Analysis and development of physical and MAC Layer protocols in mobile ad Hoc networks involving directional antenna communications

Abstract

Most recent Studies and Researches in IT (Information Technology) are bringing to an increasing development of Pervasive Communication Environments Systems such as MANET and Sensor Networks that assumed great importance, since 802.1X development IEEE Standards, due to their features based on nodes mobility and power consumption that lead to the rise of several protocols which implements different designs about routing algorithms and QoS (Quality of Service) specifications. Conventionally, these kinds of network environments are equipped in their physical layer with Isotropic and Omnidirectional Antennas Systems, that lead to a radiation pattern with a constant gain in all TX/RX directions so it results in a non-directive behavior of nodes. In this context there are lots drawbacks that heavily affect and reduce protocols efficiency and SNR (Signal to Noise Ratio) such as: communication reliability, latency, scalability, power and energy consumption. For example, using an isotropic antenna in nodes, without position knowing mechanism, bring to a notable waste of consumption energy due to the non-directive behavior because the same power is transmitted/received in all directions. To overlapping this drawback are developed in last years the so called Smart Antenna Systems that usually consists of several directive radiation elements implementing adaptive algorithms for the estimation of DOA (Direction of Arrival) and SOI (Signal Of interest); for this purpose are employed beamforming techniques that are largely used in Radar Communication Systems and Phased Array Systems. The resulted radiation pattern generates a beam that should be electronically controlled, and the main beam should be pointed towards the direction of interest in communication transmission/reception. The beam is generated according an adaptive algorithm (i.e. Least Mean Square) that models the weight vector as Smart Antenna input System. Beamforming techniques take lots advantages in medium access control, effectively, employing of SDMA (Spatial Division Multiple Access) allows a great efficiency protocol growth. MANET performance can be enhanced if more efficient antenna systems such as Massive MIMO (Multiple Input Multiple Output) systems are employed; indeed, massive MIMO underlie the development of 5G Mobile Wireless Network environments. However, despite of their capability to improve network performance they introduce different kinds of issues especially in terms of energy consumption that should be addressed. The main purpose of this thesis is to limit most of the mentioned issues related to directional communications in MANET in order to improve the current state of art referring both to protocols and network performance. From a protocol point of view, important to highlight that the most of the overall contribution of the present work aims to address energy efficiency, deafness problem and finally, mobility issues occurring at physical and MAC (Medium Access Layer) layer. The reminder of the thesis is the following: Chapter 1: introduces main concepts about network communications using directional and omnidirectional antennas in MANET and their common related issues. Chapter 2: gives basics and fundamentals theoretical notions about Smart Antenna Systems (SAS) and Massive MIMO with particular emphasis to beamforming algorithms. Chapter 3: essentially, this chapter is divided into two parts. The first one, illustrates basic features of the main instrument used for experimental analysis that is the Omnet++ network simulator. The second part exposes the most significant works produced to extend the default Omnet++ framework for enabling simulation scenarios supporting SAS and massivo MIMO systems. Chapter 4: provides a detailed discussion about deafness problem in MANET directional communications and subsequently illustrates the most significant proposals in this field with a special focus on designed Round-Robin based approaches. Chapter 5: describes main issues related to mobility and energy consumption of nodes in directional MANET with particular attention to handoff problem. Nevertheless, it illustrates novel proposed strategies aiming to mitigate energy consumption in very high gain beamforming communications employing SAS and massive MIMO systems. All of the above chapters are organized in a similar way. More specifically, each chapter consists of three main parts: Background: gives a briefly theoretical explanation of the most important concepts mentioned in the chapter. State of art: illustrates the most significant works related to topics encountered in the chapter. Personal contribution: highlights the main contribution achieved (by author of this thesis) allowing to improve the current state of art related to a particular topic.