arXiv subjects

Kyeong Soo Kim

Publications and source records attributed to Kyeong Soo Kim.

At least 37 records · Page 2Linked to original sources

arXiv2019

On the Practical Implementation of Propagation Delay and Clock Skew Compensated High-Precision Time Synchronization Schemes with Resource-Constrained Sensor Nodes in Multi-Hop Wireless Sensor Networks

In wireless sensor networks (WSNs), implementing a high-precision time synchronization scheme on resource-constrained sensor nodes is a major challenge. Our investigation of the practical implementation on a real testbed of the state-of-the-art WSN time synchronization scheme based on the asynchronous source clock frequency recovery and the reverse two-way message exchange, which can compensate for both propagation delay and clock skew for higher precision, reveals that its performance on battery-powered, low-complexity sensor nodes is not up to that predicted from simulation experiments due to the limited precision floating-point arithmetic of sensor nodes. Noting the lower computational capability of typical sensor nodes and its impact on time synchronization, we propose an asymmetric high-precision time synchronization scheme that can provide high-precision time synchronization even with resource-constrained sensor nodes in multi-hop WSNs. In the proposed scheme, all synchronization-related computations are done at the head node equipped with abundant computing and power resources, while the sensor nodes are responsible for timestamping only. Experimental results with a testbed based on TelosB motes running TinyOS demonstrate that the proposed time synchronization scheme can avoid time synchronization errors resulting from the single-precision floating-point arithmetic of the resource-constrained sensor nodes and achieve microsecond-level time synchronization accuracy in multi-hop WSNs.

cs.NI↗

arXiv2019

MTFS: Merkle-Tree-Based File System

The blockchain technology has been changing our daily lives since Bitcoin - i.e., the first decentralized cryptocurrency - was invented and released as open-source software by an unidentified person or a group called Satoshi Nakamoto in 2009. Of many applications which can be implemented based on the blockchain, storage is an important one, a notable example of which is the InterPlanetary File System (IPFS). IPFS is a distributed web based on a peer-to-peer hypermedia protocol to make the web faster, safer, and more open and focuses on public accessible files. To provide a solution for private file storage in the blockchain way, in this paper we propose a Merkle-tree-based File System (MTFS). In MTFS, the blockchain is more than a trust machine; it is an abstract of a cluster system. Distributed random nodes form a tree network cluster without a central controller to provide a secure private storage service and faster message propagation. Advance proxy re-encryption algorithm is applied to guarantee secure file exchanges under permission. Merkle tree will make sure that the files are distributed among the service nodes in a balanced way. The proposed MTFS can be used not only for personal file storage and exchange but also for industry requiring mutual trust in file uploading and downloading in making contracts like insurances.

cs.NI↗

arXiv2018

XJTLUIndoorLoc: A New Fingerprinting Database for Indoor Localization and Trajectory Estimation Based on Wi-Fi RSS and Geomagnetic Field

In this paper, we present a new location fingerprinting database comprised of Wi-Fi received signal strength (RSS) and geomagnetic field intensity measured with multiple devices at a multi-floor building in Xi'an Jiatong-Liverpool University, Suzhou, China. We also provide preliminary results of localization and trajectory estimation based on convolutional neural network (CNN) and long short-term memory (LSTM) network with this database. For localization, we map RSS data for a reference point to an image-like, two-dimensional array and then apply CNN which is popular in image and video analysis and recognition. For trajectory estimation, we use a modified random way point model to efficiently generate continuous step traces imitating human walking and train a stacked two-layer LSTM network with the generated data to remember the changing pattern of geomagnetic field intensity against (x,y) coordinates. Experimental results demonstrate the usefulness of our new database and the feasibility of the CNN and LSTM-based localization and trajectory estimation with the database.

cs.LG↗

arXiv2018

Hybrid Building/Floor Classification and Location Coordinates Regression Using A Single-Input and Multi-Output Deep Neural Network for Large-Scale Indoor Localization Based on Wi-Fi Fingerprinting

In this paper, we propose hybrid building/floor classification and floor-level two-dimensional location coordinates regression using a single-input and multi-output (SIMO) deep neural network (DNN) for large-scale indoor localization based on Wi-Fi fingerprinting. The proposed scheme exploits the different nature of the estimation of building/floor and floor-level location coordinates and uses a different estimation framework for each task with a dedicated output and hidden layers enabled by SIMO DNN architecture. We carry out preliminary evaluation of the performance of the hybrid floor classification and floor-level two-dimensional location coordinates regression using new Wi-Fi crowdsourced fingerprinting datasets provided by Tampere University of Technology (TUT), Finland, covering a single building with five floors. Experimental results demonstrate that the proposed SIMO-DNN-based hybrid classification/regression scheme outperforms existing schemes in terms of both floor detection rate and mean positioning errors.

