Block oriented digital communication system and method
View Patent ↗A method and system for estimating a time shift required for symbol synchronization in a block oriented digital communication systems such as an orthogonal frequency division multiplexing (OFDM) or a discrete multi-tone (DMT) data transmission system. The method uses an N/d inverse discrete Fourier transform (IDFT), where N is a sample number and d is a decimation factor, or alternatively an N/(2d) inverse fast Fourier transform (IFFT) for a real received signal or an N/d IDFT for a complex received signal.
1. A method for estimating a time shift for synchronizing to a synch symbol, the method comprising:
sampling a received signal to produce a sequence of samples of the signal;
performing a transform on the sequence of samples of the signal to produce a sequence of N samples of a spectrum of the signal;
multiplying the samples of the spectrum of the signal by respective samples of a spectrum corresponding to the synch symbol to produce a sequence of correlation spectral samples;
selecting a contiguous subset of the correlation spectral samples;
shifting the selected subset by a number of samples so that an N/d point inverse transform of an output spectrum derived from the shifted subset is an approximation to a decimation by d of an inverse transform of the sequence of correlation spectral samples; and
estimating the time shift by detecting a position of a peak in the inverse transform of the output spectrum.
2. The method of claim 1 , wherein the transform comprises a discrete Fourier transform.
3. The method of claim 1 , wherein the spectrum corresponding to the synch symbol comprises a complex conjugate of a transform of the synch symbol.
4. The method of claim 1 , wherein the received signal comprises a real signal.
5. The method of claim 4 , wherein selecting the contiguous subset comprises multiplying the sequence of correlation spectral samples by a window of length N/(2d).
6. The method of claim 4 , wherein the output spectrum derived from the shifted subset comprises a conjugate symmetric spectrum formed from the shifted subset.
7. The method of claim 1 , wherein the received signal comprises a complex signal.
8. The method of claim 7 , wherein selecting the contiguous subset comprises multiplying the sequence of correlation spectral samples by a window of length N/(d).
9. The method of claim 7 , wherein the output spectrum derived from the shifted subset comprises the shifted subset.
10. The method of claim 1 , wherein the contiguous subset of the correlation spectral samples have a highest average power of the correlation spectral samples.
11. A communication system, comprising:
means for sampling a received signal to produce a sequence of samples of the signal;
means for performing a transform on the sequence of samples of the signal to produce a sequence of N samples of a spectrum of the signal;
means for multiplying the samples of the spectrum of the signal by respective samples of a spectrum corresponding to the synch symbol to produce a sequence of correlation spectral samples;
means for selecting a contiguous subset of the correlation spectral samples;
means for shifting the selected subset by a number of samples so that an N/d point inverse transform of an output spectrum derived from the shifted subset is an approximation to a decimation by d of an inverse transform of the sequence of correlation spectral samples; and
means for estimating the time shift by detecting a position of a peak in the inverse transform of the output spectrum.
12. The system of claim 11 , wherein the transform comprises a discrete Fourier transform.
13. The system of claim 11 , wherein the spectrum corresponding to the synch symbol comprises a complex conjugate of a transform of the synch symbol.
14. The system of claim 11 , wherein the received signal comprises a real signal.
15. The system of claim 14 , wherein selecting the contiguous subset comprises multiplying the sequence of correlation spectral samples by a window of length N/(2d).
16. The system of claim 14 , wherein the output spectrum derived from the shifted subset comprises a conjugate symmetric spectrum formed from the shifted subset.
17. The system of claim 11 , wherein the received signal comprises a complex signal.
18. The system of claim 17 , wherein selecting the contiguous subset comprises multiplying the sequence of correlation spectral samples by a window of length N/(d).
19. The system of claim 17 , wherein the output spectrum derived from the shifted subset comprises the shifted subset.
20. The system of claim 11 , wherein the contiguous subset of the correlation spectral samples have a highest average power of the correlation spectral samples.