Physical Realizations of Multidimensional Voronoi Constellations in Optical Communication Systems

Abstract

Multidimensional geometric shaping has been shown to outperform uniform quadrature amplitude modulation (QAM) in optical communication systems but the complexity of symbol decision and bit mapping can often be significant as dimensionality increases. In this paper, a low-complexity geometric shaping method based on multidimensional lattices is investigated both in experiments and simulations. The modulation formats designed based on this method are called Voronoi constellations (VCs) and we study them in 8, 16, and 32 dimensions. We obtain transmission reach improvements of up to 22 and 70% for VCs compared to 4QAM and 16QAM, respectively, in nonlinear long-haul fiber transmission. Moreover, we compare different physical realizations of multidimensional VCs over wavelengths, polarizations, and time slots in both the Gaussian and nonlinear fiber channels. We demonstrate that different physical realizations perform similarly in the fiber-optic back-to-back channel. However, in long-haul transmission systems, spreading the dimensions over time slots can increase the transmission reach up to 4% compared to wavelengths and polarizations. Furthermore, the mutual information and generalized mutual information are estimated and compared to QAM formats at the same spectral efficiencies.

Infectious Hospital Area, the First Affiliated Hospital of University of Science and Technology of China, Hefei, China

“…To overcome the bottleneck of SE and complexity limitation for MD formats, MD Voronoi constellation (VC) as an advanced geometric shaping method, offers high shaping gain and low complexity at high SE by eliminating the need for look-up tables to store constellation points [7] . VCs have been investigated both in additive white Gaussian noise (AWGN) channel [8], [9] and optical transmission experiments across multiple physical dimensions (wavelength, polarization and time slots) of SMF [10], [11] . By combining MD VC with multi-level coding (MLC), the performance of optical transmission system can be further enhanced [12] .…”