Secrecy Rate of Cooperative MIMO in Presence of a Location Constrained Eavesdropper

We propose and study the secrecy cooperative MIMO architecture to enable and to improve the secrecy transmissions between clusters of mobile devices in presence of an eavesdropper with certain location constraint. The cooperative MIMO is formed by temporarily activating clusters of nearby trusted devices, with each cluster being centrally coordinated by its corresponding cluster head. We assume that the transmitters apply a practical eigen-direction precoding scheme and that the eavesdropper has multiple possible locations in the proximity of the legitimate devices. We first obtain the expression of the secrecy rate, where the required average mutual information between the transmit cluster and the eavesdropper is characterized by closed-form approximations. The proposed approximations are especially useful in the secrecy rate maximization, where the original non-convex problem is approximated by a sequence of convex sub-problems. Numerical results show that the achievable secrecy rate can be effectively improved by activating equal or larger number of trusted devices as compared to the number of antennas at the eavesdropper. The secrecy rate is further improved by increasing the cluster size.