  This paper considers unmanned aerial vehicle (UAV)-carried intelligent
reflecting surface (IRS) for secure data collection in wireless sensor
networks. An eavesdropper (Eve) lurks within the vicinity of the main receiver
(Bob) while several randomly placed sensor nodes beamform collaboratively to
the UAV-carried IRS that reflects the signal to the main receiver (Bob). The
design objective is to maximise the achievable secrecy rate in the noisy
communication channel by jointly optimizing the collaborative beamforming
weights of the sensor nodes, the trajectory of the UAV and the reflection
coefficients of the IRS elements. By designing the IRS reflection coefficients
with and without the knowledge of the eavesdropper's channel, we develop a
non-iterative sub-optimal solution for the secrecy rate maximization problem.
It has been shown analytically that the UAV flight time and the randomness in
the distribution of the sensor nodes, obtained by varying the sensor
distribution area, can greatly affect secrecy performance. In addition, the
maximum allowable number of IRS elements as well as a bound on the attainable
average secrecy rate of the IRS aided noisy communication channel have also
been derived. Extensive simulation results demonstrate the superior performance
of the proposed algorithms compared to the existing schemes.
