System and method for distributed cross-leyer congestion control for real-time video over wireless LAN

1. A method for controlling congestion for real-time video transmission in a wireless network connecting a plurality of video cameras to a central server, said method comprising the steps of:

receiving a packet loss rate of a video camera in a wireless network;

receiving an estimated maximum throughput of said video camera from said camera to a server;

decrementing a bit transmission rate when said packet loss rate is greater than a first predetermined threshold;

incrementing said bit transmission rate when said packet loss rate is less than a second predetermined threshold for a predetermined time period; and

transmitting said bit transmission rate to a video encoder that is part of an application layer of a network communication protocol for said wireless network.

2. The method of claim 1 , wherein said packet loss rate is received from a media access control layer of said network communication protocol.

3. The method of claim 2 , wherein said estimated maximum throughput is received from a fair airtime throughput estimator.

4. The method of claim 3 , comprising calculating said estimated maximum throughput from

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wherein G max is a theoretical maximum throughput of said video camera, N is a number of cameras in said network, and p f i is an estimated portion of video frames successfully transmitted in a given amount of airtime share.

5. The method of claim 4 , wherein p f i is calculated from a frame error rate received from said media access control layer.

6. The method of claim 2 , further comprising receiving at a contention window adaptation module said bit transmission rate from said media access control layer, calculating a contention window size from

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wherein r max is a maximum PHY bitrate for said camera, r i is an actual PHY bitrate for said camera received from said media access control layer, CW min o is an initial contention window size for said camera, and CW max is a maximum contention window size, and sending said contention window size to said media access control layer.

7. The method of claim 6 , wherein said contention window size is calculated for each video data frame immediately before said frame enters a backoff process.

8. The method of claim 3 , further comprising calculating an average estimated maximum throughput from a plurality of estimated maximum throughputs received from said fair airtime throughput estimator, and incrementing said bit transmission rate when a sum of said bit transmission rate and an increment amount is less than or equal to

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wherein G e i is the average estimated maximum throughput, η 1 is said first predetermined threshold, and V max is a maximum transmission rate.

9. The method of claim 1 , further comprising decrementing said bit transmission rate when bit transmission rate is greater than or equal to a minimum bit transmission rate plus a decrement amount.

10. A method for controlling congestion for real-time video transmission in a wireless network connecting a plurality of video cameras to a central server, said method comprising the steps of:

receiving a frame error rate of a video camera in a wireless network from a media access control layer of a network communication protocol for said wireless network;

receiving a bit transmission rate from said media access control layer;

receiving a number of cameras in said network;

calculating an estimated maximum throughput of said video camera from said frame error rate, said bit transmission rate, and said number of cameras;

sending said estimated maximum throughput to a source rate adaptation module for adjusting said bit transmission rate;

calculating a contention window size from said bit transmission rate; and

sending said contention window size to said media access control layer, wherein said contention window size maintains network airtime fairness.

11. The method of claim 10 , wherein adjusting said bit transmission rate comprises:

receiving a packet loss rate of said video camera from media access control layer;

decrementing said bit transmission rate when said packet loss rate is greater than a first predetermined threshold;

incrementing said bit transmission rate when said packet loss rate is less than a second predetermined threshold for a predetermined time period; and

transmitting said bit transmission rate to a video encoder that is part of an application layer of said network communication protocol.

12. The method of claim 10 , wherein said estimated maximum throughput of said video camera is calculated from

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1

N

·

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MAX

·

(

1

-

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f

)

,

wherein G max is a theoretical maximum throughput of said video camera, N is a number of cameras in said network, and p f i is an estimated portion of video frames successfully transmitted in a given amount of airtime share determined from said frame error rate received from said media access control layer.

13. The method of claim 10 , wherein said contention window size is calculated from

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wherein r max is a maximum PHY bitrate for said camera, r i is an actual PHY bitrate for said camera received from said media access control layer, CW min o is an initial contention window size for said camera, and CW max is a maximum contention window size.

14. The method of claim 11 , further comprising calculating an average estimated maximum throughput from a plurality of estimated maximum throughputs received from a fair airtime throughput estimator, and incrementing said bit transmission rate when a sum of said bit transmission rate and an increment amount is less than or equal to

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wherein G e i is the average estimated maximum throughput, η 1 is said first predetermined threshold, and V max is a maximum transmission rate.

15. The method of claim 11 , further comprising decrementing said bit transmission rate when bit transmission rate is greater than or equal to a minimum bit transmission rate plus a decrement amount.

16. A program storage device readable by a computer, tangibly embodying a program of instructions executable by the computer to perform the method steps for controlling congestion for real-time video transmission in a wireless network connecting a plurality of video cameras to a central server, said method comprising the steps of:

receiving a packet loss rate of a video camera in a wireless network;

receiving an estimated maximum throughput of said video camera from said camera to a server;

decrementing a bit transmission rate when said packet loss rate is greater than a first predetermined threshold;

incrementing said bit transmission rate when said packet loss rate is less than a second predetermined threshold for a predetermined time period; and

transmitting said bit transmission rate to a video encoder that is part of an application layer of a network communication protocol for said wireless network.

17. The computer readable program storage device of claim 16 , wherein said packet loss rate is received from a media access control layer of said network communication protocol.

18. The computer readable program storage device of claim 17 , wherein said estimated maximum throughput is received from a fair airtime throughput estimator.

19. The computer readable program storage device of claim 18 , the method comprising calculating said estimated maximum throughput from

G

e

≈

1

N

·

G

MAX

·

(

1

-

p

f

)

,

wherein G max is a theoretical maximum throughput of said video camera, N is a number of cameras in said network, and p f i is an estimated portion of video frames successfully transmitted in a given amount of airtime share.

20. The computer readable program storage device of claim 19 , wherein p f i is calculated from a frame error rate received from said media access control layer.

21. The computer readable program storage device of claim 17 , the method further comprising receiving at a contention window adaptation module said bit transmission rate from said media access control layer, calculating a contention window size from

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min

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wherein r max is a maximum PHY bitrate for said camera, r i is an actual PHY bitrate for said camera received from said media access control layer, CW min o is an initial contention window size for said camera, and CW max is a maximum contention window size, and sending said contention window size to said media access control layer.

22. The computer readable program storage device of claim 21 , wherein said contention window size is calculated for each video data frame immediately before said frame enters a backoff process.

23. The computer readable program storage device of claim 18 , the method further comprising calculating an average estimated maximum throughput from a plurality of estimated maximum throughputs received from said fair airtime throughput estimator, and incrementing said bit transmission rate when a sum of said bit transmission rate and an increment amount is less than or equal to

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wherein G e i is the average estimated maximum throughput, η 1 is said first predeteimined threshold, and V max is a maximum transmission rate.

24. The computer readable program storage device of claim 16 , the method further comprising decrementing said bit transmission rate when bit transmission rate is greater than or equal to a minimum bit transmission rate plus a decrement amount.