Spectrum Design for Orthogonal Chirp Division Multiplexing Transmissions

Orthogonal chirp division multiplexing (OCDM) is a spread spectrum technique that leverages the orthogonality of cyclically shifted linear chirp signals to maximize spectral efficiency. However, since each chirp spans the entire signal band, the only way to control its bandwidth is to alter the sampling rate of the digital-to-analog converter (DAC). This letter shows that the inherent relationship between the discrete Fresnel transform (DFnT) and the discrete Fourier transform (DFT) facilitates a simple method of designing the spectrum of the signal without adding significant complexity. This enables direct implementation of the digital filters proposed in literature for advanced waveforms. Subsequently, simulations corroborate the performance of the proposed method and filtered-OCDM (f-OCDM) in wireless multipath fading channels in comparison with orthogonal frequency division multiplexing (OFDM) with a given spectral mask.