How Cable Modems Fix Signal Distortions Before Sending Data
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.
Original patent title: “Apparatus and method for equalization in distributed digital data transmission systems”
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. Granted to Terayon Communication Systems Inc in 2003 with 61 claims and 188 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Instead of just trying to fix a distorted signal after it arrives, the system calculates the 'inverse' of the distortion at the destination and tells the sender to apply that inverse before transmitting.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
DOCSIS cable modem systems
Upstream broadband data transmission
Digital subscriber line (DSL) signal processing
Why it matters
The bigger picture
This technology was essential for the early deployment of high-speed cable internet (DOCSIS standards). By offloading the complexity of signal correction to the home modem, it allowed cable companies to maintain stable, high-bandwidth connections over existing, interference-prone copper cable infrastructure.
Filed
September 17, 1998
Granted
December 16, 2003
Market context
Who's building on this
Companies in this space
Major cable infrastructure providers like Cisco, Arris (now CommScope), and Broadcom have built upon these foundational signal processing techniques. The principles of iterative channel adaptation remain a core part of modern high-speed broadband standards.
Market impact
This patent helped stabilize the upstream channel in cable networks, which was historically the most difficult part of the connection to manage. It enabled the transition from dial-up to reliable, always-on broadband, effectively creating the modern cable internet market.
Claim 1 — Plain English
What this patent covers
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.
The clever bit
Instead of just trying to fix a distorted signal after it arrives, the system calculates the 'inverse' of the distortion at the destination and tells the sender to apply that inverse before transmitting.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Strong
Citation count
40/40
Highly cited
Claim breadth
20/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$126K – $403K
Midpoint $252K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
61 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Azenkot, Y., & Rakib, S. S. (2003). How Cable Modems Fix Signal Distortions Before Sending Data (U.S. Patent No. 6,665,308). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/6665308/apparatus-and-method-for-equalization-in-distributed-digital-data-transmission-systems
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Cable Modems Fix Signal Distortions Before Sending Data cover?
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.
Who owns patent US 6665308?
Terayon Communication Systems Inc owns this patent, granted in 2003.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 6665308 cited by?
This patent has been cited by 188 later patents that build on its ideas.
What problem does this patent solve?
This technology was essential for the early deployment of high-speed cable internet (DOCSIS standards). By offloading the complexity of signal correction to the home modem, it allowed cable companies to maintain stable, high-bandwidth connections over existing, interference-prone copper cable infrastructure.
What does this patent NOT cover?
Does not cover signal equalization that happens entirely within the central office without sending instructions back to the remote unit.
Patent monitoring