Time Synchronization Algorithm Research Articles

Underwater Localization with Time-Synchronization and Propagation Speed Uncertainties

Underwater acoustic localization (UWAL) is a key element in most underwater communication applications. The absence of GPS as well as the signal propagation environment makes UWAL similar to indoor localization. However, UWAL poses additional challenges. The propagation speed varies with depth, temperature, and salinity, anchor and unlocalized (UL) nodes cannot be assumed time-synchronized, and nodes are constantly moving due to ocean currents or self-motion. Taking these specific features of UWAL into account, in this paper, we describe a new sequential algorithm for joint time-synchronization and localization for underwater networks. The algorithm is based on packet exchanges between anchor and UL nodes, makes use of directional navigation systems employed in nodes to obtain accurate short-term motion estimates, and exploits the permanent motion of nodes. Our solution also allows self-evaluation of the localization accuracy. Using simulations, we compare our algorithm to two benchmark localization methods as well as to the Cramer-Rao bound (CBR). The results demonstrate that our algorithm achieves accurate localization using only two anchor nodes and outperforms the benchmark schemes when node synchronization and knowledge of propagation speed are not available. Moreover, we report results of a sea trial where we validated our algorithm in open sea.

무선 센서 네트워크에서 시각 동기 정확도 분석

센서 네트워크의 여러 핵심 기술 요소 중에서 시각 동기 기술은 센서 네트워크 응용에 필수 요소이다. 여러 노드들로부터 같은 이벤트의 중복 감지 인식, 기록된 이벤트의 발생순서 구분, 이동체의 이동 속도 계산 등에 시각 정보는 기저 데이터가 된다. 본 논문에서는 다양한 무선 센서 네트워크 시각 동기 기법 중 대표적인 시각 동기 모델인 pair-wise 시각 동기 알고리즘을 대상으로 시각 동기 오류 요소를 추출하고 이러한 오류 요소가 시각 동기 정확도에 끼치는 영향을 이론적으로 분석하였다. 또한 시뮬레이션을 통해 이론적 분석 결과를 검증하였다. 이러한 결과는 향후 센서 네트워크 시각 동기 알고리즘의 성능 개선이나 개발에 활용될 것으로 기대된다. Time synchronization is a prerequisite in wireless sensor network applications such as object tracking, consistent state update, duplication detection, and temporal order delivery. This paper analyze time synchronization accuracy of pair-wise time synchronization algorithm which is a typical time synchronization model of time synchronization method in wireless sensor networks. In addition, the analyzed results are verified by simulations. These results can be utilized for performance improvement or development of time synchronization in wireless sensor networks.

Simulation Study on Time Synchronization Based on RBS in Wireless Sensor Networks

Time synchronization is important for wireless sensor networks. In this paper RBS time synchronization algorithm principle and EECH routing protocol are introduced, and the simulation of RBS on the basis of EECH routing protocol is realized using the Synsinc software. The average synchronization error of the simulation is 25.86 us.This value is basically same with other types of simulation, which confirmed the simulation is credible.

Time synchronization algorithm based on hierarchical structure in wireless sensor network

Time synchronization is one of the key technologies for wireless sensor networks,and it plays an irreplaceable role for the work and development of the entire wireless sensor network.This paper proposed an improved Timing-sync Protocol for Sensor Networks(TPSN) algorithm based on hierarchy.This algorithm took level-broadcast in phase of level establishment,and a combined active and inactive two-way synchronization algorithm was used in phase of time synchronization,obtaining a relatively small cost of packet and system maintenance.This improved algorithm carried out time-frequency offset correction,and ensured the accuracy of the node.The improved TPSN algorithm not only enhances the accuracy of synchronization,but also saves the energy consumption for the network.

A Novel Blind Block Timing and Frequency Synchronization Algorithm for Alamouti STBC

Blind estimation algorithms have attracted considerable attention due to their potential applications in bandwidth efficient communications systems, such as the provision of spectrum awareness in cognitive radios. This paper proposes a blind block timing and frequency synchronization algorithm applicable to the Alamouti space-time block code in the context of Nakagami fading channels. The proposed algorithm exploits the space-time redundancy of the received signal to estimate the signal synchronization parameters using a single receive antenna. It has low sensitivity to clock timing synchronization errors and does not require knowledge of the channel coefficients, signal-to-noise ratio, and the modulation of the received signal. Computer simulations have confirmed that the algorithm has low sensitivity to clock timing synchronization errors and is suitable for use over Nakagami fading channels.

