  Non-orthogonal multiple access (NOMA) is a candidate multiple access scheme
in 5G systems for the simultaneous access of tremendous number of wireless
nodes. On the other hand, RF-enabled wireless energy harvesting is a promising
technology for self-sustainable wireless nodes. In this paper, we consider a
NOMA system where the near user harvests energy from the strong radio signal to
power-on the information decoder. A generalized energy harvesting scheme is
proposed by combining the conventional time switching and power splitting
scheme. The achievable rate region of the proposed scheme is characterized
under both constant and dynamic decoding power consumption models. If the
decoding power is constant, the achievable rate region can be found by solving
two convex optimization subproblems, and the regions for two special cases:
time switching and power splitting, are characterized in closed-form. If the
decoding power is proportional to data rate, the achievable rate region can be
found by exhaustive search algorithm. Numerical results show that the
achievable rate region of the proposed generalized scheme is larger than those
of time switching scheme and power splitting scheme, and rate-dependent decoder
design helps to enlarge the achievable rate region.
