A theoretical analysis is presented for a multi-hop relay system composed of QPSK-DPR's. A Direct Phase Regenerator (DPR) can regenerate a QPSK signal at carrier frequency. Special attention is given to jitter generation and accumulation. Circuit parameters characterizing jitter generation are clarified and obtained quantitatively. The required upper limit for jitter per DPR is also obtained from allotedC/Ndegradation in a multi-hop system. Simulation experiments were carried out using a novel 400 Mbit/s QPSK-DPR with less than 1 dB inherent equivalentC/Ndegradation. The results Show that a hybrid system, consisting of 4 to 9 DPR's and a base band regenerator, is feasible.