PhD defense of Tania Alhajj on May 17th, 2023

The defense of PhD thesis of Tania Alhajj will be held on May 17th, 2023 at 10:00 in the Rennes campus of IMT Atlantique (Petit amphi). It will be accessible with a conf call. The thesis is entitled “Impact of centralized-radio access network architecture on 5G performances”. It was partially funded by Région Bretagne.

Fifth Generation (5G) mobile networks are paving the way for a new Radio Access Network (RAN) architecture. This is the Centralized-RAN (C-RAN) which groups some of the Base Station (BS) functions in a Central Unit (CU) connected to Radio Units (RU) distributed in different sites where the other BS functions are implemented. This thesis studies how to take advantage of C-RAN to combine high reliability and low latency on the one hand and to minimize the power consumption of the BS on the other hand. Both single and multi-RU transmissions, as well as a mixture of both, are evaluated. We compare a single-RU approach where the Hybrid Automatic Repeat reQuest (HARQ) mechanism, which combines all the ARQ re-transmissions, is located in the RU to a multi-RU transmission with an HARQ centralized in the CU. We show that multi-RU transmissions provide high reliability and low latency due to spatial diversity, even though centralization increases the round trip time. We then consider radio resource allocation. We evaluate the energy consumed by the BSs using a consumption model that integrates both the transmission power and the energy consumed for processing. At low load, multi-RU transmissions in a C-RAN, where all RUs serve one user, save BS energy consumption, without coverage degradation, compared to serving a user with a single RU. We pose and solve an optimization problem to minimize the energy consumption and increase the capacity to moderate load by reusing radio resources between RUs.

PhD defense of Juan Carlos Vargas Rubio on March 23th, 2023

The defense of PhD thesis of Juan Carlos Vargas Rubio will be held on March 23th, 2023 at 10:00 in the Rennes campus of IMT Atlantique (Petit amphi). It will be accessible with a conf call. The thesis is entitled “Unicast versus Broadcast in Cellular Networksn 5G Radio Access Networks”. It was made in the framework of a CIFRE contract within Enensys.

Data traffic on mobile networks increases every year, especially video content. However, spectrum is scarce and expensive and operators need to optimize its use. In scenarios where the same content is transmitted at the same time to many devices in the same geographical area, the preferred solution to reduce bandwidth consumption is broadcast transmission.
Unicast transmission benefits from link adaptation techniques. However, the same content is transmitted as many times as the number of users demanding the same service. Conversely, a single broadcast transmission can cover a large number of users. Nevertheless, the bitrate in broadcast is fixed considering the users with the worst channel quality. Multicast-Broadcast Single-Frequency-Network (MBSFN) is a broadcast technique in which a group of synchronized cells transmit the same waveform. On the other hand, with Single-Cell Point-To-Multipoint (SC-PTM) each cell performs broadcast transmission independently. The problem is to determine when is it better to use unicast, MBSFN or SC-PTM.
In our work, we compare the performance of unicast, MBSFN and SC-PTM through system level simulations and analytical models. We consider base stations located according to Poisson distributions, the use of beamforming in unicast and different broadcast configurations. Furthermore, we propose an analytical method to calculate the number of users demanding the same content from which MBSFN or SC-PTM become more efficient than unicast. We prove that a switching mechanism based on this user threshold reduces bandwidth utilization and energy consumption. This method is based on stochastic geometry results for wireless networks.

PhD defense of Flavien Ronteix–Jacquet on Dec 13th, 2022

The defense of PhD thesis of Flavien Ronteix–Jacquet will be held on December 13th, 2022 at 10:00. It will be accessible with a conf call. The thesis is entitled “Reducing Latency and Jitter in 5G Radio Access Networks”. It was made in the framework of a CIFRE contract within Orange.


Cellular networks present high latencies, especially in the Radio Acccess Network (RAN). The new generation of cellular technology 5G, in addition to increasing transmission throughput, must offer low latency in mobile connectivity.The objective of this thesis is to propose mechanisms for reducing latency in the RAN. In this perspective, we set up a software-defined RAN experimentation platform based on the OpenAirInterface project and designed a tool for fine-grained measurement of RAN internal latencies called LatSeq. We show that the round-time trip latency typically reaches 30 ms in LTE divided between processing, queueing, retransmission and medium acquisition delays. We also measure a significant jitter on the uplink that affects the RAN latency but also the performance of TCP traffics, which are very common on the Internet. LatSeq highlights the role of the radio resource allocation mechanism in the jitter and latency of the uplink channel. We show how the partial knowledge of the transmission buffer length by the scheduling algorithm from Buffer Status Reports (BSRs) and Scheduling Requests (SRs) induces bursts of transmissions, significant jitter and under-utilization of the radio channel capacity. We then propose a new mechanism for estimating the terminal transmission buffer length compatible with 3GPP LTE and 5G standards. We demonstrate that this method makes it possible to reduce the latency of the uplink channel and even more the jitter experienced by packet flows.

