All digital tracking loop for OFDM symbol timing

A fine symbol timing tracking loop combined with sampling rate conversion for orthogonal frequency division multiplexing (OFDM) software receiver is investigated in this paper. Generally, symbol timing for OFDM receiver can be achieved by adjusting ADC´s sampling frequency and phase with a voltage controlled oscillator. On a software radio platform, intermediate frequency OFDM waveform is digitized with a free running clock. So, the symbol timing method of OFDM receiver for software radio is different from that of generally implemented receivers. To implement such an OFDM receiver, an interpolation loop is used to realize sampling rate to symbol rate conversion. Simultaneously, the residual coarse timing error and the sampling frequency error can be tracked by a NCO controlled loop. According to the proposed loop structure, simulation results prove it is quite effective.