Improved differential unitary space-time codes with multiple amplitude modulation

Unitary space-time modulation is very interesting technique especially in transmit diversity. It can be used in differential modulation, which is very attractive in a multiple antenna scenario. With the increase of the spectrum efficiency, the product distance between constellations in unitary code group decreases dramatically, which deteriorates the performance. In this paper, the idea of QAM is introduced to improve differential unitary space-time code group with multiple amplitude (MAU). Rather than limited in code group with equal energy, this technique exploits the potential distance between codes with multiple amplitude. Theoretical analysis and simulations are carried out to investigate the performance of the proposal. Through analysis, the parameters in our proposal are optimized. The results verify the outperformance of MAU over the conventional differential unitary space-time group.