Method and apparatus for frame-based buffer control in a communication system

• US 20030002609A1
• Filed: 06/29/2001
• Published: 01/02/2003
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.), Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Faller, Christof, Haimi-Cohen, Raziel
• Granted Patent: US 7,460,629 B2
• Time in Patent Office: Days
• US Class Current: 375/372
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• CPC Class Codes: H04H 2201/20 digital audio broadcasting [DAB]
• CPC Class Codes: H04H 60/27 Arrangements for recording or accumulating broadcast information or broadcast-related information
• 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: H04J 3/1688 the demands of the users being taken into account after redundancy removal, e.g. by predictive coding, by variable sampling reducing bandwidth of signals in general H04B1/66; in PCM-systems H04B14/046; removal of redundancy in telegraph communication H03M7/30
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer

Abstract

A method and apparatus are disclosed for controlling a buffer in a digital audio broadcasting (DAB) communication system. The decoder buffer level limits are specified in terms of a maximum number of encoded frames (or duration). The transmitter can predict the number of encoded frames, F_pred, in the decoder buffer and transmit the value, F_pred, to the receiver with the audio data. If the transmitter determines that the decoder buffer level is becoming too high, the frames being generated by the encoder are too small and additional bits are allocated to each frame for each of the N programs. Likewise, if the transmitter determines that the decoder buffer level is becoming too low, the frames being generated by the encoder are too big and fewer bits are allocated to each frame for each of the N programs. The transmitted predicted buffer level, F_pred, can also be employed to (i) determine when the decoder should commence decoding frames; and (ii) synchronize the transmitter and the receiver. The receiver fills the decoder buffer until F_pred frames are received before commencing decoding frames when the decoder first starts up or possibly when a new audio program is selected. The transmitter and receiver clocks may be synchronized by adjusting the clock at the receiver by using a feedback loop that compares the actual level of the decoder buffer to the predicted value, F_pred, received from the transmitter (a higher number of encoded frames in the buffer indicates that the clock of the receiver is too slow and should be increased, and a lower number of encoded frames in the buffer indicates that the clock of the receiver is too fast and needs to be slowed down).

Claims

1. A method for controlling a buffer level in a communication system, said method comprising the steps of:

computing a predicted number of encoded frames in said buffer; and

ensuring said predicted number of encoded frames does not exceed a maximum number of encoded frames.

2. The method of claim 1, wherein said communication system is a digital audio broadcasting (DAB) system.

3. The method of claim 1, wherein said communication system employs perceptual audio coding.

4. The method of claim 1, wherein said communication system is a multiple channel communication system and wherein said method further comprises the step of maintaining an approximately equal frame rate for each of said channels.

5. The method of claim 1, wherein step of computing said predicted number of encoded frames predicts said number of encoded frames in an encoder buffer.

6. The method of claim 1, wherein step of computing said predicted number of encoded frames predicts said number of encoded frames in a decoder buffer.

7. The method of claim 1, wherein said step of computing said predicted number of encoded frames considers a respective data rate of an encoder and a decoder and a channel bit rate of said communication system.

8. The method of claim 1, wherein said step of computing said predicted number of encoded frames is performed by a rate controller and wherein said buffer is a decoder buffer.

9. The method of claim 1, wherein said predicted number of frames is computed as follows:

F_pred=F_dec0−

(F_enc−

F_enc0)

where F_dec0 is a desired decoder buffer level, F_enc is a number of frames in an encoder buffer and F_enc0 is a desired encoder buffer level.

10. The method of claim 1, further comprising the step of receiving an indication of a number of frames in an encoder buffer and wherein step of computing said predicted number of encoded frames predicts said number of encoded frames in a decoder buffer based on said number of frames in an encoder buffer.

11. The method of claim 1, wherein said ensuring step further comprises the step of allocating an additional number of bits to each frame if said buffer level becomes too high.

12. The method of claim 1, wherein said ensuring step further comprises the step of transmitting waste bits if said buffer level becomes too high.

13. The method of claim 1, wherein said ensuring step further comprises the step of allocating a fewer number of bits to each frame if said buffer level becomes too low.

14. The method of claim 1, wherein said ensuring step further comprises the step of transmitting empty packets if said buffer level becomes too low.

16. The method of claim 15, wherein said communication system is a digital audio broadcasting (DAB) system.

17. The method of claim 15, wherein step of computing said predicted number of encoded frames predicts said number of encoded frames in a decoder buffer.

18. The method of claim 15, wherein said step of computing said predicted number of encoded frames considers a respective data rate of an encoder and a decoder and a channel bit rate of said communication system.

19. The method of claim 15, wherein said step of computing said predicted number of encoded frames is performed by a rate controller and wherein said buffer is a decoder buffer.

