Structure-based decoding for hierarchically modulated, LDPC coded signals

In this paper, we present a structured LDPC decoding algorithm for hierarchical QAM modulation systems. Unlike the traditional hierarchical demodulation approaches which suffer from serious inter-layer interference (ILI), the proposed method exploits structure information of the secondary layer to mitigate the ILI impairment, thereby offers significant gains in reception performance. An achievable rate analysis is performed to calculate the theoretical limit of the basic layer in HM reception, which in certain cases is 8 dB better than the required SINR threshold for QAM detection with all Gaussian interference. The new algorithm has been implemented on a broadband in-band on-channel (IBOC) digital radio broadcasting system. Numerical results from both simulations and experiments are provided to quantify the performance advantages of the new algorithm against the DVB-T benchmark.