Transmission mode/guard length detection circuit and method therefor
A transmission mode/guard length detection circuit that uses the Orthogonal Frequency Division Multiplexing method, in which: a difference between a reference wave having a constant period 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 and the peak value interval is calculated as a shift amount, and the shift amount is integrated for a symbol and is output, and the result of the integration for a predetermined symbol is changed on the basis of the shift amount.
1. 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.
2. The transmission mode/guard length detection circuit for a radio device according to claim 1 , wherein:
the maximum value weighting circuit includes a table having a weighting coefficient corresponding to the shift amount, multiplies the weighting coefficient by the output of the maximum value integral circuit, and outputs a resultant value.
3. The transmission mode/guard length detection circuit for a radio device according to claim 1 , further comprising at a stage subsequent to the maximum value weighting circuit:
a maximum value comparison circuit comparing the output of the maximum value weighting circuit with a predetermined threshold value, and determining a combination of the transmission mode length and the guard length on the basis of a comparison result.
4. A transmission mode/guard length detection method for a radio device using the Orthogonal Frequency Division Multiplexing method, comprising:
a one-symbol delay process in which a received principal wave including a guard interval equal to an end portion of a symbol is delayed by real data of the symbol;
a guard correlation process in which a correlation between the principal wave and an output of the one-symbol delay process is calculated;
a moving average process in which a moving average of the outputs of the guard correlation process for predetermined symbols is taken;
a maximum value detection process in which a peak value of the output of the moving average process for each of the symbols is detected;
a maximum value integral process in which the outputs of the maximum value detection process for predetermined symbols are integrated;
a guard maximum position shift amount integral process in which a difference between a reference wave having a constant period and a peak value interval of the output of the maximum value detection process is calculated, 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 process of changing the output of the maximum value integral process on the basis of the shift amount.
5. The transmission mode/guard length detection method for a radio device according to claim 4 , wherein:
in the maximum value weighting process, a table having a weighting coefficient corresponding to the shift amount is used, the weighting coefficient is multiplied by the output of the maximum value integral process, and a resultant value is output.
6. The transmission mode/guard length detection method for a radio device according to claim 4 , further comprising at a stage subsequent to the maximum value weighting process:
a maximum value comparison process in which the output of the maximum value weighting process is compared with a predetermined threshold value, and a combination of the transmission mode length and the guard length is determined on the basis of a comparison result.