On increasing spectral efficiency of frequency division multiple access using synchronized superposition-modulation

We investigate the use of synchronized superpositionmodulation for increasing spectral efficiency of frequency division multiple access systems such as the long-term evolution extension of UMTS. We present the basic concept and depict results for an arbitrary two-user scenario. In Addition, a method of optimizing constellations for multiple users is defined based on maximizing the sum-rate mutual-information. The optimization method is applied to a three-user scenario. Preliminary results motivate further research into means of implementing superpositionmodulation in FDMA systems.