Method and apparatus for communicating a plurality of asynchronous signals over a digital communication path

• US 5,138,440 A
• Filed: 10/29/1990
• Issued: 08/11/1992
• Est. Priority Date: 10/29/1990
• Status: Expired due to Term

• Current Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Radice, Anthony M.
• Primary Examiner(s): Peng, John K.
• Application Number:
  US07/604,868
• Time in Patent Office: 652 Days
• Field of Search: 358/13, 358/141, 370/94.1, 370/111, 370/112, 370/84, 370/110.1
• US Class Current: 348/472
• CPC Class Codes: H04L 2007/045 Fill bit or bits, idle words
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• CPC Class Codes: H04N 21/23611 Insertion of stuffing data into a multiplex stream, e.g. to obtain a constant bitrate synchronisation arrangements in time-division multiplex systems using bit stuffing for systems with different or fluctuating information rates H04J3/073
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083

Abstract

Multiple asynchronous signals are transmitted and received through a digital link. Each of a plurality of information signals is digitized at a digitizing rate derived from a component of the signal. For example, the color subcarrier of a television signal can be used to establish the digitizing rate for video and audio signal portions. Each digitized signal is packetized for communication at a transmission rate greater than and asynchronous with its digitizing rate. A variable time interval results between successive transmitted packets for each signal. The time interval between each successive packet for each signal is filled with a variable number of pad bits to provide a continuous data stream. The data streams for all of the signals are multiplexed to provide a combined data stream for transmission. Each packet for each of the signals contains a fixed number of data bits digitized over a fixed time interval related to the digitizing rate for the signal. The transmitted combined data stream is received, and the receipt of successive packets is monitored for each signal to determine the fixed time interval for that signal. The digitizing rate for each signal is computed from its fixed time interval. The received data packets for each signal are then converted to an analog form at the signal'"'"'s digitizing rate to reconstruct the original information signals.

Claims

1. Apparatus for communicating signals over a digital communication path comprising:

means for digitizing an information signal at a first rate to provide digital data for processing into data packets;

means for providing a periodic begin signal synchronous with said first rate and indicative of the occurrence of successive new data packets;

means for outputting said data packets for transmission at a second rate greater than and asynchronous with said first rate, thereby producing a variable time interval between successive transmitted packets; and

means, operatively associated with said outputting means and responsive to said begin signal, for filling the time intervals between successive packets with pad bits to provide a continuous data stream for transmission.

2. Apparatus in accordance with claim 1 further comprising:

receiver means for receiving the transmitted data packets;

means responsive to the received data packets for generating a timing signal corresponding to said first rate; and

means responsive to the timing signal for reconstructing said information signal from the received data packets.

3. Apparatus in accordance with claim 1 wherein:

said information signal is a communication signal having at least one subcarrier; and

said first rate is derived from the frequency of said subcarrier.

4. Apparatus in accordance with claim 1 wherein:

said information signal is a television signal; and

said first rate is derived from the color subcarrier frequency of the television signal.

5. Apparatus in accordance with claim 1 further comprising:

means for processing a plurality of channels of asynchronous information signals in the same manner as said information signal; and

means for combining said plurality of information signals to provide a multiplexed data stream for transmission at a rate that is synchronous with said second rate.

6. Apparatus in accordance with claim 5 further comprising:

receiver means for receiving the multiplexed data stream;

means for demultiplexing the received data stream to recover the data packets for each channel;

means responsive to the recovered data packets for each channel for generating an associated timing signal that corresponds to the first rate used to digitize the data for that particular channel; and

means responsive to the timing signal for each channel for reconstructing the original information signals represented by the recovered data packets.

7. Apparatus in accordance with claim 5 wherein:

said information signals are television signals; and

the first rate for each information signal is derived from its color subcarrier frequency.

8. Apparatus for communicating a plurality of asynchronous signals over a digital transmission path comprising:

means for digitizing an information signal at a first rate to provide digital data;

buffer means coupled to receive said data at said first rate for storage;

packetizing means coupled to receive said data from said buffer means at a second rate greater than said first rate for processing into data packets;

means for providing a periodic begin signal that is synchronous with said first rate and indicative of the occurrence of successive data packets;

means for outputting said data packets for transmission at said second rate with a time interval between successive packets resulting from the difference in time it takes the buffer means to receive data at said first rate and the outputting means to output data at said second rate; and

means, operatively associated with said outputting means and responsive to said begin signal, for filling the time intervals between successive packets with pad bits to provide a continuous data stream for transmission.

9. Apparatus in accordance with claim 8 wherein:

said digitizing means provide parallel data for input to said buffer means and processing by said packetizing means; and

said outputting means convert parallel data from said packetizing means to a serial output stream for transmission.

10. Apparatus in accordance with claim 8 wherein said buffer means comprise:

a pair of complementary buffers; and

switch means for coupling one buffer of said pair to receive data from the digitizing means while the other buffer of said pair is coupled to output data to said packetizing means, and vice-versa.

