Cables to Go CDM-570L manual Dynamic Power Control, Introduction

A P P E N D I X

DYNAMIC POWER CONTROL

Introduction

Dynamic Power Control (DPC) provides a mechanism whereby VIPERSAT satellite links have their transmit power levels adjusted in order to optimize the receive signal quality (as measured by the demodulator Eb/No). This optimiza- tion process acts to either increase or decrease transmitted signal levels in order to:

•Achieve a minimum level of received Eb/No consistent with providing an error free link.

•Reduce transmit power where sufficient link margin exists in order to optimize station uplink and satellite transponder power usage.

DPC can be selectively enabled and disabled on a link-by-link basis and works on both point-to-point as well as point-to-multipoint links. DPC relies on the passing of an IP message called Path Loss Data Multicast (PLDM) between the receive site (where the receive quality is being measured) and the transmit site (where the power level is to be adjusted). PLDM's are IP unicast messages, and only the transmit site whose frequency and Network ID number matches that contained in the PLDM message will act on the message.

The Vipersat CDM (modulator) units have an algorithm that can, if activated by the VMS, automatically adjust the modulator transmit power to maintain a constant nominal receive signal quality (Eb/No) at the corresponding receive station(s). This provides a mechanism to compensate for varying signal levels caused, for example, by the use of different antenna sizes in a mesh network, or if Ku band is being used as a means to compensate for rain fade conditions. The power control algorithm is a closed loop servo-mechanism with the received

Appendix C - Dynamic Power Control C-1