System and method for performing ranging in a cable modem system

• US 20020191684A1
• Filed: 06/10/2002
• Published: 12/19/2002
• Est. Priority Date: 06/08/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Min, Jonathan S., Lu, Fang
• Granted Patent: US 7,573,935 B2
• Time in Patent Office: Days
• US Class Current: 375/222
• 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 2027/002 using feedback from a remote receiver
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/34 Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04W 52/54 Signalisation aspects of the TPC commands, e.g. frame structure

Abstract

The present invention provides a system and method for performing ranging operations in a cable modem system. In accordance with embodiments of the present invention, transmission times, transmission power levels, transmission carrier frequencies, and pre-equalization parameters are adjusted to provide for robust operation of the cable modem system. More particularly, iterative processing steps are used to provide coefficient ordering, scaling, and aligning between the multiple cable modems and the cable modem termination system present in a cable modem system.

Claims

1. A method for performing ranging operations in a cable modem system that includes two or more cable modems, comprising the steps of:

(a) receiving at a cable modem, a ranging response generated by a cable modem termination system, the ranging response comprised of a plurality of ranging parameters including an upstream communications parameter, a timing adjust parameter, a power level adjust parameter, a carrier frequency offset parameter, and a plurality of equalization parameters, the equalization parameters including a number of ranging response equalizer coefficients, wherein the ranging response is the first ranging response received since the cable modem was initialized;

(b) setting a current pre-equalizer coefficient for each one of a plurality taps at the cable modem equal to the ranging response equalizer coefficients to generate new pre-equalizer coefficients, wherein one of said plurality of taps is designated a main tap and the remaining number of said plurality of taps are referred to as non-main taps and further wherein each one of said plurality of taps has a real part and an imaginary part;

(c) derotating the new pre-equalizer coefficients so that the imaginary part of the main tap is equal to zero;

(d) identifying each non-main tap having a determined magnitude squared value below a specified threshold and setting the new pre-equalizer coefficients for the real part and the imaginary part of each identified non-main tap to zero;

(e) generating scaled coefficients using the new pre-equalizer coefficients for the main tap and non-main taps obtained from steps (c) and (d); and

(f) adjusting a transmit power of the cable modem using an equalizer coefficient gain change value, the equalizer coefficient gain change value being determined from a current equalizer coefficient gain value and a new equalizer coefficient gain value in accordance with EQ3, wherein the new equalizer coefficient gain value is determined from EQ4 and {overscore (C)}_i refers to the generated scaled coefficients.

2. The method of claim 1, wherein said cable modem termination system determines said timing adjust parameter and thereafter determines said power level adjust parameter and further wherein said carrier frequency offset parameter is determined after determining said power level adjust parameter and before determining said plurality of equalization parameters.

3. The method of claim 1, wherein said generating scaled coefficients step (e) generates the scaled coefficients in accordance with EQ2A, where C_i refers to the new pre-equalizer coefficients for the real and imaginary parts of both the main tap and the non-main taps from steps (c) and (d).

4. The method of claim 1, wherein said generating scaled coefficients step (e) generates the scaled coefficients in accordance with EQ2B, where Ci refers to the new pre-equalizer coefficients for the real and imaginary parts of both the main tap and the non-main taps from steps (c) and (d).

5. The method of claim 1, wherein said receiving a ranging response step (a) comprises receiving a number of ranging response equalizer coefficients wherein the ranging response equalizer coefficients associated with the imaginary parts of the main tap and the non-main taps are negated from a coefficient equalizer set in said cable modem termination system.

6. The method of claim 1, further comprising the steps of

adjusting a transmission time parameter of the cable modem by an amount equal to the timing adjust parameter received in the ranging response prior to performing steps (b), (c), (d), (e), and (f);

adjusting a power transmission level parameter of the cable modem by an amount equal to the power level adjust parameter received in the ranging response after setting the transmission time parameter and prior to performing steps (b), (c), (d), (e), and (f); and

adjusting an upstream carrier frequency parameter of the cable modem by an amount equal to the carrier frequency offset parameter received in the ranging response after setting the power transmission level parameter and prior to performing steps (b), (c), (d), (e), and (f).

7. The method of claim 6, further comprising the step of averaging the carrier frequency offset parameter over multiple ranging iterations.

8. The method of claim 1, wherein said cable modem termination system determines said timing adjust parameter, said power level adjust parameter, and said carrier frequency offset parameter before determining said plurality of equalization parameters.

9. The method of claim 1, wherein said cable modem termination system determines said carrier frequency offset parameter before determining said plurality of equalization parameters.

10. A method for performing ranging operations in a cable modem system that includes two or more cable modems, comprising the steps of:

(a) receiving at a cable modem, a subsequent ranging response generated by a cable modem termination system after generating a first ranging response, the subsequent ranging response comprised of a plurality of ranging parameters including an upstream communications parameter, a timing adjust parameter, a power level adjust parameter, a carrier frequency offset parameter, and a plurality of equalization parameters, the equalization parameters including a main tap location and a number of ranging response equalizer coefficients;

(b) using the ranging response equalizer coefficients to convolve a number of current pre-equalizer coefficients for a main tap and one or more non-main taps located in the cable modem according to EQ1 to generate new pre-equalizer coefficients and derotating the new pre-equalizer coefficients so that an imaginary part of the main tap is equal to zero;

(c) identifying each non-main tap having a determined magnitude squared value below a specified threshold and setting the new pre-equalizer coefficient for a real part and an imaginary part of the identified non-main taps equal to zero;

(d) generating scaled coefficients using the new pre-equalizer coefficients for the main tap and no-main taps from steps (b) and (c); and

(e) adjusting a transmit power of the cable modem using a equalizer coefficient gain change value, the equalizer coefficient gain change value being determined from a current equalizer coefficient gain value and a new equalizer coefficient gain value in accordance with EQ3, wherein the new equalizer coefficient gain value is determined from EQ4 and {overscore (C)}_i refers to the generated scaled coefficients.

