  In this paper, error performance of the cooperative communication systems
with the best relay selection scheme is investigated in the presence of error
propagation from role to destination. The error propagation expression is
derived firstly when the best relay is selected within M relays. The derived
end-to-end BER expression is verified with the computer simulations. It is
shown that the best relay selection does not ensure M+1 diversity order under
the error propagation unlike perfect decoding. In addition, the threshold
selection for the relays has dominant effect on the error performance of the
system.