cs.LG↗

arXiv2017

A Scalable Deep Neural Network Architecture for Multi-Building and Multi-Floor Indoor Localization Based on Wi-Fi Fingerprinting

One of the key technologies for future large-scale location-aware services covering a complex of multi-story buildings --- e.g., a big shopping mall and a university campus --- is a scalable indoor localization technique. In this paper, we report the current status of our investigation on the use of deep neural networks (DNNs) for scalable building/floor classification and floor-level position estimation based on Wi-Fi fingerprinting. Exploiting the hierarchical nature of the building/floor estimation and floor-level coordinates estimation of a location, we propose a new DNN architecture consisting of a stacked autoencoder for the reduction of feature space dimension and a feed-forward classifier for multi-label classification of building/floor/location, on which the multi-building and multi-floor indoor localization system based on Wi-Fi fingerprinting is built. Experimental results for the performance of building/floor estimation and floor-level coordinates estimation of a given location demonstrate the feasibility of the proposed DNN-based indoor localization system, which can provide near state-of-the-art performance using a single DNN, for the implementation with lower complexity and energy consumption at mobile devices.

cs.NI↗

arXiv2017

Large-Scale Location-Aware Services in Access: Hierarchical Building/Floor Classification and Location Estimation using Wi-Fi Fingerprinting Based on Deep Neural Networks

One of key technologies for future large-scale location-aware services in access is a scalable indoor localization technique. In this paper, we report preliminary results from our investigation on the use of deep neural networks (DNNs) for hierarchical building/floor classification and floor-level location estimation based on Wi-Fi fingerprinting, which we carried out as part of a feasibility study project on Xi'an Jiaotong-Liverpool University (XJTLU) Campus Information and Visitor Service System. To take into account the hierarchical nature of the building/floor classification problem, we propose a new DNN architecture based on a stacked autoencoder for the reduction of feature space dimension and a feed-forward classifier for multi-label classification with argmax functions to convert multi-label classification results into multi-class classification ones. We also describe the demonstration of a prototype DNN-based indoor localization system for floor-level location estimation using real received signal strength (RSS) data collected at one of the buildings on the XJTLU campus. The preliminary results for both building/floor classification and floor-level location estimation clearly show the strengths of DNN-based approaches, which can provide near state-of-the-art performance with less parameter tuning and higher scalability.

cs.NI↗

arXiv2017

Multi-Hop Extensions of Energy-Efficient Wireless Sensor Network Time Synchronization

We present the multi-hop extensions of the recently proposed energy-efficient time synchronization scheme for wireless sensor networks, which is based on the asynchronous source clock frequency recovery and reversed two-way message exchanges. We consider two hierarchical extensions based on packet relaying and time-translating gateways, respectively, and analyze their performance with respect to the number of layers and the delay variations through simulations. The simulation results demonstrate that the time synchronization performance of the packet relaying, which has lower complexity, is close to that of time-translating gateways.

cs.NI↗

arXiv2016

Stacked-VLAN-Based Modeling of Hybrid ISP Traffic Control Schemes and Service Plans Exploiting Excess Bandwidth in Shared Access Networks

The current practice of shaping subscriber traffic using a token bucket filter by Internet service providers may result in a severe waste of network resources in shared access networks; except for a short period of time proportional to the size of a token bucket, it cannot allocate excess bandwidth among active subscribers even when there are only a few active subscribers. To better utilize the network resources in shared access networks, therefore, we recently proposed and analyzed the performance of access traffic control schemes, which can allocate excess bandwidth among active subscribers proportional to their token generation rates. Also, to exploit the excess bandwidth allocation enabled by the proposed traffic control schemes, we have been studying flexible yet practical service plans under a hybrid traffic control architecture, which are attractive to both an Internet service provider and its subscribers in terms of revenue and quality of service. In this paper we report the current status of our modeling of the hybrid traffic control schemes and service plans with OMNeT++/INET-HNRL based on IEEE standard 802.1Q stacked VLANs.

