Making hierarchical modulation more flexible

Abstract

In a broadcast system using the hierarchical modulation, the system delivers several streams with different waveforms and required Signal-to-Noise Ratio (SNR), typically SD- TV and HD-TV. At the application layer, each stream is delivered with a particular rate. The physical layer must be defined in order to optimize the protection of each stream with respect to the double constraints of both the data rates and the SNR thresholds. We show in this paper that a standard like DVB-SH is not always well adapted to meet these system constraints in operational typical cases. After exposing the current limitations of a classical hierarchical modulation approach, we present two possible adaptations to address these operational requirements and offer more flexibility in hierarchical modulation design.