Throughput Improvement in Hybrid MIMO Cognitive Radio Using Simultaneous Narrowband and Wideband System

Abstract

Multi Input Multi Output (MIMO) based Cognitive Radio (CR) with Software Defined Radio (SDR) has been a promising approach for the exploitation of the scarce electro-magnetic spectrum. To improvise spectral efficiency, Hybrid CR system, that switches between underlay and interweave CR techniques have been proposed. However, there are scenarios where the throughput of the hybrid CR system is near zero. In this paper, we have presented new method of improving spectral efficiency gain of an uplink Hybrid Cognitive Radio MIMO system, wherein secondary user (SU) transmits on the same spectrum as primary user (PU) to communicate with a common receiver by exploiting the null and partially utilized eigenmodes of PU and UWB technique simultaneously. In the absence of PU, narrowband Interweave technique along with UWB system is used. This paper investigates the gain in achievable throughput in simultaneous transmission in Narrowband and Ultra Wide Band. In underlay scenario, with absence of the free eigenmodes, SU can achieve non zero throughput by implementing UWB system. In absence of PU, multiple SU need to compete for access of channel. SU accessing the channel can use precoding scheme to accommodate multiple SU and other SUs can transmit in UWB or underlay mode thereby achieving a non-zero throughput.