Joint Allocation of Time, Virtual Subcarrier and Modulation for 5G Green OFDMA-PONs

Passive Optical Network (PON) is a cost-effective way to become the front haul carrier for 5G ubiquitous wireless access connectivity. To hide the difference of frame formats and multiplexing methods among WiMAX, LTE and WiFi, a typical PON is proposed based on Orthogonal Frequency-Division-Multiplexing Access (OFDMA), i.e., OFDMA-PON. In OFDMA-PONs, by virtualization, low-bitrate Virtual Subcarriers (VSs) are assigned to segments, and VS loads can be migrated from one segment to another, thus sleeping unloaded segments while ensuring the service continuity. Although the subcarrier scheduling has been discussed for the OFDMA-PON merged with LTE, it is tailored to the single segment without allocating time and modulation level. In this paper, we investigate joint allocation of time, VS and modulation for 5G green OFDMA-PONs. We formulate the problem aimed at maximizing the energy-saving effect, and the upper bound is also derived. To solve the problem in a short span of time, we propose a novel heuristic algorithm. Finally, an extensive simulation is made to demonstrate the effectiveness of our design.