Modeling and simulation comparison of two time synchronization protocols

Wireless sensor network (WSN) application for bridge structure health monitoring (SHM), requires a scalable time synchronization service enabling data consistency and coordination. This paper describes the Energy-Balanced time Synchronization protocol (EBS), especially tailored for bridge structure health monitoring application. Through analyzing the characteristics of the bridge SHM, we present the especial requirements for designing the time synchronization protocol in WSN for SHM. Following the requirements, the proposed time synchronization protocol utilizes dynamically selecting the maximum reserve energy sensor node as broadcasting node to achieve energy balance among nodes in network. In addition, the EBS protocol fully exploits the wireless broadcast channel property in bridge SHM, so the broadcast communication flow is small. The high precision performance is reached by utilizing MAC-layer time-stamp as in the existing FTSP protocol. Finally, The EBS protocol performance is evaluated and compared to FTSP protocol.

We formulate simple assumptions, implying the Robbins–Monro conditions for the Q-learning algorithm with the local learning rate, depending on the number of visits of a particular state (local clock) and the number of iteration (global clock). It is assumed that the Markov decision process is communicating and the learning policy ensures the persistent exploration. The restrictions are imposed on the functional dependence of the learning rate on the local and global clocks. The result partially confirms the conjecture of Bradkte (1994).

Existing time synchronization schemes in sensor networks were all developed to be energy-efficient, precise, and robust, but none of them were developed with security in mind. We have developed a secure, accurate and energy-efficient time synchronization protocol (SAEP). SAEP achieves accurate time synchronization service with significantly reducing the number of message exchanges. Also, it safeguards against Byzantine failure, in which nodes drop, modify, or delay time information in an attempt to disrupt the time synchronization service in multi-hop networks. SAEP takes a distributed approach where each sensor independently makes decisions based only on the information collected from multiple adjacent nodes, thus achieving a high level of resistance to various attacks while minimizing the energy cost. We investigate the misbehavior of a maliciously compromised node and analyze how SAEP can combat these attacks. In our experiment SAEP outperforms the existing time synchronization protocol in accuracy, energy consumption and it is even resilient to multiple capture attacks.

A stairs-type global strain clocking mechanism for nanomagnetic majority logic gate based on shape engineering of nanomagnets was designed in this paper. Reasonable size nanomagnets and proper strain clocking scheme ensure the computing architecture pipelined at room temperature. The optimal global strain clocking scheme was obtained by investigating the impact of magnetic layer thickness and width on clocking period and strain magnitude. Encouragingly, for the global strain clocking, information transmission speed of majority logic gate is increased 1-2 times as against the local strain clocking scheme due to decreasing the number of start-ups during information transmission. While the energy dissipated per clock cycle of the global strain clocking scheme consumes 3-4 times less energy than that of local strain clocking scheme. Moreover, global clocking is used to control a nanomagnetic logic device(NMLD), in which case single device consisted of many nanomagnets can be treated as single nanomagnet. However, magnetization switching is error-prone in the presence of thermal noise at room temperature. Therefore, the proper structure parameters of the device are obtained at room temperature, in which case the error probability of the majority logic gate is 0.5% in theoretical simulation. These results provide essential guidance for the design of energy-efficient multiferroic nanomagnetic logic devices.

Precision time synchronization provides essential services for wireless ad hoc networks, which are required for applications such as communication, positioning and power management. Precision frequency synchronization not only plays an important role in improving the accuracy and energy efficiency of time synchronization, but also greatly improves the data reliability and communication quality. This paper proposes a precision time and frequency joint synchronization protocol, combining time synchronization with frequency synchronization. The two-stage protocol, consisting of coarse and fine synchronization, obtains improvements in accuracy, energy efficiency and time continuity. Experiments validate the correctness and feasibility of the proposed protocol, obtaining timing accuracy of 17.4 ns with standard deviation 6.61 ns and frequency accuracy within 0.3Hz for 128MHz clock.

