12 research outputs found
Probabilistic Shaping for Asymmetric Channels and Low-Density Parity-Check Codes
An algorithm is proposed to encode low-density parity-check (LDPC) codes into
codewords with a non-uniform distribution. This enables power-efficient
signalling for asymmetric channels. We show gains of 0.9 dB for additive white
Gaussian noise (AWGN) channels with on-off keying modulation using 5G LDPC
codes.Comment: submitted to ISTC 202
Successive Interference Cancellation for Bandlimited Channels with Direct Detection
Oversampling increases information rates for bandlimited channels with direct
detection, but joint detection and decoding (JDD) is often too complex to
implement. Two receiver structures are studied to reduce complexity: separate
detection and decoding (SDD) and successive interference cancellation (SIC)
with multi-level coding. For bipolar modulation, frequency-domain raised-cosine
pulse shaping, and fiber-optic channels with chromatic dispersion, SIC achieves
rates close to those of JDD, thereby attaining significant energy gains over
SDD and classic intensity modulation. Gibbs sampling further reduces the
detector complexity and achieves rates close to those of the forward-backward
algorithm at low to intermediate signal-to-noise ratio (SNR) but stalls at high
SNR. Simulations with polar codes and higher-order modulation confirm the
predicted rate and energy gains.Comment: Submitted to IEEE Journal of Lightwave Technology on December 15,
2022; Resubmitted to IEEE Transactions on Communications on September 9,
2023
Probabilistically Shaped 4-PAM for Short-Reach IM/DD Links with a Peak Power Constraint
Probabilistic shaping for intensity modulation and direct detection (IM/DD)
links is discussed and a peak power constraint determined by the limited
modulation extinction ratio (ER) of optical modulators is introduced. The input
distribution of 4-ary unipolar pulse amplitude modulation (PAM) symbols is
optimized for short-reach transmission links without optical amplification nor
in-line dispersion compensation. The resulting distribution is symmetric around
its mean allowing to use probabilistic amplitude shaping (PAS) to generate
symbols that are protected by forward error correction (FEC) and that have the
optimal input distribution. The numerical analysis is confirmed experimentally
for both an additive white Gaussian noise (AWGN) channel and a fiber channel,
showing gains in transmission reach and transmission rate, as well as rate
adaptability.Comment: accepted for publication in Journal of Lightwave Technolog
Improved List Decoding for Polar-Coded Probabilistic Shaping
A modified list decoder with improved error performance is proposed for
polar-coded probabilistic shaping. The decoder exploits the deterministic
encoding rule for shaping bits to rule out candidate code words that the
encoder would not generate.Comment: 5 pages, 3 figures; submitted to ISTC 202
Experiments on Bipolar Transmission with Direct Detection
Achievable information rates of bipolar 4- and 8-ary constellations are
experimentally compared to those of intensity modulation (IM) when using an
oversampled direct detection receiver. The bipolar constellations gain up to
1.8 dB over their IM counterparts.Comment: submitted to ECOC 202
Comparison of PAM-6 Modulations for Short-Reach Fiber-Optic Links with Intensity Modulation and Direct Detection
PAM-6 transmission is considered for short-reach fiber-optic links with
intensity modulation and direct detection. Experiments show that
probabilistically-shaped PAM-6 and a framed-cross QAM-32 constellation
outperform conventional cross QAM-32 under a peak power constraint.Comment: submitted to European Conference on Optical Communication (ECOC) 202