• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1623-1626
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• 2002

본 논문에서는 IEEE 802.11a 무선 랜 모뎀에 적용할 파이프 라인구조의 FFT 설계 및 구현에 대해서 제시한다. 구현된 FFT의 기본 구조는 radix-4 Single Delay Format 이나 제안된 나비 연산기에 의해서 복잡도는 radix-2방식과 동일하며 저전력을 고려해서 구현하였다. 구현된 FFT는 $0.35{\mu}m$ LG 라이브러리를 이용하여 합성되었고 64-포인트 FFT/IFFT를 $4{\mu}s$에 수행을 하며 16MHz로 동작을 한다.

• TTA Journal
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• s.97
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• pp.166-171
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• 2005

한국정보통신기술협회(TTA)에서 제공하고 있는 상호운용성시험(ION: Interoperability ON!)은 각 기술분야에 대해 서로 다른 회사 제품들간 상호운용성을 시험하는 행사로서 2004년 12월 7일부터 9일까지 3일 동안 IEEE802.11a+g 듀얼밴드 고속무선랜 AP(Access Point)와 카드에 대한 ION을 실시하였다. 이번 ION에서는 상호운용성과 더불어 WPA(Wi-Fi Protected Access)보안, 그리고 무선랜 제품의 RF(Radio Frequency) 적합성, AP의 성능 및 안정성에 대하여 시험하였다. 총 6개의 국내업체가 참가한 가운데 TTA 기준장비와의 상호운용성 시험, 참가업체간 상호운용성 시험을 실시하여 국내업체의 802.11a+g 듀얼모드 장비 기술수준 향상 및 앞으로 진행될 무선랜 RF 및 성능에 대한 TTA 인증 안 검토에도 많은 도움을 얻을 수 있었다.

• Journal of Korean Institute of Industrial Engineers
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• v.37 no.2
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• pp.89-95
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• 2011

The distributed coordination function (DCF) and point coordination function (PCF) protocols are the basic MAC protocols for legacy IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g and IEEE 802.11n wireless LANs. When the DCF protocol is used for the various versions of IEEE 802.11 wireless LANs, the MAC performance seriously degrades due to the collisions among the stations (STAs) as more and more STAs attempt to transmit their data frames. On the other hand, the PCF MAC performance becomes poor when many STAs exist in IEEE 802.11 wireless LANs, however, only small number of STAs actually attempt to transmit their data frames. In this paper, we propose the algorithm for improving the MAC performance by selectively using the DCF and PCF protocols according to the state of IEEE 802.11 wireless LANs. Numerical examples are presented to show the MAC performance improvement by the selective use of the DCF and PCF protocols according to the network state.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.232-238
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• 2004

In this paper, radio propagation in a subway tunnel is investigated using fan beam antennas, circular polarization antennas and directional antennas at 2.4㎓ and 5.8㎓ band, respectively. The results of narrowband channel measurements show that received power level for NLOS(Non-Line-Of-Sight) path is decreased drastically as compared with LOS(Line-Of-Sight) path. Wideband channel measurements are obtained using a PN sliding correlation method. The parameters of the channel such as mean access delay and RMS delay spread are compared as to different types of directional beam at IEEE 802.11 WLAN(Wireless Local Area Network) band including 2.4㎓ and 5.8㎓ bands, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.99-109
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• 2007

IEEE 802.lie is being proposed to improve QoS by IEEE 802.11 working group. HCCA (HCF Controlled Channel Access) a centralized polling based mechanism of IEEE 802.11e, needs a scheduling algorithm that decides on how the available radio resources are allocated to the polled STAs. In IEEE 802.l1e standard Reference Scheduler is presented. Reference Scheduler Polls all STAs in a polling list by the same interval that causes ineffectively frequent polling. It increases not only the overhead but it decreases the TXOP (Transmission Opportunity) utilization. In this paper, we propose the scheduling and admission control algorithm that poll stations depending on the MSI (Maximum Service Interval)o( stations to solve these shortcomings. In our proposed algorithm a station is polled by an interval close to its MSI, so polling overhead decrease and TXOP utilization increases than Reference Scheduler. Simulation results show that our algorithm outperforms Reference Scheduler. Our algorithm maintains higher aggregate throughput and services mere stations than Reference Scheduler.

• Journal of the Korea Society of Computer and Information
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• v.13 no.6
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• pp.225-232
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• 2008

When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. The multimedia system in vehicle, especially, has researched to move to wireless environments from legacy wired environments. This paper proposes the advanced algorithm for providing synchronized services of real-time multimedia traffic in IEEE 802.11 WLANs [1]. For these, we implement the advanced IEEE 1588 Precision Time Protocol [2] and the environments for simulation. Also, we estimate and analysis performance of the algorithm, then we experiment and analysis after the porting of algorithm in wireless LAN devices (Linksys wrt-350n AP network device) to characterize timing synchronization accuracy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.12A
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• pp.1375-1379
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• 2004

In this paper, we propose a new preamble structure for channel estimation in a MIMO OFDM-based WLAN System. Moreover, both the backward compatibility with IEEE 802.11a system and low overhead are considered for the preamble design. Simulation results show that the proposed preamble has low overhead and is obtained the good performance gain for channel estimation.

• Journal of KIISE:Information Networking
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• v.35 no.5
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• pp.374-383
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• 2008

IEEE 802.11 WLANs support various data rates in order to adapt to wireless channel condition. It is known that when some WLAN stations use a lower data rate than the others, total throughput is considerably degraded. The concept of temporal fairness which provides equal time to all stations has been introduced to alleviate this performance anomaly problem. However, most previous mechanisms assume that stations have infinite backlogs in the MAC layer and do not consider transport layer. In this paper, we first examine and analyze the performance of previous methods considering transport layer protocols. We then propose two new temporal fairness guarantee methods: AP priority and dynamic CWmin adjustment. We carried out extensive performance study via ns-2 computer simulations. The results show that the proposed methods provide temporal fairness and improve the throughput of WLANs in various environments.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.387-394
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• 2005

Every MAC (Medium Access Control) sub-layers of IEEE 802.11x, including IEEE 802.11e, defines Connection-based and CF (Contention Free)-based service functions in common. In this paper, a New-CF method is proposed. In the proposed method, conventional Round Robin method, which is used as a polling method by IEEE 802.11x PCF (Point Coordination Function) or IEE 802.11e HCCA, is modified to give weights to channels with heavier traffic load and to provide those weighted channels with more services. Based on NS-2 simulations, it is verified the proposed method shows better throughput in general, particularly under unbalanced traffic load conditions.

• TTA Journal
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• s.86
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• pp.83-88
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• 2003

TTA(한국정보통신기술협회, 사무총장 임주환)에서 제공하고 있는 무선랜 장비 TTA Verified 시험은 KT 및 하나로통신의 Benchamarking Test(BMT)의 참가자격 요건으로 Wi-Fi 인증과 함께 공인되고 있는 인증시험으로써, 올해 1월부터 본격적인 시험인증 서비스를 진행해왔다. 본 고에서는 지난 2월과 3월에 걸쳐 진행된 무선랜 TTA Verified 인증시험의 내용 및 결과에 대해서 분석하고 TTA 무선랜 상호운용성 인증마크를 획득한 무선랜 Access Point (AP) 와 Station에 대해서 소개하고자 한다.