6 research outputs found
WDM channel capacity and its dependence on multichannel adaptation models
Optical multichannel systems are often characterized by the channel capacity of a single channel, assuming a certain adaptation behavior of the other channels. We investigate some common adaptation models, which lead to dramatically different capacities
Design of APSK Constellations for Coherent Optical Channels with Nonlinear Phase Noise
We study the design of amplitude phase-shift keying (APSK) constellations for
a coherent fiber-optical communication system where nonlinear phase noise
(NLPN) is the main system impairment. APSK constellations can be regarded as a
union of phase-shift keying (PSK) signal sets with different amplitude levels.
A practical two-stage (TS) detection scheme is analyzed, which performs close
to optimal detection for high enough input power. We optimize APSK
constellations with 4, 8, and 16 points in terms of symbol error probability
(SEP) under TS detection for several combinations of input power and fiber
length. Our results show that APSK is a promising modulation format in order to
cope with NLPN. As an example, for 16 points, performance gains of 3.2 dB can
be achieved at a SEP of 10^-2 compared to 16-QAM by choosing an optimized APSK
constellation. We also demonstrate that in the presence of severe nonlinear
distortions, it may become beneficial to sacrifice a constellation point or an
entire constellation ring to reduce the average SEP. Finally, we discuss the
problem of selecting a good binary labeling for the found constellations. For
the class of rectangular APSK a labeling design method is proposed, resulting
in near-optimal bit error probability.Comment: Submitted to IEEE Transactions on Communication
Capacity of a Nonlinear Optical Channel with Finite Memory
The channel capacity of a nonlinear, dispersive fiber-optic link is
revisited. To this end, the popular Gaussian noise (GN) model is extended with
a parameter to account for the finite memory of realistic fiber channels. This
finite-memory model is harder to analyze mathematically but, in contrast to
previous models, it is valid also for nonstationary or heavy-tailed input
signals. For uncoded transmission and standard modulation formats, the new
model gives the same results as the regular GN model when the memory of the
channel is about 10 symbols or more. These results confirm previous results
that the GN model is accurate for uncoded transmission. However, when coding is
considered, the results obtained using the finite-memory model are very
different from those obtained by previous models, even when the channel memory
is large. In particular, the peaky behavior of the channel capacity, which has
been reported for numerous nonlinear channel models, appears to be an artifact
of applying models derived for independent input in a coded (i.e., dependent)
scenario
Rate-Adaptive Coded Modulation for Fiber-Optic Communications
Rate-adaptive optical transceivers can play an important role in exploiting the available resources in dynamic optical networks, in which different links yield different signal qualities. We study rate-adaptive joint coding and modulation, often called coded modulation (CM), addressing non-dispersion-managed (non-DM) links, exploiting recent advances in channel modeling of these links.
We introduce a four-dimensional CM scheme, which shows a better tradeoff between digital signal processing complexity and transparent reach than existing methods. We construct a rate-adaptive CM scheme combining a single low-density parity-check code with a family of three signal constellations and using probabilistic signal shaping.
We evaluate the performance of the proposed CM scheme for single-channel transmission through long-haul non-DM fiber-optic systems with electronic chromatic-dispersion compensation. The numerical results demonstrate improvement of spectral
efficiency over a wide range of transparent reaches, an improvement over 1 dB compared to existing methods
On Signal Constellations and Coding for Long-Haul Fiber-Optical Systems
Motivated by the realization that even the enormous bandwidth available in an optical fiber is finite and valuable, the design of spectrally efficient long-haul fiber-optical communication systems has become an important research topic. Compared to other wireline technologies, e.g., transmission over coaxial cables, the main challenge comes from the inherent nonlinearity of the underlying communication channel caused by the relatively high signal intensities. In this thesis, we study the design of spectrally efficient fiber-optical systems for both uncoded and coded transmission scenarios.We consider the problem of designing higher-order signal constellations for a system that is severly impaired by nonlinear phase noise. By optimizing amplitude phase-shift keying constellations, which can be seen as the union of phase-shift keying constellation with different amplitude levels, gains of up to 3.2 dB at a symbol error probability of 10^(−2) are shown to be achievable compared to conventional constellations. We also illustrate a somewhat counterintuitive behavior of optimized constellations for very high input powers and nonlinear distortions. In particular, sacrificing a constellation point or ring may be beneficial in terms of the overall performance of the constellation.Furthermore, we study polarization-multiplexed transmission, where spectral efficiency is increased by encoding data onto both polarizations of the light. For a memoryless fiber-optical channel, we introduce a low-complexity detector which is based on an amplitude- dependent phase rotation and subsequent threshold detection. The complexity compared to the four-dimensional maximum likelihood detector is considerably reduced, albeit at the expense of some performance loss.Lastly, we consider the design of a coded fiber-optical system operating at high spectral efficiency. In particular, we study the optimization of the mapping of the coded bits to the modulation bits for a polarization-multiplexed fiber-optical system that is based on the bit-interleaved coded modulation paradigm. This technique, which we refer to as bit mapper optimization, is extended to the class of spatially coupled low-density parity- check codes, which have shown outstanding performance over memoryless binary-input channels. For a transmission scenario without optical inline dispersion compensation, the results show that the transmission reach can be extended by roughly up to 8%, without significantly increasing the system complexity
On Signal Constellations and Coding for Long-Haul Fiber-Optical Systems
Motivated by the realization that even the enormous bandwidth available in an optical fiber is finite and valuable, the design of spectrally efficient long-haul fiber-optical communication systems has become an important research topic. Compared to other wireline technologies, e.g., transmission over coaxial cables, the main challenge comes from the inherent nonlinearity of the underlying communication channel caused by the relatively high signal intensities. In this thesis, we study the design of spectrally efficient fiber-optical systems for both uncoded and coded transmission scenarios.We consider the problem of designing higher-order signal constellations for a system that is severly impaired by nonlinear phase noise. By optimizing amplitude phase-shift keying constellations, which can be seen as the union of phase-shift keying constellation with different amplitude levels, gains of up to 3.2 dB at a symbol error probability of 10^(−2) are shown to be achievable compared to conventional constellations. We also illustrate a somewhat counterintuitive behavior of optimized constellations for very high input powers and nonlinear distortions. In particular, sacrificing a constellation point or ring may be beneficial in terms of the overall performance of the constellation.Furthermore, we study polarization-multiplexed transmission, where spectral efficiency is increased by encoding data onto both polarizations of the light. For a memoryless fiber-optical channel, we introduce a low-complexity detector which is based on an amplitude- dependent phase rotation and subsequent threshold detection. The complexity compared to the four-dimensional maximum likelihood detector is considerably reduced, albeit at the expense of some performance loss.Lastly, we consider the design of a coded fiber-optical system operating at high spectral efficiency. In particular, we study the optimization of the mapping of the coded bits to the modulation bits for a polarization-multiplexed fiber-optical system that is based on the bit-interleaved coded modulation paradigm. This technique, which we refer to as bit mapper optimization, is extended to the class of spatially coupled low-density parity- check codes, which have shown outstanding performance over memoryless binary-input channels. For a transmission scenario without optical inline dispersion compensation, the results show that the transmission reach can be extended by roughly up to 8%, without significantly increasing the system complexity