Nonlinear Precoding for MLSE Receivers Using Controlled ISI
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Solution Overview
Problem
Existing linear equalization methods in communication systems suffer from noise enhancement and error propagation due to inter-symbol interference (ISI), while channel state information at the transmitter requires significant transmit power, and conventional Tomlinson-Harashima precoding (THP) cancels ISI completely, preventing decoders from exploiting residual ISI for improved decoding.
Innovation Solution
Adapted THP precoding introduces controlled ISI by modifying transmit sequences to maximize the minimum Euclidean distance of received sequences, allowing decoders like MLSE to leverage this ISI for enhanced decoding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linear equalization is used at the receiver to eliminate ISI, then ISI-free signals are achieved, but noise power is significantly enhanced
Solution Approach 1:
Instead of applying inverse filtering at the receiver to cancel ISI, the patent applies inverse filtering at the transmitter through non-linear precoding. This inverts the location of the equalization operation from receiver to transmitter, thereby eliminating ISI before transmission without enhancing noise at the receiver.
Solution Approach 2:
The patent performs ISI cancellation in advance at the transmitter using non-linear precoding algorithms (such as Tomlinson-Harashima precoding) before the signal is transmitted through the channel. This preliminary action prevents ISI from being introduced in the first place, rather than attempting to remove it after reception.
2Object-affected harmful factors
If decision-feedback equalization is used to combat noise enhancement, then noise power is reduced, but error propagation occurs when symbols are detected incorrectly
Solution Approach 1:
The patent performs ISI cancellation at the transmitter before transmission, so that by the time the signal reaches the receiver, ISI has already been removed. This eliminates the need for decision-feedback equalization at the receiver, thereby avoiding error propagation while still achieving noise power reduction.
3Reliability
If feedback equalizer is implemented at the transmitter to eliminate ISI, then ISI-free signals are achieved, but transmit power is significantly increased
Solution Approach 1:
The patent employs non-linear precoding algorithms that modify the signal parameters through non-linear transformations (such as modulo operations in Tomlinson-Harashima precoding). These parameter changes enable ISI cancellation without requiring the significant increase in transmit power that would be needed for linear feedback equalization.
Solution Approach 2:
The patent inverts the conventional approach by applying non-linear precoding at the transmitter that achieves ISI cancellation more efficiently than linear feedback equalization, thereby eliminating ISI without the associated significant power penalty.
4Object-affected harmful factors
If non-linear precoding is used to eliminate ISI at the transmitter, then noise enhancement is avoided, but device complexity increases
Solution Approach 1:
The patent employs non-linear precoding algorithms that modify signal parameters through mathematical transformations. While these algorithms are more complex than linear equalization, they avoid noise enhancement and can be implemented using standard digital signal processing techniques.
Data Source
AI summary
Aspects of the subject disclosure may include, for example, obtaining a data signal that includes a stream of symbols, modifying the data signal, resulting in a modified data signal, such that there is inter-symbol interference (ISI) when the modified data signal is received by a receiver, and transmitting the modified data signal over a channel to the receiver, wherein the ISI is distinct from an inverse of the channel and is introduced based on the modifying to be exploited by a decoder in the receiver for enhanced decoding. Other embodiments are disclosed.