Distribution Matcher Sets for Low-Latency Probabilistic Shaping
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Solution Overview
Problem
Current methods for mapping sequences of uniformly distributed bits to non-equiprobable symbols in digital communications systems face high complexity and latency due to the need for long sequences and sequential decoding algorithms, which are inefficient and lead to prohibitively high complexity and latency.
Innovation Solution
The approach involves partitioning a set of symbols into unique subsets, each with possible permutations, and transforming these subsets into blocks with non-uniform distributions that combine to achieve a target probability mass function (PMF), allowing for reduced block lengths and flexible distribution matching to achieve the desired transmission rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant composition distribution matching (CCDM) is used to map equiprobable bits onto typical sequences with desired symbol probability mass function, then good performance is achieved with arbitrarily low rate loss, but very long sequences are required which causes high complexity and latency
Solution Approach 1:
The patent segments the distribution matching process by partitioning the set of symbols into multiple unique subsets, where each subset contains a limited number of symbols. This allows the use of multiple distribution matchers with smaller output alphabets instead of a single matcher requiring long sequences, thereby reducing complexity and latency while maintaining performance.
2Reliability
If sequential mapping algorithms are used to decode each symbol in-turn in a symbol sequence, then the desired non-uniform distribution is achieved, but prohibitively high complexity and latency result
Solution Approach 1:
The patent divides the symbol set into multiple subsets and assigns different distribution matchers to each subset. This segmentation enables parallel processing of multiple symbols simultaneously, replacing the sequential one-by-one decoding approach and thereby reducing complexity and latency while maintaining distribution accuracy.
Solution Approach 2:
The patent uses multiple distribution matchers that each handle a portion of the symbol set rather than requiring a single matcher to process the entire sequence sequentially. This partial action approach allows parallel execution and reduces the computational burden per symbol while achieving the desired overall distribution.
3Loss of information
If very long sequences are used to achieve low rate-loss in distribution matching, then good performance is obtained, but high complexity and latency are caused
Solution Approach 1:
The patent partitions symbols into multiple subsets and uses multiple distribution matchers with smaller output alphabets. This segmentation achieves the desired distribution with shorter sequences, reducing both rate loss and the latency associated with processing very long sequences.
Data Source
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Figure 1B
Figure 1C
AI summary
A communication system includes a data source to receive a block of bits, a memory to store a set of distribution matchers. Each distribution matcher is associated with a probability mass function (PMF) to match equally likely input bits to a fixed number of output bits with values distributed according to the PMF of the distribution matcher. Each distribution matcher is associated with a selection probability, such that a sum of joint probabilities of all distribution matchers equals a target PMF. A joint probability of a distribution matcher is a product of PMF of the distribution matcher with the selection probability of the distribution matcher. The communication system also includes a shaping mapper to select the distribution matcher from the set of distribution matchers with the selection probability and to map the block of bits to a block of shaped bits with a non-uniform distribution using the selected distribution matcher and a transmitter front end to transmit the block of shaped bits over a communication channel, such that bits in a sequence of the blocks of shaped bits are distributed according to the target PMF.