The 'big data' scene has brought new improvement opportunities to most products and services, including education. Web-based learning has become very widespread over the last decade, which in conjunction with the MOOC phenomenon, it has enabled the collection of large and rich data samples regarding the interaction of students with these educational online environments. 

Everyone is familiar with the problem of online scheduling, even if they are not aware of it; from the way we prioritize our everyday decisions to the way a delivery service must decide on the route to follow in order to cover the ongoing requests. In computer science this is a problem of even greater importance.

Mobile cellular networks are complex system whose behavior is characterized by the superposition of several random phenomena, most of which, related to human activities, such as mobility, communications and network usage. However, when observed in their totality, the many individual components merge into more deterministic patterns and trends start to be identifiable and predictable.

Cellular service providers have been struggling with users’ demand since the emergence of mobile Internet. As a result, each generation of cellular network prevailed over its predecessors mainly in terms of connection speed.

This thesis tackles the optimization of energy efficiency in data centers in terms of network and server utilization.

In this thesis, signal propagation variations that are experience over the frequency resources of IEEE 802.11 Wireless Local Area Networks (WLANs) are studied.

The rapid growth of wireless mobile devices has led to saturation and congestion of wireless channels – a well-known fact. In the recent years, this issue is further exacerbated by the ever- increasing demand for traffic intensed multimedia content applications, which include but are not limited to social media, news and video streaming applications.

In the last decade, cellular networks are undergoing with a radical change in their basic design foundations. The huge increase in traffic demand requires a novel design of future cellular networks.

The design, standardization and future deployment of vehicular communications systems have been driven so far by safety applications. There are two more aspects of the vehicular networking that have increased their importance in the last years: Infotainment and traffic efficiency, as they can improve drivers' experience, making vehicular communications systems more attractive to end-users.

The media access control (MAC) layer of the IEEE 802.11 standard specifies a set of parameters that regulate the behavior of the wireless stations when accessing the channel. Although the standard defines a set of recommended values for these parameters, they are statically set and do not take into account the current conditions in the wireless local area network (WLAN) in terms of, e.g., number of contending stations and the traffic they generate, which results in suboptimal performance.