In conventional sensor networks, information sensed by distributed sensor nodes is collected to a sink node, and applications are executed based on this information. However, when actuator nodes in a field execute the applications, the sink node does not have to collect all the sensing information, but each actuator node collects the information required for its application. We aim to collect the required information to each actuator node, and generate a group whose members are source sensor nodes involved by each actuator node. We propose a protocol to efficiently collect sensing information of grouped source nodes. Furthermore, we experimentally demonstrate that actuator nodes can collect the information and that the proposed protocol can decrease the number of packets transmitted in the network.

This paper describes an efficient method of estimating the ratio of clock frequency between two clocks used at the two end nodes of a one-way path. This estimation method relies on the local time measurements on the packets in a data stream going from a source node to a sink node. The time durations between adjacent packets are measured at both the source and the sink nodes according to the local clocks. The ratios of clock frequencies of two local clocks can be estimated on the suitable samples of the ratios of the time durations between two adjacent packets. The suitable samples of the ratios are obtained when two adjacent packets have experienced a zero value of the one-way variable delay. A heuristic has been developed to infer the cases when two adjacent packets experienced a zero one-way variable delay. The heuristic is used to select the suitable samples of the ratios of the time duration between two adjacent packets. Evaluation results show that the estimated values of the ratio of clock frequency very closely approximate the actual ratios. The accuracy of this method is robust to packet loss and the out-of-the-order transmission of packets. This estimation method is highly efficient without requiring complicated computations.

Time synchronization in wireless sensor networks is critical for providing accurate timing service to many applications. This paper presents an Error Statistic based Time Synchronization protocol (ESTS) for wireless sensor networks. ESTS uses a flooding mechanism for basic global time synchronization and delay measurement, and achieves a fine grained synchronization through compensating per hop delay to all the nodes. It is a light weight mechanism for its simplicity in both computation and communication. Experiments show that ESTS obtains a better performance in energy efficiency than most in-situ time synchronization protocols in the same precision level.

Time synchronization is important for wireless sensor networks because it facilitates cooperation among nodes and helps raise power efficiency. Time synchronization protocols like TPSN, RBS and FTSP have provided great schemes to fulfill fast synchronization with efficiency. In some applications, nodes might hope to sleep for a long time without timestamp exchanges with other nodes. In that case, accurate time drift prediction is quite necessary. For that purpose, firstly, we propose a time synchronization scheme, which fully utilizes the broadcast nature. The scheme achieves time synchronization with fewer timestamps compared with RBS and TPSN. Secondly, we introduce a method to find relative time drift rate on the fly. Thirdly, we introduce a scheme to predict time drift rates of the next few hours. We also analyze a few factors that deteriorate frequency drift or time drift rate. The diurnal periodical environment trend, instead of mathematical extrapolation, is used for time drift rates prediction of the next few hours.

Time synchronization plays an important role in the performance of wireless sensor networks. It can enhance the throughput and the lifetime of the network by improving the energy-efficiency, the freshness of collected data and reducing the network traffic and message conflicts. Due to the constraints on sensor nodes’ energy resources and the vulnerability of the distributed infrastructure of wireless networks, an efficient, scalable and accurate time synchronization protocol is desirable. This paper presents an accurate reactive protocol, named HRTS, that synchronizes the sensor nodes’ clock based on the node’s demand. It minimizes the synchronization region dynamically to the set of nodes which request synchronization. HRTS improves the accuracy of the synchronization procedure by measuring time parameters accurately and removing delays accordingly. Compared with the conventional time synchronization protocols like PCTS and TPSN, HRTS also reduces energy consumption by decreasing the traffic overheads especially when the network is not very dense.

