Low complexity error concealment for wireless transmission

• US 7,155,654 B2
• Filed: 05/10/2003
• Issued: 12/26/2006
• Est. Priority Date: 04/04/2003
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: SST Communications Corporation (Microchip Technology Incorporated)
• Inventors: Chien, Charles, Chien, David Hsueh-Chia
• Primary Examiner(s): Lamarre, Guy J.
• Application Number:
  US10/435,176
• Publication Number:
  US 20040205438A1
• Time in Patent Office: 1,326 Days
• Field of Search: 714/758, 714/748, 714746-747
• US Class Current: 714/747
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: H03M 13/00 Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes error detection or error correction for analogue/digital, digital/analogue or code conversion H03M1/00 – H03M11/00; specially adapted for digital computers G06F11/08; for information storage based on relative movement between record carrier and transducer G11B, e.g. G11B20/18; for static stores G11C
• CPC Class Codes: H04L 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/0072 Error control for data other than payload data, e.g. control data

Abstract

An apparatus and method for concealing errors in digital data. An interpolator estimates a value of a sample of digital data from other samples of the digital data. The interpolator has an input for inputting the digital data and an output for outputting the estimated value of the sample of the digital data. A holding unit has an input for selectively receiving the sample of the digital data only when the sample is error free, and an output for outputting the error free sample. The input of the holding unit may be in parallel with the input of the interpolator. A selector selects between outputting the estimated value of the sample of the received digital data from an output of the interpolator and outputting the error free sample of the received digital data from an output of a holding unit based on at least one error indicator.

Claims

1. An apparatus for concealing errors in digital data, the apparatus having an input for receiving the digital data and an output for outputting the digital data after error concealment, the apparatus further comprising:

at least one interpolator for estimating a value of a sample of the received digital data from other samples of the received digital data, the other samples including samples besides a sample immediately previous to the sample of received digital data, the at least one interpolator having an input for inputting the received digital data and an output for outputting the estimated value of the sample of the received digital data;

at least one first holding unit having an input for selectively receiving the sample of the received digital data only when the sample is error free, and an output for outputting the error free sample of the received digital data; and

a selector for selecting between outputting the estimated value of the sample of the received digital data and outputting the error free sample of the received digital data based on at least one error indicator.

2. The apparatus recited in claim 1, wherein the input of the at least one first holding unit is in parallel with the input of the at least one interpolator.

3. The apparatus recited in claim 1, wherein the estimated value of the sample of the received digital data or the error free sample of the received digital data is outputted to the output of the apparatus.

4. The apparatus recited in claim 1, wherein the at least one error indicator results from a cyclic redundancy check (CRC) performed on at least one sample of the received digital data.

5. The apparatus recited in claim 1, wherein the at least one error indicator comprises three enor indicators, the three error indicators resulting from a cyclic redundancy check (CRC) performed on three corresponding temporally adjacent samples of the received digital data.

6. The apparatus recited in claim 1, wherein the at least one interpolator comprises at least one first-order interpolator.

7. The apparatus recited in claim 6, wherein the at least one first-order interpolator comprises at least one left audio data first-order interpolator and at least one right audio data first-order interpolator.

8. The apparatus recited in claim 6, wherein the at least one first holding unit comprises at least one left audio data first holding unit and at least one right audio data first holding unit.

9. The apparatus recited in claim 6, wherein the selector comprises at least one left audio data multiplexer (MUX) and at least one right audio data multiplexer (MUX), each of the at least one left audio data multiplexer (MUX) and the at least one right audio data multiplexer (MUX) having a first input for receiving the outputted estimated value of the sample of the received digital data, a second input for receiving the outputted error free sample of the received digital data, and an output for outputting one of the estimated value of the sample of the received digital data and the error free sample of the received digital data based on the at least one error indicator.

10. The apparatus recited in claim 9, wherein each of the at least one left audio data multiplexer (MUX) and the at least one right audio data multiplexer (MUX) includes a select line;

wherein the at least one error indicator comprises a plurality of error indicators; and

wherein the selector further comprises combinational logic having at least one input for receiving the plurality of error indicators and at least one output coupled to the select line of each of the at least one left audio data multiplexer (MUX) and the at least one right audio data multiplexer (MUX), the combinational logic generating a first logic level at the at least one output when the plurality of error indicators have a first pattern and a second logic level at the at least one output when the plurality of error indicators have a second pattern.

