# Allocation of Repetition Redundancy in LoRa

## TL;DR

This paper proposes a redundancy allocation strategy for LoRa networks that significantly improves measurement delivery reliability and reduces energy consumption by considering fading and interference effects.

## Contribution

It introduces a novel redundancy allocation method tailored for LoRa, accounting for fading and interference, to enhance reliability without acknowledgments.

## Key findings

- Up to six orders of magnitude decrease in outage probability.
- Up to 30% reduction in average energy consumption.
- Effective redundancy allocation under duty-cycle and delay constraints.

## Abstract

We consider a multipoint-to-point network in which sensors periodically send measurements to a gateway. The system uses Long Range (LoRa) communications in a frequency band with duty-cycle limits. Our aim is to enhance the reliability of the measurement transmissions. In this setting, retransmission protocols do not scale well with the number of sensors as the duty cycle limit prevents a gateway from acknowledging all receptions if there are many sensors. We thus intend to improve the reliability without acknowledgments by transmitting multiple copies of a measurement, so that the gateway is able to obtain this measurement as long as it receives at least one copy. Each frame includes the current and a few past measurements. We propose a strategy for redundancy allocation that takes into account the effects of fading and interference to determine the number of measurements to be included in a frame. Numerical results obtained using the simulation tool LoRaSim show that the allocation of redundancy provides up to six orders of magnitude decrease in the outage probability. Compared to a system that blindly allocates the maximum redundancy possible under duty-cycle and delay constraints of the gateway and memory constraints of the sensors, our technique provides up to 30% reduction in the average energy spent to successfully deliver a measurement to the gateway.