781 research outputs found
Performance Metrics for Systems with Soft-Decision FEC and Probabilistic Shaping
High-throughput optical communication systems utilize binary soft-decision
forward error correction (SD-FEC) with bit interleaving over the bit channels.
The generalized mutual information (GMI) is an achievable information rate
(AIR) in such systems and is known to be a good predictor of the bit error rate
after SD-FEC decoding (post-FEC BER) for uniform signaling. However, for
probabilistically shaped (nonuniform) signaling, we find that the normalized
AIR, defined as the AIR divided by the signal entropy, is less correlated with
the post-FEC BER. We show that the information quantity based on the
distribution of the single bit signal, and its asymmetric loglikelihood ratio,
are better predictors of the post-FEC BER. In simulations over the Gaussian
channel, we find that the prediction accuracy, quantified as the peak-to-peak
deviation of the post-FEC BER within a set of different modulation formats and
distributions, can be improved more than 10 times compared with the normalized
AIR.Comment: 4 pages, 3 figure
Hierarchical Distribution Matching for Probabilistically Shaped Coded Modulation
The implementation difficulties of combining distribution matching (DM) and
dematching (invDM) for probabilistic shaping (PS) with soft-decision forward
error correction (FEC) coding can be relaxed by reverse concatenation, for
which the FEC coding and decoding lies inside the shaping algorithms. PS can
seemingly achieve performance close to the Shannon limit, although there are
practical implementation challenges that need to be carefully addressed. We
propose a hierarchical DM (HiDM) scheme, having fully parallelized input/output
interfaces and a pipelined architecture that can efficiently perform the
DM/invDM without the complex operations of previously proposed methods such as
constant composition DM (CCDM). Furthermore, HiDM can operate at a
significantly larger post-FEC bit error rate (BER) for the same post-invDM BER
performance, which facilitates simulations. These benefits come at the cost of
a slightly larger rate loss and required signal-to-noise ratio at a given
post-FEC BER.Comment: 11 pages, 7 figure
Joint Source-Channel Coding via Compressed Distribution Matching in Fiber-Optic Communications
The variability of source entropy due to data idling is inconsistent with most studies\u27 assumptions in probabilistic shaping. We propose a distribution matcher sensitive to the source entropy, and discuss its impacts on fiber-optic communications
The 5′-AT-rich half-site of Maf recognition element: a functional target for bZIP transcription factor Maf
The Maf family of proteins are a subgroup of basic region-leucine zipper (bZIP) transcription factors, which recognize a long palindromic DNA sequence [TGCTGAC(G)TCAGCA] known as the Maf recognition element (MARE). Interestingly, the functional target enhancer sequences present in the αA-crystallin gene contain a well-conserved half-site of MARE rather than the entire palindromic sequence. To resolve how Maf proteins bind to target sequences containing only MARE half-sites, we examined their binding activities using electrophoretic gel mobility shift assays as well as in vitro and in vivo reporter assays. Our results indicate that the 5′-flanking region of the MARE half-site is required for Maf proteins to bind both in vitro and in vivo. The critical 5′-flanking sequences for c-Maf were determined by a selection and amplification binding assay and show a preference for AT-rich nucleotides. Furthermore, sequence analysis of the regulatory regions of several target genes also suggests that AT-rich sequences are important. We conclude that Maf can bind to at least two types of target sequences, the classical MARE (palindrome type) and a 5′-AT-rich MARE half-site (half-site type). Our results provide important new insights into the DNA binding and site selection by bZIP transcription factors
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