A wireless transmit/receive unit (WTRU) that may receive an asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) signal is disclosed. The ACO-OFDM signal may include an ACO-OFDM symbol and the ACO-OFDM signal may be generated with or without a pilot or training data. Where the ACO-OFDM signal may not include a pilot or training data, the WTRU may determine a correlation minimum between a first part of N samples of the ACO-OFDM symbol and a second part of N samples of the ACO-OFDM symbol. The correlation minimum may indicate an estimated boundary of the ACO-OFDM symbol which may provide the WTRU with timing synchronization information. Where the ACO-OFDM signal may include one or more ACO-OFDM pilot symbols on one or more pilot subcarriers, the WTRU may interpret an amount of training data included in the one or more ACO-OFDM pilot symbols that may provide information for channel estimation.