Field Experiment of Multi-BS Cooperative Transmission Control over X2 Interface for LTE/LTE-Advanced

摘要

The multiple base station cooperation approach has been attracting much attention recently. In 3GPP, this approach is referred to as CoMP. The promising techniques in CoMP are joint transmission and dynamic cell selection. They improve cell-edge UE throughput through the cooperation of eNBs, however, the signal-processing burden or the technical difficulties to realize the accurate synchronous transmission is high. As an alternative for improving cell-edge throughput, cooperative transmission control has been proposed, in which signal transmission is conducted from only the serving cell while transmission from its neighbor cell is stopped. This technique can mitigate the signal-processing burden or the technical difficulties of CoMP while achieving sufficient throughput improvement. However, the previous studies were based on centralized cooperation with the use of an optical fiber system such as RRH or RoF. Therefore, cooperation is possible only within the eNBs connected to the same central signal processing unit. To avoid this limitation, we propose cooperative transmission control based on a distributed cooperation approach that uses an inter- eNB interface such as X2. It allows cooperative transmission control to be realized at any cell border. We also propose the control algorithm to start and end the cooperation properly, which is a key part to improve cell-edge throughput effectively on the distributed approach. We also develop a prototype system to demonstrate the feasibility and the performance of the proposal. Through laboratory and field experiments, we show that the proposal works well with real equipment and that cell-edge UE throughput performance can be improved drastically.