Clock Data Recovery Soft Decoding Without ADC Amplitude Data
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Solution Overview
Problem
Conventional passive optical network (PON) systems lack the ability to derive soft information from digital input signals without amplitude information, limiting their ability to benefit from advanced error correction coding like LDPC codes, which require soft information for improved performance.
Innovation Solution
The development of a method to derive soft information from digital clock data recovery circuitry, allowing for the generation of log-likelihood ratios (LLR) from CDR states, enabling the use of soft information in channel decoders without the need for analog-to-digital conversion, and implementing low complexity LDPC decoder architectures to utilize this information effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If digital receivers are used in PON systems to reduce costs and maintain energy efficiency, then device complexity and energy consumption are reduced, but the ability to derive soft information for advanced error correction coding is lost
Solution Approach 1:
The patent introduces an intermediary process that extracts soft information (log-likelihood ratios) from the digital CDR states. This intermediary extraction mechanism allows digital receivers to provide soft information to LDPC decoders without requiring analog-to-digital conversion, thus maintaining cost efficiency while recovering the lost soft information capability.
Solution Approach 2:
The patent changes the parameter representation by deriving log-likelihood ratios from discrete CDR states. Instead of relying on continuous amplitude information from analog signals, the system transforms discrete digital states into soft information parameters that can be used by advanced error correction codes, enabling digital receivers to achieve performance comparable to analog systems.
2Loss of information
If analog-to-digital conversion is implemented to provide amplitude information for soft decoding, then soft information quality improves, but device complexity and cost increase
Solution Approach 1:
The patent extracts the essential soft information content from the digital CDR states without requiring full analog-to-digital conversion. By taking out only the necessary log-likelihood ratio information from the existing digital states, the system achieves soft decoding capability while avoiding the complexity and cost of analog processing and high-resolution ADCs.
3Device complexity
If conventional hard decision decoding is used in digital receivers, then device complexity is reduced, but bit error rate performance deteriorates
Solution Approach 1:
The patent changes the input parameter type for the decoder from hard decisions (binary values) to soft information (log-likelihood ratios derived from CDR states). This parameter transformation enables the use of soft decision decoding algorithms like LDPC, which provide significantly better bit error rate performance while maintaining compatibility with digital receiver architectures.
Data Source
AI summary
An apparatus for receiving a signal. The apparatus may include a demodulator configured to generate a binary signal from a received signal, a clock data recovery (CDR) circuitry configured to detect a phase error of the binary signal and generate CDR state information for the binary signal, a soft information generation circuitry configured to map the CDR state information to soft information for the binary signal, and a decoder configured to decode the binary signal using the soft information. The CDR circuitry may generate the CDR state information from multiple consecutive samples of the binary signal at least twice a symbol rate of the received signal. The soft information may be a log likelihood ratio of the binary signal, and the soft information generation circuitry may determine the log likelihood ratio based on an input bit error rate of the binary signal.