Outage performance of SU under spectrum sharing with imperfect CSI and primary user interference

Cognitive radio refers to smart technology aims to improve the spectrum utilization and alleviate the spectrum shortage by allowing the secondary user (SU) (unlicensed user) to share the existing spectrum allocated to primary user (PU). In spectrum sharing approach secondary users are allowed to access the same spectrum used by primary user provided the interference produced at PU receiver due to SU transmission remains below the predefined interference threshold defined for the PU. We consider the channel state information available at SU transmitter of the interfering link i.e. link from SU-Tx to PU-Rx is imperfect. The SU estimates its transmit power based on CSI of interfering link if PU is present, while it transmits with maximum power P_m in absence of PU. In this paper we assume the CSI available, based on MMSE estimation, at SU-Tx is imperfect. We derive closed form expression of the outage probability of SU over Rayleigh faded channel with imperfect CSI of link between SU Transmitter and PU Receiver for a given outage constraint of PU. We also studied the impact of PU interference, channel estimation error, tolerable interference threshold, and acceptable limit of PU outage on SU performance. A MATLAB based simulation has also been carried out to support the analytical result.