Low-power wide area networks (LPWANs) are wireless communication systems that enable long-distance communication with low power consumption, and have attracted attention as a wireless infrastructure for Internet of Things (IoT) systems. However, the long-distance nature of LPWANs can cause the hidden node problem, which results in a lower packet delivery ratio (PDR). To address the hidden node problem, this paper proposes a channel assignment method. First, we derive an approximate formula for PDR under the impact of hidden nodes, and then propose an optimal channel assignment method based on simulated annealing, using the derived formula. Simulation results confirm that the proposed method can mitigate the degradation of PDR and increase the capacity of LPWAN networks.

In multicast RDMA, the sender overestimates congestion signals when multiple paths are congested. This congestion path multiplicity problem is hard to be resolved because RDMA sender cannot identify the sender of congestion signals due to RDMA protocol regulation. In this paper, we propose a new approach that the branching switch filters congestion signals from the worst congested interface. Our evaluation results show that our proposed method can adequately resolve the congestion path multiplicity problem.

In a data center (DC) where inter- and intra-DC flows share high-speed data center networks (DCNs), these two types of flows have significantly different round-trip times (RTTs). When congestion occurs in a DCN, the congestion signal is detected first by the intra-DC flow, resulting in unfairness where only it reacts to congestion. This technical problem is especially important for the receiving DCN because the congestion point is far from the sender. To solve this issue, we propose DC performance enhancing proxy (DC-PEP) with ECN (Explicit Congestion Notification) buffer control as a proxy at the gateway of the receiving DCN. DC-PEP divides the end-to-end congestion control loop into two loops, which homogenizes the congestion loop inside the receiving DCN. To absorb the throughput difference between these two congestion loops, a buffer is required at DC-PEP. By implementing ECN-Echo notification, excessive queueing at DC-PEP can be avoided. Our simulation results show that our proposed DC-PEP with ECN improves fairness between inter- and intra-DC flows without incurring large queue sizes at the proxy.