This paper proposes a data gathering strategy for wireless sensor networks and an implementation based on the IEEE 802.15.4 standard. The algorithm combines the benefits of single-path and multi-path routing strategies in a hybrid solution which makes use of alternative paths when necessary. We adopt a caching and retransmission technique, which exploits some peculiar features of data aggregation, with the use of implicit acknowledgments of reception. The paper also discusses simulation results that show how the mentioned techniques, combined with exploitation of the features of the IEEE 802.15.4 standard have been used to obtain an efficient protocol that takes energy consumption into accoun
This paper proposes a network-layer protocol for wireless sensor networks based on the IEEE 802.15.4 standard. Our protocol is devised to provide reliable data gathering in latency-constrained applications, and exploits both the flexibility of the IEEE 802.15.4 MAC layer and features of data aggregation techniques, such as implicit acknowledgment of reception. The proposed protocol acts as a routing module and a control entity for the MAC layer and provides reliable communication, while managing power saving and synchronization among nodes.Without relying on MAC-layer acknowledgments, the protocol implements caching and network-layer retransmissions, triggered upon detection of a link failure. The performance of the proposed approach is studied through simulations, in which we evaluate the achieved reliability and the energy consumption with varying network settings.
The large number of nodes, typical of many sensor network deployments, and the well-known hidden terminal problem make collision avoidance an essential goal for the actual employment of WSN technology. Collision avoidance is traditionally dealt with at the MAC Layer and plenty of different solutions have been proposed, which however have encountered limited diffusion because of their incompatibility with commonly available devices.In this paper we propose an approach to collision avoidance which is designed to work over a standard MAC Layer, namely the IEEE 802.15.4 MAC, and is based on application-controlled delays of packet transmission times. The proposed scheme is simple, decentralized and scalable. We present two variants of the algorithm and we evaluate our work through simulations. Discussed results show that our scheme provides a considerable boost of performance in IEEE 802.15.4 tree-based networks, effectively addressing the hidden terminal problem and keeping radio utilization efficient.
We review the status of hybrid baryons. The only known way to study hybrids rigorously is via excited adiabatic potentials. Hybrids can be modelled by both the bag and flux-tube models. The low-lying hybrid baryon is N 1 2 + with a mass of 1.5 − 1.8 GeV. Hybrid baryons can be produced in the glue-rich processes of diffractive γN and πN production, Ψ decays and pp annihilation.
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