AU2021101603A4 - Protection against fluctuating noise - Google Patents

Abstract

Protection against fluctuating noise Solutions described allow adjusting virtual noise for communication lines connected to a distribution point unit, comprising the steps (i) detecting crosstalk on a line that is connected to the distribution point unit; and (ii) setting a virtual noise mask dependent on the crosstalk detected. Fig.2 U) LU 0 C-) (1) In 0 00 " L -C-) 0 0 0 U) NT C) 2 u) > C14 a) > cm 0 0 LO C:) U) C14 Lu C14 C:) C:) C14 C14 co C:) 0 04 0 C - E E 70 E cz E C) 0 0 0 LZ 0 0 C- 0 o C- o C- U) cz cn U) U) 'E U) U) 70 U) cz 10 - (1) U) W > 0 E cz cz E U) C) .0 C14 irmU) 0 C,4 cz 0 _j " (1) Cf) U) U) M0 C) 0 0 > C) 0 '*, C14 > > cy') C) C14 U) LU OD 64 2 I_ 0 r-- Z:) C-) 0 (1) C) 0 L 0 U) > w > cz 0 E

Description

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Description

PROTECTION AGAINST FLUCTUATING NOISE

VDSL2 or G.fast are typically deployed much closer to the actual subscriber than the legacy services ADSL2plus or POTS, which can be launched from an exchange or a central office (CO) that is usually several kilometers away.

In contrast to these legacy service, new services like VDSL2 or G.fast (also referred to herein as FTTC services) are deployed from cabinets (FTTC) or distributions points (FTTdp), with a loop length between tens and hundreds of meters. A Distribution Point Unit (DPU) is usually constructed in a way that they allow passing the legacy service from the CO using a bypass circuit or relay. This ensures that not all customers need to be switched to the new service.

However, the legacy service may cause severe crosstalk to the FTTC service. A constant crosstalk may not be a problem, because the crosstalk noise has already been considered during an initialization of the FTTC service. Unfortunately, the crosstalk may fluctuate over time due to various reasons: Legacy CPEs may be switched off and on. Also, FTTC lines may be switched off causing the bypass circuit at the DPU to re connect the line back to the pairs running from the CO to the FTTC DPU. Such re connection of the lines to the CO may lead to crosstalk in the main cable from the CO to the DPU. Also, the legacy service may have a low power mode resulting in different transmit power based on changes in user data traffic thereby significantly increasing the noise in the band used by the legacy service. Such noise, however, may cause transmission errors or reinitializations of the FTTC service.

One way of solving this problem is to mask the usage of the band occupied by the legacy service for the FTTC service. For example, if the legacy ADSL2plus service uses the frequency band up to 2.2 MHz, the VDSL2 service could start operation above 2.2 MHz. Alternatively, Virtual Noise (VN) may be used to better protect this band. Virtual Noise assumes a configurable (higher) noise level already during initialization.

As a downside, both approaches reduce the data rate that can be utilized by the FTTC VDSL2 service irrespectively of the actual ADSL2plus noise.

Hence, it is an object to improve existing approaches and in particular to improve FTTC services in a legacy environment and specially to protect VDSL2 services from (fluctuating) ADSL2plus noise.

This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims.

The examples suggested herein may in particular be based on at least one of the following solutions. In particular, combinations of the following features could be utilized in order to reach a desired result. The features of the method could be combined with any feature(s) of the device, apparatus or system or vice versa.

A method is provided for adjusting virtual noise for communication lines connected to a distribution point unit, the method comprising: - detecting crosstalk on a line that is connected to the distribution point unit; - setting a virtual noise mask dependent on the crosstalk detected.

The distribution point unit may be or it may comprise any xDSL or G.fast transceiver. The transceiver may comprise or it may be based on xDSL or G.fast technology as, e.g., defined by a standard.

According to an embodiment, detecting crosstalk further comprises: - retrieving quiet line noise; - calculating at least one mean quiet line noise level; - detecting crosstalk if the at least one mean quiet line noise level fulfills at least one condition.

According to an embodiment, the at least one condition comprises at least one of the following: - a difference between two mean quiet line noise levels that is compared with a first threshold, - a comparison of a mean quiet line noise level with a second threshold.

According to an embodiment, the difference between two mean quiet line noise levels compared with the first threshold is mQLN400 - mQLN511 > Ti, wherein - mQLN400 is a mean QLN level up to subcarrier 400, - mQLN511 is a mean QLN level for the subcarriers 401 to 511, and - Ti is the first threshold;

According to an embodiment, the comparison of the mean quiet line noise level with the second threshold is mQLN400 > T2, wherein - mQLN400 is a mean QLN level up to subcarrier 400, and - T2 is the second threshold.