PhD defense of Bruno STEVANT on May 23rd, 2022

Bruno Stevant defended his thesis on May 23, 2022 at 10:00 am in room Petri at IRISA. The title of the thesis is “Dynamic orchestration of microservices according to usage conditions.” The supervision of this thesis was provided by Jean-Louis Pazat, professor at INSA Rennes, and Alberto Blanc.


A participatory infrastructure aims to provide a hosting solution for services for a virtual community of users. Such a community has needs that are not fully met by data center hosting solutions. We therefore propose a new approach where community members host these services on their home devices. Such a participatory infrastructure raises issues related to the heterogeneity of the participating devices and networks, as well as to the variations in their computing and communication capabilities.

Through the study of existing solutions, the software architecture based on microservices has aroused our interest. It allows a more flexible placement of applications on the participating devices. The first part of our work consisted in finding a placement of the microservices on these devices that optimizes the response time of the applications. After defining a model of this response time, we used the PSO heuristic to find a solution close to the optimal one.

We tested this placement in real use conditions to evaluate the influence of network QoS variations on the application response time. This study showed that, under certain conditions, an adaptation of the placement could improve the measured performance. We have therefore added to our participatory infrastructure a mechanism capable of deciding whether an adaptation is necessary based on the measured response times, and to compute a placement adapted to the new conditions.

PhD defense of Amanvon Ferdinand ATTA on December 9th, 2021

Amanvon Ferdinand Atta defended his thesis on December9, 2021 at 8:30 am (GMT) in B3 room at Cocody Danga Campus of Institut National Polytechnique Félix Houphouët Boigny in Côte d’Ivoire. The title of the thesis is “Reconfiguration of Multicast Routing in Sparse Wavelength Converter Networks”. The direction of this thesis has been assured by Prof. Bernard Cousin and Prof. Souleymane Oumtanaga. The jury members were Michel Babri, Miklos Molnar, Eyouléki T. G. Palanga, Mouhamadou Dosso, Bernard Cousin, Souleymane Oumtanaga.


Optical networks using Wavelength Division Multiplexing (WDM) and wavelength conversion technologies are an efficient solution for very high-speed core networks. They make it possible to cope with the very high bandwidth and short delay requirements of applications such as telemedicine, distance learning, distributed computing, and online games. However, to reduce the costs of network dimensioning, it is quite practical that only some nodes of the network are equipped with wavelength conversion capability. Such a network is called a sparse wavelength converter network.

In the WDM networks, operators establish optical connections for their customers who need to use unicast or multicast applications. It is common for a customer, given the critical nature of its business, to require from the operator little or no interruption in the delivery of the optical flow it generates. In addition, following the occurrence of events such as an increase in connection requests, the network operator could be required to reconfigure the routing in order to improve network performance. However, the requirement for continuity of flow is not always easy to meet during the reconfiguration process if it is not done carefully. Reconfiguration becomes even more challenging for multicast routing in a WDM optical network with the property of partial wavelength conversion. Existing works address the reconfiguration of unicast or multicast connection routing in networks having the property of full wavelength conversion.

In this thesis, we deal on the one hand with the problem of reconfiguring the routing of a single multicast connection in a sparse wavelength converter network and on the other hand with the problem of reconfiguring the routing of a set of several multicast connections. In the first case, one aims to migrate the flow from an initial multicast routing to a final multicast routing without flow interruption. In the second case, we aim to migrate the optical flow from the initial multicast routing to the final multicast routing with a low number of flow interruptions. Note that the initial multicast routing and the final multicast routing are each supposed to be a set of light-trees.

The method denoted Para_SbSRA (Parallel Subtree by Subtree Reconfiguration Algorithm) has been proposed to solve the problem of routing reconfiguration relating to a single multicast connection and the methods LSRA (Light-tree Set Reconfiguration Algorithm) and LSRA_2 have been proposed to solve the problem of routing reconfiguration relating to a set of multicast connections. The effectiveness of these methods has been confirmed through simulations.

Keywords : Reconfiguration, flow interruption, multicast routing, WDM optical network, light-tree, wavelength conversion.

