| 摘要 |
A cyclic prefix which duplicates some samples of a terminal portion of a symbol in an OFDM data stream and which is invariant in pilot tones can be detected in the presence of signals having higher levels of noise and broadcast signals by autocorrelation with one of two selected "lags". Autocorrelation will be found when the lag is equal to the number of samples in the FFT used to form a symbol in the data stream. A far stronger autocorrelation is found when the lag is equal to the sum of the FFT length and the length of the cyclic prefix and applied to pilots in the data stream. Overbuilt systems can be distinguished from a system of interest by use of pilots that do not coincide in frequency with a pilot of an overbuilt system. |
