We present a new digital modulation technique that introduces security in digital communications. The basic principle is to transmit realizations of a stochastic process in such a manner that the transmitted waveform appears noiselike. In this paper, we have chosen to express the transmitted waveform in a subspace formalism. This allows for an elegant geometrical interpretation of the waveform, and it naturally suggests a simple and accurate matched subspace detector for the receiver. The technique is demonstrated by numerical simulations, and a comparison with an optimal Neyman-Pearson detector shows that our simple subspace detector yields a high-quality and reliable receiver for the modulated signal.
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