Performance evaluation of massive communications in future wireless access networks

This thesis contributes to the state of the art providing, both for human-type communications (HTC) and machine type communications (MTC), detailed models of network access in 4G and future 5G networks. The focus, in the case of HTC, is on types of scenarios where a huge crowd gathers in a relatively small place, such as a stadium during a music concert. In such case, on one side the metric of interest is the quality perceived by the users while on the other is the number of users to which the connectivity is guaranteed. Therefore, the presented models allow to analytically identify networks operational regions relating the number of devices and the QoS they perceive. In the case of MTC, given the specific requirements of autonomous communications, guaranteeing strict latency constraints and high reliability is of primary importance. Hence, this thesis describes a stochastic model of the behavior of autonomous devices in a Smart Factory scenario. The model allows to evaluate operational conditions and to derive the distribution of latencies experienced by network access requests. In 4G networks, and in the next generation 5G networks, access to resources is the result of a two-step operation: in the first place mobile devices notify to the network the attempt to join the network, through the RA procedure, and only in case of networks acknowledgement they can proceed and negotiate a data channel. In the latter step, devices might be refused to access resources essentially because of protocols constraints. Proven that it is possible to model the two steps separately, in this thesis it’s derived a novel formulation of the second one, based on a network of queue under product form solution, that overcomes limitations of state of the art approaches, such as the well known Erlang-B formula. Mobile network issues, such as overloading and real-time constraint, might also be studied from a different point o view. In recent years, coalesce efforts of a crowd towards a common objective has been of great appeal. That is, crowd-sourcing attracted interest in many different fields; from fundraising campaigns to crowdsourcing Internet marketplace. Borrowing the idea of cooperation, mobile devices within the same cell can group up into coalitions (a subset of devices close to each other) and communicate with the network by means of a single coalition component. That is, Device to Device (D2D) communication enables direct communications among components of a coalitions and the device depicted to communicate with the network will act as a data gatherer and relay node. Eventually, it is also shown how such mechanism is beneficial to mobile networks, both in case of HTC and MTC.