Transmit power control for spectrum underlay in cognitive radio networks

Abstract

Cognitive Radio (CR) has recently received a great attention due to the ability to improve the spectrum utilization by facilitating the realization of the dynamic spectrum management policy. It can be implemented by allowing the secondary user (SU) in the CR network to opportunistically access the licensed spectrum of the primary user (PU). Based on the approach to the opportunistic utilization, CR can be categorized into two types: spectrum overlay model and underlay model. For the overlay one, the SU identifies the idle spectrum via spectrum sensing and opportunistically utilizes the available spectrum. For the underlay one, the SU coexists with the PU sharing the primary spectrum to the extent not to deteriorate the primary communication. The underlay model can provide the SUs with more access opportunities than the overlay model but involves the risk that the priority of the PU is violated. Therefore, it is necessary to control the transmit power of the SU so that the interference temperature at the primary receiver caused by all SUs is less than or equal to the interference temperature limit (ITL) of the PU. In this thesis, we focused on the spectrum underlay in CR networks. To apply the inherent transmit power control which can maximize the number of users satisfying the quality of service (QoS) requirement by keeping the transmit power of each user at the minimum level required for reliable communication to spectrum underlay CR networks, QoS requirement of the PU is to be considered additionally. In such a CR network, the role of transmit power control is to maximize the number of SUs satisfying the QoS requirements of the SU and the PU simultaneously by controlling the transmit power of each SU. There are two approaches in the transmit power control for spectrum underlay in CR networks: centralized and distributed approach. For the centralized one, a central manager controls the transmit power of all SUs within its coverage using all information req...