According to an embodiment, setting a virtual noise mask dependent on the crosstalk detected comprises: - determining whether the virtual noise mask has already been set and - setting it if it has not yet been set; - maintaining it if it has already been set.

According to an embodiment, - the virtual noise mask is set according to a predetermined configuration, or - according to a variable configuration, which is adjusted according to the level of crosstalk detected.

According to an embodiment, the virtual noise mask is canceled or adjusted if no crosstalk has been detected for a predetermined period of time (T3).

According to an embodiment, the crosstalk is detected after the line has been initialized or during the initialization of the line.

According to an embodiment, the crosstalk is detected by a terminal and/or by the distribution point unit.

According to an embodiment, the crosstalk comprises ADSL crosstalk.

According to an embodiment, the virtual noise mask is set to enable utilization of the line via VDSL or G.fast.

Also, a device is provided for adjusting virtual noise for communication lines connected to a distribution point unit, wherein the device is arranged to - detect crosstalk on a line that is connected to the distribution point unit; - set a virtual noise mask dependent on the crosstalk detected.

According to an embodiment, the device is a VDSL or G.fast device.

Further, a distribution point unit is suggested that is connectable to terminals via communication lines, wherein the distribution point unit is arranged to - detect crosstalk on at least one of the communication lines; - set a virtual noise mask for at least one of the terminals dependent on the crosstalk detected.

According to an embodiment, the terminals comprise at least one of the following: - a VDSL terminal, - a G.fast terminal, - an ADSL terminal, - a telephone.

Also, a system is provided, said system comprising at least one distribution point unit as described herein and at least one device as described herein.

A computer program product is suggested, that is directly loadable into a memory of a digital processing device, comprising software code portions for performing the steps of the method as described herein.

The digital processing device may be a single physical unit or it may comprise several physical units, each providing processing capability.

A computer-readable medium is provided, which has computer-executable instructions adapted to cause a computer system to perform the steps of the method as described herein.

Embodiments are shown and illustrated with reference to the drawings. The drawings serve to illustrate the basic principle, so that only aspects necessary for understanding the basic principle are illustrated. The drawings are not to scale. In the drawings the same reference characters denote like features.

Fig.1 shows an exemplary diagram of a FTTC deployment scenario comprising a CO that is connected via a main cable to a DPU, wherein the DPU is further connected via a distribution cable to several terminals;

Fig.2 shows a flowchart comprising steps to improve operation with the presence of crosstalk, in particular ADSL2plus crosstalk.

Examples described herein use measurements that are available in a FTTC DPU to detect the presence of legacy ADSL2plus crosstalk.

If the DPU has detected the presence of ADSL2plus crosstalk, a preconfigured Virtual Noise (VN) pattern or shape can be set and used during an initialization phase of the VDSL2 FTTC service.

In case the DPU has determined that no ADSL2plus services are used any longer, the Virtual Noise limitation can be removed (or reduced) from the configuration and the band up to 2.2 MHz can be used by the VDSL2 FTTC service with the next initialization.

Fig.1 shows an exemplary diagram of a FTTC deployment scenario comprising a CO 101 that is connected via a main cable 102 to a DPU 103. The DPU 103 is further connected via a distribution cable 104 to several terminals, i.e., a telephone 105, an ADSL2plus CPE 106 and to a VDSL2 CPE 107.

The length of the main cable 102 may be in the order of several kilometers, whereas the length of the distribution cable 104 may be in the order of tens or hundreds of meters.

Hence, the distribution cable 104 is significantly shorter compared to the main cable 102.

The DPU 103 in the example shown in Fig.1 is a DPU supporting the services VDSL2 and G.fast. The DPU 103 is located in close proximity of the terminals 105 to 107.

The main cable 102 running from the CO 101 is connected to the DPU 103, but only the CPE 107 subscribes to the new service VDSL2, the terminal 105 is a subscriber of the POTS and the terminal 106 is a subscriber to ADSL2plus. Hence, the DPU 103 connects the CO directly to the ADSL2plus CPE 106 and to the telephone 105 via a bypass circuit 108.

It is noted that the DPU is supplied with the FTTC service via a fiber from an optical unit, e.g., an Optical Line Termination (OLT) (or any other centralized entity) not shown in Fig.1.

