Interference suppression methods for 802.11
View Patent ↗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.
1. A method for spoofing stations while transmitting data through a medium, the method comprising:
setting a duration value to a value other than a time period for a predetermined subsequent message transmission;
sending a first signal containing the duration value, wherein at least one of the stations is an obeying station that updates a network allocation vector in accordance with the duration value if a second signal is detected after the first signal and that resets the network allocation vector if the second signal is not detected after the first signal; and
sending a third signal containing the duration value, wherein if the at least one station resets the network allocation vector because the second signal is not detected after the first signal, the at least one station updates the network allocation vector in accordance with the duration value contained in the third signal.
2. The method of claim 1 , wherein the first signal is a request-to-send signal and the second signal is a clear-to-send signal.
3. The method of claim 2 , wherein the third signal is a clear-to-send signal.
4. The method of claim 1 , wherein the third signal is sent immediately after the second signal.
5. The method of claim 1 , wherein the third signal is sent immediately after the first signal.
6. The method of claim 1 , wherein the obeying station is a legacy station that does not practice an enhanced 802.11e standard.
7. The method of claim 1 , wherein the duration value represents a time period for suppressing transmissions by the obeying station.
8. The method of claim 7 , wherein transmissions of unknown protocols are given preferential use of the medium when the transmissions by the obeying station are suppressed.
9. The method of claim 7 , wherein transmissions of hidden stations are suppressed, and stations which would otherwise be suppressed are given preferential use of the medium.
10. The method of claim 7 , wherein critical transmissions are given preferential use of the medium when the transmissions by the obeying station are suppressed.
11. The method of claim 7 , wherein at least some of the stations are provided in an overlapping basic service set, and stations of the overlapping basic service set are given preferential use of the medium when the transmissions by the obeying station are suppressed.
12. The method of claim 7 , wherein stations of an enhanced version of a standard are given preferential use of the medium when the transmissions by the obeying station are suppressed.
13. A machine-readable medium having stored thereon a plurality of executable instructions, the plurality of instructions comprising instructions to:
set a duration value to a value other than a time period for a predetermined subsequent message transmission;
send a first signal containing the duration value, wherein at least one of the stations is an obeying station that updates a network allocation vector in accordance with the duration value if a second signal is detected after the first signal and that resets the network allocation vector if the second signal is not detected after the first signal; and
send a third signal containing the duration value, wherein if the at least one station resets the network allocation vector because the second signal is not detected after the first signal, the at least one station updates the network allocation vector in accordance with the duration value contained in the third signal.
14. The machine-readable medium of claim 13 , wherein the first signal is a request-to-send signal and the second signal is a clear-to-send signal.
15. The machine-readable medium of claim 13 , wherein the third signal is a clear-to-send signal.
16. The machine-readable medium of claim 13 , wherein the third signal is sent immediately after the second signal.
17. The machine-readable medium of claim 13 , wherein the third signal is sent immediately after the first signal.
18. The machine-readable medium of claim 13 , wherein the obeying station is a legacy station that does not practice an enhanced 802.11e standard.
19. The machine-readable medium of claim 13 , wherein the duration value represents a time period for suppressing transmissions by the obeying station.