{
  "patent_number": "US 6665308",
  "country": "US",
  "title": "How Cable Modems Fix Signal Distortions Before Sending Data",
  "original_title": "Apparatus and method for equalization in distributed digital data transmission systems",
  "summary": "A method for cable modems to pre-filter data so it arrives clearly at the central office, preventing signal errors caused by the messy physical wires between them.",
  "what_it_does": "This patent describes a way to clean up digital signals sent from a home modem to a central office. Instead of the central office doing all the work to fix signal distortion, it calculates the necessary corrections and sends those instructions back to the home modem. The home modem then uses a precode filter to adjust its own signal before it even leaves the house. This ensures that by the time the data travels through the noisy cable lines, it is already optimized to be read correctly by the central receiver.",
  "what_it_does_not_cover": [
    "Does not cover signal equalization that happens entirely within the central office without sending instructions back to the remote unit.",
    "Does not cover analog signal modulation techniques that do not involve digital precode filtering.",
    "Does not cover systems where the remote unit calculates its own equalization coefficients without receiving them from the central unit.",
    "Does not cover general data transmission that lacks a training phase for channel characterization."
  ],
  "filed": "1998-09-17",
  "granted": "2003-12-16",
  "expires": "2018-09-17",
  "status": "expired",
  "holder": "Terayon Communication Systems Inc",
  "holder_url": "https://patentbrief.org/company/terayon-communication-systems-inc",
  "inventors": [
    {
      "name": "Yehuda Azenkot",
      "url": "https://patentbrief.org/inventor/yehuda-azenkot"
    },
    {
      "name": "Selim Shlomo Rakib",
      "url": "https://patentbrief.org/inventor/selim-shlomo-rakib"
    }
  ],
  "times_cited": 188,
  "tags": [
    "telecommunications",
    "semiconductors",
    "mechanical"
  ],
  "abstract": "A system for bidirectional communication of digital data between a central unit and a remote unit wherein the need for tracking loops in the central unit has been eliminated. The central unit transmitter generates a master carrier and a master clock signal which are used to transmit downstream data to the remote units. The remote units recover the master carrier and master clock and synchronize local oscillators in each remote unit to these master carrier and master clock signals to generate reference carrier and clock signals for use by the remote unit receiver. These reference carrier and clock signals are also used by the remote unit transmitters to transmit upstream data to the central unit. The central unit receiver detects the phase difference between the reference carrier and clock signals from the remote units periodically and adjusts the phase of the master carrier and master clock signals for use by the central unit receiver to receive the upstream data.",
  "url": "https://patentbrief.org/patent/us/6665308/apparatus-and-method-for-equalization-in-distributed-digital-data-transmission-systems",
  "markdown_url": "https://patentbrief.org/patent/us/6665308/apparatus-and-method-for-equalization-in-distributed-digital-data-transmission-systems/md",
  "google_patents_url": "https://patents.google.com/patent/US6665308",
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}