Hybrid LDPC Interleaver for Limited-CSI BP Decoding
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Solution Overview
Problem
LDPC codes with a staircase node distribution are vulnerable to decoding failure due to limited channel state information (CSI) provided by short-term channel estimation, leading to erasures that hinder the Belief Propagation (BP) decoding algorithm.
Innovation Solution
A hybrid block-wise random interleaver is employed to restructure the Tanner graph of LDPC codes by swapping variable nodes with random connections and distributing bits over transmission hops, using a block-wise interleaver for systematic bits and a random interleaver for other bits, ensuring the BP decoding algorithm can be triggered with minimal CSI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of pilot symbols is increased to extend channel estimation span, then more fading coefficients can be estimated and provided to the LDPC decoder, but the effective data rate is reduced due to transmission of more non-data pilot symbols
Solution Approach 1:
The LDPC codeword is segmented into multiple bit groups, and bits within each group are further divided into subsets. This segmentation allows the interleaver to distribute systematic bits and non-systematic bits to different transmission hops, enabling the receiver to accumulate sufficient CSI across multiple hops without requiring a single long pilot sequence, thus maintaining both reliability and productivity
Solution Approach 2:
The patent introduces a temporal dimension by distributing bits across multiple transmission hops instead of transmitting all bits in a single hop. This allows the receiver to accumulate channel state information iteratively over time, transforming the problem from a spatial distribution challenge to a temporal accumulation process, thereby resolving the contradiction between pilot overhead and data rate
2Productivity
If a short preamble sequence is used for channel estimation, then the effective data rate is maintained, but the LDPC decoder cannot obtain sufficient CSI and BP decoding fails to start
Solution Approach 1:
The interleaver is designed in advance to place systematic bits (which carry important information) and non-systematic bits in specific positions that optimize their distribution across transmission hops. This preliminary arrangement ensures that even with a short preamble, the receiver can accumulate sufficient CSI over multiple hops to successfully trigger BP decoding, thereby maintaining both productivity and reliability
3Device complexity
If LDPC codes with staircase node distribution are used, then the decoding complexity is reduced, but the codes become vulnerable to decoding failure when channel estimator provides CSI about few symbols
Solution Approach 1:
The interleaver acts as an intermediary between the staircase-structured LDPC code and the channel estimation process. It redistributes the codeword bits across multiple transmission hops, ensuring that systematic bits are spread out in a way that allows the receiver to accumulate CSI gradually. This intermediary function protects the simple staircase structure from its vulnerability to limited CSI while maintaining low decoding complexity
Data Source
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AI summary
Embodiments provide an interleaver for interleaving an LDPC encoded bit sequence, wherein the interleaver comprises a segmentation stage configured to segment the LDPC encoded bit sequence into a plurality of chunks, the plurality of chunks comprising a first chunk and one or more other chunks, a first interleaver stage, configured to interleave the one or more other chunks or a concatenated version thereof, a second interleaver stage, configured to block wise interleave the first chunk of the plurality of chunks and an interleaved bit sequence provided by the first interleaver stage, to obtain an interleaved version of the LDPC encoded bit sequence, wherein the first chunk of the plurality of chunks consists of bits of a first type, wherein the bits of the first type are error correcting bits of the LDPC encoded bit sequence, are repeat accumulate bits of the LDPC encoded bit sequence, and/or are represented, in a Tanner graph representation of the LDPC encoded bit sequence, by variable nodes that comprise non-random connections to at least two error correcting check nodes.