MIMO beamforming using quasi-orthogonal ultrawideband-impulse waveforms

In this paper, the principles of multiple-input-multiple-output (MIMO) array beamforming based on quasi-orthogonal ultrawideband-impulse (UWBI) signals and the conventional narrowband-sinusoidal (NBS) signals are described in the time domain. Mathematical models of quasi-orthogonal UWBI signals and NBS signals modulated according to the Mary phase-shift-keying (PSK) scheme are first presented. The models are then used to derive and plot the average-power pattern of a coherent MIMO beamforming system typically considered for enhancing the resolution performance of an imaging radar. Computer plots of the MIMO beam patterns obtained for the quasi-orthogonal UWBI-PSK and NBS-PSK signals clearly demonstrate that the angular-resolution performance of MIMO beamforming based on UWBI-PSK signals is superior to that based on NBS-PSK signals. Improvement in resolution angle and peak-sidelobe level can be achieved by a trade-off between the design parameters of the UWBI-PSK signals and the MIMO array.