说明：  The model is built upon the assumption that the probabil- ity distribution of available destinations among the buered frames at the Base Station (BS) is approximately the same as the probability distribution of the trac arriving to the BS, this is, the amount of trac directed to each MN with respect to the total trac load. This assumption leads to a simple, but accurate, queueing model for Multi- user MIMO systems that accounts for the impact of a nite number of active MNs in non-saturated conditions. The model is easily applicable to any Multi-user MIMO scenario given that the probability density function of the post-processing SINR (Signal to Interference and Noise Ratio) for each MN is known.