Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Four-Dimensional Coded Modulation with Bit-wise Decoders for Future
  Optical Communications   Coded modulation (CM) is the combination of forward error correction (FEC)
and multilevel constellations. Coherent optical communication systems result in
a four-dimensional (4D) signal space, which naturally leads to 4D-CM
transceivers. A practically attractive design paradigm is to use a bit-wise
decoder, where the detection process is (suboptimally) separated into two
steps: soft-decision demapping followed by binary decoding. In this paper,
bit-wise decoders are studied from an information-theoretic viewpoint. 4D
constellations with up to 4096 constellation points are considered. Metrics to
predict the post-FEC bit-error rate (BER) of bit-wise decoders are analyzed.
The mutual information is shown to fail at predicting the post-FEC BER of
bit-wise decoders and the so-called generalized mutual information is shown to
be a much more robust metric. For the suboptimal scheme under consideration, it
is also shown that constellations that transmit and receive information in each
polarization and quadrature independently (e.g., PM-QPSK, PM-16QAM, and
PM-64QAM) outperform the best 4D constellations designed for uncoded
transmission. Theoretical gains are as high as 4 dB, which are then validated
via numerical simulations of low-density parity check codes.

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The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
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The categories of this paper are: astro-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
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The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn