MU-MIMO with Localized Downlink Base Station Cooperation and Downtilted Antennas

Multi-cellular radio systems are often limited due to the presence of cochannel interference. Proposed physical layer concepts, e.g. coordinated joint transmission and interference rejection combining, try to strengthen the signal while combating the interference. It is well known that base station cooperation yields great capacity improvement for downlink multi-antenna cellular networks. However, the proposed solutions assume a central processing unit, coordinating the information exchange and thus determining the optimal resource allocation of the overall cellular network. Recently multi-user eigenmode transmission was proposed to relax the constraint of channel state information at the transmitter. It requires the terminals to feed back their dominant eigenmodes only. To reduce the computational costs and the information exchange further, we consider limited localized base station cooperation. We demonstrate potential capacity gains in a cellular orthogonal frequency division multiplexing system using real 3D measured antenna patterns and the scaling with the number of cooperating antenna arrays. Additionally, we use minimum mean square error equalization at the terminal side to combat residual cochannel interference.