WDM/TDM-PON Timing Correction for Wavelength Switching

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Solution Overview

Problem

In wavelength-tunable WDM/TDM-PON systems, upstream signal timing control is challenged by changes in round-trip propagation delay due to wavelength switching, leading to potential collisions of upstream frames after wavelength switching, especially when optical fiber distances and dispersion vary.

Innovation Solution

A transmission start time correction method is implemented, where the station-side subscriber accommodation apparatus measures the reception time of the upstream signal indicating completion of wavelength switching and adjusts the transmission start time by adding twice the time difference between the assumed and actual reception times before and after wavelength switching, ensuring non-overlapping upstream signal transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If wavelength switching is performed to enable flexible bandwidth allocation and load balancing, then system adaptability and bandwidth capacity are improved, but round-trip propagation delay changes cause upstream signal timing errors and frame collisions

Engineering Contradiction:

Improvebandwidth allocation flexibilityVSAvoidupstream signal timing accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system measures the actual reception time of upstream signals after wavelength switching and uses this feedback to calculate timing corrections. The station-side apparatus compares expected versus actual reception times and adjusts transmission start times accordingly, creating a closed-loop correction mechanism that maintains timing accuracy despite wavelength changes

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention dynamically adjusts the transmission start time parameter based on measured propagation delay changes. By calculating the time difference between expected and actual signal reception and applying this correction to future transmission scheduling, the system adapts timing parameters to compensate for wavelength switching-induced delay variations

Inventive Principle:

Principle #35Parameter changes

2Productivity

If dynamic wavelength bandwidth allocation is implemented to achieve stepwise upgrade and load balancing, then system capacity and resource utilization are improved, but upstream frame transmission timing becomes uncertain leading to potential collisions

Engineering Contradiction:

Improvebandwidth utilization efficiencyVSAvoidupstream transmission timing uncertainty

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The station-side apparatus performs preliminary measurement of upstream signal reception times after wavelength switching occurs. By measuring the actual propagation delay in advance and using this information to calculate correction values before the next transmission cycle, the system prepares timing adjustments ahead of time to prevent collisions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention replaces fixed mechanical timing schedules with a flexible timing correction mechanism that uses measured propagation characteristics. Instead of relying on predetermined transmission slots that may not account for wavelength changes, the system uses measured actual reception times to dynamically calculate and apply timing corrections, substituting rigid scheduling with adaptive timing control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9871614B2WDM/TDM-PON system and transmission start time correction method thereof

Publication Date: 2018.01.16 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

A transmission start time correction method of a WDM/TDM-PON system includes: a completion instruction procedure in which a station-side subscriber accommodation apparatus issues an instruction using a downstream signal for instructing a subscriber apparatus to perform wavelength switching, the downstream signal including a transmission start time of an upstream signal indicating completion of the wavelength switching of the subscriber apparatus, the upstream signal being transmitted by the subscriber apparatus after the wavelength switching; an instruction completion transmission procedure in which the subscriber apparatus transmits the upstream signal indicating the completion of the wavelength switching at a wavelength after switching at the instructed transmission start time after the wavelength switching is completed in accordance with the instruction; and a transmission start time correction procedure in which the station-side subscriber accommodation apparatus measures a reception time of the upstream signal indicating the completion of the wavelength switching received after the wavelength switching and sets a time obtained by adding a time twice a time difference between a reception time of the upstream signal indicating the completion of the wavelength switching assumed before the wavelength switching and a reception time of the upstream signal indicating the completion of the wavelength switching received after the wavelength switching to the transmission start time of the upstream signal before the wavelength switching as a new transmission start time.