Doctorant sous la direction de L. ZITOUNE

Titre de la thèse: Energy Efficiency transmission Design in Dense Heterogenous Networks using Beamforming and Coordination strategies. Supervised by Véronique Vèque and co-supervised by Lynda Zitoune
Résumé de la thèse: In future 5G wireless cellular networks, dense small cell networks are considered as a cost‐effective solution to face the rapid growth of data traffic and the massive number of connected devices, also called 1000 x Data challenge [ref]. Densification is a promising solution to increase the network capacity and its spectral efficiency (SE) by reusing spatially the spectrum resources. A small cell or a femtocell is a low cost, low power base station, used to reduce the distance between the transmitter and the user equipment and consequently reduces the energy consumption and the propagation losses. Originally, femtocells are deployed in a plug and play manner by customers, to provide better capacity for voice data in indoor. They are also expected to be deployed by operators in order to offload macro‐cellular traffic, improving both capacity and coverage in outdoor utilization. Deployment of small cells within a macro cellular network forms a heterogeneous network (HetNet). However, in dense small HetNets, communications suffer from interference due to aggressive spectrum reuse and the random location of small base stations in case of indoor deployment. Several solutions are proposed for interference mitigation and resource sharing including power control, and base stations cooperation used as a MIMO scheme. When the system configuration becomes more complex, e.g. dense multi‐cell heterogeneous networks with multiple macrocells, small cells, antennas and multiple users, the EE and SE tradeoff would become even more complex. Multiple antennas and multiple users would increase the multiplexing gain and diversity order, but they also consume higher circuit and signal processing power. There are many open issues there. For example, in the MIMO channels, how to configure the optimal beamforming vectors and power jointly from an energy‐efficient perspective? How to choose the optimal energy‐efficient antenna number in a MIMO configuration under different spectral efficiency? Furthermore, determining the EE and SE performance at the scale of the entire multi‐cell cellular network can be rather challenging when considering simultaneous transmissions from multiple base stations (Coordinated Multipoint). This energy and spectral efficiency tradeoff in heterogeneous multi‐cell cellular networks is still open and the study of inter‐cell interference coordination techniques and their impact on the EE and SE performance are also necessary to enable the operator to maximize the network utility.

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