Experimental Exploration of Unlicensed Sub-GHz Massive MIMO for Massive Internet-of-Things

Abstract

IoT networks are getting overcrowded following the vast increase in number of Internet-of-Things (IoT) devices and connections. Networks can be extended with more gateways, increasing the number of supported devices. However, as investigated in this work, massive MIMO has the potential to increase the number of simultaneous connections and moreover lower the energy expenditure of these devices. We present a study of the channel characteristics of massive MIMO in the narrowband unlicensed sub-GHz band. The goal is to support IoT applications with strict requirements in terms of number of devices, power consumption, and reliability. The assessment is based on experimental measurements using both a uniform linear and a rectangular array. Our study demonstrates and validates the advantages of deploying massive MIMO gateways to serve IoT nodes. While the results are general, here we specifically focus on static nodes. The array gain and channel hardening effect yield opportunities to lower the transmit power of IoT nodes while also increasing reliability. The exploration confirms that exploiting large arrays brings great opportunities to connect a massive number of IoT devices by separating the nodes in the spatial domain. In addition, we give an outlook on how static IoT nodes could be scheduled based on partial channel state information.

A Light Signaling Approach to Node Grouping for Massive MIMO IoT Networks

“…For static nodes, these two characteristics of the channel will remain stable over a long period of time, as demonstrated in [28,29]. If there is a line-of-sight component present, this will typically constitute the dominant component, and its direction will not change unless shadowing occurs to block it.…”

“…In [37], clusters are generated homogeneously; however, our use case concerns channels that exhibit clear dominant directions [28]. To model this, for each node, we amplified the cluster with the highest power, by multiplying it by a scalar drawn uniformly randomly from the interval [2.0, 6.0].…”

Investigations of the Wireless M-Bus System Resilience under Challenging Propagation Conditions

“…An example may be the packet error rate PER measurements of the LoRa system [33]. At the same time, research is underway on the use of Massive MIMO to reduce the energy consumed by transmission devices [34]. Admittedly, determining the propagation attenuation with high accuracy is essential, but it is equally important to determine the CNIR values for which the system achieves a certain PER value.…”

Channel Charting Aided Pilot Reuse for Massive MIMO Systems With Spatially Correlated Channels

“…where α n,s,l is the complex gain of the lth path, which is assumed to be an independent and identically distributed (i.i.d.) complex Gaussian random variable with zero mean 2 In practical systems, the outdoors coverage area is usually divided into three or six sectors of 120 • or 60 • [37]. We consider S = 3 in the examples.…”