  This paper designs a molecule harvesting transmitter (TX) model, where the
surface of a spherical TX is covered by heterogeneous receptors with different
sizes and arbitrary locations. If molecules hit any receptor, they are absorbed
by the TX immediately. Within the TX, molecules are stored in vesicles that are
continuously generated and released by the TX via the membrane fusion process.
Considering a transparent receiver (RX) and molecular degradation during the
propagation from the TX to the RX, we derive the molecule release rate and the
fraction of molecules absorbed by the TX as well as the received signal at the
RX. Notably, this analytical result is applicable for different numbers, sizes,
and locations of receptors, and its accuracy is verified via particle-based
simulations. Numerical results show that different vesicle generation rates
result in the same number of molecules absorbed by the TX, but different peak
received signals at the RX.
