On the Advantage of Coherent LoRa Detection in the Presence of Interference

TL;DR

This paper investigates the performance of coherent LoRa detection under interference, demonstrating significant gains over non-coherent detection in interference-limited scenarios through derived error rate expressions and simulations.

Contribution

It provides rigorous error rate formulas and shows that coherent detection offers substantial improvements over non-coherent detection in interference conditions.

Findings

Coherent detection yields up to 10 dB gain over non-coherent detection at low SIR.

Derived error rate expressions closely match simulation results.

Coherent detection is more advantageous in interference-limited regimes than in AWGN channels.

Abstract

It has been shown that the coherent detection of LoRa signals only provides marginal gains of around 0.7 dB on the additive white Gaussian noise (AWGN) channel. However, ALOHA-based massive Internet of Things systems, including LoRa, often operate in the interference-limited regime. Therefore, in this work, we examine the performance of the LoRa modulation with coherent detection in the presence of interference from another LoRa user with the same spreading factor. We derive rigorous symbol- and frame error rate expressions as well as bounds and approximations for evaluating the error rates. The error rates predicted by these approximations are compared against error rates found by Monte Carlo simulations and shown to be very accurate. We also compare the performance of LoRa with coherent and non-coherent receivers and we show that the coherent detection of LoRa is significantly more beneficial in interference scenarios than in the presence of only AWGN. For example, we show that coherent detection leads to a 2.5 dB gain over the standard non-coherent detection for a signal-to-interference ratio (SIR) of 3 dB and up to a 10 dB gain for an SIR of 0 dB.