Gaussian multiple access channel with compact antenna arrays

We report on our investigation of the capacity region of a Gaussian multiple access channel with two independent transmitters for the case where the receiver´s antenna spacing is very small (compared to the wavelength). In contrast to common belief, we find that a rectangular capacity region can be maintained even as the distance of the antennas approaches zero. Moreover, the size of the capacity region even increases as the antenna separation is reduced. Therefore, high-performance multiple access is perfectly possible in confined space situations such as in hand-held mobile devices using standard frequencies for mobile communications.