Method to mitigate effects of ISDN off/on transitions in ADSL

• US 20030123560A1
• Filed: 11/14/2002
• Published: 07/03/2003
• Est. Priority Date: 12/27/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Wiese, Brian R., Agah, Michael D., Jacobsen, Krista S.
• Granted Patent: US 7,184,467 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

The present invention provides for a method and apparatus for allocating data to subchannels used for ADSL transmission over a communication link which supports further system transmissions. An expected interference impact from the further system transmissions is estimated for the ADSL subchannels. Signal-to-noise ratios (SNRs) for the subchannels are determined for bit loading by an estimator (220). In one embodiment, actual noise associated with the communication link is used at initialization to determine a SNR which is subsequently modified by an adjusting unit (205) prior to bit loading responsive to the estimated interference impact. In another embodiment, a virtual noise signal, indicative of the estimated interference impact and generated by a noise signal generator (235), is summed with the actual noise prior to determining a SNR for bit loading. Prior to transmitting, the data is allocated to the subchannels by a bit loader (210) based on respective SNRs modified responsive the estimated interference impact.

Claims

1. A method of supporting a digital communication on a plurality of frequency channels, comprising:

allocating information bits to the frequency channels based on respectively corresponding channel quality indicators that include respective noise margins; and

increasing the noise margin corresponding to at least one of a selected group of said frequency channels that are more susceptible to a predetermined type of interference than are the remaining frequency channels.

2. The method of claim 1, wherein said predetermined type of interference includes one of same-pair residual Integrated Service Digital Network (ISDN) signal interference and near-end crosstalk from Time-Compression Multiplexing ISDN signal interference.

3. The method of claim 1, wherein said increasing step includes increasing only the noise margins corresponding to the frequency channels of said group that are not experiencing said predetermined type of interference but are expected to during said digital communication.

4. The method of claim 3, including determining which frequency channels of said group are not experiencing said predetermined type of interference based on information indicative of actual interference conditions on said group of frequency channels.

5. The method of claim 4, including updating said actual interference information during said digital communication, and repeating said determining step during said digital communication based on said updated actual interference information.

6. The method of claim 1, wherein said channel quality indicators are SNR values, said increasing step including decreasing the SNR value associated with said at least one frequency channel.

7. The method of claim 6, wherein said decreasing step includes arithmetically decreasing said at least one SNR value.

8. The method of claim 7, wherein said arithmetically decreasing step includes subtracting an excess noise margin SNR value from said at least one SNR value.

9. The method of claim 8, including determining said excess noise margin SNR value based on information indicative of an actual interference condition on said at least one frequency channel.

10. The method of claim 9, including updating said actual interference information during said digital communication, and repeating said determining step during said digital communication based on said updated actual interference information.

11. The method of claim 10, including determining during said digital communication which frequency channels of said group are not experiencing said predetermined type of interference based on said updated actual interference information, said increasing step including increasing only the noise margins corresponding to the frequency channels of said group that have been determined not to be experiencing said predetermined type of interference but are expected to during said digital communication.

12. The method of claim 1, wherein said increasing step includes, for said at least one frequency channel, providing first information indicative of a first interference condition that is worse than an actual interference condition on said at least one frequency channel, said increasing step further including producing said channel quality indicator for said at least one frequency channel in response to said first information.

13. The method of claim 12, wherein said increasing step includes performing said providing step only for those frequency channels of said group that are not experiencing said predetermined type of interference but are expected to during said digital communication, and further including producing said channel quality indicators for all other frequency channels of said group in response to corresponding actual interference conditions.

14. The method of claim 12, wherein said providing step includes providing second information indicative of said actual interference condition and adjusting said second information to produce said first information.

15. The method of claim 14, wherein said channel quality indicator is an SNR value and said adjusting step includes combining said second information with third information indicative of a virtual noise signal to produce said first information.

16. The method of claim 14, wherein said adjusting step includes combining said second information with third interference information to produce said first information.

17. The method of claim 16, wherein said third interference information is a zero-mean pseudo-random complex number sequence with constant amplitude.

18. The method of claim 16, including determining said third information based on said second information.

19. The method of claim 18, including updating said second information during said digital communication, and repeating said determining step during said digital communication based on said updated second information.

20. The method of claim 19, including determining during said digital communication which frequency channels of said group are not experiencing said predetermined type of interference based on said updated second information, said increasing step including increasing only the noise margins corresponding to the frequency channels of said group that have been determined not to be experiencing said predetermined type of interference but are expected to during said digital communication.

