Polybinary Modulation for Optical Link Error Reduction
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Solution Overview
Problem
In optical communication systems, high-bandwidth opto-electronic and electro-optic components are costly, leading to signal distortion and strong intersymbol interference, which degrades the performance of maximum likelihood sequence detection modules due to additive white Gaussian noise and low-pass filtering effects.
Innovation Solution
A communication method involving N rounds of operations on modulated signals, using delay modules to reduce the probability of consecutive bit errors, and adaptive modulation schemes like PAM-M and QAM-E, where the output of each operation is processed based on previous signals delayed by specific symbol periods, and modulo or exclusive OR operations are performed to mitigate noise effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-bandwidth components are used to transmit high-rate signals, then system cost is reduced, but signal distortion and intersymbol interference increase
Solution Approach 1:
The patent applies parameter changes by modifying the modulation format from traditional PAM4 to polybinary modulation (e.g., 7-level or 13-level PAM). This changes the signal parameters to better match the limited bandwidth of low-cost components, reducing intersymbol interference while maintaining system affordability.
Solution Approach 2:
The patent introduces dynamic adaptive equalization at the receiver end to compensate for signal distortion. The equalizer dynamically adjusts its coefficients to counteract the low-pass filtering effects of inexpensive components, maintaining signal quality despite using cost-effective hardware.
2Reliability
If feed forward equalizer is used to cancel low-pass filtering effect, then signal distortion is reduced, but noise is filtered and power spectrum becomes non-flat
Solution Approach 1:
The patent changes the modulation parameter from 4-level PAM to polybinary levels (7-level, 13-level PAM), which inherently provides better noise tolerance and reduces the aggressive filtering needed, thereby preserving noise characteristics while still compensating for distortion.
Solution Approach 2:
The patent introduces a noise whitening filter as an intermediary component that restores the flat power spectrum of the noise after it has been colored by the equalizer, thus preserving the statistical properties of the noise for optimal detection.
3Measurement precision
If maximum likelihood sequence detection is used on channel with ISI and AWGN, then detection performance is optimized, but consecutive bit errors occur when noise non-whitening is strong
Solution Approach 1:
The patent changes the modulation parameter from PAM4 to polybinary modulation formats (7-level, 13-level PAM), which provides better immunity to ISI and noise, reducing the occurrence of consecutive bit errors while maintaining detection performance.
Solution Approach 2:
The patent introduces a noise whitening filter as an intermediary before the maximum likelihood sequence detector. This filter restores the white noise characteristics by compensating for the colored noise introduced by the equalizer, thereby preventing consecutive bit errors while maintaining optimal detection performance.
4Device complexity
If PAM4 modulation is used for short-distance interconnection, then implementation complexity and power consumption are reduced, but bandwidth requirement is halved compared to OOK
Solution Approach 1:
The patent changes the modulation parameter from 4-level PAM to polybinary levels (7-level, 13-level PAM). This parameter change allows the system to achieve higher effective data rates within the same bandwidth constraint, or alternatively, reduces the bandwidth requirement for a given data rate while maintaining implementation simplicity.
Data Source
AI summary
A communication method, a communications apparatus, and a storage medium are disclosed, to reduce a probability that consecutive bit errors occur in a communications system. A received to-be-sent signal is modulated to obtain a modulated signal, and N rounds of operations are further performed on the modulated signal to obtain an encoded signal. An output of the 1st-round operation in the N rounds of operations is determined based on the modulated signal and an output that is of the Nth-round operation and that is processed by a first delay circuit, and an output of the ith-round operation in the N rounds of operations is determined based on an output of the (i−1)th-round operation and an output that is of the Nth-round operation and that is processed by a second delay circuit, where i is an integer greater than 1 and less than or equal to N.