AM compatible digital audio broadcasting signal transmision using digitally modulated orthogonal noise-like sequences

A digital modulation technique, broadcast system, and apparatus for the spectral superposition of an analog AM signal and a novel digitally modulated signal. Multiple mutually orthogonal, continuous-valued noise-like sequences are amplitude and phase modulated. Preferably, modulation coefficients are mapped from the formatted data to be transmitted and basis waveforms are generated which are then modulated by the modulation coefficients. These modulated waveforms may be ASK modulated lowpass waveforms and QAM or in-phase ASK modulated bandpass waveforms. Alternatively, the modulated waveforms may be double sideband QAM modulated lowpass waveforms and QAM modulated bandpass waveforms. In the broadcast system of the present invention, an amplitude modulated signal having a first frequency spectrum is broadcast simultaneously with a plurality of amplitude and/or phase modulated orthogonal noise-like signals having a bandwidth which encompasses the first frequency spectrum. The amplitude modulated signal includes a first carrier modulated by an analog signal. A first group of the amplitude and/or phase modulated orthogonal noise-like signals lying within the first frequency spectrum are modulated in-quadrature with said first carrier signal. The second and third groups of the amplitude and/or phase modulated orthogonal noise-like signals lie outside of the first frequency spectrum and are modulated both in-phase and in-quadrature with the first carrier signal.