Polarization-based Signaling Technique for LOS MIMO Channels

Abstract

Recently, various signaling techniques based on the activation of a single antenna (or a number of antennas)according to information bits have been proposed for multiple-input multiple-output (MIMO) channels under richscattering environments. In strong line-of-sight (LOS) environments, however, the columns of MIMO channel matricesbecome almost identical, so the activated antenna index (or indices) cannot convey information. In this paper, wepropose the use of multiple dual-polarized antennas for signaling by antenna activation over the strong LOS MIMOchannels. The proposed technique is based on the observation that the columns of LOS MIMO channel matrices can bemade distinct by physically rotating polarized antennas with distinct angles. It was shown that the rank of dualpolarizedLOS MIMO channels is two regardless of the number of antennas. Consequently, at most two spatial streamscan be transmitted simultaneously over dual-polarized LOS MIMO channels even when a large number of antennas areemployed. In the proposed dual-polarized LOS MIMO systems, information is transmitted by the index of the activateddual-polarized antenna in addition to the two spatial streams. It is shown that the complexity of optimal detection in theproposed signaling technique is low thanks to the orthogonality of two branches of a dual-polarized antenna. We derivethe error performance of the proposed system with optimal detection and show that the error performance isindependent of the rotation angles of the dual polarized receiver antennas. We also derive the optimal rotation angles ofthe dual-polarized transmitter antennas to achieve the minimum error for 4-QAM and 16-QAM. We perform a set ofcomputer simulations to demonstrate the efficacy of the proposed technique.