Spektrin sensorointiin perustuva kanavanvalinta kognitiivisessa radiojärjestelmässä: Pro gradu

The use of wireless devices is increasing continuously but frequencies where the devices operate are limited. This causes a growing need to allocate spectrum frequencies more efficiently. Cognitive radio has been proposed as a solution to this problem. A cognitive radio system aims at reusing sparsely occupied frequency bands. The objective of this research was to study WLAN channel sensing time and channel switching time using a cognitive radio system named CORAL in the ISM band. In addition, possibilities of using the historical data in channel selection were discussed. Constructive research was used as a research method in this work. Information was gathered from scientific articles for this research. Channel sensing times were studied by making channel sensing algorithms which print out the sensing times. Channel switching times were measured by studying the video streams from one computer to another. The use of historical data in channel selection was studied with literature. The research provided knowledge about channel sensing times and channel switching times in the CORAL system. The study shows that historical data can be used to make better channel selections in cognitive radio systems. The median sensing time in the CORAL system was 6 seconds with one channel. The sensing time was 13 seconds for two channels, 17 seconds for three channels, and 25 seconds for eleven channels. The median channel switching times in CORAL system was 9.6 seconds with eleven channels, 2.9 seconds with three channels, and 2.8 seconds with one channel.