Precoded Faster Than Nyquist Signaling With Tomlinson-Harashima
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Solution Overview
Problem
Current high-speed digital communication systems face challenges in increasing spectral efficiency and managing inter-symbol interference (ISI) introduced by Faster-than-Nyquist (FTN) signaling, which leads to performance degradation and error propagation due to high computational complexity and modulo loss in Tomlinson-Harashima Precoding (THP) receivers.
Innovation Solution
The integration of Tomlinson-Harashima Precoding (THP) with FTN signaling, where THP is applied at the transmitter to pre-compensate for ISI, and log-likelihood ratios (LLRs) are computed based on an extended constellation at the receiver without modulo operation, mitigating modulo loss and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Tomlinson-Harashima Precoding (THP) is applied at the receiver to compensate for ISI in FTN signaling, then inter-symbol interference compensation is achieved, but computational complexity increases and modulo loss occurs
Solution Approach 1:
The patent applies THP precoding at the transmitter before signal transmission, pre-compensating for the ISI that will be introduced by FTN signaling. This preliminary action shifts the computational burden from the receiver to the transmitter, simplifying the receiver while maintaining ISI compensation effectiveness
Solution Approach 2:
Instead of applying THP at the receiver to undo ISI (conventional approach), the patent inverts the approach by applying THP at the transmitter to pre-compensate for ISI. This inversion eliminates the need for complex receiver processing and avoids modulo loss at the receiver
2Reliability
If conventional THP with modulo operation is used, then ISI pre-compensation is achieved, but modulo loss degrades BER performance
Solution Approach 1:
The patent removes the modulo operation from the THP processing chain entirely. By formulating THP without modulo constraints, the system eliminates modulo loss while maintaining ISI pre-compensation capability, directly improving BER performance
Solution Approach 2:
The patent changes the operational parameters of THP by eliminating the modulo constraint and operating in an extended constellation space. This parameter change transforms THP from a modulo-based system to a linear system, avoiding the performance degradation caused by modulo wrapping
3Productivity
If FTN signaling is used to increase spectral efficiency, then bandwidth utilization improves, but inter-symbol interference increases
Solution Approach 1:
The patent applies THP precoding at the transmitter to pre-compensate for the ISI that will be introduced by FTN signaling before transmission. This preliminary compensation allows the system to operate at higher spectral efficiencies while maintaining signal integrity through advance ISI mitigation
Data Source
AI summary
Systems and methods of precoded faster than Nyquist (FTN) signalling are provided. In the transmitter, Tomlinson-Harashima Preceding (THP) is applied to produce precoded symbols. The THP is based on inter-symbol interference (ISI) due to using faster than Nyquist (FTN) signalling. An inverse modulo operation is not performed in the receiver. Instead, in the receiver, FTN processing is performed based on a matched filter output by determining log a-posteriori probability ratio LAPPR values computed for an nth bit bn of a kth received symbol and pre-computed a-priori probabilities of an extended constellation for a given pulse shape h(t) and FTN acceleration factor combination.