Minimum latency scheduling has arisen as one of the most crucial problems for broadcasting in duty‐cycled Wireless Sensor Networks (WSNs). Typical solutions for the broadcast scheduling iteratively search for nodes able to transmit a message simultaneously. Other nodes are prevented from transmissions to ensure that there is no collision in a network. Such collision‐preventions result in extra delays for a broadcast and may increase overall latency if the delays occur along critical paths of the network. To facilitate the broadcast latency minimization, we propose a novel approach, critical‐path aware scheduling (CAS), which schedules transmissions with a preference of nodes in critical paths of a duty‐cycled WSN. This paper presents two schemes employing CAS which produce collision‐free and collision‐tolerant broadcast schedules, respectively. The collision‐free CAS scheme guarantees an approximation ratio of (Δ − 1)T in terms of latency, where Δ denotes the maximum node degree in a network. By allowing collision at noncritical nodes, the collision‐tolerant CAS scheme reduces up to 10.2 percent broadcast latency compared with the collision‐free ones while requiring additional transmissions for the noncritical nodes experiencing collisions. Simulation results show that broadcast latencies of the two proposed schemes are significantly shorter than those of the existing methods.

Data aggregation is used to reduce the average number of transmissions and to save energy by aggregating multiple packets into a single packet in Wireless Sensor Networks (WSNs). Data aggregation scheduling problems have been extensively studied to make sure collision-free packet delivery to a sink node, with the goal of minimizing the aggregation time. Almost all existing data aggregation schemes have a continuous energy consumption problem of RF transceiver because they assume that each node is always in an active state. Recently, the data aggregation scheduling in duty-cycled WSNs is considered to reduce energy consumption. In this paper, we propose a delay-aware data aggregation scheduling scheme to minimize latency in duty-cycled WSNs. In a data aggregation tree construction phase, our proposed scheme constructs Connected Dominating Set (CDS) tree on the shortest path in terms of delay according to an active time slot of each node. The CDS tree is used as virtual backbone for efficient data aggregation. In a scheduling phase, the proposed scheme ensures collision-free data aggregation to the sink with reduced latency by considering data receiving time in each node. The simulation results show that comparing to related work, our proposed scheme can reduce the average time for data aggregation to the sink by 54% and 50% with various node densities and duty cycle respectively.

This paper studies three-stage Clos (1953) switching networks for multicast communications in terms of their blocking probabilities on a random traffic model. Even though the lack of multicast capability in input-stage switches requires a prohibitively large number of middle switches to provide compatible requests with nonblocking paths, the probabilistic model gives an observation that the blocking probability decreases drastically and then approaches zero as the number of middle switches is far less than the theoretical bound. The S-shaped curves of blocking probability versus degree of fanout indicate that high fanout requests are mostly blocked at some given reference network utilization. A split routing algorithm and its blocking probability are introduced to enhance the routability of the high fanout requests. We also corroborate the analytic model by performing network simulations based on a random request generator and a random routing strategy.