11. The method of claim 10, wherein the current equalizer coefficient gain value used in adjusting step (e) is equal to the new equalizer coefficient gain value.

12. The method of claim 10, wherein said cable modem termination system determines said timing adjust parameter and thereafter determines said power level adjust parameter and further wherein said carrier frequency offset parameter is determined after determining said power level adjust parameter and before determining said plurality of equalization parameters.

13. The method of claim 10, wherein said generating scaled coefficients step (d) generates the scaled coefficients in accordance with EQ2A, where C_i refers to the new pre-equalizer coefficients for the real and imaginary parts of both the main tap and the non-main taps from steps (b) and (c).

14. The method of claim 10, wherein said generating scaled coefficients step (d) generates the scaled coefficients in accordance with EQ2B, where Ci refers to the new pre-equalizer coefficients for the real and imaginary parts of both the main tap and the non-main taps from steps (b) and (c).

15. The method of claim 10, wherein said receiving a subsequent ranging response step (a) comprises receiving a number of ranging response equalizer coefficients, wherein the ranging response equalizer coefficients associated with the imaginary parts of the main tap and the non-main taps are negated from a coefficient set in the cable modem termination system.

16. The method of claim 10, further comprising the steps of

adjusting a transmission time parameter of the cable modem by an amount equal to the timing adjust parameter received in the ranging response prior to performing steps (b), (c), (d), and (e);

adjusting a power transmission level parameter of the cable modem by an amount equal to the power level adjust parameter received in the ranging response after setting the transmission time parameter and prior to performing steps (b), (c), (d), and (e); and

adjusting an upstream carrier frequency parameter of the cable modem by an amount equal to the carrier frequency offset parameter received in the ranging response after setting the power transmission level parameter and prior to performing steps (b), (c), (d), and (e).

17. The method of claim 10, further comprising the step of averaging the frequency offset parameter over multiple ranging iterations.

18. The method of claim 10, wherein said cable modem termination system determines said timing adjust parameter, said power level adjust parameter, and said carrier frequency offset parameter before determining said plurality of equalization parameters.

19. The method of claim 10, wherein said cable modem termination system determines said carrier frequency offset parameter before determining said plurality of equalization parameters.

20. A system for performing ranging operations in a cable modem system including two or more cable modems, comprising:

(a) means for receiving a subsequent ranging response at a cable modem, the subsequent ranging response comprised of a plurality of ranging parameters including an upstream communications parameter, a timing adjust parameter, a power level adjust parameter, a carrier frequency offset parameter, and a plurality of equalization parameters, the equalization parameters including a main tap location, and a number of ranging response equalizer coefficients;

(b) means for convolving a number of current equalizer coefficients for a main tap and a number of non-main taps located at the cable modem according to EQ1 using the ranging response equalizer coefficients to generate new equalizer coefficients and means for derotating the new equalizer coefficients so that an imaginary part of the main tap is equal to zero;

(c) means for identifying each non-main tap having a determined magnitude squared value below a specified threshold and setting the new pre-equalizer coefficient for a real part and an imaginary part equal to zero;

(d) means for generating scaled coefficients; and

(e) means for adjusting a transmit power of the cable modem using a equalizer coefficient gain change value, the equalizer coefficient gain change value being determined from a current equalizer coefficient gain value and a new equalizer coefficient gain value in accordance with EQ3, wherein the new equalizer coefficient gain value is determined from EQ4 and {overscore (C)}_i refers to the generated scaled coefficients.

21. A system for performing ranging operations in a cable modem system, comprising:

(a) a cable modem termination system configured to generate a ranging response, the ranging response comprised of a plurality of ranging parameters including an upstream communications parameter, a timing adjust parameter, a power level adjust parameter, a carrier frequency offset parameter, and a plurality of equalization parameters, the equalization parameters including a main tap location, and a number of ranging response equalizer coefficients;

(b) one or more cable modems configured to convolve a number of current pre-equalizer coefficients for a main tap and a number of non-main taps associated with each cable modem according to EQ1 using the ranging response equalizer coefficients to generate new pre-equalizer coefficients and to derotate the new pre-equalizer coefficients so that an imaginary part of the main tap is equal to zero.

22. The system of claim 21, wherein the one or more cable modems are further configured to identify each non-main tap having a determined magnitude squared value below a specified threshold and set the new pre-equalizer coefficient for a real part and an imaginary part equal to zero.

23. The system of claim 22, wherein the one or more cable modems are further configured to generate scaled coefficients using EQ2A, where C_i refers to the new pre-equalizer coefficients for the real and imaginary parts of the main tap and non-main taps.

24. The system of claim 22, wherein the one or more cable modems are further configured to generate scaled coefficients using EQ2B, where C_i refers to the new pre-equalizer coefficients for the real and imaginary parts of the main tap and non-main taps.

25. The system of claim 22, wherein the one or more cable modems are further configured to adjust a transmit power of the cable modem using a equalizer coefficient gain change value, the equalizer coefficient gain change value being determined from a current equalizer coefficient gain value and a new equalizer coefficient gain value in accordance with EQ3, wherein the new equalizer coefficient gain value is determined from EQ4 and {overscore (C)}_i refers to the generated scaled coefficients.