PhD defense of Ahmad FADEL on October 8th, 2021

Ahmad FADEL will defend his thesis on October 8, 2021 at 2:00 pm in Aurigny room at Irisa (building 12D), Campus universitaire de Beaulieu in Rennes. The title of the thesis is “Management of Radio Resources in a 5G Heterogeneous Network using Beamforming Technique & Millimeter Waves”. The direction of this thesis has been assured by Prof. Bernard Cousin. The jury members will be Véronique Vèque, Nadjib Ait Saadi, Carlos Faouzi Bader, Yassine Hadjadj-Aoul, Loutfi Nuaymi, Bernard Cousin.


Wireless system designers has been facing the continuously increasing demand for high data rates, improving the system capacity and mobility required by new wireless applications. Moreover, increasing the user throughput have become essential concerns for the future fifth-generation (5G) wireless communication network. In this context, densifying macro cells by small cells is proposed as potential solution that may bring many benefits such as improving the bit rate and signal quality, but leads to constraints operations on the management of radio resources.
Notably, millimeter wave (mmWave) installed for small cells base station (BS) due to its limited features is proposed as potential solution to avoid the interference between macro cell and small cells. Beamforming technique is used to increase the spatial domain utilization and the user rate in a cellular network. Thus, the challenge is to find new radio resource management approaches that aim to minimize the interference between adjacent cells, reductions in energy consumption, increase the total system throughput and enhance the spectrum and spectral efficiency in cellular networks. Accordingly, proper radio resource management is needed to exploit the benefits of the 5G and guarantee the quality of service (QoS) of the users.

The works in this dissertation focus on the user selections algorithm in a heterogeneous network (HetNet) in a way to achieve our objectives. In particular, this thesis first addresses the formulation of an optimization problem for joint beamforming, power allocation and user selection in a heterogeneous cellular network which aims to maximize the total system throughput. A modified version of well-know sub-optimal algorithms for resource allocation were proposed to the solve the problem. Equally important, we generate a frequency allocation angular based with fairness algorithm (FAABF) for a multi-user scenario to get a good solution for the proposed optimisation problem for a user selection based on angle-of-arrival (AoA) between user equipment and its serving base station, that aims to jointly maximizing the system throughput, spectrum efficiency and guarantees fairness between selected users.


Visit of Pr Oriol Sallent

Adopnet is happy to welcome Professor Oriol Sallent, full professor at UPC for a 1-month visit in July 2021.

Oriol Sallent has participated in a wide range of European projects and contributed to standardization bodies such as 3GPP, IEEE, and ETSI. He has published 200+ papers, mostly in IEEE journals and conferences. His research interests include self-organizing networks, radio network optimization, and QoS provisioning in heterogeneous wireless networks. This is in conjunction with the axes of Adopnet and this visit is a great opportunity to develop a cooperation between our research groups.

PhD defense of Malo MANINI on January 28th, 2021

The defense of PhD thesis of Malo MANINI will be held on January 28th, 2021 at 10:00. It will be accessible with a conf call (due to the Covid-19 pandemy situation). The thesis is entitled “Resource allocation and scheduling in 5G networks”. It was made within B<>COM.


The increasing number of wireless network users and the diversification of their usage call for an evolution of the resource management methods. This thesis is based on 5G resource allocation techniques. In regular wireless networks, cells are managed independently. In this context, we propose a resource allocation algorithm with the aim of fairly guaranteeing the best service to users. When the cell charge is low enough to guarantee a sufficient quality of service, the algorithm redirects dynamically its priorities towards energy saving. This behavior allows to obtain an efficient compromise between capacity and energy consumption at different charge levels. In order to extend network capacity, the adding of new cells allows to broaden the available bandwidth and to reduce the distance induced signal attenuation. We present an algorithm of user repartition in a multi-cell context, which intervenes before the resource allocation stage. A user can be covered by several cells using different frequencies, thus its repartition will have strong repercussions on the cell charge balance and on the general quality of service in the system. The maximal number of cells in a sector is limited by its geographical environment. The Massive-MIMO allows to increase the cell functionalities while allowing a better energy directivity, and thus adding the spatial component to the resource allocation. We propose a new indicator evaluating the spatial compatibility of users based on past allocations. Once integrated in an allocation algorithm, it takes advantage of the superior capacities of Massive-MIMO.



PhD defense of Cédric Morin on November 18th, 2020

The defense of PhD thesis of Cédric MORIN will be held on November 18th, 2020 at 14:00 with a conf call (due to the Covid-19 pandemy situation). The thesis is entitled “Algorithms for implementing network services with a guaranteed quality of service in an SDN-NFV environment”. It was made in the framework of a CIFRE thesis with TDF and within a B<>COM project.


(Français) Explorer la 5G

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