Cable Modem Timing Offset Automation for PTP Accuracy
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Solution Overview
Problem
Wireless base stations in proximity to each other experience interference due to concurrent transmissions, and existing time synchronization methods, such as DOCSIS Time Protocol (DTP), fail to provide the necessary precision for state-of-the-art wireless systems, especially in indoor locations without line-of-sight to GNSS satellites.
Innovation Solution
An automated method for determining a timing offset for DOCSIS Time Protocol (DTP) to achieve precision time protocol (PTP) accuracy, where a cable modem receives a timestamp from a cable modem termination system (CMTS), calculates downstream travel time, and sets its PTP clock by incrementing the timestamp with internal delay time, ensuring synchronization with a primary reference clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DOCSIS Time Protocol (DTP) is used for time synchronization, then wireless base stations can operate without GNSS access, but the timing precision is insufficient for state-of-the-art wireless systems
Solution Approach 1:
The patent changes the timing parameters by introducing automated offset determination and incremental adjustment mechanisms. The system dynamically modifies timing parameters by determining offsets between DTP and PTP timebases and incrementally adjusting the DTP timebase to match PTP accuracy requirements, thereby improving measurement precision while maintaining adaptability
Solution Approach 2:
The patent implements feedback mechanisms where the cable modem continuously monitors the time difference between DTP and PTP timebases, determines timing offsets, and adjusts the DTP timebase accordingly. This closed-loop feedback system ensures that timing precision is maintained at PTP accuracy levels while operating without GNSS access
2Measurement precision
If automated timing offset determination is implemented, then PTP accuracy is achieved, but device complexity increases
Solution Approach 1:
The patent enables the cable modem to automatically determine its own timing offset and adjust its DTP timebase without external intervention. The system performs self-diagnosis and self-correction by monitoring time differences and autonomously applying timing adjustments, thereby achieving PTP accuracy without proportionally increasing operational complexity
Solution Approach 2:
The patent combines the DTP and PTP synchronization mechanisms by having the cable modem participate in both protocols simultaneously. The automated offset determination merges the timing functions of both protocols, allowing the system to leverage PTP's precision while maintaining DTP's operational flexibility, thereby achieving high accuracy without excessive complexity
Data Source
AI summary
Automated determination of a timing offset for DOCSIS time protocol to provide precision time protocol accuracy. A cable modem receives, from a cable modem termination system (CMTS), a message that includes a timestamp that is correlated to a primary reference clock. The cable modem determines a downstream travel time representative of a period of time between a generation of the timestamp by the CMTS and a first timing reference point of the cable modem. The cable modem accesses an internal delay time representative of a period of time for the timestamp to travel from the first timing reference point to a second timing reference point of the cable modem, and sets a precision time protocol (PTP) clock of the cable modem to a time equal to the timestamp incremented by the downstream travel time and the internal delay time.