Measurement-Based Evaluation of the LTE MIMO Downlink at Different Antenna Configurations

Multi-antenna transmission modes are an integral feature of the 3GPP LTE downlink. While these modes are well defined in the standard there are no restrictions on the choice of transmit and receive antennas. In order to investigate the impact of the basestation antenna configuration on the LTE open loop downlink, a measurement campaign, comparing horizontally and vertically spaced antenna configurations for the two and four antenna case was performed whereas a considerable difference in performance depending on the antenna configuration is observed. Besides the evaluation in terms of LTE physical layer throughput the channel capacity and other measures have been calculated as upper bounds for the performance of a communication system. A comparison of the results for one, two and four transmit antennas shows that less than 50% of the channel capacity are reached and the higher the number of transmit antennas, the larger the gap between channel capacity and achievable throughput.