Improving spectral efficiency in broadcasting employing hierarchical QAM

Hierarchical Quadrature Amplitude Modulation is considered to enhance the aggregate Spectral Efficiency (SE) in broadcast systems operating under fading conditions. Closed-form and series representations for SE are derived assuming that the user terminals are uniformly distributed as to their distance from the Base Station and employ Maximum Likelihood detection. The modulation parameters are adjusted to optimize system performance. Numerical results and Monte Carlo simulations show that by adjusting the constellation diagram of the Hierarchical Modulation scheme, the SE performance may be significantly enhanced, especially under fading conditions.