• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.3
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• pp.119-123
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• 2006

The orthogonal frequency-division multiplexing (OFDM) technique is well known to be robust against the frequency-selective fading in wireless channels. It is due to the exploitation of a guard interval that is inserted at beginning of each OFDM symbol. Based on the conventional OFDM and a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique, we developed an adaptive beamforming algorithm for antenna arrays. The proposed algorithm would lead to an efficient use of channel, since it is possible to eliminate a guard interval and also easily suppress interchannel interference at the same time. In this paper, a series of computer simulations have been provided to show the performance of the proposed system.

• Proceedings of the KIEE Conference
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• 2005.07d
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• pp.2998-3000
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• 2005

The orthogonal frequency-division multiplexing (OFDM) technique is well known to be robust against the frequency-selective fading in wireless channels. It is due to the exploitation of a guard interval that is inserted at beginning of each OFDM symbol. Based or the conventional OFDM and a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique, we developed an adaptive beamforming algorithm for antenna arrays. The proposed algorithm would lead to an efficient use of channel, since it is possible to eliminate a guard interval and also easily suppress interchannel interference at the same time. In this paper, a series of computer simulations have been provided to show the performance of the proposed system.

• Journal of the Korea Society of Computer and Information
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• v.14 no.5
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• pp.77-83
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• 2009

In this parer, an improved backoff algorithm is proposed by supplementing a multiple of persistence factor for IEEE 802.11 Wireless LAN MAC. This algorithm is proposed to complement the shortcomings of the conventional BEB (Binary Exponential Backoff) algorithm which is used for retransmission to control a new contention window in DCF/EDCF MAC. In channel utilization, collision rate and Goodput viewpoint, we analysis the improved backoff algorithm and compared the result with that of the conventional algorithm In this result, we showed that the performance for PFA backoff algorithm is 10% higher than that for the conventional BEB algorithm when the number of station is 40.

• 한국초전도학회:학술대회논문집
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• v.15
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• pp.12-12
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• 2005

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.283-293
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• 2024

In this study, advanced unscented Kalman filter (UKF) and particle filter (PF) implementations are introduced and applied to perform system identification (SI) for sudden structural damage induced by seismic loading. These two methods are then compared to validate their applicability to SI tasks. For this validation, the Bouc- Wen model is used to simulate the nonlinear shear-building response, and an adaptive rule (i.e., an adaptive tracking method) is applied to the two filter methods to improve their tracking performance during sudden changes in system properties. When the original UKF and PF are applied to an earthquake scenario, both methods fail to estimate the damage initiation time and post-damage parameter values. After applying the adaptive tracking method, it is found for both methods that although the occurrence time is identified, the estimation of the damage state is still not accurate. To improve the accuracy, an adjusted adaptive tracking method is applied, and the two methods then derive accurate estimates. Finally, when considering the computation time, UKF is promoted as a better choice for practical applications, provided that a proper adaptive tracking method is implemented.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10d
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• pp.261-266
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• 2007

UMTS release 5 에서 소개된 HSDPA 를 위해 도입된 새로운 기술 Adaptive Modulation and Coding, Hybrid Automatic Repeal reQuest, Fast Packet Scheduling 에 대해 알아보고 여기서 key role 이 되는 Fast Packet Scheduling 알고리즘 가운데 대표적인 세 가지 Round Robin(RR), Promotional Fairness(PF), Maximum Channel Quality Index(Max CQI) 알고리즘의 성능을 시스템 수율과 공평성의 관점에서 분석해보았다. 시스템 수율에서는 Max CQI, PF. RR 알고리즘 순이었으며 공평성 측면에서는 RR, PF Max CQI 알고리즘 순으로 나타났다. 같은 시스템, 같은 망 구조 내에서라면 알고리즘을 최적화하여 QoS와 성능을 극대화할 수 있도록 지속적인 연구가 필요하다.

• Speech Sciences
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• v.7 no.3
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• pp.185-195
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• 2000

This paper seeks to compare the feature parameters used in speaker identification systems under noisy environments. The feature parameters compared are LP cepstrum (LPCC), Cepstral mean subtraction(CMS), Pole-filtered CMS(PFCMS), Adaptive component weighted cepstrum(ACW) and Postfilter cepstrum(PF). The GMM-based text independent speaker identification system is designed for this target. Some series of experiments show that the LPCC parameter is adequate for modelling the speaker in the matched environments between train and test stages. But in the mismatched training and testing conditions, modified parameters are preferable the LPCC. Especially CMS and PFCMS parameters are more effective for the microphone mismatching conditions while the ACW and PF parameters are good for more noisy mismatches.

• Journal of Internet Computing and Services
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• v.5 no.6
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• pp.11-20
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• 2004

Proportional Fair (PF) share policy has been adopted as a downlink scheduling scheme in CDMA2000 l×EV-DO standard. Although It offers optimal performance in aggregate throughput conditioned on equal time share among users, it cannot provide a bandwidth guarantee and a strict delay bound. which is essential requirements of real-time (RT) applications. In this study, we propose a new scheduling policy that provides quality-of-service (QoS) guarantees to a variety of traffic types demanding diverse service requirements. In our policy data traffic is categorized Into three classes, depending on sensitivity of Its performance to delay or throughput. And the primary components of our policy, namely, Proportional Fair (PF), Weighted Fair Queuing (WFQ), and delay-based prioritized scheme are intelligently combined to satisfy QoS requirements of each traffic type. In our policy all the traffic categories run on the PF policy as a basis. However the level of emphasis on each of those ingredient policies is changed in an adaptive manner by taking into account the channel conditions and QoS requirements. Such flexibility of our proposed policy leads to offering QoS guarantees effectively and. at the same time, maximizing the throughput. Simulations are used to verify the performance of the proposed scheduling policy. Experimental results show that our proposal can provide guaranteed throughput and maximum delay bound more efficiently compared to other policies.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.7
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• pp.743-747
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• 2008

Hierarchical overlay of heterogeneous wireless cells is considered as a promising architecture for next-generation wireless networks. This paper considers a special form of such architecture, WWAN/WLAN two-hop wireless relay networks. We first describe an undesirable scheduling phenomenon that the conventional proportional fair algorithm can cause in such networks. We, then, propose an enhanced proportional fair scheduling to remedy this problem. We demonstrate the performance of the proposed scheme via a simulation of UMTS/WLAN networks using NS-2.

• Journal of Communications and Networks
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• v.9 no.3
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• pp.219-228
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• 2007

In this paper, we present a novel blind adaptive multiuser detector structure and three robust recursive filters to improve the performance in CDMA environments: Sigma point kalman filter (SPKF), particle filter (PF), and Gaussian mixture sigma point particle filter (GMSPPF). Our proposed robust recursive filters have superior performance over a conventional extended Kalman filter (EKF). The proposed multiuser detector algorithms initially use Kalman prediction form to estimated channel parameters, and unknown data symbol be predicted. Second, based on this predicted data symbol, the robust recursive filters (e.g., GMSPPF) is a refined estimation of joint multipaths and time delays. With these estimated multipaths and time delays, data symbol detection is carried out (Kalman correction form). Computer simulations show that the proposed algorithms outperform the conventional blind multiuser detector with the EKF. Also we can see it provides a more viable means for tracking time-varying amplitudes and time delays in CDMA communication systems, compared to that of the EKF for near-far ratio of 20 dB. For this reason, it is believed that the proposed channel estimators can replace well-known filter such as the EKF.