Pulse-coupled Synchronization Research Articles

Pulse-Coupled Synchronization Protocol and Its Optimized Algorithm for Wireless Sensor Networks

This paper proposed a pulse-coupled synchronization protocol for wireless sensor networks. The time information of the node can be encoded at the Mac layer and then sent and received in the form of pulse waves. During the exchange of time information between a pair of nodes, one node will adjust its own clock information according to certain rules after receiving the pulse time signal of the other node. This process is repeated in the entire wireless sensor network. Under certain environmental and estimated parameter conditions, all nodes in the network can finally converge to a coherent frequency and phase, thus realizing time synchronization. The relationship between time synchronization and coupling coefficient was proved theoretically, and the optimal coupling coefficient was derived. An optimized algorithm was proposed after the optimization of the protocol. Finally, the correctness of the proposed protocol and its optimized algorithm was verified by data simulation.

Pulse-Coupled Synchronization With Guaranteed Clock Continuity

Clock synchronization is a widely discussed topic in the engineering literature. Ensuring that individual clocks are closely aligned is important in network systems, since the correct timing of various events in a network is usually necessary for proper system implementation. However, many existing clock synchronization algorithms update clock values abruptly and instantaneously, resulting in discontinuous clocks, which have been shown to lead to undesirable behavior. In this paper, we explore the generalization of the pulse-coupled oscillator model to guarantee clock continuity, achieving continuous phase evolution in any pulse-coupled oscillator network. We provide rigorous mathematical proof for pulse-coupled synchronization under the proposed phase continuity methods, along with analysis of the time to synchronization under phase continuity. Two simple methods to achieve the desired continuity are presented. We further provide simulation and experimental results supporting these proofs, analyzing the effects of the phase continuity methods to convergence. We also investigate the convergence behavior of other pulse-coupled oscillator synchronization algorithms using the proposed methods.

Attack-Resilient Pulse-Coupled Synchronization

Synchronization of pulse-coupled oscillators is gaining increased popularity in sensor networks and wireless communications due to its simplicity, implicit scalability, and high energy efficiency. However, most existing results are obtained in the absence of malicious attacks. This paper addresses pulse-coupled synchronization resilient to malicious attacks. Not only is the condition for stealthy attacks obtained, but we also prove analytically that pulse-coupled synchronization can be guaranteed despite the presence of a stealthy attacker, even when legitimate oscillators have different initial phases. This is in distinct difference from most of the existing attack-resilient synchronization algorithms (including the seminal paper from Lamport and Melliar-Smith) that require a priori (almost) synchronization among legitimate nodes. Numerical simulations confirm the theoretical results.

A kernel module for pulse-coupled time synchronization of sensor networks

The biologically-inspired synchronization paradigm of pulse-coupled oscillators has received increased attention in the communications and sensor network communities as an appealing alternative to traditional packet-based synchronization strategies. Its inherent scalability, simplicity, and decentralized nature make pulse-coupled synchronization an attractive choice for time synchronization in wireless ad-hoc networks. However, in most current implementations, the pulse-coupled synchronization algorithm is coded in the application layer, which makes its performance susceptible to CPU processing load variations. Implementation of the pulse-coupled synchronization strategy in the physical layer is also reported, which however, is subject to difficulties in migration between different platforms. In this paper, we present the design, implementation, and evaluation of the pulse-coupled synchronization strategy as a Linux kernel module. Our goal is to leverage the high portability and prioritized CPU access of kernel modules to 1) reduce the influence of disturbances from application layer programs on the synchronization performance; and 2) simultaneously make the synchronization strategy easily installable in Linux-based sensor networks. Both lab experiments and field tests were conducted to confirm the effectiveness of the results.

Pulse-coupled time synchronization for distributed acoustic event detection using wireless sensor networks

Time synchronization has proven to be critical in sensor fusion applications where the time of arrival is utilized as a decision variable. Herein, the application of pulse-coupled synchronization to an acoustic event detection system based on a wireless sensor network is presented. The aim of the system is to locate the source of acoustic events utilizing time of arrival measurements for different formations of the sensor network. A distributed localization algorithm is introduced that solves the problem locally using only a subset of the time of arrival measurements and then fuses the local guesses using averaging consensus techniques. It is shown that the pulse-coupled strategy provides the system with the proper level of synchronization needed to enable accurate localization, even when there exists drift between the internal clocks and the formation is not perfectly maintained. Moreover, the distributed nature of pulse-coupled synchronization allows coordinated synchronization and distributed localization over an infrastructure-free ad-hoc network.

PulseSS: A Pulse-Coupled Synchronization and Scheduling Protocol for Clustered Wireless Sensor Networks

The pulse-coupled synchronization and scheduling (PulseSS) protocol is proposed in this paper for simultaneous synchronization and scheduling of communication activities in clustered wireless sensor networks (WSNs), by emulating the emergent behavior of pulse-coupled oscillator (PCO) networks in mathematical biology. Different from existing works that address synchronization and scheduling (i.e., desynchronization) separately, PulseSS provides a coordination signaling mechanism that achieves decentralized network synchronization and time division multiple access scheduling simultaneously at different time scales for clustered WSNs. Here, we assume that the nodes are connected only locally via their respective cluster heads. Moreover, PulseSS addresses the issue of propagation delays, that may plague the accuracy of PCO synchronization in practice, by providing ways to estimate and precompensate for these values locally at the sensors (i.e., PCOs). At the same time the protocol retains the adaptivity and light-weight nature of PCO protocols both in terms of signaling and computations. Simulations of both physical and medium access control layers show a synchronization accuracy of factions of microseconds above 15 dB of signal to interference and noise ratio for a five cluster network. A hardware implementation of PulseSS using TinyOS is also provided to corroborate the real world applicability of our protocol.

