Wireless LAN using RSSI and BER parameters for transmission rate adaptation

• US 7,369,510 B1
• Filed: 03/24/2004
• Issued: 05/06/2008
• Est. Priority Date: 05/06/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: Wong, Michael S. Y., Barratt, Craig H., Gilbert, Jeffrey M.
• Primary Examiner(s): Perez-Gutierrez; Rafael
• Assistant Examiner(s): PEREZ, JULIO R
• Application Number:
  US10/809,287
• Time in Patent Office: 1,504 Days
• Field of Search: 370/333, 370/458, 370/252, 370/465, 370/352, 370/356
• US Class Current: 370/252
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 1/20 using signal quality detector

Abstract

Dynamic conditions present in a channel can quickly degrade signal quality, thereby reducing the data rate usable by a WLAN transmitter. For maximum throughput, the highest, reliable data rate available should be used. In accordance with one feature of an adaptive rate technique, a lookup RSSI from one or more acknowledgment packets can be determined. One or more valid data rates can then be determined, wherein a valid data rate has an RSSI threshold less than or equal to the lookup RSSI. An achievable throughput can be computed for each valid data rate based on a theoretical rate and a packet error rate (PER). The valid data rate having the highest achievable throughput can be chosen as the new transmission rate. A rate control table, which can include RSSI thresholds, UDP rates, and PERs for each supported data rate, can be updated based on actual transmission information.

Claims

1. A method of determining a transmission rate (TxRate) for a WLAN transmitter, the method including:

determining a lookup received signal strength indicator (RSSI) from one or more acknowledgement (ACK) packets;

determining one or more valid data rates, wherein a valid data rate has an RSSI threshold less than or equal to the lookup RSSI;

computing an achievable user throughput for each valid data rate by computing a product of a theoretical rate and 1 minus a packet error rate (PER); and

choosing the valid data rate having a highest achievable user throughput as the TxRate.

2. The method of claim 1, wherein determining the lookup RSSI includes determining a median value of RSSIs from three ACK packets.

3. The method of claim 1, further including:

determining if a size of a frame to be transmitted is greater than a predetermined value; and

if the size is greater, then reducing the lookup RSSI by a predetermined amount before determining valid data rates.

4. The method of claim 1, further including:

biasing the lookup RSSI based on age before determining valid data rates, wherein an older lookup RSSI is reduced more than a more recent lookup RSSI.

5. The method of claim 1, further including determining whether the optimal data rate is greater than a maximum data rate (maxRate),

wherein if the TxRate is greater than the maxRate, then determining whether a probe rate is appropriate,

wherein if the probe rate is successful, then resetting the TxRate to one rate higher than the maxRate.

6. The method of claim 5, wherein if the probe rate is not appropriate, then resetting the TxRate to the maxRate.

7. The method of claim 1, further including updating a rate control table.

8. The method of claim 7, wherein updating the rate control table is based on a number of retries to successfully transmit a packet at the TxRate.

9. The method of claim 8, wherein updating the rate control table is further based on whether the TxRate is a probe rate.

10. The method of claim 9, wherein if excessive retries are performed, then updating the rate control table includes adjusting the PER and the RSSI threshold of the TxRate.

11. The method of claim 10, wherein if the TxRate is not a probe rate and the PER is greater than a predetermined value, then

ensuring that data rates above the TxRate have higher RSSI thresholds than that of the TxRate;

and

ensuring that data rates below the TxRate have lower RSSI thresholds than that of the TxRate as well as PERs less than or equal to the PER of the TxRate.

12. The method of claim 9, wherein if excessive retries are not performed, then updating the rate control table includes

computing the PER of the TxRate based on the number of retries.

13. The method of claim 12, wherein if the TxRate is a probe rate and has few retries, then

resetting the PER of the TxRate;

significantly reducing a probe interval; and

setting maxRate to the probe rate.

14. The method of claim 13, wherein if the TxRate is not a probe rate and has no retries on a predetermined number of packets sent at TxRate, then reducing the RSSI threshold of the TxRate.

15. The method of claim 14, wherein if the TxRate is not a probe rate and the PER is greater than a predetermined value, then

ensuring that data rates above the TxRate have higher RSSI thresholds than that of the TxRate;

and

ensuring that data rates below the TxRate have lower RSSI thresholds than that of the TxRate as well as PERs less than or equal to the PER of the TxRate.

16. The method of claim 7, wherein updating the rate control table includes periodically aging values.

17. The method of claim 16, wherein aging values includes:

reducing RSSI thresholds by a predetermined amount; and

reducing PERs by a predetermined factor.

