  In this work, we propose a novel rate control algorithm for Versatile Video
Coding (VVC) standard based on its distinct rate-distortion characteristics. By
modelling the transform coefficients with the composite Cauchy distribution,
higher accuracy compared with traditional distributions has been achieved.
Based on the transform coefficient modelling, the theoretically derived R-Q and
D-Q models which have been shown to deliver higher accuracy in characterizing
RD characteristics for sequences with different content are incorporated into
the rate control process. Furthermore, to establish an adaptive bit allocation
scheme, the dependency between different levels of frames is modelled by a
dependency factor to describe relationship between the reference and
to-be-coded frames. Given the derived R-Q and D-Q relationships, as well as the
dependency factor, an adaptive bit allocation scheme is developed for optimal
bits allocation. We implement the proposed algorithm on VVC Test Model (VTM)
3.0. Experiments show that due to proper bit allocation, for low delay
configuration the proposed algorithm can achieve 1.03% BD-Rate saving compared
with the default rate control algorithm and 2.96% BD-Rate saving compared with
fixed QP scheme. Moreover, 1.29% BD-Rate saving and higher control accuracy
have also been observed under the random access configuration.
