This paper studies non-integer power of two-ary quadrature amplitude modulation (QAM) for long-haul optical fiber transmission systems.Numerical simulations show that 12-QAM and 24-QAM provide intermediate solutions on reachable transmission distances among traditional M-QAM such as C8-QAM, 16-QAM, and 32-QAM.In addition, short block length probabilistic shaping of 24-QAM not only provides an intermediate solution with nonlinear tolerance, but also yields greater transmission distances than 16-QAM for the same information data rates.
