Method and apparatus for decoding data in a layered modulation system

• US 20060171283A1
• Filed: 01/10/2006
• Published: 08/03/2006
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Vijayan, Rajiv, Chung, Seong Taek, Sun, Thomas
• Granted Patent: US 8,223,853 B2
• Time in Patent Office: Days
• US Class Current: 369/94
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0065 Serial concatenated codes
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 1/007 Unequal error protection for format H04L1/0078; for codes per se H03M13/35
• CPC Class Codes: H04L 2001/0098 Unequal error protection
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/26524 Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation
• CPC Class Codes: H04L 27/3488 Multiresolution systems
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A decoder for a layered modulation system can be configured to independently and concurrently decode each of a base and enhancement layer. The base layer decoder and enhancement layer decoder can be configured substantially in parallel and can each operate concurrently on the same received layered modulation symbol. Each of the base and enhancement layer decoders can be configured with a bit metric module that is configured to determine a signal quality metric based on the received symbol. In systems having turbo encoded data, the bit metric module can be configured to determine a log likelihood ratio. The ratio is based in part on a channel estimate and an energy ratio used in the layered modulation constellation.

Claims

1. A receiver configured to decode a received signal having layered modulation data, the receiver comprising:

an RF processor configured to receive the layered modulation data and configured to frequency convert the layered modulation data to substantially a baseband frequency;

a base layer decoder coupled to the RF processor and configured to decode a base layer data from the layered modulation data; and

an enhancement layer decoder coupled to the RF processor and configured to decode an enhancement layer data from the layered modulation data, the enhancement layer decoder operating substantially independent of the base layer decoder.

2. The receiver of claim 1, wherein the base layer decoder and the enhancement layer decoder are configured to concurrently process a same received layered modulation constellation point from the layered modulation data.

3. The receiver of claim 1, wherein the base layer decoder and the enhancement layer decoder are configured to operate on the layered modulation data corresponding to a same subcarrier within a multi-carrier system.

4. The receiver of claim 1, wherein the base layer decoder is configured to turbo decode one or more base layer symbols to generate the base layer data.

5. The receiver of claim 1, wherein the base layer decoder comprises a bit metric module configured to determine a log likelihood ratio (LLR) based in part on the layered modulation data.

6. The receiver of claim 1, further comprising a channel estimator coupled to the RF processor and configured to generate a channel estimate corresponding to a channel carrying the layered modulation data.

7. The receiver of claim 6, wherein the base layer decoder comprises a bit metric module coupled to the RF processor and the channel estimator, and configured to determine a log likelihood ratio (LLR) based in part on the layered modulation data and the channel estimate.

8. The receiver of claim 7, wherein the channel estimator is configured to compare a component of the channel estimate to a threshold value and select as an updated channel estimate component one of a predetermined value and the channel estimate component, based in part on the comparison.

9. The receiver of claim 1, wherein each of the base layer decoder and enhancement layer decoder comprises a bit metric module configured to determine a log likelihood ratio based in part on the layered modulation data.

10. The receiver of claim 9, further comprising a channel estimator configured generate a channel estimate, in part, by comparing a channel estimate component to a threshold value and selecting as an updated channel estimate component one of a predetermined value and the channel estimate component, based in part on the comparison.

11. The receiver of claim 10, wherein the bit metric module in each of the base layer decoder and enhancement layer decoder is configured to use the same channel estimate.

12. A receiver configured to decode a received signal having layered modulation data, the receiver comprising:

an RF processor configured to receive an OFDM symbol, wherein at least one subcarrier in the OFDM symbol carries layered modulation data;

an FFT module coupled to the RF processor and configured to transform the OFDM symbol to a plurality of subcarriers;

a base layer decoder coupled to the FFT module and configured to decode a base layer data from the at least one subcarrier carrying the layered modulation data; and

an enhancement layer decoder coupled to the FFT module and configured to decode an enhancement layer data from the at least one subcarrier carrying the layered modulation data, the enhancement layer decoder operating substantially independent of the base layer decoder.

13. A receiver configured to decode a received signal having layered modulation data, the receiver comprising:

an RF processor configured to receive the layered modulation data;

a base layer decoder coupled to the RF processor and configured to decode a base layer data from the layered modulation data, the base layer decoder comprising a base bit metric module configured to determine a log likelihood ratio of base layer data from the layered modulation data; and

an enhancement layer decoder coupled to the RF processor and configured to decode an enhancement layer data from the layered modulation data, the enhancement layer decoder comprising an enhancement bit metric module configured to determine a log likelihood ratio of enhancement layer data from the layered modulation data.

14. The receiver of claim 13, further comprising a channel estimator coupled to the RF processor and configured to generate a channel estimate, in part, by comparing a channel estimate component to a threshold value and select as an updated channel estimate component one of a predetermined value and the channel estimate component, based in part on the comparison.

15. A method of decoding a layered modulation signal, the method comprising:

receiving a layered modulation signal;

decoding a base layer data from the layered modulation signal; and

decoding an enhancement layer data from the layered modulation signal substantially concurrently with decoding the base layer data.

16. The method of claim 15, wherein decoding the enhancement layer data comprises decoding the enhancement layer data from the layered modulation signal substantially independent of the base layer data.