The bypass circuit 108 disconnects the line to the main cable 102 (i.e., the CO 101) in case the DPU 103 provides the VDSL2 service as is shown in Fig.1 for the VDSL2 CPE 107. The bypass circuit 108 has a closed connection to the main cable 102 to connect the telephone 105 and the ADSL2plus CPE 106 to the CO 101.

The ADSL2plus service from the CO 101 generates crosstalk to other lines of the same cable binder, e.g., the distribution cable 104.

Even if there are no ADSL2plus customers in the DPU's service area, there could be crosstalk from other ADSL2plus lines sharing the same main cable 102. In addition, a VDSL2 line of the distribution cable 104 may be switched off resulting in the bypass circuit 108 to re-connect its line to the CO 101. This may happen if the VDSL2 CPE 107 with supplies power to the DPU 103 is switched off. Without further power by this CPE 107, the bypass circuit 108 closes the connection towards the CO 101. Based on the re-connection to the CO 101, additional crosstalk is introduced to the ADSL2plus CPE 106. Also, such re-connection introduces crosstalk to at least one other VDSL2 line / VDSL2 CPE (not shown).

Hence, it may not suffice to know whether there are ADSL2plus customers in the service area of the DPU 103.

In order to detect the presence of ADSL2plus crosstalk, test parameters specified in the VDSL2 recommendation ITU-T G.993.2 may be used. ITU-T G.993.2 specifies the measurement procedure for Quiet Line Noise (QLN). Such QLN measurements are available from the DPU as well as the CPE. The DPU measures the QLN in the upstream bands and the CPE measures the QLN in the downstream bands.

Since there is only a small USO band that might not be used at all and most of the ADSL2plus band overlaps with the VDSL2 downstream band, the QLN measurements from the CPE are suitable to detect ADSL2plus crosstalk.

A VDSL2 system with no ADSL2plus crosstalk can use the full VDSL2 spectrum without any restrictions. In case ADSL2plus crosstalk is detected, the VDSL2service may advantageously be protected against fluctuating noise in the ADSL2plus band. Predefined profiles can be used that may be activated for a selection of lines or for all lines connected to the DPU. Such approach may in particular be applied, if ADSL2plus crosstalk is detected on at least one of the lines administered by the DPU.

The profile may mask the full ADSL2plus band using parameters like CARMASK (carrier masking). However, such masking bears the disadvantage that the band is not usable at all for data transmission. As an alternative, Virtual Noise (VN) may be introduced, which may still allow some data transmission (with reduced bandwidth).

VN can be introduced to the modem (e.g., the VDSL2 CPE 107) to consider a certain (high) level of fluctuating noise already during its initialization. Hence, a VN power spectral density (PSD) mask can be provided to and used by the modem during initialization. This is also referred to as VN protection. The modem measures the external noise (i.e., thermal noise, crosstalk) and uses the maximum of the external noise and the configured VN PSD for further processing, e.g., SNR calculation and bit allocation. Advantageously, during showtime of the modem, fluctuating crosstalk will have no impact (e.g., on noise margin) as long as it does not exceed the level configured via the VN PSD mask.

A suitable VN PSD that matches an expected maximum ADSL2plus crosstalk could be preconfigured in the DPU and applied if ADSL2plus crosstalk is detected. According to an embodiment, the VN PSD may be adjusted, e.g., scaled, with the level of crosstalk detected in the ADSL2plus band.

If the VN PSD mask is set (including a reset or modification of the VN PSD mask), it will be considered during the next initialization of the modem. This initialization may be triggered by the DPU, the CPE, it may occur pursuant to an interruption of the communication due to errors on the line and the initialization may happen subsequent to a predefined time-out and/or based on any predefined action or time.

ADSL2plus crosstalk up to 2.2 MHz (up to subcarrier 511) may be much stronger than potential crosstalk from other VDSL2 lines. The latter could be identified by the alternating upstream downstream bands up to 17.6 MHz (subcarrier 4095). VDSL2 crosstalk may be weaker because of the short distribution cable resulting in a shorter coupling length and the lower transmit PSD of VDSL2 especially at higher frequencies. Also, there may be a low level of crosstalk just before the end of the ADSL2plus band (e.g., due to a reduced ADSL2plus PSD mask) at subcarrier 511, which could be used to detect the ADSL2plus crosstalk.

