  We consider the multiplexing gain (MUXG) of the fully connected K-user
line-of-sight (LOS) interference channels (ICs). A polarimetric antenna
composed of 3 orthogonal electric dipoles and 3 orthogonal magnetic dipoles is
considered where all 6 dipoles are co-located. In case of K-user IC with single
polarization, the maximum achievable MUXG is K regardless of the number of
transmit and receive antennas because of the key-hole effect. With
polarization, a trivial upper bound on the MUXG is 2K. We propose a zero
forcing (ZF) scheme for the K-user LOS IC, where each user uses one or more
polarimetric antennas. By using the proposed ZF scheme, we find minimal antenna
configurations that achieve this bound for K <= 5. For K > 5, we show that the
optimal MUXG of 2K is achieved with M = (K+1)/6 polarimetric antennas at each
user.
