Method and apparatus for providing time synchronization in a digital television system

1. An apparatus for transmitting a signal comprising:

a modulator that generates a signal by modulating data into a plurality of modulation symbols, said data divided into frames, and said data comprising time synchronization information available for two modes of frame generation, wherein the time synchronization information includes

a frame length mode parameter indicating one of said two modes, and

one of a time offset parameter and a frame length parameter selected according to the frame length mode parameter; and

a transmitter interface that transmits said signal over a communication medium;

wherein the time synchronization information is used to adjust a system clock associated with a receiver of said signal.

2. The apparatus according to claim 1 wherein said frame length mode parameter indicates that a frame is one of a time aligned frame and a symbol aligned frame, said time offset parameter indicates a time interval between a reference time value and a beginning of a first modulation symbol of the frame, and said frame length parameter indicates a length of the frame.

3. The apparatus according to claim 2 wherein the reference time value is a closest time boundary value that is on or before the beginning of the first modulation symbol of the frame.

4. The apparatus according to claim 3 wherein the time boundary value is a multiple of one millisecond.

5. The apparatus according to claim 2 wherein the data includes the time offset parameter when the frame length mode parameter indicates that the frame is symbol aligned.

6. The apparatus according to claim 2 wherein the data includes the frame

length parameter when the frame length mode parameter indicates that the frame is time aligned.

7. The apparatus according to claim 1 wherein the frame length parameter is in units of five milliseconds.

8. The apparatus according to claim 1 wherein the frame length mode parameter and one of the time offset parameter and the frame length parameter are included in a preamble modulation symbol of said frame, said preamble comprising signaling data.

9. The apparatus according to claim 1 further comprising:

a channel encoder for channel encoding said data prior to the modulator.

10. The apparatus according to claim 1 wherein the modulator is a multicarrier modulator that allocates said modulation symbols to a plurality of carriers.

11. The apparatus according to claim 10 wherein the multi-carrier modulation is orthogonal frequency division multiplex (OFDM).

12. The apparatus according to claim 1 further comprising:

a source that provides said data.

13. The apparatus according to claim 1 wherein said signal is compliant with an Advanced Television System Committee standard.

14. A method of transmitting a signal comprising:

modulating data into a plurality of modulation symbols to generate a signal,

said data divided into frames and comprising time synchronization information available for two modes of frame generation, wherein the time synchronization information includes

a frame length mode parameter indicating one of said two modes, and

one of a time offset parameter and a frame length parameter selected according to the frame length mode parameter; and

transmitting said signal over a communication medium;

wherein the time synchronization information is used to adjust a system clock associated with a receiver of said signal.

15. The method according to claim 14 wherein said frame length mode parameter indicates that a frame is one of a time aligned frame and a symbol aligned frame, said time offset parameter indicates a time interval between a reference time value and a beginning of a first modulation symbol of the frame, and said frame length parameter indicates a length of the frame.

16. The method according to claim 15 wherein the reference time value is a closest time boundary value that is on or before the beginning of the first modulation symbol of the frame.

17. The method according to claim 16 wherein the time boundary value is a multiple of one millisecond.

18. The method according to claim 15 wherein the data includes the time offset parameter when the frame length mode parameter indicates that the frame is symbol aligned.

19. The method according to claim 15 wherein the data includes the frame

length parameter when the frame length mode parameter indicates that the frame is time aligned.

20. The method according to claim 14 wherein the frame length parameter is in units of five milliseconds.

21. The method according to claim 14 wherein the frame length mode parameter and one of the time offset parameter and the frame length parameter are included in a preamble modulation symbol of the frame, said preamble comprising signaling data.

22. The method according to claim 14 further comprising:

channel encoding said data prior to modulating.

23. The method according to claim 14 wherein the modulator is a multi-carrier modulator that allocates said modulation symbols to a plurality of carriers.

24. The method according to claim 23 wherein the multi-carrier modulation is orthogonal frequency division multiplex (OFDM).

25. The method according to claim 14 further comprising:

a source that provides said data.

26. The method according to claim 14 wherein said signal is compliant with an Advanced Television System Committee standard.

