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System and method for performing ranging in a cable modem system

  • US 7,573,935 B2
  • Filed: 06/10/2002
  • Issued: 08/11/2009
  • Est. Priority Date: 06/08/2001
  • Status: Active Grant
First Claim
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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
    Δ

    P(dB)=10 log 10 (Pcur/Pnew),wherein the new equalizer coefficient gain value is determined from P =

    i = 1
    N


    ( ( C _ real

    i
    )
    2
    + ( C _ imag

    i
    )
    2
    )
    wherein Pnew represents a new equalizer coefficient gain value, Pcur is a current equalizer gain value, N refers to a number of feedforward taps, and Ci refers to the generated scaled coefficients.

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