The Use of Frequency-Orthogonal Pseudonoise (FOPN) Sounding Signals for Identifying Transmissions From Different Transmit Antennas

A method is described for identifying simultaneous signals from different transmit antennas in multiantenna sounders. Multiple-orthogonal signals are produced from one pseudonoise code by using it to modulate RF carriers at precalculated offset frequencies. Although their frequency spectra are interleaved and they occupy the same band, the spectral lines from different transmitters are separable after Fourier transformation at the receiver output. Since there is a one-to-one relationship between the length of the signal required for Fourier analysis and the number of orthogonal sounding signals, any arbitrary number of such signals can be generated, but Doppler spreads limit the number that can be employed with acceptable isolation among them.