Transmitter and Method for Transmitting Soft Pilot Symbols in a Digital Communication System

• US 20090310708A1
• Filed: 09/29/2008
• Published: 12/17/2009
• Est. Priority Date: 06/17/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Cheng, Jung-Fu, Fulghum, Tracy, Cairns, Douglas
• Granted Patent: US 8,750,407 B2
• Time in Patent Office: Days
• US Class Current: 375/298
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers
• CPC Class Codes: H04L 1/0017 where the mode-switching is based on Quality of Service requirement
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/0068 by puncturing
• CPC Class Codes: H04L 2001/0098 Unequal error protection
• CPC Class Codes: H04L 2025/03401 PSK
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03509 fractionally spaced H04L2025/03515 takes precedence
• CPC Class Codes: H04L 2025/03796 Location of reference signals
• CPC Class Codes: H04L 2027/0061 remodulation
• CPC Class Codes: H04L 2027/0093 Intermittant signals
• CPC Class Codes: H04L 25/021 Estimation of channel covariance
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/0236 using estimation of the other symbols
• CPC Class Codes: H04L 25/03044 using fractionally spaced delay lines or combinations of fractionally integrally spaced taps
• CPC Class Codes: H04L 25/03324 Provision of tentative decisions
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/227 : using coherent demodulation
• CPC Class Codes: H04L 27/3455 : in order to facilitate carrier recovery at the receiver end, e.g. by transmitting a pilot or by using additional signal points to allow the detection of rotations
• CPC Class Codes: H04L 27/3818 : using coherent demodulation, i.e. using one or more nominally phase synchronous carriers H04L27/227 and H04L27/389 take precedence

Abstract

A transmitter, channel coder, and method for coding and transmitting a sequence of symbols in a digital communication system utilizing soft pilot symbols. In one embodiment, the transmitter transmits a set of soft pilot symbols with higher reliability than the remaining symbols in the sequence by modulating the soft pilot symbols with a lower order modulation such as BPSK or QPSK while modulating the remaining symbols with a higher order modulation such as 16 QAM or 64 QAM. The transmitter shares the modulation type and location (time/frequency/code) of the soft pilot symbols with a receiver. Unlike traditional fixed pilots, the soft pilots still carry some data. Additionally, the soft pilots are particularly helpful in establishing the amplitude reference essential in demodulating the higher order modulation symbols. In another embodiment, soft pilot symbols are inserted by low-level puncturing of channel encoded bits and replacing the punctured bits with known bit patterns.

Claims

1. A method of transmitting a radio signal that includes a sequence of transmitted symbols, said method comprising the steps of:

inserting a set of soft pilot symbols into the symbol sequence;

modulating the symbol sequence, wherein the soft pilot symbols are modulated with a simpler, lower order modulation compared to the rest of the symbol sequence; and

transmitting the radio signal.

2. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits with modulation-dependent puncturing positions.

3. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits that are mapped to the least reliable bit labels.

4. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits that are mapped to the last bit labels of a modulation symbol.

5. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits that are mapped to the last two bit labels of a 16 QAM modulation symbol.

6. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits that are mapped to the last four bit labels of a 64 QAM modulation symbol.

7. The method as recited in claim 1, wherein the soft pilot symbols include at least one bit with a known value of 1.

8. The method as recited in claim 1, wherein as a result of the inserting and modulating steps, the soft pilot symbols are modulated, in effect, with scaled Quadrature Phase Shift Keying (QPSK).

9. The method as recited in claim 1, wherein as a result of the inserting and modulating steps, the soft pilot symbols are modulated, in effect, with scaled Binary Phase Shift Keying (BPSK).

10. The method as recited in claim 1, wherein the soft pilot symbols have constant quadrature amplitudes.

11. The method as recited in claim 1, wherein the soft pilot symbols have constant in-phase amplitudes.

12. The method as recited in claim 1, further comprising sending an indication to a receiver indicating locations in the sequence for the soft pilot symbols.

13. The method as recited in claim 1, further comprising sending an indication to a receiver indicating a modulation type for the soft pilot symbols.

14. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits, and the method further comprises sending an indication to a receiver indicating the punctured bit label positions.

15. The method as recited in claim 1, further comprising pre-agreeing by the transmitter and a receiver upon the locations of soft pilot symbols.

16. The method as recited in claim 1, further comprising pre-agreeing by the transmitter and a receiver upon a modulation type for the soft pilot symbols.

