Tile-based MIMO OFDM systems: The impact of inaccurate channel state information

Advanced multiple-input multiple-output (MIMO) techniques frequently entail high computational complexity and large feedback overhead, which often prevents their full realization in practice. In order to alleviate this problem, resource bundling has been proposed. By applying the same precoding on a block (tile) of adjacent OFDM subcarriers, both the complexity of the system and the feedback overhead can be reduced significantly, at the cost of a slight performance degradation. In this paper, we consider the realistic situation where the available channel state information is noisy or inaccurate due to estimation errors or feedback delays. The robustness of the performance of a multi-user uplink system is studied for various tile sizes. We show that under channel uncertainty, optimal performance is no longer achieved with the smallest possible tile size. Thus, in this setting, tile-based processing achieves a performance gain, in addition to reducing complexity and overhead.