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In the conventional pilot-symbol-aided channel estimation for the MIMO-OFDM system, the pilots should be orthogonal in frequency, time, code, or spatial domain to mitigate the inter- antenna interference. In the frequency domain multiplexed (FDMed) pattern, the training pilots transmitted from different antennas conventionally occupy different sub-carriers exclusively within the same OFDM symbol duration. However, this method dramatically increases the pilot overhead as the number of the transmit antennas increases. In this paper a joint pilot-aided and blind decision-directed channel estimation (PA-DDCE) scheme is proposed to achieve a good tradeoff between the pilots overhead and the system performance. The proposed scheme utilizes the initial estimated channel obtained by the conventional channel estimation to detect the transmitted data symbol in the middle sub-carrier between any two adjacent pilot sub-carriers. Then these symbols are regarded as the "extra pilot symbols" and are applied to estimate the channel on the whole frequency band. From our simulation results the proposed PA-DDCE scheme can outperform the conventional channel estimation significantly in both the BER and the throughput performances.