• Journal of IKEEE
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• v.17 no.2
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• pp.96-103
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• 2013

Since multimedia data takes large part of realtime transmission in wireless communication environments such as IEEE 802.11, QoS issues became one of the important problems with network performance. 802.11e MAC provides differentiated services based on priority schemes to solve existing 802.11 MAC problems. The TXOP is an important factor with the priority to improve network performance and QoS because it defines the time duration in which multiple frames can be transferred at one time for each station. In this paper, therefore frame sizes, TXOP Limit, and Priority values in accordance with the number of stations are experimented and derived for best network performance and QoS. Using 802.11e standard parameters, simulation results show the best throughput when the number of stations is 5 and TXOP Limit value is 6.016ms. For fairness, the best result is achieved at 3.008ms of TXOP Limit value and 15-31 of CW(Contention Window) that is lower priority than CW 7-15.

• Journal of Communications and Networks
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• v.16 no.1
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• pp.81-91
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• 2014

This paper proposes hidden-node aware grouping (HAG) algorithm to enhance the performance of institute of electrical and electronics engineers (IEEE) 802.15.4 networks when they undergo either severe collisions or frequent interferences by hidden nodes. According to the degree of measured collisions and interferences, HAG algorithm dynamically transforms IEEE 802.15.4 protocol between a contention algorithm and a contention-limited one. As a way to reduce the degree of contentions, it organizes nodes into some number of groups and assigns each group an exclusive per-group time slot during which only its member nodes compete to grab the channel. To eliminate harmful disruptions by hidden nodes, especially, it identifies hidden nodes by analyzing the received signal powers that each node reports and then places them into distinct groups. For load balancing, finally it flexibly adapts each per-group time according to the periodic average collision rate of each group. This paper also extends a conventional Markov chain model of IEEE 802.15.4 by including the deferment technique and a traffic source to more accurately evaluate the throughput of HAG algorithm under both saturated and unsaturated environments. This mathematical model and corresponding simulations predict with 6%discrepancy that HAG algorithm can improve the performance of the legacy IEEE 802.15.4 protocol, for example, even by 95% in a network that contains two hidden nodes, resulting in creation of three groups.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.6-9
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• 2006

IEEE 802.15.4는 저전력 무선 개인 네트워크 기술의 표준으로서 USN(ubiquitous sensor network)의 핵심 무선 통신 기술로 각광을 받고 있다. 그러나 IEEE 802.15.4는 제한된 RF 전송범위와 스타 토폴로지를 기반으로 하는 통신 기법만을 제공하고 있으며, 인접한 PAN 간(inter-PAN)의 통신 기술은 정의되어 있지 않다. 이러한 기술상의 제약으로 IEEE 802.15.4는 통신 영역이 매우 제한적이며, 이에 따라 통신시 음영지역이 발생하는 문제점을 가지고 있다. 현재까지 통신영역 확장을 위한 주요 기술적 사항인 효율적인 토폴로지 형성방법, 주소할당 및 라우팅 방법, 인접 네트워크 간의 비콘 충돌 회피 기법 등에 대한 활발한 연구가 진행되어 왔다. 이중 인접한 네트워크간의 비콘 충돌 방지 기법은 IEEE 802.15.4의 네트워크가 비콘에 의해서 관리된다는 점을 고려하였을 때 데이터 전송 및 네트워크 유지를 위해 우선적으로 해결되어야 할 사항이다. 본 연구에서는 제안된 비콘 충돌 회피 기법을 분석하고, 이중 비활성 구간(inactive portion)을 활용한 기법에 대한 구체적인 구현 방안을 제시 하였다. 또한 상용 임베디드 장치인 Nano-24에 설계한 비콘 충돌 회피 기법을 구현하여 동작을 검증, 분석하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.4
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• pp.84-91
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• 2011

