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.
Highlights
I NTERNET-OF-THINGS technology opens up a plethora of new applications and services in various domains
We focus in particular on massive multiple-input and multiple-output (MIMO) technology as it bears a great potential in view of the above listed requirements: 1) It can support an unprecedented number of simultaneous connections through extensive spatial multiplexing
When investigating the impact of the number of base station antennas, we selected Ms subsequent array elements according to their numbering
Summary
I NTERNET-OF-THINGS technology opens up a plethora of new applications and services in various domains. While the results are generally applicable, we here focus on communication tailored for IoT This means that (i) a narrowband signal is used, (ii) the carrier frequency is subGHz, (iii) the number of gateway antennas are more limited than in cellular networks and (iv) the nodes can be considered static. Whereas commonly the single-antenna device is denoted as the user equipment (UE) in a massive MIMO or Long-Term Evolution (LTE) context, in an Internet-of-Things setting the term node or IoT node is used. We assess the potential of deploying massive MIMO in the unlicensed sub-GHz band for upgraded IoT connectivity based on the measured channel responses. Our contributions reported on here are (i) an analysis of channel propagation characteristics for large antenna array systems and (ii) an assessment of massive MIMO opportunities and challenges for IoT. The set of complex numbers is denoted by the symbol C
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