17. The method of claim 15, wherein decoding the base layer data comprises determining a log likelihood ratio (LLR) of base layer bits based on the layered modulation signal and a channel estimate.

18. The method of claim 15, further comprising generating a channel estimate based on a received OFDM symbol and a channel estimation threshold value.

19. The method of claim 18, wherein generating the channel estimate comprises:

comparing an actual channel estimate component to the channel estimation threshold value; and

selecting as a channel estimate component, one of the actual channel estimate component or a predetermined value based on the comparison.

20. The method of claim 19, wherein the predetermined value comprises a substantially insignificant value.

21. The method of claim 15, wherein decoding the enhancement layer comprises determining a (LLR) of enhancement layer bits based on the layered modulation signal and a channel estimate.

22. The method of claim 21, wherein the channel estimate comprises a plurality of channel estimate components, each of the plurality of channel estimate components comprising one of an actual channel estimate component or a predetermined value based on a comparison of the actual channel estimate component to a threshold value.

23. A machine readable storage device configured to store one or more processor usable instructions comprising:

receiving an OFDM symbol including data in a layered modulation channel;

generating a channel estimate based in part on the OFDM symbol;

decoding a base layer data from the layered modulation channel; and

decoding an enhancement layer data from the layered modulation channel concurrently with decoding the base layer data and substantially independent of the base layer decoding.

24. The storage device of claim 23, wherein generating the channel estimate comprises:

comparing each of a plurality of channel estimate components to a threshold value; and

selecting, for each of the plurality of channel estimate components, one of the channel estimate component or a predetermined value based on the comparison of the channel estimate component to the threshold value.

25. The storage device of claim 23, wherein decoding the base layer data comprises determine a log likelihood ratio (LLR) based in part on the data in the layered modulation channel.

26. A transmitter configured to encode a signal having layered modulation data, the transmitter comprising:

a base layer encoder configured to encode base layer data to base layer symbols;

an enhancement layer encoder configured to encode enhancement layer data to enhancement layer symbols;

a signal mapper coupled to the base layer encoder and enhancement layer encoder and configured to map at least one base layer symbol in combination with at least one enhancement layer symbol to a layered modulation constellation point; and

a subcarrier assignment module configured to modulate at least one tone from a logical channel with the layered modulation constellation point based on an energy ratio selected from a plurality of energy ratios.

27. The transmitter of claim 26, wherein the plurality of energy ratios comprise an energy ratio of approximately four and an energy ratio of approximately nine.

28. The transmitter of claim 26, wherein the subcarrier assignment module is further configured to assign the logical channel to a subset of OFDM subcarriers, where the subset of OFDM subcarriers includes the at least one tone.

29. The transmitter of claim 26, wherein the subcarrier assignment module is further configured combine the at least one tone from logical channel with a distinct subcarrier modulated with a distinct constellation point having a distinct energy ratio.

30. A method of transmitting a signal having layered modulation data, the method comprising:

encoding a base layer signal to base layer symbols;

encoding an enhancement layer signal to enhancement layer symbols; and

mapping a base layer symbol in conjunction with an enhancement layer symbol to a constellation point in a layered modulation constellation having an energy ratio selected from a plurality of energy ratios.

31. The method of claim 30, further comprising modulating a subcarrier with the constellation point.

32. The method of claim 31, wherein the subcarrier is selected from a plurality of subcarriers of an OFDM symbol.

33. The method of claim 31, further comprising transmitting an OFDM symbol comprising the subcarrier.

34. A receiver configured to decode a received signal having layered modulation data, the receiver comprising:

means for receiving a layered modulation signal;

means for decoding a base layer data from the layered modulation signal; and

means for decoding an enhancement layer data from the layered modulation signal substantially concurrently with decoding the base layer data.

35. The receiver of claim 34, further comprising means for channel estimation configured to generate a channel estimate based on the layered modulation signal.

36. The receiver of claim 35, wherein the means for channel estimation comprises:

means for comparing an actual channel estimate component to a channel estimation threshold value; and

means for selecting as a channel estimate component, one of the actual channel estimate component or a predetermined value based on the comparison.

37. The receiver of claim 34, wherein the layered modulation signal comprises an OFDM symbol, and wherein the receiver further comprises:

means for transforming the OFDM symbol to a plurality of subcarriers; and

means for generating a channel estimate based on at least one subcarrier from the plurality of subcarriers.

38. The receiver of claim 34, wherein the layered modulation signal comprises an OFDM symbol comprising a plurality of subcarriers, at least two of the plurality of subcarriers modulated with layered modulation data having different energy ratios.

39. A transmitter configured to encode a signal having layered modulation data, the transmitter comprising:

means for encoding a base layer signal to base layer symbols;

means for encoding an enhancement layer signal to enhancement layer symbols; and

means for mapping a base layer symbol in conjunction with an enhancement layer symbol to a constellation point in a layered modulation constellation having an energy ratio selected from a plurality of energy ratios.

40. The transmitter of claim 39, further comprising means for modulating a subcarrier from a plurality of OFDM subcarriers with the constellation point.

41. The transmitter of claim 40, further comprising means for transmitting an OFDM symbol comprising the plurality of subcarriers.