User's Manual

40 ALFOplus 24GHz (North America) - Release 01.05.0x - MN.00395.E - 004

• Lower modulation - When propagation into the given radio channel is in the worst condition (low

Rx S/N), the radio link is working at the minimum throughput, defined at Lower Modulation: the

lowest modulation profile that ACM can employ

7.1.7 ATPC and ACM interaction

The Automatic Transmission Power Control (ATPC) regulates the RF output power of the local transmitter

depending on the value of the RF level at the remote terminal. This value has to be preset from the local

terminal as threshold high and low. The difference between the two thresholds must be equal or higher

than 3 dB.

As soon as the received level crosses the preset threshold level low due to the increase of the hop atten-

uation, a microprocessor (µP), embedded in the ALFOplus, at the receiver side of the remote terminal

sends back to the local terminal a control to increase the transmitted power.

A good set of the thresholds is to put the ATPC Low Level threshold higher (or even slightly higher) than

the threshold of the highest modulation scheme of the ACM; this way, the ATPC start to work before the

received signal is reduced and by consequence will force the system to downgrade the modulation. The

behaviour of the system is to always try to increase the PTX and so the System Gain, before being forced

to reduce capacity due to modulation downgrade.

Resuming, the correct setting of the thresholds is when the two windows, the ATPC one and the ACM one,

are not overlapped, as per Fig.10

Fig.10 - ATPC diagram

Thresh High

Thresh Low

Hop attenuation (dB)

ATPC range

PTx max.

PTx min.

Remote PRx

dBm

Local PTx

dBm

Hop attenuation (dB)

PTx actuation

Local

Remote

PRx recording

Transmission

of PTx control

level

PTx control

ACM

range

Threshold

highest ACM

profile