Layered Offset Hierarchical QAM Modulation for Intersymbol Interference Reduction

Layered offset hierarchical QAM modulation scheme is proposed to enhance the high priority stream error performance by reducing the intersymbol interference from the superimposed symbols of the low priority stream. The proposed scheme shifts the symbols of the two priority layers by half the symbol duration, whereas the detector performs multi-stage maximum-likelihood detection with interference cancellation. The simulations demonstrate the performance and design options offered by the proposed scheme compared to conventional hierarchical schemes where no time offset exists between the superimposed symbols.