September 1969 | NTIA Technical Memo ERLTM ITS 198

An ionospheric channel simulator

Clark C. Watterson

Abstract: An ionospheric channel simulator with characteristics based on an experimentally verified channel model is described. In the channel model, the input (transmitted) signal feeds a delay line that delivers undistorted delayed versions of the input signal to a limited number of adjustable taps with delays corresponding to the relative propagation times of typical ionospheric modes. Each delayed signal is modulated in amplitude and phase by an independent baseband complex bivariate Gaussian random tap-gain function with a zero mean value and quad­rature components with equal RMS values that produce Rayleigh fading. Each tapgain function has a spectrum that, in general, is the sum of two Gaussian functions of frequency, one for each magnetoionic component, which have independently adjustable amplitudes, frequency shifts, and two-sigma frequency spreads. The delayed and modulated signals are summed to form the output (received) signal. Detailed specifications are presented for the channel simulator, and descriptions are given of the analog and digital circuit techniques used.

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