Orthogonal Chirp Division Multiplexing

TLDR

Chirp waveforms enable pulse compression and spread spectrum in radar and communications, and the Fresnel transform underpins OCDM to achieve the maximum spectral efficiency of chirp spread spectrum. This paper proposes orthogonal chirp‑division multiplexing (OCDM), a principle for multiplexing a bank of orthogonal chirps to enable high‑speed communication. OCDM is implemented digitally using the discrete Fresnel transform, with efficient DSP for channel dispersion compensation, compatibility with existing OFDM systems, and simulations confirming feasibility. The results show that OCDM exploits multipath diversity to outperform OFDM and is more resilient to interference caused by insufficient guard intervals than single‑carrier frequency‑domain equalization.

Abstract

Chirp waveform plays a significant role in radar and communication systems for its ability of pulse compression and spread spectrum. This paper presents a principle of multiplexing a bank of orthogonal chirps, termed orthogonal chirp-division multiplexing (OCDM) for high-speed communication. As Fourier transform is the kernel of orthogonal frequency-division multiplexing (OFDM), which achieves the maximum spectral efficiency (SE) of frequency-division multiplexing, Fresnel transform underlies the proposed OCDM system, which achieves the maximum SE of chirp spread spectrum. By using discrete Fresnel transform, digital implementation of OCDM is introduced. According to the properties of Fresnel transform, the transmission of OCDM signal in linear time-invariant channel is studied. Efficient digital signal processing is proposed for channel dispersion compensation. The implementation of the OCDM system is discussed with the emphasis on its compatibility to the OFDM system; it is shown that it can be easily integrated into the existing OFDM systems. Finally, the simulations are provided to validate the feasibility of the proposed OCDM. It is shown that the OCDM system can efficiently exploit multipath diversity and thus outperforms the OFDM, and that it is more resilient against the interference due to insufficient guard interval than single-carrier frequency-domain equalization.