Method and apparatus for frame-based buffer control in a communication system
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).
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, 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; 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 a decoder buffer.
6. 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.
7. The method of claim 1 , wherein said predicted number of frames is computed as follows:
F pred =F dec 0 −( F enc −F enc 0 )
Where F dec 0 is a desired decoder buffer level, F enc is a number of frames in an encoder buffer and F enc 0 is a desired encoder buffer level.
8. 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.
9. 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.
10. The method of claim 1 , wherein said ensuring step further comprises the step of transmitting waste bits if said buffer level becomes too high.
11. 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.
12. The method of claim 1 , wherein said ensuring step further comprises the step of transmitting empty packets if said buffer level becomes too low.
13. 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, 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; and
transmitting said predicted number of encoded frames to a receiver.
14. The method of claim 13 , wherein said communication system is a digital audio broadcasting (DAB) system.
15. The method of claim 13 , wherein step of computing said predicted number of encoded frames predicts said number of encoded frames in a decoder buffer.
16. The method of claim 13 , 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.
17. The method of claim 13 , wherein said transmitting step further comprises the step of quantizing said predicted number of encoded frames before transmission to a receiver.
18. A method for controlling a buffer in a communication system, said method comprising the steps of:
receiving a predicted number of encoded frames, wherein said predicted number of encoded frames indicates a number of encoded frames in a decoder buffer; and
using said predicted number of encoded frames to determine when to commence a decoding of said frames.
19. The method of claim 18 , further comprising the step of determining when to decode said frames after a decoder is first started using said predicted number of encoded frames.
20. The method of claim 18 , further comprising the step of determining when to decode said frames after a new program is selected using said predicted number of encoded frames.
21. The method of claim 18 , wherein said communication system is a digital audio broadcasting (DAB) system.
22. The method of claim 18 , wherein said predicted number of encoded frames considers a respective data rate of an encoder and decoder and a channel bit rate of said communication system.
23. The method of claim 18 , wherein said predicted number of encoded frames is determined by an encoder and wherein said buffer is a decoder buffer.
24. 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 by considering a respective data rate of an encoder and a decoder and a channel bit rate of said communication system; and
ensure said predicted number of encoded frames does not exceed a maximum number of encoded frames.
25. The system of claim 24 , wherein said processor is further configured to transmit said predicted number of encoded frames to a receiver.
26. 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 by considering a respective data rate of an encoder and a decoder and a channel bit rate of said communication system; and
means for ensuring said predicted number of encoded frames does not exceed a maximum number of encoded frames.