Square-Law Selector and Square-Law Combiner for Cognitive Radio Systems: An Experimental Study

Cognitive Radio communication is foreseen as one of the possible candidates that can resolve spectrum scarcity currently faced by the upcoming wireless technologies. This scarcity can be solved by enabling secondary access to the licensed spectrum. The interference at the primary receiver can be avoided by employing a detector (spectrum sensing) at the Secondary Transmitter (ST). Energy detection is widely used due to its low complexity and applicability to a large range of primary user signals. Recently, antenna diversity techniques such as square-law selector and square-law combiner have been used to enhance the detection performance at the ST. In this context, the detector's performance pertaining to the antenna diversity techniques has been characterized analytically. However, issues such as RF impairments and deploying a fading model render hardware implementation of such techniques challenging. Motivated by this fact, this paper presents the deployment of a hardware, and subsequently utilize the theoretical expressions to validate the performance of a multi-antenna system at the ST that exploits antenna diversity techniques in a realistic environment. Finally, we emphasize the challenges faced during the hardware implementation and present our approach to address these challenges.