In this paper we analyse the downlink performance of a rank adaptive multiple input multiple output (MIMO) system in a busty traffic cellular network. A LTE-Advanced system with multiple component carriers was selected as a study case. To highlight the advantage of using MIMO techniques, we used a single input multiple output (SIMO) system as a baseline for performance comparison. The gain mechanisms of the MIMO system over the SIMO system are investigated and their characteristic at different traffic load conditions are highlighted. The simulation results are used to verified our proposed model to predict the performance of the SIMO and MIMO systems in a bursty traffic network.