# IoT-U: Cellular Internet-of-Things Networks over Unlicensed Spectrum

## TL;DR

This paper proposes IoT-U, a scheme for cellular IoT networks utilizing unlicensed spectrum to support more devices efficiently by optimizing device association and power usage.

## Contribution

It introduces a novel unlicensed spectrum scheme for cellular IoT networks and develops an efficient optimization framework for device scheduling and association.

## Key findings

- Supports more IoT devices than licensed spectrum alone
- Efficient optimization reduces transmit power
- Decoupling approach solves NP-hard problem effectively

## Abstract

In this paper, we consider an uplink cellular Internet-of-Things (IoT) network, where a cellular user (CU) can serve as the mobile data aggregator for a cluster of IoT devices. To be specific, the IoT devices can either transmit the sensory data to the base station (BS) directly by cellular communications, or first aggregate the data to a CU through Machine-to-Machine (M2M) communications before the CU uploads the aggregated data to the BS. To support massive connections, the IoT devices can leverage the unlicensed spectrum for M2M communications, referred to as IoT Unlicensed (IoT-U). Aiming to maximize the number of scheduled IoT devices and meanwhile associate each IoT devices with the right CU or BS with the minimum transmit power, we first introduce a single-stage formulation that captures these objectives simultaneously. To tackle the NP-hard problem efficiently, we decouple the problem into two subproblems, which are solved by successive linear programming and convex optimization techniques, respectively. Simulation results show that the proposed IoT-U scheme can support more IoT devices than that only using the licensed spectrum.