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Agenda

01/12/2016

Doctorate thesis defense of Asma Selmi




Doctorate thesis defense on December 01st 2016 at 14H00 AM ,in Amphi I, Sup’Com.


Entitled :CROSS-LAYER DESIGNS FOR LINK ADAPTATION

Presented by : Asma Selmi 





Committee


Chair

Ridha Bouallegue

Professor at Sup'Com, Tunisia

 

 

 

Reviewers

Mohamed Slim Alouini

Professor at KAUST, Saudi Arabia

 

Mohamed Lassaad AMMARI

Associate Professor, ENISO, Tunisia

 

Examiners

Leila Najjar Atallah

Associate Professor at Sup'Com, Tunisia

 

Supervisors:

Mohamed Siala

Professor at Sup'Com, Tunisia

 

Hatem Boujemaa

Professor at Sup’Com, Tunis.

 

Abstract


Provisioning higher data rates remains always a key driver in wireless communication networks evolution. The next-generation wireless system, so-called the 5th generation, will, for instance, need to support around 1 Gbps of downlink data rates. To achieve these unprecedented rates, a higher spectrum efficiency is needed, motivating for a further optimization of the used wireless resources. Future wireless communication systems are also expected to suffer from limited bandwidths and power resources, and to face highly time-variant propagation environments and user mobility. In this context, adaptive techniques seem to be among the most promising solutions to better respond to the challenging requirements, through an efficient management of power and spectral resources and channel impairments.


The link adaptation (LA) is one method of tackling the variations in the instantaneous channel quality, through appropriate processing prior to data transmission. There are two link adaptation techniques, namely Adaptive Modulation and Coding (AMC) and Power Control (PC). Recent systems, such as HSPA, employ AMC at the physical (PHY) layer, to maximize throughput, while keeping the transmit power unchanged. In this setup, both modulation and coding schemes are dynamically selected, based on switching signal to noise ratio (SNR) thresholds, in order to match the transmis-sion rates to time-varying channel conditions. On the other hand, systems like UMTS, use PC at the PHY layer, to guarantee a given target signal to interference ratio, by tracking and compensating instantaneous channel variations, while using a single modulation scheme.


In order to reach high reliability at the physical layer, the transmission rate must be reduced by using either small size constellations, or, powerful but low-rate error-control codes, or both. An alternative efficient method to decrease packet loss rate is to rely on the Automatic Repeat reQuest (ARQ) protocol at the data link (DL) layer. This protocol requests retransmissions of erroneously received packets, which helps improving system throughput, relative to the use of forward error correction alone at the PHY layer. The ARQ protocol can be seen as a mechanism for handling variations in the in-stantaneous channel quality after transmission and hence nicely and synergically complements link adaptation.


Aiming at improving the spectral efficiency, one may wish to jointly exploit the adaptability of LA techniques to the radio channel conditions and the error-correcting capacity of ARQ. Such challenges require the use of cross-layer approaches, which involve dynamic interactions between the PHY layer and the DL layer to enable the compensation for mismatching of requirements and resources. In this context, we focus in this thesis on the opti-mal combination of all three techniques, aiming at reducing the energy consumption while maximizing the offered average transmission rate.


Keywords


Link Adaptation, Power Control, Adaptive Modulation and Coding, Error Control, Automatic Repeat reQuest Protocol, Hybrid ARQ Protocol, For-ward Error Correction, QoS-guaranteed Communications,SISO, MIMO, Spatial Multiplexing, SVD.