Pre-equalization technique for upstream communication between cable modem and headend

• US 7,120,123 B1
• Filed: 11/09/2000
• Issued: 10/10/2006
• Est. Priority Date: 10/30/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Denney, Lisa V., Chen, Feng, Min, Jonathan S., Jones, Christopher R., Samueli, Henry, Nazareth, Sean F., Lu, Fang, Quigley, Thomas J.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Boakye, Alexander O.
• Application Number:
  US09/710,238
• Time in Patent Office: 2,161 Days
• Field of Search: 370/252, 370/435, 370/352, 370/420, 370/421, 370/486, 370/487, 370/489, 370/493, 370/286, 370/289, 370/290, 370/521, 375/222
• US Class Current: 370/252
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04J 3/0655 using timestamps
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/203 Details of error rate determination, e.g. BER, FER or WER
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 2025/03808 Transmission of equaliser coefficients
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

A number of features for enhancing the performance of a cable transmission system in which data is transmitted between a cable modem termination system at a headend and a plurality of cable modems located different distances from the headend. The power transmission level, slot timing, and equalization of the cable modems are set by a ranging process. Data is transmitted by the modems in fragmented form. Various measures are taken to make transmission from the cable modems robust. The upstream data transmission is controlled to permit multiple access from the cable modems.

Claims

1. A cable modem termination system (CMTS) that can receive signal bursts transmitted on an upstream channel of a cable modem system, the CMTS comprising:

a demodulator for receiving the signal bursts on the upstream channel;

a media access controller (MAC) that generates for downstream transmission MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel, the MAP messages including idle slots that are assigned to no cable modems;

a transmitter that transmits the MAP messages with the idle slots downstream to the cable modems; and

an adaptive notch filter connected to the demodulator, wherein coefficients of the adaptive notch filter are adjusted to suppress noise on the upstream channel sensed during the idle slots.

2. The CMTS of claim 1, additionally comprising a decision feedback equalizer coupled to the demodulator and the notch filter, the decision feedback equalizer having a feedback filter using the adjusted coefficients of the adaptive notch filter to compensate for distortion introduced by the adaptive notch filter.

3. The CMTS of claim 2, in which the decision feedback equalizer has a feedforward filter for establishing pre-equalization coefficients.

4. The CMTS of claim 3, in which the demodulator converts the signal bursts to binary data, the system additionally comprising a signal path for carrying the binary data from the demodulator to the MAC, the notch filter and the decision feedback equalizer being in the signal path.

5. The CMTS of claim 4, in which the signal path carries both the binary data and pre-equalization coefficients to the MAC in band such that the coefficients are appended to the binary data.

6. The CMTS of claim 5, in which the pre-equalization coefficients do not reflect noise received by the demodulator, the system additionally comprising an upstream transmitter for transmitting the pre-equalization coefficients established by the feedforward filter.

7. The CMTS of claim 6, in which the upstream transmitter is connected to the MAC to transmit the pre-equalization coefficients established by the feed forward filter.

8. A cable modem termination system (CMTS) that can receive a signal transmitted in a cable modem system on an upstream channel, the CMTS comprising:

a demodulator;

a notch filter connected to the demodulator, the notch filter having coefficients that are adjustable to cancel noise applied to the demodulator;

a media access controller (MAC) that processes binary data and generates for downstream transmission MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel; and

a decision feedback equalizer coupled to the demodulator, the decision feedback equalizer including a feedforward filter for establishing pre-equalization coefficients.

9. The CMTS of claim 8, in which both binary data and pre-equalization coefficients are provided to the MAC in band such that the coefficients are appended to the binary data.

10. The CMTS of claim 9, in which the pre-equalization coefficients do not reflect noise applied to the demodulator, the system additionally comprising an upstream transmitter connected to the MAC to transmit the pre-equalization coefficients established by the feedforward filter.

11. A method for compensating for conditions on an upstream channel from a plurality of cable modems to a cable modem termination system (CMTS), the method comprising the steps of:

transmitting on a downstream channel from the CMTS to a plurality of cable modems MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel, the MAP messages including idle slots that are assigned to no cable modems;

monitoring conditions on the upstream channel during the idle slots;

compensating for the monitored conditions on the upstream channel; and

receiving at the CMTS signal bursts on the upstream channel after such compensation.

12. The method of claim 11, in which the monitoring step comprises sensing the noise on the upstream channel during the idle slots.

13. The method of claim 12, in which the compensating step comprises adjusting the coefficients of a notch filter to compensate for the sensed noise on the upstream channel during the idle slots.

14. The method of claim 13, in which the compensating step further comprises adjusting a feedback filter of a decision feedback filter in series with the notch filter to have the same coefficients as the notch filter to compensate for its distortion.

15. The method of claim 14, additionally comprising the steps of:

receiving on the upstream channel a ranging signal from a cable modem;

adjusting coefficients of a feedforward filter of the decision feedback filter responsive to the received ranging signal to compensate for intersymbol interference on the upstream channel; and

transmitting the adjusted coefficients on a downstream channel to the cable modem for the purpose of pre-equalization.

16. The method of claim 15, in which the transmitting steps transmit the MAP messages and the adjusted coefficients on the same channel.

17. A method for compensating for conditions on an upstream channel from a plurality of cable modems to a cable modem termination system (CMTS), the method comprising the steps of:

compensating for noise on an upstream channel;

receiving on the compensated upstream channel a ranging signal from one of the cable modems;

adjusting filter coefficients to compensate for intersymbol interference on the upstream channel responsive to the received ranging signal; and

transmitting the adjusted coefficients on a downstream channel to the cable modem for the purpose of pre-equalization of the upstream channel.

18. The method of claim 17, in which the adjusting step comprises adjusting coefficients of a feedforward filter of a decision feedback filter.

19. The method of claim 18, in which the compensating step comprises adjusting the coefficients of a notch filter in series with the decision feedback filter.

20. The method of claim 19, in which the compensating step further comprises adjusting a feedback filter of the decision feedback filter to have the same coefficients as the notch filter to compensate for its distortion.

21. The method of claim 20, additionally comprising the step of transmitting on a downstream channel from the CMTS to the cable modems MAP messages that assign time slots in which cable modems may transmit signal bursts on the upstream channel.

22. The method of claim 21, in which the transmitting steps transmit the MAP messages and the adjusted coefficients on the same channel.