Kyoung-Lae Noh

Novel Clock Phase Offset and Skew Estimation Using Two-Way Timing Message Exchanges for Wireless Sensor Networks

Recently, a few efficient timing synchronization protocols for wireless sensor networks (WSNs) have been proposed with the goal of maximizing the accuracy and minimizing the power utilization. This paper proposes novel clock skew estimators assuming different delay environments to achieve energy-efficient network-wide synchronization for WSNs. The proposed clock skew correction mechanism significantly increases the re-synchronization period, which is a critical factor in reducing the overall power consumption. The proposed synchronization scheme can be applied to the conventional protocols without additional overheads. Moreover, this paper derives the Cramer-Rao lower bounds and the maximum likelihood estimators under different delay models and assumptions. These analytical metrics serves as good benchmarks for the thus far reported experimental results

A New Approach for Time Synchronization in Wireless Sensor Networks: Pairwise Broadcast Synchronization

This letter proposes an energy-efficient clock synchronization scheme for Wireless Sensor Networks (WSNs) based on a novel time synchronization approach. Within the proposed synchronization approach, a subset of sensor nodes are synchronized by overhearing the timing message exchanges of a pair of sensor nodes. Therefore, a group of sensor nodes can be synchronized without sending any extra messages. This paper brings two main contributions: 1. Development of a novel synchronization approach which can be partially or fully applied for implementation of new synchronization protocols and for improving the performance of existing time synchronization protocols. 2. Design of a time synchronization scheme which significantly reduces the overall network-wide energy consumption without incurring any loss of synchronization accuracy compared to other well-known schemes.

On the Joint Synchronization of Clock Offset and Skew in RBS-Protocol

Motivated by the necessity of having a good clock synchronization amongst the nodes of wireless ad-hoc sensor networks, the joint maximum likelihood (JML) estimator for clock phase offset and skew under exponential noise model for reference broadcast synchronization (RBS) protocol is formulated and found via a direct algorithm. The Gibbs sampler is also proposed for joint clock phase offset and skew estimation and shown to provide superior performance relative to JML- estimator. Lower and upper bounds for the mean-square errors (MSE) of JML-estimator and Gibbs Sampler are introduced in terms of the MSE of the uniform minimum variance unbiased (UMVU) estimator and the conventional best linear unbiased estimator (BLUE), respectively.

Extension of pairwise broadcast clock synchronization for multicluster sensor networks

Time synchronization is crucial for wireless sensor networks (WSNs) in performing a number of fundamental operations such as data coordination, power management, security, and localization. The Pairwise Broadcast Synchronization (PBS) protocol was recently proposed to minimize the number of timing messages required for global network synchronization, which enables the design of highly energy-efficient WSNs. However, PBS requires all nodes in the network to lie within the communication ranges of two leader nodes, a condition which might not be available in some applications. This paper proposes an extension of PBS to the more general class of sensor networks. Based on the hierarchical structure of the network, an energy-efficient pair selection algorithm is proposed to select the best pairwise synchronization sequence to reduce the overall energy consumption. It is shown that in a multicluster networking environment, PBS requires a far less number of timing messages than other well-known synchronization protocols and incurs no loss in synchronization accuracy. Moreover, the proposed scheme presents significant energy savings for densely deployed WSNs.

Pairwise Broadcast Clock Synchronization for Wireless Sensor Networks

This paper proposes an energy-efficient clock synchronization scheme for Wireless Sensor Networks (WSNs) based on a novel time synchronization approach. Within the proposed synchronization approach, a subset of sensor nodes are synchronized by over-hearing the timing message exchanges of a pair of sensor nodes. Therefore, a group of sensor nodes can be synchronized without sending any extra messages. This paper brings two main contributions: 1. Development of a novel synchronization approach which can be partially or fully applied for implementation of new synchronization protocols and for improving the performance ofexisting time synchronization protocols. 2. Design of a time synchronization scheme which significantly reduces the overall network-wide energy consumption without incurring any loss of synchronization accuracy compared to other well-known schemes.

CTH15-2: Analysis of Clock Offset and Skew Estimation in Timing-sync Protocol for Sensor Networks

Recently, a few protocols for synchronizing the nodes of wireless sensor networks (WSNs) to a common time frame have been proposed with the goal of maximizing the accuracy and minimizing the power utilization. Thus far, the performance of the existing protocols for time synchronization is assessed only through computer simulations and experiments without using any rigorous analytical metrics. The goal of this paper is to fill up this gap by deriving the Cramer-Rao lower bound (CRLB) for the clock offset in one of the most popular synchronization algorithms, namely timing-sync protocol for sensor networks (TPSN), assuming commonly used exponential and Gaussian delay models, respectively. Furthermore, this paper proposes novel and practical clock skew estimators requiring no prior information of the fixed portion of delays, which makes the TPSN algorithm very suitable to synchronization in light of its power efficiency constraint.

Optimum Cooperation of the Cooperative Coding Scheme for Frequency Division Half-Duplex Relay Channels

This paper analyzes the effects of the level of cooperation (LOC) on the performance of a practical cooperative coding scheme for frequency division half-duplex relay links in general wireless ad-hoc networks. The end-to-end bit error probability (BEP) and the corresponding optimum LOG minimizing the end-to-end BEP are investigated for specific realizations using a family of rate compatible punctured convolutional (RCPC) codes. This paper shows that the BEP of the cooperative coding scheme depends on the LOC and there exists an optimum LOC for every specific realization. Further, it is shown that more than a certain level of cooperation is required to achieve possible cooperative gains in practical signal-to-noise ratio (SNR) regions, and increasing LOC does not effect much on the BEP performance for sufficiently large LOCs

Adaptive multi-hop timings synchronization for wireless sensor networks

Time synchronization for wireless sensor networks has been studied in recent years as a fundamental and critical design problem. This paper proposes an adaptive multi-hop timing synchronization (AMTS) which aims at minimizing overall network-wide energy consumption in timing synchronization. According to the current network status, AMTS determines the synchronization mode either the always on or sensor initiated mode, then adjusts the re-synchronization period to minimize energy consumption. Besides, it adapts a joint clock offset and skew estimation mechanism to achieve long term reliability of synchronization. AMTS has significant benefits in terms of energy-efficiency, and can be applied to various types of wireless sensor networks having different regulations.

Power-Efficient Clock Synchronization using Two-Way Timing Message Exchanges in Wireless Sensor Networks

A number of time synchronization protocols for wireless sensor networks (WSNs) have been recently proposed aiming at maximizing the accuracy and minimizing the power efficiency. This paper proposes novel clock skew estimators for the protocols based on two-way timing message exchanges to achieve long term reliability of synchronization. The proposed clock synchronization mechanism is far more power efficient than the conventional ones by significantly increasing the re-synchronization period. Moreover, it can be applied to the conventional protocols without any additional overhead. In fact, the proposed estimators assume simple steps and low complexity, a feature which is strongly demanding for WSNs consisting of cheap and small nodes