Enhancing wireless LAN capacity using transmission power control

• US 6,907,229 B2
• Filed: 11/01/2002
• Issued: 06/14/2005
• Est. Priority Date: 05/06/2002
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Extricom Limited (Allied Telesis Holdings KK)
• Inventors: Shpak, Eran
• Primary Examiner(s): Corsaro, Nick
• Assistant Examiner(s): Lee, John J.
• Application Number:
  US10/285,869
• Publication Number:
  US 20030207699A1
• Time in Patent Office: 956 Days
• Field of Search: 455/525, 455/69, 455/68, 455/70, 455/522, 455/434, 455/419, 455/445, 455/446, 455/447, 455/515, 455/526, 455/517, 455/63.1, 455/63.2, 455/63.3, 370/338, 370/442, 370/462, 370/322, 370/461
• US Class Current: 455/69
• CPC Class Codes: H04B 1/7163 using impulse radio
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/346 distributing total power among users or channels
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: H04W 92/045 between access point and backbone network device

Abstract

A method for mobile communication by access points in a wireless local area network (WLAN) includes transmitting a first downlink signal on a common frequency channel from a first access point to a first mobile station, at a first downlink power level, which is adjusted responsively to a first uplink power level transmitted from the first mobile station to the first access point. If the first downlink signal received at a second access point is below a predetermined interference threshold, the second access point may transmit a second downlink signal on the common frequency channel to a second mobile station, simultaneously with transmission of the first downlink signal from the first access point to the first mobile station. The capacity of the WLAN may thus be substantially increased.

Claims

1. A method for mobile communication by access points in a wireless local area network (WLAN), wherein the access points include at least first and second access points and are configured to communicate on a common frequency channel with mobile stations, including at least first and second mobile stations, the method comprising:

receiving a first uplink signal from the first mobile station at the first access point with a first uplink power level;

transmitting a first downlink signal on the common frequency channel from the first access point to the first mobile station in response to the first uplink signal, at a first downlink power level, which is adjusted responsively to the first uplink power level to be less than a maximum downlink power level;

making a determination that while the first access point is transmitting the first downlink signal at the first downlink power level, the first downlink signal received at the second access point is below a predetermined interference threshold;

receiving a second uplink signal from the second mobile station at the second access point; and

responsive to the determination, transmitting a second downlink signal on the common frequency channel from the second access point to the second mobile station in response to the second uplink signal, simultaneously with transmission of the first downlink signal from the first access point to the first mobile station.

2. A method according to claim 1, wherein the access points have respective service areas within a region served by the WLAN, and wherein the access points are arranged so that at least some of the service areas substantially overlap.

3. A method according to claim 2, wherein transmitting the second downlink signal comprises partitioning the region served by the WLAN so as to define non-overlapping first and second sub-regions served respectively by the first and second access points.

4. A method according to claim 1, wherein the access points are arranged so that when the first access point transmits the first downlink signal at the maximum power level, the first downlink signal received at the second access point is above the predetermined interference threshold.

5. A method according to claim 1, wherein the first and second downlink signals are transmitted substantially in accordance with IEEE Standard 802.11.

6. A method according to claim 1, wherein transmitting the first downlink signal comprises arbitrating among the access points so as to select the first access point to transmit the first downlink signal.

7. A method according to claim 6, wherein arbitrating among the access points comprises sending broadcast messages from the access points receiving the first uplink signal, and selecting the first access point responsive to the broadcast messages.

8. A method according to claim 1, wherein transmitting the first downlink signal comprises making a first association between the first access point and the first mobile station, and informing the second access point of the first association, and wherein making the determination comprises measuring the first downlink signal received at the second access point responsively to the first association.

9. A method according to claim 8, wherein informing the second access point of the first association comprises notifying the second access point of one or more time intervals during which the first access point is to transmit the first downlink signal, and wherein measuring the first downlink signal comprises monitoring signals received by the second access point during at least one of the time intervals.

10. A method according to claim 9, wherein transmitting the second downlink signal comprises transmitting the second downlink signal during the one or more time intervals after determining that the first downlink signal received at the second access point is below the predetermined interference threshold.

11. A method according to claim 1, wherein making the determination comprises receiving the first downlink signal at the second access point, and identifying a signature of the first access point in the received first downlink signal.

