DEVELOPMENT OF A RADIO SPECTRUM UTILISATION TECHNIQUE FOR COGNITIVE RADIOS

Abstract

Parts of licensed radio spectrum for data transmission are idle because they are not used at some points in time or location by the user. Cognitive radios which are software radios equipped with sensors and other functionalities are being developed to opportunistically use this idle licensed spectrum. Cognitive radios use dynamic spectrum access methods classified as overlay and underlay to utilise idle television frequency in the radio spectrum. However, simultaneous transmissions of data by licensed and cognitive radio users are not possible in overlay, while restriction is on the usage of the idle spectrum in underlay. Consequently, the potentials of cognitive radios are not effectively maximised. Therefore, this research was aimed at the development of a band access technique in radio frequency to improve the usage of the idle television frequency. The matched filtering technique of overlay for detecting idle licensed signal and interference temperature management of underlay for controlling interference were adapted to develop a new technique referred to as Matched Filtering-Interference Temperature Management (MAFITM). A conceptual transmission model for three different scenarios representing overlay, underlay and MAFITM techniques was created for television frequency access. Simulation of the three techniques in the television frequency band that covered 54 to 862 MHz and three different licensed signal transmission powers was implemented with Java programming language. A cognitive radio access point was simulated to transmit between nodes for the three different scenarios in the presence and absence of licensed television signal. The first, second and third transmission scenarios were simulated using overlay, underlay, and MAFITM techniques respectively. The results generated were compared using the performance metrics of transmission distance, data rates, spectrum efficiency and margin of interference in the presence and absence of licensed signal. In the absence of licensed signal, for both MAFITM and overlay techniques the transmission distance, the maximum achievable data rate and the spectral efficiency (100 km, 163 Mb/s and 9.537 b/s/Hz), respectively were significantly higher compared with those of underlay technique (25 m, 44 Mb/s and 12.429 b/s/Hz), respectively. In the presence of licensed signal, transmission of data was possible in MAFITM and underlay techniques but not in overlay technique. With the presence of licensed signal, for MAFITM technique, the maximum transmission distance, the maximum achievable data rate, the spectral efficiency and margin of interference were (3.5 km, 789 Kb/s, 0.045 b/s/Hz and 0.81), respectively. For underlay technique the maximum transmission distance, the maximum achievable data rate, the spectral efficiency and margin of interference were (25 m, 2.81 Mb/s, 0.001 b/s/Hz and -0.04), respectively. The results reflected a better utilisation of the licensed spectrum using the MAFITM technique. The developed technique produced an improved utilisation of spectrum in areas with stronger presence of licensed signal and allowed data transmission alongside licensed signal without restriction. Matched Filtering-Interference Temperature Management technique is recommended to enhance the effectiveness of cognitive radios in utilising idle licensed frequencies.