Abstract

Rain is the dominant attenuator for radio systems operating above 10 GHz. Correctly configuring systems that can dynamically compensate for rain fading requires a detailed knowledge of spatial and temporal rain field variation. Ideally, this would be provided by a database of meteorological radar measurements. Unfortunately, such data is scarce. Alternatives to radar measurements are methods for simulating rain fields in time and space. This paper discusses a monofractal, additive (in the logarithmic domain) discrete cascade model for simulating rain fields in two spatial dimensions. The model produces events-on-demand, customised to an input rain rate parameter and desired rain event type (stratiform or convective). In order to test the long term statistics of a proposed radio system, simulated rain field datasets are required which will reproduce the annual rain statistics for the average year. Work towards a method to convert from a set of single events into a set capable of reproducing annual statistics is presented in this paper.

Highlights

  • The rain field simulator is based on the Voss [1985] successive random additions algorithm for simulating fractional Brownian motion

  • The key parameters are the Hurst exponent H, which determines the fractal dimension of the simulated field and the lacunarity rl which determines whether the simulated fields are stratiform-like or convective-like

  • The simulated rain fields presented here have been used in this context, in a case study of a switching algorithm for a two site Earth-space system using site diversity as a fade mitigation techniques (FMT), and in a project investigating the implementation of Adaptive Transmit Power Control (ATPC) on terrestrial links for bands above 18GHz

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Summary

Rain field simulator

The rain field simulator is based on the Voss [1985] successive random additions algorithm for simulating fractional Brownian motion. It is an additive discrete cascade process and produces a monofractal field in the logarithmic domain. The key parameters are the Hurst exponent H, which determines the fractal dimension of the simulated field and the lacunarity rl (equivalent to the cascade branching number) which determines whether the simulated fields are stratiform-like or convective-like. Each simulated field is independent of the others. The resulting simulated rain fields have appropriate spectral density exponent, fractal dimension, and behaviour that is visually consistent with experimentally observed convective or stratiform type of events (according to what is desired)

Conclusions and Further Work
Application of fractal rain fields to radio systems
CDFs of measured rain events in comparison with simulated events

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