Interference as an Issue and a Resource in Wireless Networks

This dissertation will be focused on the phenomenon of interference in wireless net- works. On one hand, interference will be viewed as a negative factor that one should mitigate in order to improve the performance of a wireless network in terms of achiev- able rate, and on the other hand as an asset to increase the performance of a network in terms of security. The problems that will be investigated are, first, the character- isation of the performance of a communication network modelled as an interference channel (IC) when interference alignment (IA) is used to mitigate the interference with imperfect knowledge of the channel state, second, the characterisation of the secrecy in the Internet-of-Things (IoT) framework where some devices may use artificial noise to generate interference to potential eavesdroppers. Different scenarios will be studied in the case where interference is unwanted; the first one is when the channel error is bounded. A lower bound on the capacity achievable in this case is provided and a new performance metric namely the saturating SNR is derived. The derived lower bound is studied with respect to some parameters of the estimation strategy when using Least-Square estimation to estimate the channel ma- trices. The second scenario deals with unbounded Gaussian estimation errors, here the statistical distribution of the achievable rate is given along with a new performance metric called outage probability that simplifies the study of the IC with IA under im- perfect CSI. The results are used to optimise the network parameters and extend the analysis further to the case of cellular networks. In the wanted interference situation, the secrecy of the worst-case communication is studied and the conditions for secrecy are provided. Furthermore the average number of secure links achievable in the network is studied according to a theoretical model that is developed for the IoT case