17. The method as recited in claim 1, wherein the inserting step includes puncturing channel coded bits, and the method further comprises pre-agreeing by the transmitter and a receiver upon bit label positions for puncturing.

18. The method as recited in claim 1, wherein the inserting step comprises high-level puncturing of channel coded bits.

19. The method as recited in claim 1, wherein the inserting step comprises low-level puncturing of channel coded bits.

20. A method of channel coding a radio signal for a radio channel, said method comprising the steps of:

channel interleaving the radio signal;

inserting soft pilot symbols by low-level puncturing of channel coded bits; and

replacing the punctured bits with known bit patterns.

21. The method as recited in claim 20, wherein the radio channel is a High Speed Downlink Shared Channel (HS-DSCH).

22. The method as recited in claim 21, wherein the inserting step is performed after modulation constellation rearrangement.

23. The method as recited in claim 21, wherein the inserting step includes puncturing channel coded bits that are mapped to the last two bit labels of a 16 QAM modulation symbol.

24. The method as recited in claim 21, wherein the inserting step includes puncturing channel coded bits that are mapped to the last four bit labels of a 64 QAM modulation symbol.

25. The method as recited in claim 21, wherein as a result of the inserting and replacing steps, the soft pilot symbols are modulated, in effect, with scaled Quadrature Phase Shift Keying (QPSK).

26. The method as recited in claim 21, wherein the soft pilot symbols have constant quadrature amplitudes.

27. The method as recited in claim 21, wherein the soft pilot symbols have constant in-phase amplitudes.

28. The method as recited in claim 20, wherein the radio channel is an Enhanced Dedicated Channel (E-DCH).

29. The method as recited in claim 28, wherein the inserting step includes puncturing channel coded bits that are mapped to the last bit label of a 4PAM modulation symbol.

30. The method as recited in claim 28, wherein the soft pilot symbols are effectively modulated with scaled Binary Phase Shift Keying (BPSK).

31. The method as recited in claim 28, wherein the soft pilot symbols have constant amplitudes.

32. The method as recited in claim 20, wherein the inserting step includes puncturing channel coded bits with modulation-dependent puncturing positions.

33. The method as recited in claim 20, wherein the inserting step includes puncturing channel coded bits that are mapped to the last bit labels.

34. The method as recited in claim 20, wherein the known bit patterns include at least one bit with a value of 1.

35. The method as recited in claim 20, wherein the soft pilot symbols are inserted in at least one code.

36. The method as recited in claim 20, wherein the soft pilot symbols are not consecutive in time.

37. The method as recited in claim 36, wherein the soft pilot symbols are inserted with a periodic time pattern.

38. The method as recited in claim 20, wherein the soft pilot symbols are inserted at the same time location in different codes.

39. The method as recited in claim 20, wherein the soft pilot symbols are inserted at different time locations in different codes.

40. The method as recited in claim 20, further comprising sending an indication to a receiver indicating locations in the sequence for the soft pilot symbols, said locations being defined in terms of time and code.

41. The method as recited in claim 20, further comprising sending an indication to a receiver indicating a modulation type for the soft pilot symbols.

42. The method as recited in claim 20, further comprising sending an indication to a receiver indicating the punctured bit label positions.

43. The method as recited in claim 20, further comprising pre-agreeing by a transmitter and a receiver upon locations of the soft pilot symbols, said locations being defined in terms of time and code.

44. The method as recited in claim 20, further comprising pre-agreeing by a transmitter and a receiver upon a modulation type for the soft pilot symbols.

45. The method as recited in claim 20, further comprising pre-agreeing by a transmitter and a receiver upon bit label positions for puncturing.

46. A transmitter for transmitting a radio signal that includes a sequence of transmitted symbols, said transmitter comprising:

means for inserting a set of soft pilot symbols into the symbol sequence;

means for modulating the symbol sequence, wherein the soft pilot symbols are modulated with a simpler, lower order modulation compared to the rest of the symbol sequence; and

means for transmitting the radio signal.

47. A channel coder for channel coding a radio signal for a radio channel, said channel coder comprising:

means for channel interleaving the radio signal;

means for inserting soft pilot symbols by low-level puncturing of channel coded bits; and

means for replacing the punctured channel coded bits with known bit patterns.

48. The channel coder as recited in claim 47, wherein the radio channel is a High Speed Downlink Shared Channel (HS-DSCH).

49. The channel coder as recited in claim 47, wherein the radio channel is an Enhanced Dedicated Channel (E-DCH).