NC-OFDM Cognitive Radio Wireless Networks with Efficient LDPC Codes

In this paper, a random Low-Density Parity-Check (LDPC) code is proposed for Noncontiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) Cognitive Radio (CR) systems. Unlike other encoding schemes which achieve a system code rate of only 1/4 when half of the subcarriers are active, the proposed scheme achieves a system code rate of 1/2. The LDPC code is used to enhance the data transmission rate. A binary erasure channel (BEC) concatenated with an uncorrelated fading channel and AWGN channel model is adopted for NC-OFDM CR. Moreover, the adopted channel model is employed with density evolution algorithm to obtain good degree distribution pairs for the LDPC code. Thereafter, a modified shortest-path (MSP) algorithm is used to construct the parity-check matrix for the LDPC code. Simulations results show that the proposed LDPC code performs well in terms of both error rate and data transmission rate.