Determining whether a received signal is of OFDM construction

摘要

A method and apparatus for detecting the presence of a broadcast OFDM (Orthogonal Frequency Division Multiplex) signal in a received signal. The arrangement described utilises the property of OFDM symbols having highly correlated (guard interval, which is a copy of the tail portion of a data portion of the symbol by definition) and highly uncorrelated (rest of the symbol) portions. The arrangement described checks for correlation in the guard interval and lack of correlation outside the guard interval to identify whether or not a received signal is of OFDM construction. Sliding correlation is firstly performed to identify the position of any guard interval in a received symbol. Phase correction is then performed to achieve a phase corrected signal. The first and second correlations are performed. The first correlation is performed using the guard interval of the symbol with the corresponding tail portion of the symbol (which should be highly correlated if an OFDM signal has been received). The second correlation is performed on the data portion of the symbol and the data portion of a subsequent symbol (which should be of low correlation if an OFDM signal has been received). Whether an OFDM signal has been received or not is determined using the result of the first and second correlation with possible comparison to a threshold. The first correlation may result in a metric being determined of a count of the number of received correlating samples that lie in the negative complex plane. The second correlation may result in a metric being determined from the angular distribution of received correlating samples. The OFDM signal may be a DAB ensemble.