Methods for joint PAPR and spectral improvement of correlatively coded OFDM system

Although correlative codes can significantly improve the spectral performance of the rectangularly pulsed orthogonal frequency-division multiplexing (OFDM) signals, they usually have high peak to average power ratio (PAPR) values. Two methods are proposed in this paper to reduce the PAPR values of the correlatively coded OFDM signals. First, a precoding matrix for improving the spectral performance of the correlatively coded OFDM is established. Through the singular value decomposition (SVD), a replacing procedure on the set of singular values of the precoding matrix is executed to constitute a new precoding matrix. Hence, the correlatively coded OFDM with the precoding matrix can jointly lessen the PAPR values and spectral sidelobes. For the second method, the Constant Amplitude Zero Auto Correlation (CAZAC) sequence is applied for expanding the constellation points of correlatively coded OFDM signals such that the relevance between frequency symbols is decreased for PAPR reduction of the correlative codes OFDM signals. We also develop two systematic procedures to establish the precoding matrix and the CAZAC transformation matrix respectively for the two proposed schemes. Simulation results show that both the proposed schemes have a PAPR performance improvement of 3 dB compared with the correlative codes OFDM.