System and method for obtaining frequency and time synchronization in a wideband communication system

1. A method of measuring frequency offset in wideband signals of bandwidth X within a communications system having a coherency time constant of T, comprising:

generating a synchronization signal during a preamble of a data frame, wherein generating the synchronization signal includes:

generating a first chirp signal that sweeps a portion of bandwidth X; and

generating a second chirp signal that sweeps approximately the same portion of bandwidth X in a direction opposite to the first chirp signal;

transmitting the synchronization signal;

receiving a wideband signal at a receiver;

generating a receiver chirp signal in the receiver;

detecting a first offset as a function of the first chirp signal and the receiver chirp signal;

detecting a second offset as a function of the second chirp signal and the receiver chirp signal; and

calculating the frequency offset as a function of the first and second offsets; and

tracking a time offset over the data frame based on the calculated frequency offset.

2. The method of claim 1 , wherein receiving a wideband signal includes detecting the synchronization signal, wherein detecting includes:

generating a detection signal from the receiver chirp signal, wherein the detection signal is a complex conjugate of at least a portion of the synchronization signal;

correlating the received wideband signal with the detection signal; and

indicating when the synchronization signal is detected within the wideband signal.

3. The method of claim 1 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

4. The method of claim 1 , wherein generating a synchronization signal further includes modulating a pseudo-noise (PN) sequence with the synchronization signal.

5. The method of claim 4 , wherein the PN sequence has a length M, wherein M is less than T.

6. The method of claim 4 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

7. The method of claim 1 , wherein the wideband signal is a spread spectrum signal.

8. A method of correcting frequency offset in wideband signals of bandwidth X within a communications system having a coherency time constant of T, comprising:

generating a synchronization signal during a preamble of a data frame, wherein generating the synchronization signal includes:

generating a first chirp signal that sweeps a portion of bandwidth X; and

generating a second chirp signal that sweeps approximately the same portion of bandwidth X in a direction opposite to the first chirp signal;

transmitting the synchronization signal;

receiving a wideband signal at a receiver;

generating a receiver chirp signal in the receiver;

detecting a first offset as a function of the first chirp signal and the receiver chirp signal;

detecting a second offset as a function of the second chirp signal and the receiver chirp signal;

calculating the frequency offset as a function of the first and second offsets;

removing the calculated frequency offset; and

tracking a time offset over the data frame based on the calculated frequency offset.

9. The method of claim 8 , wherein receiving a wideband signal includes detecting the synchronization signal, wherein detecting includes:

generating a detection signal from the receiver chirp signal, wherein the detection signal is a complex conjugate of at least a portion of the synchronization signal;

correlating the received wideband signal with the detection signal; and

indicating when the synchronization signal is detected within the wideband signal.

10. The method of claim 8 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

11. the method of claim 8 , wherein generating a synchronization signal further includes modulating a pseudo-noise (PN) sequence with the synchronization signal.

12. The method of claim 11 , wherein the PN sequence has a length M, wherein M is less than T.

13. The method of claim 11 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

14. The method of claim 8 , wherein the wideband signal is a spread spectrum signal.

15. A method of determining time offset of wideband signals of bandwidth X within a communications system having a coherency time constant of T, comprising:

generating a synchronization signal during a preamble of a data frame, wherein generating the synchronization signal includes:

generating a first chirp signal that sweeps a portion of bandwidth X; and

generating a second chirp signal that sweeps approximately the same portion of bandwidth X in a direction opposite to the first chirp signal;

transmitting the synchronization signal;

receiving a wideband signal at a receiver;

generating a receiver chirp signal in the receiver;

detecting a first offset as a function of the first chirp signal and the receiver chirp signal;

detecting a second offset as a function of the second chirp signal and the receiver chirp signal;

calculating the time offset as a function of the first and second offsets; and

tracking the time offset over the data frame.

16. The method of claim 15 , wherein receiving a wideband signal includes detecting the synchronization signal, wherein detecting includes:

generating a detection signal from the receiver chirp signal, wherein the detecting signal is a complex conjugate of at least a portion of the synchronization signal;

correlating the received wideband signal with the detection signal; and

indicating when the synchronization signal is detected within the wideband signal.

17. The method of claim 15 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

18. A transmitter, comprising:

a synchronization signal generator, wherein the synchronization signal generator generates a synchronization signal during a preamble of a data frame, wherein the synchronization signal includes a first chirp signal and a second chirp signal, wherein the second chirp signal sweeps in a direction opposite to the first chirp signal;

a data source;

one or more modulators, wherein the modulators modulate data from the data source to form a data-modulated wideband signal of bandwidth X and wherein the modulators modulate the synchronization signal to form a modulated synchronization signal that sweeps a portion of bandwidth X; and

a transmitter circuit connected to the one or more modulators, wherein the transmitter circuit transmits the modulated synchronization signal and the data-modulated wideband signal at different times.

19. The transmitter of claim 18 , wherein each chirp signal is a linear frequency chirp signal.

20. The transmitter of claim 18 , wherein the chirp signals, when modulated, sweep linearly across the portion of bandwidth X such that's each frequency is occupied for only a single chirp sample during each sweep.

21. The transmitter of claim 18 , wherein the transmitter transmits the modulated synchronization signal as a preamble to the data modulated wideband signal.

22. The transmitter of claim 18 , wherein the synchronization signal generator further includes a pseudo-noise generator, wherein the pseudo-noise generator generates a PN sequence of length M, wherein the PN sequence is modulated by the chirp signal to form the synchronization signal.

