1,059 research outputs found
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
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
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
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
A super-nyquist architecture for reliable underwater acoustic communication
A natural joint physical and link layer transmission architecture is developed for communication over underwater acoustic channels, based on the concept of super-Nyquist (SNQ) signaling. In such systems, the signaling rate is chosen significantly higher than the Nyquist rate of the system. We show that such signaling can be used in conjunction with good "off- the-shelf" base codes, simple linear redundancy, and minimum mean-square error decision feedback equalization (MMSE-DFE) to produce highly efficient, low complexity rateless (i.e., "fountain") codes for the severe time-varying intersymbol-interference channels typical of this application. We show that not only can SNQ rateless codes approach capacity arbitrarily closely, but even particularly simple SNQ-based rateless codes require the transmission of dramatically fewer packets than does traditional ARQ with Chase combining.United States. Office of Naval Research. Multidisciplinary University Research Initiative (Grant N00014-07-1-0738)United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0183)Israel Science Foundation (Grant 1557/10
FTN Signaling In the Saturation Regime: Spectral Efficiency Improvement
Faster-than-Nyquist (FTN) signaling is investigated in future satellite communication standardization for an improved spectral efficiency considering the increasingly constrained resource. Previous studies showed that FTN lower modulation orders compressed in time-domain could reach the spectral efficiency of uncompressed higher modulation orders. The FTN gain in terms of transmission rate is obtained at the price of a turbo-equalization at the receiver, increasing the complexity. The increased capacity in DVB-S2X’s transmissions is due to innovations increasing the fluctuation of the complex envelop of the transmitted signal. Since the satellite’s payload introduces higher non-linear distortions with increased fluctuations, the growing receiver’s complexity is unavoidable. However, in this non linear regime, the complexity of the FTN receiver is not this detrimental compared with those of a classical Nyquist receiver. For a similar spectral efficiency, its lower Peak to Average Power Ratio (PAPR), making the non-linearities treatment easier, makes this innovation suitable for future satellite communications, especially when the payload is operated in the saturation regime. In this paper, we show that compression offers a gain between 10 and 20 in terms of spectral efficiency when compared to Nyquist signaling, both equalized thanks to the MAP symbol detection based on the Volterra series model of non-linearities
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