This paper presents a new distributed methodology for source destination synchronization for interactive teleconferencing. The method is based on a reference clock, which is synthesized from a distributed global clock. The global clock is generated by periodically exchanging inband synchronization signals with neighboring nodes. The timing jitter achieved with this method can be arbitrarily close to the jitter obtained by the centralized synchronous methods which usually use an out-of-band, hard-wired reference clock. The global clock synchronization algorithm, used in this work, guarantees frequency locking of all the network nodes to the slowest clock in the system. As a result, the slowest clock can be used as an implicit reference clock for source-destination synchronization protocols, such as synchronous frequency encoding technique (SFET) and synchronous residual time stamp (SRTS). This inband synchronization method does not require the explicit knowledge of which clock is actually the slowest in the system. Therefore, if the slowest clock fails, then another clock on a different node will be the slowest, and the nodes will use it as a reference clock for the source-destination synchronization protocol. The existing out-of-band reference clock techniques do not have this strong fault tolerant property.

Wireless sensor networks are a nascent type of ad-hoc networks that had drawn the interest of the research community in last few years. They require working together for distributed tasks. Accurate and reliable time is one of the needs for some of its applications. The use of traditional time synchronization protocols for wired network is restricted by severe energy constraint in sensor network. The realization of time synchronized network poses many challenges, which are the subject of active research in the fileld. In this paper we argue that clock synchronization provides a lot of overhead, and can be eliminated in some of the cases. We advocate that sensor should be allowed to run unsynchronized. The time when any event of interest occurs, the sensor node records that event in its memory with timestamp from its cluster head's clock, instead of its local clock.

This chapter presents a combined approach to visualize the IoT and cyber-physical system in any wireless communication networks. The brief overview of IoT and its applications in wireless sensor network (WSN) are elaborated in current era. In today’s present situation and the challenges faced during COVID-19 pandemic how the things can be monitored through IoT is being focused in this chapter. Also, the threats challenges and monitoring of cyber-physical system for security is presented in analysis form. WSN provides a bridge between the physical and virtual world and finds use in numerous applications like environmental monitoring, civil structural health monitoring and industrial process monitoring. Lately, it has found much use in the latest technology called Internet of Things (IoT). It seems that IoT has a great potential in shaping our future where everything will be connected together all the time. The major challenges faced by WSN include energy-efficiency, heterogeneity, and systematic design. WSN comprise of autonomous sensors which are capable of wirelessly transmitting their sensed parameter-values (also called packets) to remotely 188located sink node. The sink node is a WSN node which has the capability to assemble the data from all the nodes and forward it to farther distances to the remote base station through wired connections. The data transmission from source node to sink node is done by taking multi-hops which means that data is not sent directly to the destination node but through jumping from one intermediate node to another until the sink is reached. The sensor nodes also act as wireless routers which transmit data to other sensor-routers. So, sensor devices are very useful in deployment, collection of data, act as a IoT sensor devices as an application in technology. IoT is a device which can be used as application while a cyber-physical system is a collection of various mechanical components which are controlled and managed by different devices and algorithms. An IFM (Information Flow Monitor) is an application to backtrack queries and find the culprit in an error that has occurred in the cyber system. However, while backtracking and flow monitoring is not always guaranteed in terms of secure and efficient transaction. In some cases, the sender may deny the authority of the data so the information flow monitors may fail to provide a trustful and authentic source of data. Thus, the chapter focuses on both the issues of IoT integration with cyber-physical security (CPS) system. The key challenges and some solutions are proposed for the researchers for future work.

Distributed audio sensing with homeostasis-inspired autonomous communication

The ever increasing popularity of the particle swarm optimization (PSO) algorithm is recently attracting attention to the embedded computing world. Although PSO is considered efficient compared to other contemporary population based optimization techniques, for many continuous multimodal and multidimensional problems, it still suffers from performance loss when it is targeted onto embedded application platforms. Examples of such target applications include small mobile robots and distributed sensor nodes in sensor network applications. In a previous work we presented a novel, modular, efficient and portable hardware architecture to accelerate the performance of the PSO for embedded applications. This paper extends the work by presenting a parallelization technique for further speedup of the PSO algorithm by dividing the swarm into a set of subswarms that are executing in parallel. The underlying communication topology and messaging protocols are described. Finally, the performance of the proposed system is evaluated on mathematical and real-world benchmark functions.