  In this paper, we consider a two-hop molecular communication network
consisting of one nanotransmitter, one nanoreceiver, and one nanotransceiver
acting as a relay. We consider two different schemes for relaying to improve
the range of diffusion-based molecular communication. In the first scheme, two
different types of messenger molecules are utilized at the relay node for
transmission and detection. In the second scheme, we assume that there is only
one type of molecule available to be used as an information carrier. We
identify self-interference as the performance-limiting effect for the second
relaying scheme. Self-interference occurs when the relay must detect the same
type of molecule that it also emits. Furthermore, we consider two relaying
modes analogous to those used in wireless communication systems, i.e.,
full-duplex and half-duplex. In particular, while our main focus is on
full-duplex relaying, half-duplex relaying is employed as a means to mitigate
self-interference. In addition, we propose the adaptation of the decision
threshold as an effective mechanism to mitigate self-interference at the relay
for full-duplex transmission. We derive closed-form expressions for the
expected error probability of the network for both considered relaying schemes.
