On modeling antenna coupling for adaptive MIMO-OFDM systems

The influence of mutual coupling of antenna elements is usually not considered when dealing with MIMO (Multiple Input Multiple Output) communication systems. This is justifiable if mobile subscribers feature only one antenna and base station antenna elements are separated by a distance of several wavelengths. However, regarding pico-cell base stations that consist of multiple antenna elements, the coupling has to be taken into account due to the reduced antenna element spacing. In this paper, the influence of antenna coupling on adaptive MIMO-OFDM (Orthogonal Frequency Division Multiplex) systems is investigated in terms of the attainable signal-to-interference-plus-noise ratio (SINR). The mutual coupling of the antenna elements is calculated for different antenna models based on the ”infinitesimally thin” lambda/2 dipole and the Hertzian dipole. Additionally, a coupling model based on the isotropic radiator is considered. The different results for the SINR stemming from the antenna models when exploiting linear pre-equalization are presented. It is shown that using an isotropic radiator based model is not sufficient for describing the effect of mutual coupling for lambda/2 dipoles.