  In some communication networks, such as passive RFID systems, the energy used
to transfer information between a sender and a recipient can be reused for
successive communication tasks. In fact, from known results in physics, any
system that exchanges information via the transfer of given physical resources,
such as radio waves, particles and qubits, can conceivably reuse, at least
part, of the received resources. This paper aims at illustrating some of the
new challenges that arise in the design of communication networks in which the
signals exchanged by the nodes carry both information and energy. To this end,
a baseline two-way communication system is considered in which two nodes
communicate in an interactive fashion. In the system, a node can either send an
"on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or
"0"), which does not require any energy expenditure. Upon reception of a "1"
signal, the recipient node "harvests", with some probability, the energy
contained in the signal and stores it for future communication tasks. Inner and
outer bounds on the achievable rates are derived. Numerical results demonstrate
the effectiveness of the proposed strategies and illustrate some key design
insights.
