  Movable antenna (MA) array is a novel technology recently developed where
positions of transmit/receive antennas can be flexibly adjusted in the
specified region to reconfigure the wireless channel and achieve a higher
capacity. In this letter, we, for the first time, investigate the MA
array-assisted physical-layer security where the confidential information is
transmitted from a MA array-enabled Alice to a single-antenna Bob, in the
presence of multiple single-antenna and colluding eavesdroppers. We aim to
maximize the achievable secrecy rate by jointly designing the transmit
beamforming and positions of all antennas at Alice subject to the transmit
power budget and specified regions for positions of all transmit antennas. The
resulting problem is highly non-convex, for which the projected gradient ascent
(PGA) and the alternating optimization methods are utilized to obtain a
high-quality suboptimal solution. Simulation results demonstrate that since the
additional spatial degree of freedom (DoF) can be fully exploited, the MA array
significantly enhances the secrecy rate compared to the conventional
fixed-position antenna (FPA) array.
