On the difficulty of bit-interleaved coded modulation for differentially encoded transmission over fading channels

The application of bit-interleaved coded modulation (BICM) in combination with differential encoding and non-coherent reception over flat fading channels is assessed. Since the labeling plays a central role for BICM we propose a suitable definition of Gray labeling for differentially encoded transmission. We show that for multiple symbol detection such a Gray labeling does not exist. Finally, we illustrate the consequences on the capacity by comparing BICM and an optimum coded modulation scheme.