21. The method of claim 12, wherein said channel quality indicators are SNR values, said increasing step including decreasing the SNR value corresponding to said at least one frequency channel.

22. An apparatus for supporting a digital communication on a plurality of frequency channels, comprising:

a bit loader for allocating information bits to the frequency channels based on respectively corresponding channel quality indicators that include respective noise margins; and

a channel quality indication unit coupled to said bit loader for providing said channel quality indicators thereto, said channel quality indication unit operable for increasing the noise margin corresponding to at least one of a selected group of said frequency channels that are more susceptible to a predetermined type of interference than are the remaining frequency channels.

23. The apparatus of claim 22, wherein said predetermined type of interference includes one of same-pair residual Integrated Service Digital Network (ISDN) signal prying and near-end crosstalk from Time-Compression Multiplexing ISDN signal interference.

24. The apparatus of claim 22, wherein said channel quality indication unit includes an input for receiving information indicative of actual interference conditions on said group of frequency channels, and logic coupled to said input and responsive to said actual interference condition information for determining which frequency channels of said group are not experiencing said predetermined type of interference, and for increasing only the noise margins corresponding to the frequency channels of said group that have been determined not to be experiencing said predetermined type of interference but are expected to during said digital communication.

25. The apparatus of claim 24, wherein said input is further for receiving during said digital communication updated information indicative of updated actual interference conditions on said group of frequency channels, said logic responsive to said updated actual interference information during said digital communication for making an updated determination as to which frequency channels of said group are not experiencing said predetermined type of interference.

26. The apparatus of claim 22, wherein said channel quality indicators are SNR values, and said channel quality indication unit including logic for decreasing the SNR value associated with said at least one frequency channel.

27. The apparatus of claim 26, wherein said logic is for subtracting an excess noise margin SNR value from said at least one SNR value.

28. The apparatus of claim 27, wherein said channel quality indication unit includes an input for receiving information indicative of an actual interference condition on said at least one frequency channel, and further logic coupled to said input for determining said excess noise margin SNR value based on said actual interference information.

29. The apparatus of claim 28, wherein said input is further for receiving updated information indicative of an updated actual interference condition on said at least one frequency channel during said digital communication, said further logic for making an updated determination of said excess noise margin SNR value during said digital communication based on said updated actual interference information.

30. The apparatus of claim 22, wherein said channel quality indication unit includes an estimator having an input for receiving first information indicative of a first interference condition that is worse than an actual interference condition on said at least one frequency channel, said estimator for producing said channel quality indicator for said at least one frequency channel in response to said first information.

31. The apparatus of claim 30, wherein said channel quality indication unit includes an input for receiving information indicative of actual interference conditions on said group of frequency channels, and logic coupled to said input and responsive to said actual interference condition information for determining which frequency channels of said group are not experiencing said predetermined type of interference, and for increasing only the noise margins corresponding to the frequency channels of said group that have been determined not to be experiencing said predetermined type of interference but are expected to during said digital communication.

32. The apparatus of claim 30, wherein said channel quality indication unit includes an input for receiving second information indicative of said actual interference condition, and logic coupled to said last-mentioned input and said estimator input for adjusting said second information to produce said first information.

33. The apparatus of claim 32, wherein said channel quality indicator is an SNR value and said logic includes a combiner for combining said second information with third information indicative of a virtual noise signal to produce said first information.

34. The apparatus of claim 32, wherein said logic includes a combiner for combining said second information with third interference information to produce said first information.

35. The apparatus of claim 34, wherein said third interference information is a zero-mean pseudo-random complex number sequence with constant amplitude.

36. The apparatus of claim 34, wherein said channel quality indication unit includes further logic coupled to said last-mentioned input for determining said third information based on said second information.

37. The apparatus of claim 36, wherein said last-mentioned input is further for receiving during said digital communication an update of said second information, said further logic responsive to said updated second information during said digital communication for making an updated determination of said third information.

38. A digital communication apparatus, comprising:

a transmitter for performing digital communication on a plurality of frequency channels, including a bit loader for allocating information bits to the frequency channels based on respectively corresponding channel quality indicators that include respective noise margins; and

a channel quality indication unit coupled to said bit loader for providing said channel quality indicators thereto, said channel quality indication unit operable for increasing the noise margin corresponding to at least one of a selected group of said frequency channels that are more susceptible to a predetermined type of interference than are the remaining frequency channels.

39. The apparatus of claim 38, provided as an ADSL apparatus.