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

• US 6,393,029 B1
• Filed: 11/10/1999
• Issued: 05/21/2002
• 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): Chin, Wellington
• Assistant Examiner(s): JONES, PRENELL P
• Application Number:
  US09/438,555
• Time in Patent Office: 923 Days
• Field of Search: 370/419, 370/522, 370/497, 370/449, 370/452, 370/465, 370/203, 370/207, 375/232-242, 375/222-231, 375/211, 375/295, 455/16, 455/503, 455/70
• US Class Current: 370/419
• 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 of communication over a communication channel linking a first site and a second site comprising the steps of:

(a) converting first digital communication signals encoded with a first number of information bits per symbol at a prescribed data rate into second digital communication signals encoded with a second number, higher than said first number, of information bits per symbol at said prescribed data rate; and

(b) transmitting said second digital communication signals to said second site.

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

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

3. A method according to claim 1, wherein step (a) comprises subjecting said first digital communication signals to an error correcting coding mechanism that is effective to produce said second number of bits per symbol, and subjecting said second digital communication signals to Tomlinson preceding prior to transmission to said second site in step (b).

4. An arrangement for transmitting digital communication signals from a first site to a second site, comprising:

a line code converter which is operative to convert first digital communication signals encoded at a first number of information bits per symbol at a prescribed data rate into changed symbol rate digital communication signals encoded at a second number of information bits per symbol, higher than said first number, at said prescribed data rate; and

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

5. The arrangement according to claim 4, wherein said second site includes a receiver which receives said output signals transmitted from said first site and recovers therefrom said first digital communication signals.

6. The arrangement according to claim 5, wherein said output signals have a one-dimensional symbol coding space, and wherein said receiver is 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.

7. A method for communicating digital communication signals over a telephone link from a first site to a second site, comprising the steps of:

at said first site,

(a) scrambling high-bit-rate digital communication signals, having a first number of bits per symbol at a prescribed data rate, to produce randomized high-bit-rate digital communication signals;

(b) trellis coded modulating said randomized high-bit-rate digital communication signals into encoded high-bit-rate digital communication signals having a second number of bits per symbol, higher than said first number of bits per symbol, at said prescribed data rate; and

(c) mapping said encoded high-bit-rate digital communication signals produced in step (c) into encoded pulse tin amplitude modulation signals for transmission over said telephone link from to said second site.

8. A method according to claim 7, wherein

said randomized high-bit-rate digital communication signals produced in step (a) have a serial format,

step (b) includes performing serial-to-parallel conversion of said randomized high-bit-rate digital communication signals to a K-bit parallel format, and trellis coded modulating said randomized high-bit-rate digital communication signals into encoded high-bit-rate digital communication signals having a K+1 bit parallel format, and

step (c) comprises mapping said K+1 bit parallel format encoded high-bit-rate digital communication signals into said encoded pulse amplitude modulation signals for transmission over said telephone link to said second site.

9. A method according to claim 7, wherein step (c) comprises mapping said encoded high-bit-rate digital communication 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.

10. A method according to claim 7, further including the step (d) of processing said encoded pulse amplitude modulation signals produced in step (c) by a precoding filtering operator.

11. A method according to claim 10, wherein said precoding filtering operator comprises a Tomlinson precoder.

12. A method according to claim 10, 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 telephone link.

13. A method according to claim 7, further including the steps of:

at said first site,

(d) transmitting said encoded pulse amplitude modulation signals over said telephone link to said second site; and

at said second site,

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

14. An arrangement for communicating digital communication signals over a telephone link comprising:

a data scrambler that is operative to scramble high-bit-rate digital communication signals having a first number of bits per symbol at a prescribed data rate into randomized high-bit-rate digital communication signals; and

a trellis coded modulation encoder that is operative to trellis code modulate said randomized high-bit-rate digital communication signals into encoded high-bit-rate digital communication signals having a second number of bits per symbol, higher than said first number of bits per symbol, at said prescribed data rate, and to map said encoded high-bit-rate digital communication signals into encoded pulse amplitude modulation signals for transmission over said telephone link.

15. An arrangement according to claim 14, further comprising a preceding filtering operator, that filters said encoded pulse amplitude modulation signals, a digital-to-analog converter that converts the output of said precoding filtering operator into an analog signal, and a spectral filter which filters said analog signal for application to said telephone link.

16. An arrangement according to claim 15, wherein said precoding filtering operator comprises a Tomlinson precoder.

17. An arrangement according to claim 14, wherein said randomized high-bit-rate digital communication signals have a serial format, and said trellis coded modulation encoder performs serial-to-parallel conversion of said randomized high-bit-rate digital communication signals into a K-bit parallel format, and produces trellis encoded high-bit-rate digital communication signals having a K+1 bit parallel format, and maps said K+1 bit parallel format trellis-encoded high-bit-rate digital communication signals into said encoded pulse amplitude modulation signals for transmission over said telephone link.

18. An arrangement according to claim 14, wherein trellis coded modulation encoder is operative to map said encoded high-bit-rate digital communication 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.

19. An arrangement according to claim 14, further including a receiver coupled to receive said encoded pulse amplitude modulation signals from said telephone link and to process the received encoded pulse amplitude modulation signals and recover said high-bit-rate digital communication signals.