A Low-Complexity LoRa Synchronization Algorithm Robust to Sampling Time Offsets

LoRaWAN is nowadays one of the most popular protocols for low-power Internet-of-Things communications. Although its physical layer, namely LoRa, has been thoroughly studied in the literature, aspects related to the synchronization of LoRa receivers have received little attention so far. The estimation and correction of carrier frequency and sampling time offsets is however crucial to attain the low sensitivity levels offered by the LoRa spread-spectrum modulation. The goal of this paper is to build a low-complexity, yet efficient synchronization algorithm capable of correcting both offsets. To this end, a complete analytical model of a LoRa signal corrupted by these offsets is first derived. Using this model, we propose a new estimator for the sampling time offset. We also show that the estimations of the carrier frequency and the sampling time offsets cannot be performed independently. Therefore, to avoid a complex joint estimation of both offsets, an iterative lowcomplexity synchronization algorithm is proposed. To reach a packet error rate of 10, performance evaluations show that the proposed receiver requires only 1 or 2 dB higher SNR than a theoretical perfectly synchronized receiver, while incurring a very low computational overhead.

[1]  Gang Wei,et al.  A Noniterative Frequency Estimator With Rational Combination of Three Spectrum Lines , 2011, IEEE Transactions on Signal Processing.

[2]  Barry G. Quinn,et al.  Estimation of frequency, amplitude, and phase from the DFT of a time series , 1997, IEEE Trans. Signal Process..

[3]  Nicolas Deparis,et al.  Low Complexity LoRa Frame Synchronization for Ultra-Low Power Software-Defined Radios , 2020, IEEE Transactions on Communications.

[4]  Peter J. Kootsookos,et al.  Fast, Accurate Frequency Estimators , 2007 .

[5]  Christophe Delacourt,et al.  On Time-Frequency Synchronization in LoRa System: From Analysis to Near-Optimal Algorithm , 2021 .

[6]  Utz Roedig,et al.  Do LoRa Low-Power Wide-Area Networks Scale? , 2016, MSWiM.

[7]  Alexios Balatsoukas-Stimming,et al.  On the Advantage of Coherent LoRa Detection in the Presence of Interference , 2020, IEEE Internet of Things Journal.

[8]  Mahesh Sooriyabandara,et al.  Does Bidirectional Traffic Do More Harm Than Good in LoRaWAN Based LPWA Networks? , 2017, GLOBECOM 2017 - 2017 IEEE Global Communications Conference.

[9]  Thomas Watteyne,et al.  Understanding the Limits of LoRaWAN , 2016, IEEE Communications Magazine.

[10]  Wen Hu,et al.  Measurement, Characterization, and Modeling of LoRa Technology in Multifloor Buildings , 2019, IEEE Internet of Things Journal.

[11]  Andreas Peter Burg,et al.  Lora Digital Receiver Analysis and Implementation , 2018, ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP).

[12]  Matthew Knight,et al.  Decoding LoRa: Realizing a Modern LPWAN with SDR , 2016 .

[13]  James Myers,et al.  F1: Intelligent energy-efficient systems at the edge of IoT , 2018, 2018 IEEE International Solid - State Circuits Conference - (ISSCC).

[14]  Konstantin Mikhaylov,et al.  On the coverage of LPWANs: range evaluation and channel attenuation model for LoRa technology , 2015, 2015 14th International Conference on ITS Telecommunications (ITST).

[15]  Wim Lamotte,et al.  A Multi-Channel Software Decoder for the LoRa Modulation Scheme , 2018, IoTBDS.

[16]  Ingrid Moerman,et al.  A Survey of LoRaWAN for IoT: From Technology to Application , 2018, Sensors.

[17]  Alexandre Marquet,et al.  Investigating Theoretical Performance and Demodulation Techniques for LoRa , 2019, 2019 IEEE 20th International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM).

[18]  Alexandre Marquet,et al.  Towards an SDR implementation of LoRa: Reverse-engineering, demodulation strategies and assessment over Rayleigh channel , 2020, Comput. Commun..

[19]  Gennaro Boggia,et al.  Energy Harvesting in LoRaWAN: A Cost Analysis for the Industry 4.0 , 2018, IEEE Communications Letters.

[20]  Alexios Balatsoukas-Stimming,et al.  An Open-Source LoRa Physical Layer Prototype on GNU Radio , 2020, 2020 IEEE 21st International Workshop on Signal Processing Advances in Wireless Communications (SPAWC).

[21]  Dominique Dallet,et al.  An Enhanced Receiver to Decode Superposed LoRa-Like Signals , 2020, IEEE Internet of Things Journal.

[22]  Lorenzo Vangelista,et al.  Frequency Shift Chirp Modulation: The LoRa Modulation , 2017, IEEE Signal Processing Letters.

[23]  Liesbet Van der Perre,et al.  Characterization of LoRa Point-to-Point Path Loss: Measurement Campaigns and Modeling Considering Censored Data , 2020, IEEE Internet of Things Journal.

[24]  Alexios Balatsoukas-Stimming,et al.  Coded LoRa Frame Error Rate Analysis , 2019, ICC 2020 - 2020 IEEE International Conference on Communications (ICC).

[25]  Stephen Brown,et al.  Analysis and Enhancement of the LoRaWAN Adaptive Data Rate Scheme , 2020, IEEE Internet of Things Journal.

[26]  David Bol,et al.  An 802.15.4 IR-UWB Transmitter SoC with Adaptive-FBB-Based Channel Selection and Programmable Pulse Shape , 2020 .

[27]  Fernand Meyer,et al.  A comparative study of LPWAN technologies for large-scale IoT deployment , 2019, ICT Express.

[28]  E. Jacobsen,et al.  Fast, Accurate Frequency Estimators [DSP Tips & Tricks] , 2007, IEEE Signal Processing Magazine.

[29]  Gennaro Boggia,et al.  Energy-Efficient LoRaWAN for Industry 4.0 Applications , 2020, IEEE Transactions on Industrial Informatics.

[30]  Alexios Balatsoukas-Stimming,et al.  On the Error Rate of the LoRa Modulation With Interference , 2020, IEEE Transactions on Wireless Communications.

[31]  Marco Chiani,et al.  On the LoRa Modulation for IoT: Waveform Properties and Spectral Analysis , 2019, IEEE Internet of Things Journal.