Coupling Data Transmission

We consider a signaling format where information is modulated via a superposition of independent data streams. Each data stream is formed by error-correction encoding, constellation mapping, replication and permutation of symbols, and application of signature sequences. The relations between data bits and the modulation symbols transmitted over the channel can be represented in the form of a sparse graph. In case when the modulated data streams are transmitted with time offsets the receiver observes spatial coupling of the individual graph representations into a graph chain enabling efficient demodulation/decoding. We prove that a two-stage demodulation/decoding method, in which iterative demodulation based on symbol estimation and interference cancellation is followed by parallel error correction decoding, achieves capacity on the additive white Gaussian noise (AWGN) channel asymptotically. We compare the performance of the two-stage receiver to a receiver which utilizes hard feedback between the errorcorrection encoders and the iterative demodulator.