Patent ID: 7782977

Claim:
An automatic gain control device in an orthogonal frequency division multiplexing system, comprising: a variable gain amplifier for controlling a gain of an input signal; an analog to digital converter for converting the input signal into a digital signal, and providing the digital signal to an energy calculator; the energy calculator for calculating an energy of the digital signal; a truncator for accumulating the calculated energies, finding an average thereof, and generating a Direct Current (DC) offset of the input signal; a subtracter for subtracting a predefined reference value from the DC offset, and outputting a signal; a pulse density modulation signal generator for processing the signal output by the subtracter to be a pulse density modulation signal; and a Resistor-Capacitor (RC) filter for feeding the value output by the pulse density modulation signal generator back to the variable gain amplifier so that the value output by the pulse density modulation signal generator may be used for an automatic gain control, wherein the predefined reference value includes a reference power generated based on a saturation to Root-Mean-Square (RMS) ratio for minimizing a bit error rate of the orthogonal frequency division multiplexing system.