Apparatus and method for recovering frequency in an orthogonal frequency division multiplexing system

An apparatus for recovering a carrier frequency of a received signal using a predefined symbol in an orthogonal frequency division multiplexing (OFDM) system, the apparatus comprising:

• a maximum value detector for detecting at least three auto-correlation values and their corresponding offsets in descending order among auto-correlation values calculated within a specific frequency offset range between a received signal and a predefined symbol;
• and
• a frequency offset corrector for comparing a ratio of a first auto-correlation value to a second auto-correlation value with a first threshold, determining whether first and second frequency offsets corresponding to the first and second auto-correlation values are adjacent to each other if the ratio of the first and second auto-correlation values is less than the first threshold, and determining an initial carrier frequency offset using a difference between the first frequency offset and a frequency offset correction value determined according to system, if the first and second frequency offsets are adjacent to each other and a ratio of the second auto-correlation value and a third auto-correlation value is greater than a second threshold;
• wherein the first to third auto-correlation values represent the calculated auto-correlation values in descending order.

An apparatus for recovering a carrier frequency of a received signal using a predefined symbol in an orthogonal frequency division multiplexing (OFDM) system, the apparatus comprising:

• an auto-correlation level calculator for receiving an FFT output signal in a position of a predefined symbol and for calculating an auto-correlation value with a PN sequence;
• a maximum value detector for detecting at least three auto-correlation values and their corresponding offsets in descending order among auto-correlation values calculated within a specific frequency offset range between a received signal and a predefined symbol;
• and
• a frequency offset estimator for receiving a greatest maximum value (Max1) among the maximum values from the maximum value detector and for estimating a frequency offset for an Integer Frequency Offset (IFO);
• a frequency offset corrector for comparing a ratio of a first auto-correlation value to a second auto-correlation value with a first threshold, determining whether first and second frequency offsets corresponding to the first and second auto-correlation values are adjacent to each other if the ratio of the first and second auto-correlation values is less than the first threshold, and determining an initial carrier frequency offset using a difference between the first frequency offset and a frequency offset correction value determined according to system, if the first and second frequency offsets are adjacent to each other and a ratio of the second auto-correlation value and a third auto-correlation value is greater than a second threshold;
• wherein the first to third auto-correlation values represent the calculated auto-correlation values in descending order.