11. Apparatus in accordance with claim 10 wherein said switch means are responsive to said begin signal for alternately coupling said buffers to receive data and output data in complement.

12. Apparatus in accordance with claim 8 wherein said information signal is a television signal and said first rate is derived from a subcarrier frequency thereof.

13. Apparatus in accordance with claim 8 wherein said information signal is a television signal and said digitizing means comprise:

a first analog to digital converter for digitizing a video portion of said television signal at said first rate; and

a second analog to digital converter for digitizing an audio portion of said television signal at a digitizing rate that is synchronous with said first rate.

14. Apparatus in accordance with claim 13 wherein said buffer means comprise:

a first pair of complementary buffers associated with said first analog to digital converter;

first switch means for coupling one buffer of said first pair to receive video data while the other buffer of said first pair is coupled to output video data to said packetizing means, and vice-versa;

a second pair of complementary buffers associated with said second analog to digital converter; and

second switch means for coupling one buffer of said second pair to receive audio data while the other buffer of said second pair is coupled to output audio data to said packetizing means, and vice-versa.

15. Apparatus in accordance with claim 14 wherein said first and second switch means are responsive to said begin signal for switching said buffers.

16. Apparatus in accordance with claim 8 further comprising:

means for inputting packet header data to said packetizing means for incorporation into said data packets.

17. Apparatus in accordance with claim 16 wherein said packetizing means is responsive to said begin signal for incorporating header data into said packets.

18. Apparatus in accordance with claim 16 further comprising:

means for inputting auxiliary data to said packetizing means for incorporation into said data packets.

19. Apparatus in accordance with claim 8 further comprising:

means for processing a plurality of channels of asynchronous information signals in the same manner as said information signal; and

means for combining said plurality of information signals to provide a multiplexed data stream for transmission at a rate that is synchronous with said second rate.

20. Apparatus in accordance with claim 19 wherein said information signals are television channel signals.

21. Apparatus in accordance with claim 20 wherein each television signal is digitized at a corresponding first rate derived from its color subcarrier frequency.

22. Apparatus in accordance with claim 20 wherein said digitizing means comprise:

first analog to digital converter means for digitizing a video portion of each television channel signal at a respective first rate for the signal; and

second analog to digital converter means for digitizing an audio portion of each television channel signal at a digitizing rate that is synchronous with the respective first rate for the signal.

23. Apparatus in accordance with claim 22 wherein said buffer means comprise:

a first pair of complementary buffers associated with the first analog to digital converter means for each channel signal;

first switch means associated with the first pair of buffers for each channel signal for coupling one buffer of each first pair to receive video data while the other buffer of each first pair is coupled to output video data to said packetizing means, and vice-versa;

a second pair of complementary buffers associated with the second analog to digital converter means for each channel signal; and

second switch means associated with the second pair of buffers for each channel signal for coupling one buffer of each second pair to receive audio data while the other buffer of each second pair is coupled to output audio data to said packetizing means, and vice-versa.

24. Apparatus in accordance with claim 23 wherein said first and second switch means for each channel signal are responsive to that channel signal'"'"'s begin signal to switch the associated buffers.

25. Apparatus in accordance with claim 19 further comprising:

receiver means for receiving a plurality of channels of transmitted data packets contained in said multiplexed data stream;

means for demultiplexing said data stream to recover the data packets for each channel;

means, responsive to an interval in which the recovered data packets for each channel are received, for generating a timing signal for each channel corresponding to the first rate used to digitize the data for that particular channel; and

means responsive to said timing signals for reconstructing the original information signals represented by the recovered data packets.

26. Apparatus in accordance with claim 25 wherein:

said information signals are television signals; and

the first rate for each information signal is derived from its color subcarrier frequency.

27. Apparatus in accordance with claim 8 further comprising:

receiver means for receiving the transmitted data packets;

means, responsive to an interval in which successive data packets are received, for generating a timing signal corresponding to said first rate; and

means responsive to the timing signal for reconstructing said information signal from the received data packets.

28. Apparatus in accordance with claim 27 wherein:

said information signal is a television signal; and

said first rate is derived from the color subcarrier frequency of the television signal.

29. Apparatus in accordance with claim 8 wherein said information signal contains a plurality of signals which are separately digitized for input to said buffer means at rates that are synchronous with said first rate and less than said second rate.

30. Apparatus in accordance with claim 29 wherein:

said information signal is a television signal; and

said plurality of signals include a video signal and an audio signal.

31. Apparatus in accordance with claim 30 further comprising:

means for inputting header data to said packetizing means for incorporation into said data packets.

32. Apparatus in accordance with claim 31 further comprising:

means for inputting auxiliary data to said packetizing means for incorporation into said data packets.

33. Apparatus in accordance with claim 8 further comprising:

means for inputting header data to said packetizing means for incorporation into said data packets.

34. Apparatus in accordance with claim 33 further comprising:

means for inputting auxiliary data to said packetizing means for incorporation into said data packets.

