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 for receiving said OFDM signal and producing a sequence of samples therefrom;
an initial time and frequency offset estimator coupled to said synchronization sampler for producing from said sequence of samples a time offset estimate and an initial frequency offset estimate, said time offset estimate being supplied to said receiver; and
a frequency offset estimate refinement unit coupled to said sampler and said estimator, said frequency offset estimate refinement unit receiving a reference multitone synchronization signal in addition to said sequence of samples and said initial frequency offset estimate and producing therefrom an improved frequency offset which is supplied to said receiver.
5 Assignments
0 Petitions
Accused Products
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.
-
Citations
12 Claims
-
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 for receiving said OFDM signal and producing a sequence of samples therefrom; an initial time and frequency offset estimator coupled to said synchronization sampler for producing from said sequence of samples a time offset estimate and an initial frequency offset estimate, said time offset estimate being supplied to said receiver; and a frequency offset estimate refinement unit coupled to said sampler and said estimator, said frequency offset estimate refinement unit receiving a reference multitone synchronization signal in addition to said sequence of samples and said initial frequency offset estimate and producing therefrom an improved frequency offset which is supplied to said receiver. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
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:
-
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 produce a time offset estimate and an initial frequency offset estimate; performing a frequency offset refinement process on the initial frequency offset estimate to produce an improved frequency offset, said refinement process using said samples, said multitone synchronization signal, and said initial frequency offset estimate as inputs to said frequency offset refinement process; and supplying the improved frequency offset to said receiver and said time offset estimate for use in processing said received signal. - View Dependent Claims (9)
-
-
10. An orthogonal frequency division multiplexing (OFDM) communication device, comprising:
-
means for receiving an OFDM signal containing a multitone synchronization signal; means for receiving said OFDM signal and producing a sequence of samples therefrom; means for producing, from said sequence of samples, a time offset estimate and an initial frequency offset estimate, said time offset estimate being supplied to said means for receiving the OFDM signal, said means for producing the time offset estimate and the initial frequency offset estimate being-coupled to said means for producing the sequence of samples; and means for producing, from i) a received reference multitone synchronization signal;
ii) said sequence of samples and iii) said initial frequency offset estimate, an improved frequency offset, said means for producing an improved frequency offset being coupled to said means for producing the sequence of samples and said means for producing the time offset estimate and the initial frequency offset estimate. - View Dependent Claims (11, 12)
-
Specification