US-12627331-B2 - Gain adaptation for downstream vectoring systems

US12627331B2US 12627331 B2US12627331 B2US 12627331B2US-12627331-B2

Abstract

In accordance with an embodiment, the method includes detecting an update event whereupon a precoder needs to be updated, sending signal adjustment information to a receiver remotely coupled to a subscriber line out of the plurality of subscriber lines indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel bias caused by the scheduled precoder update, and time-coordinating the precoder update with the enforcement of the signal compensation factor at the receiver.

Inventors

Jochen Maes
Michael Timmers
Dirk VANDERHAEGEN
Carl Nuzman
Danny Van Bruyssel

Assignees

ALCATEL LUCENT

Dates

Publication Date: 20260512
Application Date: 20220110
Priority Date: 20130111

Claims (19)

1 . A communication controller for controlling a communication over a subscriber line out of a plurality of subscriber lines, the communications over the plurality of subscriber lines making use of communication signals that are jointly processed through a linear precoder for crosstalk pre-compensation, wherein the communication controller is configured to receive signal adjustment information from a transmitter remotely coupled to the subscriber line indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel equalization bias caused at least by a corresponding transmit signal scaling to be applied at the transmitter to scale down a transmit communication signal for conformance to a transmit Power Spectral Density (PSD) mask after joint processing of the communication signals through an updated linear precoder, the updated linear precoder being the linear precoder after a linear precoder update, and the communication controller is configured to send adjusted bit loading values in response to receiving the signal adjustment information, time-coordinate an enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update from a data symbol index received from the transmitter, and compensate for the channel equalization bias resulting from the linear precoder update based on the enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update.
2 . A subscriber device comprising: the communication controller according to claim 1 .
3 . A method for controlling communications over a plurality of subscriber lines, the communications making use of communication signals that are jointly processed through a linear precoder for crosstalk pre-compensation, the method comprising: updating one or more coupling coefficients of the linear precoder for mitigating crosstalk from a subscriber line into one or more victim lines, sending signal adjustment information to a receiver remotely coupled to the subscriber line indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel equalization bias caused by crosstalk pre-compensation signals superimposed over the one or more victim lines and corresponding to the respective one or more updated coupling coefficients of the linear precoder after joint processing of the communication signals through an updated precoder, the updated precoder being the linear precoder after a precoder update; and time-coordinating the precoder update with an enforcement of the signal compensation factor at the receiver, and the sending the signal adjustment information to the receiver being in response to a determination that the precoder update results in the channel equalization bias at the receiver.
4 . The method according to claim 3 , wherein the signal compensation factor is a real factor that compensates for an amplitude equalization bias.
5 . The method according to claim 3 , wherein the signal compensation factor is a complex factor that compensates for both an amplitude equalization bias and a phase equalization bias.
6 . The method according to claim 3 , wherein the linear precoder is updated in two steps, a first precoder update with partial precoding gains and limited channel equalization bias, and a second precoder update with full precoding gains, and wherein the sending step takes place between the first and second precoder updates, and the second precoder update is time-coordinated with the enforcement of the signal compensation factor at the receiver.
7 . The method according to claim 3 , wherein the method further comprises: a step of, upon receipt of gain adjustment information, returning an adapted bit loading value and/or an adapted fine gain tuning factor for a respective carrier to a corresponding transmitter.
8 . The method according to claim 3 , wherein the communication signals are multi-carrier signals, and wherein gain adjustment information and the corresponding signal compensation factor are determined on a per carrier basis.
