An apparatus for detecting a guard interval length (type) of a transmission symbol
among the structure of an orthogonal frequency division multiplexing (OFDM) system
receiver, to ensure proper operation of a symbol start detector and a fast Fourier
transform (FFT) window position controller, is provided. This apparatus includes
an analog-to-digital converter (ADC) for converting a received OFDM signal into
digital complex samples, a symbol start position detector for detecting a symbol
start position with reference to information on a guard interval length among the
complex samples output by the ADC, a symbol start position difference detector
for detecting the difference between the symbol start position detected by the
symbol start position detector and a symbol start position delayed for a predetermined
symbol time, a guard interval length detector for comparing the symbol start position
difference detected by the symbol start position difference detector with a predetermined
guard interval decision reference value and detecting the length of the guard interval,
and an FFT window position controller for shifting the FFT window position using
the guard interval length detected by the guard interval length detector and the
symbol start information detected by the symbol start detector, to activate an
FFT at the shifted FFT window position. The lengths of various guard intervals
are automatically detected in the OFDM receiver, thus performing accurate FFT window recovery.
