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For Non-Contiguous OFDM (NC-OFDM) a based communication system, especially NC-OFDM-based Cognitive Ratio (CR) systems, one of critical challenges is to establish spectrum synchronization between the transmitter and receiver before data transmission. A Posterior Probability (APP) detection algorithm has been proposed for the receiver to detect the subchannels occupied by the transmitter (active subchannels). However, the encoding scheme adopted is a concatenation of a convolutional coder and a low rate repetition coder so that the system code rate is only 1/4 when half of the subcarriers are active. In this paper, the authors consider using Low Density Parity Check (LDPC) codes to improve the system data transmission rate.
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