Voting block for identifying WLAN signal modulation type

• US 7,386,063 B1
• Filed: 10/31/2003
• Issued: 06/10/2008
• Est. Priority Date: 10/31/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: Husted, Paul J.
• Primary Examiner(s): Fan; Chieh M.
• Assistant Examiner(s): Lee; Siu M
• Application Number:
  US10/698,666
• Time in Patent Office: 1,684 Days
• Field of Search: 375/341, 375/345, 375/262, 375/137, 375/355, 375/316, 375/340, 375/260, 375/343, 375/365, 375/346, 375/368, 375/234, 375/347, 375/130, 375/324
• US Class Current: 375/316
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation

Abstract

A WLAN device operating in an 802.11g mode can receive signals of different modulations. A technique is provided that quickly and accurately identifies signals of different modulation types when received by the WLAN device. This technique includes beginning demodulation of the received signal using components associated with potential types of modulation. One or more identification values can be provided to a voting block for potential types of modulation based on the received signal. The voting block can advantageously determine the most probable modulation based on such identification value(s). At this point, components associated with the determined modulation can be used to correctly decode the received signal and components not associated with the determined modulation can be deactivated, thereby saving valuable power resources in the device.

Claims

1. A method of determining a modulation type of a received signal, the method comprising:

beginning demodulation of the received signal using components associated with each potential type of modulation;

providing an identification value to a voting block for each potential type of modulation based on the received signal; and

using a technique in the voting block to determine the modulation type, wherein the technique is based at least on the identification values and including determining a strength of the received signal,

wherein if the strength of the received signal is equal to or less than a predetermined threshold value, thereby characterizing the received signal as weak, then the identification value includes a normalized correlation value based on characteristics of the modulation type.

2. The method of claim 1, wherein if the strength of the received signal is greater than the predetermined threshold value, thereby characterizing the received signal as strong or intermediate, then the identification value includes an absolute modulation-specific correlation value.

3. The method of claim 1, wherein if the strength of the received signal is greater than the predetermined threshold value, thereby characterizing the received signal as strong or intermediate, then the identification value includes a modulation-specific received signal strength indicator (RSSI).

4. The method of claim 3, wherein the modulation-specific RSSI is computed by:

performing a noise floor measurement; and

determining the strength of the received signal above the noise floor measurement.

5. The method of claim 3, wherein the technique includes computing a bias value, wherein the bias value adjusts a probability of choosing a particular modulation.

6. The method of claim 5, wherein the bias value is based at least on an environment of the received signal.

7. The method of claim 6, wherein the environment includes multipath.

8. A method of determining a modulation type of a received signal, the method comprising:

beginning demodulation of the received signal using components associated with each potential type of modulation;

providing an identification value to a voting block for each potential type of modulation based on the received signal; and

using a technique in the voting block to determine the modulation type, wherein the technique is based at least on the identification values and including determining a strength of the received signal,

wherein if the strength of the received signal is equal to or less than a predetermined threshold value, thereby characterizing the received signal as a weak signal, then a determination can be made whether a raw RSSI is greater than a threshold RSSI.

9. The method of claim 8, wherein if the strength of the received signal is greater than the predetermined threshold value, thereby characterizing the received signal as a strong signal, or if the raw RSSI is greater than the threshold RSSI, thereby characterizing the received signal as an intermediate signal, then the identification value includes a modulation-specific correlation value.

10. The method of claim 8, wherein if the raw RSSI is less than the threshold RSSI, then the identification value includes a normalized correlation value.

11. A method of conserving power while optimizing signal demodulation in a wireless local area network (WLAN) receiver, the method comprising:

beginning demodulation of a received signal using receiver components associated with each potential type of modulation;

providing an identification value to a voting block of the receiver for each potential type of modulation based on the received signal;

using a technique in the voting block to determine an actual modulation of the received signal, wherein the technique is based at least on the identification values and depends on a strength of the received signal; and

deactivating receiver components associated with modulations other than that of the determined modulation,

wherein if the strength of the received signal is equal to or less than a predetermined threshold value, thereby characterizing the received signal as weak, then the identification value includes a normalized correlation value based on characteristics of the potential type of modulation.

12. The method of claim 11, wherein the identification value includes an absolute modulation-specific correlation value.

13. The method of claim 11, wherein if the strength of the received signal is greater than the predetermined threshold value, thereby characterizing the received signal as strong or intermediate, then the identification value includes a modulation-specific received signal strength indicator (RSSI).

14. The method of claim 13, wherein the technique includes computing a bias value, wherein the bias value adjusts a probability of choosing a particular modulation.

15. A system for determining a modulation of a received signal in a receiver, the system comprising:

modulator identifiers for providing identification values for potential types of modulation based on the received signal;

means for determining a strength of the received signal; and

a voting block for determining the modulation, wherein the voting block uses a technique based at least on the identification values and the strength of the received signal,

wherein the means for determining the strength controls whether the voting block uses a correlation value or an RSSI based on a type of modulation for the identification value.

16. The system of claim 15, wherein at least one of the modulator identifiers includes means for generating a normalized correlation value based on characteristics of the type of modulation.

17. The system of claim 15, wherein at least one of the modulator identifiers includes means for computing an absolute modulation-specific correlation value.

18. The system of claim 15, wherein the means for determining the strength further includes means for determining whether a raw received signal indicator (RSSI) is greater than a threshold RSSI.

19. The system of claim 17, wherein the means for computing the absolute modulation-specific correlation includes:

means for performing a noise floor measurement; and

means for determining a strength of the received signal above the noise floor measurement.

20. The system of claim 19, wherein the means for computing the absolute modulation-specific correlation includes means for adding a bias value, wherein the bias value adjusts a probability of choosing a particular modulation.

21. The system of claim 20, further including means for determining an environment of the received signal, wherein the means for determining an environment provides an output to the means for computing the bias value.