Physical-Layer Multicasting Design for Downstream G.fast DSL Transmission

This paper studies the physical-layer multicasting design for downstream G.fast digital subscriber line (DSL) transmission, which corresponds to a multi-user multi-tone (i.e., multi-carrier) scenario. The design goal is to maximize the weighted-sum-group-rate (WSGR) under per-line power constraints. First, as an information-theoretic upper bound, full-rank precoding-based multicasting is considered with joint channel coding across tones. For a single multicast group, this problem corresponds to a non-linear convex semidefinite program (SDP), which is coupled across tones. To reduce the computational complexity, a Lagrange dual decomposition method is developed. This approach is then extended toward multiple multicast groups based on difference-of-convex (DC) programming. Furthermore, a practical multicasting scheme is considered based on rank-one single-stream precoding and independent per-tone channel coding. For this case, instead of relying on computationally complex semidefinite relaxation, a successive convex approximation-based trust-region algorithm is developed. Finally, the simulations of a G.fast cable binder show that the practical multicasting scheme operates close to the information-theoretic multicasting upper bound.