Way to design an orthogonal frequency-division multiple access-base station receiver disturbed by a narrowband interfering cognitive radio signal

This study deals with an interweave cognitive-radio (CR) system, where an uplink orthogonal frequency-division multiple access system is considered for the primary users (PUs). Our purpose is to estimate the PU carrier frequency offsets (PU-CFOs) as well as the channels to estimate the transmitted symbols. However, in wideband wireless communications, the PU received-signal spectrum usually exhibits a localised fading because of the multipath propagation channel. When the PU faded frequencies are used by the CR system, the PU system is contaminated by a CR narrowband interference (CR-NBI). In that case, if a Kalman filter (KF)-based approach is used for the estimations of the CFOs and the channels, the state-space representation does not necessarily take into account the CR-NBI; this hence has a negative impact on the algorithm performance. Therefore the authors propose to make this solution more robust to the CR-NBI by detecting when it appears and disappears to avoid using the data disturbed by the CR-NBI. The authors´ contribution is to assume that the CR-NBI is because of the transmission of contiguous blocks and to propose various criteria based on the covariance matrix of the KF innovation.