Interference limiting for surveillance messages
In some examples, a system includes a transceiver configured to transmit a first surveillance message at a first power level at or below a first maximum power level. The system also includes processing circuitry coupled to the transceiver, the processing circuitry configured to determine that a threshold condition exists. The processing circuitry is also configured to determine a second maximum power level in response to determining that the threshold condition exists, where the second maximum power level is lower than the first maximum power level. The transceiver is configured to transmit, in response to the processing circuitry determining that the threshold condition exists, a second surveillance message at a second power level, wherein the second power level is at or below the second maximum power level.
1 . A system configured to be mounted on an ownship vehicle, the system comprising:
a transceiver configured to transmit a first surveillance message at a first power level at or below a first maximum power level; and
processing circuitry coupled to the transceiver, the processing circuitry being configured to:
determine a first reduction in the first maximum power level for the ownship vehicle according to interference limiting standards;
determine a closure rate for the ownship vehicle based on a speed of the ownship vehicle;
determine a second reduction in the first maximum power level for the ownship vehicle based on the closure rate, wherein a magnitude of the second reduction is less than a magnitude of the first reduction; and
determine a second maximum power level based on the second reduction, and
wherein the transceiver is configured to transmit a second surveillance message at a second power level at or below the second maximum power level.
2 . The system of claim 1 , wherein the processing circuitry is configured to determine the closure rate based on the speed and an altitude of the ownship vehicle.
3 . The system of claim 1 , wherein the processing circuitry is configured to determine the first reduction based on a number of transmitting vehicles in an area around the ownship vehicle.
4 . The system of claim 3 , wherein the processing circuitry is configured to determine a maximum reduction based on the number of transmitting vehicles in the area, and wherein the magnitude of the first reduction is less than or equal to a magnitude of the maximum reduction.
5 . The system of claim 4 , wherein the processing circuitry is configured to determine a third maximum power level based on the maximum reduction, and wherein the second maximum power level is greater than or equal to the third maximum power level.
6 . The system of claim 1 , wherein the processing circuitry is configured to:
determine a surveillance range of the ownship vehicle based on the closure rate and a surveillance time; and
determine the second reduction based on the closure rate and the surveillance range.
7 . The system of claim 1 ,
wherein the transceiver includes a TCAS II transmitter, and
wherein the processing circuitry is further configured to:
determine that a power output of the TCAS II transmitter is less than a power output allowed by applicable requirements for a TCAS I system; and
suppress TCAS broadcast interrogations transmitted by the transceiver in response to determining that the power output of the TCAS II transmitter is less than the power output allowed by applicable requirements for the TCAS I system.