Interference Cancellation for LoRa Gateways and Impact on Network Capacity

Domenico Garlisi,Fabrizio Giuliano,Stefano Mangione,Ilenia Tinnirello,Daniele Croce,Giovanni Garbo

doi:10.1109/access.2021.3108021

Abstract

In this paper we propose LoRaSyNc (LoRa receiver with SyNchronization and Cancellation), a second generation LoRa receiver that implements Successive Interference Cancellation (SIC) and time synchronization to improve the performance of LoRa gateways. Indeed, the chirp spread spectrum modulation employed in LoRa experiences very high capture probability, and cancelling the strongest signal in case of collisions can significantly improve the cell capacity. An important feature of LoRaSyNc is the ability to track the frequency and clock drifts between the transmitter and receiver, during the whole demodulation of the interfered frame. Due to the use of low-cost oscillators on end-devices, a signal cancellation scheme cannot result accurate without such a tracking, especially at the lower data rates. We validate the performance of LoRaSyNc in presence of collisions by implementing a receiver prototype on software-defined-radios, and perform several experiments in different realistic scenarios, by also comparing our receiver with commercial gateways. Finally, we simulate a cell deployment with one or more gateways, showing that the proposed scheme improves performance by almost 50% compared to a traditional receiver.

Highlights

In the last years, we have assisted to a steep increase of Internet of Things (IoT) applications and devices
IMPACT OF SIGNAL CANCELLATION ON LoRa CELL DEPLOYMENTS We evaluate the performance achieved by LoRaSyNc in terms of capacity improvements, which can be achieved in a cell, where all devices are configured on the same Spreading Factors (SFs)
LoRa modulation has been demonstrated to be very robust to different interference sources, including co-channel interference generated by collisions between multiple overlapping frames

Summary

INTRODUCTION

We have assisted to a steep increase of Internet of Things (IoT) applications and devices. The proposed LoRaSyNc receiver is accompanied by a clock drift tracking scheme which, as we will show, is fundamental to keep the residual cancellation noise at a minimum and improve performance when working with low-cost oscillators (typical of LoRaWAN devices). In [19] and [20] the scalability of a LoRa network is studied considering the impact of the capture effects These results could significantly be improved considering the interference cancellation scheme proposed in this paper. The work in [7] proposes a receiver capable of processing LoRa collisions using commercialized LoRa chips These studies present good results in realistic settings, none of them draw conclusions on the performance that such schemes could achieve in a scenario with thousands of active end-devices and many GWs covering the same area. Promising, these techniques are orthogonal to the LoRaSyNc approach presented in this paper and could be included in future works to further improve the performances of an enhanced LoRa GW

BACKGROUND

LoRa MODULATION AND FRAMING

CARRIER AND TIME SYNCHRONIZATION

DATA EXTRACTION RATE IN CASE OF COLLISIONS

Findings

CONCLUSION