  In this paper the negative impacts of interference transmitters on automatic
modulation classification (AMC) have been discussed. We proposed two approaches
for AMC in the presence of interference: single user modulation classification
(SUMC) and multiuser modulation classification (MUMC). When the received power
of one transmitter is larger than the other transmitters, SUMC approach
recognizes the modulation type of that transmitter and other transmitters are
treated as interferences. Alternatively when the received powers of all
transmitters are close to each other we propose MUMC method to recognize the
modulation type of all of the transmitted signals. The features being used to
recognize the modulation types of transmitters for both approaches, SUMC and
MUMC are higher order cumulants. The super-position property of cumulants for
independent random variables is utilized for SUMC and MUMC. We investigated the
robustness of our classifier with respect to different powers of the received
signals via analytical and simulation results and we have shown the analytical
results will be confirmed by simulations. Also we studied the effect of signal
synchroni-zation error via simulation results in the both condition for MUMC
and SUMC.
