  In this paper, random coding error exponents and cutoff rate are studied for
noncoherent Rician fading channels, where neither the receiver nor the
transmitter has channel side information. First, it is assumed that the input
is subject only to an average power constraint. In this case, a lower bound to
the random coding error exponent is considered and the optimal input achieving
this lower bound is shown to have a discrete amplitude and uniform phase. If
the input is subject to both average and peak power constraints, it is proven
that the optimal input achieving the random coding error exponent has again a
discrete nature. Finally, the cutoff rate is analyzed, and the optimality of
the single-mass input amplitude distribution in the low-power regime is
discussed.
