An algorithm for cooperative Dynamic Spectrum Access in Cognitive Radio networks is presented. The proposed algorithm utilizes Medium Access Control layer mechanisms for message exchange between secondary nodes that operate in license exempt spectrum bands, in order to achieve interference mitigation. A fuzzy logic reasoner is utilized in order to take into account the effect of the coexistence of a large number of users in the interference as well as to cope for uncertainties in the message exchange, caused by the nodes' mobility and the large delays in the updating of the necessary information. The proposed algorithm is applied in Filter Bank Multicarrier, as well as Orthogonal Frequency Division Multiplexing systems, and its performance is evaluated through extensive simulations that cover a wide range of typical scenarios. Experimental results indicate improved behaviour compared to previous schemes, especially in the case of uncertainties that cause underestimation of the interference levels. 1. Introduction The proliferation of mobile devices, coupled with the ever-increasing demand for higher data rates’ support, constitutes static frequency allocation schemes suboptimal, as they frequently result in spectrum underutilization. Cognitive Radios (CRs) supporting Opportunistic Spectrum Access (OSA) [1] emerged as a new paradigm that offers an effective solution to the problem of spectrum scarcity. However, the increased variance in spectrum availability combined with the end users’ diverse characteristics and Quality of Service (QoS) requirements poses a number of challenges that need to be addressed. More specifically, for Cognitive Radio systems operating in licensed spectrum bands with coexistence of both primary and secondary users, the operations of spectrum sensing, defined as the identification of the spectrum bands that are available for transmission, and spectrum mobility, that is, the vacation of the wireless channel when a primary user is detected, are of key importance. On the other hand, Cognitive Radio systems operating in license exempt spectrum bands, where different operators coexist, require efficient spectrum decision and spectrum sharing algorithms as well as power control mechanisms for interference mitigation. For example, if all users transmit at the maximum valid power level, then every user is causing significant interference to all the others, a fact that can result in reduced total utility from the network perspective and, finally, poor QoS for the end users. In this scope, algorithms that employ cooperative spectrum
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