Real-Life Indoor MIMO Performance with Ultra-Compact LTE Nodes

Abstract

With the ever increasing demand for mobile broadband service with very high bitrates to indoor users, there is large industry traction around different types of In Building Solutions (IBS) for Long Term Evolution (LTE). Multiple Input Multiple Output (MIMO) is a key feature in LTE enabling significantly improved user bitrates, and the indoor channel characteristics are also expected to be in favor for MIMO performance. Despite this, due to deployment constraints and design constraints on the IBS antenna design and size, many IBS deployments of today do not support MIMO. As the market evolves, this is finally changing and in this paper, the 2x2 MIMO performance is measured in real-life with small-size radio equipment, a commercial smartphone and a low-power radio head, both with a size of approximately a wavelength. Despite the small antennas, the performance is found to be very good supporting rank-2 transmission on almost the whole 2500 m² office floor with only 100 mW transmission power. In more than half of the area, the user bitrate exceeds the maximum rank-1 bitrate, demonstrating the value of MIMO. Also in Line-Of-Sight (LOS) conditions, traditionally a weakness for MIMO performance, the indoor channel richness facilitates rank-2 transmission. The 2x2 MIMO performance is found to be limited rather by propagation loss than MIMO channel characteristics and antenna size, which demonstrates the potential for ultra-compact 2x2 MIMO indoor antenna heads.