# Temporal Analysis of Measured LOS Massive MIMO Channels with Mobility

## TL;DR

This study presents the first measured results of LOS massive MIMO channels with mobility, analyzing how mobility affects channel state information update rates and system performance in a practical scenario.

## Contribution

It provides empirical data on the impact of mobility on massive MIMO channels and quantifies the increased CSI update rate needed for large antenna systems under mobility.

## Key findings

- CSI update rate may increase by 7 times with 100 antennas under mobility.
- Power control update rate can decrease by at least 5 times with 100 antennas.
- Channel correlation degrades with vehicle speeds up to 29 km/h.

## Abstract

The first measured results for massive multiple-input, multiple-output (MIMO) performance in a line-of-sight (LOS) scenario with moderate mobility are presented, with 8 users served by 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the inherent propagation and processing delay has a critical relationship with the rate of change, as the use of outdated channel information can result in severe detection and precoding inaccuracies.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 correlation of the MIMO channel vector over time is inspected for vehicles moving up to 29 km/h. 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.