Time synchronization in WSN Research Papers (original) (raw)

Time synchronization in wireless sensor networks is a critical requirement for distributed and collaborative processing among the nodes. This paper presents a coarse grained hierarchical time synchronization scheme ‘LevelSync’ which synchronizes nodes in a sensor network with regards to their distance from the sink or master node. A hierarchical tree is dynamically constructed during the synchronization with master node acting as the root. The master node initiates and controls the synchronization phase and is responsible for normalizing the virtual time with the corresponding UTC. Each node is assigned a level and maintains a virtual clock which runs at a frequency different than that of its physical clock. Virtual clocks run at a fixed frequency calculated by the root or reference nodes hence are free from the drifts. LevelSync decreases the number of messages required for the synchronization and the resynchronization periods. We evaluate the performance and energy efficiency of the LevelSync through simulation and compare with existing time synchronization protocols. LevelSync is computationally light, energy efficient and achieves long lasting synchronizations.

- by and +1
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- Time synchronization in WSN

Low power and limited processing are characteristics of nodes in Wireless sensor networks. Therefore, optimal
consumption of energy for WSN protocols seems essential. In a number of WSN applications, sensor nodes sense data
periodically from environment and transfer it to the sink. Because of limitation in energy and selection of best route,
for the purpose of increasing network remaining energy a node with most energy level will be used for transmission
of data. The most part of energy in nodes is wasted on radio transmission; thus decreasing number of transferred
packets in the network will result in increase in node and network lifetimes. In algorithms introduced for data
transmission in such networks up to now, a single route is used for data transmissions that results in decrease in
energy of nodes located on this route which in turn results in increasing of remaining energy. In this paper a new
method is proposed for selection of data transmission route that is able to solve this problem. This method is based
on learning automata that selects the route with regard to energy parameters and the distance to sink. In this method
energy of network nodes finishes rather simultaneously preventing break down of network into two separate parts.
This will result in increased lifetime. Simulation results show that this method has been very effective in increasing of
remaining energy and it increases network lifetime.

In this paper, we apply adaptive control method to derive new results for the global chaos synchronization of 4-D chaotic systems, viz. identical Lorenz-Stenflo(LS) systems (Stenflo, 2001), identical Qi systems (Qi, Chen and Du, 2005) and non-identical LS and Qi systems. In this paper, we shall assume that the parameters of both master and slave systems are unknown and we devise adaptive control schemes for synchronization using the estimates of parameters for both master and slave systems. Our adaptive synchronization schemes derived in this paper are established using Lyapunov stability theory. Since the Lyapunov exponents are not required for these calculations, the adaptive control method is very effective and convenient to synchronize identical and non-identical LS and Qi systems. Numerical simulations are shown to demonstrate the effectiveness of the proposed adaptive synchronization schemes for the identical and non-identical, uncertain LS and Qi 4-D chaotic systems.

Sistem pendeteksi kendaraan di area parkir pada umumnya menggunakan metode konvensional, yaitu metode yangg menggunaan mikrokontroler sebagai control system, sensor sebagai komponen pengambil data dan kabel sebagai media pengiriman data. Pada umumnya sistem tersebut menggunakan satu mikrokontroler dalam mengolah data dari banyak sensor node secara bersamaan. Hal ini dapat menimbulkan masalah berupa data collision atau tabrakan data. Ketika data dikirimkan secara bersamaan, data dapat saling menginterferensi satu sama lain dan memungkinkan hilangnya informasi yang dikirimkan oleh masing-masing sensor node. Selain itu, penggunaan kabel sebagai media komunikasi data dianggap kurang efisien apabila diterapkan pada lingkup area yang luas jika dibandingkan dengan media komunikasi wireless yang praktis dan proses instalasi mudah. Untuk mencegah permasalah tersebut, pada penelitian ini diterapkan metode penjadwalan pengiriman data menggunakan protokol Time Division Multiple Access (TDMA) pada masing-masing node client. Diterapkan juga metode penyetaraan waktu Timing-synch Protocol for Sensor Network (TPSN) untuk menunjang metode penjadwalan. Pada penelitian ini juga menerapkan komunikasi data berbasis wireless dengan menggunakan modul wireless nRF24L01. Dari hasil implementasi, didapatkan hasil pengiriman data menggunakan protokol TDMA oleh masing-masing node client. Selain itu, node client dapat mengirimkan data sesuai jadwal yang telah didapatkan tanpa terjadi data collision. Pengiriman data tersebut telah berhasil dilakukan sesuai dengan slot waktu pengiriman yang telah diterapkan, dimana pada implementasinya slot waktu pengiriman dibagi menjadi 5 buah slot. Implementasi penyetaraan waktu juga telah berhasil diimplementasikan dengan rata-rata waktu dalam proses penyetaraan kurang dari 50 detik.

Wireless sensor networks (WSNs) have emerged as an attractive and key research area over the last decade. Time synchronization is a vital part of infrastructure for any distributed system. In embedded sensor networks, time synchronization is an essential service for correlating data among nodes and communication scheduling. This is realized by exchanging messages that are time stamped using the local clocks on the nodes. Various time synchronization protocols have been proposed aiming to attain high synchronization accuracy, high efficiency and low communication overhead. However, it requires that the time between resynchronization intervals to be as large as possible to obtain a system which is energy efficient having low communication overhead. This paper presents a simple but effective skew compensation algorithm that measures the skew rate of the sensor nodes with respect to the reference node and calibrates itself to compensate for the difference in the frequencies of the nodes. The proposed method can be incorporated with any existing time synchronization protocol for WSNs.

- by Shiu Kumar
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- Embedded Systems, Wireless Sensor Networks, Time synchronization in WSN