  In a directional modulation (DM) network, the issues of security and privacy
have taken on an increasingly important role. Since the power allocation of
confidential message and artificial noise will make a constructive effect on
the system performance, it is important to jointly consider the relationship
between the beamforming vectors and the power allocation (PA) factors. To
maximize the secrecy rate (SR), an alternating iterative structure (AIS)
between the beamforming and PA is proposed. With only two or three iterations,
it can rapidly converge to its rate ceil. Simulation results indicate that the
SR performance of proposed AIS is much better than the null-space projection
(NSP) based PA strategy in the medium and large signal-to-noise ratio (SNR)
regions, especially when the number of antennas at the DM transmitter is small.
