Subspace detectors for stochastic process shift keying

We present a new digital modulation technique that introduces covertness in digital communications in a simple fashion. The basic principle is to transmit realizations of a stochastic process in such a manner that the transmitted waveform appears noiselike. The transmitted waveform is expressed in a subspace formalism, allowing for an elegant geometrical interpretation of the waveform, and a simple and accurate subspace detector for the receiver. The effect of inter-symbol-interference (ISI) is also studied, and a simple zero-forcing subspace detector is suggested. The technique is demonstrated by numerical simulations, and it shows that our simple subspace detectors yield high-quality and reliable receivers.