PHY Security Improvement of Wireless Sensor Networks in Presence of an Untrusted User

This paper proposes a new hybrid secure transmission scheme, TAS-SC-ZFB for wireless sensor networks (WSNs). This scheme uses transmit antenna selection (TAS) at the base station (BS) and adopts selection combining (SC) over legitimate nodes. Aditionally, zeroforcing beamforming (ZFB) is applied at the friendly jammer to confuse the effects of the eavesdropping node. Particularly, exact closed-form expressions for the secrecy outage probability (SOP) and the effective secrecy throughput are derived. Using these expressions, the optimal power allocation factor between the BS and jammer and optimal secrecy rate are obtained to minimize the SOP and maximize the secrecy throughput, respectively. Numerical results are used to validate the theoretical analysis and to compare with the existing state of the art.