Low complexity spectrum sensing using variable digital filters for cognitive radio based air-ground communication

Cognitive radios (CRs) enable efficient usage of the radio frequency spectrum by sensing their operating environments and adapting their transceiver characteristics accordingly. This ability of CRs makes them a feasible choice to achieve green radio networks. CRs perform spectrum sensing, wherein presence and/or absence of licensed users´ signals is detected in the wideband input frequency range in order to allow opportunistic access of the vacant frequency bands to unlicensed users. Variable digital filters (VDFs) which can provide frequency responses with variable cutoff frequencies are widely used for spectrum sensing in CRs. In this paper, we propose an energy detector based spectrum sensing scheme which employs such VDFs based on first order all pass transformation and the modified coefficient decimation method. With the help of design example of an air-ground communication scenario, we show that VDFs employed in the proposed scheme are low complexity alternatives to the other relevant VDFs in literature. The proposed spectrum sensing scheme can be useful not only for solving the anticipated spectrum scarcity caused by the existing static spectrum allocation scheme in current air-ground communication systems, but also in achieving energy efficient green communications.