18. A transmission rate for a packet, the transmission rate being computed based on a received signal strength indicator (RSSI) of one or more packets, RSSI thresholds of possible data rates, theoretical universal data protocol (UDP) rate values of the possible data rates, and packet error rates (PERs) of the possible data rates.

19. The transmission rate of claim 18, the transmission rate being further computed based on a size of a frame to be transmitted.

20. The transmission rate of claim 18, the transmission rate being further computed based on an age of multiple packets.

21. A computer readable medium encoded with instructions capable of being executed by a computer for determining a transmission rate (TxRate) in a WLAN transmitter, the instructions comprising:

a first set of instructions for determining a lookup received signal strength indicator (RSSI) from one or more acknowledgement (ACK) packets;

a second set of instructions for determining one or more valid data rates, wherein a valid data rate has a stored RSSI value less than or equal to the lookup RSSI;

a third set of instructions for computing an achievable user throughput for each valid data rate by computing a product of a theoretical rate and 1 minus a packet error rate (PER); and

a fourth set of instructions for choosing the valid data rate having highest achievable user throughput as the TxRate.

22. The computer readable medium of claim 21, wherein the first set of instructions for determining the lookup RSSI includes instructions for determining a median value of RSSIs from three ACK packets.

23. The computer readable medium of claim 21, further including:

a fifth set of instructions for determining if a size of a frame to be transmitted is greater than a predetermined value; and

if the size is greater, then a sixth set of instructions for reducing the lookup RSSI by a predetermined amount before determining valid data rates.

24. The computer readable medium of claim 21, further including:

a fifth set of instructions for biasing the lookup RSSI based on age before determining valid data rates, wherein an older lookup RSSI is reduced more than a more recent lookup RSSI.

25. The computer readable medium of claim 21, further including a fifth set of instructions for determining whether the optimal data rate is greater than a maximum data rate (maxRate),

wherein if the TxRate is greater than the maxRate, then the computer-implemented program further comprises a sixth set of instructions for determining whether a probe rate is appropriate,

wherein if the probe rate is appropriate, then the computer-implemented program further comprises a seventh set of instructions for resetting the TxRate to one rate higher than the maxRate.

26. The computer readable medium of claim 25, wherein if the probe rate is not appropriate, then the computer-implemented program further comprises an eighth set of instructions for resetting the TxRate to the maxRate.

27. The computer readable medium of claim 21, further including a fifth set of instructions for updating a rate control table.

28. The computer readable medium of claim 27, wherein updating the rate control table is based on a number of retries to successfully transmit a packet at the TxRate.

29. The computer readable medium of claim 28, wherein updating the rate control table is further based on whether the TxRate is a probe rate.

30. The computer readable medium of claim 29, wherein if excessive retries are performed, then the fifth set of instructions for updating the rate control table includes instructions for adjusting the PER and the RSSI threshold of the TxRate.

31. The computer readable medium of claim 30, wherein if the TxRate is not a probe rate and the PER is greater than a predetermined value, then the computer-implemented program further comprises:

a sixth set of instructions for ensuring that data rates above the TxRate have higher RSSI thresholds than that of the TxRate; and

a seventh set of instructions for ensuring that data rates below the TxRate have lower RSSI thresholds than that of the TxRate as well as PERs less than or equal to the PER of the TxRate.

32. The computer readable medium of claim 27, wherein if excessive retries are not performed, then the fifth set of instructions for updating the rate control table includes instructions for updating the PER of the TxRate based on the number of retries.

33. The computer readable medium of claim 32, wherein if the TxRate is a probe rate and has few retries, then the computer-implemented program further comprises a sixth set of instructions for resetting the PER of the TxRate, significantly reducing a probe interval, and setting maxRate to the probe rate.

34. The computer readable medium of claim 33, wherein if the TxRate is not a probe rate and has no retries on a predetermined number of packets sent at TxRate, then the computer-implemented program further comprises a seventh set of instructions for reducing the RSSI threshold of the TxRate.

35. The computer readable medium of claim 34, wherein if the TxRate is not a probe rate and the PER is greater than a predetermined value, then the computer-implemented program further comprises:

an eighth set of instructions for ensuring that data rates above the TxRate have higher RSSI thresholds than that of the TxRate; and

a ninth set of instructions for ensuring that data rates below the TxRate have lower RSSI thresholds than that of the TxRate as well as PERs less than or equal to the PER of the TxRate.

36. The computer readable medium of claim 27, wherein the fifth set of instructions for updating the rate control table includes instructions for periodically aging values.

37. The computer readable medium of claim 36, wherein the instructions for aging values includes:

instructions for reducing RSSI thresholds by a predetermined amount; and

instructions for reducing PERs by a predetermined factor.