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Abstract

A method and apparatus are disclosed for achieving symbol (frame) synchronization of digital data in an OFDM channel such as an OFDM/FM radio link. The method and apparatus are suitable for use in a pure ALOHA environment because synchronization is achieved on a frame-by-frame basis. The required bandwidth overhead is less than 10%. The bit-error-rate performance achievable with this technique is within 1.5 dB of the performance assuming ideal synchronization. The method and apparatus provide a three-stage synchronization process. First the onset of an ODFM frame is detected. Second, coarse synchronization is achieved by sampling the received signal, and measuring the correlation between the received signal and a reference signal. Coarse synchronization provides synchronization to within .+-.1/2 sample period. The correlation is preferably carried out in the frequency domain after carrying out a Fast Fourier Transform on the sampled signal data. Third, synchronization is achieved by calculating the time-shift between the coarse synchronization point and the actual synchronization point and using the calculated time shift to determine the phase correction to apply to each data carrying sub-carrier. Finally the transmitted data is recovered by decoding the information obtained about the phase and amplitude of the data-carrying sub-carriers.

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First Claim