  As an excellent aided communication tool, intelligent reflecting surface
(IRS) can make a significant rate enhancement and coverage extension. In this
paper, we present an investigation on beamforming in an IRS-aided directional
modulation (DM) network. To fully explore the advantages of IRS, two
beamforming methods with enhanced secrecy rate (SR) performance are proposed.
The first method of maximizing secrecy rate (Max-SR) alternately optimizes
confidential message (CM) beamforming vector, artificial noise (AN) beamforming
vector and phase shift matrix. The first optimization vector is directly
computed by the Rayleigh ratio and the last two are solved with generalized
power iteration (GPI). This method is called Max-SR-GPI. To reduce the
computational complexity, a new method of maximizing receive power with
zero-forcing constraint (Max-RP-ZFC) of only reflecting CM and no AN is
proposed. Simulation results show that the proposed two methods harvest about
30 percent rate gains over the cases of random-phase IRS and no IRS, and the
proposed Max-SR-GPI performs slightly better than the Max-RP-ZFC in terms of
SR, particularly in the small-large IRS.
