  A passive optical network (PON) based on non-orthogonal multiple access
(NOMA) meets low latency and high capacity. In the NOMA-PON, the asynchronous
clock between the strong and weak optical network units (ONUs) causes the
timing error and phase noise on the signal of the weak ONU. The theoretical
derivation shows that the timing error and phase noise can be independently
compensated. In this Letter, we propose a timing recovery (TR) algorithm based
on an absolute timing error detector (Abs TED) and a pilot-based carrier phase
recovery (CPR) to eliminate the timing error and phase noise separately. An
experiment for 25G NOMA-PON is set up to verify the feasibility of the proposed
algorithms. The weak ONU can achieve the 20% soft-decision forward error
correction limit after compensating for timing error and phase noise. In
conclusion, the proposed TR and the pilot-based CPR show great potential for
the NOMA-PON.