Statistical Analysis of the Pulse-Coupled Synchronization Strategy for Wireless Sensor Networks

Pulse-coupled synchronization is attracting increased attention in the sensor network community. Yet its properties have not been fully investigated. Using statistical analysis, we prove analytically that by controlling the number of connections at each node, synchronization can be guaranteed for generally pulse-coupled oscillators even in the presence of a refractory period. The approach does not require the initial phases to reside in half an oscillation cycle, which improves existing results. We also find that a refractory period can be strategically included to reduce idle listening at nearly no sacrifice to the synchronization probability. Given that reduced idle listening leads to higher energy efficiency in the synchronization process, the strategically added refractory period makes the synchronization scheme appealing to cheap sensor nodes, where energy is a precious system resource. We also analyzed the pulse-coupled synchronization in the presence of unreliable communication links and obtained similar results. QualNet experimental results are given to confirm the effectiveness of the theoretical predictions.

A Crystal-Less Self-Synchronized Bit-Level Duty-Cycled IR-UWB Transceiver System

A self-synchronized dual-band OOK IR-UWB transceiver system for short-range, low-data rate sensor networks is demonstrated. The transceiver system utilizes asynchronous non-coherent energy detection coupled with a novel pulse-coupled injection-locking scheme to synchronize transceivers throughout the network at nanosecond-scale precision. The pulse-coupled synchronization scheme compensates for intrinsic frequency variation so that all timing in the system can be derived from an integrated relaxation oscillator operating at a nominal frequency of 150 KHz. A low-jitter PLL and simple combinational logic is used for timing generation and control. The system is duty cycled between the expected arrival times of the sync and data pulses, allowing a demonstrated average RF duty cycle of less than 1% while being able to maintain synchronization for nearly 1 million cycles. Total measured system power consumption is 119 μW while actively communicating with 1200 bit packets. The transceiver was designed in a 90 nm IBM CMOS process and occupies 1.7 mm2 of active area.

Energy-Efficient Pulse-Coupled Synchronization Strategy Design for Wireless Sensor Networks Through Reduced Idle Listening

Synchronization is crucial to wireless sensor networks due to their decentralized structure. We propose an energy-efficient pulse-coupled synchronization strategy to achieve this goal. The basic idea is to reduce idle listening by intentionally introducing a large refractory period in the sensors' cooperation. The large refractory period greatly reduces idle listening in each oscillation period, and is analytically proven to have no influence on the time to synchronization. Hence, it significantly reduces the total energy consumption in a synchronization process. A topology control approach tailored for pulse-coupled synchronization is given to guarantee a k-edge strongly connected interaction topology, which is tolerant to communication-link failures. The topology control approach is totally decentralized and needs no information exchange among sensors, and it is applicable to dynamic network topologies as well. This facilitates a completely decentralized implementation of the synchronization strategy. The strategy is applicable to mobile sensor networks, too. QualNet case studies confirm the effectiveness of the synchronization strategy.

Optimal Phase Response Functions for Fast Pulse-Coupled Synchronization in Wireless Sensor Networks

Synchronization is crucial to wireless sensor networks. Recently a pulse-coupled synchronization strategy that emulates biological pulse-coupled agents has been used to achieve this goal. We propose to optimize the phase response function such that synchronization rate is maximized. Since the synchronization rate is increased independently of transmission power, energy consumption is reduced, hence extending the life of battery-powered sensor networks. Comparison with existing phase response functions confirms the effectiveness of the method.

Physical-layer distributed synchronization in wireless networks and applications

Physical-layer (pulse-coupled) techniques for distributed synchronization in wireless networks are attracting significant attention for their efficiency and scalability. In this paper, the model of pulse-coupled discrete Phase Locked Loops is reviewed and further investigated in two directions. At first, we extend the characterization of (frequency or phase) synchronous states and convergence conditions from homogeneous networks, where all the nodes have the same power constraints, to more general heterogeneous networks. Towards this goal, we build on recent results on algebraic graph theory for generally non-bidirectional graphs, and derive: (i) necessary and sufficient conditions for global synchronization of the network; (ii) closed-form expressions for the asymptotic values of frequency and phases, as a function of the network topology. In the second part of the paper, an application of pulse-coupled synchronization is considered, namely data collection in a sensor network. The energy efficiency of two medium access protocols for data collection from a set of randomly located sensors to an access point is compared: (i) basic ALOHA (which does not require time synchronization among the sensors); (ii) slotted ALOHA, where time synchronization is achieved via pulse-coupled clocks. Analysis shows that the energy spent for maintaining synchronization in slotted ALOHA pays off in terms of total energy consumption with respect to basic ALOHA provided that the number of sensors is sufficiently small. Moreover, the energy gain is proved to depend explicitly on the system load (in terms of packets /s), hardware and topology of the network.