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.