Physical Limits to the Capacity of Wide-band Gaussian MIMO Channels

In this letter a physical limit to the information capacity of a multiple-input multiple-output (MIMO) Gaussian channel is presented exploiting the theory of non-redundant sampling of scattered fields. For a MIMO narrow-band system of arbitrarily large spatial extension, the information capacity limit is the same as the one of a single-input single-output (SISO) ultra-wide band (UWB) system. For MIMO systems of finite size, transmitting over a range of frequencies, space and frequency diversities can be optimally combined by allocating the signal power uniformly across space, and increasing linearly across frequency.