• 한국정보통신설비학회:학술대회논문집
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• 2005.08a
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• pp.67-73
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• 2005

For power constrained applications, IEEE 802.15.4 networks may be operated in beacon enabled mode with inactive period. In this paper, we propose the Virtual Arrival Mechanism (VAM) to avoid the congestion at the beginning of each contention access period (CAP). Virtual Arrival Mechanism (VAM) is a kind of traffic shaping that spread the traffics congested at the beginning of CAP into the whole CAP. By using VAM, collisions and energy consumption can be reduced. Finally, we evaluate the performance enhancement of VAM using NS-2 simulator.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.2
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• pp.45-54
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• 2008

In this paper, a dynamic GTS scheduling method based on IEEE 802.15.4 is proposed for wireless control system. The proposed method can guarantee a transmission of real-time periodic and sporadic data within the time frame in factory environment. The modified superframe of IEEE 802.15.4 was used to the dynamic scheduling method of real-time mixed traffic(periodic data, sporadic data, and non real-time message). By separating CFP and CAP properly, the sporadic and non real-time messages are transmitted effectively and guarantee real-time transmission within a deadline. The simulation results show the improvement of real-time performance of periodic and sporadic data.

• The Journal of the Korea Contents Association
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• v.9 no.2
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• pp.10-17
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• 2009

This paper analyze the effect of frequency offset for the IEEE 802.15.4b LR-WPAN(Low-Rate Wireless Personal Area Network) with 915MHz bandwidth noncoherent DSSS O-QPSK based receiver system, and presents a compensation method with addition of differential filter to the system for compensation of frequency offset problem. DSSS PSSS-ASK and DSSS O-QPSK modulation techniques are accepted within the regularization of IEEE 802.15.4b. These new method can obtain 250kbps transmission rate. The DSSS O-QPSK modulation method that is used in this paper has no BER variation below 40ppm(frequency offset 36.6kHz), but if the offset frequency become high above 40ppm, then the system cannot have stable receiving condition due to worse BER. To solve this problem, we present a more stabilized receiver system at maximum frequency offset ${\pm}80ppm$ using MDDF unti a correlator of DSSS O-QPSK modulator. Moreover computer simulation results will be presented to evaluate the performance of the proposed algorithm unde various AWGN and frequency offset environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.101-108
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• 2007

There nay be collisions among beacons from several full function devices in IEEE 802.15.4 sensor networks. These collision of beacons may cause devices to lose time synchronization, and thus be unable to association. To solve this problem, the IEEE 802.15.4b defines a new Post Beacon Period(PBP), but it does not still alleviate the beacon collision problem. In this paper, we propose two automatic beacon alignment schemes that a node itself can decide its beacon start time using its short address that has been assigned during association. We also simulate and investigate our proposed automatic beacon collision avoidance schemes using NS-2 simulator.

• Journal of Internet Computing and Services
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• v.10 no.4
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• pp.213-222
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• 2009

IEEE 802.15.3 HR-WPAN is designed to enable wireless connectivity of high-speed, low-power, low-cost multimedia-capable portable consumer electronic devices. For quality of service, the standard specifies the use of TDMA (Time Division Multiple Access). However, during low contention TDMA gives much lower channel utilization and higher delays than CSMA (Carrier Sensing Multiple Access) because in TDMA, a node can transmit only during its scheduled time slots whereas in CSMA, nodes can transmit at any time as long as there is no contention. By mixing CSMA and TDMA, Hybrid MAC becomes more robust to timing failures, time-varying channel conditions, slot assignment failures and topology changes than a stand-alone TDMA.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.238-243
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• 2009

Now, the production process systems are largely based on automatic system using the wired network. The production process systems using wired network has disadvantage that it is expensive when the installed and replaced equipment. The each equipment happens to repair cost for control and management in production processes. And the replaced equipment has also the additional expense and breaks production process. These problems are solved through wireless communication between the industrial equipments. So, we propose wireless production process system based on IEEE 802.15.4 technology. It solves a complicated space and stops by replaced equipment in the factory. Then we simulated and analyzed IEEE 802.15.4 for Industrial Equipment based on Wireless Network.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.11
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• pp.32-40
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• 2016

IEEE 802.15.4 is the one of the protocols for radio communication in a personal area network. Because of low cost and low power communication for IoT communication, it requires the highest optimization level in the implementation. Recently, the studies of location aware algorithm based on IEEE802.15.4 standard has been achieved. Location estimation is performed basically in equal consideration of reference node information and blind node information. However, an error is not calculated in this algorithm despite the fact that the coordinates of the estimated location of the blind node include an error. In this paper, we enhanced a conventual maximum likelihood estimation using weighted coefficient and implement the hardwired location aware engine for small code size and low power consumption. On the field test using test-beds, the suggested hardware based location awareness method results better accuracy by 10 percents and reduces both calculation and memory access by 30 percents, which improves the systems power consumption.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.26 no.6
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• pp.1561-1569
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• 2016

As the use of the sensor device increases in IoT environment, the need for device security is becoming more and more important When a sensor device is deployed in IEEE 802.15.4-based LoWPAN, it has to perform the join operation with PAN Coordinator and the binding operation with another device. In the join and binding process, authentication and key distribution of the device are performed using the pre-distributed network key or certificate. However, the network key used in the conventional method has problems that it's role is limited to the group authentication and individual identification is not applied in certificate issuing. In this paper, we propose a secure join and binding protocol in LoWPAN environment that solves the problems of pre-distributed network key.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.3
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• pp.132-137
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• 2009

In this paper, a position recognition system is designed, implemented, and tested using IEEE 802.15.4a PHY (CSS) hardware and Tiny OS environment. The system is designed with extensibility and flexibility. The system consists of five kinds of nodes which have different functions from each other. Three communication channels are used for collision avoidance. In each cell, an arbiter node is used to minimize message collisions. The proposed arbitration protocol is designed to support mobility of arbitrary target nodes. Target nodes calculates their locations with communications to four location reference nodes which are placed on the comers of each cell.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5C
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• pp.519-533
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• 2006

The number of channels specified in IEEE 802.15.4 Low-Rate Wireless Personal Area Networks(LRWPANs) is too few to operate many applications of WPANs in the same area. To overcome this limit, we introduce Virtual Channel, a novel concept to increase the number of available channels when various WPAN applications coexist. Basically, a virtual channel is a newly-created channel via superframe scheduling within the inactive period of a logical channel preoccupied by other WPANs. To maximize the coexistence capability of WPANs using virtual channels, we propose Least Collision superframe scheduler(LC-scheduler), its less complex heuristics both for a given single channel, and Virtual Channel Selector(VCS) to efficiently manage multiple available logical channels. In addition, a simple but practical synchronization method is developed to compensate different time drifts among coexisting WPANs. The simulation results demonstrate that a remarkable improvement on the coexistence capability of the 802.15.4 can be achieved through the proposed schemes.