23. The transmitter of claim 22 , wherein the transmitter is designed to operate in a system having a coherency time constant of T and wherein M is chosen to be less than T.

24. The transmitter of claim 22 , wherein each chirp signal is a linear frequency chirp signal.

25. The transmitter of claim 22 , wherein each chirp signal, when modulated, sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

26. The transmitter of claim 18 , wherein the wideband signal is a spread spectrum signal.

27. A receiver for use in a communications system having a coherency time constant of T and a transmitter that transmits a wideband signal including a synchronization signal modulated to sweep a portion of a bandwidth X, wherein the synchronization signal includes a first chirp signal and a second chirp signal in a preamble of a data frame, wherein the second chirp signal sweeps in a direction opposite to the first chirp signal, the receiver comprising:

a receiver circuit for receiving a wideband signal of bandwidth X;

a chirp generator circuit for generating a receiver chirp signal;

a frequency offset circuit, wherein the frequency offset circuit detects a first offset as a function of the first chirp signal and the receiver chirp signal, detects a second offset as a function of the second chirp signal and the receiver chirp signal, and calculates a frequency offset as a function of the first and second offsets;

a frequency offset correcting circuit, wherein the frequency offset correcting circuit modifies the wideband signal to remove the calculated frequency offset; and

a demodulator connected to the synchronization signal detector, wherein the demodulator recovers data from the wideband signal after the frequency offset is removed;

wherein the receiver is configured to track a time offset over the data frame based on the calculated frequency offset.

28. The receiver of claim 27 , wherein each chirp signal is a linear frequency chirp signal.

29. The receiver of claim 27 , wherein each chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

30. The receiver of claim 27 , wherein the synchronization signal is transmitted as a preamble.

31. The receiver of claim 27 , wherein the receiver further includes a synchronization signal detector, connected to the receiver circuit, wherein the synchronization signal detector detects the synchronization signal within the wideband signal, wherein the synchronization signal detector includes:

a detection signal generator, wherein the detection signal generator generates a detection signal from the receiver chirp signal, wherein the detection signal is a complex conjugate of at least a portion of the synchronization signal; and

a correlator, wherein the correlator correlates the received wideband signal with the detection signal and indicates when the synchronization signal is detected.

32. The receiver of claim 31 , wherein the synchronization signal includes a pseudo-noise (PN) sequence modulated by the chirp signal, wherein the PN sequence is of length M, wherein M is less than a coherency time constant.

33. The receiver of claim 32 , wherein the chirp signal is a linear frequency chirp signal.

34. The receiver of claim 32 , wherein the chirp signal sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

35. A communication system having a coherency time constant T, comprising:

one or more transmitters, wherein each transmitter includes:

a synchronization signal generator, wherein the synchronization signal generator generates a synchronization signal during a preamble of a data frame, wherein the synchronization signal includes a first chirp signal and a second chirp signal, wherein the second chirp signal sweeps in a direction opposite to the first chirp signal;

a data source;

one or more modulators, wherein the modulators modulate data from the data source to form a data-modulated wideband signal of bandwidth X and wherein the modulators modulate the synchronization signal to form a modulated synchronization signal that sweeps a portion of bandwidth X; and

a transmitter circuit connected to the one or more modulators, wherein the transmitter circuit transmits the modulated synchronization signal and the data-modulated wideband signal at different times; and

one or more receivers, wherein the receivers include:

a receiver circuit for receiving a wideband signal of bandwidth X;

a chirp generator circuit for generating a receiver chirp signal;

a frequency offset circuit, wherein the frequency offset circuit detects a first offset as a function of the first chirp signal and the receiver chirp signal, detects a second offset as a function of the second chirp signal and the receiver chirp signal, and calculates a frequency offset as a function of the first and second offsets;

a frequency offset correcting circuit, wherein the frequency offset correcting circuit modifies the wideband signal to remove the calculated frequency offset; and

a demodulator connected to the synchronization signal detector, wherein the demodulator recovers data from the wideband signal after the frequency offset is removed;

wherein the one or more receivers are configured to track a time offset over the data frame based on the calculated frequency offset.

36. The system of claim 35 , wherein each chirp signal is a linear frequency chirp signal.

37. The system of claim 35 , wherein each chirp signal, when modulated, sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.

38. The system of claim 35 , wherein the modulated synchronization signal is transmitted as a preamble.

39. The system of claim 35 , wherein the receiver further includes a synchronization signal detector, connected to the receiver circuit, wherein the synchronization signal detector detects the synchronization signal within the wideband signal, wherein the synchronization signal detector includes:

a detection signal generator, wherein the detection signal generator generates a detection signal from the receiver chirp signal, wherein the detection signal is a complex conjugate of at least a portion of the synchronization signal; and

a correlator, wherein the correlator correlates the received wideband signal with the detection signal and indicates when the synchronization signal is detected.

40. The system of claim 39 , wherein the synchronization signal includes a pseudo-noise (PN) sequence modulated by the chirp signal, wherein the PN sequence is of length M, wherein M is less T.

41. The system of claim 40 , wherein each chirp signal is a linear frequency chirp signal.

42. The system of claim 40 , wherein each chirp signal, when modulated, sweeps linearly across the portion of bandwidth X such that each frequency is occupied for only a single chirp sample during each sweep.