RTSP: An Accurate and Energy-Efficient Protocol for Clock Synchronization in WSNs

Wireless sensor networks need accurate time synchronization for data consistency and coordination. Although the existing algorithms for time synchronization offer very good accuracy, their energy consumption is high, and distant nodes are poorly synchronized. We propose a Recursive Time Synchronization Protocol (RTSP) which accurately synchronizes all the nodes in a network to a global clock using multi-hop architecture in an energy-efficient way. It achieves better performance due to the MAC-layer time-stamping based on Start of Frame Delimiter byte, infrequent broadcasts by a dynamically elected reference node, compensation of the propagation delay and adjustment of the timestamps at each hop, estimation of the relative skew and offset using least square linear regression on two data points (2LR), adaptive re-synchronization interval, aggregation of the synchronization requests, and energy awareness. A detailed analysis of the sources of errors is also provided. Simulation results show that the RTSP can achieve an average accuracy of 0.3 microseconds in a large multi-hop flat network while using five-times lesser energy than that of FTSP in the long run and performs even better in a clustered network where it can achieve an average accuracy of 0.23 microseconds while using seven-times lesser energy.

Time and Frequency Synchronization for Multicarrier Transmission on Hexagonal Time-Frequency Lattice

In this paper, a novel synchronization acquisition approach, including preamble structure, time and frequency synchronization algorithms, is proposed for hexagonal multicarrier transmission (HMCT) system. Specifically, a novel signal acquisition scheme based on time-frequency subspace projection (TFSP) and its simplified form are proposed for reliable signal acquisition. Time and frequency synchronization is divided into three steps: 1) the coarse time offset (TO) and coarse fractional carrier frequency offset (CFO) estimation; 2) fine TO and integer CFO estimation; and 3) fine fractional CFO estimation. The closed-form Cramér-Rao lower bound of the proposed CFO estimation scheme is given. Theoretical analyses and simulation results show that the proposed preamble structure, time and frequency synchronization algorithms for HMCT system can obtain robust performance over doubly dispersive (DD) channel, and the simulation results show excellent agreement with theoretical analyses.

Semiblind frequency-domain timing synchronization and channel estimation for OFDM systems

In this article, we propose unit vectors in the high dimensional Cartesian coordinate system as the preamble, and then propose a semiblind timing synchronization and channel estimation scheme for orthogonal frequency division multiplexing (OFDM) systems. Due to the lack of useful information in the time-domain, a frequency-domain timing synchronization algorithm is proposed. The proposed semiblind approach consists of three stages. In the first stage, a coarse timing offset related to the delayed timing of the path with the maximum gain in multipath fading channels is obtained. Then, a fine time adjustment algorithm is performed to find the actual delayed timing in channels. Finally, the channel response in the frequency-domain is obtained based on the final timing estimate. Although the required number of additions in the proposed algorithm is higher than those in conventional methods, the simulation results show that the proposed approach has excellent performance of timing synchronization in several channel models at signal-to-noise ratio (SNR) smaller than 6 dB. In addition, for a low-density parity-check coded single-input single-output OFDM system, our proposed approach has better bit-error-rate performance than conventional approaches for SNR varying from 3 to 8 dB.

Improvement and Simulation of an Autonomous Time Synchronization Algorithm for a Layered Satellite Constellation

Autonomous time synchronization for satellite constellations is a key technology to establish a constellation system time without the use of a ground station. The characteristics of satellite visibility time for layered satellite constellations containing geostationary earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) satellites are simulated by establishing a visible satellite model. Based on the satellite visible simulation results for a layered constellation, this study investigates the autonomous time synchronization algorithm that corresponds to the layered constellation structure, analyzes the main error of the time synchronization algorithm, and proposes methods to improve the characteristics of satellite movement in the constellation. This study uses an improved two-way time synchronization algorithm for autonomous time synchronization in the GEO-MEO satellite layer of a layered satellite constellation. The simulation results show that in a condition with simulation errors, the time synchronization precision of this improved algorithm can be controlled within 5 ns and used in high-precision autonomous time synchronization between layered satellite constellations.

