SUMMARYThis paper reviews applications of fuzzy logic to telecommunications and proposes a novel fuzzy combining scheme for cooperative spectrum sensing in cognitive radio systems. A summary of previous applications of fuzzy logic to telecommunications is given outlining also potential applications of fuzzy logic in future cognitive radio systems. In complex and dynamic operational environments, future cognitive radio systems will need sophisticated decision making and environment awareness techniques that are capable of handling multidimensional, conflicting and usually non-predictable decision making problems where optimal solutions can not be necessarily found. The results indicate that fuzzy logic can be used in cooperative spectrum sensing to provide additional flexibility to existing combining methods. key words: cognitive radio, cooperative sensing, efficient spectrum use, fuzzy logic, radio resource management, spectrum sensing

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This paper presents distributed and directional spectrum occupancy measurements in the 2.4 GHz ISM band. Spectrum occupancy measurements can be used to assess how efficiently the spectrum bands are used today. Future cognitive radio systems can improve the spectrum occupancy by filling the gaps in the prevailing spectrum by opportunistically using unoccupied channels. Most of the spectrum occupancy measurements in the literature have been conducted by using a single measurement device with an omnidirectional antenna. The resulting spectrum occupancy values have presented an average of the overall situation. To characterize the influence of the spatial dimension on the spectrum occupancy in a given area, we introduce the directional spectrum occupancy metric. Directional spectrum occupancy is defined as the fraction of time that the received power in a channel exceeds a threshold in a given measurement direction. We have used two separately located measurement devices with directional antennas to measure the directional spectrum occupancy in an office area with heavy traffic load. The results indicate that the spectrum occupancy is heavily dependent on the measurement location and direction. The influence of the spatial dimension is therefore very crucial in the development of future cognitive radio systems.

We first introduce a non-adaptive fuzzy logic controller (FLC) for the control of live steam temperature in a coal-fired power plant. For further enhancing performance, we introduce a self-tuning method for the FLC that modifies the scaling factor of one FLC output. To make the FLC more portable to other similar plants and more robust we add another self-tuning mechanism that runs on-line and modifies the membership functions of the fuzzy rule set. We have used the meta-rule approach in the tuning mechanisms. The performance of the FLC is compared to a cascade PI controller.

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