Hybrid analog-digital coding scheme based on parallel concatenation of linear random projections and LDGM codes

This paper aims at designing a hybrid analog-digital coding scheme that can be applied for rate adaption in a broad dynamic range of channel conditions. The hybrid scheme is constructed by generating most of the output symbols from standard linear combinations of the input bits, as in Rate Compatible Modulation (RCM), and a few of them using a Low Density Generator Matrix (LDGM) code. RCM is able to achieve smooth rate adaption, but its performance is far from the Shannon theoretical limits. The few coded bits proceeding from the LDGM code are able to substantially reduce the number of uncorrected errors in the RCM scheme, substantially improving the system performance.