MIMO in Tunnels: Influence of the Position of the Array Elements on the Channel Capacity

J.-M. Molina-Garcia-Pardo (Spain), M. Lienard, E. Simon, and P. Degauque (France)


MIMO channel, tunnel, polarization diversity.


A reference scenario is first introduced for describing the diversity richness of the propagation channel in a tunnel, independently on the array characteristics. One considers in this case a uniform excitation of the tunnel, which would be obtained by a dense planar transmitting array put in the transverse plane of the tunnel. To get simple analytical expression of the propagation characteristics, a straight rectangular tunnel is considered. The capacity of a usual linear array is calculated assuming either a uniform array or an array whose element spacing is optimized. A parametric study shows that if the frequency is high enough, typically above 2 GHz in a road or subway tunnel, uniform linear arrays are well suited for improving the channel capacity. However, the element spacing must be large enough to minimize the correlation between array elements. To maintain compact arrays, a solution based on polarization diversity is studied. In this case, measurement campaigns have been carried out in order to determine, in practical cases, the MIMO channel matrix for various antenna configurations. Then, assuming a constant transmitting power and a given element spacing, MIMO capacities based on co-polarized antennas or on polarization diversity, are compared.

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