  This paper proposes a novel imperfect spherical transmitter (TX) model,
namely the membrane fusion (MF)-based TX, that adopts MF between a vesicle and
the TX membrane to release molecules encapsulated within the vesicle. For the
MF-based TX, the molecule release probability and the fraction of molecules
released from the TX membrane are derived. Incorporating molecular degradation
and a fully-absorbing receiver (RX), the end-to-end molecule hitting
probability at the RX is also derived. A simulation framework for the MF-based
TX is proposed, where the released point on the TX membrane and the released
time of each molecule are determined. Aided by the simulation framework, the
derived analytical expressions are validated. Simulation results verify that a
low MF probability or low vesicle mobility slows the release of molecules from
the TX, extends time required to reach the peak release probability, and
reduces the end-to-end molecule hitting probability at the RX.
