Multi-user Detection to Improve Downlink Communication of CSS-based LoRa-like Networks

Scalability is a crucial challenge in the Internet of Things. Especially Low Power wide area networks are planned with very wide cells a radius that can be of several km where a large number of devices may be located. One of the challenges of densification is downlink. Indeed the access point has to address a large number of devices but is constrained by the duty cycle. We propose a superposition scheme to send multiple packets to multiple devices in a single channel resource block. This scheme is applied to the specific physical layer proposed by LoRa, based on the chirp spread spectrum. Our proposal includes the power allocation scheme and the decoding algorithm which are very specific to this physical layer and show a significant performance improvement, increasing the number of devices that can be connected at least by ten.