  We focus on a scenario where two wireless source nodes wish to exchange
confidential information via an RF energy harvesting untrusted two-way relay.
Despite its cooperation in forwarding the information, the relay is considered
untrusted out of the concern that it might attempt to decode the confidential
information that is being relayed. To discourage the eavesdropping intention of
the relay, we use a friendly jammer. Under the total power constraint, to
maximize the sum-secrecy rate, we allocate the power among the sources and the
jammer optimally and calculate the optimal power splitting ratio to balance
between the energy harvesting and the information processing at the relay. We
further examine the effect of imperfect channel state information at both
sources on the sum-secrecy rate. Numerical results highlight the role of the
jammer in achieving the secure communication under channel estimation errors.
We have shown that, as the channel estimation error on any of the channels
increases, the power allocated to the jammer decreases to abate the
interference caused to the confidential information reception due to the
imperfect cancellation of jammer's signal.