12. A method according to claim 1, wherein transmitting the second downlink signal comprises sending a message from the second access point to the first access point so as to inform the first access point that the second access point is transmitting simultaneously with the first access point.

13. A method according to claim 1, wherein receiving the second uplink signal comprises receiving the second uplink signal at the second access point with a second uplink power level, and wherein transmitting the second downlink signal comprises adjusting a second downlink power level of the second downlink signal in response to the second uplink power level, so that the second downlink signal received at the first access point is below the predetermined interference threshold.

14. A method according to claim 13, wherein receiving the second uplink signal comprises sensing a change in the second uplink power level, and wherein transmitting the second downlink signal comprises, responsive to the change, ceasing to transmit the second downlink signal simultaneously with the transmission of the first downlink signal.

15. Apparatus for mobile communication, comprising a plurality of access points arranged in a wireless local area network (WLAN) and configured to communicate on a common frequency channel with mobile stations, including at least first and second mobile stations, the access points comprising at least first and second access points,

wherein in response to receiving a first uplink signal from the first mobile station at the first access point with a first uplink power level, the first access point transmits a first downlink signal on the common frequency channel to the first mobile station at a first downlink power level, which is adjusted responsively to the first uplink power level to be less than a maximum downlink power level, and

wherein the second access point is adapted to make a determination that while the first access point is transmitting the first downlink signal at the first downlink power level, the first downlink signal received at the second access point is below a predetermined interference threshold, and

wherein in response to receiving a second uplink signal from the second mobile station at the second access point, and responsive to the determination, the second access point transmits a second downlink signal on the common frequency channel to the second mobile station simultaneously with transmission of the first downlink signal from the first access point to the first mobile station.

16. Apparatus according to claim 15, wherein the access points have respective service areas within a region served by the WLAN, and wherein the access points are arranged so that at least some of the service areas substantially overlap.

17. Apparatus according to claim 16, wherein the access points are adapted to communicate with one another in order to partition the region served by the WLAN so as to define non-overlapping first and second sub-regions served respectively by the first and second access points.

18. Apparatus according to claim 15, wherein the access points are arranged so that when the first access point transmits the first downlink signal at the maximum power level, the first downlink signal received at the second access point is above the predetermined interference threshold.

19. Apparatus according to claim 15, wherein the first and second downlink signals are transmitted substantially in accordance with IEEE Standard 802.11.

20. Apparatus according to claim 15, wherein the access points are adapted to communicate with one another so as to carry out an arbitration procedure in order to select the first access point to transmit the first downlink signal.

21. Apparatus according to claim 20, and comprising a communication medium interconnecting the access points, wherein the access points receiving the first uplink signal are adapted to send broadcast messages over the communication medium, and to select the first access point responsive to the broadcast messages.

22. Apparatus according to claim 15, wherein the first access point is adapted to make a first association between the first access point and the first mobile station, and to inform the second access point of the first association, and wherein the second access point is adapted to make the determination that the first downlink signal is below the predetermined interference threshold by measuring the first downlink signal received at the second access point responsively to the first association.

23. Apparatus according to claim 22, wherein the first access point is adapted to notify the second access point of one or more time intervals during which the first access point is to transmit the first downlink signal, and wherein the second access point is adapted to measure the signals received by the second access point during at least one of the time intervals.

24. Apparatus according to claim 23, wherein the second access point is adapted to transmit the second downlink signal during the one or more time intervals after determining that the first downlink signal received at the second access point is below the predetermined interference threshold.

25. Apparatus according to claim 15, wherein the second access point is adapted to make the determination by receiving the first downlink signal, and identifying a signature of the first access point in the received first downlink signal.

26. Apparatus according to claim 15, wherein the second access point is adapted to send a message to the first access point so as to inform the first access point that the second access point is transmitting simultaneously with the first access point.

27. Apparatus according to claim 15, wherein upon receiving the second uplink signal at a second uplink power level, the second access point is adapted to adjust a second downlink power level of the second downlink signal in response to the second uplink power level, so that the second downlink signal received at the first access point is below the predetermined interference threshold.

28. Apparatus according to claim 27, wherein the second access point is adapted to detect a change in the second uplink power level, and responsive to the change, to cease to transmit the second downlink signal simultaneously with the transmission of the first downlink signal.