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Orthogonal frequency division multiplexing (OFDM) can be used with a multiple-input multiple-output (MIMO) system to improve communication quality and capacity. Pilot-symbol-aided or decision-directed channel estimation must be used to track channel variations in MIMO-OFDM systems. While pilot symbols facilitate channel estimation, they reduce the transmit energy for data symbols under a fixed total transmit power constraint. We analyze the effects of pilot-symbol-aided channel estimation on the lower bound of the capacity and derive the optimal pilot-to-data power ratio (PDPR) in MIMO-OFDM systems with three different types of pilot patterns: independent, scattered, and orthogonal. The result implies that implementing the optimal PDPR in an actual MIMO-OFDM system should prove relatively straightforward, since there is a surprisingly broad range of PDPR values over which near optimal capacity is achieved.