Spectrum Sensing and Interference Mitigation Schemes in MIMO CR Systems

Abstract

Recent surveys are showing that majority of the spectrum i.e more than 70% is underutilized. So to utilize the spectrum efficiently, we have to decide first weather the required spectrum is in currently use or not. This decision can make using spectrum sensing techniques like Energy Detection, Matched Filter detection, and Cyclo-stationary Detection. Their function is to detect the vacant/underutilized spectrum holes of the primary users, which can be allocated to SUs transmissions without interfering the PUs. Here we investigate the conventional energy detection, energy detection based cooperative spectrum sensing techniques to know the presence of licensed users. In addition, we also investigate interference mitigation schemes such as post-whitening scheme, pre-whitening scheme and proposed pre-whitening scheme for MIMO based CR environment to increase PUs and SUs capacity. In MIMO based CR network the PUs and SUs cooperate each other. It means they share the CSI of the interference links. If we adapt post-whitening scheme, it requires CSI of interference link, in advance, at PR which causes violation to the philosophy of CR. To overcome this, we adapt pre-whitening scheme, this scheme assumes CSI of interference link is perfectly known at secondary transmitter (ST) in advance and also agrees with the philosophy of CR. But in this scheme as amount of feedback information increases, the processing burden of the network also increases. To overcome this and to get the same performance unlike conventional pre-whitening scheme, we are proposing a pre-whitening scheme with only the direction information on the interference channel i.e using only partial CSI.