Improvements to OFDM symbol synchronisation

摘要

Improved synchronization of OFDM signals is achieved. A controlled oscillator (8) provides clock pulses to derive complex samples of an input signal which are applied both to a fast Fourier transform (5) for data recovery and to a synchronization unit (9). The synchronization unit shown generates 22 the complex product XY* of the delayed input and the complex conjugate of that input, which product is applied to a high-pass filter 30 to suppress frequencies below the symbol frequency. The filter output is applied through a symbol comb filter 40 to an adaptive slicer 50 which determines the larger magnitude of the real and imaginary components of the signal. A pulse processor 60 generates a single pulse at the leading edge of the symbol pulse which is applied to a symbol counter 70. The symbol counter includes two count stages arranged to lock in quickly and yet be variable to accommodate different guard intervals in the OFDM signal.