Multi-tier networks comprising of macro-cellular network overlaid with less power, short range, home-base station like femtocells provide an economically feasible solution for meeting the unrelenting traffic demands. However, femtocells that use co-channel allocation with macrocells result in cross-tier interference which eventually degrades the system performance. It is for this reason that, cross-polarized data transmission is proposed in this paper as a potential approach towards improving the spectral efficiency of cellular systems and at the same time permitting co-channel allocation. Here two independent information channels occupying the same frequency band can be transmitted over a single link. The paper evaluates a scenario where femtocell network makes use of right hand circular polarization (RHCP) and macrocell network makes use of left hand circular polarization (LHCP) for signal transmission. The polarizations being orthogonal to each other due to their sense of rotation ensure isolation between the networks and enable both of them to use the same spectral resources simultaneously. Analytical and simulation results prove that this opens the scope for an easily implementable, remarkable opportunity in the context of two-tier femto–macro network that can increase the system capacity. The paper closes by discussing the technical challenges involved in the implementation as well as the possible solutions to overcome the same. 
Orthogonal circular polarized transmission for interference control in femto–macro networks