It is argued that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization (RBS) and verify this by implementing RBS on motes and use simulations to verify its accuracy over large-scale networks.
Abstract:
Wireless ad-hoc sensor networks have emerged as an interesting and important research area in the last few years. The applications envisioned for such networks require collaborative execution of a distributed task amongst a large set of sensor nodes. This is realized by exchanging messages that are time-stamped using the local clocks on the nodes. Therefore, time synchronization becomes an indispensable piece of infrastructure in such systems. For years, protocols such as NTP have kept the clocks of networked systems in perfect synchrony. However, this new class of networks has a large density of nodes and very limited energy resource at every node; this leads to scalability requirements while limiting the resources that can be used to achieve them. A new approach to time synchronization is needed for sensor networks.In this paper, we present Timing-sync Protocol for Sensor Networks (TPSN) that aims at providing network-wide time synchronization in a sensor network. The algorithm works in two steps. In the first step, a hierarchical structure is established in the network and then a pair wise synchronization is performed along the edges of this structure to establish a global timescale throughout the network. Eventually all nodes in the network synchronize their clocks to a reference node. We implement our algorithm on Berkeley motes and show that it can synchronize a pair of neighboring motes to an average accuracy of less than 20ms. We argue that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization (RBS) and verify this by implementing RBS on motes. We also show the performance of TPSN over small multihop networks of motes and use simulations to verify its accuracy over large-scale networks. We show that the synchronization accuracy does not degrade significantly with the increase in number of nodes being deployed, making TPSN completely scalable.
TL;DR: The maximum likelihood (ML) estimator for all the clock parameters in a two-way timing exchange model with exponential delays is derived and the same estimation procedure can be applied to one- way timing exchange models with little modification.
TL;DR: A power-efficient timing synchronization protocol (PETSP) which aims to fulfill the synchronization job with the minimum energy consumption and decreases 47% and 75% the power consumption and average maximum clock drift as compared to the IEEE 802.11, respectively.
TL;DR: An average based time synchronization algorithm is presented, which can provide continuous global time in a cluster with similar synchronization precision during leader re-elections and a self measure and query based adaptive mechanism is integrated into it to adjust synchronization period dynamically.
TL;DR: The MSSSN architecture provides scalability, extends sensor lifetime by letting them operate with limited transmission range and provides connectivity between isolated regions of sensor nodes.
TL;DR: This paper proposes an implementable asynchronous DSA scheme by practically considering the timing misalignment with multiple SUs competing for the spectrum opportunity and identifies the feasible operating region, achieving optimal equilibrium that is not only reaching a win-win situation in the sense of PU throughput and spectrum utilization maximization but is robust to potential selfish behavior of SUs as well.
TL;DR: This work presents the Tiny AGgregation (TAG) service for aggregation in low-power, distributed, wireless environments, and discusses a variety of optimizations for improving the performance and fault tolerance of the basic solution.
TL;DR: This paper believes that localized algorithms (in which simple local node behavior achieves a desired global objective) may be necessary for sensor network coordination.
TL;DR: A novel approach to the localization of sensors in an ad-hoc network that enables sensor nodes to discover their locations using a set distributed iterative algorithms is described.
TL;DR: Reference Broadcast Synchronization (RBS) as discussed by the authors is a scheme in which nodes send reference beacons to their neighbors using physical-layer broadcasts, and receivers use their arrival time as a point of reference for comparing their clocks.
TL;DR: A suite of algorithms for self-organization of wireless sensor networks in which there is a scalably large number of mainly static nodes with highly constrained energy resources and support slow mobility by a subset of the nodes, energy-efficient routing, and formation of ad hoc subnetworks.
Q1. What are the contributions mentioned in the paper "Timing-sync protocol for sensor networks" ?
However, this new class of networks has a large density of nodes and very limited energy resource at every node ; this leads to scalability requirements while limiting the resources that can be used to achieve them. In this paper, the authors present Timing-sync Protocol for Sensor Networks ( TPSN ) that aims at providing network-wide time synchronization in a sensor network. In the first step, a hierarchical structure is established in the network and then a pair wise synchronization is performed along the edges of this structure to establish a global timescale throughout the network. The authors implement their algorithm on Berkeley motes and show that it can synchronize a pair of neighboring motes to an average accuracy of less than 20μs. The authors argue that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization ( RBS ) and verify this by implementing RBS on motes. The authors also show the performance of TPSN over small multihop networks of motes and use simulations to verify its accuracy over large-scale networks. The authors show that the synchronization accuracy does not degrade significantly with the increase in number of nodes being deployed, making TPSN completely scalable.
Q2. What scheme could be used to maintain a relative clock between the adjacent nodes?
a scheme such as RBS [7] could be used to maintain a relative clock between the adjacent nodes that lie on the boundary, providing synchronization in the whole network.
Q3. What is the main motivation for deploying a sensor network?
The need for unobtrusive and remote monitoring is the main motivation for deploying a sensing and communication network (sensor network) consisting of a large number of these battery-powered nodes.
Q4. What are the applications of sensor networks?
The applications envisioned for sensor networks vary from monitoring inhospitable habitats and disaster areas to operating indoors for intrusion detection and equipment monitoring.
Q5. What is the main reason for the use of sensor networks?
Advances in microelectronics fabrication have allowed the integration of sensing, processing and wireless communication capabilities into low-cost and small form-factor embedded systems called sensor nodes [1], [2].
Q6. how do you remove the critical source of error in a sensor network?
However in case of sensor networks, by having the flexibility of time stamping the packets at the MAC layer, the authors remove this critical source of error.
Q7. How many nodes will have a new level in the hierarchy?
Assuming the network is still connected, the node will have at least one node in its neighbor set and thus it will surely be assigned a new level in the hierarchy.
Q8. How many times would a node retransmit the synchronization pulse?
It has already been explained that in order to handle collisions, a node would retransmit the synchronization_pulse after somerandom amount of time.
Q9. What is the best-case scenario for RBS?
Let us assume the best-case scenario for RBS, when the variation in propagation time is the same as in TPSN, equal to η time units.
Q10. What is the need of maintaining a unique and global timescale throughout the network?
On the other hand, to facilitate deployment of MAC protocols such as TDMA, there might be a need of maintaining a unique and global timescale throughout the network.
Q11. What is the importance of time synchronization in the implementation of MAC protocols?
Time synchronization is also indispensable in the implementation of the commonly used medium access control (MAC) protocols such as TDMA [4].
Q12. What is the way to measure the performance of a multihop network?
The authors provide an implementation on motes that integrates TPSN with post-facto synchronization and gauge its performance on a multihop network of motes.