Vector Orthogonal Chirp Division Multiplexing Over Doubly Selective Channels

In this letter, we extend orthogonal chirp division multiplexing (OCDM) to vector OCDM (VOCDM) to provide more design freedom to deal with doubly selective channels. The VOCDM modulation is implemented by performing M parallel N-size inverse discrete Fresnel transforms (IDFnT). Based on the complex exponential basis expansion model (CE-BEM) for doubly selective channels, we derive the VOCDM input-output relationship, and show performance tradeoffs of VOCDM with respect to (w.r.t.) its modulation parameters M and N. Specifically, we investigate the diversity and peak-to-average power ratio (PAPR) of VOCDM w.r.t. M and N. Under doubly selective channels, VOCDM exhibits superior diversity performance as long as the parameters M and N are configured to satisfy some constraints from the delay and the Doppler spreads of the channel, respectively. Furthermore, the PAPR of VOCDM signals decreases with a decreasing N. These theoretical findings are verified through numerical simulations.

Carrier Frequency Offset Estimation for OCDM with Null Subchirps

In this paper, we investigate the carrier frequency offset (CFO) identifiability problem in orthogonal chirp division multiplexing (OCDM) systems. We propose a transmission scheme by inserting consecutive null subchirps. A CFO estimator is accordingly developed to achieve a full acquisition range. We further demonstrate that the proposed transmission scheme not only help to resolve CFO identifiability issues but also enable multipath diversity for OCDM systems. Simulation results corroborate our theoretical findings.