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Preamble and Pilot Symbol Design for Channel Estimation in OFDM

The presence of null subcarriers in orthogonal frequency division multiplexing system complicates the design of both training preamble for channel estimation and pilot symbols for pilot-aided channel estimation that minimize the mean square error (MSE) of estimates of frequency-selective channels. In this paper, we numerically find optimal preambles, casting the MSE minimization problem into a semidefinite programming problem. Then, based on the optimal preamble, we also design pilot symbols for pilot-aided channel estimation. A design example under the same setting as IEEE 802.11a is provided to verify the efficacy of our proposal.