Blind timing synchronization and low complexity channel estimation in ACO-OFDM systems
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.
1. A wireless transmit/receive unit (WTRU), configured at least in part to:
receive an asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) signal, the ACO-OFDM signal including one or more ACO-OFDM symbols and the ACO-OFDM signal being generated absent either a pilot or a training sequence; and
determine a correlation between a first block of N/2 samples of the one or more ACO-OFDM symbols and a second block of N/2 samples of the one or more ACO-OFDM symbols, the first block of N/2 samples and the second block of N/2 samples representing a first block set of N/2 samples, N being an integer representing a number of samples of the one or more ACO-OFDM symbols.
2. The WTRU of claim 1 , wherein the correlation determines that the first block set of N/2 samples includes an estimated boundary of the one or more ACO-OFDM symbols upon a detection of a minimum between the first block of N/2 samples and the second block of N/2 samples, the estimated boundary of the one or more ACO-OFDM symbols providing the WTRU with timing synchronization information.
3. The WTRU of claim 1 , wherein the first block set of N/2 samples and one or more respective additional block sets of N/2 samples are respectively represented as block set (X), where X is an integer, and X=1 represents the first block set of N/2 samples, and subsequent values of X are indexed respectively to the one or more additional block sets of N/2 samples, and the WTRU is further configured to:
determine a correlation for the respective one or more additional block sets of N/2 samples; and
determine that block set (X) includes an estimated ACO-OFDM symbol boundary of the one or more ACO-OFDM symbols upon a detection of a positive difference between a determined correlation for block set (X) and a determined correlation for block set (X+1), the estimated ACO-OFDM symbol boundary of the one or more ACO-OFDM symbols providing the WTRU with timing synchronization information.
4. The WTRU of claim 3 , wherein the WTRU is further configured to:
determine a value D, the value D representing a delay between the estimated ACO-OFDM symbol boundary and an actual ACO-OFDM symbol boundary for which a probability of the delay is within a predetermined interval; and
advance the estimated ACO-OFDM symbol boundary by D samples.
5. The WTRU of claim 3 , wherein the one or more ACO-OFDM symbols had been respectively extended by a number of dummy samples, the number of dummy samples reducing a difference between an expected ACO-OFDM symbol timing location and an increase in the determined correlations.
6. The WTRU of claim 5 , wherein the WTRU is further configured to remove the number of dummy samples in at least one of the one or more ACO-OFDM symbols based at least in part on the estimated ACO-OFDM symbol boundary.
7. The WTRU of claim 3 , wherein the WTRU is further configured to adjust the estimated ACO-OFDM symbol boundary based on a phase slope determined by a comparison of consecutive ACO-OFDM symbols of the one or more ACO-OFDM symbols.