  UAVs are capable of improving the performance of next generation wireless
systems. Specifically, UAVs can be exploited as aerial base-stations (UAV-BS)
for supporting legitimate ground users in remote uncovered areas or in
environments temporarily requiring high capacity. However, their communication
performance is prone to both channel estimation errors and potential
eavesdropping. Hence, we investigate the effective secrecy throughput of the
UAV-aided uplink, in which rate-splitting multiple access (RSMA) is employed by
each legitimate user for secure transmission under the scenario of massive
access. To maximize the effective network secrecy throughput in the uplink, the
transmission rate vs. power allocation relationship is formulated as a max-min
optimization problem, relying on realistic imperfect CSI of both the legitimate
users and of the potential eavesdroppers (Eves). We then propose a novel
transformation of the associated probabilistic constraints for decoupling the
variables, so that our design problem can be solved by alternatively activating
the related block coordinate decent programming. In the model considered, each
user transmits a superposition of two messages to a UAV-BS, each having
different transmit power and the UAV-BS uses a SIC technique to decode the
received messages. Given the non-convexity of the problem, it is decoupled into
a pair of sub-problems. In particular, we derive a closed form expression for
the optimal rate-splitting fraction of each user. Then, given the optimal
rate-splitting fraction of each user, the \epsilon-constrainted transmit power
of each user is calculated by harnessing SPCA programming.
