Cognitive radios real-time implementation on software defined radio for public safety communications

Cognitive radio (CR) is introduced to efficiently and opportunistically use the limited spectrum to minimize the spectrum scarcity issues. Usually, service providers purchase the spectrum license from the policy-makers and spectrum regulator authority. The non-licensed users cannot utilize the licensed bands even though primary user is not transmitting. It sometimes results in under-utilization of frequency bands, which in turn decreases the spectral efficiency. The CR can opportunistically use the freely available licensed spectrum. To solve the spectrum scarcity problem, we implemented CR using software defined radio on frequency modulated radio band (88-108MHz), because of ease in access and availability. The proposed solution is equally valid for other frequency bands as well, because the printed circuit board adopted here supports frequency from 50MHz to 2.2GHz. The proposed solution uses energy-detection based spectrum-sensing technique for primary user (PU) detection, and afterwards secondary user starts the data transmission over the vacant frequency band. We presented real-time experimental results for the detection probabilities by testing under various false alarm probabilities to verify the efficiency of the designed system. Experimental results show that we can achieve high detection probability even at low receiver sensitivity. When PU becomes active, then the proposed system quickly shift the public-safety user to other available white spaces to avoid halting the licensed user transmission. This solution is beneficial for security and defense organization such as army, traffic wardens, city wardens, and police.