34 research outputs found
Replacing the Soft FEC Limit Paradigm in the Design of Optical Communication Systems
The FEC limit paradigm is the prevalent practice for designing optical
communication systems to attain a certain bit-error rate (BER) without forward
error correction (FEC). This practice assumes that there is an FEC code that
will reduce the BER after decoding to the desired level. In this paper, we
challenge this practice and show that the concept of a channel-independent FEC
limit is invalid for soft-decision bit-wise decoding. It is shown that for low
code rates and high order modulation formats, the use of the soft FEC limit
paradigm can underestimate the spectral efficiencies by up to 20%. A better
predictor for the BER after decoding is the generalized mutual information,
which is shown to give consistent post-FEC BER predictions across different
channel conditions and modulation formats. Extensive optical full-field
simulations and experiments are carried out in both the linear and nonlinear
transmission regimes to confirm the theoretical analysis
Achievable Information Rates for Coded Modulation with Hard Decision Decoding for Coherent Fiber-Optic Systems
We analyze the achievable information rates (AIRs) for coded modulation
schemes with QAM constellations with both bit-wise and symbol-wise decoders,
corresponding to the case where a binary code is used in combination with a
higher-order modulation using the bit-interleaved coded modulation (BICM)
paradigm and to the case where a nonbinary code over a field matched to the
constellation size is used, respectively. In particular, we consider hard
decision decoding, which is the preferable option for fiber-optic communication
systems where decoding complexity is a concern. Recently, Liga \emph{et al.}
analyzed the AIRs for bit-wise and symbol-wise decoders considering what the
authors called \emph{hard decision decoder} which, however, exploits \emph{soft
information} of the transition probabilities of discrete-input discrete-output
channel resulting from the hard detection. As such, the complexity of the
decoder is essentially the same as the complexity of a soft decision decoder.
In this paper, we analyze instead the AIRs for the standard hard decision
decoder, commonly used in practice, where the decoding is based on the Hamming
distance metric. We show that if standard hard decision decoding is used,
bit-wise decoders yield significantly higher AIRs than symbol-wise decoders. As
a result, contrary to the conclusion by Liga \emph{et al.}, binary decoders
together with the BICM paradigm are preferable for spectrally-efficient
fiber-optic systems. We also design binary and nonbinary staircase codes and
show that, in agreement with the AIRs, binary codes yield better performance.Comment: Published in IEEE/OSA Journal of Lightwave Technology, 201
Performance Prediction Recipes for Optical Links
Although forward error-correction (FEC) coding is an essential part of modern
fiber-optic communication systems, it is impractical to implement and evaluate
FEC in transmission experiments and simulations. Therefore, it is desirable to
accurately predict the end-to-end link performance including FEC from
transmission data recorded without FEC. In this tutorial, we provide
ready-to-implement "recipes" for such prediction techniques, which apply to
arbitrary channels and require no knowledge of information or coding theory.
The appropriate choice of recipe depends on properties of the FEC encoder and
decoder. The covered metrics include bit error rate, symbol error rate,
achievable information rate, and asymptotic information, in all cases computed
using a mismatched receiver. Supplementary software implementations are
available
Amplifier Limited Information Rates in High-Speed Optical Fiber Communication Systems
Due to the high transmission capacity, optical fiber systems have been extensively applied, as significant components, in the modern telecommunication infrastructure to meet the ever-increasing demand of data traffic. Optical amplifiers have been employed to amplify optical signals and to compensate for the transmission losses. They play a key role in relaying the signals in ultra-wideband optical fiber communication systems. However, the amplified spontaneous emission (ASE) noise will be introduced during such process, and it will degrade the performance of optical fiber systems and will pose constraints on the transmission information rates. The mutual information (MI) and the generalized mutual information (GMI) have been applied and investigated, as figures of merit, to evaluate the information rates in communication systems. The MI measures the highest achievable information rate (bits per symbol) that can be realized in a channel based on ideal symbol-wise encoder and decoder. The GMI, also known as the bit-interleaved coded modulation (BICM) capacity, indicates an upper bound on the number of bits per symbol that can be reliably transmitted through a channel based on the bit-wise decoding. Although the MI and the GMI are equal when the signal-to-noise ratio (SNR) tends to infinity, the MI is strictly higher than the GMI in any practical transmission scenarios. This discrepancy depends on the constellation cardinality and the binary labeling. In this work, we have investigated the impact of ASE noise on the MI and the GMI, and have developed corresponding analyses and estimations across different modulation formats, in linear optical fiber communication systems. Our work aims to explore the limit and requirements on optical amplifiers and to provide a comprehensive insight for the design of next-generation ultra-wideband optical fiber communication systems
Multi-non-binary turbo codes
International audienceThis paper presents a new family of turbo codes called multi-non-binary turbo codes (MNBTCs) that generalizes the concept of turbo codes to multi-non-binary (MNB) parallel concatenated convolutional codes (PCCC). An MNBTC incorporates, as component encoders, recursive and systematic multi-non-binary convolutional encoders. The more compact data structure for these encoders confers some advantages on MNBTCs over other types of turbo codes, such as better asymptotic behavior, better convergence, and reduced latency. This paper presents in detail the structure and operation of an MNBTC: MNB encoding, trellis termination, Max-Log-MAP decoding adapted to the MNB case. It also shows an example of MNBTC whose performance is compared with the state-of-the-art turbo code adopted in the DVB-RCS2 standard
Zigzag Decodable Fountain Codes
This paper proposes a fountain coding system which has lower space decoding
complexity and lower decoding erasure rate than the Raptor coding systems. The
main idea of the proposed fountain code is employing shift and exclusive OR to
generate the output packets. This technique is known as the zigzag decodable
code, which is efficiently decoded by the zigzag decoder. In other words, we
propose a fountain code based on the zigzag decodable code in this paper.
Moreover, we analyze the overhead for the received packets, decoding erasure
rate, decoding complexity, and asymptotic overhead of the proposed fountain
code. As the result, we show that the proposed fountain code outperforms the
Raptor codes in terms of the overhead and decoding erasure rate. Simulation
results show that the proposed fountain coding system outperforms Raptor coding
system in terms of the overhead and the space decoding complexity.Comment: 11 pages, 15 figures, submitted to IEICETransactions, Oct. 201