Traffic-aware ONU grouping and downstream bandwidth allocation for multicast services in flexible-rate PONs

In flexible-rate passive optical networks (PONs), optical network units (ONUs) with different channel conditions can achieve different data rates by implementing flexible transmission parameters, e.g., modulation format, thereby enhancing system capacity. Correspondingly, the downstream frame is divided into multiple subframes, each being received and processed only by ONUs in its targeted group. However, for downstream multicast services, the data need to be duplicated and encapsulated into multiple subframes for ONUs belonging to different groups, resulting in data redundancy and degradation of effective throughput (i.e., throughput without redundant data). To improve resource utilization, ONU grouping should be dynamically adjusted according to both channel conditions and time-varying network factors, e.g., traffic loads and multicast memberships. For this, we first enhance the current downstream scheduling protocol to support dynamic ONU grouping in a multicast scenario and propose a traffic-aware ONU grouping (TAOG) algorithm to improve effective throughput, which optimizes ONU grouping by considering time-varying network conditions. As ONUs belonging to different groups have different data rates, we further propose a group-based downstream time slot allocation (GBDTA) algorithm to adjust time slots for each service by considering their demands and ONU data rates. Exhaustive simulation results show that the integrated TAOG-GBDTA scheme adapts effectively to dynamic network conditions and, compared to conventional schemes, it effectively improves effective throughput, reduces redundancy, and achieves lower packet latency under various multicast scenarios.