黑料福利网

Optical fibres nowadays play a vital role in the technological infrastructure underpinning the Internet. However, current optical fibre systems are showing clear signs of throughput saturation, due to the exhaustion of the available optical bandwidth. Next-generation optical transceivers are required to accommodate more data per second within the same spectral window. Therefore, high spectral-efficiency (SE) optical transceivers is today a key research area in optical fibre communications.

The main limitation to increasing SE of optical transmission is currently imposed by fibre nonlinear effects, which result in a signal distortion that grows with the transmitted power. As such, current state-of-the-art optical communication systems can be operated up to a maximum SE. Over the last years, research has endeavored to push upward the SEs through the application of digital communication techniques such as multi-dimensional modulation formats, digital nonlinearity compensation, and, more recently, constellation shaping.

Constellation shaping is a technique mostly studied in linear channels through which the transmitted symbols are cleverly designed, i.e. the way data is encoded into waveforms is optimized. The corresponding shaping algorithms work on blocks, and to be most efficient in terms of net data rate, shaping sequences should have a very long block length. This comes however, at the cost of these algorithms being more complex. Certain algorithms, e.g., sphere shaping, are capable of achieving higher gains than other algorithms at much lower block lengths, and thus at reduced complexity. For the optical channel, this reduction in block length comes with another advantage: It has been shown that long shaping blocklengths have a negative impact on tolerance against fiber nonlinearities, while the opposite is true for short blocklengths. As a result of this effect, a tradeoff exists between rate loss (~linear gain) and tolerance against fiber nonlinearities (~nonlinear gain).

The goal of this project is to go beyond linear-channel-optimal constellation shaping and introduce more general shaping approaches which are tailored to the nonlinear optical fibre channel. To this end, we first considered enumerative sphere shaping (ESS), which is optimal for the linear Gaussian channel, for the nonlinear optical channel. Then we developed optical communication-tailored variants of ESS, i.e., kurtosis-limited ESS (K-ESS) and energy-band-limited ESS (B-ESS).

This project is a collaboration between the 黑料福利网 and Fujitsu Network Communications.