Multiuser phase coded costas signals with improved cross-correlation and partial cross-ambiguity properties
Résumé
Costas codes are a variant of frequency hopping codes that achieve the «thumbtack» auto-ambiguity function needed in radar applications. However, they may show poor cross- ambiguity properties when selected and assigned randomly which makes them poorly adapted to multiuser radar applications. In this paper, we propose a multiuser adaptation of phase coded Costas signals. In fact, this modified version of Costas signals consists in replacing Costas constant frequency sub-pulses with phase codes. This modification allows to suppress autocorrelation function grating lobes that appears when orthogonality condition of Costas codes is not satisfied. Furthermore, the later design adds a degree of freedom for a possible adaptation of these waveforms to a multiuser context. Indeed, in the current work, the sub- pulse phase codes are used to generate a set of waveforms with good cross-correlation properties. Specific conditions on these codes are stated in order to achieve the needed cross-correlation properties, using a same Costas code. The auto-ambiguity and cross-ambiguity properties are also remarkable but within a bounded Doppler region. Furthermore, the families are expanded using different Costas codes with particular properties. Hence, since the phase codes and Costas codes diversity are used, the number of synthesized waveforms is improved.