OLT Ranging Without Quiet Windows for Low-Latency PON

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Solution Overview

Problem

In optical communication networks, the use of quiet windows for ONU ranging introduces significant latency, which is unacceptable for latency-sensitive applications like mobile fronthaul requiring low end-to-end latency, such as 5G vehicular applications, and constant throughput scenarios.

Innovation Solution

A method where the Optical Line Terminal (OLT) transmits a predetermined optical signal with a time delay at a different frequency than the downstream frame to introduce errors, allowing the new ONU to determine its distance and synchronize without requiring quiet windows, enabling continuous upstream traffic.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If quiet windows are used for ONU ranging, then measurement precision of roundtrip delay is improved, but loss of time (latency) increases significantly

Engineering Contradiction:

Improveroundtrip delay measurementVSAvoidupstream traffic latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies preliminary action by having the OLT transmit a predetermined optical signal to the new ONU before the ranging measurement process. This optical signal contains timing information that allows the new ONU to pre-synchronize its transmission, eliminating the need for quiet windows and periodic traffic suspensions for ranging measurements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of optical signal characteristics by using a predetermined optical signal with specific timing and frequency properties. This optical signal is transmitted at a different frequency than downstream frames and introduces controlled errors that help the new ONU determine its distance and synchronize without requiring traffic interruption.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If quiet windows are used for ONU ranging, then newly attached ONUs can be discovered and registered, but upstream traffic must be buffered periodically causing infinite latency growth in constant throughput scenarios

Engineering Contradiction:

ImproveONU discovery and registrationVSAvoidbuffered data latency

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The OLT transmits a predetermined optical signal to the new ONU before ranging measurement to enable pre-synchronization. This preliminary action allows the new ONU to be registered without requiring quiet windows, enabling continuous upstream traffic buffering-free operation even in constant throughput scenarios.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If high power activation signal is transmitted, then activation reliability is improved, but harmful factors (interferometric crosstalk) increase on upstream signals of active ONUs

Engineering Contradiction:

ImproveONU activation reliabilityVSAvoidinterferometric crosstalk

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent uses a predetermined optical signal as an intermediary that carries timing information from the OLT to the new ONU. This optical signal is transmitted at a different frequency than downstream frames and enables synchronization without requiring high power activation signals that would cause interferometric crosstalk on upstream signals of active ONUs.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3474567B1Methods and products for ONU start-up procedure

Publication Date: 2020.05.06 NOKIA SOLUTIONS & NETWORKS OY

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AI summary

The present invention discloses a method in an Optical Line Terminal, OLT (110), of assisting a first Optical Network Unit, ONU (130c), starting up a communication with the OLT (110), the OLT (110) being communicatively coupled to the first ONU (130c) that is not yet in operation and a first number of ONUs (130a, 130b, 130d) that are already in operation, wherein, the first number is a natural number; the method comprising: a) transmitting a predetermined data within a predetermined time interval in a downstream frame to the first ONU (130c), b) transmitting a predetermined optical signal with a time delay of transmission (tdelay,Tx) to the first ONU (130c), wherein, the predetermined optical signal and the downstream frame are transmitted at different optical frequencies, the time delay of transmission (tdelay,Tx) being a time between a predetermined bit of the downstream frame and a predetermined bit of the predetermined optical signal when they are transmitted by the OLT (110), and wherein, the predetermined optical signal introduces errors in the downstream frame in the predetermined time interval when the downstream frame is received by the first ONU (130); c) assigning to each of the first number of ONUs (130a, 130b, 130d) a time interval within an upstream frame to transmit an upstream burst signal to the OLT (110), while leaving at least one predetermined time slot in the upstream frame reserved for a burst signal from the first ONU (130c); d) transmitting a first indication to the first ONU (130c), wherein, the first indication indicating a starting time (teq) located within the at least one predetermined time slot in the upstream frame; e) receiving a burst signal from the first ONU (130c) in the at least one predetermined time slot.