Wireless infrared digital audio receiving system

• US 6,614,849 B1
• Filed: 10/25/1999
• Issued: 09/02/2003
• Est. Priority Date: 10/25/1999
• Status: Expired due to Fees

• Current Assignee: FreeSystems Pte Ltd.
• Original Assignee: FreeSystems Pte Ltd.
• Inventors: Chan, Chee Oei, Chua, Beng Huat, Siew, Chee Kong, Lee, Kah Yong
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/427,020
• Time in Patent Office: 1,408 Days
• Field of Search: 375/259, 375/260, 375/261, 375/295, 375/316, 375/302, 375/322, 375/354, 455/66, 455/103, 455/110, 455/112, 455/131, 455/93, 455/102, 381/77, 381/105, 381/102, 381/80, 381/81, 708/300, 708/313, 708/316
• US Class Current: 375/259
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence

Abstract

A system for transmitting, receiving, recovering, and reproducing digitized samples of analog signals while concealing unrecoverable digitized samples of analog signals to maintain a level of fidelity in reproducing the analog signals. The digitized samples of the analog signals are burst transmitted such that the probability of interference with the transmission and thus corruption of the digitized samples of the analog signals is minimized. The digitized samples are received without synchronizing a receiving clock with a transmitting clock to capture the digitized samples of the analog signals. The digitized samples are converted from various sampling rates to digitized samples of the analog signals having a rate. Any large groups of digitized samples that are in error or corrupted in transmission are softly muted to avoid annoying clicks. Any long term difference between a transmit clock and a receive clock is tracked and the digitized samples are interpolated or decimated to eliminate any underrun or overrun of the digitized samples.

Claims

1. A receiving system for receiving a modulated carrier signal from a communication medium, whereby said modulated carrier signal contains digitized samples of an analog signal comprising:

a receiver connected to the communication medium to recover said modulated carrier signal and extract a modulated transmit frame;

a demodulator connected to said receive to demodulate the modulated transmit frame and recover the transmit frame and extract the groups of interleaved multiple digitized samples of the analog signals with the appended error correction code;

a received data buffer to retain the group of interleaved multiple digitized samples of the analog signals with the appended error correction code;

a received data buffer controller connected to the demodulator and the received data buffer to control transfer of the group of interleaved multiple digitized samples of the analog signals with the appended error correction code from the demodulator to the received data buffer;

an error check and correction circuit connected to the received data buffer controller to receive one group of the multiple digitized samples of the analog signals with the appended error correction code, to check and correct errors in said one of the multiple digitized samples analog signals, to replace the corrected one group of the multiple digitized samples of the analog signals to the received data buffer, and to identify any non-correctable group of the multiple digitized samples analog signals;

a block recovery circuit connected to the received data buffer controller to interpolate the non-correctable group of the multiple digitized samples of the analog signals to conceal an effect of said non-correctable group of the multiple digitized samples analog signals;

a soft muting circuit connected to the received data buffer controller to access those the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors and those of the multiple digitized samples of the analog signals that are correct and adjacent to the multiple digitized samples of the analog signals with non-correctable and non-concealable errors, to apply a smoothing function to said multiple digitized samples of the analog signals to bring those of the multiple digitized samples of the analog signals with the non-correctable and non-concealable error to a null value;

a jitter tracking circuit to compare a block transmission timing signal with a clock signal of said receiver subsystem to determine overrun and underrun of the contents of the group of interleaved multiple digitized samples of the analog signals with the appended error correction code, whereby said block transmission timing signal indicates a boundary between groups of the multiple interleaved digitized samples analog signals;

an interpolation and decimation circuit connected to the jitter tracking circuit and the received data buffer controller to generate or eliminate digitized samples of the analog signals if the jitter tracking circuit indicates overrun or underrun of the contents of the group of interleaved multiple digitized samples analog signals; and

an interface circuit connected to the received data buffer controller to translate the digitized samples of the analog signals to a format acceptable by subsequent circuitry.

2. The receiving system of claim 1 wherein the digitized samples of the analog signals are audio signals digitized and encoded as a non-return to zero digital samples of the analog signal.

3. The receiving system of claim 1 wherein the communication medium is selected from the communication media consisting of wired media and wireless media.

4. The receiving system of claim 3 wherein the modulated carrier signal is transmitted as light.

5. The receiving system of claim 1 wherein the modulated carrier signal is transmitted as a radio frequency signal.

6. The receiving system of claim 3 wherein the wire media comprise coaxial cable, fiber optic cable, and two wire audio cable.

7. The receiving system of claim 1 wherein the error correction code word is a forward error correction code word generated using a Reed-Solomon encoder circuit.

8. The receiving system of claim 1 wherein the error correction code word has a data block size of 238 bytes and one control byte and 16 parity bytes.

9. The receiving system of claim 1 wherein the interleaved group of the multiple digitized samples of the analog signals comprises a plurality of least significant bytes of the even designated digitized samples of the analog signals of the group of multiple digitized samples analog signals, a plurality of most significant of the even designated digitized samples analog signals, a first command byte, a first plurality of error correction parity bytes, a plurality of least significant bytes of the odd designated digitized samples analog signals, a plurality of most significant bytes of the odd designated digitized samples analog signals, a second command byte, and a second plurality of error correction parity bytes.

