Analog Digital Belief Propagation and its application to multi stage decoding systems

Next generation wireless systems will need to have higher spectral efficiency as the expected traffic volumes per unit bandwidth and dimension will inevitably grow. As a consequence, it is necessary to design coding schemes with performances close to the theoretical limits, having at the same time high flexibility and low complexity requirements at the receiver. In this paper we start by pointing out some of the main drawbacks of the Bit Interleaved Code Modulation (BICM) technique which is the state of the art adopted in several standards and then propose some lower complexity alternatives. These low complexity alternatives are obtained by applying the recently introduced Analog Digital Belief Propagation (ADBP) algorithm to a two stage encoding scheme. First we show that the loss in performance can be kept quite small by using a hard decoder in all stages of a multistage decoder (MSD) except the two lowest levels with a reasonable flexibility of choosing the code rates. Then we apply the ADBP algorithm to further reduce the decoding complexity of the soft decoded stages