cs.NI↗

arXiv2016

On The Multi-Hop Extension of Energy-Efficient WSN Time Synchronization Based on Time-Translating Gateways

We report preliminary results of a simulation study on the multi-hop extension of the recently-proposed energy-efficient wireless sensor network time synchronization scheme based on time-translating gateways. Unlike the single-hop case, in multi-hop time synchronization a sensor node sends measurement data to a head node through gateways which translate the timestamp values of the received measurement data. Through simulations for two-hop time synchronization, we analyze the impact of the addition of a gateway and its translation of timestamp values on the clock frequency and measurement time estimation and thereby demonstrate the feasibility of the multi-hop extension of the energy-efficient WSN time synchronization based on time-translating gateways.

cs.NI↗

arXiv2016

Simulation Study of an Energy-Efficient Time Synchronization Scheme based on Source Clock Frequency Recovery in Asymmetric Wireless Sensor Networks

In this paper we report preliminary results of a simulation study on an energy-efficient time synchronization scheme based on source clock frequency recovery (SCFR) at sensor nodes in asymmetric wireless sensor networks (WSNs), where a head node --- serving as a gateway between wired and wireless networks --- is equipped with a powerful processor and supplied power from outlet, and sensor nodes --- connected only through wireless channels --- are limited in processing and battery-powered. In the SCFR-based WSN time synchronization scheme, we concentrate on battery-powered sensor nodes and reduce their energy consumption by minimizing the number of message transmissions from sensor nodes to the head node. Through simulation experiments we analyze the performance of the SCFR-based WSN time synchronization scheme, including the impact of SCFR on time synchronization based on two-way message exchange, and demonstrate the feasibility of the proposed time synchronization scheme.

cs.NI↗

arXiv2016

Energy-Efficient Time Synchronization Based on Asynchronous Source Clock Frequency Recovery and Reverse Two-Way Message Exchanges in Wireless Sensor Networks

We consider energy-efficient time synchronization in a wireless sensor network where a head node (i.e., a gateway between wired and wireless networks and a center of data fusion) is equipped with a powerful processor and supplied power from outlet, and sensor nodes (i.e., nodes measuring data and connected only through wireless channels) are limited in processing and battery-powered. It is this asymmetry that our study focuses on; unlike most existing schemes to save the power of all network nodes, we concentrate on battery-powered sensor nodes in minimizing energy consumption for time synchronization. We present a time synchronization scheme based on asynchronous source clock frequency recovery and reverse two-way message exchanges combined with measurement data report messages, where we minimize the number of message transmissions from sensor nodes, and carry out the performance analysis of the estimation of both measurement time and clock frequency with lower bounds for the latter. Simulation results verify that the proposed scheme outperforms the schemes based on conventional two-way message exchanges with and without clock frequency recovery in terms of the accuracy of measurement time estimation and the number of message transmissions and receptions at sensor nodes as an indirect measure of energy efficiency.

cs.NI↗

arXiv2016

Comments on "On Clock Synchronization Algorithms for Wireless Sensor Networks Under Unknown Delay"

The generalization of the maximum-likelihood-like estimator for clock skew by Leng and Wu in the above paper is erroneous because the correlation of the noise components in the model is not taken into account in the derivation of the maximum likelihood estimator, its performance bound, and the optimal selection of the gap between two subtracting time stamps. This comment investigates the issue of noise correlation in the model and provides the range of the gap for which the maximum likelihood estimator and its performance bound are valid and corrects the optimal selection of the gap based on the provided range.

cs.DC↗

arXiv2016

Comments on "IEEE 1588 Clock Synchronization using Dual Slave Clocks in a Slave"

In the above letter, Chin and Chen proposed an IEEE 1588 clock synchronization method based on dual slave clocks, where they claim that multiple unknown parameters --- i.e., clock offset, clock skew, and master-to-slave delay --- can be estimated with only one-way time transfers using more equations than usual. This comment investigates Chin and Chen's dual clock scheme with detailed models for a master and dual slave clocks and shows that the formulation of multi-parameter estimation is invalid, which affirms that it is impossible to distinguish the effect of delay from that of clock offset at a slave even with dual slave clocks.

cs.AR↗

arXiv2015

On enery-efficient time synchronization based on source clock frequency recovery in wireless sensor networks

