Opportunistic Spectrum Access in Cognitive Radio Network

Cognitive radio (Mitola III, 2000) also known as opportunistic spectrum access (OSA) has emerged as a promising solution to increase the spectrum efficiency Haykin (2005). In OSA, the SU finds spectrum holes (white space) by sensing the radio frequency spectrum. The presence of spectrum holes in the PU channels are highlighted in Fig. 1. These spectrum holes are used by the SU for its transmission. This scheme is often referred to as opportunistic spectrum access (OSA). No concurrent transmission of the PU and the SU is allowed. The SU must vacate the channel as soon as the PU reappears, which leads to the forced termination of the SU connection. Since the SU has no control over the resource availability, the transmission of the SU is blocked when the channel is occupied by the PU. The forced termination and blocking of a SU connection is shown in Fig. 2. The forced termination probability and blocking probability are the key parameters which determine the throughput of the SU, and thus its viable existence. The forced termination depends on the traffic behaviour of the PUs and the SUs (e.g. arrival rates, service time etc.). In the case of multiple SU groups with different traffic statistics, the forced termination and blocking probabilities lead to unfairness among the SU groups. The QoS provisioning task becomes difficult.