We use space shift keying (SSK), which is the simplest form of spatial modulation (SM), to present and analyze the idea of spatial modulation in line-of-sight (LOS) conditions. We show that SSK can operate effectively in LOS conditions provided that the antennas are properly placed at TX and RX such that a high-rank LOS-MIMO channel is constructed. The operating conditions for LOS-SSK with parallel uniform linear arrays are established and two schemes, namely orthogonal SSK and bi-orthogonal SSK, are introduced.
The bit error probabilities for both methods are derived and given in closed form. It is shown that LOS-SSK (more generally LOS-SM) is a promising technique and might especially be attractive in millimeter-wave communications which, due to its high frequency and small wavelength, inherently prefers LOS transmission and also enables packing of a large number of antennas in terminals.