100,494 research outputs found
Signal overlap for elastic optical networks
No full textIn Elastic Optical Networks, advanced transmission techniques based on coherent detection strategies have been proposed and exploited to provide high flexibility in resource allocation. So far, these techniques have assumed the constraint of each optical signal being transmitted along a dedicated frequency slot, by carefully avoiding frequency overlap with other optical signals. In this study, an overlap technique, that enables uncorrelated optical signals to be superimposed along the same spectrum resources, is designed and validated through simulations, both in terms of performance bounds and bit-error rate in coded transmissions. In particular, it is demonstrated how this technique allows each overlapped signal to be correctly received and detected. The proposed technique is less spectrally efficient and more complex to implement than increasing the constellation size and using non overlapping frequency slots, but it warrants consideration for flexible networking. The proposed technique is first theoretically detailed and justified. Then, networking scenarios and implementation schemes suitable for its effective utilization are identified and applied in the case of two overlapped 112 Gb/s polarization-multiplexed quadrature phase shift keying signals. Simulation results show that, applying 3-dB optical signal-to-noise ratio margin on the achieved bounds, optical reaches of around 800 km can be successfully supported by the proposed overlap technique
BICM and TCM comparison in 100 Gbps optical coherent links in nonlinear regime
No full textThe popular single-carrier QPSK modulation format is compared with 8PSK BICM and TCM schemes in 100 Gbps optical links in linear and nonlinear regime, with or without inline dispersion compensation. © 2011 Optical Society of America
Synchronization for Variable Data Rate LEO Direct-to-Earth Optical Links
No full textThe recent developments in the field of direct-to-Earth (DTE) for low-Earth-orbit (LEO) satellite optical links have shown the potential benefits of on-off-keying-based communications with the variable data rate (VDR) technique, in contrast to the traditional constant data rate (CDR) approach. In this paper, relevant link level aspects are analyzed, namely: time, frame, and amplitude synchronization, showing that reliable and performing techniques allow to fully exploit the advantages offered by the VDR strategy
Stop-and-Go Algorithm for Blind Equalization in QAM Single-Carrier Coherent Optical Systems
No full textCoherent detection has recently allowed the adoption
of high-order modulation formats in single-carrier optical systems
where a simple feed-forward equalizer, in proper configuration, is
able to perfectly compensate for fiber linear impairments, such as
group velocity dispersion and polarization-mode dispersion. In this
letter, the blind update of the equalizer taps is investigated with
reference to a 16-ary quadrature amplitude modulation (QAM)
format in the presence of different channel impairments. A novel
algorithm is proposed, which represents an improvement of the
stop-and-go, through the use of a powerful asynchronous detection
strategy
Maximum likelihood sequence detection with closed-form metrics in OOK optical systems impaired by GVD and PMD
No full textThis paper thoroughly investigates the maximum-likelihood sequence detection (MLSD) receiver for the optical ON-OFF keying (OOK) channel in the presence of both polarization mode dispersion and group velocity dispersion (GVD). A reliable method is provided for computing the relevant performance for any possible value of the system parameters, with no constraint on the sampling rate. With one sample per bit time, a practically exact expression of the statistics of the received samples is found, and therefore the performance of a synchronous MLSD receiver is evaluated and compared with that of other electronic techniques such as combined feedforward and decision-feedback equalizers (FFE and DFE). It is also shown that the ultimate performance of electronic processing can be obtained by sampling the received signal at twice the bit rate. An approximate accurate closed-form expression of the receiver metrics is also identified, allowing for the implementation of a practically optimal MLSD receiver
Signal processing for 100Gb/s: OFDM vs single-carrier
No full textOFDM is compared to the well-established single-carrier data transmission using high-level modulation formats and coherent detection. The analysis of the two alternative solutions is carried out in the 100 Gb/s scenario
Maximum likelihood sequence estimation in optical fibre communication systems
No full textA method of and a receiver for detection of a received signal in an optical fibre communication system using Viterbi algorithm methodology in which branch metrics are obtained using approximated expressions to calculate the branch metrics. Use of the expressions results in practically the same performance as a receiver based on exact metrics
Channel estimation algorithms for MLSD in optical communication systems
No full textMaximum likelihood sequence detection represents the most efficient technique in the electrical domain to combat fiber impairments such as polarization-mode dispersion and group-velocity dispersion. In order to successfully apply this technique, it is mandatory to estimate some key channel parameters needed by the Viterbi processor.We propose a simple and effective solution based on the least-mean-square algorithm to perform such an estimation
Multilevel optical modulations with closed-form optical metrics for MLSE receiver insensitive to GVD and PMD
No full textImpact of phase noise and compensation techniques in coherent optical systems
No full textOne of the most severe impairments that affect coherent optical systems employing high-order modulation formats is phase noise due to transmit and receive lasers. This is especially detrimental in uncompensated links, where an ideal compensator for channel distortions and laser phase noise should first eliminate receive phase noise, then equalize channel distortions, and only later compensate for transmit phase noise. Unfortunately, the simultaneous presence of transmit and receive phase noise makes
very difficult to discriminate between them, even in the presence of a pilot tone. Moreover, the picture is different for optical systems using single-carrier or orthogonal frequency division multiplexing, where transmit and receive phase noise components may have a different impact. All these aspects are analyzed and discussed in this paper. A novel digital coherence enhancement (DCE) technique, able to significantly reduce the phase noise of transmit or receive lasers by using an interferometric device plus a very simple electronic processing, is also described. The performance of this technique and the statistical properties of the residual phase noise are analytically derived and verified by simulations, showing a high increase of the maximum bit-rate-distance product. The practical implementation of DCE is finally discussed and some alternative implementation schemes are presented
- …