11. The apparatus recited in claim 10, wherein the plurality of error indicators comprises three error indicators corresponding respectively to three samples of the received digital data;

and wherein the first pattern indicates that a first one of the three samples has an error while a second one and a third one of the three samples does not have an error, the second one and the third one of the three samples each being temporally adjacent to the first one of the three samples.

12. The apparatus recited in claim 10, wherein the first logic level selects the error free sample of the received digital data to be outputted at the output of the at least one left audio data multiplexer (MUX) and the at least one right audio data multiplexer (MUX), and the second pattern selects the estimated value of the sample of the received digital data to be outputted at the outputs of the at least one left audio data multiplexer (MUX) and the at least one right audio data multiplexer (MUX).

13. The apparatus recited in claim 1, wherein the at least one interpolator comprises at least one second-order interpolator.

14. The apparatus recited in claim 13, wherein the at least one error indicator comprises three error indicators corresponding respectively to three samples of the digital data;

wherein the at least one first holding unit selectively receives a first sample of the three samples only when the first sample is error free; and

wherein the at least one second-order interpolator comprises;

at least one second holding unit including an input for selectively receiving a combination of a second sample and a third sample of the three samples only when the second sample and the third sample are both error free, and an output for outputting the error free combination of the second sample and the third sample; and

at least one third holding unit including an input for selectively receiving a combination of the first sample, the second sample and the third sample of the three samples only when the first sample, the second sample and the third sample are all error free, and an output for outputting the error free combination of the first sample, the second sample and the third sample.

15. The apparatus recited in claim 14, wherein the interpolator further comprises an adder for summing the error free first sample, the error free combination of the second sample and the third sample, and the error free combination of the first sample, the second sample and the third sample to produce a summed output, the adder having inputs for receiving the error free first sample, the error free combination of the second sample and the third sample, and the error free combination of the first sample, the second sample and the third sample, and an output for outputting the summed output.

16. The apparatus recited in claim 14, wherein each of the at least one first holding unit, the at least one second holding unit and the at least one third holding unit each comprise an enable line;

and

wherein cach of the error free first sample, the error free combination of the second sample and the third sample, and the error free combination of the first sample, the second sample and the third sample are received by respective ones of the at least one first holding unit, the at least one second holding unit and the at least one third holding unit only when the corresponding enable line is active.

17. The apparatus recited in claim 16, wherein the selector comprises at least one multiplexer (MUX) having a first input for receiving the error free first sample, a second input for receiving the summed output, and an output for outputting one of the error free first sample and the summed output based on at least one of the three error indicators.

18. The apparatus recited in claim 17, wherein the at least one multiplexer (MUX) includes a select line;

and

wherein the selector further comprises at least one logic gate having at least one input for receiving at least one of the three error indicators and at least one output for controlling at least one of the select line of the at least one multiplexer (MUX) and the enable line of the at least one first holding unit, the at least one logic gate generating a first logic level at the at least one output when the at least one of the three error indicators has a first state and a second logic level at the at least one output when the at least one of the three error indicators has a second state.

19. The apparatus recited in claim 16, wherein the selector further comprises at least one logic gate having at least two inputs for receiving at least two of the three error indicators and at least one output coupled to the enable line of the at least one second holding unit, the at least one logic gate generating a first logic level at the at least one output when the at least two of the three error indicators have a first pattern and a second logic level at the at least one output when the at least two of the three error indicators have a second pattern.

20. The apparatus recited in claim 16, wherein the selector further comprises at least one logic gate having at least three inputs for receiving the three error indicators and at least one output coupled to the enable line of the at least one third holding unit, the at least one logic gate generating a first logic level at the at least one output when the three error indicators have a first pattern and a second logic level at the at least one output when the three error indicators have a second pattern.

21. The apparatus recited in claim 14, wherein each of the at least one first holding unit, the at least one second holding unit and the at least one third holding unit comprise at least one register.

22. The apparatus recited in claim 21, wherein the at least one register is at least one of a D-type flip-flop and an RS flip-flop.

23. The apparatus recited in claim 1, wherein the at least one interpolator comprises at least one third-order interpolator.

24. The apparatus recited in claim 1, wherein the at least one interpolator conipi-ises a multiple-order interpolator.

25. The apparatus recited in claim 24, wherein the multiple-order interpolator comprises multiple selectable interpolators.

26. The apparatus recited in claim 25, wherein the multiple selectable interpolators are selectable based on at least one of a signal-to-noise ratio (SNR) and an error rate.