20. The method of claim 15, wherein said transmitting step further comprises the step of quantizing said predicted number of encoded frames before transmission to a receiver.

15. A method for controlling a buffer in a communication system, said method comprising the steps of:

computing a predicted number of encoded frames in said buffer; and

transmitting said predicted number of encoded frames to a receiver.

21. A method for controlling a buffer in a communication system, said method comprising the steps of:

receiving a predicted number of encoded frames in said buffer; and

using said predicted number of encoded frames to determine when to commence a decoding of said frames.

22. The method of claim 21, further comprising the step of determining when to decode said frames after a decoder is first started using said predicted number of encoded frames.

23. The method of claim 21, further comprising the step of determining when to decode said frames after a new program is selected using said predicted number of encoded frames.

24. The method of claim 21, wherein said communication system is a digital audio broadcasting (DAB) system.

25. The method of claim 21, wherein said predicted number of encoded frames indicates a number of encoded frames in a decoder buffer.

26. The method of claim 21, wherein said predicted number of encoded frames considers a respective data rate of an encoder and a decoder and a channel bit rate of said communication system.

27. The method of claim 21, wherein said predicted number of encoded frames is determined by an encoder and wherein said buffer is a decoder buffer.

29. The method of claim 28, wherein said communication system is a digital audio broadcasting (DAB) system.

30. The method of claim 28, wherein predicted number of encoded frames indicates number of encoded frames in a decoder buffer.

31. The method of claim 28, wherein said predicted number of encoded frames considers a respective data rate of an encoder and a decoder and a channel bit rate of said communication system.

32. The method of claim 28, wherein said predicted number of encoded frames is determined by an encoder and wherein said buffer is a decoder buffer.

33. The method of claim 28, wherein said adjusting step increases said clock frequency if said predicted number of encoded frames is lower than said actual number of encoded frames in said buffer.

34. The method of claim 28, wherein said adjusting step decreases said clock frequency if said predicted number of encoded frames is higher than said actual number of encoded frames in said buffer.

36. The system of claim 35, wherein said processor is further configured to transmit said predicted number of encoded frames to a receiver.

38. The system of claim 37, wherein said processor is further configured to adjust a clock frequency based on said comparison.

39. The system of claim 38, wherein said processor is further configured to increase said clock frequency if said predicted number of encoded frames is lower than said actual number of encoded frames in said buffer.

40. The system of claim 38, wherein said processor is further configured to decrease said clock frequency if said predicted number of encoded frames is higher than said actual number of encoded frames in said buffer.

41. The system of claim 37, wherein said processor is further configured to determine when to commence a decoding of said frames using said predicted number of encoded frames.

42. The system of claim 41, wherein said processor waits approximately said predicted number of encoded frames before decoding said frames after a decoder is first started.

43. The system of claim 41, wherein said processor waits approximately said predicted number of encoded frames before decoding said frames after a new program is selected.

44. The system of claim 37, wherein said communication system is a digital audio broadcasting (DAB) system.

47. The system of claim 46, further comprising means for adjusting a clock frequency based on said comparison.

48. The system of claim 46, further comprising means for waiting until said buffer contains approximately said predicted number of encoded frames before decoding said frames.

28. A method for synchronizing a receiver and a transmitter in a communication system, said method comprising the steps of:

receiving a predicted number of encoded frames in a buffer;

comparing said predicted number of encoded frames to an actual number of encoded frames in said buffer; and

adjusting a clock frequency based on said comparison.

35. A system for controlling a buffer level in a communication system, comprising:

a memory that stores computer-readable code; and

a processor operatively coupled to said memory, said processor configured to implement said computer-readable code, said computer-readable code configured to;

compute a predicted number of encoded frames in said buffer; and

ensure said predicted number of encoded frames does not exceed a maximum number of encoded frames.

37. A system for controlling a buffer level in a communication system, comprising:

a memory that stores computer-readable code; and

a processor operatively coupled to said memory, said processor configured to implement said computer-readable code, said computer-readable code configured to;

receive a predicted number of encoded frames in a buffer; and

compare said predicted number of encoded frames to an actual number of encoded frames in said buffer.

45. A system for controlling a buffer level in a communication system, comprising:

a buffer for storing frames of encoded data; and

means for computing a predicted number of encoded frames in said buffer; and

means for ensuring said predicted number of encoded frames does not exceed a maximum number of encoded frames.

46. A system for controlling a buffer level in a communication system, comprising:

a buffer for storing frames of encoded data; and

an input port for receiving a predicted number of encoded frames in a buffer; and

means for comparing said predicted number of encoded frames to an actual number of encoded frames in said buffer.