Time Synchronization for Mobile Underwater Sensor Networks

Time synchronization is very crucial for the implementation of energy constricted underwater wireless sensor networks (UWSN). The purpose of this paper is to present a time synchronization algorithm which is suitable to UWSN. Although several time synchronization protocols have been developed, most of them tend to break down when implemented on mobile underwater sensor networks. In this paper, we analyze the effect of node mobility, and propose a Mobile Counteracted Time Synchronization approach, called “Mc-Sync”, which is a novel time synchronization scheme for mobile underwater acoustic sensor networks. It makes use of two mobile reference nodes to counteract the effect of node mobility. We also analyze and design the optimized trajectories of the two mobile reference nodes in underwater environment. We show through analysis and simulation that Mc-Sync provides much better performance than existing schemes.

Snowball Effect Time Synchronization Based on Energy Optimization for Wireless Sensor Networks

In large scale of WSNs (wireless sensor networks), a centralized algorithm is not suitable for WSNs. Distributed algorithm has the obvious advantage over traditional time synchronization algorithm. The paper proposes a distributed time synchronization algorithm for WSNs, called SNOWBALL effect time synchronization. In the algorithm, a node needs only to communicate with its neighbor node, synchronizing itself clock based on the neighbor nodes information. The algorithm is a continuous synchronization process. The network will reach balance and clock consistency after repeated algorithm iterations. In the algorithm, we achieve network energy optimization by reducing unnecessary message exchange.

Collision Based Time Synchronization for Underwater Sensor Networks

To synchronize nodes’ time in mobile underwater sensor networks, a collision based time synchronization scheme called “Coll-Sync” is proposed, which is a novel time synchronization approach for underwater acoustic environment. Collision has been identified as a major challenge to communication, and current systems implement sophisticated solutions to detect and avoid it. Coll-Sync shows that collision contains highly useful information that can be leveraged to improve time synchronization greatly. It is the first time synchronization algorithm that does not suffer but benefit from collision in underwater acoustic channel. Simulation results show that Coll-Sync has high precision and low energy cost. It significantly outperforms existing time synchronization schemes.

Self-Correcting Time Synchronization Based on Cross Layer for Wireless Sensor Network

Due to energy restrictions, node distribution density and hardware computing power etc., the traditional time synchronization mechanism is not suitable for wireless sensor network. The paper discussed the main reason that caused asynchronization and proposed an improved time synchronization algorithm based on cross layer optimization for wireless sensor network. Considering the stability of crystal oscillation and the linearity of crystal deviation in the physical layer, the improved time synchronization mechanism implemented a self-correction by the cross-layer MAC protocol. Estimating the crystal oscillation drift, the crystal deviation had been self-corrected just by a few times data broadcast. The experiment on the MCU Si1000 physical layer platform has demonstrated the practicability of the algorithm. The synchronization algorithm is able to keep a stable network operation in the way of extending the synchronization period and reducing the synchronization cost. The synchronization mechanism is applicable to the active acquisition network, especially the realtime one.

An Improved OFDM Timing Synchronization Algorithm

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier communication system and the system is very sensitive to synchronization errors. The problem that synchronization is not accurate can reduce the system performance largely. Based on the research of Schmidl & Cox and Minn algorithms, the paper proposed an improved timing synchronization algorithm by using the new training sequence in the frequency domain. The improved algorithm eliminates the peak platform problem and side lobe peak problem of the conventional synchronization algorithms in this article. The simulation at MATLAB shows that the improved algorithm overcomes the problems of the conventional algorithms and the timing judgment curve of the improved algorithm also has a very sharp peak at the timing synchronization position, compared with the conventional algorithm. So, the timing synchronization performance of the algorithm is better.

