Positional precoding deration for cooperative MIMO
Presented herein are techniques to ensure power emitted by APs during a cooperative MIMO transmission is within certain limits. For a transmission to be made from two or more wireless access points using cooperative multiple-input multiple-output (MIMO) techniques, a measure of separation is determined between the two or more access points. Precoding of signals to be transmitted by the two or more access points is adjusted so as to derate the signals to be transmitted or disable the cooperative nature of the transmission from the two or more access point depending on the measure of separation so that a combined output power from the two or more access points is within a limit.
1. A method comprising:
for a transmission to be made from two or more wireless access points using cooperative multiple-input multiple-output (MIMO) techniques, determining a measure of separation between the two or more access points; and
adjusting precoding of signals to be transmitted by the two or more access points so as to derate the signals to be transmitted or disable the cooperative nature of the transmission from the two or more access points depending on the measure of separation so that a combined output power from the two or more access points is within a limit.
2. The method of claim 1 , wherein the measure of separation is determined from one or more of: access point installation; receive signal strength information measurements between the two or more access points to determine a path loss; time difference of arrival (TDOA) location transactions between the two or more access points; and channel sounding between the two or more access points.
3. The method of claim 1 , wherein adjusting comprises gradually derating the precoding of signals to be transmitted by the access points as a function of the measure of separation between the two or more access points.
4. The method of claim 1 , wherein adjusting comprises disabling cooperative MIMO operation for the transmission when the measure of separation is less than a predetermined threshold.
5. The method of claim 1 , wherein the transmission includes multiple spatial streams.
6. The method of claim 1 , wherein the transmission includes a single stream that is to be beamformed to produce a plurality of beamformed versions of the same stream.
7. The method of claim 1 , wherein adjusting comprises, when the measure of separation between any two access points is less than a predetermined threshold, disabling cooperation of the two access points across spatial streams of the transmission, and when the measure of separation between any two access points is greater than the predetermined threshold, fully enabling cooperation of the two access points across spatial streams of the transmission.
8. The method of claim 1 , wherein adjusting comprises derating power allocated to a spatial stream for which two or more access points cooperate based on the measure of separation between the two or more access points.
9. An apparatus comprising:
a network interface configured to enable network communication with two or more wireless access points that are configured to wirelessly communicate using cooperative multiple-input multiple-output (MIMO) techniques with one or more wireless clients in a wireless network; and
a processor coupled to the network interface, wherein the processor is configured to:
determine a measure of separation between the two or more access points; and
adjust precoding of signals to be transmitted by the two or more access points so as to derate the signals to be transmitted or disable the cooperative nature of the transmission from the two or more access points depending on the measure of separation so that a combined output power from the two or more access points is within a limit.
10. The apparatus of claim 9 , wherein the processor is configured to adjust by gradually derating the precoding of signals to be transmitted by the access points as a function of the measure of separation between the two or more access points.
11. The apparatus of claim 9 , wherein the processor is configured to adjust by disabling cooperative MIMO operation for the transmission when the measure of separation is less than a predetermined threshold.
12. The apparatus of claim 9 , wherein the transmission includes multiple spatial streams.
13. The apparatus of claim 9 , wherein the transmission includes a single stream that is to be beamformed to produce a plurality of beamformed versions of the same stream.
14. The apparatus of claim 9 , wherein the processor is configured to adjust by, when the measure of separation between any two access points is less than a predetermined threshold, disabling cooperation of the two access points across spatial streams of the transmission, and when the measure of separation between any two access points is greater than the predetermined threshold, fully enabling cooperation of the two access points across spatial streams of the transmission.
15. The apparatus of claim 9 , wherein the processor is configured to adjust by derating power allocated to a spatial stream for which two or more access points cooperate based on the measure of separation between the two or more access points.
16. A system comprising:
two or more wireless access points configured to send a transmission using cooperative multiple-input multiple-output (MIMO) techniques; and
a controller coupled to the two or more wireless access points, wherein the controller is configured to adjust precoding of signals to be transmitted by the two or more access points so as to derate the signals to be transmitted or disable the cooperative nature of the transmission from the two or more access points depending on the measure of separation so that a combined output power from the two or more access points is within a limit.
17. The system of claim 16 , wherein the controller is configured to adjust by gradually derating the precoding of signals to be transmitted by the access points as a function of the measure of separation between the two or more access points.
18. The system of claim 16 , wherein the controller is configured to adjust by disabling cooperative MIMO operation for the transmission when the measure of separation is less than a predetermined threshold.
19. The system of claim 16 , wherein the controller is configured to, when the measure of separation between any two access points is less than a predetermined threshold, disabling cooperation of the two access points across spatial streams of the transmission, and when the measure of separation between any two access points is greater than the predetermined threshold, fully enabling cooperation of the two access points across spatial streams of the transmission.
20. The system of claim 16 , wherein the controller is configured to adjust by derating power allocated to a spatial stream for which two or more access points cooperate based on the measure of separation between the two or more access points.