Impact of antenna downtilt on cooperative uplink detection in a large scale field trial

The spectral efficiency of today´s cellular networks that feature small inter-site distance and high spectral reuse is limited by inter-cell interference. An effective means to cope with the signal radiation across cell boundaries in the cellular uplink is joint detection of multiple users at cooperative base stations (BSs), a concept known as network MIMO or coordinated multipoint (CoMP). However, it is well known that the cluster size of cooperating base stations is limited in a real system due to backhaul, latency and signaling constraints. Thus, cooperation of base station needs to be applied jointly with other methods for inter cell interference reduction. An important lever is the usage of antenna downtilt to control the direction of the vertical antenna pattern and, therefore, the distance of signal propagation. In this work, we investigate the effect of the antenna downtilt on the performance of cooperative uplink detection in a large scale field trial and show the importance of downtilt optimization for cooperative systems.