1,721,050 research outputs found
Direct detection of bipolar pulse amplitude modulation
Full text linkPulse amplitude modulation (PAM) is a widely employed digital modulation format. PAM formats are generally classified as bipolar PAM (BPAM) if using both positive and negative amplitude levels, and unipolar PAM (UPAM) if using only non-negative amplitude levels. While BPAM formats are in principle more energy efficient, they are not compatible with conventional direct detection (DD) schemes, so that UPAM formats are usually preferred for short-reach optical communications. In this work, we propose a novel DD scheme that employs oversampling at two samples per symbol to extract both the amplitude and phase information from the received optical signal, enabling the detection of BPAM signals. The proposed scheme uses a single photodetector, has no special requirements in terms of bandwidth, and requires only some minimal additional processing compared to a conventional scheme. A theoretical analysis, confirmed by numerical simulations, shows that, in the presence of optical amplifier noise, the proposed BPAM/DD transmission technique provides large optical signal-to-noise ratio gains compared to a more conventional UPAM/DD transmission and a good tolerance to group velocity dispersion and non-ideal filtering
Metodo basato sui parametri di Stokes per la regolazione adattativa di compensatori di PMD in sistemi di comunicazione a fibra ottica e compensatore secondo il metodo
No full textMethod based on the Stokes parameters for the adaptive adjustment of PMD compensators in optical fiber communication systems and compensator in accordance with said method
No full textSequence-Selection-Based Constellation Shaping for Nonlinear Channels
Full text linkProbabilistic shaping is, nowadays, a pragmatic and popular approach to improve the performance of coherent optical fiber communication systems. In the linear regime, the potential of probabilistic shaping in terms of shaping gain and rate granularity is well known, and its practical implementation has been mostly mastered. In the nonlinear regime, the advantages offered by probabilistic shaping remain not only valid, but might also increase thanks to the appealing opportunity to use the same technique to mitigate nonlinear effects and obtain an additional nonlinear shaping gain. Unfortunately, despite the recent research efforts, the optimization of conventional shaping techniques, such as probabilistic amplitude shaping (PAS), yields a relevant nonlinear shaping gain only in particular scenarios of limited practical interest, e.g., in the absence of carrier phase recovery. Recently, a more theoretical approach, referred to as sequence selection, has been proposed to understand the performance and limitation of nonlinear constellation shaping. Sequence selection shapes the distribution of the transmitted symbols by selecting or discarding the sequences generated by a certain source according to a metric that measures their quality. In this manuscript, after a brief review of conventional probabilistic shaping, we use sequence selection to investigate through simulations the potential, opportunities, and challenges offered by probabilistic shaping for nonlinear channels. First, we show that ideal sequence selection is able to provide up to 0.13 b/s/Hz additional gain with respect to PAS with an optimized blocklength. However, this additional gain is obtained only if the selection metric accounts for the signs of the symbols, ruling out the possibility of using one of the simple recently proposed sign-independent metrics. We also show that, while the signs must be known to compute the selection metric, there is no need to shape them, since nearly the same gain can be obtained by properly selecting the amplitudes (with a sign-dependent metric) and leaving the signs uniform i.i.d. Furthermore, we show that the selection depends in a non-critical way on the symbol rate and link length: the sequences selected for a certain scenario still provide a relevant gain if the link length or baud rate are modified (within a reasonable range). Then, we analyze and compare several practical implementations of sequence selection by taking into account interaction with forward error correction (FEC), information loss due to selection, and complexity. Overall, we conclude that the single block and the multi block FEC-independent bit scrambling are the best options for the practical implementation of sequence selection, with a gain up to 0.08 b/s/Hz. The main challenge and limitation to their practical implementation remains the evaluation of the metric, whose complexity is currently too high. Finally, we show that the nonlinear shaping gain provided by sequence selection persists when carrier phase recovery is included, in contrast to the nonlinear shaping gain offered by optimizing the blocklength of conventional PAS techniques
Probabilistic Shaping Methods for Linear and Nonlinear Channels
No full textThe main methods and achievements regarding probabilistic shaping are reviewed, highlighting the primary difficulties and opportunities
Sequence selection for nonlinear probabilistic shaping: toward a practical implementation
Full text linkMitigating the impact of noise on nonlinear frequency division multiplexing
No full textIn the past years, nonlinear frequency division multiplexing (NFDM) has been investigated as a potentially revolutionary technique for nonlinear optical fiber communication. However, while NFDM is able to exploit the Kerr nonlinearity, its performance lags behind that of conventional systems. In this work, we first highlight that current implementations of NFDM are strongly suboptimal, and, consequently, oversensitive to noise: the modulation does not ensure a large minimum distance between waveforms, while the detection is not tailored to the statistics of noise. Next, we discuss improved detections strategies and modulation techniques, proposing some effective approaches able to improve NFDM. Different flavors of NFDM are compared through simulations, showing that (i) the NFDM performance can be significantly improved by employing more effective detection strategies, with a 5.6 dB gain in Q-factor obtained with the best strategy compared to the standard strategy; (ii) an additional gain of 2.7 dB is obtained by means of a simple power-tilt modulation strategy, bringing the total gain with respect to standard NFDM to 8.3 dB; and (iii) under some parameters range (rate efficiency η ≤ 30%), the combination of improved modulation and detection allows NFDM to outperform conventional systems using electronic dispersion compensation
Adorni G., Onori T., Venzo M.I., Laurearsi a Roma in utroque iure. Forestieri e stranieri nei primi Registra doctorum et decretorum, in Venire a Roma, restare a Roma. Forestieri e stranieri fra Quattro e Settecento, acd Cabibbo S., Serra A., Roma 2017, pp. 101-118 – in “Roma nel Rinascimento”, (2018), Scheda n. 2, pp. 105-107.
No full textRecensione: Adorni G., Onori T., Venzo M.I., Laurearsi a Roma in utroque iure. Forestieri e stranieri nei primi Registra doctorum et decretorum, in Venire a Roma, restare a Roma. Forestieri e stranieri fra Quattro e Settecento, acd Cabibbo S., Serra A., Roma 2017, pp. 101-118 – in “Roma nel Rinascimento”, (2018), Scheda n. 2, pp. 105-107
Interplay of Probabilistic Shaping and Carrier Phase Recovery for Nonlinearity Mitigation
No full textMethod based on mean square error for the adaptive adjustment of PMD compensators in optical fiber communication systems and compensator in accordance with said method
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