Upper and lower bounds to the information rate transferred through the Pol-Mux channel

Pol-Mux transmission is a well established technique that enhances spectral efficiency by simultaneously transmitting over horizontal and vertical polarizations of the electrical field. However, cross-coupling of the two polarizations impairs transmission. Under the assumption that the cross-coupling matrix is a Markov process with free-running state, we propose upper and lower bounds to the information rate that can be transferred through the channel. Simulation results show that the two bounds are tight for values of the cross-coupling power of practical interest and modulation formats up to 16-QAM (quadrature amplitude modulation).