Ordered Tomlinson-Harashima Precoding in G.fast Downstream

G.fast is an upcoming next generation DSL standard envisioned to use bandwidth up to 212 MHz. Far-end crosstalk (FEXT) at these frequencies greatly overcomes direct links. Its cancellation based on non-linear Tomlinson-Harashima Precoding (THP) proved to show significant advantage over standard linear precoding. This paper proposes a novel THP structure in which ordering of successive interference pre-cancellation can be optimized for downstream with non-cooperating receivers. The optimized scheme is compared to existing THP structure denoted as equal-rate THP which is widely adopted in wireless downlink. Structure and performance of both methods differ significantly favoring the proposed scheme. The ordering that maximizes the minimum rate (max-min fairness) for each tone of the discrete multi-tone modulation is the familiar V-BLAST ordering. However, V-BLAST does not lead to the global maximum when applied independently on each tone. The proposed novel Dynamic Ordering (DO) strategy takes into account asymmetric channel statistics to yield the highest minimum aggregated rate.Comment: 7 pages, 11 figures, Accepted at the 2015 IEEE Globecom 2015, Selected Areas in Communications: Access Networks and Systems, 6-10 December, 201

Ordered Tomlinson-Harashima Precoding in G.fast Downstream

G.fast is an upcoming next generation DSL standard envisioned to use bandwidth up to 212 MHz. Far-end crosstalk (FEXT) at these frequencies greatly overcomes direct links. Its cancellation based on non-linear Tomlinson-Harashima Precoding (THP) proved to show significant advantage over standard linear precoding. This paper proposes a novel THP structure in which ordering of successive interference pre-cancellation can be optimized for downstream with non-cooperating receivers. The optimized scheme is compared to existing THP structure denoted as equal-rate THP which is widely adopted in wireless downlink. Structure and performance of both methods differ significantly favoring the proposed scheme. The ordering that maximizes the minimum rate (max-min fairness) for each tone of the discrete multi-tone modulation is the familiar V-BLAST ordering. However, V-BLAST does not lead to the global maximum when applied independently on each tone. The proposed novel Dynamic Ordering (DO) strategy takes into account asymmetric channel statistics to yield the highest minimum aggregated rate

Per-line power controlled lattice-reduction aided zero-forcing precoding for G.fast downstream

Linear precoding for Far-End CrossTalk (FEXT) cancellation is supported by the first release of the next generation DSL standard G.fast utilizing bandwidth up to 106 MHz. The cancellation precoding for the second release (bandwidth up to 212 MHz with much stronger FEXT) has not been standardized yet. Non-linear Tomlinson-Harashima Precoding (THP) is a promising candidate as it outperforms the linear precoding. Nevertheless, sequential processing of THP introduces unfavorable additional delay proportional to the number of lines. In this paper, we focus on non- linear precoding based on Lattice Reduction aided Zero-Forcing (ZF-LR) which can be implemented in parallel without any sequential processing delay. ZF-LR precoding has been proposed in wireless scenario using scalar scaling to adjust average transmit power. We modify this scheme to comply with per-line per-carrier power constraint and enable power control of each line individually (e.g., to adapt power for different line lengths). Optimized Power Allocation (OPA) for the modified scheme maximizing weighted sum-rate leads to the signomial optimization problem. Similarly to THP, ZF-LR precoding with OPA outperforms the linear precoding as well