  For downlink multiple-user (MU) transmission based on non-orthogonal multiple
access (NOMA), the advanced receiver strategy is required to cancel the
inter-user interference, e.g., successive interference cancellation (SIC). The
SIC process can be applicable only when information about the co-scheduled
signal is known at the user terminal (UT) side. In particular, the UT should
know whether the received signal is OMA or NOMA, whether SIC is required or
not, and which modulation orders and power ratios have been used for the
superposed UTs, before decoding the signal. An efficient network, e.g.,
vehicular network, requires that the UTs blindly classify the received signal
and apply a matching receiver strategy to reduce the high-layer signaling
overhead which is essential for high-mobility vehicular networks. In this
paper, we first analyze the performance impact of errors in NOMA signal
classification and address ensuing receiver challenges in practical MU usage
cases. In order to reduce the blind signal classification error rate, we
propose transmission schemes that rotate data symbols or pilots to a specific
phase according to the transmitted signal format. In the case of pilot
rotation, a new signal classification algorithm is also proposed. The
performance improvements by the proposed methods are verified by intensive
simulation results.