9 . A communication controller for controlling communications over a plurality of subscriber lines, the communications making use of communication signals that are jointly processed through a linear precoder for crosstalk pre-compensation, the communication controller comprising: at least one processor; and at least at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the communication controller to update one or more coupling coefficients of the linear precoder for mitigating crosstalk from a subscriber line into one or more victim lines, to send signal adjustment information to a receiver remotely coupled to the subscriber line indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel equalization bias caused by crosstalk pre-compensation signals superimposed over the one or more victim lines and corresponding to the respective one or more updated coupling coefficients of the linear precoder, after joint processing of the communication signals through an updated precoder, the updated precoder being the linear precoder after a precoder update, and to time-coordinate the precoder update with an enforcement of the signal compensation factor at the receiver, and the sending the signal adjustment information to the receiver being in response to a determination that the precoder update results in the channel equalization bias at the receiver.
10 . An access node comprising the communication controller according to claim 9 .
11 . A communication controller for controlling a communication over a subscriber line out of a plurality of subscriber lines, the communications over the plurality of subscriber lines making use of communication signals that are jointly processed through a linear precoder for crosstalk pre-compensation, the communication controller comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the communication controller to receive signal adjustment information from a transmitter remotely coupled to the subscriber line indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel equalization bias caused by crosstalk pre-compensation signals superimposed over one or more victim lines and corresponding to respective one or more updated coupling coefficients of the linear precoder after joint processing of the communication signals through an updated precoder, the updated precoder being the linear precoder after a precoder update, send adjusted bit loading values in response to receiving the signal adjustment information, time-coordinate an enforcement of the signal compensation factor with a corresponding transmit signal scaling and the linear precoder update from a data symbol index received from the transmitter, and compensate for the channel equalization bias resulting from the linear precoder update based on enforcing the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update.
12 . A subscriber device comprising: the communication controller according to claim 11 .
13 . A communication controller for controlling a communication over a subscriber line out of a plurality of subscriber lines, the communications over the plurality of subscriber lines making use of communication signals that are jointly processed through a linear precoder for crosstalk pre-compensation, wherein the communication controller is configured to receive signal adjustment information from a transmitter remotely coupled to the subscriber line indicative of a signal compensation factor to be applied to a receive communication signal to compensate for a channel equalization bias caused at least by a corresponding transmit signal scaling to be applied at the transmitter to scale down a transmit communication signal for conformance to a transmit Power Spectral Density (PSD) mask after joint processing of the communication signals through an updated linear precoder, the updated linear precoder being the linear precoder after a linear precoder update, and the communication controller is configured to time-coordinate an enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update, and compensate for the channel equalization bias resulting from the linear precoder updated based on the enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update, wherein the communication controller is configured to time-coordinate the enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update by sending an acknowledgment signal to the transmitter.
14 . The communication controller of claim 13 , wherein the communication controller is configured to time-coordinate the enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update from a data symbol index onwards after sending the acknowledgment signal, or the communication controller is configured to time-coordinate the enforcement of the signal compensation factor with the corresponding transmit signal scaling and the linear precoder update from a data symbol index received from the transmitter.
15 . The method of claim 3 , wherein the time-coordinating of the precoder update with the enforcement of the signal compensation factor at the receiver is based on a received acknowledgment signal.
16 . The method of claim 15 , wherein the time-coordinating of the precoder update with the enforcement of the signal compensation factor at the receiver is from a data symbol index onwards after the received acknowledgment signal, or the time-coordinating of the precoder update with the enforcement of the signal compensation factor at the receiver is from a data symbol index sent to the receiver.
17 . The communication controller of claim 9 , wherein the communication controller is configured to time-coordinate the precoder update with the enforcement of the signal compensation factor at the receiver based on an acknowledgment signal.
18 . The communication controller of claim 17 , wherein the communication controller is configured to time-coordinate the precoder update with the enforcement of the signal compensation factor at the receiver from a data symbol index onwards after receiving the acknowledgment signal, or the communication controller is configured to time-coordinate the precoder update with the enforcement of the signal compensation factor at the receiver from a data symbol index sent to the receiver.
