Dynamic Resource Allocation for Energy Efficient Transmission in Digital Subscriber Lines

N. Zhang, Z. Yao, Y. Liu, S. Boyd, and Z.-Q. Luo

IEEE Transactions on Signal Processing, 65(16):4353–4366, June 2017.
Shorter version with title Optimal Resource Allocation for Energy Efficient Transmission in DSL appeared in Proceedings IEEE Global Communications Conference, 2016.

Linear matrix precoding, also known as vectoring, is a well-known technique to mitigate multi-user interference in the downlink Digital Subscriber Line (DSL) transmission. While effective in canceling interference, vectoring does incur major communication overhead and computational overhead in terms of the transmission of idle symbols and precoder-data multiplications at each data frame, resulting in significant energy consumption when the number of lines is large. To facilitate energy efficient transmission, it has been recently proposed (in the G.fast standard) that each data frame is divided into a normal operating interval (NOI) and a discontinuous operating interval (DOI). In the NOI, all lines (or users) are involved in a common vectoring group, which requires a large matrix precoder. While in the DOI, the lines are subdivided into multiple small non-overlapping vectoring subgroups and are transmitted in a TDMA manner, requiring small matrix multiplications and thus improving the energy efficiency. In this paper, we consider the key dynamic resource allocation (DRA) problems in downlink DSL: given the real-time demands, determine the optimal transmission scheme: the optimal NOI and DOI size in each data frame as well as the optimal grouping strategy in the DOI, and optimally adjust the transmission scheme. We formulate these optimal dynamic resource allocation problems and propose efficient real-time algorithms to solve them to global optimality. Simulation results are shown to demonstrate the efficiency and the effectiveness of the proposed algorithms.