  When simultaneous wireless information and power transfer is carried out, a
fundamental tradeoff between achievable rate and harvested energy exists
because the received power is used for two different purposes. The tradeoff is
well characterized by the rate-energy region, and several techniques have been
proposed to improve the achievable rate-energy region. However, the existing
techniques still have a considerable loss in either energy or rate and thus the
known achievable rate-energy regions are far from the ideal one. Deriving tight
upper and lower bounds on the rate-energy region of our proposed scheme, we
prove that the rate-energy region can be expanded almost to the ideal upper
bound. Contrary to the existing techniques, in the proposed scheme, the
information decoding circuit not only extracts amplitude and phase information
but also combines the extracted information with the amplitude information
obtained from the rectified signal. Consequently, the required energy for
decoding can be minimized, and thus the proposed scheme achieves a near-optimal
rate-energy region, which implies that the fundamental tradeoff in the
achievable rate-energy region is nearly eliminated. To practically account for
the theoretically achievable rate-energy region, we also present practical
examples with an $M$-ary multi-level circular QAM with Gaussian maximum
likelihood detection.
