Robust techniques for optimal upstream communication between cable modem subscribers and a headend

• US 20010055319A1
• Filed: 02/09/2001
• Published: 12/27/2001
• Est. Priority Date: 10/30/1998
• Status: Active Grant

• 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.
• Granted Patent: US 7,139,283 B2
• Time in Patent Office: Days
• US Class Current: 370/480
• 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 3/0664 unidirectional 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: H04J 3/1694 Allocation of channels in TDM/TDMA networks, e.g. distributed multiplexers Passive Optical Networks H04Q11/0062
• 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
• CPC Class Codes: H04L 49/90 Buffering arrangements
• CPC Class Codes: H04L 49/9094 Arrangements for simultaneous transmit and receive, e.g. simultaneous reading/writing from/to the storage element
• CPC Class Codes: H04L 7/0004 Initialisation of the receiver H04L7/0075 and H04L7/10 take precedence
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

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 for a cable plant comprising:

a burst receiver for processing data signals having physical layer parameters transmitted on an upstream channel of the cable plant;

a transmitter for sending messages on a downstream channel of the cable plant to cable modems;

a monitoring circuit for collecting packet based statistics representative of the quality of the upstream channel, the monitoring circuit sending a message to the transmitter for the cable modems to change a physical layer parameter responsive to the collected statistics and to the burst receiver to process data signals based on the changed physical layer parameter.

2. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of packets and the number of undetected packets.

3. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of packets and the number of packets without a unique word.

4. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of packets and the number of packets with corrected errors.

5. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of packets and the number of packets with uncorrectable errors.

6. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of FEC blocks and the number of FEC blocks with corrected errors.

7. The cable modem termination system of

claim 1

, in which the monitoring circuit collects statistics about the number of FEC blocks and the number of FEC blocks with uncorrectable errors.

8. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7, in which the monitoring circuit sends a message to change the type of modulation.

9. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7, in which the monitoring circuit sends a message to change the coding gain.

10. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7, in which the monitoring circuit sends a message to change the symbol rate.

11. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7, in which the monitoring circuit sends a message to change the guard time.

12. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7, in which the monitoring circuit sends a message to change the constellation size of the modulation.

13. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7 in which the monitoring circuit sends a message to change the physical layer parameters in real time.

14. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7 in which the monitoring circuit sends a message to change the frequency of the carrier.

15. The cable modem termination system of

claim 1

,

2

, 3, 4, 5, 6, or 7 in which the monitoring circuit sends a message to change the frequency of the carrier in a non-uniform manner.

16. A headend terminal for a bidirectional asymmetric, transmission system having a downstream channel that broadcasts data from the head end terminal to a plurality of subscriber terminals and an upstream channel that unicasts data from the individual subscriber terminals to the head end terminal, the headend terminal comprising:

a burst receiver for processing data signals having physical layer parameters transmitted on the upstream channel;

a transmitter for sending messages on the downstream channel;

a monitoring circuit for collecting statistics about the physical layer parameters transmitted on the upstream channel, the monitoring circuit sending a message to the transmitter for the cable modems to change a physical layer parameter responsive to the collected statistics and to the burst receiver to process data signals based on the changed physical layer parameter.

17. A method for transmitting data over a cable system in an upstream direction to a headend from a plurality of subscriber stations located different distances from the headend such that the transmission paths to the headend are different, the method comprising the steps of:

establishing an upstream channel from the subscriber stations to the headend;

monitoring at the headend the quality of the upstream channel;

establishing a downstream channel from the headend to the subscriber stations;

transmitting to the subscriber stations over the downstream channel a command to change the mode of transmission to the headend over the upstream channel if the monitored quality fails to meet a prescribed threshold level;

receiving the command at the subscriber stations; and

transmitting data over the upstream channel from the subscriber stations to the headend in accordance with the changed mode of transmission after receipt of the command.

18. The method of

claim 17

, in which the monitoring step monitors the noise power on the upstream channel.

19. The method of

claim 17

, in which the monitoring step monitors the signal-to-noise ratio of a signal received on the upstream channel.

20. The method of

claim 17

, in which the monitoring step monitors the channel statistics of the upstream channel.

21. The method of

claim 20

, in which the monitored statistics comprise the number of undetected packets.

22. The method of

claim 20

, in which the monitored statistics comprise the number of packets with corrected errors.

23. The method of

claim 20

, in which the monitored statistics comprise the number of packets with uncorrected errors.

24. The method of

claim 20

, in which the monitored statistics comprise the number of FEC blocks with corrected errors.

25. The method of

claim 20

, in which the monitored statistics comprise the number of FEC blocks with uncorrected errors.

26. The method of

claim 20

, in which the monitored statistics comprise a combination of two or more of the following:

the number of undetected packets, the number of packets with corrected errors, the number of packets with uncorrected errors, the number of FEC blocks with corrected errors, and the number of FEC blocks with uncorrected errors.

27. The method of

claim 17

, in which the command transmitting step comprises transmitting a command to change the type of modulation from a first type that can reliably transmit at a high bit rate over a high quality channel to a second type that can reliably transmit at a lower bit rate over a lower quality channel if the monitored quality at the first type of modulation fails to meet the prescribed threshold level.

28. The method of

claim 27

, in which the first type of modulation is QAM and the second type of modulation is QPSK.

29. The method of

claim 27

, in which the data transmitting step transmits data to the headend in accordance with the second type of modulation after the command.

30. The method of

claim 29

, in which the command transmitting step additionally comprises transmitting a command to change the position of the channel in the spectrum if the monitored quality at the second type of modulation fails to meet the prescribed threshold level.

31. The method of

claim 30

, in which the command transmitting step additionally comprises transmitting a command to change one or more physical layer parameters.

32. The method of

claim 17

, in which the step of establishing an upstream channel establishes a channel that has a narrow bandwidth and the step of establishing a downstream channel establishes a channel that has a broad bandwidth.

33. The method of

claim 17

, additionally comprising the step of adjusting a notch filter at the headend to establish coefficients that reject one or more bands of common noise.

34. The method of

claim 33

, in which the monitoring step comprises FFT processing of the filter coefficients to determine the inverse of the channel spectrum.

35. The method of

claim 34

, in which the command transmitting step transmits a command to change the position of the channel in the spectrum to avoid ingress noise.

36. A cable modem transmission system having an upstream channel shared among a plurality of cable modems and a burst receiver connected to the upstream channel to process physical layer signals transmitted on the upstream channel, a monitoring circuit for collecting packet based statistics representative of the quality of the upstream channel, the monitoring circuit comprising an input for receiving the physical layer signals from the burst receiver, means for sensing parameters of the physical layer signals, and a plurality of counters for collecting the sensed physical layer parameters.

37. The cable modem termination system of

claim 36

, in which the monitoring circuit collects statistics about the number of packets and the number of undetected packets.

38. The cable modem termination system of

claim 36

or

37

, in which the monitoring circuit collects statistics about the number of packets and the number of packets without a unique word.

39. The cable modem termination system of

claim 36

or

37

, in which the monitoring circuit collects statistics about the number of packets and the number of packets with corrected errors.

40. The cable modem termination system of

claim 36

or

37

, in which the monitoring circuit collects statistics about the number of packets and the number of packets with uncorrectable errors.

41. The cable modem termination system of

claim 36

or

37

, in which the monitoring circuit collects statistics about the number of FEC blocks and the number of FEC blocks with corrected errors.

42. The cable modem termination system of

claim 36

or

37

, in which the monitoring circuit collects statistics about the number of FEC blocks and the number of FEC blocks with uncorrectable errors.