Methods and apparatus for synchronization of training sequences

1. A receiver for receiving a signal comprising a carrier modulated with a known training sequence comprising:

a frequency offset estimation unit for receiving the signal and obtaining an estimate of a carrier frequency offset from an autocorrelation signal obtained by autocorrelation of the part of the received signal containing a known training sequence;

a frequency offset compensation unit for compensating the received signal with the estimate of the frequency offset obtained from the frequency offset estimation unit to form a compensated received signal;

a time reference determining unit for obtaining a timing reference for the received signal by cross-correlation of the compensated received signal with a known training sequence; and

wherein the receiver is adapted to

obtain a timing reference obtained from the received signal by autocorrelation of the received signal,

compare the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence and the timing reference determined by autocorrelation of the received signal,

output a reset signal if the two timing references differ by more than a threshold value, and

otherwise output the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence.

2. The receiver according to claim 1 , wherein the frequency offset estimation unit comprises means for determining a phase shift in the autocorrelation signal of the received signal.

3. The receiver according to claim 1 , wherein the receiver comprises means to detect a characteristic curve indicative of a known training sequence in the phase of the autocorrelation signal.

4. The receiver according to claim 1 , wherein the receiver comprises means to detect a characteristic curve indicative of a known training sequence in the amplitude of the autocorrelation signal.

5. The receiver according to claim 2 , wherein the frequency offset estimation unit comprises means for determining the carrier frequency offset from the phase shift.

6. The receiver according to claim 1 , wherein the receiver comprises means to determine a sign of the carrier frequency offset (CFO) from the phase of the autocorrelation signal from a known sequence.

7. The receiver according to claim 6 , wherein the receiver has means for determining a phase shift in the autocorrelation signal from a further known sequence of the received signal.

8. The receiver according to claim 1 , wherein the time reference determining unit comprises means to determine a characteristic curve indicative of a known training sequence in the amplitude of the autocorrelation signal.

9. The receiver according to claim 1 , wherein the time reference determining unit comprises means to determine a characteristic curve indicative of a known training sequence in the phase of the autocorrelation signal.

10. The receiver according to claim 1 , wherein the time reference determining unit comprises means to determine a characteristic curve indicative of a known training sequence in the amplitude of the cross-correlation of the compensated received sequence with the known training sequence.

11. The receiver according to claim 1 wherein the time reference determining unit is adapted to determine a symbol timing from a correlation peak in the cross-correlation of the received signal with the training sequence.

12. The receiver according to claim 1 , wherein the received signals also contain a cyclic prefix, further comprising: means for obtaining an accurate value for the carrier frequency offset by autocorrelation of the cyclic prefix with the received signal.

13. An OFOM telecommunications system including the receiver of claim 1 .

14. The receiver according to claim 1 , comprising:

an autocorrelation unit for generating a phase and an amplitude autocorrelation signal by autocorrelation of a known sequence in the received signal; and

the time reference determining unit comprising means to detect synchronization using both the phase and amplitude signals.

15. The receiver according to claim 1 , further comprising:

an autocorrelation unit for generating the autocorrelation signal by autocorrelation of a known sequence in the received signal; and

the time reference determining unit comprising means to detect synchronization by detecting at least two synchronization conditions in the autocorrelation signal.

16. A receiver for receiving a signal comprising a carrier modulated with a known training sequence comprising:

a frequency offset estimation unit for receiving the signal and obtaining an estimate of a carrier frequency offset from an autocorrelation signal obtained by autocorrelation of the part of the received signal containing a known training sequence;

a frequency offset compensation unit for compensating the received signal with the frequency offset obtained from the frequency offset estimation unit to form a compensated received signal;

a time reference determining unit for obtaining a timing reference for the received signal by cross-correlation of the compensated received signal with a known training sequence; and

wherein the receiver is adapted to

output the timing reference obtained from the received signal by autocorrelation of the received signal if the timing reference obtained by cross-correlation of the compensated received signal with the known training sequence is not present,

compare the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence when present and the timing reference determined by autocorrelation of the received signal,

output a reset signal if the two timing references differ by more than a threshold values, and

otherwise output the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence.

17. A method for processing a received signal comprising a carrier modulated with a known training sequence, comprising:

obtaining an estimate of a carrier frequency offset from an autocorrelation signal obtained by autocorrelation of the part of the received signal containing a known training sequence;

compensating the received signal with the obtained estimate of the frequency offset to form a compensated received signal;

obtaining a timing reference for the received signal by cross-correlation of the compensated received signal with a known training sequence;

obtaining a timing reference obtained from the received signal by autocorrelation of the received signal;

comparing the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence and the timing reference determined by autocorrelation of the received signal;

outputting a reset signal if the two timing references differ by more than a threshold value, and

otherwise outputting the timing reference for the received signal obtained by cross-correlation of the compensated received signal with the known training sequence.

18. A method according to claim 17 , comprising:

generating a phase and an amplitude autocorrelation signal-by autocorrelation of a known sequence in the received signal, and

obtaining the timing reference for the received signal by detecting synchronization using both the phase and the amplitude signals.

19. A method according to claim 17 , further comprising:

generating an autocorrelation signal by autocorrelation of a known sequence in the received signal; and

obtaining a timing reference for the received signal by detecting synchronization using at least two synchronization conditions in the autocorrelation signal.