Patent ID: 7864888

Claim:
A transmission mode/guard length detection circuit for a radio device using the Orthogonal Frequency Division Multiplexing method, comprising: a one-symbol delay circuit delaying a received principal wave including a guard interval equal to an end portion of a symbol, by real data of the symbol; a guard correlation circuit calculating a correlation between the principal wave and an output of the one-symbol delay circuit; a moving average circuit taking a moving average of the outputs of the guard correlation circuit for predetermined symbols; a maximum value detection circuit detecting a peak value of the output of the moving average circuit for each of the symbols; a maximum value integral circuit integrating the outputs of the maximum value detection circuit for predetermined symbols; a guard maximum position shift amount integral circuit calculating a difference between a reference wave having a constant period and a peak value interval of the output of the maximum value detection circuit, said reference wave being generated on the basis of a transmission mode length that is a time period length of the predetermined symbol and a guard length that is a time period length of the guard interval, handling a resultant difference as a shift amount, integrating the shift amount for each of the symbols, and outputting a resultant value; and a maximum value weighting circuit changing the output of the maximum value integral circuit on the basis of the shift amount.