Use of modified line encoding and low signal-to-noise ratio based signal processing to extend range of digital data transmission over repeaterless two-wire telephone link

• US 5,999,542 A
• Filed: 08/12/1998
• Issued: 12/07/1999
• Est. Priority Date: 08/18/1995
• Status: Expired due to Term

• Current Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Original Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Inventors: Turner, Michael D., Goodson, Richard L., Schneider, Kevin W., Burch, Richard A.
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US09/133,061
• Time in Patent Office: 482 Days
• Field of Search: 370/310, 370/333, 370/465, 370/468, 370/472, 370/497, 370/522, 370/203, 370/207, 370/488, 375/232, 375/233, 375/242, 375/298, 455/13.1, 455/13.2, 455/13.3, 455/13.4
• US Class Current: 370/497
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 25/4917 using multilevel codes
• CPC Class Codes: H04L 25/497 by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems transversal equalizers at the transmitter end H04L25/03343
• CPC Class Codes: H04L 25/4975 Correlative coding using Tomlinson precoding, Harashima precoding, Trellis precoding or GPRS
• CPC Class Codes: H04Q 11/0435 Details
• CPC Class Codes: H04Q 11/0471 Terminal access circuits
• CPC Class Codes: H04Q 2213/1303 Pulse amplitude modulation, PAM
• CPC Class Codes: H04Q 2213/13034 A/D conversion, code compression/expansion
• CPC Class Codes: H04Q 2213/13094 Range extender
• CPC Class Codes: H04Q 2213/1319 Amplifier, attenuation circuit, echo suppressor
• CPC Class Codes: H04Q 2213/13199 Modem, modulation
• CPC Class Codes: H04Q 2213/13209 ISDN
• CPC Class Codes: H04Q 2213/13216 Code signals, frame structure
• CPC Class Codes: H04Q 2213/13322 Integrated circuits

Abstract

The range of digital data communication services, such as a basic rate 2B1Q ISDN channel, to customer premises located beyond the industry standard achievable range of a two-wire loop can be extended by increasing the capacity of the ISDN line code from two information bits per symbol to three information bits per symbol, so as to reduce the effective symbol rate, which is error correction encoded to an effective 4B1H line code for defining a sixteen level PAM signal waveform, and employing enhanced low signal-to-noise ratio signal processing techniques in both the transmitter and receiver to accommodate the increased insertion loss of the two-wire line resulting from its extended length. Such enhanced low signal-to-noise ratio signal processing techniques include a Tomlinson precoder in the transmitter, and an adaptive linear equalizer and a module unit in the receiver.

Claims

1. A method for extending the distance for transporting digital communication signals from a first site to a second site, comprising the steps of:

(a) converting first digital communication signals that are encoded at a first number of information bits per symbol at a prescribed data rate into second digital communication signals that are encoded at a second number of information bits per symbol, different from said first number, at said prescribed data rate; and

(b) processing said second digital communication signals for transport to said second site.

2. The method according to claim 1, wherein said first and second digital communication signals comprise one of DSL signals, HDSL signals, DDS signals and ISDN signals.

3. The method according to claim 1, wherein said first number is two and said second number is three.

4. The method according to claim 3, wherein step (b) comprises processing said second digital communication signals for transport to said second site as 4B1H communication signals.

5. The method according to claim 1, further including the steps of:

(c) transporting said second digital communication signals to said second site; and

(d) receiving said second digital communication signals at said second site and processing said received second digital communication signals to recover said first digital communication signals.

6. The method according to claim 5, wherein step (a) comprises transporting said second digital communication signals over a two-wire telephone link to said second site.

7. The method according to claim 1, wherein said first digital communication signals comprise first ISDN communication signals, and step (a) comprises subjecting said first ISDN communication signals to an error correcting code that is effective to produce second ISDN communication signals having an increased number of bits per symbol, and wherein step (b) includes subjecting said second ISDN communication signals to Tomlinson preceding prior to transmission to said second site.

8. An arrangement for extending the transmission distance for basic rate integrated services digital network (ISDN) communication signals over a two-wire transmission path between a first site and a second site, comprising:

a line code converter which is operative to convert said basic rate ISDN communication signals encoded at a first number of information bits per symbol at a prescribed data rate into changed symbol rate ISDN communication signals that are encoded at a second number of information bits per symbol, different than from said first number, at said prescribed data rate; and

a signal processor which processes said changed symbol rate ISDN communication signals into output signals for transmission over said two-wire transmission path to said second site, and causes said output signals to be transmitted over said two-wire transmission path at said prescribed data rate.

9. The arrangement according to claim 8, wherein said output signals have a 4B1H line code.

10. The arrangement according to claim 8, wherein said second site includes a receiver which receives said output signals transported over said two-wire transmission path and recovers therefrom said basic rate ISDN communication signals.

11. An arrangement according to claim 8, wherein said line code converter is operative to convert said basic rate ISDN communication signals having a first, basic rate 2B1Q line code into first reduced symbol rate ISDN signals having three information bits per symbol, and wherein said signal processor includes an error correction encoder which performs error correction encoding of said first reduced symbol rate ISDN communication signals to transform said first reduced symbol rate ISDN communication signals into second reduced symbol rate ISDN communication signals having a 4B1H line code for transmission to said second site.

