Performance Characterization of a Real-Time Massive MIMO System With LOS Mobile Channels

Abstract

The first measured results for massive multipleinput, multiple-output (MIMO) performance in a line-of-sight (LOS) scenario with moderate mobility are presented, with eight users served in real-time using a 100-antenna base Station (BS) at 3.7 GHz. When such a large number of channels dynamically change, the inherent propagation and processing delay has a critical relationship with the rate of change, as the use of outdated channel information can result in severe detection and precoding inaccuracies. For the downlink (DL) in particular, a time division duplex (TDD) configuration synonymous with massive MIMO deployments could mean only the uplink (UL) is usable in extreme cases. Therefore, it is of great interest to investigate the impact of mobility on massive MIMO performance and consider ways to combat the potential limitations. In a mobile scenario with moving cars and pedestrians, the massive MIMO channel is sampled across many points in space to build a picture of the overall user orthogonality, and the impact of both azimuth and elevation array configurations are considered. Temporal analysis is also conducted for vehicles moving up to 29 km/h and realtime bit error rates (BERs) for both the UL and DL without power control are presented. For a 100-antenna system, it is found that the channel state information (CSI) update rate requirement may increase by 7 times when compared to an 8-antenna system, whilst the power control update rate could be decreased by at least 5 times relative to a single antenna system.

Massive MIMO Performance—TDD Versus FDD: What Do Measurements Say?

“…UEs send pilots on the uplink (UL); all UE-to-BS channels are estimated, and each antenna has its own RF electronics. The concept has, since its introduction a decade ago [1], [3], matured significantly: rigorous information-theoretic analyses are available [2], field-trials have demonstrated its performance in scenarios with moderate mobility [5]- [7], and circuit prototypes have shown the true practicality of implementations [8].…”

Efficient DSP and Circuit Architectures for Massive MIMO: State of the Art and Future Directions

“…Smart processing at the array exploits differences among the propagation signatures of the terminals to perform spatial multiplexing. Massive MIMO offers two main benefits: 1) Excellent spectral efficiency, achieved by spatial multiplexing of many terminals in the same time-frequency resource [4], [5]. Efficient multiplexing requires channels to different terminals to be sufficiently distinct.…”

Hardware Distortion Correlation Has Negligible Impact on UL Massive MIMO Spectral Efficiency

“…The typical Massive MIMO configuration is M ≈ 100 antennas and K ∈ [10,50] UEs [8,Sec. 7.2], [14], [15], which is "massive" as compared to conventional multiuser MIMO. These parameter ranges are what we refer to as Massive MIMO in this paper.…”