Wireless infrared digital audio system

• US 6,671,325 B2
• Filed: 10/30/2002
• Issued: 12/30/2003
• Est. Priority Date: 10/25/1999
• Status: Expired due to Fees

• Current Assignee: FreeSystems Pte Ltd.
• Original Assignee: FreeSystems Pte Ltd.
• Inventors: Lee, Kah Yong, Chua, Beng Huat, Chan, Chee Oei, Siew, Chee Kong
• Primary Examiner(s): Vo, Don N.
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US10/283,470
• Publication Number:
  US 20030053548A1
• Time in Patent Office: 426 Days
• Field of Search: 375/259, 375/239, 375/260, 375/261, 375/295, 375/298, 375/316, 375/326, 375/342, 375/346, 375/278, 375/285, 455/3.01, 455/66, 455/91, 455/102, 455/93, 455/103, 455/110, 455/118, 455/131, 381/77, 381/79, 381/80, 381/85, 381/2, 381/7, 381/13, 381/14
• 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
• CPC Class Codes: H04L 7/0066 detection of error based on transmission code rule

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 digital communication system for transmitting and receiving digitized data samples of analog signals comprising:

a transmission subsystem connected to an external signal source for receiving said analog signal from the external signal source, sampling said analog signals to create fixed rate digitized data samples of said analog signals, generating error correction codes for said fixed rate digitized data samples to allow correction of errors in said fixed digitized samples that occur during transmitting of said fixed rate digitized data samples, formatting said fixed rate digitized data samples into groups of interleaved digitized samples, appending the error correction codes, a preamble timing signal and a start signal to said group of interleaved digitized samples to form a transmit frame, modulating a carrier signal with said transmit frame and transmitting as a short burst said modulated carrier signal;

a communication medium connected to the transmission subsystem to transfer said modulated carrier signal; and

a receiving subsystem connected to the communication medium for receiving said modulated carrier signal, demodulating said modulated carrier signal to recover said transmit frame, extracting the group of interleaved digitized samples and the error correction codes from said transmit frame, checking and correcting said group of interleaved digitized samples, identifying any of said group of interleaved digitized samples that are uncorrectable, if any of said group of interleaved digitized samples are uncorrectable, interpolating from adjacent interleaved digitized samples an estimated sample value of those uncorrectable digitized samples to conceal any effect of said uncorrectable digitized samples, applying a smoothing function to said digitized samples to bring those of the digitized samples with the non-correctable and non-concealable errors to a null value, jitter tracking to determine overrun and underrun of the contents of the group of interleaved multiple digitized samples to compare block transmission signal with a clock signal of said receiver subsystem, generating or eliminating digitized samples of the analog signals if the jitter tracking indicates overrun or underrun of the contents of the group of interleaved multiple digitized samples analog signals, and transferring the digitized samples to a digital-to-analog converter for restoration of said analog signal.

2. The communication system of claim 1 wherein said transmission subsystem comprises:

a sampled data receiver to receive said digitized samples of the analog signals from the external source of the digitized samples analog signals;

a data buffer to retain a plurality of the digitized samples analog signals,

a data buffer controller connected to the data buffer to control the placement and removal of the plurality of digitized samples of the analog signals within the data buffer;

an error correction code generator connected to the data buffer controller to receive multiple digitized samples of the analog signals through said data buffer controller from said data buffer, to generate an error correction word to be appended to said multiple digitized samples analog signals, and to return the multiple digitized samples of the analog signals with the appended error correction word through the data buffer controller to the data buffer;

a frame formatter connected to the data buffer controller to receive an interleaved group of the multiple digitized samples of the analog signals and append a preamble timing signal and a start signal before said interleaved group of the multiple digitized samples of the analog signals to form a transmit frame;

a pulse position modulator connected to the frame formatter to receive the transmit frame and modulate according to a bit value of the transmit frame a pulse position within a carrier signal with the transmit frame; and

a burst transmitter connected between the pulse position modulator and the communication medium to convey a modulated carrier signal to said communication medium, whereby said modulated carrier signal is transmitted as the short burst within a short time period to minimize probability of interference on said communication medium.

3. The communication system of claim 2 wherein the transmission subsystem receives said digitized data samples of the analog signals that are sampled at a plurality of sampling rates and converts said digitized data samples sampled at the plurality of sampling rates to fixed rate digitized data samples, and wherein said transmission subsystem comprising a variable sampling rate converter connected to said sampled data receiver to convert the digitized samples of the analog signals at the one rate of the plurality of sampling rates to digitized samples of the analog signals sampled at a fixed rate.

4. The communication system of claim 1 wherein the receiving subsystem comprises:

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

a demodulator connected to said receiver 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 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 the non-correctable and non-concealable errors, to apply the 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 the null value;

a jitter tracking circuit to compare the block transmission signal with the clock signal of said receiver subsystem to determine the 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 of said group of the multiple digitized samples analog signals;

a synchronization 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.

5. The communication system of claim 1 wherein the analog signals are digitized and formatted to form the digitized samples having a non-return to zero encoding.

