Field Evaluations on a Prototype System of Cooperative Multi-Cell MIMO Transmission for Asynchronous Inter-Site Base Station Networks

For next generation cellular mobile communication systems, cooperative multi-cell MIMO transmission (cooperative MIMO) technologies, in which multiple base stations (BSs) coordinate their wireless transmission, have recently been receiving considerable attention due to their potential cell-boundary throughput improvement. However, there are few studies that provide field evaluation of cooperative MIMO in real radio-propagation environments. To evaluate cooperative MIMO in a real field, BSs located at different sites should be synchronized to each other with high accuracy in asynchronous inter-site BS networks. We develop a prototype of an experimental system by using a GPS (Global Positioning System)-based inter-BS synchronous controller. We conduct field experiments on two cooperative MIMO transmission schemes: (i) cooperative MIMO-SDM based on space division multiplexing and (ii) Cooperative MIMO-SFBC based on space frequency block coding. We confirm that cooperative MIMO technologies improve the cell-boundary throughput in real radio-propagation environments. This paper describes the developed field experimental system and its field evaluation results. It also shows the effectiveness of cooperative MIMO wireless transmission at the cell-boundary.