Field Experiments on 1-Gbps Data Transmission Using 4-by-2 Multi-User MIMO with Cross-Polarized Linear Antenna Array in LTE-Advanced Downlink

This paper presents field experimental results on real-time 1-Gbps data transmission using 4-by-2 multi-user (MU) multiple-input multiple-output (MIMO) when a cross-polarized linear antenna array is employed as the base station (BS) transmitter antennas in the Long Term Evolution (LTE)-Advanced downlink. In the evaluations, we clarify the influence of the difference between directions of departure (DoDs) for two spatially multiplexed mobile stations (MSs) on the achievable throughput using experimental equipment, where eigenvalue decomposition (EVD)-based channel state information (CSI) feedback for each subband is implemented for MU-MIMO operation. Field experiments are conducted in urban and suburban areas where one MS travels at the average speed of 10 km/h and the other MS is static. Field experimental results show that the total throughput of greater than 1 Gbps can be achieved for Rank-4 MU-MIMO by utilizing a cross-polarized linear antenna array with low and high correlated antenna pairs when the difference between the DoDs for the spatially multiplexed MSs is within the range of approximately 40 to 70 and 50 to 55 degrees in suburban and urban areas, respectively. Furthermore, we show that the achievable throughput for Rank-2 MU-MIMO is relatively robust against the difference in the DoD and line-of-sight (LOS) or non-LOS (NLOS) conditions.