This article presents a semianalytical approximation of symbol error rate (SER) for the well known long-range (LoRa) Internet of Things (IoT) modulation scheme in the following two scenarios: 1) in multipath frequency selective fading channel with additive white Gaussian noise (AWGN) and 2) in the presence of a second interfering LoRa user in the flat-fading AWGN channel. Performances for both coherent and noncoherent cases are derived by considering the common discrete Fourier transform (DFT)-based detector on the received LoRa waveform. By considering these two scenarios, the detector exhibits parasitic peaks that severely degrade the performance of the LoRa receiver. We propose in that sense a theoretical expression for this result, from which a unified framework based on peak detection probabilities allows us to derive SER, which is validated by Monte Carlo simulations. Fast computation of the derived closed-form SER allows to carry out deep performance analysis for these two scenarios.

This article presents a novel long-range (LoRa) receiver operating in the frequency selective multipath channel (MPC). The dechirped received LoRa waveforms under MPC allows us to derive a simple and efficient LoRa receiver scheme by using a matched filter (MF) approach that aims to maximize the signal-to-noise ratio (SNR) at the symbol index frequency of the discrete Fourier transform (DFT) output. We show that the MF receiver can be seen as a RAKE structure where interference peaks related to multipath, exhibited at DFT output, are recombined in a constructive way. Detection performance is driven by channel energy and the benefit of this novel MF/RAKE receiver over original coherent and noncoherent receiver appears only for MPC that exhibits significant paths energy. These two MF and RAKE receivers have however different implementation complexities that are studied in detail. We provide in that sense recommendations on which receiver variant to use for real operations, depending on complexity constraints. Finally, the proposed MF/RAKE receiver outperforms previous results on time-delay estimation LoRa (TDEL) receiver over MPC, especially at low SNR and higher LoRa spreading factor (SF) parameter, at the cost of higher but reasonable complexity.

In this paper, we present a new LoRa transceiver scheme to ensure discrete communications secure from potential eavesdroppers by leveraging a simple and elegant spread spectrum philosophy. The scheme modifies both preamble and payload waveforms by adapting a current state-of-the-art LoRa synchronization front-end. This scheme can also be seen as a self-jamming approach. Furthermore, we introduce a new payload demodulation method that avoids the adverse effects of the traditional cross-correlation solution that would otherwise be used. Our simulation results show that the self-jamming scheme exhibits very good symbol error rate (SER) performance with a loss of just 0.5 dB for a frequency spread factor of up to 10.

A LoRa self‐jamming scheme that enables secure and covert communications by adding jamming symbols when transmitting is proposed. The scheme has been validated in simulations. The work is continued by evaluating the scheme on real‐world software defined radio (SDR) equipment. Experiments immediately showed that a demodulation is impossible as the received signal is highly distorted. This comes from the fact that adding symbols at transmission actually generates high peak‐to‐average power ratio (PAPR) preventing proper waveform generation by the equipment's hardware. This paper presents a PAPR correction scheme that modifies the waveform. The properties of this modified waveform are analysed and the performances are assessed in simulations with realistic time and frequency synchronization assumption. For the ideal 0 dB PAPR corrected output, the SER performances are close to that of a legacy LoRa communication, while preserving the physical layer security capabilities of the self‐jamming scheme. It is finally shown that our PAPR correction scheme effectively recovers the self‐jamming properties on SDR devices.

Cette thèse a pour objectif de proposer des améliorations pour le standard de l’Internet des Objets (IoT) LoRa selon deux axes : 1) la modification du récepteur classique pour améliorer les performances de démodulation en présence d’un canal multi-trajets et 2) proposer une sécurisation de la couche physique pour renforcer la confidentialité des transmissions. Pour le premier axe, une étude de l’impact des canaux multi-trajets est proposée et débouche sur le calcul de l’expression analytique du taux d’erreur symbole LoRa. Fort de cette étude, le récepteur améliore LoRa RAKE exploitant de façon constructive l’énergie des trajets est conçu et évalué pour le scénario réaliste d’un canal multi-trajets à répliques proches du trajet direct avec prise en compte de la synchronisation. Pour le second axe, une étude de l’impact des brouilleurs classiques Band et Tone Jamming est réalisée et montre les performances sous-optimales de ces brouilleurs. Ainsi, un schéma d’auto-brouillage de la forme d’onde LoRa est proposé, réduisant fortement les capacités de démodulation des intercepteurs, renforçant ainsi le niveau de confidentialité de la transmission. Le Peak-to-Average Power Ratio (PAPR) généré par ce schéma est étudié et une méthode de réduction de ce dernier est proposée. Enfin, des expérimentations sur des matériels de type Software Defined Radio (SDR) sont menées et démontrent la viabilité du schéma d’auto-brouillage.