PON Power Leveling via OLT Advertised Signal Strength
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Solution Overview
Problem
In Passive Optical Networks (PONs), differential path loss causes signal power variations, leading to unacceptable levels of crosstalk and interference between channels, particularly in next-generation PONs like NGPON2, where power leveling is crucial to maintain optimal signal strength and prevent communication impairment.
Innovation Solution
The Optical Line Terminal (OLT) advertises its transmit power level and desired receive signal strength to Optical Network Units (ONUs), allowing them to calculate and set their upstream transmission power levels automatically, eliminating the need for iterative power leveling and reducing initialization time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative power leveling is used during ONU activation, then power levels can be adjusted to reduce crosstalk, but initialization time increases due to delays while ONU transmits at low power levels
Solution Approach 1:
The OLT performs preliminary measurements of the ONU's transmit power capability during the activation process before actual data transmission begins. By measuring the upstream signal strength during the ranging phase and calculating the required power adjustment, the OLT determines the optimal power level in advance, eliminating the need for iterative adjustments during operational phases and reducing overall initialization time
2Reliability
If ONU transmits at high power levels during activation, then signal strength is sufficient for OLT detection, but crosstalk into neighboring channels becomes unacceptable
Solution Approach 1:
The OLT continuously monitors the upstream signal strength from the ONU during the activation process and provides feedback directives to adjust the ONU's transmit power level. By measuring the received signal power and comparing it against target levels, the OLT sends adjustment commands to the ONU's power control mechanism, enabling precise power level optimization that achieves sufficient signal detection while minimizing crosstalk into neighboring channels
3Device complexity
If differential path loss is not compensated, then power leveling is unnecessary, but signal power variations cause communication impairment due to spectral tail interference
Solution Approach 1:
The system applies differential power leveling where each ONU's transmit power is individually adjusted based on its specific path characteristics and distance from the OLT. Rather than using a uniform power level for all ONUs, the OLT calculates and directs specific power adjustments for each ONU, compensating for local variations in path loss and ensuring that signals from all ONUs arrive at the OLT with comparable power levels, thereby preventing spectral tail interference
Data Source
AI summary
Systems and methods are provided for an optical network unit (ONU) to automatically set its output power level for messages to be transmitted on a passive optical network. The ONU can autonomously determine the appropriate power level based on information provided to the ONU by an optical line terminal (OLT) and characterization by the ONU of optical signals it receives from the fiber. Specifically, the OLT can provide the ONU with control data indicative of the power level used by the OLT to transmit the message and the desired power level of the OLT for messages from the ONU. The ONU can measure the power level of at least one message received from the OLT and determine the path loss based on the measured power and the control data. The ONU can then automatically determine a suitable power level for its response message such that unacceptable levels of crosstalk between channels are avoided without having to perform an iterative power-leveling process that otherwise may introduce significant delays.