Directional Modulation Technique for Linear Sparse Arrays

As millimeter-wave technology becomes more and more mature, directional modulation (DM) based on large uniform linear arrays, where the adjacent antennas spaced half-wavelength of the frequency of interest, can be realized to ensure the security of millimeter-wave systems. However, for small inter-element spacings, the mutual coupling effects are severe. Therefore, a DM technique using linear sparse arrays (LSAs) is presented to improve spatial resolution and mitigate the effects of mutual coupling. The main idea for DM signal synthesis is to modulate the radiation pattern at the symbol rate by randomly selecting a sparse rate, i.e., a filling fraction, from the given interval [α _min , α _max ] and an array formation, i.e., an antenna subset, from the codebook P. This results in a directional radiation pattern that projects a standard constellation in the desired direction and distorted randomized constellations in other directions, which offers security for wireless communication. Numerical comparisons of the symbol error rate performance of the proposed DM technique against conventional array transmission and antenna subset modulation are presented to highlight the advantages of the DM technique for LSAs.