Abstract
G.fast suffers from strong far-end crosstalk at high frequencies in cable binders containing a large number of twisted copper pairs. For the 212-MHz G.fast spectrum, the power penalty incurred by the conventional zero-forcing precoding-based linear vectoring (LV) scheme is far more substantial than it was over the 30-MHz VDSL2 spectrum. In this paper, we propose a novel non-LV (NLV) scheme based on Babai’s nearest plane approximation of the closest lattice point problem on the reduced lattice basis. Similar to the conventional Tomlinson–Harashima precoding (THP)-based NLV, the proposed approximate perturbation aided lattice encoding (APPLE) scheme closely approaches the dirty paper coding capacity which provided that the system employs a fully rate-adaptive power allocation policy per tone per pair. However, if the system employs a scalar power policy that is only rate-adaptive with respect to each tone, APPLE becomes capable of achieving a higher throughput per binder than THP. APPLE’s transmitter complexity is considerably lower than that of the conventional lattice encoding schemes (e.g., vector perturbation) and comparable to that of THP.
Highlights
G.fast has emerged as the new standard of the copper based digital subscriber line (DSL) technology
We will first characterize the performance of lattice reduction, and we present the coice of the additive signal coolant l based on the lattice reduction aided transmit precoding (TPC) scheme of [20]
The sum-rate achieved by APPLE is compared against those achieved by the conventional linear vectoring (LV) and NLV, as well as against the capacity given by the sum-rate of dirty paper coding (DPC)
Summary
G.fast has emerged as the new standard of the copper based digital subscriber line (DSL) technology. The main purpose of downstream vectoring is to maximize the throughput of a DSL binder via a FEXT canceller and a power controller. Applying the back-end signal coolant l i to the users’ message symbol vector ui will reduce the power boost incurred by the FEXT canceller i. Represented by the non-negative real-valued diagonal matrix Ai, it is used for coordinating the transmit power allocated to each message symbol uik in order to achieve a similar quality of service for all users, while simultaneously maximizing the throughput under the limit of the TxPSD mask and the ATP budget. The front-end FEXT canceller i is a linear filter that, together with the signal coolant, maps the message vector ui to a multi-dimensional signal space related to the inverse channel Gi = (H i)−1. Since DSL channels are essentially time invariant, we will assume that the DTU has perfect knowledge of the downstream CSI, which is acquired during the initialization process
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