27. The apparatus recited in claim 26, wherein the digital data is contained in a packet having at least one audio data block, and wherein the error rate is at least one of a bit error rate, an audio data block error rate, or a packet error rate.

28. The apparatus recited in claim 27, wherein the bit error rate is estimated.

29. The apparatus recited in claim 27, wherein the packet error rate and the block error rate are computed based on a number of error indicators occurring over at least one of a plurality of packets and a plurality of audio data blocks.

30. The apparatus recited in claim 25, wherein the multiple selectable interpolators are selectable based on a comparison of a signal-to-noise ratio (SNR) of a received baseband signal to a threshold signal-to-noise ratio (SNR).

31. The apparatus recited in claim 25, wherein the multiple selectable interpolators are selectable based on a comparison of an error rate in the received digital data to a threshold error rate.

32. The apparatus recited in claim 1, wherein the selector comprises at least one multiplexer (MUX) having a first input for receiving the outputted estimated value of the sample of the received digital data, a second input for receiving the outputted error free sample of the received digital data, and an output for outputting one of the estimated value of the sample of the received digital data and the error free sample of the received digital data based on the at least one error indicator.

33. The apparatus recited in claim 1, wherein the at least one interpolator comprises at least one additional holding unit and wherein the selector selectively enables the at least one additional holding unit.

34. The apparatus recited in claim 1, wherein the digital data is audio data.

35. The apparatus recited in claim 1, wherein the digital data is formatted as a packet.

36. The apparatus recited in claim 35, wherein the packet comprises an error correction code.

37. The apparatus recited in claim 35, wherein the packet comprises:

a preamble;

a three bit SOF field;

an eight bit header field with an eight bit cyclic redundancy check (CRC); and

at least one audio data block, the at least one audio data block having an eight bit cyclic redundancy check (CRC).

38. The apparatus recited in claim 37, wherein the at least one audio data block comprises an Audio Data (Right) channel and an Audio Data (Left) channel.

39. The apparatus recited in claim 38, wherein each of the Audio Data (Right) channel and the Audio Data (Left) channel has 20 bits.

40. The apparatus recited in claim 37, wherein the packet further comprises an eight bit command field with an eight bit cyclic redundancy check (CRC).

41. The apparatus recited in claim 37, wherein the at least one audio data block comprises 40 bits.

42. The apparatus recited in claim 37, wherein the at least one audio data block comprises a plurality of audio data blocks, and wherein the header field specifies how many audio data blocks are in the plurality of audio data blocks.

43. The apparatus recited in claim 37, wherein the plurality of audio data blocks are interleaved.

44. The apparatus recited in claim 1, wherein the at least one first holding unit includes an enable line, and wherein the sample of the received digital data is received only when the enable line is active.

45. The apparatus recited in claim 1, wherein the at least one first holding unit comprises at least one register.

46. The apparatus recited in claim 45, wherein the at least one register is at least one of a D-type flip-flop and a RS flip-flop.

47. The apparatus recited in claim 45, wherein the at least one register is clocked by a clock at a multiple of at least one of 44.1 KHz and 48 KHz.

48. A receiver for receiving a signal including digital data in the form of packets transmitted from a transmitter, and for concealing errors in the digital data, the receiver comprising:

an interpolator section including;

at least one interpolator for estimating a value of a sample of received digital data from other samples of the received digital data, the other samples including samples besides a sample immediately previous to the sample of received digital data, the at least one interpolator having an input for inputting the received digital data and an output for outputting the estimated value of the sample of the received digital data;

at least one holding unit having an input for selectively receiving the sample of the received digital data only when the sample is error free and an output for outputting the error free sample of the received digital data; and

a selector for selecting between outputting the estimated value of the sample of the received digital data and outputting the error free sample of the received digital data based on at least one error indicator.

49. The receiver recited in claim 48, wherein the at least one interpolator comprises at least one additional holding unit and wherein the selector selectively enables the at least one additional holding unit.

50. The receiver recited in claim 48, wherein the input of the at least one holding unit is in parallel with the input of the at least one interpolator.

51. The receiver recited in claim 48, wherein the estimated value of the sample of the received digital data or the error free sample of the received digital data is outputted to an output of the interpolator section.

52. The receiver recited in claim 48, further comprising:

a radio frequency (RF) receiver section for receiving the transmitted digital data as in-phase (I) and quadrature (Q) components of a baseband signal;

a sampling device coupled to the radio frequency (RF) receiver for digitizing each of the in-phase (1) and quadrature (Q) components; and

a demodulator coupled to the sampling device for recovering transmitted symbols.

