User's Manual

USER
MANUAL
MPD-1611291-A
EXACT-V2 High End Rack Modulator / Exciter
3/10/2017
MPD-1611291-A
Page 29/94
2.7.2.2 Crest Factor Optimization Parameter
In order to allow the best amplifier efficiency a “Crest Factor Optimization” parameter
has also been added. It is active when the crest factor reduction is enabled (value ≠
0).
For a given “Crest Factor”, the “Crest Factor Optimization” enhances the signal
shoulders. Finding the best value for this parameter allows the user to gain dB on the
shoulders of the signal, thus optimizing the amplifier power.
This shoulder optimization involves a limited reduction in MER performance. That is
why the user must find the best trade-off for the best efficiency.
This parameter can vary in a range from 0 to 255 (no unit). Figure shows the variation
of the shoulder level and the MER for different parameter values at a given crest factor.
When the Crest Factor Optimization parameter is increased, the shoulder level becomes
better (from -33dBm to -50dBm). At the same time, the MER performance decreases
(from 28dB to 15dB). As explained earlier, a trade-off between the two is necessary to
obtain the best overall optimization.
In addition, due to curve shape we see there is an ideal range for the Crest Factor
Optimization parameter of about 70 to 150. In this range the variation of both shoulder
level and MER are significant. Out of this range the loss of MER is too severe for little
or no shoulder level gain. For instance, for a Crest Factor Optimization of 120, we
observe a gain of 10dB for the shoulder level and a loss of only 3dB for the MER.
Hitachi-Comark therefore recommends that this parameter be set in the ideal range of
70 to 150.
Figure 12: Crest Factor Optimization Impact