Symbol synchronization for downhole OFDM telemetry

Enhanced symbol synchronization methods suitable for use in narrowband orthogonal frequency division multiplexed (OFDM) telemetry systems. In at least some embodiments, a logging while drilling (LWD) tool assembly communicates with the surface using low frequency electromagnetic (EM) signals. The telemetry transmitter employs OFDM modulation to fully exploit the narrow range of available bandwidth, resulting in signals that have relatively long frames. At the surface a receiver digitizes the receive signal and applies an enhanced symbol synchronization technique to identify frame boundaries before demodulation is attempted. The enhanced symbol synchronization technique employs a pulse train filter to clean up a cyclic prefix correlation signal that otherwise behaves badly in the narrowband regime. The improved timing information from the enhanced symbol synchronization significantly reduces the error rate in the demodulated signal.