Recently, WBAN(Wireless Body Area Network) which has progressed standardization based on IEEE 802.15.6 standardization is a network for the purpose of the short-range wireless communications within around 3 meters from the inner or outer human body. Effective QoS control technique and data efficient management in limited bandwidth such as audio and video are important elements in terms of users and loads in short-range wireless networks. In this paper, for high-speed WBAN IEEE 802.15.6 standard, the dynamic allocation to give an efficient bandwidth management and weighted fair queueing algorithm have been proposed through the adjustment of the super-frame about limited data and Quality of Service (QoS) based on the queuing algorithm. Weighted Fair Queueing(WFQ) Algorithm represents the robust performance about elements to qualitative aspects as well as maintaining fairness and maximization of system performance. The performance results show that the dynamic allocation expanded transmission bandwidth five times and the weighted fair queueing increased maximum 24.3 % throughput and also resolved delay bound problem.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1386-1390
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• 2011

The IEEE 802.11 MAC uses DCF for media access among the participating network nodes. But DCF alone is neither capable nor suitable for fulfilling the QoS requirements of realtime applications. There are many ways in which QoS is provided by modifying DCF based MAC. This paper proposes (m,k)-collision scheme which is based on IEEE 802.11 and (m,k)-firm scheme tries to improve DCF functionality. The proposed scheme uses different Contention Window according to the number of collision in the node. The simulation result shows that the proposed scheme helps improve the throughput of the DCF.

• Information and Communications Magazine
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• v.33 no.10
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• pp.17-23
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• 2016

본고에서는 저전력 단말이 infra 없이 device-to-device 로 주변 기기를 탐색하여 ad hoc으로 네트워크를 구성할 수 있는 피어 인지 통신용 (Peer Aware Communication: PAC) PHY와 MAC 개발을 목표로 하는 IEEE 802.15 Task Group 8의 표준화 동향을 소개하였다. IEEE 802.15 TG8은 2016년 6월 첫번째 Working Group Letter Ballot을 끝냈으며, RevCom 승인은 2017년 7월을 목표로 하고 있다.

• International Journal of Control, Automation, and Systems
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• v.6 no.1
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• pp.119-125
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• 2008

This paper examines the use of a wireless Fieldbus based on IEEE 802.15.4 MAC protocol. The superframe of IEEE 802.15.4 is applied to a transmission scheme of real-time mixed data. The transmission and bandwidth allocation scheme are proposed for real-time communication using a superframe. The proposed wireless Fieldbus protocol is able to transmit three types of data (periodic data, sporadic data, and non real-time messages), and guarantee realtime transmission simultaneously within a limited timeframe.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.6
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• pp.18-26
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• 2008

In this paper, dynamic GTS scheduling method based on IEEE 802.15.4 is proposed for wireless control system considering reliability and real-time property. The proposed methods can guarantee a transmission of real-time periodic and sporadic data within the limited time frame in factory environment. The superframe of IEEE 802.15.4 is used for the dynamic transmission method of real-time mixed traffic (periodic data, sporadic data, and non real-time message). By separating CFP and CAP properly, the periodic, 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 at the same time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1589-1598
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• 2014

To support the WBAN, IEEE 802.15 Task Group 6 announced standardized documents on technical requirements of the PHY and MAC. In the IEEE 802.15.6 MAC protocol, CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) algorithm is performed based on the eight-level priorities according to the type of traffics of the periodic data from medical sensor nodes. Several nodes, which detected the changed bio signals, transmit emergency data at the same time, so latency could be higher than emergency latency and energy consumption will increase. In this thesis, we proposed a CSMA/CA algorithm in WBAN to solve these problems. Simulations are performed using a Castalia based on the OMNeT++ network simulation framework to estimate the performance of the proposed superframe and algorithms. Performance evaluation results show that the packet transmission success rate and energy efficiency are improved by reducing the probability of collision using the proposed MAC protocol.

• ETRI Journal
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• v.30 no.5
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• pp.674-684
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• 2008

This paper proposes a dual addressing scheme (DAS) for IPv6 over IEEE 802.15.4 wireless sensor networks (WSN). DAS combines a global unicast address to cope with association link changes and node mobility, and it links local addresses to lighten the overhead of the system to save energy and resources. This paper describes DAS address formats, address autoconfiguration, and address translation tables in the gateway. A detailed description of DAS is provided through examples. Simulations are performed to demonstrate the performance improvements of the DAS compared with the IPv6-based WSN, which uses the conventional single address.