27. An apparatus for receiving a signal comprising:

a receiver interface that receives a signal over a communication medium; and

a demodulator that demodulates said signal to generate a plurality of demodulated symbols, said demodulated symbols comprising data divided into frames, said data comprising time synchronization information available for two modes of frame generation, wherein the time synchronization information includes a frame length mode parameter indicating one of said two modes, and one of a time offset parameter and a frame length parameter selected according to the frame length mode parameter,

said time synchronization information used to recover a frame of data;

wherein the time synchronization information is used to adjust a system clock associated with the receiver interface.

28. The apparatus according to claim 27 wherein said frame length mode parameter indicates that a frame of data is one of a time aligned frame and a symbol aligned frame, said time offset parameter indicates a time interval between a reference time value and a beginning of a first modulation symbol of the frame, and said frame length parameter indicates a length of the frame.

29. The apparatus according to claim 28 wherein the reference time value is a closest time boundary value that is on or before the beginning of the first modulation symbol of the frame.

30. The apparatus according to claim 29 wherein the time boundary value is a multiple of one millisecond.

31. The apparatus according to claim 29 wherein the data includes the time offset parameter when the frame length mode parameter indicates that the frame is symbol aligned.

32. The apparatus according to claim 28 wherein the data includes the frame length parameter when the frame length mode parameter indicates that the frame is time aligned.

33. The apparatus according to claim 27 wherein the frame length parameter is in units of five milliseconds.

34. The apparatus according to claim 27 wherein said frame length mode parameter and one of the time offset parameter and the frame length parameter are included in a preamble modulation symbol of the frame, said preamble comprising signaling data.

35. The apparatus according to claim 27 further comprising:

a channel decoder that channel decoding said data after the demodulator.

36. The apparatus according to claim 27 wherein the demodulator is a multicarrier demodulator that demodulates the signal from a plurality of carriers.

37. The apparatus according to claim 36 wherein the multi-carrier modulation is orthogonal frequency division multiplex (OFDM).

38. The apparatus according to claim 27 further comprising:

a signaling data detector that detects said data from said plurality of demodulated symbols and recovers the time synchronization information.

39. The apparatus according to claim 27 wherein said signal is compliant with an Advanced Television System Committee standard.

40. A method for receiving a signal at a receiver comprising:

receiving a signal over a communication medium; and

demodulating said signal to generate a plurality of demodulated symbols, said demodulated symbols comprising data divided into frames, said data comprising time synchronization information available for two modes of frame generation, wherein the time synchronization information includes a frame length mode parameter indicating one of said two modes, and one of a time offset parameter and a frame length parameter selected according to the frame length mode parameter, said time synchronization information used to recover a frame of data;

further wherein the time synchronization information is used to adjust a system clock associated with the receiver.

41. The method according to claim 40 wherein said frame length mode parameter indicates that a frame of data is one of a time aligned frame and a symbol aligned frame, said time offset parameter indicates a time interval between a reference time value and a beginning of a first modulation symbol of the frame, and said frame length parameter indicates a length of the frame.

42. The method according to claim 41 wherein the reference time value is a closest time boundary value that is on or before the beginning of the first modulation symbol of the frame.

43. The method according to claim 42 wherein the time boundary value is a multiple of one millisecond.

44. The method according to claim 41 wherein the data includes the time offset parameter when the frame length mode parameter indicates that the frame is symbol aligned.

45. The method according to claim 41 wherein that data includes the frame length parameter when the frame length mode parameter indicates that the frame is time aligned.

46. The method according to claim 40 wherein the frame length parameter is in units of five milliseconds.

47. The method according to claim 40 wherein said frame length mode parameter and one of the time offset parameter and the frame length parameter are included in a preamble modulation symbol of the frame, said preamble comprising signaling data.

48. The method according to claim 40 further comprising:

channel decoding said data after demodulating.

49. The method according to claim 40 wherein the demodulating is multicarrier demodulating that demodulates the signal from a plurality of carriers.

50. The method according to claim 49 wherein the multi-carrier modulation is orthogonal frequency division multiplex (OFDM).

51. The method according to claim 40 further comprising:

detecting said data from said plurality of demodulated symbols; and

recovering the time synchronization information.

52. The method according to claim 40 wherein said signal is compliant with an Advanced Television System Committee standard.