Secure wireless multicasting through co-existing MIMO radio systems

We consider the problem of secure wireless multicasting through multiple-input multiple-output (MIMO) radio system in which two co-existing users communicate with two groups of receivers in the presence of multiple eavesdroppers. At first, we calculate the secrecy multicast capacity of each group and investigate the impact of interferences on it. Then, we use zero-forcing (ZF) precoding at a relay to enhance the secrecy multicast capacity of each group removing the impact of interferences. Finally, we propose a scheme to improve the secrecy multicast capacity of each group making use of interference energy that already exists in the communication medium employing selective precoding at the relay. In the proposed scheme, interference provides an additional source of energy that enhances secrecy multicast capacity at each group without the need to increase the transmitted power. Our results show that exploiting free interference power, the performance of coexisting wireless multicasting can be improved without affecting the performance of each other.