• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.9
• /
• pp.19-28
• /
• 2010

The GTS(Guaranteed Time Slot) of the IEEE 802.15.4 standard, which is the contention free access mechanism, is used for low-latency applications or applications requiring specific data bandwidth. But it has some problems such as delay of service due to FIFS(First In First Service) scheduling. In this paper, we proposes a weight based GTS allocation scheme for fair queuing in IEEE 802.15.4 LR-WPAN. The proposed scheme uses a weight that formed by how much more weight we give to the recent history than to the older history for a new GTS allocation. This scheme reduces service delay time and also guarantees transmission simultaneously within a limited time. The results of the performance analysis shows that our approach improves the performance as compared to the native explicit allocation mechanism defined in the IEEE 802.15.4 standard.

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

• Proceedings of the IEEK Conference
• /
• 2007.07a
• /
• pp.91-92
• /
• 2007

LR-UWB utilizes BPSK and PPM for the transmission, which embeds the information in the transmitted pulse position. Meanwhile, by using coherent method, there is approximately 3dB enhancement on the BER performance over that using non-coherent method. However, due to the variable channel conditions, conventional system which uses fixed modulation is not efficient. To maximize the efficient and performance, in this paper, we propose an adaptive method including 4PPM+BPSK mode and 2PPM mode, in which the modulation method is dynamically changed depending on the channel condition which is determined according to the preamble correlation output.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2009.04a
• /
• pp.1363-1365
• /
• 2009

현대 사회에서 유비쿼터스 센서 네트워크 환경을 제공하기 위해 활발한 활동이 이루어지고 있다. LR-WPAN 기술인 IEEE802.15.4가 표준화 되면서 유비쿼터스 센서 네트워크의 중심 기술로 자리 매김하게 되었다. IEEE802.15 표준은 WPAN(Wireless Personal Area Network) 즉, 비교적 짧은 거리에서 휴대하여 이동할 수 있는 장치들이 근처의 다른 장치들과 통신이 가능하도록 만든 무선 네트워크 통신 표준이다. 이러한 IEEE802.15 표준들은 PHY와 MAC에 대해서만 표준을 정의 하고 있다. 센서 네트워크에서 가장 중요한 이슈중의 하나는 제한된 자원 즉, 센서 노드에 주어진 에너지를 활용하여 네트워크의 수명을 최대로 연장 하는 것이다. 본 논문에서는 NS-2 시뮬레이션을 통해 WPAN에서 노드의 전송거리에 따른 에너지 효율을 분석한다.

• Proceedings of the KIEE Conference
• /
• 2005.07d
• /
• pp.2992-2994
• /
• 2005

수십 센티미터 이내의 오차를 만족시키는 거리/위치판별 기능 및 저속 데이터 송수신 기능 구현을 주목적으로 발족된 저속 무선 개인영역 네트워크(LR-WPAN: Low Rate Wireless Personal Area Network)의 표준인 IEEE802.15.4a는 간단하고 경제적이며 전력 소모가 적은 송수신기 구조를 요구한다. 이에 본 논문에서는 PEWB(Parallel Energy Window Banks)를 이용한 독창적인 비동기(noncoherent) OOK(On-Off Keying) UWB(Ultra-Wide Band) 송수신기 구조를 제안한다. 또한 무선 다중경로 채널상황을 다소 극복할 수 있는 펄스와 비트 반복 기법을 사용한다. 제안된 송수신기의 잡음 특성 분석을 위해 chi-square 분포가 사용되며, 반복적 계산을 통해 얻어진 임계값을 적용하여 BER(Bit Error Rate) 성능을 분석한다.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1937-1938
• /
• 2008

본 논문에서는 868/915MHz 대역 IEEE 802.15.4b LR-WPAN(Low-Rate Wireless Personal Area Network; ZigBee)시스템의 수신기를 위한 주파수 옵셋 영향을 감소시키는 알고리즘을 제안한다. 저가 구현을 지향하는 LR-WPAN 시스템의 특성에 맞추어 반송파 중심주파수의 $\pm$80ppm에 해당하는 주파수 옵셋 환경에서 안정된 수신을 보장할 수 있는 알고리즘으로 868/915MHz수신기 Correlator에 multiple delay differential filter를 적용함으로써 주파수 옵셋에 대한 강인성 및 수신 성능의 안정성을 증대시켰다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2005.07a
• /
• pp.169-171
• /
• 2005

현재 IEEE 802.15.4(Low-Rate WPAN)를 구성하는 디바이스들은 파워, 메모리 용량, 연산처리 등의 물리적 제약으로 인해 보안을 위한 공유키 생성은 대칭키 기반의 메카니즘을 사용하고 있다. 그러나 대칭키 기반 메카니즘은 키 관리, 키 분배, 디바이스의 이동성지원과 같은 부분에 문제점을 가지게 된다. 또한 LR-WPAN 환경은 해당 어플리케이션에 따라 차별된 보안 정책을 가질 수 있으며, 디바이스의 물리적 상태에 따라 보안강도를 결정하는 경우도 발생할 수 있다. 본 논문에서는 타원곡선 기반의 EC-MQV 알고리즘을 사용하여 공개키 기반의 공유키 생성 메카니즘을 제안한다. 또한, 코디네이터를 활용하여 각 디바이스의 연산을 최소화하여 디바이스의 에너지 소비를 줄이는 방법을 제시하고, 보안 레벨에 따른 키 생성에 관하여 설명한다.

• Journal of Korea Society of Industrial Information Systems
• /
• v.19 no.1
• /
• pp.53-60
• /
• 2014

IEEE 802.15.4 is one of the most widely adopted physical layer standards in the area of LR-WPAN(Low-Rate Wireless Personal Area Network). Numerous previous researches have contributed to deep insights on energy efficiency, transmission throughput, and reliability that IEEE 802.15.4 delivers to the LR-WPAN. As a research that is orthogonal and complementary to previous researches, we explore the implementation and practical performance evaluation of IEEE 802.15.4 MAC software. We implement the MAC software from the perspective of the networking stack, exploring the issues raised when the MAC software serves as a functional component in a complete networking stack consisting of MAC, network as well as well as application support layers. The performance is evaluated on a realistic experimental software environment integrated with operating system, networking stack, and applications.

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

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.6
• /
• pp.10-21
• /
• 2010

In the cluster-tree network which covers wide area network and has many nodes for monitoring purpose traffic is concentrated around the sink. There are long transmit delay and high data loss due to the intensive traffic when IEEE 802.15.4 is adapted to the cluster-tree network. In this paper we propose Dynamic Channel Allocation algorithm which dynamically allocates channels to increase the channel usage and the transmission success rate. To evaluate the performance of DCA, we assumed the monitoring network that consists of a cluster-tree in which sensing data is transmitted to the sink. Analysis uses the traffic data which is generated around the sink. As a result, DCA is superior when much traffic is generated. During the experiment assuming the least amount of traffic, IEEE 802.15.4, has the minimum length of active period and 90% data transmission success rate. However DCA maintains 11.8ms of active period length and results in 98.9% data transmission success rate.