pleumeur‐Bodou (France) are given. Also, preliminary details of the time transfer experiment between Pleumeur‐Bodou and Ottawa (Canada) are described.

Estimation of attenuation by rain on terrestrial radio links in the UK at frequencies from 10 tp 100GHz

Methods are given for estimating attenuation caused by rain during the average year, worst year and worst month of a 20-year period and during the worst month of the average year of that period. Probability distributions of point rain rates are modified by temporal and spatial factors derived from long-term and short-term rainfall records to obtain probability distributions of line rates RL, over paths up to 60 km long. Attenuation A is calculated from A = γRηL, where γ and η are parameters dependent on polarisation and frequency. Estimated values are compared with experimental observations at frequencies near 11, 20, 36, 60 and 110 GHz.

Estimation of attenuation by rain on terrestrial radio links in the UK at frequencies from 10 tp 100GHz

Methods are given for estimating attenuation caused by rain during the average year, worst year and worst month of a 20-year period and during the worst month of the average year of that period. Probability distributions of point rain rates are modified by temporal and spatial factors derived from long-term and short-term rainfall records to obtain probability distributions of line rates RL, over paths up to 60 km long. Attenuation A is calculated from A = γRηL, where γ and η are parameters dependent on polarisation and frequency. Estimated values are compared with experimental observations at frequencies near 11, 20, 36, 60 and 110 GHz.

Depolarization at 11.6 GHz on a terrestrial radio link

This paper presents some early data from an 11.6 GHz, 18 km terrestrial radio link operating in circular, linear horizontal and vertical polarizations. Rain, snow and clear weather effects are presented and analysed together with cumulative statistics over a fourteen month period. Observations indicate that rain depolarization is most severe on the circularly polarized transmission followed in order of magnitude by horizontal and vertical polarizations. Linear polarizations usage on a practical microwave link appears to be limited primarily by clear weathereffects. A good agreement with theoretical models for rainfall is obtained on circular and linear polarizations. During snow the variability of effects precludes a definitive classification of this type of precipitation, however, circular polarization exhibits a marked sensitivity to depolarization, generally less than that for the same rain attenuation level. The attenuation experienced during snow can be markedly different from event to event.

Measurements of rainfall for studies of millimetric radio attenuation

Point and line rates of intense convective rain, measured between 1970 and 1976, with rapid-response gauges sited mainly in SE England, are presented in forms relevant to the estimation of attenuation by rain on terrestrial millimetric radio links; e.g. annual probability distributions of point rates for a range of gauge integration times, distributions of the duration and return periods of specific point rates and relationships between line and point rates. Statistical models have been deduced for the temporal and spatial variations and the frequency of occurrence of intense rain events in the UK and comparisons have been made with estimated long-term average values and models from other records. The models are being used to assist the development of prediction procedures for network planning.

Crosspolarisation measurements at 11 GHz

Three years measurements of crosspolarisation and attenuation at 11 GHz are presented. They were taken on a 13.6km terrestrial radio link using horizontal and vertical polarisations. A semi-empirical law based on Oguchi's point-matching attenuation and phase coefficients and relating crosspolarisation discrimination (c.p.d.) to fade depth, is derived. Comparison of this semi-empirical law with measured c.p.d. values shows that the use of an equivalent mean canting angle of 4° gives c.p.d. exceeded for 90% of the time. Typical c.p.d. values for deep fades are given by using an equivalent mean canting angle of 2 or 3°. Yearly cumulative statistics and monthly histograms of c.p.d. and attenuation are presented for the three year period.

Model of intense convective rain cells for estimating attenuation on terrestrial millimetric radio links

The movement of intense rain over a line of rapid-response rain gauges is shown to be related to the wind speed at the 700 mbar level. This relationship is used to deduce model rainfall intensity/distance profiles from intensity/time profiles recorded at a point. The model is applicable to the calculation of attenuation at frequencies above about 30 GHz.

Statistical Behavior of Rain Attenuation*

Thirty-one sets of experimental data on the statistics of microwave rain attenuation at frequencies above 10 GHz, in the U.S.A., England, Japan, Italy, and Canada, indicate that: (i) the distribution of rain attenuation α, in dB, is approximately lognormal with a standard deviation σ α of log 10 α ranging from 0.46 to 0.71 for earth-space paths, and from 0.33 to 0.86 for terrestrial paths; (ii) the distribution of the rain fade duration τ is also approximately lognormal with a standard deviation σ τ of log 10 τ ranging from 0.44 to 0.76 for both earth-space paths and terrestrial paths. We propose a theory to explain this general behavior. A theoretical upper bound for the fade duration distribution in the tail region is also given. The findings in this paper simplify the determination of rain attenuation statistics needed for the design of earth-satellite radio links and terrestrial radio links.