Time-Modulated OFDM Directional Modulation Transmitters

In this paper, directional modulation (DM) transmitters, designed for orthogonal frequency-division multiplexing (OFDM) wireless data transfer are proposed using time-modulated arrays. It is shown that by properly designing the switch controlling time sequences the proposed time-modulated OFDM DM systems exhibit promising features, such as 1) requires only one radio frequency chain, 2) the conventional efficient OFDM signal construction approach, i.e., by using inverse fast Fourier transform modules, can be adopted, 3) it is “DM synthesis-free,” meaning that there is no need to resynthesize the array excitation vectors for different secure communication directions, different modulation schemes, and different DM power efficiencies, and 4) the tradeoff between secrecy performance and power efficiency can be flexibly adjusted.