Patent ID: 7539125

Claim:
A circuit for frequency offset estimation in frequency domain for a receiver of an orthogonal frequency division multiplexing (OFDM) system, wherein an input signal of the circuit is transmitted via 52 subcarriers of the OFDM system, the circuit comprising: a fast Fourier transformation module, for processing the input signal with fast Fourier transformation (FFT) to generate a first signal; a channel estimation module, coupled to the fast Fourier transformation module, for estimating a channel estimation coefficient of a k-th subcarrier of the 52 subcarriers, wherein the index k ranges from 1 to 52 and represents the order of subcarrier; an equalizer, coupled to the fast Fourier transformation module and the channel estimation module, for compensating the first signal for channel distortion with the channel estimation coefficient to generate a second signal; a square circuit, coupled to the channel estimation module, for calculating a square of an absolute value of the channel estimation coefficient of the k-th subcarrier; a multiplier, coupled to the equalizer and the square circuit, for multiplying the signal field of the second signal on the k-th subcarrier by its real part and the square of the absolute value of the channel estimation coefficient of the k-th subcarrier to generate a product value regarding the k-th subcarrier; an accumulator, coupled to the multiplier, for accumulating the product value regarding all the 52 subcarriers to generate an accumulation value; an ArTan module, coupled to the accumulator, for calculating a phase angle of the accumulation value; and a frequency offset error module, estimating a frequency offset error with at least one frequency offset estimation process based on a short preamble in time domain according to a ratio of the phase angle and a sampling period of the OFDM system.