Method and apparatus for time and frequency synchronization of OFDM communication systems
First Claim
1. An orthogonal frequency division multiplexing (OFDM) communication device, comprising:
- an OFDM receiver for receiving an OFDM signal containing a multitone synchronization signal;
a synchronization interval sampler coupled to said receiver;
an initial time and frequency offset estimator connected to said sampler and said receiver; and
a frequency offset estimate refinement unit connected to said receiver, said sampler and said estimator, wherein a reference multitone synchronization signal is used by said estimator and said refinement device in calculating a time offset and a frequency offset of said multitone synchronization signal, said receiver utilizing said time offset and said frequency offset to synchronize with said received OFDM signal.
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Abstract
A method and apparatus for joint time and frequency synchronization for orthogonal frequency division multiplexing (OFDM) systems. A multitone pilot signal is sent in a designated OFDM symbol period. The receiver synchronizes to the pilot signal in a two-stage procedure. The first stage estimates the frequency offset coarsely with a frequency-domain correlation method and estimates the time offset with smoothed time-domain correlation. In a multipath channel, the smoothed time offset estimate is used to locate a cyclic prefix interval which captures the maximum total signal energy. The second stage improves the frequency estimate with a computationally efficient numerical optimization method.
25 Citations
12 Claims
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1. An orthogonal frequency division multiplexing (OFDM) communication device, comprising:
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an OFDM receiver for receiving an OFDM signal containing a multitone synchronization signal;
a synchronization interval sampler coupled to said receiver;
an initial time and frequency offset estimator connected to said sampler and said receiver; and
a frequency offset estimate refinement unit connected to said receiver, said sampler and said estimator, wherein a reference multitone synchronization signal is used by said estimator and said refinement device in calculating a time offset and a frequency offset of said multitone synchronization signal, said receiver utilizing said time offset and said frequency offset to synchronize with said received OFDM signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of synchronizing an orthogonal frequency division multiplexing (OFDM) receiver with a received OFDM signal comprising a multitone synchronization signal, comprising the steps of:
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obtaining a coarse time offset estimate of said received signal;
sampling said received signal in a selected time interval to derive samples of said multitone synchronization signal;
analyzing said samples with respect to a reference multitone synchronization signal to obtain, for each sample analyzed, a time offset, a frequency offset, and a signal energy;
selecting a one of said analyzed samples with the greatest signal energy to yield a selected time offset estimate and a selected frequency offset estimate for use by said receiver in synchronizing with said received OFDM signal. - View Dependent Claims (9)
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10. A method of carrying out OFDM communications comprising:
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receiving an OFDM signal including within it a multitone synchronization signal;
locating said synchronization signal within said OFDM signal;
determining a time offset value of said synchronization signal;
determining an initial frequency offset value of said synchronization signal; and
recursively refining said frequency offset estimate to yield a selected pair of time and frequency offset values to be used by said OFDM receiver. - View Dependent Claims (11, 12)
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Specification