Optical Receiver Phase Estimation for Faster CDR Initialization
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Solution Overview
Problem
In passive optical networks (PONs), the clock-and-data recovery (CDR) process is critical for synchronizing upstream communication, but the initial phase error between the received optical signal and the reference clock can significantly impact performance, leading to inefficiencies and longer synchronization times.
Innovation Solution
An optical receiver with phase estimation circuitry and CDR circuitry that initializes the CDR process by estimating the initial phase error through sampling at multiple positions within a unit interval, using methods like oversampling, phase detection functions, and discrete frequency transformations to quickly determine and compensate for phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the CDR process is initialized with an arbitrary initial phase error, then the device complexity is reduced, but the synchronization time increases and performance deteriorates
Solution Approach 1:
The patent applies preliminary action by performing a quick phase estimation before the main CDR process to obtain an initial phase error estimate. This preliminary estimation uses a simplified approach with limited sampling positions and curve fitting, which is computationally less intensive than the full CDR process. By performing this estimation in advance, the system can initialize the CDR circuitry with a better starting point, reducing the number of iterations needed and overall synchronization time, while avoiding the need for complex continuous phase tracking during the entire CDR process.
2Measurement precision
If multiple sampling positions are used for phase estimation, then the measurement precision of initial phase error improves, but the device complexity and processing time increase
Solution Approach 1:
The patent applies partial action by using a limited number of sampling positions (at least one, preferably multiple but not all possible positions) within each unit interval rather than exhaustive sampling. This partial sampling approach provides sufficient accuracy for phase error estimation while significantly reducing the computational burden and circuit complexity compared to full exhaustive sampling. The curve fitting process then processes this partial set of samples to derive the initial phase error, achieving a balance between measurement precision and device complexity.
Data Source
AI summary
An optical receiver for a passive optical network, comprising a phase estimation circuitry and a clock-and-data recovery, CDR, circuitry, wherein the CDR circuitry is configured to be initialised with an estimate of an initial phase error between a received optical signal and a reference clock, and wherein the phase estimation circuitry is configured to estimate the initial phase error by: sampling a portion of an optical signal during consecutive unit intervals; wherein the sampling is performed in at least one of a plurality of possible sampling positions; wherein the sampling is performed such that a plurality of samples is obtained for each of the possible sampling positions; determining a temporal property in the respective sampling position at least from the plurality of samples corresponding to the possible sampling position; fitting a curve characterising the temporal property within a unit interval; and estimating the initial phase error from the fitted curve.