In a half-duplex relay system, the end-to-end performance decreases significantly as the number of relay nodes increases because each relay node cannot forward a packet until packet reception is completed. In-band full-duplex transmission is considered a promising technology to improve the end-to-end performance of the multi-hop relay system. However, the transmission of full-duplex relay nodes experiences interference from that of other simultaneous relay nodes as well as residual self-interference. We consider a decode-and-forward relay scenario and derive an unsaturated full-duplex relay model that considers packet drops during relay forwarding. We also propose centralized and distributed power adjustment schemes for improving the end-to-end outage performance of the relay system by adjusting the transmit power at each node.