10. The receiving system of claim 1 wherein said pulse position is determined by the binary value of paired bits within said transmit frame.

11. The receiving system of claim 1 wherein the digitized samples of the analog signals are a non-return to zero encoding of said analog signals.

12. The receiving system of claim 1 the receiver comprises a light sensitive diode that receives light radiated from an infrared light emitting diode.

13. The receiving system of claim 1 wherein the receiver locks onto the modulated carrier signal by oversampling said modulated carrier signal to determine an evaluation point of said modulated carrier signal to recover said transmit frame.

14. The receiving system of claim 1 wherein the receiver circuit detects the preamble timing signal and the start signal to indicate a location of the interleaved group of the multiple digitized samples of the analog signals within the transmit frame.

15. The receiving system of claim 1 wherein the block recovery circuit conceals the effect of said non-correctable group of the multiple digitized samples of the analog signals by interpolating adjacent correct digitized samples of the analog signals to estimate a correct magnitude for said non-correctable group of the multiple digitized samples analog signals.

16. The receiving system of claim 1 wherein the smoothing function applies a Hanning window to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors and those of the multiple digitized samples of the analog signals that are correct and adjacent to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to smoothly decrease those of the multiple digitized samples of the analog signals that are correct and adjacent to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to allow a gentle muting.

17. The receiving system of claim 1 wherein the soft muting circuit, upon bringing multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to a null value, further setting subsequent multiple digitized samples of the analog signals to a null value preventing repetitive interference on said communication medium.

18. A method for receiving, and recovering digitized samples of analog signals comprising the steps of:

receiving a modulated carrier signal;

demodulating said modulated carrier signal to recover said transmit frame;

extracting a plurality of groups of interleaved digitized samples with appended error correction codes from the recovered transmit frame;

checking and correcting the groups of interleaved digitized samples;

if any of the digitized samples have uncorrectable errors, concealing any effect of said uncorrectable errors by interpolating from adjacent correct digitized samples an estimate of a sample value of said digitized samples with uncorrectable errors;

comparing a block transmission timing signal with a receiver clock signal to track jitter between said receiver clock and said block transmission timing signal to determine overrun and underrun of the contents of the group of interleaved multiple digitized samples of the analog signals with the appended error correction code;

interpolating and decimating to generate or eliminate digitized samples of the analog signals if the jitter tracking circuit indicates overrun or underrun of the contents of the group of interleaved multiple digitized samples analog signals; and

soft muting any of the digitized samples that have uncorrectable or non-concealable errors; and

transferring the digitized samples to a digital-to-analog converter to restore the analog signal.

19. The method of claim 18 wherein said the digitized analog signals are formatted as a non-return to zero encoding of the digitized samples of the analog signal.

20. The method of claim 18 wherein the communication medium is selected from the communication media consisting of wired media and wireless media.

21. The method of claim 18 wherein the modulated carrier signal is transmitted as light.

22. The method of claim 18 wherein the modulated carrier signal is transmitted as a radio frequency signal.

23. The system of claim 20 wherein the wire media comprise coaxial cable, fiber optic cable, and two wire audio cable.

24. The method of claim 18 whereby said digitized samples have a sampling rate selected from a plurality of sampling rates.

25. The method of claim 24 wherein the digitized samples have a fixed rate.

26. The method of claim 25 wherein the fixed rate is 48 kHz.

27. The method of claim 25 wherein the fixed rate is 44.1 kHz.

28. The method of claim 18 wherein the error correction code is generated using a Reed-Solomon error correction method.

29. The method of claim 28 wherein the error correction code has a data block size of 238 bytes and 1 control byte and 16 parity bytes.

30. The method of claim 18 wherein the group of interleaved digitized samples are comprised of a plurality of least significant bytes of the even designated digitized samples of the group of multiple digitized samples, a plurality of most significant of the even designated digitized samples, a first command byte, a first plurality of error correction parity bytes, a plurality of least significant bytes of the odd designated digitized samples, a plurality of most significant bytes of the odd designated digitized samples, a second command byte, and a second plurality of error correction parity bytes.

31. The method of claim 18 wherein said carrier signal is modulated by a pulse positioned modulation whereby said pulse positioned modulation is positioning of a pulse of said carrier signal within a period of said carrier signal according to a binary value of a plurality of bits within said transmit frame.

32. The method of claim 31 wherein said plurality of bits is a pair of bits within said transmit frame.

33. The method of claim 18 where demodulating the carrier signal comprises the step of oversampling said modulated carrier signal to determine an evaluation point of said modulated carrier signal to recover said transmit frame.

34. The method of claim 18 wherein extracting the plurality of groups of interleaved digitized samples and error correction codes comprises the step of detecting the preamble timing signal and the start signal to indicate a location of the interleaved group of the multiple digitized samples of the analog signals within the transmit frame.

35. The method of claim of 18 wherein the smoothing function applies a Hanning window to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors and those of the multiple digitized samples of the analog signals that are correct and adjacent to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to smoothly decrease those of the multiple digitized samples of the analog signals that are correct and adjacent to those of the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to allow a gentle muting.

36. The method of claim 18 further comprising the step of, upon soft muting multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to a null value, further setting multiple digitized samples of the analog signals that are subsequent to the multiple digitized samples of the analog signals with non-recoverable and non-concealable errors to a null value preventing repetitive interference on said communication medium.