The Role of the Cooperative Paradigm in Traditional and Cognitive Wireless Networks

The scope of this thesis is to show that the cooperative paradigm in wireless networks is an effective way to counteract the impairments of wireless channels caused by the fading effects, through the exploitation of the spatial diversity, and so to guarantee satisfactory performance that otherwise would not be achievable through an individual action. More specifically, the advantages of the cooperative paradigm are shown with reference to both traditional relay networks, for cooperative transmission, and the emerging cognitive radio networks, for cooperative spectrum sensing. In the first part of the thesis, the performance analysis of distributed Space-Time Block Coding schemes involving multiple decode-and-forward relays is carried out in the presence of impulsive noise, which, together with multipath fading, is one of the major sources of performance degradation in many wireless systems. The impact of impulsive noise on average bit-error rate, coding gain and diversity order, is studied for different receiving structures. In the second part, the performance analysis of several cooperative spectrum sensing techniques in cognitive radio networks is carried out for two different decision approaches, according to the role of the decision maker (i.e., the entity who takes the cooperative decision). The criteria for an effective decision-approach selection are analytically derived with the object of maximizing the detection accuracy in presence of realistic channel propagation effects. Finally, in the last part, the spatio-temporal spectrum sensing design problem for cognitive radio networks in the presence of PU mobility is addressed, with the aim to optimize the sensing time that maximizes the actual transmission capacity achieved by the CU with a limited sensing accuracy, while satisfying the PU interference constraints.