Pseudo Frequency Division Multiplexing for Optical Signal Noise Averaging
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Solution Overview
Problem
Optical communications systems face challenges in maintaining low Bit Error Rate (BER) due to signal degradation caused by noise, nonlinearity, polarization-dependent loss, and frequency-dependent effects, which can lead to erroneous data recovery and increased overhead from Forward Error Correction (FEC) techniques.
Innovation Solution
The implementation of pseudo frequency division multiplexing (pFDM) transformations at both the transmitter and receiver, which involve matrix operations to average frequency-dependent degradations, allowing for the generation of multiple pseudo FDM channels that can reduce noise variability and improve symbol estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Forward Error Correction (FEC) encoding is used to reduce Bit Error Rate, then reliability is improved, but overhead increases
Solution Approach 1:
The patent applies pseudo frequency division multiplexing (pFDM) transformation to change the frequency domain parameters of the signal. By transforming the signal into multiple pseudo-FDM channels with different frequency characteristics, the system achieves more uniform noise distribution across channels, thereby reducing BER without requiring additional FEC overhead
Solution Approach 2:
The patent replaces the traditional FEC-based error correction mechanism with a signal processing approach using pFDM transformation. Instead of adding redundant bits through FEC encoding, the system uses matrix-based frequency domain transformation to inherently reduce noise variability and improve symbol estimation accuracy
2Productivity
If signal transmission is performed over optical communications channel, then data transmission is achieved, but signal degradation occurs due to noise and frequency-dependent effects
Solution Approach 1:
The patent segments the transmitted signal into multiple pseudo-FDM channels through pFDM transformation. Each channel experiences different frequency-dependent degradations, but by combining estimates from multiple channels, the system achieves more uniform noise characteristics and reduced overall signal degradation
Solution Approach 2:
The patent introduces pseudo-FDM channels as intermediary representations of the original signal. These intermediate channels allow the system to process and combine signal estimates in a way that averages out frequency-dependent degradations and noise variations, ultimately recovering the original signal with improved quality
Data Source
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AI summary
An optical transmitter (102,200) is operable to generate an optical signal (260) by modulating a number N of frequency divisional multiplexing (FDM) subcarriers using transformed digital signals which are determined by applying a pseudo FDM (pFDM) transformation to preliminary digital signals representative of multi-bit symbols. Rather than experiencing the effects of the number N of FDM channels, the optical signal experiences the effects of a different number M of pFDM channels, where M ≠ N. In some examples, the number M of pFDM channels is less than the number N of FDM channels, and frequency-dependent degradations may be averaged across different symbol streams. In other examples, the number Mof pFDM channels is greater than the number N of FDM channels, and different symbol streams may experience different frequency-dependent degradations. An optical receiver (102,300) is operable to apply an inverse pFDM transformation to recover estimates of the multi-bit symbols.