softdecisioninformationer

Softdecisioninformationer is not a standard term in technical literature; it appears to be a variant or misspelling of the concept commonly called soft decision information. In digital communications, soft decision information refers to probabilistic or confidence-based information about transmitted symbols produced by a receiver. Unlike hard decisions, which map a received signal to a single binary value, soft information provides a measure of reliability for each decision, typically in the form of log-likelihood ratios or posterior probabilities.

Formally, for a binary bit b transmitted over a channel observed as y, the soft information can be expressed as the log-likelihood ratio LLR = log P(b=1|y) / P(b=0|y). This extends to higher-order constellations by operating on symbol-level probabilities. The soft information can be represented as LLRs, probability vectors, or quantized reliability levels. Soft information preserves channel reliability information that would be lost in a hard-decision mapping.

Role in decoding: Soft decision information is used as input to soft-input decoders, enabling iterative decoding and improved error performance. It is essential for modern codes such as turbo codes and LDPC codes. The decoders use soft information to refine estimates through algorithms like belief propagation, MAP, or related iterative schemes, often yielding substantial performance gains over hard-decision decoding.

Representation and practical aspects: In hardware and software implementations, soft information is often quantized to a small number of levels and exchanged between demodulation and decoding stages. Accurate channel modeling and calibration improve the reliability of the soft information.

Applications: Soft decision information is central in wireless communications (including cellular standards and Wi‑Fi), optical communications, and data storage systems, where soft-output demodulation and soft-input decoding provide performance gains.

History and context: The utility of soft information in decoding matured with turbo codes in the 1990s and LDPC codes around the same period, though the underlying concept of probabilistic reliability dates earlier in information theory.