In this paper we study energy-efficient time synchronization schemes with focus on asymmetric wireless sensor networks, where a head node, which is connected to both wired & wireless networks, is equipped with a powerful processor and supplied power from outlet, and sensor nodes, which are connected only through wireless channels, are limited in processing and battery-powered. It is this asymmetry that we focus our study on; unlike existing schemes saving the power of all sensor nodes in the network (including the head node), we concentrate on battery-powered sensor nodes in minimizing energy consumption for synchronization. Specifically, we discuss a time synchronization scheme based on source clock frequency recovery, where we minimize the number of message transmissions from sensor nodes to the head node, and its extension to network-wide, multi-hop synchronization through gateway nodes.

cs.NI↗

arXiv2014

Designing pricing schemes based on progressive tariff and consumer grouping in migration to a future smart grid

We study the design of pricing schemes for a group of consumers with smart meters (e.g., in a Greenfield area) who are connected through a gateway to a traditional electricity greed with a progressive tariff. Because the progressive tariff cannot take into account the time aspect of electricity demands, we apply it to consumers in both an individual and a group basis over a shorter time period, which can flatten the overall demand over time and thereby reduce peak load. This scenario for the coexistence of traditional and smart girds and the pricing schemes under this scenario can enable smooth migration to a future smart grid.

cs.CE↗

arXiv2014

Deficit Round-Robin-Based ISP Traffic Control Scheme Enabling Excess Bandwidth Allocation in Shared Access Networks

In shared access shaping subscriber traffic based on token bucket by ISPs wastes network resources when there are few active subscribers, because it cannot allocate excess bandwidth in the long term. To address it, traffic control schemes based on core-stateless fair queueing (CSFQ) and token bucket meters (TBMs) have been proposed, which can allocate excess bandwidth among active subscribers proportional to their token generation rates. Using FIFO queue for all packets, however, degrades the short-term performance of conformant traffic due to the presence of non-conformant packets already in the queue. Also, the rate estimation based on exponential averaging makes it difficult to react to rapid changes in traffic conditions. In this paper we propose a new traffic control scheme based on deficit round-robin (DRR) and TBMs to guarantee the quality of service of conformant packets in all time scales while allocating excess bandwidth among active subscribers proportional to their token generation rates, whose advantages over the CSFQ-based schemes are demonstrated through simulation results.

cs.NI↗

arXiv2014

Toward Fully-Shared Access: Designing ISP Service Plans Leveraging Excess Bandwidth Allocation

Shaping subscriber traffic based on token bucket filter (TBF) by Internet service providers (ISPs) results in waste of network resources in shared access when there are few active subscribers, because it cannot allocate excess bandwidth in the long term. New traffic control schemes have been recently proposed to allocate excess bandwidth among active subscribers proportional to their token generation rates. In this paper we report the current status of our research on designing flexible yet practical service plans exploiting excess bandwidth allocation enabled by the new traffic control schemes in shared access networks, which are attractive to both ISP and its subscribers in terms of revenue and quality of service (QoS) and serve as a stepping stone to fully-shared access in the future.

cs.NI↗

arXiv2014

The Effect of ISP Traffic Shaping on User-Perceived Performances in Broadband Shared Access Networks

Recent studies on the practice of shaping subscribers' traffic by ISPs give a new insight into the actual performance of broadband access networks at a packet level. Unlike metro and backbone networks, however, access networks directly interface with end-users, so it is important to base the study and design of access networks on the behaviors of and the actual performance perceived by end-users. In this paper we study the effect of ISP traffic shaping using traffic models based on user behaviors and application/session-layer metrics providing quantifiable measures of user-perceived performance for HTTP, FTP, and streaming video traffic. To compare the user-perceived performance of shaped traffic flows with those of unshaped ones in an integrated way, we use a multivariate non-inferiority testing procedure. We first investigate the effect of the token generation rate and the token bucket size of a token bucket filter on user-perceived performance at a subscriber level with a single subscriber. Then we investigate their effect at an access level where shaped traffic flows from multiple subscribers interact with one another in a common shared access network. The simulation results show that for a given token generation rate, a larger token bucket provides better user-perceived performance at both subscriber and access levels. It is also shown that the loose burst control resulting from the large token bucket --- up to 100 MB for access line rate of 100 Mbit/s --- does not negatively affect user-perceived performance with multiple subscribers even in the presence of non-conformant subscribers; with a much larger token bucket, however, the negative effect of non-conformant subscribers on the user-perceived performance of conformant subscribers becomes clearly visible because the impact of token bucket size and that of token generation rate are virtually indistinguishable in this case.

cs.NI↗