Patent ID: 8446970

Claim:
A receiver detects and recovers data from received Orthogonal Frequency Division Multiplexed (OFDM) symbols, the OFDM symbols including a plurality of sub-carrier symbols formed in the frequency domain and transformed into the time domain for transmission, the time domain OFDM symbols including a guard interval, the guard interval being one of a plurality of predetermined temporal lengths and formed by repeating time domain samples of the OFDM symbols from a useful part of the OFDM symbols for a first period corresponding to the guard interval, the receiver comprising: a demodulator to detect a signal representing the OFDM symbols, and to generate a sampled version of the OFDM symbols in the time domain, a guard detector to identify from the time domain samples of the OFDM symbols, useful samples of the OFDM symbols, a Fourier transform processor to receive the time domain version of the OFDM symbols and to perform a Fourier transform on the useful samples of the OFDM symbols to form a frequency domain version of the OFDM symbols, and a detector to recover data from data bearing sub-carriers of the OFDM symbols, wherein the guard detector includes: a correlator to correlate the time domain samples at a separation determined in accordance with the useful samples of the OFDM symbols (Tu), and for each of a plurality of possible guard intervals (Tg) combining the correlated time domain samples for a second period equal to the guard interval, for a plurality of consecutive OFDM symbols, to form a correlation output value for each of the plurality of possible guard intervals, and a guard interval identifier to receive an output from the correlator and to identify one of the guard intervals used for the received OFDM symbols from the correlation output value for each of the plurality of possible guard intervals, wherein the received OFDM symbols include signalling data indicating the guard interval of the received OFDM symbols, and a number of samples of the useful part of the OFDM symbols varies between a predetermined number of discrete values in accordance with a transmitter operating mode, wherein the detector recovers the signalling data from the OFDM symbols and provides the guard detector with an indication of the guard interval indicated by the signalling data, and wherein the guard interval identifier determines the guard interval from the correlation output value or the signalling data depending on whether the signalling data is available before the guard interval is determined from the correlation output value.