Tx Power is one of most important parametrs for Radio Links planning.
Tx Power is very complex parameter with plenty of dependencies and restrictions.
All ePMP 1000 devices have 3 main operating modes:
TDD mode — Supports Time Division Duplex with GPS sync, best suits for PMP(point-to-multipoint) networks. TDD PTP is almost the same TDD with only difference — only one SM can be registered on AP.
ePTP Master/Slave mode - Focused to provide minimum possible latency on PTP(point-to-point) links. Does not support GPS sync.
Standard Wi-Fi mode — Totally based on 802.11a/b/g/n standard. Widely used for migration from Standard 802.11 systems to ePMP systems.
Every ePMP device can be used in Access Point(AP) or Subscriber Module(SM) role.
Important to know difference between Tx Power shown on UI for AP and SM.
In general ePMP devices distinguish two types of traffic — data traffic and management traffic.
ePMP always try to send Data traffic on the highest possible MCS, Management traffic always uses MCS1 or MCS0(Configurable option on UI).
Becauses of this Tx Power for Data packets and for Management packets will be different.
Each AP may have several SMs registered on it. Therefore it was decided that AP will indicate Tx Power of Management packets on UI and SMs will indicate Tx Power of all packets(Data + Management). AP communicates with all registered on it SMs and Data packets TX Power will be different for each of them. Only Data Tx Power transmitted with same value for all registered SMs.
Over all there are three things which limits Tx Power:
ATPC (Automatic Transmission Power Control) — works only in TDD and TDD PTP mode;
Dynamic Tx Power.
Regulatory — all wireless devices in bands 2.4 GHz and 5 GHz should follow rules established by the State. Regulatory limitation depends on Country Code, Frequency Band, Operating Mode(PTP/PMP). APs and SMs follow regulatory policies.
Automatic Transmit Power Control (ATPC) is a feature used in Wireless systems that adjusts transmitter output power based on the varying signal level at the receiver. ATPC allows the transmitter to operate at lower than maximum power for most of the time, transmit power will be increased as needed until the maximum is reached in case of changed environment. An ATPC provides several advantages over a fixed transmit power system, including less transmitter power consumption, longer amplifier component life, and reduced interference for other Wireless systems. Especially important in case of Frequency Reuse with sync network. SMs from one sector do not produce heavy interference for AP in adjacent sector.
ATPC options are available for configuration on AP in Power Control section on UI.
Subscriber Module Target Receive Level is the desired Uplink RSSI level. Tx Power on SM will be increased till Subscriber Module Target Receive Level is not reached. In case of redundant Tx Power of SM in will be reduced.
On SM side there is option Max Tx Power Auto or Manual. In auto mode ATPC completely controls Tx Power.
Please be careful, in case of Manual mode, ATPC controls Tx Power too, but entered value will be the upper line, above which Tx Power can not be increased.
Dynamic TX Power - the restriction caused by the transceiver system quality indicators. Transmitter power limit associated with an increased error vector magnitude (EVM - Error Vector Magnitude) on higher MCSs with more complex modulation types. Limitation has frequency dependence, and also depends on the device type. For each ePMP device platform there are separate tables with Dynamic Tx Power limitation.