19 . The communication controller of claim 11 , wherein the communication controller is configured to enforce the signal compensation factor from the data symbol index onwards after sending an acknowledgement signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This is a Continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 14/654,690, filed Jun. 22, 2015, which is a National Phase of PCT/EP2014/050102, filed Jan. 7, 2014, which claims priority to EP 13305023.7 filed Jan. 11, 2013, the entire contents of each of which are hereby incorporated by reference. TECHNICAL FIELD OF THE INVENTION The present invention relates to a method and apparatus for controlling communications over a plurality of subscriber lines, the communications making use of communication signals that are jointly processed through a precoder for crosstalk pre-compensation. TECHNICAL BACKGROUND OF THE INVENTION Crosstalk (or inter-channel interference) is a major source of channel impairment for Multiple Input Multiple Output (MIMO) communication systems, such as Digital Subscriber Line (DSL) communication systems. As the demand for higher data rates increases, DSL systems are evolving toward higher frequency bands, wherein crosstalk between neighboring transmission lines (that is to say transmission lines that are in close vicinity over part or whole of their length, such as twisted copper pairs in a cable binder) is more pronounced (the higher frequency, the more coupling). A MIMO system can be described by the following linear model: Y⁡(k)=H⁡(k)⁢X⁡(k)+Z⁡(k),(1) wherein the N-component complex vector X, respectively Y, denotes a discrete frequency representation, as a function of the frequency/carrier/tone index k, of the symbols transmitted over, respectively received from, the N channels, wherein the N×N complex matrix H is referred to as the channel matrix: the (i,j)-th component of the channel matrix H describes how the communication system produces a signal on the i-th channel output in response to a signal being transmitted to the j-th channel input; the diagonal elements of the channel matrix describe direct channel coupling, and the off-diagonal elements of the channel matrix describe inter-channel coupling (also referred to as the crosstalk coefficients), and wherein the N-component complex vector Z denotes additive noise over the N channels, such as Radio Frequency Interference (RFI) or thermal noise. Different strategies have been developed to mitigate crosstalk and to maximize effective throughput, reach and line stability. These techniques are gradually evolving from static or dynamic spectral management techniques to multi-user signal coordination (or vectoring). One technique for reducing inter-channel interference is joint signal precoding: the transmit data symbols are jointly passed through a precoder before being transmitted over the respective communication channels. The precoder is such that the concatenation of the precoder and the communication channel results in little or no inter-channel interference at the receiver. For instance, a linear precoder performs a matrix-product in the frequency domain of a transmit vector X(k) with a precoding matrix P(k), the precoding matrix P(k) being such that the resulting channel matrix H(k)P(k) is diagonalized, meaning the off-diagonal coefficients of the overall channel H(k)P(k)—and thus the inter-channel interference—mostly reduce to zero. Practically, the precoder superimposes anti-phase crosstalk pre-compensation signals over the victim line along with the direct signal that destructively interfere at the receiver with the actual crosstalk signals from the respective disturber lines. A further technique for reducing inter-channel interference is joint signal post-processing: the receive data symbols are jointly passed through a postcoder before being detected. The postcoder is such that the concatenation of the communication channel and the postcoder results in little or no inter-channel interference at the receiver. The choice of the vectoring group, that is to say the set of communication lines, the signals of which are jointly processed, is rather critical for achieving good crosstalk mitigation performances. Within a vectoring group, each communication line is considered as a disturber line inducing crosstalk into the other communication lines of the group, and the same communication line is considered as a victim line receiving crosstalk from the other communication lines of the group. Crosstalk from lines that do not belong to the vectoring group is treated as alien noise and is not canceled. Ideally, the vectoring group should match the whole set of communication lines that physically and noticeably interact with each other. Yet, local loop unbundling on account of national regulation policies and/or limited vectoring capabilities may prevent such an exhaustive approach, in which case the vectoring group would include a sub-set only of all the physically interacting lines, thereby yielding limited vectoring gains. Signal vectoring is typically performed at a traffic aggregation point, whereat all the data symbols concurrently transmitted over, or r