6-Input LUT ACS Circuit for Shorter Trellis Decoder Critical Paths
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Solution Overview
Problem
Conventional Add-Compare-Select (ACS) blocks in trellis decoders require significant area and critical path lengths, limiting the efficiency and speed of error correction processes in telecommunications applications.
Innovation Solution
The implementation of optimized ACS circuits using 3-input adder modules and 6-input lookup tables (LUTs) reduces the area required and allows for parallel calculations, decreasing the critical path and increasing operating frequency, while also incorporating memory for enhanced accuracy in Turbo decoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional ACS blocks are used in trellis decoders, then the decoding function can be performed, but the area required is significant and the critical path length is long
Solution Approach 1:
The ACS block is divided into multiple independent modules, each handling specific calculations. The adder unit, comparator unit, and selector unit operate as separate functional blocks that can be implemented in parallel, reducing the overall critical path length while maintaining the complete decoding function.
Solution Approach 2:
The patent transforms the sequential calculation process into a parallel architecture by introducing multiple operational units that work simultaneously. The critical path is shortened by organizing calculations in a multi-dimensional parallel structure rather than a single sequential chain.
2Speed
If conventional ACS blocks are used in trellis decoders, then the decoding function can be performed, but the critical path length is long
Solution Approach 1:
Multiple functional units (adder, comparator, selector) are merged into a single integrated ACS block structure. This consolidation allows the units to operate cooperatively with shared data paths and control signals, achieving high-speed parallel operation while maintaining a compact, manageable device architecture.
Solution Approach 2:
The ACS block is designed as a universal module that can be instantiated multiple times to handle different states in the trellis decoder. Each instance performs the same set of operations (addition, comparison, selection) but on different data, allowing the system to achieve high throughput through parallel instantiation of a standardized functional unit.
3Reliability
If more ACS blocks are used to improve decoding accuracy, then the decoding performance improves, but the area required increases significantly
Solution Approach 1:
The patent optimizes the internal parameters of the ACS block, such as the word length and precision of arithmetic operations, to achieve the required decoding accuracy with minimal resource usage. By carefully selecting parameter values, the design maintains high reliability while reducing the area required for each block instance.
Data Source
AI summary
An Add-Compare-Select circuit for use with a trellis decoder can include a first module and a second module. The first module can provide a difference signal specifying an indication of a difference between a second path cost and a first path cost of a trellis. The second path cost can be a sum of a second state cost and a second branch metric and the first path cost can be a sum of a first state cost and a first branch metric. The second module can select the first path cost or the second path cost as a new cost according to the difference signal of the first module.