• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.335-338
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• 2005

In this paper, we propose a downlink power control scheme to apply in the unequal error protection multi-code CDMA mobile medicine system. The mobile medicine system contains (i) blood pressure and body temperature measurement value, (ii) ECG medical signals measured by the electrocardiogram device, (iii) mobile patient's history, (iv) G.729 audio signal, MPEG-4 CCD sensor video signal, and JPEG2000 medical image. By the help of the multi-code CDMA spread spectrum communication system with downlink power control scheme and unequal error protection strategy, it is possible to transmit mobile medicine media and meet the quality of service. Numerical analysis and simulation results show that the system is a well transmission platform in mobile medicine.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2597-2615
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• 2013

This paper proposes a dynamic downlink load control scheme that jointly employs dynamic load threshold management and virtual coverage management schemes to reduce the degree of performance degradation due to traffic overload in two-tier femtocell networks. With the proposed scheme, the downlink load in a serving macrocell is controlled with a load threshold which is adjusted dynamically depending on the varying downlink load conditions of neighboring macrocells. In addition, traffic overloading is alleviated by virtually adjusting the coverage of the overloaded serving macrocell, based on the adjusted load threshold of the serving macrocell. Simulation results show that the proposed scheme improves the performance of two-tier femtocell networks in terms of the outage probability and sum throughput. This improvement is significantly increased with appropriate values of load thresholds and with an intermediate-level adjustment of the virtual coverage area (i.e., handover hysteresis margin: HOM). Furthermore, the proposed scheme outperforms both a previously proposed load control scheme with a static load threshold and the LTE system without a HOM adjustment.

• Journal of KIISE:Information Networking
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• v.30 no.1
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• pp.65-74
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• 2003

In this Paper, we propose a downlink service admission strategy that considers users QoS requirements by using a novel service quality prediction index for multi-service WCDMA mobile systems. The Proposed downlink service admission strategy is obtained by computing average received Power of each service, assuming a relative other-cell interference factor. With the proposed method we obtain a downlink service admission region where users of different services properly can be admitted. And adding the fairness at the proposed downiinh service admission strategy, we Propose another downlink service admission strategy. In the numerical examples, the downlink service admission region with fairness and the downlink service admission region without fairness of voice service and data services are obtained by proposed downlink service admission strategies, respectively.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.111-116
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• 2013

Because LEO (Low Earth Orbit) satellite has very limited contact time between satellite and ground station, all telemetry data generated on satellite are stored in a mass memory and transmitted to the ground during the contact time. There are two downlink modes, real-time mode and playback mode. Only real-time data frames are transmitted to the ground in real-time mode, real-time and playback data frames stored into mass memory are transmitted to the ground in playback mode. In accordance with the data transmission rate, there are two downlink rates, low downlink rate and high downlink rate. This paper briefly introduces downlink interfaces and flight software of a LEO satellite developed in KARI. And it presents the telemetry storage method, real-time and playback downlink management method, and downlink channel and rate control method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.153-156
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• 2017

In this paper, we propose a novel uplink congestion control scheme, which enhances downlink TCP throughput by improving response time of TCP acknowledgements without TCP modification. Through the experimental results, it is manifested that the proposed scheme is able to achieve better downlink TCP throughput.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.405-405
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• 2004

• ETRI Journal
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• v.43 no.2
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• pp.232-245
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• 2021

As wireless communication continues to develop in limited frequency resource environments, it is becoming important to identify the state of spectrum utilization and predict the amount needed in future. It is essential to collect reliable information for data analysis. This paper introduces a platform that enables the gathering of the scheduling information of a long-term evolution (LTE) cellular system without connecting to the network. A typical LTE terminal can confirm its assigned resource information using the configuration parameters delivered from a network. However, our platform receives and captures only the LTE signal over the air and then enables the estimation of the data relevant to scheduling for all terminals within an LTE cell. After extracting the control channel signal without loss from all LTE subframes, it detects valid downlink control information using the proposed algorithm, which is based on the error vector magnitude of depatterned symbols. We verify the reliability of the developed platform by comparing it with real data from mobile phones and service operators. The average difference in resource block utilization is only 0.28%.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.308-315
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• 2008

When operating in frequency-division duplex (FDD) mode, transmit beamforming in multiple-input single-output (MISO) wireless communication systems typically requires accurate knowledge of downlink channel state information (CSI) at the transmitter. In practical FDD systems, obtaining such downlink CSI at the transmitter is challenging, if not impractical. To circumvent such challenge and support user mobility, we present a new method for transmit beamforming based on simple beam-control commands (BCCs) in MISO FDD mobile systems. We then numerically evaluate the effects of BCC errors in terms of transmit power efficiency, system capacity, and outage probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.3012-3028
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• 2017

In this paper, we propose a joint power control strategy for both the uplink and downlink transmission by considering the energy requirements of the user equipments' uplink data transmissions in data and energy integrated communication networks (DEINs). In DEINs, the base station (BS) adopts the power splitting (PS) aided simultaneous wireless information and power transfer (SWIPT) technique in the downlink (DL) transmissions, while the user equipments (UEs) carry out their own uplink (UL) transmissions by exploiting the energy harvested during the BS's DL transmissions. In our DEIN model, there are M UEs served by the BS in order to fulfil both of their DL and UL transmissions. The orthogonal frequency division multiple access (OFDMA) technique is adopted for supporting the simultaneous transmissions of multiple UEs. Furthermore, a transmission frame is divided into N time slots in the medium access control (MAC) layer. The mathematical model is established for maximizing the sum-throughput of the UEs' DL transmissions and for ensuring their fairness during a single transmission frame T, respectively. In order to achieve these goals, in each transmission frame T, we optimally allocate the BS's power for each subcarrier and the PS factor for each UE during a specific time slot. The original optimisation problems are transformed into convex forms, which can be perfectly solved by convex optimisation theories. Our numerical results compare the optimal results by conceiving the objective of maximising the sum-throughput and those by conceiving the objective of maximising the fair-throughput. Furthermore, our numerical results also reveal the inherent tradeoff between the DL and the UL transmissions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.4
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• pp.1424-1441
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• 2014

Two-tier femtocell networks, consisting of a conventional cellular network underlaid with femtocell hotspots, play an important role in the indoor coverage and capacity of cellular networks. However, the cross- and co-tier interference will cause an unacceptable quality of service (QoS) for users with universal frequency reuse. In this paper, we propose a novel downlink interference mitigation strategy for spectrum-shared two-tier femtocell networks. The proposed solution is composed of three parts. The first is femtocells clustering, which maximizes the distance between femtocells using the same slot resource to mitigate co-tier interference. The second is to assign macrocell users (MUEs) to clusters by max-min criterion, by which each MUE can avoid using the same resource as the nearest femtocell. The third is a novel adaptive power control scheme with femtocells downlink transmit power adjusted adaptively based on the signal to interference plus noise ratio (SINR) level of neighboring users. Simulation results show that the proposed scheme can effectively increase the successful transmission ratio and ergodic capacity of femtocells, while guaranteeing QoS of the macrocell.