# Distributed MIMO Measurements for Integrated Communication and Sensing in an Industrial Environment
## 1 Introduction  
With the advances of the fifth and sixth generation of mobile communication systems, new application fields are emerging such as vehicle-to-everything, machine-to-machine communication, and smart cities [1]. With new applications, requirements on, e.g., data rates, the number of connected devices and reliability increase. Furthermore, many applications need to be able to communicate and sense the environment. In order to do so integrated communication and sensing (ICAS), where the same hardware and spectrum can be used for both purposes, has been given much attention in recent research. An application with very stringent requirements and that could benefit from ICAS is the industrial scenario [2], which is the focus here. As part of the development of wireless systems, new frequency bands are becoming available for communication, which also enables applications where sensing and communication coexist in the same band and use the same infrastructure and hardware [3, 4]. However, due to the more favorable propagation conditions, most systems will probably still operate in the sub-6 GHz band. Furthermore, in fifth-generation networks, massive MIMO technology is seen as the main enabler of many requirements due to its potential to improve signal-to-noise ratio (SNR) and increase coverage due to the array gain, the ability to simultaneously serve many users, and improved reliability; the latter us partly due to the fact that small-scale fading effects effectively vanish as the number of antennas increases. This effect is called channel hardening [5, 6]. With the small-scale fading effects significantly reduced, the experienced reliability is to a large extent dependent on the large-scale fading effects. To combat this, distributed (massive) MIMO, where the antennas are spread over a larger physical area, has emerged as a candidate. Solutions such as cell-free massive MIMO [7; 8] and holographic MIMO [9] are also being examined. Another candidate is RadioWeaves [3], which is a proposed network architecture that combines distributed arrays and active, large intelligent surfaces [10] with distributed computationto achieve high ultrareliable, low-latency communication. At the same time, the required amount of power to transmit is reduced due to the proximity of the users. Ultrareliable, low-latency communication is especially important in the industrial scenario. This scenario is a complex and rich environment from a propagation point of view, and channel characterization therefore becomes of great importance for designing radio systems to enable better communication quality and reliability. Hence, fading statistics need to be well studied in a given environment. These fading statistics are of great importance for the design of radio channel models and radio systems and for the development or investigation of, e.g., network schemes and coding techniques [11; 12] for a given application. With large aperture antenna arrays, such as in distributed MIMO, the commonly used assumption of wide-sense stationary and uncorrelated scatterers (WSSUS) channels is no longer valid. There are two types of nonstationarities: (1) The first is related to the large aperture and distributed MIMO, in which the plane wave propagation assumption breaks down and becomes the spherical wave propagation assumption, i.e., an operation in the near field [13]. Different subarrays experience different channels, e.g., due to the various distances to a user and the difference in observing the line-of-sight (LoS) and non-LoS (NLoS) paths among different antennas. (2) The second is related to the temporal nonstationarity of the environment due to the fact that the channel statistics change over time in dynamic scenarios with the movement of users and other objects. If both of these are violated, the channel is said to be doubly underspread [14]. As new concepts emerge, there is also a need to test the feasibility of these concepts, and an important part of this is designing and building test beds.