In this paper we analyze the link-to-system interface for MIMO-OFDM system level simulations and propose a computationally efficient method for calculation of the effective SINR. The accuracy of the proposed fast approximation of the effective SINR is evaluated both analytically with error bound estimation and by simulated BLER performance comparison. The system level simulations in typical 3GPP LTE downlink scenario show that the proposed model is capable of accurate estimation of receiver performance for MIMO-OFDM transmission and brings up to 74% reduction in CPU simulation time.