Jury:

• Marion BERBINEAU, Director of Research, IFSTTAR (Thesis supervisor)
• Iyad DAYOUB, Professor, UPHF (Co-Director of thesis)
• Kosai RAOOF, Professor, University of Le Mans (Examiner)
• Loic BRUNEL, Research Director, Mitsubishi Electric R&D Centre Europe (Examiner)
• Karine AMIS, Professor, IMT Atlantique (Rapporteur)
• Michel TERRE, University Professor, CNAM (Rapporteur)

Summary:

With the increasing automation of command and control functions in the rail sector, we are now seeing a drastic increase in information exchanges. These exchanges are crucial to the deployment of autonomous trains, reducing operating and maintenance costs and improving safety. At the same time, many new information and entertainment services based on communication systems are being offered to passengers. However, there is no single technology today that can satisfy all the demanding needs in terms of performance. As a result, a number of industrial and academic research projects are underway at European and international level to develop the Future Railway Mobile Communication System (FRMCS). This system will be based on IP technology and will be adaptive, agnostic to radio technology and resilient to technological change. It will also have to offer high data rates, low latency, high bandwidth and efficient use of spectrum.

FRMCS will need to be able to choose in real time between different available radio access technologies depending on the needs of the applications and the railway environment. The available access technologies include Wi-Fi, LTE, satellite and the 5G NR standard currently under development. Thus, the contributions of this doctoral thesis fall within the framework of the development of an adaptable communication system (ACS) for railways, taking into account the cutting-edge technologies of the future 5G NR standard and beyond.

Various key technologies have recently been proposed as part of the 5G NR standard and beyond. Among these, radio access techniques play a major role in key metrics such as efficient use of available spectrum, high data rates and transceiver system complexity. One of the major technological developments in this area is the introduction of various multi-carrier modulation (MCM) and non-orthogonal multiple access (NOMA) techniques.

In this doctoral thesis, we begin by studying MCM technology in the context of the challenges posed by high-speed rail. A performance evaluation is carried out considering different multi-carrier systems in different scenarios. The Filtered Bank Multi-Carrier (FBMC) waveform offers high robustness in high mobility scenarios while making efficient use of the available spectrum. However, the advantages of FBMC modulation are accompanied by additional intrinsic interference that challenges traditional transceiver design techniques. Thus, we propose various contributions that concern channel estimation and equalization techniques for the FBMC waveform. The contributions aim at increasing the final performance at the cost of negligible additional complexity compared to the existing literature.

Finally, in order to exploit the throughput gains associated with the emerging multiple access technique, NOMA, we have considered a global NOMA system associated with multi-carrier techniques. We first highlight the advantages of the various NOMA systems associated with multi-carrier techniques compared with the traditional orthogonal multiple access system associated with multi-carrier techniques. However, the non-orthogonal multiple access systems associated with multi-carrier techniques (NOMA-MCM) suffer from two types of intrinsic interference which originate from the NOMA and MCM techniques respectively. Based on this observation, we proposed a common iterative interference cancellation scheme. This scheme is evaluated in different railway propagation channel scenarios and we present the performance improvements obtained.

Abstract:

Nowadays, a huge amount of data exchanges is needed in the railway system. This is particularly to support autonomous train, reduce operation and maintenance costs, increase safety and security. At the same time, many new services are offered to passengers. There is no unique technology that can satisfy all these needs. Consequently, different industrial and academic research projects are on-going at European and International levels to develop the Future Railway Mobile Communications System (FRMCS). FRMCS will be IP-based, adaptable, agnostic to radio technology and resilient to technological evolutions. In addition, it should support high data rate, low latency, large bandwidth, and efficient spectrum utilization.

The FRMCS is expected to be able to choose in real time between different available radio access technologies in function of applications needs and the surrounding railway environment. Among these technologies, we can mention the Wi-Fi, LTE, satellites and the 5G NR standard in development. Thus, the contributions of this PhD thesis are part of the development of an Adaptable Communication System (ACS) for the railway by considering cutting-edge technologies of the future 5G NR system and beyond.

Different key enabling technologies have been proposed recently under the umbrella of 5G and Beyond communication systems. Among which, radio access techniques play major role over key metrics, such as the efficient utilization of the available spectrum, the high data rates, and the computational complexity of the transceiver system. One of the major technological evolution in that domain concerns the introduction of different Multi-Carrier Modulation (MCM) and Non-Orthogonal Multiple Access (NOMA) techniques.

In this Ph.D thesis, we start by considering the MCM technology in the context of high speed railway. A performance evaluation study is conducted where different MCM schemes are highlighted in different scenarios. The Filtered Bank Multi-Carrier (FBMC) waveform presents high robustness to high mobility scenarios while exploiting the available spectrum efficiently. However, FBMC advantages come with additional built-in interference that challenges traditional transceiver design techniques. Thereby, we propose different contributions that handle the channel estimation and equalization aspects of the FBMC waveform. The contributions aims to assure better performance at the cost of negligible additional complexity compared with the literature.

Finally, to exploit the data rate gains accompanied with the emerging NOMA technology, we consider the overall MCM based NOMA system. We start by emphasizing the accompanied gains of the different MCM based NOMA schemes compared with the traditional orthogonal multiple access schemes. Thereafter, and to handle the MCM and NOMA induced interference in MCM based NOMA systems, we propose a joint iterative interference cancellation scheme that deals with both interference components. We evaluate this study in different channel scenarios and present accompanied improvements.