Transmitter Power Control

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Transmitter Power Control , also for short TX Power Control or abbreviated TPC , is a control of the transmission power in radio systems with mobile users. The purpose is to reduce radio interference and extend the battery life of mobile devices.

Working principle

The functional principle can be explained using the example of a GSM cellular base station (BS) and a mobile station (MS):

The receiver in the MS measures the received field strength of the signal coming from the transmitter of the BS. The measured value is transmitted to the BS in a signaling message ( measurement report ). The BS (or a higher-level network element) decides on the basis of predetermined threshold values ​​and hysteresis whether it should reduce, increase or maintain its transmission power.

In practice, more complex algorithms are usually used for power control. In particular, not only the reception field strength but also the quality (e.g. bit error rate ) is taken into account in order to avoid the transmission power of a disturbed signal from being reduced even further. In addition, several measurement reports are averaged (partially weighted) in order to avoid unnecessary upward and downward regulation of the transmission power through brief level changes.

In the area of ​​the UMTS network / 3G, a highly dynamic transmission power control is a fundamental component of the radio link from the mobile phone to the base station. Taking into account constantly changing path attenuation (e.g. user leaves the elevator), the control must raise the received field strength at the base station antenna to an identical level for all users of the radio cell in order to optimally enable CDMA decoding.