Polarization in Wireless Communications

Wireless communications exploits the electromagneticmedium,which is intrinsically polarization-sensitive. Much wireless technology, however, has been devised without explicit consideration of polarization. Past decades of wireless technology has mainly exploited the dimensions of time, frequency and space. As such, polarization is a logical next step in this progression. This special issue focuses on cutting-edge novel exploitation of polarization for wireless communication applications and the assessment of performance gain when using polarization sensitive devices as compared to standard hardware. After a rigorous peer review process, we present the following six papers for the Issue. The first paper, entitled ‘‘The effect of polarization separation on the performance of Candecomp/Parafac-based vector sensor array processing ’’ [1] assesses the importance of polarization diversitywhen separating two closely-located sources using a vector-sensor array. A novel polarization separation measure, for spatially non-collocated sources, is provided along with geometrical interpretation. A multilinear data acquisition scheme is used for illustration because of its interesting identifiability properties. In the secondpaper ‘‘Study of the asymptotic Cramér–Rao Bound for the COLD uniform linear array’’ [2], the authors study another polarization sensitive array configuration known as the Cocentered Orthogonal Loop and Dipole pairs Uniform Linear Array (COLD-ULA). Closed-form expressions of the deterministic Cramér–Rao Bound (CRB) for the direction and polarization parameters are derived under the assumption that the number of sensors is sufficiently large. The authors show that in practice, the closed-form expression is a good approximation to the CRB even if the number of sensors is moderate (about ten) in the case when the sources are not too spatially close. Using this closed-form CRB, several interesting results on the performance of the COLD array are derived. The next paper, ‘‘Tri-polarized MIMO systems in realworld channels: Channel investigation and performance analysis’’ [3], studies the benefit of tri-polarized MIMO (Multiple Input Multiple Output) systems over their dual-polarized counterparts. It is shown, starting from the polarization mechanisms in wireless propagation channels, that dual-polarized MIMO systems possess high