Experimental Verification of Multilevel Coded Modulation for 16-Ary Constellations

We present an experimental demonstration of multilevel coded modulation (MLCM) for 16-ary constellations. Performance of MLCM coding is compared for two 16 QAM constellations: 1) a phase noise optimized and 2) a square constellation. We quantify experimentally the phase noise regimes where the optimized constellation outperforms square 16 QAM. While MLCM coding is designed for one linewidth at a given symbol time, for the same overhead we show it outperforms uniform rate coding over a wide range of linewidths. The MLCM coding strategy minimizes block error rate under some simplifying assumptions. We show that under realistic conditions, the MLCM also gives good post forward error correction and quantify the advantage over uniform rate coding experimentally.