Interference Control of Indoor Cognitive Radio Systems

Abstract

To enhance the e ciency of spectrum utilisation, the broadcast television (TV) (pri- mary) bands are currently open (or to be opened) for unlicensed (secondary) operation by spectrum management regulators around the world. Nevertheless, a considerably large geographic area still remains excluded from the secondary operation due to potential in- terference to the licensed (primary) users. The area of exclusion lies within the protection contour around each TV transmitter. This thesis explores possible re-use of the primary spectrum within the protection contour. This thesis investigates the aggregated interference power (AIP) in a broadcast TV system due to multiple transmitting secondary users (SUs). The COST-231 building pen- etration model is also used in this investigation to assess the bene t of re-using spectrum indoors. It is identi ed that there is an opportunity to use primary spectrum within the protection contour if the re-use occurs inside a building that shields radio signals and re- duces interference to the primary system. However buildings typically do not have equal radio shielding ability. The SUs will be required to adjust their transmit powers according to their locations in the building in order to minimise the interference to outdoor primary users (PUs). A novel localisation-less indoor cognitive radio (CR) system is developed allowing SUs to access the primary spectrum inside a building within the protection con- tour. The system utilises an indoor sensor network for i) interference sensing, ii) transmit power control, to limit the interference to the outdoor primary receiving antennas. A power control model of the indoor system is developed to estimate permissible transmit power for the indoor users. A power control algorithm is developed as a practical imple- mentation of the power control model and its e ectiveness is assessed through simulations in which realistic propagation scenarios are considered, e.g. when internal partition walls and multipath fading are present. Mixed indoor/outdoor propagation measurements have also been conducted to con rm the applicability of the COST-231 building penetration model, which was developed to predict outdoor-to-indoor penetration loss, in the scenarios considered in this thesis. It is also shown that interference measured by sensors deployed inside the buildings can be used to control the interference occurring at outdoor locations.