Hi vantienphap,
Actually there are three mechanisms on ePMP boards which affect TX Power:
1. Regulatory - limits transmitter power in accordance with the requirements of the government agencies depending on the Country Code. It depends on the Country Code, band, mode (PMP / PTP).
Regulatory limits Tx Power both on AP and on the SM.
2. ATPC - Automatic Transmit Power Control.
ATPC Settings on AP:
AP will perform control over TX Power on SM to get UL RSSI the same as configured in Subscriber Module Target Receive Level.
Tx Power on SMs can be configured in two ways:
- Auto - ATPC will completely control Tx Power on SM.
- Manual - in manual mode ATPC will controll Tx Power too but configured value will be upper limit for Tx Power on SM.
3. Dynamic Tx Power - Tx Power limitation caused by quality indicators of transceiver system.
Tx power limitation is the result of increased error vector magnitude (EVM - Error Vector Magnitude) at higher MCS with more complex modulation types. Limitation has frequency dependency, and also depends on the device type. For each ePMP device there are separate tables with Dynamic Tx Power vs MCS.
Thank you.