  With the assistance of singular value decomposition (SVD), a multi-beam
directional modulation (DM) scheme based on symmetrical multi-carrier frequency
diverse array (FDA) is proposed. The proposed DM scheme is capable of achieving
range-angle dependent physical layer secure (PLS) transmissions in free space
with much lower complexity than the conventional zero-forcing (ZF) method.
Theoretical and simulated results about secrecy rate and complexity verify the
improved computational efficiency and considerable memory savings despite a
very small penalty of secrecy rate.