12. The arrangement according to claim 11, wherein said output signals to be transmitted over said two-wire transmission path have a one-dimensional symbol coding space, and wherein said second site includes a receiver which receives said output signals transported over said two-wire transmission path and recovers therefrom said basic rate ISDN communication signals, said receiver being operative to process received signals in accordance with a modulo index operator, which adjusts the output of said received signals, as necessary, to fall within said one-dimensional symbol coding space.

13. The arrangement according to claim 8, further including, at a respective site, an echo canceler coupled between said signal processor and said receiver.

14. A method for providing high-bit-rate digital subscriber line service over a two-wire telephone link, comprising the steps of:

(a) scrambling high-bit-rate digital data signals, having a first number of bits per symbol at a prescribed data rate, to be transported over said two-wire telephone link to produce randomized high-bit-rate digital data signals;

(b) subjecting said randomized high-bit-rate digital data signals to trellis coded modulation that produces encoded high-bit-rate digital data signals having a second number of bits per symbol, different from said first number of bits per symbol, at said prescribed data rate; and

(c) mapping said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals for transport over said two-wire telephone link from a first site to a second site.

15. The method according to claim 14, wherein said randomized high-bit-rate digital data signals have a serial format, and step (b) includes performing serial-to-parallel conversion of said randomized high-bit-rate digital data signals to a K-bit parallel format, and wherein said trellis coded modulation produces encoded high-bit-rate digital data signals having a K+1 bit parallel format, and wherein step (c) comprises mapping said K+1 bit parallel format encoded high-bit-rate digital data signals into said encoded pulse amplitude modulation signals for transport over said two-wire telephone link to said second site.

16. The method according to claim 14, wherein step (c) comprises mapping said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals having a four binary, one hex/sixteen level output line code.

17. The method according to claim 14, wherein step (c) comprises mapping said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals having one of sixteen pulse amplitude modulation levels:

-15, -13, -11, -9, -7, -5, -3, -1, +1, +3, +5, +7, +9, +11, +13, +15.

18. The method according to claim 14, further including the step (d) of processing said encoded pulse amplitude modulation signals produced in step (c) by means of a precoding filtering operator.

19. The method according to claim 18, wherein said preceding filtering operator comprises a Tomlinson precoder.

20. The method according to claim 18, further including the step (e) of converting the output of said precoding filtering operator into analog format and filtering the resultant analog signal for application to said two-wire telephone link.

21. The method according to claim 14, further including the steps of:

(d) transporting said encoded pulse amplitude modulation signals over said two-wire telephone link to said second site; and

(e) receiving said encoded pulse amplitude modulation signals at said second site and processing said received encoded pulse amplitude modulation signals to recover said high-bit-rate digital data signals.

22. An arrangement for providing high-bit-rate digital subscriber line service over a two-wire telephone link comprising:

a data scrambler that is operative to scramble high-bit-rate digital data signals having a first number of bits per symbol at a prescribed data rate, and intended for transport over said two-wire telephone link, into randomized high-bit-rate digital data signals; and

a trellis coded modulation encoder that is operative to subject said randomized high-bit-rate digital data signals to trellis coded modulation, producing encoded high-bit-rate digital data signals having a second number of bits per symbol, different from said first number of bits per symbol, at said prescribed data rate, and to map said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals for transport over said two-wire telephone link from a first site to a second site.

23. The arrangement according to claim 22, further comprising a preceding filtering operator, that is operative to filter said encoded pulse amplitude modulation signals, a digital-to-analog converter that is operative to convert the output of said preceding filtering operator into an analog signal, and a spectral filter through which said analog signal is filtered for application to said two-wire telephone link.

24. The arrangement according to claim 23, wherein said precoding filtering operator comprises a Tomlinson precoder.

25. The arrangement according to claim 22, wherein said randomized high-bit-rate digital data signals have a serial format, and said trellis coded modulation encoder operative to perform serial-to-parallel conversion of said randomized high-bit-rate digital data signals to a K-bit parallel format, and to produce trellis encoded high-bit-rate digital data signals having a K+1 bit parallel format, and to map said K+1 bit parallel format trellis-encoded high-bit-rate digital data signals into said encoded pulse amplitude modulation signals for transport over said two-wire telephone link to said second site.

26. The arrangement according to claim 22, wherein said trellis coded modulation encoder is operative to map said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals having a four binary, one hex/sixteen level output line code.

27. The arrangement according to claim 22, wherein trellis coded modulation encoder is operative to map said encoded high-bit-rate digital data signals into encoded pulse amplitude modulation signals having one of sixteen pulse amplitude modulation levels:

-15, -13, -11, -9, -7, -5, -3, -1, +1, +3, +5, +7, +9, +11, +13, +15.

28. The arrangement according to claim 22, further including a receiver coupled to said two-wire telephone link at said second site, and being operative to receive said encoded pulse amplitude modulation signals and to process said encoded pulse amplitude modulation signals to recover said high-bit-rate digital data signals.