Performance Prediction of Nonbinary Forward Error Correction in Optical Transmission Experiments

In this paper, we compare different metrics to predict the error rate of optical systems based on nonbinary forward error correction (FEC). It is shown that the correct metric to predict the performance of coded modulation based on nonbinary FEC is the mutual information. The accuracy of the prediction is verified in both simulations and optical transmission experiments over recirculating loops. Besides giving details on how to implement the performance prediction, we also show some pitfalls when using hard decision decoding.