ABSTRACT
The chapter provides an in-depth description of number of cooperative spectrum acquisition techniques including decision-based cooperative spectrum sensing (CSS) using energy detection, hybrid automatic repeat request (HARQ), and cooperative diversity. To show the need for CSS, consider, for example, the hidden terminal problem, which is one of the common challenges in wireless communication systems. The CSS process consists of three stages. These are sensing period, reporting period, and broadcast period. During the sensing period, every network terminal, including the fusion center itself, senses the examined channel using some sensing method, like the energy detector. Unlike Automatic repeat request, HARQ protocol gives the receiver the ability to correct some of the detected errors. In HARQ, the receiver sends an acknowledgment (ACK) if the channel is good and a negative ACK (NACK) if the channel is bad. Cooperative diversity has been proposed in the pioneering works of Sendonaris and Laneman as means to enhance the performance of cellular networks through user cooperation.
