  This paper studies secrecy transmission with the aid of a group of wireless
energy harvesting (WEH)-enabled amplify-and-forward (AF) relays performing
cooperative jamming (CJ) and relaying. The source node in the network does
simultaneous wireless information and power transfer (SWIPT) with each relay
employing a power splitting (PS) receiver in the first phase; each relay
further divides its harvested power for forwarding the received signal and
generating artificial noise (AN) for jamming the eavesdroppers in the second
transmission phase. In the centralized case with global channel state
information (CSI), we provide closed-form expressions for the optimal and/or
suboptimal AF-relay beamforming vectors to maximize the achievable secrecy rate
subject to individual power constraints of the relays, using the technique of
semidefinite relaxation (SDR), which is proved to be tight. A fully distributed
algorithm utilizing only local CSI at each relay is also proposed as a
performance benchmark. Simulation results validate the effectiveness of the
proposed multi-AF relaying with CJ over other suboptimal designs.
