Mathematical Modelling of Spectrum Sharing in Cognitive Radio Communication Systems

Abstract

Due to exponential increase in the number of wireless connected devices (such as internet-of-things (IOTs), machine-to-machine communication (M2MC), wireless sensor networks (WSNs) etc.), these are predicted to be 75.44 billion in 2025 which is almost five times more as compared to that of the 15.41 in the year 2015. This demands huge bandwidth in the next generation communication systems however, it is a limited resource that is already allocated for certain services such as mobile telephony, military services, satellite services etc. (30 KHz - 300 GHz) which results in the spectrum scarcity. The prominent solution for spectrum scarcity is the cognitive radio (CR) technology which exploits the concept of dynamic spectrum access where the unlicensed/cognitive users (CUs) use the spectrum of licensed/ primary users (PUs) in such a way that the PUs communication remains impervious. The CUs perceive the state of channel (active/ idle) through the spectrum sensing and accesses the channel through spectrum accessing technique (interweave/ underlay). In the interweave spectrum accessing strategy, the CU establishes communication on the idle sensed channels with full-power however, CUs establish communication on active sensed channels and interference at PU is avoided by constraining the transmitted power in the underlay technique. In the interweave spectrum accessing technique, the CU needs to stop the communication on active sensed channels which is a key challenge for seamless communication, however, has limited capacity due to constrained power transmission in the underlay technique. To enjoy the benefits and avoid the limitations of both the strategies, the combination of interweave and underlay spectrum accessing strategy is proposed and known as the hybrid spectrum accessing strategy according to which the CU accesses the idle and active sensed channels with interweave and underlay strategy, respectively.