Two-level signaling for IPACT in passive optical networks

The use of two-level intensity signal for interleaved polling with adaptive cycle time (IPACT) in passive optical networks (PONs) is presented. In the scheme, two different optical powers are used by two-grouped optical network units (ONUs) for their OOK modulation formats, and combined through the passive optical coupler on the way to the optical line terminal (OLT). The resultant quaternary signals are received, from which the receiver extracts each of data bits concurrently transmitted by the ONUs. Our two-level scheme allows to shorten the polling cycle time, which limits the fundamental performance of PONs. Quaternary signal reception at the OLT is analyzed in terms of bit error rate to be feasible with 5 dB power penalty compared to binary signal reception in typical PONs. Simulation results show that our two-level scheme offers smaller delay than IPACT, which is a benchmark Ethernet PON (EPON) polling protocol [1].