Abstract: A tetrahedron modem phase modulates input serial binary data and demodulates input waveforms based on a four dimensional vector set. The phase modulation scheme has four possible state vectors (or symbols), that form a tetrahedron in four dimensional space. This symbol geometry improves the bit error rate performance over conventional PSK methods for a given signal to noise ratio. In addition the tetrahedron modem aids bit synchronization and eliminates phase ambiguity in the receiver. Lastly, the tetrahedron modulator outputs a constant envelope waveform, which may be subjected to non-linear devices and channels without fear of negative effects due to amplitude distortion.

Abstract: Digital information is convolved with a pseudorandom code and then transmitted at radio frequency in a spread spectrum signal to a receiver also containing the same pseudorandom code. Since the transmitted signal is below the noise floor for that bandwidth, it is virtually unjammable and undetectable without possession of the pseudorandom code. Successful extraction of the transmitted information depends upon precise matching of the transmitted frequency and the exact phase matching of the pseudorandom code at the receiver with the convolved pseudorandom code in the transmitted signal.