Method and apparatus for rate fallback in a wireless communication system
A method and apparatus are disclosed for reducing a transmission rate for retransmission of a current frame in a wireless communication system. The reduced transmission rate increases the probability that the current frame is correctly transmitted and acknowledged. The transmission rate is progressively reduced for the current frame to avoid the expiration of the frame's retry count, while not affecting the transmission rate of subsequent frames. The next frame should be transmitted at the highest rate permitted by the signal quality. A disclosed retry count expiry avoidance algorithm increases the reliability of a retransmission by lowering the transmission rate for the current frame when an acknowledgement is not received. When an acknowledgement is not received, the transmitting station proceeds to a retransmitting state where the transmitting station first attempts to retransmit the frame at the same rate. When the number of “equal rate attempts” is exceeded, the retry count expiry avoidance algorithm enters to a fallback state, where the transmission rate is decreased in a progressive manner.
1. A wireless communication device, comprising:
a controller to control transmission of data at a transmission data rate and to control retransmission of said data at a retransmission data rate, wherein said retransmission is performed if an acknowledgement is not received for a current frame; and
a rate selection mechanism that progressively reduces said retransmission data rate to at least one of two or more lower retransmission data rates only for said current frame if an acknowledgement is not received for a current frame after n attempts of transmission at said transmission data rate, wherein a second lower retransmission data rate is selected if an acknowledgement is not received for a current frame after m attempts of retransmission at a first lower retransmission data rate, wherein m equals a maximum number of attempts parameter corresponding to said first lower retransmission data rate, wherein m and n are integers, and wherein m and n are greater than one.
2. The wireless communication device of claim 1 , wherein a transmission data rate for a subsequent frame is selected based on an available signal quality.
3. The wireless communication device of claim 1 , wherein said retransmission data rate is progressively reduced until an acknowledgement is received for said current frame or a retry count for said current frame is exceeded.
4. The wireless communication device of claim 1 , wherein said retransmission data rate is selected from a table of available rates.
5. The wireless communication device of claim 4 , wherein said table of available rates is populated with at least a portion of rates supported by a receiving station.
6. The wireless communication device of claim 1 , wherein said retransmission data rate is determined by an algorithm that selects said retransmission data rate based on current conditions.
7. The wireless communication device of claim 1 , wherein said device is implemented in accordance with the IEEE 802.11 Standard.
8. The wireless communication device of claim 1 , wherein said rate selection mechanism restores a transmission data rate that was in use before said retransmission data rate was reduced.
9. The wireless communication device of claim 1 , wherein said rate selection mechanism proceeds directly to a fallback state if a signal quality is not sufficient to support a data rate associated with an equal rate retry.
10. The wireless communication device of claim 1 , wherein said rate selection mechanism selects one of said lower retransmission data rate based on the robustness of a corresponding modulation technique.
11. A method for wireless communication, comprising the steps of:
transmitting one or more frames at a transmission data rate and retransmitting said data at a retransmission data rate, wherein said retransmission is performed if an acknowledgement is not received for a current frame; and
reducing a retransmission rate only for a current frame when an acknowledgement is not received for said current frame, wherein said reduced retransmission data rate is progressively reduced to at least one of two or more lower retransmission data rates if an acknowledgement is not received for a current frame after n attempts of transmission at said transmission data rate, wherein a second lower retransmission data rate is selected if an acknowledgement is not received for a current frame after m attempts of retransmission at a first lower retransmission data rate, wherein m equals a maximum number of attempts parameter corresponding to said first lower retransmission data rate, wherein m and n are integers, wherein m and n are greater than one, wherein at least one of said steps is performed by an electronic device.
12. The method of claim 11 , further comprising the step of selecting a transmission data rate for a subsequent frame based on an available signal quality.
13. The method of claim 11 , wherein said reducing step is performed iteratively until an acknowledgement is received for said current frame or a retry count for said current frame is exceeded.
14. The method of claim 11 , wherein said reducing step further comprises the step of selecting said retransmission data rate from a table of available rates.
15. The method of claim 14 , wherein said table of available rates is populated with at least a portion of rates supported by a receiving station.
16. The method of claim 11 , wherein said reducing step further comprises the step of selecting said retransmission data rate based on current conditions.
17. The method of claim 11 , wherein said method is performed in accordance with the IEEE 802.11 Standard.
18. The method of claim 11 , further comprising the step of restoring a transmission data rate that was in use before said retransmission data rate was reduced.
19. The method of claim 11 , wherein said reducing step proceeds directly to a fallback state if a signal quality is not sufficient to support a data rate associated with an equal rate retry.
20. The method of claim 11 , wherein one of said lower retransmission data rates is selected based on the robustness of a corresponding modulation technique.
21. A wireless communication device, comprising:
a controller to control transmission of data at a transmission data rate and to control retransmission of said data at a retransmission data rate, wherein said retransmission is performed if an acknowledgement is not received for a current frame; and
a rate selection mechanism that progressively reduces said retransmission data rate to at least one of two or more lower retransmission data rates only for said current frame if an acknowledgement is not received for a current frame and increases said transmission data rate for a subsequent frame after n attempts of transmission at said transmission data rate, wherein a second lower retransmission data rate is selected if an acknowledgement is not received for a current frame after m attempts of retransmission at a first lower retransmission data rate, wherein m equals a maximum number of attempts parameter corresponding to said first lower retransmission data rate, wherein m and n are integers, and wherein m and n are greater than one.
22. The wireless communication device of claim 21 , wherein a transmission data rate for a subsequent frame is selected based on an available signal quality.
23. The wireless communication device of claim 21 , wherein said retransmission data rate is progressively reduced until an acknowledgement is received for said current frame or a retry count for said current frame is exceeded.
24. The wireless communication device of claim 21 , wherein said rate selection mechanism restores a transmission data rate that was in use before said retransmission data rate was reduced.
25. The wireless communication device of claim 21 , wherein said rate selection mechanism selects one of said lower retransmission data rate based on the robustness of a corresponding modulation technique.