53. The receiver recited in claim 52, wherein the demodulator is a non-coherent demodulator.

54. The receiver recited in claim 53, wherein the non-coherent demodulator comprises differential detectors for multiplying the in-phase (I) and quadrature (Q) components of the baseband signal by a delayed version of the in-phase (I) and quadrature (Q) components of the baseband signal.

55. The receiver recited in claim 54, wherein the delayed version of the in-phase (I) and quadrature (Q) components of the baseband signal has a delay equal to a period of a symbol clock for clocking the sampling device at the symbol rate.

56. The receiver recited in claim 54, wherein the non-coherent demodulator further comprises:

an adder having inputs for receiving outputs of the differential detectors, the adder for adding the received outputs of the differential detectors and for generating a soft decision value at an output of the adder; and

a slicer having an input for receiving the soft decision value and for generating a demodulated symbol based on the soft decision value at an output of the slicer.

57. The receiver recited in claim 53, wherein the non-coherent demodulator demodulates differentially encoded binary phase shift key (BPSK) signals.

58. The receiver recited in claim 52, further comprising a forward error correction (FEC) decoder coupled to the demodulator for recovering originally transmitted data from the recovered transmitted symbols.

59. The receiver recited in claim 58, further comprising a packet deformatter for deformatting the packets, the packet deformatter having an input coupled to the forward error correction (FEC) decoder and an output coupled to the interpolator section.

60. The receiver recited in claim 59, further comprising an audio interface section for processing the digital data, the audio interface section having an input coupled to the interpolator section and an output for outputting the digital data in a standard format.

61. The receiver recited in claim 60, wherein the digital data is audio digital data, and wherein the standard format is an I2S format.

62. The receiver recited in claim 60, wherein the digital data is audio digital data, and wherein the standard format is a Sony Phillips Digital Interface (SPDIF) form at.

63. The receiver recited in claim 59, wherein the packets transmitted from the transmitter include a plurality of audio data blocks;

wherein the transmitter includes an audio data block interleaver for interleaving an original sequence of the plurality of audio data blocks; and

wherein the packet deformatter comprises an audio data block de-interleaver for reverting the interleaved plurality of audio data blocks to the original sequence.

64. The receiver recited in claim 63, wherein the audio data block interleaver comprises:

a buffer for buffering the audio data blocks; and

an interleaver sequencer for interleaving the buffered audio data blocks.

65. The receiver recited in claim 63, wherein the audio data block de-interleaver comprises:

a buffer for buffering the interleaved audio data blocks; and

a de-interleaver sequencer for de-interleaving the interleaved audio data blocks.

66. The receiver recited in claim 65, wherein the audio data block de-interleaver further comprises a parser for parsing the audio data blocks into data corresponding to a plurality of audio channels.

67. The receiver recited in claim 59, wherein the packet deformatter detects a dropped packet and sends an error indicator corresponding to a sample of the received digital data contained in the dropped packet to the interpolation section.

68. The receiver recited in claim 48, wherein the digital data is audio digital data, and wherein the audio digital data is sampled at an audio sampling rate of 44.1 KHz or 48 KHz.

69. The receiver recited in claim 48, wherein the packets transmitted from the transmitter comprise an error correction code.

70. The receiver recited in claim 48, wherein the packets transmitted from the transmitter comprise:

a preamble;

a three bit SOF field;

an eight bit header field with an eight bit cyclic redundancy cheek (CRC); and

at least one audio data block, the at least one audio data block having an eight bit cyclic redundancy check (CRC).

71. The receiver recited in claim 70, wherein the at least one audio data block comprises a plurality of audio data blocks, and wherein the plurality of audio data blocks are interleaved.

72. The receiver recited in claim 48, wherein the receiver further comprises a mute signal activation section for activating a mute signal.

73. The receiver recited in claim 72, wherein the packets comprise at least one audio data block;

and

wherein the mute signal is activated based on a threshold number of contiguous audio data blocks having errors and a threshold number of contiguous audio data blocks that do not contain any errors.

74. The receiver recited in claim 73, wherein the mute signal activation section activates the mute signal when a number of contiguous audio data block errors is greater than the threshold number of contiguous audio data blocks having errors.

