An OFDM system with the decision-aided channel tracking technique for a long frame application is proposed. The OFDM system in wireless LAN applications assumes static channel response in a short frame and it is enough to use two long training symbols for channel estimation. We build a wireless surveillance system which may transmit data symbols in a seamless manner. The channel estimation with the symbol-by-symbol tracking is then required. We show that the proposed channel tracking method outperforms the channel estimation by only preamble in static and time-varying channels. The channel tracking module adds about 18% circuits to the whole system in our design.