  Exploring the interference-emitting friendly jammers to protect the sensitive
communications in the presence of eavesdroppers has increasingly being
investigated in literature. In parallel, scavenging energy from abient radio
signals for energy-constrained devices, namely \emph{wireless energy
harvesting} (WEH), has also drawn significant attention. Without relying on
external energy supply, the wireless-powered friendly jammer by WEH from
legitimate wireless devices is an effective approach to prolong their lifetime
and gain the flexibility in deployments. This paper studies the online
optimization of the placement and WEH of a set of friendly jammers in a
geographic location with the energy-efficiency (EE) consideration. We adopt a
simple "time switching" protocol where power transfer and jammer-assisted
secure communications occur in different time blocks when WEH requests are
launched. Our scheme has the following important advantages: 1) The proposed
online jammers placement and interfering power allocation to attack
eavesdroppers is the first distributed and scalable solutions within any
specified geographic region, 2) We model the WEH for jammers as a \emph{JAM-NET
lifetime maximization problem}, where online scheduling algorithms with
heterogeneous energy demands of each jammer (from energy sources) are designed,
3) Under our model, the problem of placing a minimum number of jammers with
distance-based power assignments is NP-hard, and near optimal PTAS
approximation algorithms are provided, 4) When durations of the eavesdropping
and legitimate communicating are available and the scenario is extended to the
multi-channels setting, our results are strengthened to see further improved EE
and reduced number of jammers. Simulations back up our theory.
