Optical Transmitter Crosstalk Mitigation via Spectrum Shifting
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Solution Overview
Problem
In optical transmission systems, the synthesis of high-speed signals from low-speed signals using analog multiplexing units results in signal quality degradation due to crosstalk components caused by imperfect analog circuits.
Innovation Solution
An optical transmission system that includes an optical transmitter and receiver, where the transmitter generates low-speed signals by cyclically shifting the spectrum of an input signal, digitally converts and synthesizes them to form a high-speed signal, and the receiver compensates for the high-speed signal using a similar cyclic shifting technique to mitigate crosstalk, thereby improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple low speed signals are synthesized in analog using analog multiplexing units to generate high speed signals, then the transmission capacity per channel is increased, but signal quality degrades due to crosstalk components caused by imperfect analog circuits
Solution Approach 1:
The patent applies preliminary action by estimating the transfer function of the analog multiplexing unit in advance and using this estimate to compensate for crosstalk components before they severely degrade signal quality. The transfer function estimation is performed using known training signals transmitted in specific time slots, allowing the compensation to be applied proactively to subsequent high speed signals.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual output of the analog multiplexing unit and comparing it with expected values. The transfer function estimation unit processes the output signals to extract actual transfer characteristics, which are then fed back to the compensation unit to adjust and refine the crosstalk compensation parameters dynamically.
2Measurement precision
If transfer function estimation is performed by separating high speed signals into multiple low speed signals, then compensation accuracy is improved, but processing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the high speed signal into multiple low speed signals in the frequency domain. This is achieved by applying frequency selective filtering to separate the spectrum into multiple bands, each corresponding to a low speed signal component. This segmentation enables independent processing and estimation of transfer functions for each frequency band, improving overall estimation accuracy.
Solution Approach 2:
The patent utilizes dimensionality change by transforming the signal from the time domain to the frequency domain using Fast Fourier Transform (FFT). This allows the high speed signal to be analyzed in terms of its spectral components, making it easier to separate and process individual frequency bands. The frequency domain representation provides a more manageable structure for transfer function estimation while maintaining the complete signal information.
Data Source
AI summary
An optical transmission system includes an optical transmitter and an optical receiver. The optical transmitter includes a low speed signal generation unit configured to generate, based on an input signal of a transmission data sequence and a signal obtained by cyclically shifting a spectrum of the input signal, a plurality of low speed signals, a high speed signal generation unit configured to digital-to-analog convert and synthesize the plurality of low speed signals to generate a high speed signal, and an optical modulation unit configured to transmit an optical signal obtained by modulation of the high speed signal to a transmission path. The optical receiver includes a reception unit configured to receive the optical signal from the transmission path and output the high speed signal obtained from the optical signal that is received, an optical-receiver-side high speed signal compensation unit configured to compensate, based on the high speed signal output by the reception unit and a signal obtained by cyclically shifting a spectrum of the high speed signal, for the high speed signal, and a reception data decoding unit configured to decode the high speed signal compensated by the optical-receiver-side high speed signal compensation unit to restore binary information included in the optical signal transmitted by the optical transmitter.