Method and apparatus for indicating the presence of a wireless local area network by detecting signature sequences

• US 6,754,194 B2
• Filed: 09/13/2002
• Issued: 06/22/2004
• Est. Priority Date: 03/18/2002
• Status: Expired due to Term

• Current Assignee: InterDigital Patent Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: Wang, Charles Chuanming, Knutson, Paul Gothard, Gao, Wen, Ramaswamy, Kumar, Litwin, Louis Robert Jr.
• Primary Examiner(s): Patel, Ajit
• Application Number:
  US10/243,228
• Publication Number:
  US 20040052231A1
• Time in Patent Office: 648 Days
• Field of Search: 370/328, 370/331, 370/332, 370/338, 370/351-356, 370/401, 370/389, 455/422, 455/432, 455/436-444
• US Class Current: 370/331
• CPC Class Codes: H04W 36/0088 Scheduling hand-off measurements
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/1446 wherein at least one of the networks is unlicensed
• CPC Class Codes: H04W 48/18 Selecting a network or a communication service
• CPC Class Codes: H04W 52/0229 where the received signal is a wanted signal
• CPC Class Codes: H04W 52/0245 according to signal strength
• CPC Class Codes: H04W 52/0254 detecting a user operation or a tactile contact or a motion of the device
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus for detecting the presence of a wireless local area network (WLAN) (104) detects at least one signature sequence in a radio frequency (RF) signal associated with a WLAN (104). The present invention indicates the presence of a WLAN (104) in response to the detection of the at least one signature sequence in the RF signal.

Claims

1. A method, comprising:

detecting at least one signature sequence in a radio frequency (RF) signal associated with a wireless local area network (WLAN); and

indicating the presence of the WLAN in response to the detection of the at least one signature sequence,

wherein the detecting step includes filtering samples of the RF signal to correlate the RF signal with a stored signature sequence indicative of the WLAN and sensing at least one peak in the filtered RF signal.

2. The method of claim 1, further comprising:

activating circuitry in a mobile device configured to communicate with the WLAN in response to the detection of the at least one signature sequence.

3. The method of claim 2, further comprising:

transferring communications in the mobile device from a wireless communication system to the WLAN.

4. The method of claim 3, wherein the wireless communication system is a cellular telephone network.

5. The method of claim 1, further comprising:

deactivating the circuitry in the mobile device configured to communicate with the WLAN in response to a decrease below a predetermined threshold in quality of signal received from the WLAN.

6. The method of claim 1, wherein the at least one signature sequence is at least one of a Barker sequence, a short symbol sequence associated with an IEEE 802.11a WLAN, and an A symbol sequence associated with a Hiperlan/2 WLAN.

7. The method of claim 1, wherein the sensing step comprises:

comparing the largest sample of the RF signal in a correlation period to a predetermined threshold.

8. The method of claim 1, wherein the sensing step comprises:

averaging the samples of the RF signal over a correlation period to produce an average value; and

comparing the largest sample of the RF signal in the correlation period with the average value to determine if the comparison exceeds a predetermined threshold.

9. The method of claim 8, wherein the largest sample of the RF signal is removed from the average value.

10. The method of claim 1, wherein the sensing step comprises:

detecting a first peak in a first correlation period to produce a search window; and

detecting at least one additional peak in the search window for at least one additional correlation period.

11. An apparatus, comprising:

a detector for detecting at least one signature sequence in a radio frequency (RF) signal associated with a wireless local area network (WLAN); and

means for indicating the presence of the WLAN in response to the detection of the at least one signature sequence,

wherein the detector includes a matched filter for correlating samples of the RF signal with a stored signature sequence indicative of the WLAN and a peak detector for sensing at least one peak in the filtered RF signal.

12. The apparatus of claim 11, further comprising:

means for activating circuitry in a mobile device configured to communicate with the WLAN in response to the detection of the at least one signature sequence.

13. The apparatus of claim 12, further comprising:

means for transferring communications in the mobile device from a wireless communication system to the WLAN.

14. The apparatus of claim 13, wherein the wireless communication system is a cellular telephone network.

15. The apparatus of claim 11, further comprising:

deactivating circuitry in the mobile device configured to communicate with the WLAN in response to a decrease below a predetermined threshold in quality of signal received from the WLAN.

16. The apparatus of claim 11, wherein the at least one signature sequence is at least one of a Barker sequence, a short symbol sequence associated with an IEEE 802.11a WLAN, and an A symbol sequence associated with a Hiperlan/2 WLAN.

17. The apparatus of claim 15, wherein the peak detector is configured to compare the largest sample of the RF signal in a correlation period to a predetermined threshold.

18. The apparatus of claim 15, wherein the peak detector is configured to:

average the samples of the RF signal over a correlation period to produce an average value; and

compare the largest sample of the RF signal in the correlation period with the average value to determine if the comparison exceeds a predetermined threshold.

19. The apparatus of claim 18, wherein the peak detector is further configured to:

remove the effect of the largest sample of the RF signal from the average value.

20. The apparatus of claim 15, wherein the peak detector is configured to:

detect a first peak in a first correlation period to produce a search window; and

detect at least one additional peak in the search window for at least one additional correlation period.

21. In a mobile device configured to communication with a wireless communication network and a wireless local area network (WLAN), an apparatus comprising:

a first front end for receiving an RF signal associated with the wireless communication system;

a second front end for receiving an RF signal associated with the WLAN;

a first baseband circuit for processing the RF signal received by the first front end;

a second baseband circuit for processing the RF signal received by the second front end; and

a WLAN scanner for detecting at least one signature sequence in the RF signal associated with the WLAN and for indicating the presence of the WLAN in response to the detection of the at least one signature sequence.