Methods and apparatus for providing robust synchronization of radio transceivers

• US 6,690,740 B1
• Filed: 08/11/1999
• Issued: 02/10/2004
• Est. Priority Date: 08/19/1998
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Haartsen, Jacobus Cornelius, Mattisson, Sven, Persson, Joakim
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): WILLIAMS, LAWRENCE B
• Application Number:
  US09/372,250
• Time in Patent Office: 1,644 Days
• Field of Search: 375/344, 375/316, 375/319, 375/295, 714/745, 714/746, 360/45-65
• US Class Current: 375/295
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only
• CPC Class Codes: H04L 27/142 Compensating direct current components occurring during the demodulation and which are caused by mistuning
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal
• CPC Class Codes: H04L 7/046 using a dotting sequence

Abstract

Methods and apparatus for performing synchronization and DC-offset compensation in FM transmission systems significantly reduce the overhead associated with transmitting a conventional digital preamble at the start of each of a succession of transmitted digital data packets. According to exemplary embodiments, a multi-part digital preamble includes a short, substantially DC-free leading part followed by a code-protected synchronization part which is not necessarily substantially DC-free. The leading part provides for coarse DC offset estimation and synchronization, while the coded synchronization part carries timing and/or other useful information which can be unique for each packet. One or more substantially DC-free trailing parts follow the synchronization part, or are included in the synchronization part itself, and provide for fine tuning of the DC-offset estimate. Since the substantially DC-free leading and trailing parts are extremely short, and since the synchronization part carries useful information, the overhead associated with a preamble according to the invention is significantly reduced as compared to a conventional, entirely DC-free, preamble.

Claims

1. A radio transmitter, comprising:

a modulator transmitting a succession of digital data packets by modulation of a carrier signal,

wherein said modulator provides a digital preamble for each transmitted digital data packet, and

wherein each digital preamble includes a synchronization part and at least two substantially DC-free parts including a first substantially DC-free part for use in forming a coarse estimate of a DC offset for a corresponding one of the digital data packets after reception, and a second substantially DC-free part for use in forming a fine estimate of the DC offset for a corresponding one of the digital data packets after reception.

2. A radio transmitter according to claim 1, wherein each digital preamble includes a substantially DC-free leading part, a synchronization part, and one or more substantially DC-free trailing parts.

3. A radio transmitter according to claim 2, wherein each synchronization part is coded to protect against detection errors at a receiver.

4. A radio transmitter according to claim 2, wherein each synchronization part includes timing information.

5. A radio transmitter according to claim 2, wherein each synchronization part includes information specific to the digital data packet with which the synchronization part is included.

6. A radio transmitter according to claim 5, wherein each synchronization part includes at least one of a channel identifier, a destination address and a recipient identification for the digital data packet with which the synchronization part is associated.

7. A radio transmitter according to claim 2, wherein a synchronization word is generated to provide the digital preamble for each digital data packet, each synchronization word being coded to include a substantially DC-free leading sequence, a synchronization sequence and one or more substantially DC-free trailing sequences.

8. A radio transmitter according to claim 2, wherein a leading sequence, a synchronization sequence and one or more trailing sequences are generated separately and combined to provide the digital preamble for each digital data packet.

9. A radio transmitter according to claim 8, wherein the leading sequence of each digital preamble is substantially DC-free.

10. A radio transmitter according to claim 8, wherein a trailing sequence of each digital preamble is substantially DC-free.

11. A radio transmitter according to claim 8, wherein an m-bit leading sequence is chosen based on a first k bits of a corresponding synchronization sequence so that a first k+m bits of each digital preamble is substantially DC-free.

12. A radio transmitter according to claim 8, wherein an m-bit trailing sequence is chosen based on a last k bits of a corresponding synchronization sequence so that a last k+m bits of each digital preamble is substantially DC-free.

13. A radio transmitter according to claim 8, wherein each digital preamble includes a leading sequence of alternating logical ones and logical zeroes, followed by a synchronization sequence, followed by a trailing sequence of alternating logical ones and logical zeroes.

14. A radio transmitter according to claim 13, wherein each leading sequence is four bits in length, wherein each synchronization sequence is sixty-four bits in length, wherein each trailing sequence is four bits in length, and wherein each trailing sequence is chosen based on one or more final bits of the synchronization sequence to ensure that each digital preamble concludes with a six-bit DC-free sequence.

15. A radio transmitter according to claim 14, wherein each trailing sequence is generated by selectively inverting a stored DC-free sequence in dependence upon a final bit of the synchronization sequence.

16. A radio receiver, comprising:

a detector receiving and demodulating a succession of digital data packets, each digital data packet including a digital preamble, each digital preamble including a synchronization part and at least two substantially DC-free parts; and

an estimation and synchronization processor estimating and removing a DC offset from an output of said detector and synchronizing the output of said detector,

wherein said processor provides a coarse estimate of the DC offset for each digital data packet based on one of the substantially DC-free parts of the data packet preamble, synchronizes each digital data packet based on the synchronization part of the data packet preamble once the coarse estimate for the data packet is established, and provides a fine estimate of the DC offset for each digital data packet based on another of the substantially DC-free parts of the data packet preamble once synchronization for the data packet is established.

17. A radio receiver according to claim 16, wherein each digital preamble includes a substantially DC-free leading part, a synchronization part, and one or more substantially DC-free trailing parts.

18. A radio receiver according to claim 17, wherein each synchronization part is coded to protect against detection errors at a receiver.

