Field Experiment of CoMP Joint Transmission over X2 Interface for LTE-Advanced

Multiple base station cooperation techniques have been attracting much attention for the improvement in cell-edge throughput recently. In 3GPP, such techniques are referred to as CoMP and studied actively. Joint transmission is a promising technique in CoMP. In CoMP JT, previous studies have mainly focused on intra-eNB CoMP because it is relatively easy to implement. The intra-eNB CoMP JT in combination with optical fiber systems such as RRH or RoF can realize throughput improvement at cell edge. However, the number of RRHs being able to be connected to the same eNB is usually limited to a few because of the signal-processing capability of eNB. Therefore, CoMP JT can be used only within the cells connected to the same eNB, which makes it impossible to use CoMP JT between at any cell border. To enable all cell-edge UEs enjoy the merit of CoMP JT, CoMP JT based on a distributed cooperation approach using inter-eNB interface such as X2 interface has been proposed. In the distributed cooperation, CoMP JT can be realized in a distributed manner, so that CoMP JT can be used at any cell border. However, the previous studies focused on only concepts or evaluation by computer simulations. To verify the feasibility and its effect with real system, we developed a prototype system of CoMP JT realized on a distributed cooperation approach using inter-eNB interface. The technical details to realize it is shown in this paper. We also conducted laboratory and field experiments and demonstrated its feasibility. Also, we confirmed that drastic throughput improvement at cell edge can be realized with the real system.