System and method for robust ofdm synchronization
AssigneeHughes Network Systems, LLC
InventorsDonglei Fan, Bassel Beidas
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Abstract
Disclosed methods include transmitting an OFDM signal including a succession of frames spaced apart by a set of training symbols that are symmetric in time and each formed by a plurality of even-frequency sub-carriers, spaced by odd frequency zeros. The OFDM signal is received and sampled and timing metrics are determined. Local maximums, or peaks of the timing metrics are detected, and from the peaks a coarse time offset is determined. A correlation metric, at sample indexes within a region determined by the coarse time offset, is applied and, based on a peak, an estimated time offset is generated. A correlation metric of the estimated time offset is determined and, based on the correlation metric, an estimated frequency offset is generated.
Claims21
A system for synchronizing a receiving of an orthogonal frequency division multiplexing (OFDM), the system comprising:
- an input data interface configured to receive a sequence signal samples and associated indexes;
- a processing unit;
- and
- a memory configured to a store a plurality of instructions that when read and executed by the processing unit cause the processing unit to:
- detect a timing metric at each of a succession of the indexes and determine, as a first peak, an index at which the timing metric is at a local maximum,
- detect the timing metric at indexes within a first region of the indexes and determine, as a second peak, an index at which the timing metric is at another local maximum, the first region being based in part on the first peak,
- select a coarse offset as the smaller of the first peak and the second peak,
- detect a correlation metric at each of a plurality of indexes within a second region of the indexes, the second region being based at least in part on the coarse offset,
- generate, as an estimated time offset, an index at which the detected correlation metric is at a local maximum, and
- apply a synchronization correction to a recovery of symbols from the signal samples, based at least in part on the estimated time offset.
A method for communicating a robust synchronization orthogonal frequency division multiplexing (OFDM) frame, comprising:
- generating an OFDM symbol frame;
- adding a training symbol prefix to the OFDM symbol frame, the training symbol prefix including a plurality of training symbols, each of the training symbols including N sub-symbol fields, wherein
- a first N/2 of the sub-symbol fields are set at a zero value,
- a second of the N/2 sub-symbol fields carry corresponding symbols of a N/2 sub-symbol pseudo random training symbol, and
- a first half of the pseudo random training symbol is symmetrical to a second half of the pseudo random training symbol;
- and
- transmitting the training symbol prefix as a multi-carrier transmission within an OFDM N-sub-carrier transmission, wherein
- the multi-carrier prefix transmission carries signal power on a first N/2 of the N sub-carriers and suppresses signal power on a second N/2 of the sub-carriers, the first N/2 sub-carriers and the second N/2 sub-carriers being aligned at alternating positions in the frequency domain.
A method for synchronizing a receiving of an orthogonal frequency division multiplexing (OFDM) communication, comprising:
- receiving a sequence of signal samples and associated indexes;
- detecting a timing metric at each of a succession of the indexes and determining, as a first peak, an index at which the timing metric is at a local maximum;
- detecting the timing metric at indexes within a first region of the indexes and determining, as a second peak, an index at which the timing metric is at another local maximum, the first region being based in part on the first peak;
- selecting a coarse offset as the smaller of the first peak and the second peak;
- detecting a correlation metric at a plurality of indexes within a second region of the indexes, the second region being based at least in part on the coarse offset;
- determining, as an estimated time offset, an index at which the correlation metric is a local maximum;
- and
- applying a synchronization correction, based at least in part on the estimated time offset.
Dependencies are inferred from the claim text.