98 research outputs found
Time-Frequency Packing for High Capacity Coherent Optical Links
We consider realistic long-haul optical links, with linear and nonlinear
impairments, and investigate the application of time-frequency packing with
low-order constellations as a possible solution to increase the spectral
efficiency. A detailed comparison with available techniques from the literature
will be also performed. We will see that this technique represents a feasible
solution to overcome the relevant theoretical and technological issues related
to this spectral efficiency increase and could be more effective than the
simple adoption of high-order modulation formats.Comment: 10 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1406.5685 by other author
Optical Time-Frequency Packing: Principles, Design, Implementation, and Experimental Demonstration
Time-frequency packing (TFP) transmission provides the highest achievable
spectral efficiency with a constrained symbol alphabet and detector complexity.
In this work, the application of the TFP technique to fiber-optic systems is
investigated and experimentally demonstrated. The main theoretical aspects,
design guidelines, and implementation issues are discussed, focusing on those
aspects which are peculiar to TFP systems. In particular, adaptive compensation
of propagation impairments, matched filtering, and maximum a posteriori
probability detection are obtained by a combination of a butterfly equalizer
and four 8-state parallel Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. A novel
algorithm that ensures adaptive equalization, channel estimation, and a proper
distribution of tasks between the equalizer and BCJR detectors is proposed. A
set of irregular low-density parity-check codes with different rates is
designed to operate at low error rates and approach the spectral efficiency
limit achievable by TFP at different signal-to-noise ratios. An experimental
demonstration of the designed system is finally provided with five
dual-polarization QPSK-modulated optical carriers, densely packed in a 100 GHz
bandwidth, employing a recirculating loop to test the performance of the system
at different transmission distances.Comment: This paper has been accepted for publication in the IEEE/OSA Journal
of Lightwave Technolog
Improving the Spectral Efficiency of Nonlinear Satellite Systems through Time-Frequency Packing and Advanced Processing
We consider realistic satellite communications systems for broadband and
broadcasting applications, based on frequency-division-multiplexed linear
modulations, where spectral efficiency is one of the main figures of merit. For
these systems, we investigate their ultimate performance limits by using a
framework to compute the spectral efficiency when suboptimal receivers are
adopted and evaluating the performance improvements that can be obtained
through the adoption of the time-frequency packing technique. Our analysis
reveals that introducing controlled interference can significantly increase the
efficiency of these systems. Moreover, if a receiver which is able to account
for the interference and the nonlinear impairments is adopted, rather than a
classical predistorter at the transmitter coupled with a simpler receiver, the
benefits in terms of spectral efficiency can be even larger. Finally, we
consider practical coded schemes and show the potential advantages of the
optimized signaling formats when combined with iterative detection/decoding.Comment: 8 pages, 8 figure
High spectral efficiency for long-haul optical links: time-frequency packing vs high-order constellations
We investigate the time-frequency packing technique on long-haul optical links in order to increase the spectral efficiency. This solution is compared to high-order formats at equal bit or baud rate, demonstrating that higher spectral efficiency can be more effectively reached
Next-generation long-haul optical links: Higher spectral efficiency through time-frequency packing
We consider realistic long-haul optical links, where nonlinear effects represent the main impairment, and investigate the application of time-frequency packing with low-order constellations as a the most viable solution to increase the spectral efficiency. We will see that this technique allows to overcome the relevant theoretical and technological issues related to this spectral efficiency increase and is more effective than the simple adoption of high-order modulation formats which are more sensitive to nonlinear effects
Sub-Nyquist Field Trial Using Time Frequency Packed DP-QPSK Super-Channel Within Fixed ITU-T Grid
Sub-Nyquist time frequency packing technique was demonstrated for the first
time in a super channel field trial transmission over long-haul distances. The
technique allows a limited spectral occupancy even with low order modulation
formats. The transmission was successfully performed on a deployed Australian
link between Sydney and Melbourne which included 995 km of uncompensated SMF
with coexistent traffic. 40 and 100 Gb/s co-propagating channels were
transmitted together with the super-channel in a 50 GHz ITU-T grid without
additional penalty. The super-channel consisted of eight sub-channels with
low-level modulation format, i.e. DP-QPSK, guaranteeing better OSNR robustness
and reduced complexity with respect to higher order formats. At the receiver
side, coherent detection was used together with iterative maximum-a-posteriori
(MAP) detection and decoding. A 975 Gb/s DP-QPSK super-channel was successfully
transmitted between Sydney and Melbourne within four 50GHz WSS channels (200
GHz). A maximum potential SE of 5.58 bit/s/Hz was achieved with an OSNR=15.8
dB, comparable to the OSNR of the installed 100 Gb/s channels. The system
reliability was proven through long term measurements. In addition, by closing
the link in a loop back configuration, a potential SE*d product of 9254
bit/s/Hz*km was achieved
Conditioned pilots for ISI channels
One of the proposals to increase the spectral efficiency of the DVB-S2 standard is based on time-frequency packing. This technique causes intersymbol and interchannel interferences to arise, requiring a significant growth of the number of pilots used to carry out frequency and phase synchronization. Therefore, a new pilot design will be introduced and suited optimal and suboptimal reduced-complexity algorithms derived. We will show that the proposed pilot strategy may outperform the classical one in terms of bit error rate and spectral efficiency
Spectral Efficiency Optimization in Flexi-Grid Long-Haul Optical Systems
Flexible grid optical networks allow a better exploitation of fiber capacity,
by enabling a denser frequency allocation. A tighter channel spacing, however,
requires narrower filters, which increase linear intersymbol interference
(ISI), and may dramatically reduce system reach. Commercial coherent receivers
are based on symbol by symbol detectors, which are quite sensitive to ISI. In
this context, Nyquist spacing is considered as the ultimate limit to
wavelength-division multiplexing (WDM) packing.
In this paper, we show that by introducing a limited-complexity trellis
processing at the receiver, either the reach of Nyquist WDM flexi-grid networks
can be significantly extended, or a denser-than-Nyquist channel packing (i.e.,
a higher spectral efficiency (SE)) is possible at equal reach. By adopting
well-known information-theoretic techniques, we design a limited-complexity
trellis processing and quantify its SE gain in flexi-grid architectures where
wavelength selective switches over a frequency grid of 12.5GHz are employed.Comment: 7 pages, 9 figure
Next Generation High Throughput Satellite System
This paper aims at presenting an overview of the state-of-the-art in High Throughput Satellite (HTS) systems for Fixed Satellite Services (FSS) and High Density-FSS. Promising techniques and innovative strategies that can enhance system performance are reviewed and analyzed aiming to show what to expect for next generation ultra-high capacity satellite systems. Potential air interface evolutions, efficient frequency plans,feeder link dimensioning strategies and interference cancellation techniques are presented to show how Terabit/s satellite myth may turn into reality real soon
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