75. The receiver recited in claim 74, wherein the mute signal activation section:

determines if a number of contiguous audio data blocks that do not contain any errors is greater than the threshold number of contiguous audio data blocks that do not contain any errors; and

deactivates the mute signal when the number of contiguous audio data blocks that do not contain any errors is greater than the threshold number of contiguous audio data blocks that do not contain any errors.

76. The receiver recited in claim 48, further comprising an error monitoring section for monitoring a audio data block error rate.

77. The receiver recited in claim 76, wherein a audio data block error is determined when the error indicator indicates an error.

78. The receiver recited in claim 76, wherein the error monitoring section determines a number of audio data block errors occurring over 64 audio data blocks and generates an error count corresponding to the determined number of audio data block errors.

79. The receiver recited in claim 78, wherein the error monitoring section generates an error monitor signal having a frequency based on the generated error count.

80. The receiver recited in claim 79, wherein the error monitor signal is a square wave.

81. The receiver recited in claim 78, wherein the error monitor signal drives a visual indicator.

82. The receiver recited in claim 81, wherein the visual indicator is a light emitting diode (LED).

83. The receiver recited in claim 48, wherein the signal including digital data in the form of packets is transmitted from the transmitter to the receiver on a carrier frequency within a shared band of frequencies, the shared band having designated channels with designated bandwidths, a first designated bandwidth of a first channel ending at a first predetermined frequency within the shared band and a second designated bandwidth of a second channel beginning at a second predetermined frequency within the shared band, the carrier frequency being centered between the first predetermined frequency and the second predetermined frequency.

84. The receiver recited in claim 83, wherein the first predetermined frequency and the second predetermined frequency are the same frequency.

85. The receiver recited in claim 83, wherein the designated bandwidths of the designated channels begin and end at respective 10 dB down points of the designated bandwidths.

86. The receiver recited in claim 83, wherein the shared band is the Industrial Scientific Medical (ISM) band.

87. The receiver recited in claim 83, wherein the carrier frequency is selected from the group consisting of 5.165 Giga Hertz (GHz), 5.19 GHz, 5.21 GHz, 5.23 GHz, 5.25 GHz, 5.27 GHz, 5.29 GHz, 5.31 GHz, 5.335 GHz, 5.735 GHz, 5.755 GHz, 5.775 GHz, 5.795 GHz, 5.815 GHz, 2.427 GHz, 2.4245 GHz or 2.425 GHz, 2.457 GHz, 2.4495 GHz or 2.450 GHz, and 2.47275 GHz or 2.473 GHz.

88. A communication system comprising:

a transmitter for transmitting digital data; and

a receiver for receiving the transmitted digital data, the receiver including;

at least one interpolator for estimating a value of a sample of received digital data from other samples of the received digital data, the other samples including samples besides a sample immediately previous to the sample of received digital data, the at least one interpolator having an input for inputting the received digital data and an output for outputting the estimated value of the sample of the received digital data;

at least one holding unit having an input for selectively receiving the sample of the received digital data only when the sample is error free, and an output for outputting the error free sample of the received digital data; and

a selector for selecting between outputting the estimated value of the sample of the received digital data and outputting the error free sample of the received digital data based on at least one error indicator.

89. The communication system recited in claim 88, wherein the input of the at least one holding unit is in parallel with the input of the at least one interpolator.

90. A method for concealing errors in digital data, the method comprising:

providing at least one interpolator for estimating a value of a sample of digital data from other samples of the digital data, the other samples including samples besides a sample immediately previous to the sample of received digital data, the at least one interpolator having an input for inputting the digital data and an output for outputting the estimated value of the sample of the digital data;

providing at least one holding unit having an input for selectively receiving the sample of the digital data only when the sample is error free and an output for outputting the error free sample of the digital data; and

providing a selector for selecting between outputting the estimated value of the sample of the digital data and outputting the error free sample of the digital data based on at least one error indicator.

91. The method recited in claim 90, wherein the input of the at least one holding unit is in parallel with the input of the at least one interpolator.

92. The method recited in claim 90, wherein the at least one error indicator results from a cyclic redundancy check (CRC) performed on at least one sample of the received digital data.

93. The method recited in claim 90, wherein the at least one error indicator comprises three error indicators, the three error indicators resulting from a cyclic redundancy check (CRC) performed on three corresponding temporally adjacent samples of the digital data.

94. The method recited in claim 90, wherein the digital data is audio data.

95. The method recited in claim 90, wherein the digital data is formatted as a packet.