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7.7
Enhanced Adaptative Equalizer
The Equalizer has been developed to specifically match TIER0, 1 and 2 waveforms.
Its utilization is very simple as it has only to be turned on or off. For TIER0, an estimation of the
modulation index needs to be programmed.
As IRIG106 does not define any pilots for channel estimation, the equalizer is using signal statistics
and it is mandatory to have a randomized transmission for a good efficiency.
Hence, Safran Data Systems strongly recommends to have randomized data when using the equalizer
and to have a modulation index as close as possible to 0.7 in PCM-FM.
For multipath mitigation, it is also very useful to have a very fast AGC time constant (0.1 ms).
The equalizer aims to statistically minimize several signal distortions:
Control of the signal amplitude → CMA algorithm
Control of the phase trajectory → additional criteria for the algorithm (up to 4)
Block-based algorithm: allows tracking of channel variations
It is also important to notice that the equalizer will, most of the time, clearly improve the transmission.
As shown on the previous figure without equalization, transmission is not possible.
When activating the Equalizer, the transmission becomes possible but requires a higher Eb/No to get
the same BER.
Adding a FEC is then a solution to reach a QEF transmission.
Note : A FEC alone, without equalization, will not improve at all the transmission. Any kind of FEC will
improve the transmission only in Gaussian conditions. But in presence of Multipath, the channel is not
Gaussian anymore.
To make it simple, the Equalizer will convert a Multipath channel into a Gaussian or quasi Gaussian
channel. Then a FEC will be very efficient.
© Safran Data Systems – IMP000074 e14r1
RX-1 Compact Operational Receiver
User's Manual
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Ref.
D104047
Is.Rev
08
Previous Ref.:
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Date:
21/06/2021
Safran Data Systems
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