• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.464-466
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• 2018

In this paper, a dense cellular network is considered in which each base station equipped with multiple antennas simultaneously communicates with multiple single-antenna users. Based on limited feedback, each user feeds back its quantized channel state information (CSI) to its associated transmitter, and the transmitter broadcasts multiple data streams prepared for the scheduled users using a space-division multiple access scheme. As the amount of CSI is limited at the transmitter, the downlink throughput increases with the number feedback bits. However, the increased number of feedback bits requires the correspondingly increased amount of uplink resources. Thus, an appropriate balance between the downlink throughput and the uplink resource usage should be considered in realistic systems. A net spectral efficiency defined in this context is used in this paper, and the optimal number of feedback bits that maximizes the net spectral efficiency is analyzed. This paper particularly focuses on the case when the received signal power is much smaller than the noise power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.906-914
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• 2009

SC-FDMA is employed in the 3GPP-LTE standard as the uplink transmission scheme. SC-FDMA has advantages that the signal has a low PAPR property and a simple equalizer such as FD-LE can be implemented. But FD-LE has inferior performance to Hybrid-DFE composed of frequency-domain feedforward filter and time-domain feedback filter. Recently, several IB-DFE algorithms have been proposed to overcome the disadvantages of implementation and processing complexity of Hybrid-DFE and to obtain superior performance to FD-LE. In this paper, we apply several IB-DFE algorithms to 3GPP-LTE uplink system and compare their performance by calculating BER. We investigate the effects of channel estimation errors and Doppler shift on performance. Finally, by analyzing computational complexity of IB-DFEs, we present some criteria to choose appropriate algorithm and to decide the number of iterative processes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.10
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• pp.1254-1260
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• 2019

Recently, 5G cellular systems have been attracted great attention as a key enabler for Industry 4.0. In this paper, we propose a novel random access based on pilot-assisted opportunistic transmission to support internet-of-things (IoT) scenario in cellular networks. A key feature of our proposed scheme is to enable each of IoT devices to attempt opportunistic transmission of its data packet in Step 3 with randomly selected uplink pilot signal. Both the opportunistic transmission and the pilot randomization in Step 3 are effective to significantly mitigate the occurrence of packet collisions. We mathematically analyze our proposed scheme in terms of packet collision probability and uplink resource efficiency. Through simulations, we verify the validity of our analysis and evaluate the performance of our proposed scheme. Numerical results show that our proposed scheme outperforms other competitive schemes.

• Journal of Advanced Navigation Technology
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• v.27 no.6
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• pp.782-787
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• 2023

Korea augmentation satellite system (KASS) integration, verification, qualification (IVQ) activity is verification of requirements for KASS system and its sub-system that were performed based on the inspection, analysis, review of design, test (IART) method from factory acceptance test (FAT) to test readiness review (TRR) after critical design review (CDR) was closed. In the FAT phase, developed equipment was installed on the test platform and we were verified interfaces between sub-systems and coupling test with the kass control station (KCS). In the site aceeptance test (SAT) phase, on-site verification was conducted by installing equipment verified by FAT such as kass reference station (KRS), kass processing station (KPS), kass uplink station (KUS), KCS. However, considering the developed plan and status, SAT was divided into 3 phases and coupling test was performed. In the TRR phase, the KASS system verification was performed through FAT's test list and additional test list using the satellite based augmentation system (SBAS) broadcast signal from geostationary earth orbit (GEO) 1.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1900-1911
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• 2015

In this paper, we introduce backscatter communication for power-limited sensors to enable long-range transmission in wireless sensor networks, and envision a way to avoid doubly near-far problem in wireless-powered communication network (WPCN) with this technology. In backscatter based WPCN, users harvest energy from both the signal broadcasted by the hybrid access point and the carrier signal transmitted by the carrier emitter in the downlink, and then transmit their own information in a passive way via the reflection of the carrier signal using frequency-shift keying modulation in the uplink. We characterize the energy-free condition and the signal-to-noise ratio (SNR) outage zone in backscatter based WPCN. Further, we propose backscatter based harvest-then-transmit protocol to maximize the sum-throughput of the backscatter based WPCN by optimally allocating time for energy harvesting and information transmission. Numerical results demonstrate that the backscatter based WPCN increases significantly the transmission range and diminishes greatly the SNR outage zone.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.58-67
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• 1994

In this paper, It was designed the 2.8GHz local oscillator which convert 14.5 14.8GHz uplink frequency to 11.7 12.0GHz downlink frequency by the receiving mixer on the communication satellite transponder according to the rating of domestic satellite. Mukunghwa 1. To prevent the variation of the communication channel bandwidth, it needs a high stability and low phase noise characteristics. So we designed to get the target frequencey by multipling the output signal from the crystal oscillator. We got the simplicity of the circuit by manufacturing the X4 multiplier with transistor which is ordinarily used as a device of a below X3 multiplier for the efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1059-1066
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• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.2
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• pp.178-182
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• 2011

A FSK receiver RF block has been developed for Dubaisat-1 Low Earth Orbit satellite. The receiver has Doppler tracking function which compensate frequency shift on uplink channel for commanding the satellite. It consist of LNA, downconverter and IF module. The IF module has Doppler tracking circuitry which sweep and lock on to input signal. It satisfies the requirement of the Dubaisat-1 in mass, power consumption, tracking speed and BER performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.2
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• pp.3-9
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• 2016

In this paper, we propose a Radio over Fiber system for small cell applications and for mobile fronthaul networks supporting cloud-radio access networks(RAN). We built a system with a downlink employing orthogonal frequency division multiplexing (OFDM) techniques and an uplink using single carrier-frequency multiple access(SC-FDMA). System parameters are evaluated for various subcarrier modulations and the results of link performance measurements are analyzed.

• Journal of Advanced Information Technology and Convergence
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• v.8 no.2
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• pp.13-25
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• 2018

The paper analyzes the sum spectral efficiency (SE) for a heterogeneous cellular network (HetNet) which has the backhaul, provided with wireless full-duplex massive multiple-input multiple-out (MIMO) with hardware distortions. We derive approximate expressions to obtain the uplink/downlink sum SE of the backhaul. The analytic results have been shown to be exact when compared to Monte Carlo simulations. From the analysis, it is shown that the desired signal and the hardware distortion noise have the same order. The sum SE generally improves when the number of receive antennas increases but degrades when the hardware quality reduces. A sum SE performance ceiling is introduced by the hardware quality level.