Wavecom W61PC V7.5.0 - Manual (Page 259)

WAVECOM Decoder W61PC/LAN Manual V7.5 Classifier (Optional)  249
Caveats
Even though the classifier has been carefully designed, the extreme complexity of classification requires
the user to be aware of a few caveats. Common sense and visual inspection, as well as prior monitoring
experience, are helpful when dealing with these issues.
Half-Duplex Signals
The classifier will only classify half-duplex or burst signals with difficulty. This is due to the nature of the
signal, which is only present for a relatively small fraction of the total sampling time.
Multi-channel Systems
The current version of the classifier will only classify a 12-channel PSK CIS-12 signal as a single, aggre-
gate signal – for all other multi-channel systems the classifier will classify each sub-channel as an individ-
ual signal.
MFSK
The current version of the classifier may indicate an incorrect number of tones for MFSK signals.
PSK A and B signal confusion
Under certain conditions the classifier cannot distinguish between the A and B variants of PSK modulation.
A PSK signal of one variant may be mistaken for the other variant if the signal is offset from the real cen-
ter frequency with a certain fraction of its baud rate; i.e. for PSK-2 ¼, for PSK-4 1/8 and PSK-16 1/16 of
the baud rate. This behavior also includes multiples of the fractions.
OQPSK
The current version of the classifier has difficulties in correctly evaluating the baud rate of OQPSK signals,
e.g. Inmarsat-Aero. Additionally, the phase constellation diagram may be incorrect.
Handling of synchronous and asynchronous speeds
The handling of asynchronous Baudot signals with 1.5 stop bits is a challenge. If the classifier does not
succeed in recognizing the stop bits, it will classify the signal as a synchronous signal having the double
speed of the actual signal.
CW recognition
The classifier may confuse a low rate FSK signal with a fast CW signal, particularly at the edges of the
classification bandwidth. To lower the probability of such behavior, a classification model may be selected
which only allows CW signals below 30 Bd to be classified at the edges of the classification bandwidth.
Classifier Code Check HF (CCC)
The HF Classifier Code Check is a versatile analysis tool for the classification of unknown signals and the
determination of the protocol (mode) in use. The CCC combines a classifier with a table-based mode check
and an advanced code check. The CCC will attempt to process all signals within a bandwidth of up to 4.8
kHz depending on settings. As is obvious from its name, the HF Classifier Code Check primarily addresses
the requirements for the analysis of signals below 30 MHz, but it will of course work with signals in other
frequency ranges if they fall within the bandwidth, and fulfil the other criteria, used by the CCC processes.
How the Classifier Code Check works
The CCC processes input signals in up to four successive steps as shown in the block diagram below,
which also shows the possible signal paths. The user can select how many steps should be involved in the
analysis of the signal(s) under investigation.