On the Impact of Optimal Modulation and FEC Overhead on Future Optical Networks

The potential of optimum selection of modulation and forward error correction (FEC) overhead (OH) in future transparent nonlinear optical mesh networks is studied from an information theory perspective. Different network topologies are studied as well as both ideal soft-decision (SD) and hard-decision (HD) FEC based on demap-and-decode (bit-wise) receivers. When compared to the de-facto QPSK with 7% OH, our results show large gains in network throughput. When compared to SD-FEC, HD-FEC is shown to cause network throughput losses of 12%, 15%, and 20% for a country, continental, and global network topology, respectively. Furthermore, it is shown that most of the theoretically possible gains can be achieved by using one modulation format and only two OHs. This is in contrast to the infinite number of OHs required in the ideal case. The obtained optimal OHs are between 5% and 80%, which highlights the potential advantage of using FEC with high OHs.Comment: Some minor typos were correcte

Designing adaptive coded modulation for optical networks via achievable information rates

© 2017 IEEE. Achievable information rates are discussed as a tool to analyse and design optical networks. It is shown that the maximum throughput of the network and its dependency of different network parameters can be predicted with such a tool

Throughput Gains From Adaptive Transceivers in Nonlinear Elastic Optical Networks

In this paper, we link the throughput gains, due to transceiver adaptation, in a point-to-point transmission link to the expected gains in a mesh network. We calculate the maximum network throughput for a given topology as we vary the length scale. We show that the expected gain in the network throughput due to transceiver adaptation is equivalent to the gain in a point-to-point link with a length equal to the mean length of the optical paths across the minimum network cut.We also consider upper and lower bounds on the variation of the gain in the network throughput due to transceiver adaptation, where integer-constrained channel bandwidth assignment and quantized adaptations are considered. This bounds the variability of results that can be expected and indicates why some networks can give apparently optimistic or pessimistic results. We confirm the results of previous authors that show finer quantization steps in the adaptive control lead to an increase in the throughput since the mean loss of throughput per transceiver is reduced. Finally, we consider the likely network advantage of digital nonlinear mitigation and show that a significant tradeoff occurs between the increase in the signal-to-noise ratio for larger mitigation bandwidths and the loss of throughput when routing fewer large-bandwidth superchannels.This work was supported by the U.K. Engineering and Physical Sciences Research Council through Program Grant UNLOC [EP/J017582/1] and project INSIGHT [EP/L026155/1]

Design of next generation optical transmission systems

In this thesis investigations were performed into the design of optical channels for coherent optical fibre transmission systems for future optical networks. Firstly, an overview of traditional optical networks design and next generation concepts under research for the next generation of optical networks is given. The coherent receiver was then investigated experimentally as an investigative tool to provide information for channel provisioning, by fast C-band spectral analysis and estimating neighbouring channel power. An algorithm incorporated these two abilities and successfully provisioned a polarization multiplexed quadrature phase shift keying (PM-QPSK) signal in a populated system. Probabilistic versus traditional deterministic design methodology was examined to determine its advantages by perturbing intra-link optical power. Experimental results showed that due to the non-linearity of the transmission medium, a more ideal provisioning point could be determined. A three parameter model was proposed to fit the behaviour of optical power and was shown to fit the behaviour of a single channel system. A wavelength division multiplexed (WDM) system was then used to validate the model’s prediction ability with high accuracy. In light of the potential increased polarization dependent loss (PDL) of next generation optical networks, the influence of up to 6 dB distributed link PDL is investigated for a 35 Gbaud coherent WDM system over 120,000 discrete instantiations for PM-QPSK and polarization multiplexed 16-level quadrature amplitude modulation (PM-16QAM) using commercial transceivers. Less than a 1 dB penalty to SNR was observed for a 6 dB range of optical launch powers. This thesis concludes with a method for estimating the performance margin for a PM-16QAM system using a pre-existing PM-QPSK system with the intended use for adaptive change of modulation format on the fly. The largest error in estimation of this margin is less than 0.4 dB over a range of 4 dB optical launch powe

Parameter selection in optical networks with variable-code-rate transceivers

Orientadores: Darli Augusto de Arruda Mello, Jacklyn Dias ReisDissertação (mestrado) ¿ Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Os futuros transceptores ópticos coerentes serão capazes de ajustar parâmetros do sinal transmitido (formato de modulação, taxa de símbolo, taxa de codificação e número de subportadoras) de acordo com as condições do enlace óptico, de modo a usar o espectro disponível de modo mais eficiente. Quanto maior for a flexibilidade do transceptor, mais complexa se torna a tarefa de encontrar o conjunto ótimo de parâmetros para cada situ- ação, devido ao grande número de possibilidades. Esse trabalho utiliza uma combinação de derivações teóricas e resultados experimentais para recomendar o melhor conjunto de parâmetros para satisfazer uma demanda a ser roteada, levando em conta limitações reais dos algoritmos de processamento digital de sinais e dos transceptores. Os formatos de modulação utilizados foram 4-/8-/16-/64-QAM em taxas de símbolo variando de 8 a 32 GBd em passos de 2 GBd. Os resultados mostram que, quanto maior a granularidade de taxas de código implementadas pelo codificador/decodificador, maior a capacidade de redução da banda ocupada. Além disso, observa-se que os pontos ótimos de operação exi- gem cabeçalhos de FEC que variam de quase 0 até 145%, uma importante diretriz para o desenvolvimento de novos transceptores flexíveisAbstract: Future coherent optical transceivers will be able to adjust several parameters of the trans- mitted signal (modulation format, symbol rate, coding rate and number of subcarriers) according to optical link conditions so as to use the network as efficiently as possible. The greater the flexibility of the transceiver, the more complex the task of finding the optimal set of parameters for each situation, due to the large number of possibilities. This work uses a combination of theoretical derivations and experimental results to recommend the best set of parameters to satisfy a demand to be routed, accounting for limitations of digital signal processing algorithms and transceivers. The modulation formats used were 4-/8-/16-/64-QAM at symbol rates ranging from 8 to 32 GBd in 2-GBd steps. The results show that the higher the code rate granularity implemented by the encoder/decoder, the greater the bandwidth reduction capacity. In addition, it is noted that the optimal points require FEC overheads ranging from almost 0 to 145%, an important guideline for the development of future flexible transceiversMestradoTelecomunicações e TelemáticaMestre em Engenharia Elétric

On the Impact of Optimal Modulation and FEC Overhead on Future Optical Networks

The potential of optimum selection of modulation and forward error correction (FEC) overhead (OH) in future wavelength-routed nonlinear optical mesh networks is studied from an information theory perspective. Different network topologies are studied as well as both ideal soft-decision (SD) and hard-decision (HD) FEC based on demap-and-decode (bit wise) receivers. When compared to the somewhat standard assumption of QPSK with 7% OH, the results show large gains in network throughput. When compared to SD-FEC, HD-FEC is shown to cause network throughput losses of 12%, 15%, and 20% for a national, continental, and transcontinental topology, respectively. Furthermore, it is shown that for national and continental network topologies, using one modulation format and only two OHs achieves at least 75% of the maximum theoretical throughput. This is in contrast with the infinite number of OHs required in the ideal case. The obtained optimal OHs are between 5% and 80%, highlighting the advantage of using FEC with high OHs

On the impact of optimal modulation and FEC overhead on future optical networks

Transceivers employing square PM-QAM with up to two FEC overheads are optimized based on the SNR distribution. For NSFNET two FEC overheads with PM-16QAM give an 82% throughput increase compared with PM-QPSK with 7% overhead