Fig. 3

Taxonomy of directional modulation techniques for physical layer security against passive eavesdropping. This figure captures the essence of the framework proposed in this paper. It categorizes directional modulation techniques into two broad categories; angular and range-angular DM. Angular DM techniques secure data only along spatial angular direction, while range-angular DM techniques transmit secure data along spatial angular direction within specified spatial range of intended receiver. The sub-categorization has been done based on the under-lying physical layer parameter used to achieve security; space, time, frequency, phase and polarization