• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.282-290
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• 2006

In this paper, we propose an enhanced Timing Estimator algorithm for 2.45GHz LR-WPAN receiver. Because an expensive and highly efficient oscillator can't be used for low-cost implementation, a Timing Estimator algorithm having stable operation in the channel environment with center frequency tolerance of 80 ppm is required. To enhance the robustness to frequency offset and the stability of receiver performance, multiple delay differential filter is adopted. By utilizing the characteristic that the correlation result between the output signal of Multiple delay differential filter and reference signal is restricted on the In-phase part of the correlator output, a coherent detection scheme instead of the typical noncoherent one is adopted for Timing Estimator. The application of the coherent detection scheme is suitable for LR-WPAN receiver aimed at low-cost, low-power, and low-complexity, since it can remove performance degradation due to squaring loss of I/Q squaring operation and decrease implementation complexity. Computer simulation results show that the proposed algorithm achieved performance improvement compared with the differential detection-based noncoherent scheme by 2dB in average.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.3
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• pp.533-541
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• 2001

In this paper, we proposed lowpass filter using all-pass sums of flat delay characteristics. this filter consisted of all-pass filter of parallel structure, the general analog filter is impossible to adjust the phase and the delay, using the Proposed filter, it has advantage to adjust them. And, we compared and analyzed this filter with passband width and magnitude characteristics, and the relation of group delay characteristics and cut-off frequency. Also, in order to obtain desired cut-off frequency, forming the weighing, we obtained desired cut-off frequency and group delay characteristics.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.7
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• pp.1-16
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• 1994

In this paper, we propose a new multiple access scheme for VSAT(Very Small Aperture Terminal) data communications. The proposed scheme has better performance in terms of delay throughput than Controlled Multiaccess Scheme which has excellent performance. The proposed scheme use the spare reservation method, adaptation method to offered load, and fixed bandwidth reservation method. In this paper, we analyze the performance using simple queueing model and present the simulation results. When network traffic is very low, the new scheme and the controlled multiaccess scheme have almost the same access delay characteristic. As the network load becomes higher, the new scheme's access delay gain becomes larger. Futhermore, even when the network traffic is very high it is possible to access satellite link within the delay similar to one round-trip delay. In addition to access delay performance enhancement, the new scheme has facility that supports fixed bandwidth reservation. So it shows more enhanced performance in the environment that stream traffic is dominant such as in VSAT communication environment.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.23-32
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• 1996

This paper proposes a new buffer management scheme to service delay-sensitive traffic and loss-sensitive traffic fairly in ATM networks. The proposed scheme uses tow buffers for delay-sensitive traffic and loss-sensitive traffic. To satisfy the average delay time of delay-sensitive traffic, cells in real-time buffer are served first. When congestion occurs in nonreal-time buffer, low loss priority cell in real-time buffer can be pushed out by high loss priority cell in nonreal-time buffer can be transferred to real-time buffer considering threshold value in real-time buffer. Using computer simulation, the existing methods and proposed scheme are compared and analyzed with respect to cell loss rate and average delay time. Simulation results show that the proposed scheme have superior performance to conventional schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2218-2230
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• 2012

In this paper, we propose an efficient channel delay estimation method for orthogonal frequency-division multiplexing (OFDM) systems, especially over doubly-selective fading channels which are selective in both the symbol time domain and subcarrier frequency domain. For the doubly-selective fading channels in single frequency network (SFN), long and strong echoes exist and thus the conventional discrete Fourier Transform (DFT) based channel delay estimation system often fails to produce the exact channel delay profile. Based on the analysis of the discrete-time frequency response of the channel impulse response (CIR) coefficients in the DFT-based channel delay estimation system, we develop a method to effectively extract the true CIR from the aliased signals by employing a simple narrow-band low-pass filter (NB-LPF). The performance of the proposed system is verified using the COST207 TU6 SFN channel model.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.373-378
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• 2009

An Ethernet passive optical network (EPON) is a low-cost, high-speed solution to the bottleneck problem of a broadband access network. This paper analyzes the delay and the jitter performance of dynamic bandwidth allocation (DBA) schemes for differentiated services in EPONs. Especially, the average packet delay and the delay jitter of the expedited forwarding (EF) traffic class are compared, with consideration as to whether a cyclic or an interleaved polling scheme is superior. This performance evaluation reveals that the cyclic polling based DBA scheme provides constant and predictable average packet delay and improved jitter performance for the EF traffic class without the influence of load variations.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.4
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• pp.57-67
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• 1996

This paper aims to support delay-sensitive multimedia applications by suggesting a mechanism in which maintains almost constant end-to-end delay thus providing the optimum playout synchronization. For this task the sum of network delay and buffering delay is entiredly managed and to eliminate little delay fluctuations and instantaneous delays at a buffer and a network, a low pass filter is used. Furthermore the correction function, which is used for maintaining the buffering level ot a reference value, is a non-linear step function, unlike the existing linear and continuous function. it has a different step sizes adapting to a traffic characteristics of a network congestion. the proposed mechanism has been confirmed of it sefficiency through SLAM-II netowrk.

• Journal of Internet Computing and Services
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• v.9 no.2
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• pp.43-50
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• 2008

In IEEE 802.11b wireless LAN, stations keep synchronization by receiving beacons being periodically sent by the AP (access point) when they run in low power mode. Beacon transmission is delayed if wireless channel is busy at a scheduled TBTT (target beacon transmission time), and stations must be awake until they receive the delayed beacon. In this paper, we propose a scheme that stations get their transmission delayed if they have little time for successful data transmission by the next TBTT. Beacon transmission without delay is guaranteed at every TBTT with this method so that the awake time of low power stations to receive beacon can be reduced. The proposed method is simulated and its characteristics ore described with the analysis of the results. The measured results in terms of beacon delay show some enhancement in energy consumption.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.811-814
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• 1998

This paper proposes a constant time-delay filter with low sensitivity, which can be used for hard-disk drive. The sensitivity of 2nd order lowpass filter by two kinds of method, one is based on lossy integrators and the other is lossy and lossless integrators is analyzed and designed. SPICE simulation shows fesibility of a filter by the proposed approach.

• Kyungpook Mathematical Journal
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• v.62 no.1
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• pp.119-132
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• 2022

Virotherapy is an effective method for the treatment of cancer. The oncolytic virus specifically infects the lyse cancer cell without harming normal cells. There is a time delay between the time of interaction of the virus with the tumor cells and the time when the tumor cells become infectious and produce new virus particles. Several types of viruses are used in virotherapy and the delay varies with the type of virus. This delay can play an important role in the success of virotherapy. Our present study is to explore the impact of this delay in cancer virotherapy through a mathematical model based on delay differential equations. The partial success of virotherapy is guarenteed when one gets a stable non-trivial equilibrium with a low level of tumor cells. There exits Hopf-bifurcation by considering the delay as bifurcation parameter. We have estimated the length of delay which preserves the stability of the non-trivial equilibrium point. So when the delay is less than a threshold value, we can predict partial success of virotherapy for suitable sets of parameters. Here numerical simulations are also performed to support the analytical findings.