로버스트한 최소 M-추정기법을 이용한 비가시선 상의 멀티스태틱 레이더 클락 동기 기술 연구

논문에서는 최근에 무선 센서 관련 연구에서 제안된 높은 정확도를 가진 센서 간의 클락 동기 기술을 멀티스태틱 레이더 시스템을 위한 무선 시간동기 알고리즘에 적용을 고려하고 특히 비가시선 상에 있는 노드들 간에 적용 될 수 없는 기존 이론의 한계를 극복하는 알고리즘을 제안한다. 제안된 알고리즘에서는 두 노드에서의 얻어진 타임 스탬프 관찰 결과 정보를 바탕으로 recursive robust least M-estimation (RLM) 기법을 이용하여 두 개의 센서 노드 간의 상대적인 클락 스큐(skew)와 위상 차이를 추정한다. 그 과정에서 NLOS 환경으로 인해 uplink와 downlink시에 발생하는 지연시간의 차이를 추적하여 억제시킴으로써 알고리즘의 성능 향상시킨다. 또한 mean square error (MSE)를 계산하여 알고리즘의 성능을 기존 maximum-liklihood (ML) 기법을 이용한 알고리즘과 비교 분석한다. In this paper, we propose the algorithm which considers applying recently proposed clock synchronization techniques with quite high accuracy in a few wireless sensor networks researches to time synchronization algorithm for multi-static radar system and especially overcomes the limitation of previous theory, cannot be applied between nodes in non-line of sight (NLOS). Proposed scheme estimates clock skew and clock offset using recursive robust least M-estimator with information of time stamp observations. And we improve the performance of algorithm by tracking and suppressing the time delays difference caused by NLOS system. Futhermore, this paper derive the mean square error (MSE) to present the performance of the proposed estimator and comparative analysis with previous methods.

Energy attenuation-based time synchronization for mobile underwater sensor networks

This article investigates the characteristics of underwater acoustic sensor networks, and presents an energy attenuation-based time synchronization algorithm, called Ea-Sync. It is a novel time synchronization method for mobile underwater sensor networks, which makes use of mobile beacon node to assist time synchronization and eliminates the effect of node mobility. Ea-Sync computes out the relationship between node movement and propagation delay by comparing the difference of energy attenuation. This paper also puts forward the mobile beacon node's trajectories based on the feature of underwater acoustic velocity. Simulation results show that Ea-Sync achieves high precision, low cost time synchronization, and outperforms existing time synchronization algorithms obviously.

Initial Condition Monitoring Experience on a Wind Turbine

The initial installation of a condition monitoring system (CMS) on a utility scale wind turbine produced a number of unexpected results. The CMS was installed on the TechnoCentre éolien Repower MM92. The installation allowed testing of a MEMS (microelecctromechanical system) based sensor technology and allowed and in-depth analysis of vibration data and revolutions per minute (RPM) data. A large 3/revolution effect, due to tower shadow and wind shear, required the development of an enhanced time synchronous average algorithm. The ability to easily measured changes in main rotor RPM, as a result of tower shadow and wind shear phenomenology, may also facilitate the detection of icing or blade pitch error.

Timing Synchronization and Frequency Offset Estimation for OFDMA/TDD Mode in Downlink of IEEE 802.16-2004

Abstract Timing and frequency synchronization are the important task in receiver. This paper proposes a timing synchronization and carrier frequency offset (CFO) estimation algorithm for orthogonal frequency division multiple access (OFDMA) downlink in IEEE 802.16e standard. This method has high performance and estimates CFO. The proposed scheme utilizes the conjugate symmetry property of preamble structure. Simulations are conducted for AWGN and multipath channels to demonstrate the performance of the proposed timing metric. Our proposed method can achieve reasonable performance at low SNR.

协作分集OFDM系统中的时频同步

In the cooperative relay system, different frames from different relays are not aligned in the time domain, and have different carrier frequency offsets (CFOs). Estimation of these time offsets and CFOs is a crucial and challenging task. In cooperative orthogonal frequency division multiplexing (OFDM) systems, a new preamble structure is designed to assist the destination node to distinguish the signals from different relays, and the corresponding time and frequency synchronization algorithms are also presented. In the aspects of the timing synchronization, the coarse timing offset estimation is accomplished by using the symmetric conjugate of the training symbol presented in this paper and the fine timing offset estimation is accomplished by segmented moving correlation. In the aspects of the frequency synchronization, the fractional frequency offset is estimated by using the phase difference of the received signal and the integral frequency offset is estimated by utilizing the good autocorrelation of the training symbol in frequency domain. The analysis and the simulation results show that, compared with the traditional scheme, the proposed scheme not only has a significantly smaller MSE of timing and frequency offset estimation but also has a lower complexity. Therefore, it is more suitable for the time and frequency synchronization of OFDM-based cooperative systems.

A Study on Parallel Processing Video Splicing System with Multi-Processor

Here to introduce a parallel processing video splicing system with multi-processor. The main processor gets the encoded video data from video source and outputs the video data to the coprocessors simultaneously after decoding the data. Those coprocessors capture the video data needed for splicing and display it on the objective monitor. Owing to this method, the sophisticated time synchronization algorithm is no longer needed. The proposed approach also lowers the system resources consuming, and promotes the accuracy of the video synchronization from multiple coprocessors.