Efficient M2M communications via random access satellite channels

According to data traffic forecast reports, the volume of data transported by Internet in 2020 will exceed the threshold of 2.0 zettabytes per year, generated by more than trillion of devices. Only a minor portion of the traffic will be generated by PCs, as commonly observed in the recent past. On the contrary, a large quota of Internet traffic is expected to be generated by TVs, tablets, smartphones, and M2M devices. In particular, it has been highlighted that M2M traffic will experience a growth rate in the order of 60%. M2M refers to technologies that allow both wireless and wired systems to communicate with other devices of the same ability, sensors and actuators, without any human intervention. M2M applications are largely diffused in several deployments and have pushed the scientific community to thoroughly investigate the network design implications. The large amount of traffic contributed by these applications will have an important impact on the design of future network architecture and on dimensioning the capacity of the telecommunication infrastructures. From this standpoint, a special note has to be reserved to the case of M2M services distributed via satellite, whose related industry is continuously increasing in size, which is the main focus of this work. More generally, the research problem can be stated as follows: a large and dense population of M2M devices exchanges short data bursts over a shared satellite medium; support for sporadic and unpredictable access activity and/or support to delay-critical applications is required. Random Access (RA) schemes for handling uncoordinated multiple access can nowadays compete with the throughput offered by typical coordinated techniques, making the former ones strongly attractive to support large populations of M2M terminals, while contemporary providing immediate access to the channel, without any reservation delays that are typical of coordinated access schemes. Therefore, the focus of this Ph.D. Thesis is on analysing, analytically and empirically, the behaviour of the most common M2M protocol stacks on RA satellite links and on suggesting guidelines to improve the achievable performance level. The first part of this Thesis presents a load control algorithm to maximize the throughput achievable by RCSTs, focusing on the exploitation of linear code prior to transmission, in order to improve the transmission robustness at the cost of some capacity waste because of the redundancy. Furthermore, an innovative hybrid access protocol is designed, aiming at allowing the coexistence of M2M and non-M2M RCSTs in the same network. The second part of this Thesis studies the performance of M2M protocol stacks via RA satellite channels, when a reliable data delivery is needed in channels suffering of erasures due to collisions. Two metrics are taken into account: the completion time, in presence of short data bursts, and the throughput, in presence of a sustained load. A cross-layer study is proposed, in order to characterize the interactions among application, transport and M2M layers of a M2M protocol stack sending data via a RA satellite channel.