19. A radio receiver according to claim 17, wherein each synchronization part includes timing information.

20. A radio receiver according to claim 17, wherein each synchronization part includes information specific to the digital data packet with which the synchronization part is included.

21. A radio receiver according to claim 20, wherein each synchronization part includes at least one of a channel identifier, a destination address and a recipient identification for the digital data packet with which the synchronization part is associated.

22. A radio receiver according to claim 17, wherein a synchronization word is included in the digital preamble for each digital data packet, each synchronization word being coded to include a substantially DC-free leading sequence, a synchronization sequence and one or more substantially DC-free trailing sequences.

23. A radio receiver according to claim 17, wherein a leading sequence, a synchronization sequence and one or more trailing sequences are combined in the digital preamble of each digital data packet.

24. A radio receiver according to claim 23, wherein the leading sequence of each digital preamble is substantially DC-free.

25. A radio receiver according to claim 23, wherein a trailing sequence of each digital preamble is substantially DC-free.

26. A radio receiver according to claim 23, wherein an m-bit leading sequence is chosen based on a first k bits of a corresponding synchronization sequence so that a first k+m bits of each digital preamble is substantially DC-free.

27. A radio receiver according to claim 23, wherein an m-bit trailing sequence is chosen based on a last k bits of a corresponding synchronization sequence so that a last k+m bits of each digital preamble is substantially DC-free.

28. A radio receiver according to claim 23, wherein each digital preamble includes a leading sequence of alternating logical ones and logical zeroes, followed by a synchronization sequence, followed by a trailing sequence of alternating logical ones and logical zeroes.

29. A radio receiver according to claim 28, wherein each leading sequence is four bits in length, wherein each synchronization sequence is sixty-four bits in length, wherein each trailing sequence is four bits in length, and wherein each trailing sequence is chosen based on one or more final bits of the synchronization sequence to ensure that each digital preamble concludes with a six-bit DC-free sequence.

30. A radio receiver according to claim 29, wherein each trailing sequence is generated by selectively inverting a stored DC-free sequence in dependence upon a final bit of the synchronization sequence.

31. A radio receiver according to claim 16, wherein said estimation and synchronization processor includes a filter resistor, a storage capacitor and a comparator.

32. A radio receiver according to claim 31, wherein said estimation and synchronization processor further includes a correlation processor and a switch.

33. A method for communicating a digital data packet, comprising the steps of:

generating a digital preamble for the digital data packet, the preamble including a synchronization part and at least two substantially DC-free parts including a first substantially DC-free part for use in forming a coarse estimate of a DC offset for the digital data packet after reception, and a second substantially DC-free part for use in forming a fine estimate of the DC offset for the digital data packet after reception; and

transmitting the digital preamble, with the digital data packet, from a transmitter to a receiver.

34. A method according to claim 33, wherein each digital preamble includes a substantially DC-free leading part, a synchronization part, and one or more substantially DC-free trailing parts.

35. A method according to claim 34, wherein each synchronization part is coded to protect against detection errors at a receiver.

36. A method according to claim 34, wherein each synchronization part includes timing information.

37. A method according to claim 34, wherein each synchronization part includes information specific to the digital data packet with which the synchronization part is included.

38. A method according to claim 37, wherein each synchronization part includes at least one of a channel identifier, a destination address and a recipient identification for the digital data packet with which the synchronization part is associated.

39. A method according to claim 34, wherein a synchronization word is generated to provide the digital preamble for each digital data packet, each synchronization word being coded to include a substantially DC-free leading sequence, a synchronization sequence and one or more substantially DC-free trailing sequences.

40. A method according to claim 34, wherein a leading sequence, a synchronization sequence and one or more trailing sequences are generated separately and combined to provide the digital preamble for each digital data packet.

41. A method according to claim 40, wherein the leading sequence of each digital preamble is substantially DC-free.

42. A method according to claim 40, wherein a trailing sequence of each digital preamble is substantially DC-free.

43. A method according to claim 40, wherein an m-bit leading sequence is chosen based on a first k bits of a corresponding synchronization sequence so that a first k+m bits of each digital preamble is substantially DC-free.

44. A method according to claim 40, wherein an m-bit trailing sequence is chosen based on a last k bits of a corresponding synchronization sequence so that a last k+m bits of each digital preamble is substantially DC-free.

45. A method according to claim 40, wherein each digital preamble includes a leading sequence of alternating logical ones and logical zeroes, followed by a synchronization sequence, followed by a trailing sequence of alternating logical ones and logical zeroes.

46. A method according to claim 45, wherein each leading sequence is four bits in length, wherein each synchronization sequence is sixty-four bits in length, wherein each trailing sequence is four bits in length, and wherein each trailing sequence is chosen based on one or more final bits of the synchronization sequence to ensure that each digital preamble concludes with a six-bit DC-free sequence.

47. A method according to claim 46, wherein each trailing sequence is generated by selectively inverting a stored DC-free sequence in dependence upon a final bit of the synchronization sequence.

48. A method according to claim 35, further comprising the steps of:

providing, at the receiver, a coarse estimate of a DC offset for the digital data packet based on one of the substantially DC-free parts of the data packet preamble;

synchronizing the digital data packet at the receiver based on the synchronization part of the data packet preamble and the coarse estimate; and

providing, at the receiver, a fine estimate of the DC offset for the digital data packet based on another of the substantially DC-free parts of the data packet preamble once synchronization for the data packet is established.