Interference suppression methods for 802.11

• US 7,523,205 B1
• Filed: 10/28/2006
• Issued: 04/21/2009
• Est. Priority Date: 03/02/2001
• Status: Expired due to Term

• Current Assignee: Kyocera Corporation
• Original Assignee: AT&T, Inc.
• Inventors: Sherman, Matthew J.
• Primary Examiner(s): Meky; Moustafa M
• Application Number:
  US11/588,567
• Time in Patent Office: 906 Days
• Field of Search: 709200-202, 709223-227, 709/246, 709/338, 709/443, 709/447, 709/448, 709/461, 370/445, 370/462
• US Class Current: 709/226
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters
• CPC Class Codes: H04W 74/0808 using carrier sensing, e.g. carrier sense multiple access [CSMA]
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

An 802.11 source station transmits a signal with the duration field other than that required for the transmission to prevent transmission by other stations during known sequences. Thus, the source station uses the duration field to spoof the actual time the medium will be occupied, to stations within range of the signal. A station within range of the transmitted signal will check the duration field of the transmitted signal, and update the station'"'"'s network allocation vector. Thus, the station will not transmit because the station'"'"'s network allocation vector indicates that the medium is in use, even though the station maybe unable to hear the carrier. Accordingly, spoofed stations may, for example, 1) delay transmission until a more critical transmission has completed, 2) allow unknown or foreign protocol to have preferential use of the medium, 3) prevent interference from hidden stations, and 4) allow sharing of the medium by overlapping basic service sets.

Claims

1. A method for communicating in a wireless environment having a plurality of mobile stations and at least one access point, comprising:

at a first mobile station of said plurality of stations;

responsive to an RTS frame received from an access point, selecting a duration value to a value that is greater than the time required to complete communication that the access point initiated by the RTS frame; and

sending a CTS frame containing the selected duration value in a field whose content is used by mobile stations of said plurality of stations that receive the CTS frame to set a NAV timer the prevents said mobile stations from transmitting while the NAV timer value is greater than zero.

2. The method of claim 1 further comprising the steps of:

at a second mobile station said of said plurality of mobile stations that receives the CTS frame

setting a NAV timer that is normally set upon receipt of a RTS frame from an access point with the duration value contained in the received CTS frame.

3. The method of claim 2 where said step of setting is executed by the second mobile station when an address contained in said CTS frame explicitly or implicitly is addressed to said second module station.

4. The method of claim 2 where the second mobile station employs a CSMA/CA protocol that is not identical to a CSMA/CA protocol that is employed by the first mobile station.

5. The method of claim 1 where the second mobile station communicates with the same access point with which the first mobile station communicates.

6. The method of claim 1 where the CTS frame includes an address that makes the selected duration relevant to less that all of said plurality of mobile stations that receive the CTS frame.

7. The method of claim 6 where the information specifies those of said plurality of mobile stations to which the selected duration is relevant.

8. The method of claim 6 where the information specifies those of said plurality of mobile stations to which the selected duration is irrelevant.

9. The method of claim 6 where the address is a group address.

10. The method of claim 6 where the address is a multicast address.

11. The method or claim 6 where the address is a broadcast address.

12. The method of claim 1 where said step of sending the CTS signal is independent of whether said first mobile station expects to receive or to send data.

13. A machine-readable medium having stored thereon a plurality of executable instructions which, when executed by a processor implement a method comprising:

responsive to an RTS frame received from an access point, select a duration value to a value that is greater than the time required to complete communication that the access point initiated by the RTS frame; and

send a CTS frame responsive to the RTS frame that contains the duration value.

14. The machine readable medium of claim 13 that is adapted to instill the instructions in a mobile station that communicates with the access point.