Abstract: A speed estimation method is provided, detecting relative speed of a transmitter and a receiver transmitting symbols by OFDM sub-carriers through a channel. First, a first correlation table is established, indicating conceptual relationships between the relative speed and the channel characteristic based on Doppler shift theory. Thereafter, channel characteristic caused by movement is estimated. The first correlation table is checked to determine the relative speed according to the estimated channel characteristic. The channel characteristic is a correlation value generated by auto-correlating received symbols with a delay factor. The first correlation table is established with a first delay factor, associating correlation values to a first plurality of presumed shift frequencies in view of the first delay factor. The first presumed shift frequencies scale from zero to a first maximum value, and the relative speed is proportional to the shift frequencies.