  In this work, a directional modulation-based technique is devised to enhance
the security of a multi-antenna wireless communication system employing M-PSK
modulation to convey information. The directional modulation method operates by
steering the array beam in such a way that the phase of the received signal at
the receiver matches that of the intended M-PSK symbol. Due to the difference
between the channels of the legitimate receiver and the eavesdropper, the
signals received by the eavesdropper generally encompass a phase component
different than the actual symbols. As a result, the transceiver which employs
directional modulation can impose a high symbol error rate on the eavesdropper
without requiring to know the eavesdropper's channel. The optimal directional
modulation beamformer is designed to minimize the consumed power subject to
satisfying a specific resulting phase and minimal signal amplitude at each
antenna of the legitimate receiver. The simulation results show that the
directional modulation results in a much higher symbol error rate at the
eavesdropper compared to the conventional benchmark scheme, i.e., zero-forcing
precoding at the transmitter.
