On enhancing hierarchical modulation

Hierarchical modulation offers an important coverage/throughput tradeoff for wireless communication, however it has received relatively little attention to date. Regular hierarchical modulation suffers from the interference between layers. It results in both achievable capacity decrease and bit- error rate increase. In this paper, an enhanced hierarchical modulation technique along with three optimization schemes, in which the enhancement-layer signal constellation is rotated, are presented and analyzed. The first optimization scheme is proposed to maximize the achievable spectral efficiency with rotating the enhancement-layer signal constellation. The second scheme is proposed to lower the demodulation symbol-error rate with maximizing the modulation efficiency and asymptotic modulation efficiency. The parameters, modulation efficiency and asymptotic modulation efficiency, are formulated for quantizing inter-layer interference. The last one is proposed to maximize RF power amplifier efficiency with reducing the peak-to-average- power ratio of modulated symbols. This perspective is especially important for multi-carrier communications. All proposed schemes are simple and efficient. They can help recover the performance loss of regular hierarchical modulation due to inter-layer interference with little complexity increase. Computer simulations are provided to support our conclusions.