Opportunistic communications in multi-rate CDMA systems for cell capacity improvement using cognitive radio

In this paper, a two phase algorithm for spectrum sensing and power control of a secondary user (S-user) or cognitive radio is proposed. In the first phase, the primary base station (P-BS), which is conscious of the number of primary active users, broadcasts the percentage of the spectrum usage of the cell by primary users (P-users). If the cell is not fully loaded, the S-user and/or S-BS estimates interference to check if condition for data transmission is hold. If this is so, the second phase of the algorithm, the transmit power control of S-user is started. In this paper, a new method based on fluctuations of estimated covariance matrix of the received signal is proposed for identifying the interference of secondary and P-users. Computer simulations show that the proposed algorithm performs properly in the SNR of -5 dB.