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

7. The communication system of claim 1 wherein the modulated carrier signal is transmitted as light.

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

9. The communication system of claim 1 wherein the wired media comprise coaxial cable, fiber optic cable, and two wire audio cable.

10. The communication system of claim 2 wherein the transmission subsystem further converts the analog signals to digitized samples.

11. The communication system of claim 10 wherein the transmission subsystem is further comprising at least one analog-to-digital converter connected between the external source and the data buffer controller to receive the analog signals and to generate the digitized samples of the analog signals.

12. The communication system of claim 1 wherein the digitized samples are sampled at one of a plurality of sampling rates.

13. The communication system of claim 12 wherein the plurality of sampling rates comprise 32 kHz, 44.1 kHz, and 48 kHz.

14. The communication system of claim 3 wherein the fixed sampling rate is selected from a group of sampling rates consisting of 48 kHz and 44.1 kHz.

15. The communication system of claim 1 wherein the error correction code is a forward error correction code using a Reed Solomon encoding.

16. The communication system of claim 15 wherein the error correction code word has a data block size of 238 bytes and one control byte and 16 parity bytes.

17. The communication system of claim 1 wherein the interleaved group of the multiple digitized samples comprises 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.

18. The communication system of claim 1 wherein said carrier signal is modulated with 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.

19. The communication system of claim 18 wherein said plurality of bits is a pair of bits within said transmit frame.

20. The communication system of claim 19 wherein the digitized samples are a non-return to zero encoding.

21. The communication system of claim 2 wherein said burst transmitter comprises an infrared light emitting diode and a diode switching circuit connected between the pulse position modulator and the infrared light emitting diode to activate and deactivate said infrared light emitting diode with the modulated carrier signal.

22. The communication system of claim 4 wherein the receiver comprises a light sensitive diode that receives light radiated from the infrared light emitting diode.

23. The communication system of claim 4 wherein the demodulator demodulates 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.

24. The communication system of claim 4 wherein the demodulator 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.

25. The communication system of claim 4 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.

26. The communication system of claim 4 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.

27. The communication system of claim 4 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 sets subsequent multiple digitized samples of the analog signals to a null value preventing repetitive interference on said communication medium.

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

acquiring said analog signals;

sampling said analog signals at a fixed sampling rate to generate said digitized signals;

interleaving the digitized samples to separate adjacent digitized samples decreasing a probability of loss of fidelity of said analog signal due to unrecoverable errors;

generating an error correction code to provide a group of interleaved digitized samples with redundancy to recover interleaved digitized samples having errors created during transmitting and receiving;

forming a transmit frame with a plurality of groups of interleaved digitized samples, error correction codes, a preamble timing signal, and a start signal;

modulating a carrier signal with said transmit frame;

transmitting as a burst the modulated carrier signal on a communication medium, whereby said burst is a short period of time relative to a time of sampling represented by said digitized samples within the transmit frame;

receiving the modulated carrier signal;

demodulating said modulated carrier signal to recover said transmit frame;

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

checking and correcting the groups of interleaved digitized samples;

identifying any of said group of interleaved digitized samples that are uncorrectable;

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;

applying a smoothing function to said digitized samples to bring those of the digitized samples with the non-correctable and non-concealable errors to a null value;

jitter tracking to determine overrun and underrun of the contents of the group of interleaved multiple digitized samples to compare a block transmission signal with a clock signal of said receiver subsystem;

generating or eliminating digitized samples of the analog signals if the utter tracking indicates overrun or underrun of the contents of the group of interleaved multiple digitized samples analog signals; and

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

29. The method of claim 28 further comprising the steps of:

digitizing said analog signals, and

formatting the digitized analog signal as a non-return to zero encoding of the digitized samples of the analog signal.

30. The method of claim 28 wherein the communication medium is selected from the communication media consisting of wired media and wireless media.

31. The method of claim 28 wherein the modulated carrier signal is transmitted as light.

32. The method of claim 28 wherein the modulated carrier signal is transmitted as a radio frequency signal.

33. The system of claim 30 wherein the wire media comprise coaxial cable, fiber optic cable, and two wire audio cable.

34. The method of claim 28 further comprising the steps of:

receiving digitized data samples of the analog signals, whereby said digitized samples of the analog signal have a sampling rate selected from a plurality of sampling rates; and

converting said digitized data samples sampled at one of the plurality of sampling rates to the fixed rate digitized data samples.

35. The method of claim 34 wherein the plurality of sampled rates of 32 kHz, 44.1 kHz, and 48 kHz.

36. The method of claim 28 wherein the fixed rate is 48 kHz.

37. The method of claim 28 wherein the fixed rate is 44.1 kHz.

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

39. 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.

40. The method of claim 28 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 panty bytes.

41. The method of claim 28 wherein modulating said carrier signal comprises the step of positioning 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.

42. The method of claim 41 wherein said plurality of bits is a pair of bits within said transmit frame.

43. The method of claim 28 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.

44. The method of claim 28 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.

45. The method of claim 28 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.

46. The method of claim 28 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.