ADSL2plus crosstalk can be detected by comparing a mean QLN level up to subcarrier 400 (mQLN40)with a mean QLN level for the subcarriers 401 to 511 (mQLN5i). If mQLN40 exceeds mQLN5 by a certain threshold Ti, e.g., 10 dB, ADSL2plus crosstalk is detected:

mQLN400- mQLN511 > Ti. (Condition I)

In addition, a second criterion may be used to improve the crosstalk detection, which involves an absolute level of the mean QLN level mQLN4aa exceeding a threshold level T2, e.g., -110 dBm:

mQLN400> T2. (Condition II)

Hence, if Condition I and/or Condition II is/are fulfilled, ADSL2plus crosstalk is detected.

The crosstalk detection may use QLN measurements by the CPE during initialization. If the VDSL2 CPE does not update the QLN measurement during showtime, a subsequent measurement can be performed when the line re-initializes. Advantageously, if the line is initialized using the described crosstalk algorithm in combination with the VN protection, the line is more stable and does not easily trigger reinitialization due to crosstalk fluctuation.

Advantageously, VN protection is removed if ADSL2plus crosstalk is no longer present, which may be the case if the last ADSL2plus customer affecting the DPU's service area has migrated to the new VDSL2 service. This, however, may take months or even years. Hence, it may suffice to keep the protection in place and remove it, if none of the VDSL2 lines detects ADSL2plus crosstalk for a certain period of time T3, e.g., three month.

Advantageously, any initialization can be based on updated QLN measurements. If, e.g., no ADSL2plus crosstalk is detected on any of the DPU's line for this period of time T3, the VN protection is removed and the VDSL2 lines will operate at a higher data rate.

Fig.2 shows a flowchart comprising steps to improve operation with the presence of (fluctuating) crosstalk, in particular ADSL2plus crosstalk. The flowchart comprises the following steps:

Step 201: The VDSL2 line of the DPU is initialized.

Step 202: A QLN measurement is conducted comprising receiving measurements from the CPE. The mean QLN level up to subcarrier 400 (mQLN4a) and the mean QLN level for the subcarriers 401 to 511 (mQLN51 i) are determined.

Step 203: It is determined whether ADSL2plus crosstalk is present. The ADSL2plus crosstalk can be detected by comparing the mean QLN level up to subcarrier 400 (mQLN400) with the mean QLN level for the subcarriers 401 to 511 (mQLN5l), i.e., by determining whether a difference exceeds the threshold Ti mQLN400- mQLN511 > Ti (Condition I) and by determining an absolute level of the mean QLN level mQLN400 exceeding the threshold level T2 mQLN400 > T2. (Condition II). If, e.g., both Condition I and Condition II are true, then crosstalk is detected, it is branched to step 204, otherwise it is continued with step 207.

Step 204: As this step applies if ADSL2plus crosstalk has been detected, it is checked whether the VN PSD mask (also referred to as VN protection) has been set and is already present. If this is true, it is branched to step 206, otherwise it will be continued with step 205.

Step 205: As the VN PSD mask (VN protection) has not been set, it is now configured for all lines of the DPU. Next is step 206.

Step 206: The modem (VDSL2 line) conducts normal operation (in showtime). At some point, the modem leaves showtime. Such exit from showtime could be triggered by the DPU, the CPE, communication errors on the line and/or any other reason. Next is step 201.

Step 207: As this step applies if ADSL2plus crosstalk has not been detected, it is checked whether ADSL2plus crosstalk is absent for at least the time T3. If this applies, it is continued with step 208, otherwise step 206 is next.

Step 208: As the ADSL2plus crosstalk has been absent for more than the time T3, the VN protection is removed for all lines of the DPU. It is continued with step 206.

Hence, when a VDSL2 line initializes, QLN measurements from the CPE are retrieved using, e.g., an embedded operations channel (eoc). Next, the mean QLN levels mQLN40 and mQLN51 are calculated and it is determined whether or not ADSL2plus crosstalk is present. If ADSL2plus crosstalk is detected, it will be checked if the VN protection is in place. If not, VN protection is applied to all lines connected to the DPU. In case no ADSL2plus crosstalk is detected, still it is determined if no ADSL2plus crosstalk has been present for at least the time T3on any of the DPU's lines. If this is the case, the VN protection (if any) is removed for all lines connected to the DPU. This approach is repeated at any initialization of any of the DPU's line.

The procedure as described may be implemented in the DPU and/or the VDSL2 CPE. The measurements can be processed locally at the CPE and the CPE may determine a VN PSD mask pursuant to static or variable requirements and/or configurations. The DPU may set VN PSD masks for more than a single line, whereas the CPE may directly or indirectly set the VN PSD mask for the connection between the DPU in this particular CPE.

