Symbol-independent weight magnitude design for antenna array based directional modulation

Directional modulation (DM) as a physical layer security technique has been studied from many different aspects. Recently, a constant magnitude constraint for all antennas of an array for a given modulation symbol was proposed. However, the proposed design does not work for multiple beams. In practice, multi-beam DM may often be required. As a compromise, instead of setting the same magnitude for all antennas for a given symbol, in this paper, a symbol independent magnitude constraint for each antenna is proposed for the first time. With the same magnitude for different symbols for each antenna, only phase changes between different symbols are needed, which can form multiple DM beams simultaneously, while still reducing the implementation complexity of the whole system. Design examples are provided to show the effectiveness of the proposed design.