40 research outputs found
LDPC Coded Modulation with Probabilistic Shaping for Optical Fiber Systems
An LDPC coded modulation scheme with probabilistic shaping, optimized
interleavers and noniterative demapping is proposed. Full-field simulations
show an increase in transmission distance by 8% compared to uniformly
distributed input.Comment: 3 pages, 3 figures. Paper is accepted for presentation at OFC 2015.
Following the submission to OFC, the blue box in Fig. 1 has been corrected
and reference [3] has been update
On Achievable Rates for Long-Haul Fiber-Optic Communications
Lower bounds on mutual information (MI) of long-haul optical fiber systems
for hard-decision and soft-decision decoding are studied. Ready-to-use
expressions to calculate the MI are presented. Extensive numerical simulations
are used to quantify how changes in the optical transmitter, receiver, and
channel affect the achievable transmission rates of the system. Special
emphasis is put to the use of different quadrature amplitude modulation
formats, channel spacings, digital back-propagation schemes and probabilistic
shaping. The advantages of using MI over the prevailing -factor as a figure
of merit of coded optical systems are also highlighted.Comment: Hard decision mutual information analysis added, two typos correcte
Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments
We experimentally investigate mutual information and generalized mutual
information for coherent optical transmission systems. The impact of the
assumed channel distribution on the achievable rate is investigated for
distributions in up to four dimensions. Single channel and wavelength division
multiplexing (WDM) transmission over transmission links with and without inline
dispersion compensation are studied. We show that for conventional WDM systems
without inline dispersion compensation, a circularly symmetric complex Gaussian
distribution is a good approximation of the channel. For other channels, such
as with inline dispersion compensation, this is no longer true and gains in the
achievable information rate are obtained by considering more sophisticated
four-dimensional (4D) distributions. We also show that for nonlinear channels,
gains in the achievable information rate can also be achieved by estimating the
mean values of the received constellation in four dimensions. The highest gain
for such channels is seen for a 4D correlated Gaussian distribution
Sensitivity Gains by Mismatched Probabilistic Shaping for Optical Communication Systems
Probabilistic shaping of quadrature amplitude modulation (QAM) is used to
enhance the sensitivity of an optical communication system. Sensitivity gains
of 0.43 dB and 0.8 dB are demonstrated in back-to-back experiments by shaping
of 16QAM and 64QAM, respectively. Further, numerical simulations are used to
prove the robustness of probabilistic shaping to a mismatch between the
constellation used and the signal-to-noise ratio (SNR) of the channel. It is
found that, accepting a 0.1 dB SNR penalty, only four shaping distributions are
required to support these gains for 64QAM.Comment: Title and introduction were updated and the discussion of Section
IV-B was extended. Additionally, some minor modifications were made to the
manuscrip
Probabilistic Shaping for Finite Blocklengths: Distribution Matching and Sphere Shaping
In this paper, we provide for the first time a systematic comparison of
distribution matching (DM) and sphere shaping (SpSh) algorithms for short
blocklength probabilistic amplitude shaping. For asymptotically large
blocklengths, constant composition distribution matching (CCDM) is known to
generate the target capacity-achieving distribution. As the blocklength
decreases, however, the resulting rate loss diminishes the efficiency of CCDM.
We claim that for such short blocklengths and over the additive white Gaussian
channel (AWGN), the objective of shaping should be reformulated as obtaining
the most energy-efficient signal space for a given rate (rather than matching
distributions). In light of this interpretation, multiset-partition DM (MPDM),
enumerative sphere shaping (ESS) and shell mapping (SM), are reviewed as
energy-efficient shaping techniques. Numerical results show that MPDM and SpSh
have smaller rate losses than CCDM. SpSh--whose sole objective is to maximize
the energy efficiency--is shown to have the minimum rate loss amongst all. We
provide simulation results of the end-to-end decoding performance showing that
up to 1 dB improvement in power efficiency over uniform signaling can be
obtained with MPDM and SpSh at blocklengths around 200. Finally, we present a
discussion on the complexity of these algorithms from the perspective of
latency, storage and computations.Comment: 18 pages, 10 figure