**Authors:**

**Reference:**

submitted to IEEE Transactions on Communications, July 2012

**Abstract:**

The small carrier wavelength at millimeter-wave (mm-Wave) frequencies enables featuring a large number of co-located antennas. This paper exploits the potential of large antenna arrays to develop a low-complexity directional modulation technique, Antenna Subset Modulation (ASM), for point-topoint secure wireless communication. The main idea in ASM is to modulate the radiation pattern at the symbol rate by driving only a subset of antennas in the array. Two techniques for implementing antenna subset selection are proposed. The first technique selects an antenna subset randomly for every symbol. While randomly switching antenna subsets does not affect the symbol modulation for a desired receiver along the main direction, it effectively randomizes the amplitude and phase of the received symbol for an eavesdropper along a sidelobe. Using a simplified statistical model, an expression for the average uncoded symbol error rate (SER) is derived as a function of the observation angle. Secondly, to overcome the problem of large sidelobes in random antenna subset switching, an optimized antenna subset selection procedure based on simulated annealing is further proposed. Numerical comparisons of the SER performance and secrecy capacity of the proposed techniques against those of conventional array transmission are presented.