Capacity Measurements in a Cooperative MIMO Network

Cooperation between adjacent base stations (BSs) may reduce intercell interference in future cellular networks and enhance network capacity in this way. The potential of cooperation is evaluated in this paper based on measurements conducted at 5.2 GHz in a campus environment with four overlapping cells. For each individual link of the four BS and five terminal locations, a 10 times 16 antenna configuration with cross-polarized elements is used. Results show that the direct signal is much stronger than scattering due to the small intersite distances. The polarized line-of-sight (LOS) signal creates two degrees of freedom in the spatial domain, which is also confirmed by a 3-D propagation model. Rich multipath scattering is characteristic for the rest of the links where the direct signal is blocked. Results for a multilink scenario where all users are jointly served by all BSs confirm that such cooperation leads to enhanced rank of the compound channel matrix. The spectral efficiency is five times higher with cooperation, compared with a conventional frequency reuse system, where different radio resources are assigned to adjacent cells. Hence, our measurements confirm the benefits of cooperation in cellular systems.