Performance enhancement of underlay cognitive radio networks through precise localization, optimum resource selection and transmission power optimization

Abstract

Cognitive radio technology has emerged as an efficient solution to utilize underutilized or unutilized radio-frequency spectrum through the dynamic spectrum access mechanism. This thesis work has focused on the design of a cost-effective but reliable underlay cognitive radio network (CRN). However, the reliable operation of a radio network requires multiple design parameters. Out of the various design constraints, this thesis work has focused on precise localization, optimum resource selection, and transmission power optimization. The purpose of localization is to detect the accurate physical coordinates of the primary users (PUs) in the CRNs. The received signal strength indicator (RSSI) parameter has been considered for the localization process. However, the uncertainty in radio communication due to the link noise and system-generated internal noise leads to false detection and miss detection probabilities of the primary transmitted signal. Therefore, this thesis work has considered the log-normal shadowing model with a correction factor to mitigate the shadowing effects on the radio link. A suitable FIR (Finite Impulse Response) filter has also been designed after the demodulator stage of a CR receiver circuit to minimize the internal noise. One of the fundamental design problems is how the underlay CRUs will decide when and which licensed channel to consider for communication. Hence, a channel selection scheme has been developed and tested in this work. However, during the cognitive-communication on a selected channel frequency, the interference probability with the primary receivers is very high. Therefore a receiver-initiated (RI) MAC protocol has been developed to conduct channel allocation and data communication. The receiver initiated channel selection scheme has reduced the collision probabilities with the hidden PUs. However, the RI MAC protocol cannot minimize the outage probability at the primary receiver due to the fixed secondary transmit power. Therefore, to keep the interference level at the primary receiver within a limit, transmit power optimization of the secondary user (SU) is necessary. Hence, a transmitter-initiated (TI) MAC protocol with a flexible transmit power selection strategy has also been developed to minimize the outage probability at the primary receiver.