MIMO systems with adaptive modulation

We investigate adaptive modulation (AM) schemes in multiple-input-multiple-output (MIMO) systems with various degrees of freedom (D.F.s), such as the subchannel BER, power and spectral efficiency (SE), to be adapted. The adaptation is considered as a nonlinear constrained nonlinear optimization problem in the spatial domain. We obtained both analytical and numerical solutions for uncoded continuous SE systems and showed that the average spectral efficiency (ASE) achieved is insensitive to the number of adaptable D.F.s and which D.F. is adapted. The discrete SE systems are shown to have some penalty compared with the continuous SE cases, but have similar insensitivity.