Feedforward Pilot-Aided Phase Noise Estimation for Coherent Optical M-QAM
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Solution Overview
Problem
Coherent optical systems with high-order quadrature-amplitude-modulation (QAM) signaling face challenges in managing amplified spontaneous emission noise and laser phase noise, which affect signal reliability and spectral efficiency, particularly due to the sensitivity of feedback processing in receiver digital signal processing subsystems.
Innovation Solution
A pilot-aided phase noise estimation technique using discrete cosine transform (DCT) orthonormal basis functions, where pilot symbols are specifically positioned within transmission frames to enable feed-forward and accurate phase noise estimation, allowing for low overhead and efficient phase noise compensation in high-speed digital coherent receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-order QAM signaling is used to increase spectral efficiency, then information transfer rate is improved, but sensitivity to laser phase noise and amplified spontaneous emission noise increases
Solution Approach 1:
The patent applies preliminary action by estimating phase noise using pilot symbols before the actual data symbols are processed. The receiver first extracts pilot symbols from the received signal, estimates the phase noise based on these known pilot values, and then uses this estimated phase noise to correct the data symbols. This preliminary estimation approach allows the system to compensate for phase noise effects before they degrade the high-order QAM signal reliability.
2Measurement precision
If feedback processing is used in receiver digital signal processing, then phase noise compensation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent inverts the conventional feedback approach by using a feedforward method. Instead of using decided data symbols to update phase noise estimates in a feedback loop, the system uses known pilot symbols to estimate phase noise in advance and applies this estimate to correct data symbols without requiring feedback iterations. This inversion simplifies the receiver architecture while maintaining effective phase noise compensation.
3Measurement precision
If pilot symbols are inserted for phase noise estimation, then phase noise compensation accuracy is improved, but spectral efficiency decreases due to overhead
Solution Approach 1:
The patent applies partial action by inserting pilot symbols at specific positions within the transmission frame rather than continuously. The pilot symbols are placed periodically or at frame boundaries, providing sufficient phase noise estimation points without occupying excessive bandwidth. This partial insertion strategy balances the need for accurate phase noise estimation with the requirement to maintain high spectral efficiency for data transmission.
Data Source
AI summary
An apparatus includes an electronic digital signal processor having electrical inputs for receiving a first sequence of measurements of values of a transmitted modulated optical carrier received in a coherent optical receiver and having electrical outputs for a stream of determined transmitted data values demodulated therein from the first sequence. The electronic digital signal processor has first circuitry to determine phase offsets of received pilot values from the first sequence. Additionally, the electronic digital signal processor has second circuitry to correct phase offsets of received ones of the data values from the determined phases of pilot values and data values being temporally interleaved in the transmitted modulated optical carrier. A system and a method are also included.