  Physical-layer security for wireless networks has become an effective
approach and recently drawn significant attention in the literature. In
particular, the deployment and allocation of resources such as relays to assist
the transmission have gained significant interest due to their ability to
improve the secrecy rate of wireless networks. In this work, we examine relay
selection criteria with arbitrary knowledge of the channels of the users and
the eavesdroppers. We present alternative optimization criteria based on the
signal-to-interference and the secrecy rate criteria that can be used for
resource allocation and that do not require knowledge of the channels of the
eavesdroppers and the interference. We then develop effective relay selection
algorithms that can achieve a high secrecy rate performance without the need
for the knowledge of the channels of the eavesdroppers and the interference.
Simulation results show that the proposed criteria and algorithms achieve
excellent performance.
