Quantum and Evolution Series Installation and Operating Handbook
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being transmitted, Tx traffic may be disrupted.
Once the channel has been sounded,
a conventional unpredistorted 16QAM constellation is transmitted. The resulting
demodulated constellation is captured and displayed in the top right of the
predistorter monitor pane. The Tx constellation is then modified in such a way as to
optimise the received constellation.
6. When the Rx EVM converges to a stationary value or when the required number of
algorithm iterations has been completed, the adaption process stops. The resultant
Tx constellation can then be saved allowing it to be recalled if necessary some time
later. Note that it is necessary to go through this learning process whenever the
operating point of the HPA is changed. Consequently, it may be convenient to
generate and save the predistortion information for all HPA operating points in
advance and simply select the appropriate saved configuration whenever the HPA
operating point is changed.
7. The predistorted Tx constellation and resulting Rx constellation are shown bottom left
and right respectively of the monitor pane.
Note that not all nonlinearities can be equalized fully. This is especially the case if the
nonlinearity is being driven well into saturation, or if the nonlinearity is hard-limiting. For
further information on the predistorter, please consult the white paper available at the
Paradise Datacom website.
Predistorter Screen set to adapt and stop on convergence
