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The Physical Layer for Low Power Wide Area Networks: A Study of Combined Modulation and Coding Associated with an Iterative Receiver


Directeur de thèse :     Laurent ROS

École doctorale : Electronique, electrotechnique, automatique, traitement du signal (EEATS)

Spécialité : Signal, image, parole, télécoms

Structure de rattachement : Autre

Établissement d'origine : INP-PHELMA

Financement(s) : CIFRE


Date d'entrée en thèse : 12/05/2014

Date de soutenance : 10/07/2017


Composition du jury :
M. Didier LE RUYET - Rapporteur :
M. Charly POULLIAT - Rapporteur : charly.poulliat@ens
M. Michel JéZéQUEL - Examinateur :
M. Guillaume VIVIER - Examinateur :
M. Stephan TEN BRINK - Examinateur :
M. Jean-Marc BROSSIER - Examinateur :
Encadrants: Jean-Baptiste DORE et Vincent BERG (CEA), Laurent ROS (Gipsa-lab)


Résumé : Résumé: More than 10% of the Internet-of-Things (IoT) connections are expected to be realized through Low Power Wide Area (LPWA) networks, representing several billions of connected devices. Several industrial solutions have been developed and a standardization process is ongoing. The low levels of sensitivity and low data rate required for the long range communication are achieved by the means of two strategies: a narrow-band strategy and a low spectral efficiency strategy. Considering the limits of the information theory, additional gains in the communication's energy efficiency can be achieved. Nonetheless, a trade-off between spectral efficiency and energy efficiency should always be made. Reliable transmission with high energy efficiency will necessarily result in poor spectral efficiency, and in comparison, a system with a higher spectral efficiency has to consume more energy to transmit the same amount of bits with the same arbitrary level of error. This work considers the low spectral efficiency strategy. The combination of orthogonal modulations and a powerful channel code is studied. The scheme, so-called Turbo-FSK, associates the low spectral efficiency of Frequency Shift Keying (FSK) with the energy efficiency gain of a turbo receiver. Low levels of spectral efficiency can be achieved while optimizing the use of the available resource. The parameters of the scheme are optimized using a classic tool for iterative receivers, the Extrinsic Information Transfer (EXIT) chart. Performance of Turbo-FSK compared to existing LPWA solutions demonstrates the potential of the proposed solution to achieve low levels of sensitivity and to outperform existing schemes. However, the restrictions on low levels of spectral efficiency reduces the number of possible applications for the scheme. By introducing a linear component in the alphabet and a puncturing procedure, flexibility in spectral efficiency is achieved. A large range of spectral efficiencies can be obtained while maintaining performance close to the channel capacity theoretical limit. Eventually, more practical scenarios are considered for evaluating the performance of the scheme. Frequency selective channels are considered and an encapsulation in a Fast Fourier Transform (FFT) based system is implemented. Various indicators are studied and the Turbo-FSK scheme is compared to well-known technologies, such as schemes using Orthogonal Frequency Division Multiplexing (OFDM) associated with a powerful Forward Error Correction (FEC) scheme, namely Turbo Code (TC).

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