MIMO capacity at 2.1 GHz while entering tunnels

A ray-launching model based on the application of the uniform theory of diffraction (UTD) and geometrical optics (GO) has been used to study the propagation in an idealized tunnel for an 8/spl times/8 MIMO system. Capacity has been studied for 4 positions of the transmitter, and it is shown that there exists a zone from the entrance to a certain distance where capacity remains high, and after this zone capacity decreases sharply. This distance depends on the position of the transmitter and can be directly related to the excitation zone.