  Harvesting energy from ambient environment is a new promising solution to
free electronic devices from electric wire or limited-lifetime battery, which
may find very significant applications in sensor networks and body-area
networks. This paper mainly investigate the fundamental limits of information
transmission in wireless communication system with RF-based energy harvesting,
in which a master node acts not only as an information source but also an
energy source for child node while only information is transmitted back from
child to master node. Three typical structures: optimum receiver, orthogonal
receiver and power splitting receiver are considered where two way information
transmission between two nodes under an unique external power supply constraint
at master node are jointly investigated in the viewpoint of systemic level. We
explicitly characterize the achievable capacity-rate region and also discuss
the effect of signal processing power consumption at child node. The optimal
transmission strategy corresponding to the most energy-efficient status, namely
the point on the boundary of achievable capacity-rate region, is derived with
help of conditional capacity function. Simulation confirms the substantial
gains of employing optimal transmission strategy and optimum receiver
structure. Besides, a typical application on minimizing required transmit power
to green system is presented.
