  Mission-critical communications (MCC) involve all communications between
people in charge of the safety of the civil society. MCC have unique
requirements that include improved reliability, security and group
communication support. In this paper, we propose a secure and robust
Multiple-Input-Multiple-Output (MIMO) transceiver, designed for multiple Base
Stations supporting multicast MCC in presence of multiple eavesdroppers. We
formulate minimization problems with the Sum-Mean-Square-Error (SMSE) at
legitimate users as an objective function, and a lower bound for the MSE at
eavesdroppers as a constraint. Security is achieved thanks to physical layer
security mechanisms, namely MIMO beamforming and Artificial Noise (AN).
Reliability is achieved by designing a system which is robust to Channel State
Information errors. They can be of known distribution or norm-bounded. In the
former case, a coordinate descent algorithm is proposed to solve the problem.
In the latter case, we propose an worst-case based iterative algorithm.
Numerical results at physical layer and system level reveal the crucial role of
robust designs for reliable MCC. We show the interest of both robust design and
AN to improve the security gap. We show that full BS cooperation in preferred
for highly secured and reliable MCC but dynamic clustering allows to trade-off
security and reliability against capacity.