35. A data receiver for processing data packets from a digital communication path comprising:

means for receiving serially transmitted data packets at a serial transmission rate, said data packets containing data representing a digitized information signal;

means, responsive to an interval in which successive data packets are received, for generating a timing signal corresponding to a digitizing rate at which said information signal was digitized; and

means responsive to said timing signal for reconstructing said information signal from the received data packets.

36. A data receiver in accordance with claim 35 wherein:

said data packets contain a fixed number of samples of a predetermined type; and

said timing signal is generated by dividing said interval by said fixed number.

37. A data receiver in accordance with claim 36 wherein:

said information signal is a television signal and said samples are video data samples.

38. A data receiver in accordance with claim 36 further comprising:

means for detecting a header in each received data packet; and

means responsive to said detecting means for determining said interval.

39. A data receiver in accordance with claim 35 further comprising:

buffer means for receiving data from said packets at a first rate that is synchronous with said serial transmission rate; and

means responsive to said timing signal for reading said data out of said buffer means at a second rate that is synchronous with said digitizing rate;

wherein the data read out of said buffer is input to said reconstructing means for reconstruction of said information signal.

40. A data receiver in accordance with claim 39 wherein said first rate is greater than said second rate.

41. A data receiver in accordance with claim 40 wherein said buffer means comprise:

a pair of complementary buffers; and

switch means for coupling one buffer of said pair to receive data from said packets at said first rate while the other buffer of said pair is coupled to output data to said reconstructing means, and vice-versa.

42. A data receiver in accordance with claim 41 wherein said switch means are responsive to actuation signals derived from received data packets.

43. A data receiver in accordance with claim 42 wherein:

said information signal is a television signal having video and audio portions; and

said buffer means comprise a separate pair of complementary buffers and associated switch means for each of said video and audio portions.

44. A data receiver in accordance with claim 43 further comprising:

an additional pair of complementary buffers and associated switch means for processing auxiliary data contained in said data packets.

45. A data receiver in accordance with claim 35 wherein:

said receiving means receive data packets from a plurality of channels carrying different asynchronous digitized information signals;

said generating means generate timing signals for each channel corresponding to the digitizing rate at which the information signal carried by the channel was digitized; and

said reconstructing means reconstruct the information signals for each channel in response to the timing signal for that channel.

46. A data receiver in accordance with claim 45 wherein said channels are television signal channels.

47. A data receiver in accordance with claim 46 further comprising:

means for coupling said receiving means to a cable television network for receipt of said channels.

48. A data receiver in accordance with claim 46 wherein:

said data packets contain a fixed number of samples of a predetermined type; and

said timing signal is generated by dividing said interval by said fixed number.

49. A data receiver in accordance with claim 48 wherein said samples are video data samples.

50. A data receiver in accordance with claim 49 wherein said information signal digitizing rates are derived from the color subcarrier frequency of the respective television signal.

51. A method for communicating signals over a digital communication path comprising the steps of:

digitizing an information signal at a first rate;

packetizing said digitized signal for transmission at a second rate greater than and asynchronous with said first rate, wherein a variable time interval results between successive transmitted packets; and

filling the time interval between each successive packet with pad bits to provide a continuous data stream for transmission.

52. A method in accordance with claim 51 wherein each packet contains a fixed number of data bits digitized over a fixed time interval related to said first rate.

53. A method in accordance with claim 52 wherein:

said information signal is a television signal; and

said first rate is derived from a subcarrier frequency of said television signal.

54. A method in accordance with claim 52 comprising the further steps of:

receiving said continuous data stream after transmission;

monitoring the receipt of successive packets to determine said fixed time interval;

computing said first rate from said fixed time interval; and

converting said data packets to an analog signal at the computed first rate to reconstruct said information signal.

55. A method in accordance with claim 54 wherein said information signal is a television signal having a video portion and an audio portion.

56. A method in accordance with claim 55 wherein said first rate is computed at the receiving end of said transmission by dividing said fixed time interval by a number of video data samples contained in a packet.

57. A method in accordance with claim 56 wherein said first rate is derived from a subcarrier frequency of the television signal.

58. A method for communicating a plurality of asynchronous communication signals over a digital communication path comprising the steps of:

digitizing each of a plurality of information signals at a digitizing rate derived from a component of the signal;

packetizing each digitized signal for communication at a transmission rate greater than and asynchronous with its digitizing rate, wherein a variable time interval results between successive transmitted packets for each signal;

filling the time interval between each successive packet for each signal with pad bits to provide a continuous data stream; and

multiplexing the data streams for all of said signals to provide a combined data stream for transmission.

59. A method in accordance with claim 58 wherein each packet for each of said signals contains a fixed number of data bits digitized over a fixed time interval related to the digitizing rate for the signal.

60. A method in accordance with claim 59 comprising the further steps of:

receiving said combined data stream after transmission;

monitoring the receipt of successive packets for each signal to determine the fixed time interval for the signal;

computing the digitizing rate for each signal from its fixed time interval; and

converting the data packets for each signal to an analog form at the computed digitizing rate for the signal to reconstruct said plurality of information signals.