• Journal of Communications and Networks
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• v.13 no.4
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• pp.345-359
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• 2011

Decode-and-forward relaying is a promising enhancement to existing radio access networks and is already standardized in 3rd generation partnership project (3GPP) as a part of long term evolution (LTE)-Advanced Release 10. Two inband operation modes of relay nodes are supported, namely type 1 and type lb. Relay nodes promise to offer considerable gain for system capacity or coverage, depending on the deployment prioritization, in a cost-efficient way. Yet, in order to fully exploit the benefits of relaying, the inter-cell interference which is increased due to the presence of relay nodes should be limited. Moreover, large differences in the received power levels from different users should be avoided. The goal is to keep the receiver dynamic range low in order to retain the orthogonality of the single carrier-frequency division multiple access system. In this paper, an evaluation of the relay based heterogeneous deployment within the LTE-Advanced uplink framework is carried out by applying the standardized LTE Release 8 power control scheme both at evolved node B and relay nodes. In order to enhance the overall system performance, different power control optimization strategies are proposed for 3GPP urban and suburban scenarios. A comparison between type 1 and type 1b relay nodes is as well presented to study the effect of the relaying overhead on the system performance in inband relay deployments. Comprehensive system level simulations show that the power control is a crucial means to increase the cell edge and system capacities, to mitigate inter-cell interference and to adjust the receiver dynamic range for both relay node types.

• Journal of Advanced Navigation Technology
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• v.12 no.5
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• pp.437-443
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• 2008

In this paper, we derive the optimum number of users which can maximize the information theoretic sum capacity in multiuser OFDM virtual MIMO uplink system. In which, there are multiple antennas at the base station and a number of users with single transmit antenna. Pilot-assisted channel state estimation is assumed for a block fading channel and time-varying fading channel. We analyze the tradeoff between the multiplexing gain and pilot overhead especially in low SNR regime and conclude that the optimum number of users is min ($N_r$,LT/2 ) in frequency nonselective block fading channel and approximately equal to min ($N_r$, ${\lfloor}{\sqrt{LT+1}}-1{\rfloor}$) in time varying fading channel. assuming the same pilot and signal pwoer.

• Journal of Advanced Navigation Technology
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• v.20 no.3
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• pp.232-237
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• 2016

As a possible standardization of wireless local area network (WLAN), IEEE 802.11 LRLP is under discussion in order to support long range and low power (LRLP) communication for internet of things (IoT) including drones and many other IoT devices. In this paper, an efficient adaptive resource unit allocation scheme for uplink multiuser transmission in IEEE 802.11 LRLP networks is proposed. In the proposed scheme, which adopts OFDMA random access based transmission scheme of IEEE 802.11ax, in order to enhance the efficiency of the slotted OFDMA random access, access point (AP) traces the history of the sizes of successfully transmitted uplink data, and adjusts the sizes of resource units for the next uplink multiuser transmission adaptively. Our simulation results corroborate that the proposed scheme significantly improves the system throughput.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.37-42
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• 2021

NOMA (Non-orthogonal multiple Access) system has been focused on the next generation cellular system for higher spectral efficiency. However, this requires user scheduling as the NOMA system is a multi-user system which accesses simultaneously. There are two representative scheduling schemes, proportionate scheduling (FP) and cumulative distribution function (CFD) scheduling. The PF scheduling is applied, the cell edge user is hard to obtain a transmit opportunity. Recently, CDF scheduling is obviously noted that it offers the same possibility of transmission for a user regardless of the location in a cell. We consider an uplink NOMA system with CDF scheduling, and obtain the channel access probabilities, the outage probabilities of the system with different number of users and different kinds of weights through simulation. The results indicate that the likelihood of each user accessing the channel is the same and the probability of failure decreases as the number of users increases. We found that the effect of the probability of failure is negligible as the weight of the cell edge user increases.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.43-46
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• 1998

The performance of a receiver that empolys a multi-stage inter-ference cancellation scheme for uplink fading channel is analyzed when there is carrier frequency offset. And the conditions to permit the performance improvement are analytically obtained. Numerical results show the effectiveness of the proposed system under Rayleigh fading channel assuming that carrier frequency offset is present.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.210-213
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• 2003

This paper presents a beamforming algorithm for the uplink application of a linear array antenna for WCDMA system. A steering beamforming algorithm is designed using a block DFT algorithm and its performance is analyzed and verified using computer simulations. Various environmental parameters such as the number of antenna elements, the number of users, the mobility of the target user, and the status of fast power control are reflected in the simulation study providing themselves as useful design and implementation guides for the reverse link beamforming of WCDMA system.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.103-104
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• 2006

In this paper, we analyze the UAV datalink design with calculating link budget of long-distance (200 km) Ku-band LOS wireless link. We calculate C/N of the real system and compare it with the required C/N, using the CCIR reports. In the rainy day of summer on the Korean peninsula, to maintain percent reliability 90% and BER 10^(-5) together, link budget of uplink of the system has a lot of margin at 200 km, link budget of downlink using the block turbo code is enough for distance 200 km.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.110-115
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• 2006

STSAT-2 is the first satellite which will be launched by the first Korean Space Launch Vehicle(KSLV). Ground station Baseband Control system(GBC) is now developed for STSAT-2. GBC has two functions. One is control data path between satellite control computers and ground station antennas(1.5M, 3.7M, 13M) automatically. The other is sending and receiving data between ground station and satellite. GBC is implemented by FPGA(Field-Programmable Gate Array) which includes almost all logic(for MODEM, PROTOCOL and GBC system control). MODEM in GBC has two uplink FSK modulators(1.2[kbps], 9.6[kbps]) and six downlink FSK demodulators(9.6[kbps], 38.4[kbps]). In hardware, STSAT-2 GBC is smaller than STSAT-1 GBC. In function, STSAT-2 GBC has more features than STSAT-1 GBC. This paper is about GBC structure, functions and test results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.608-616
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• 2007

OFDM Systems for multi-user use adaptive modulation and ending (AMC) which is a method that selects suitable modulation order and code rate depending on channel state of each user. Using AMC, OFDM system can provide high quality and reliable communication. Base station using AMC scheme requires downlink channel information of each terminal to operate optimality. However, under practical system environment, it is unsuitable to transmit all channel information because uplink bandwidth of the system is limited. In this paper, we propose a flexible block-wise loading (FBL) algorithm combined with a novel CQI feedback scheme with reduced number of required bits to optimize the performance of AMC system. Proposed algorithm allocates sub-carrier groups dynamically to improve the sector throughput and outage probability performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11A
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• pp.1076-1084
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• 2006

In this paper, we first review a concept of hybrid division duplexing (HDD) scheme, which has been proposed as a new type of duplexing scheme useful for a next generation mobile communication system and its implementation issues, including the unified radio resource management for HDD scheme. The HDD scheme maintains the advantages of both TDD and FDD at the same time while providing a useful structure to control the inter-cell interference, caused by an asymmetric traffic load of multimedia services over uplink and downlink in the TDD scheme. Employing two frequency bands, one for TDD scheme and the other for FDD scheme, uplink is operating under the TDD scheme only, while downlink is operating under the TDD or FDD scheme, depending on the location of mobile station. In the HDD scheme, therefore, it must determine a type of duplexing scheme to employ in the downlink and futhermore, a ratio of uplink and downlink duration to meet a given traffic load of asymmetric service, which requires some unified radio resource management for handling the subsequent inter-cell interference. In this paper, we propose a distributed adaptive control approach as a means of unified radio resource management for a HDD system that maximizes the overall system efficiency by fully utilizing the resource in TDD band, while minimizing the inter-cell interference.