Although various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be obvious to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. It should be mentioned that features explained with reference to a specific figure may be combined with features of other figures, even in those cases in which this has not explicitly been mentioned. Further, the methods of the invention may be achieved in either all software implementations, using the appropriate processor instructions, or in hybrid implementations that utilize a combination of hardware logic and software logic to achieve the same results. Such modifications to the inventive concept are intended to be covered by the appended claims.

List of Abbreviations:

ADSL Asymmetric DSL CO Central Office CPE Customer Premises Equipment (terminal) DPU Distribution Point Unit DSL Digital Subscriber Line FTTdp Fiber To The distribution point FTTC Fiber To The Curb G.fast High-speed versions of DSL POTS Plain Old Telephone System PSD Power Spectral Density QLN Quiet Line Noise OLT Optical Line Termination SNR Signal-to-Noise Ratio VDSL Very High Speed DSL VN Virtual Noise

Claims (18)

Claims

1. A method for adjusting virtual noise for communication lines connected to a distribution point unit, the method comprising: - detecting crosstalk on a line that is connected to the distribution point unit; - setting a virtual noise mask dependent on the crosstalk detected.

2. The method according to claim 1, wherein detecting crosstalk further comprises: - retrieving quiet line noise; - calculating at least one mean quiet line noise level; - detecting crosstalk if the at least one mean quiet line noise level fulfills at least one condition.

3. The method according to claim 2, wherein the at least one condition comprises at least one of the following: - a difference between two mean quiet line noise levels that is compared with a first threshold, - a comparison of a mean quiet line noise level with a second threshold.

4. The method according to claim 3, wherein the difference between two mean quiet line noise levels compared with the first threshold is mQLN400 - mQLN511 > Ti, wherein - mQLN400 is a mean QLN level up to subcarrier 400, - mQLN511 is a mean QLN level for the subcarriers 401 to 511, and - Ti is the first threshold;

5. The method according to any of claims 3 or 4, wherein the comparison of the mean quiet line noise level with the second threshold is mQLN400 > T2, wherein - mQLN400 is a mean QLN level up to subcarrier 400, and - T2 is the second threshold.

6. The method according to any of the preceding claims, wherein setting a virtual noise mask dependent on the crosstalk detected comprises: - determining whether the virtual noise mask has already been set and - setting it if it has not yet been set; - maintaining it if it has already been set.

7. The method according to any of the preceding claims, wherein - the virtual noise mask is set according to a predetermined configuration, or - according to a variable configuration, which is adjusted according to the level of crosstalk detected.

8. The method according to any of the preceding claims, wherein the virtual noise mask is canceled or adjusted if no crosstalk has been detected for a predetermined period of time (T3).

9. The method according to any of the preceding claims, wherein the crosstalk is detected after the line has been initialized or during the initialization of the line.

10. The method according to any of the preceding claims, wherein the crosstalk is detected by a terminal and/or by the distribution point unit.

11. The method according to any of the preceding claims, wherein the crosstalk comprises ADSL crosstalk.

12. The method according to any of the preceding claims, wherein the virtual noise mask is set to enable utilization of the line via VDSL or G.fast.

13. A device for adjusting virtual noise for communication lines connected to a distribution point unit, wherein the device is arranged to - detect crosstalk on a line that is connected to the distribution point unit; - set a virtual noise mask dependent on the crosstalk detected.

14. The device according to claim 13, wherein the device is a VDSL or G.fast device.

15. A distribution point unit that is connectable to terminals via communication lines, wherein the distribution point unit is arranged to - detect crosstalk on at least one of the communication lines; - set a virtual noise mask for at least one of the terminals dependent on the crosstalk detected.

16. The distribution point unit according to claim 15, wherein the terminals comprise at least one of the following: - a VDSL terminal, - a G.fast terminal, - an ADSL terminal, - a telephone.

17. A system comprising at least one distribution point unit according to any of claims 15 or 16 and at least one device according to any of claims 13 or 14.

18. A computer program product directly loadable into a memory of a digital processing device, comprising software code portions for performing the steps of the method according to any of claims I to 12.

Fig.1

101 102 104 POTS 105 main cable  distribution cable CO ADSL2plus 106 CPE

VDSL2 107 1/2

CPE 108 VDSL2/ G.fast DPU

Fig.2 201 VDSL2 line initialization

202 QLN measurement

204 203 YES VN protection YES Crosstalk detected? present? NO NO 2/2

208 207 Remove VN protection for YES No crosstalk for 205 Configure VN protection all lines of DPU time T3? for all lines of DPU

NO

VDSL2 enters showtime; Operation in showtime; VDSL2 leaves showtime