Reduced-Complexity MLSD for M-ary Signaling
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Solution Overview
Problem
Current digital communications receivers face challenges in achieving low error rates due to intersymbol interference (ISI) and noise, especially as data rates approach channel capacity, with linear and decision feedback equalizers being insufficient and maximum likelihood sequence detectors being complex and power-intensive.
Innovation Solution
The implementation of reduced-complexity maximum likelihood sequence detectors (rMLSD) that evaluate state metrics only for the most and second most likely symbol decisions, using a decision feedback equalizer to derive initial symbol decisions and a competitive decision circuit to determine equalization errors, reducing the complexity of symbol detection in high-rate signaling systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If maximum likelihood sequence detector (MLSD) is used to achieve optimal error rate performance, then detection accuracy is improved, but device complexity and power consumption increase prohibitively
Solution Approach 1:
The patent segments the full MLSD complexity by dividing the constellation into multiple clusters and processing each cluster separately with dedicated sub-detectors. Each sub-detector handles a subset of constellation points, reducing the search space and computational complexity while maintaining near-MLSD performance through coordinated operation of multiple simplified detectors
Solution Approach 2:
The patent applies partial action by evaluating only the most likely symbol decisions and their immediate neighbors rather than exhaustively evaluating all possible constellation points. This selective evaluation of partial candidates achieves sufficient detection accuracy without the prohibitive complexity of complete MLSD
2Productivity
If data rate is increased to meet throughput requirements, then productivity is improved, but intersymbol interference and noise impact worsen detection accuracy
Solution Approach 1:
The patent applies preliminary action through an equalization stage that precedes detection, using decision feedback equalizers or other equalization techniques to mitigate intersymbol interference and noise effects before the symbol detection process. This preliminary conditioning of the received signal improves detection accuracy even at high data rates where ISI and noise are severe
Data Source
AI summary
Reduced-complexity maximum likelihood sequence detectors (rMLSD) are disclosed for detecting multibit symbols such as those found in pulse amplitude modulation (PAM), quadrature amplitude modulation (QAM), and phase shift keying (PSK) signal constellations with more than two constellation points. One illustrative digital communications receiver includes: an initial equalizer that derives an initial sequence of symbol decisions from a filtered receive signal, each symbol decision in the initial sequence having a second most likely symbol decision; and a rMLSD that derives a final sequence of symbol decisions by evaluating state metrics only for each symbol decision in the initial sequence and its second most likely symbol decision.