An OFDM modem is presented that uses a pilot sub-carrier signal structure for channel estimation to reduce link latency of the modem, or alternatively, a pseudo-random number sequence inserted into the OFDM signal for later detection for channel estimation. The OFDM signal includes multiple symbols, each symbol having a plurality of closely-spaced, orthogonal data sub-carrier signals carrying data. In some implementations, one or more pilot sub-carrier signals are inserted with the data sub-carrier signals. Each pilot sub-carrier signal is modulated with a predetermined pilot modulation scheme. Each pilot sub-carrier signal is placed at a different sub-carrier signal location for each successive symbol duration of the OFDM signal to form a sliding pilot sub-carrier signal.