• ETRI Journal
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• v.34 no.5
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• pp.759-762
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• 2012

Carrier aggregation is an essential feature in the Long Term Evolution-Advanced (LTE-A) system, which allows the scalable expansion of the effective bandwidth to be delivered to user equipment (UE) through the concurrent use of radio resources across multiple component carriers (CCs). This system's optimal radio-resource use has received much attention under simultaneous access (SA) scenarios for multiple CCs (m-CCs). This letter establishes how many CCs a UE should simultaneously connect to maintain maximum uplink capacity. Under the m-CC LTE-A system, the spectral efficiency of the m-CC SA scheme ($m{\geq}2$) is compared with that of CC selection (CCS). Numerical results reveal that the 2-CC SA scheme outperforms CCS and performs almost equally to the m-CC SA scheme ($m{\geq}3$).

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.39-44
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• 2013

Long Term Evolution (LTE) - Advanced has developed Heterogeneous Network (HetNet) that consists of a mix of macrocells and low-power nodes such as picocells to improve the system performance. Also, to encourage data offloading in HetNet, Cell Range Expansion (CRE) have been introduced. In this paper, we propose a cell selection scheme based on Signal to Interference plus Noise Ratio (SINR) for optimal offloading effect. And we manage the interference for user located in cell range expanded region using Almost Blank Subframe (ABS) with flexible ABS ratio to improve the spectrum efficiency in time domain. Simulation results show that proposed scheme can improve spectrum efficiency of macrocell and picocell user. Eventually, proposed scheme can imporve overall user performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.45-52
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• 2013

Coordinated Multi-Point (CoMP) is considered as a technology in the 3rd Generation Partnership Project(3GPP) Long Term Evolution-Advanced (LTE-A) system. In this paper, we design and analyze the performance of the Coordinated Beamforming (CB) technique, which is one major category of CoMP. We perform Monte Carlo simulations with a Heterogeneous Network (HetNet) in LTE-A, and confirm the performance through a graph of the Cumulative Distribution Function (CDF). From the simulation results, we show significant performance gain with the CoMP technique, and better performance when we apply various schemes of scheduling and precoding.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.9
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• pp.1-7
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• 2009

LTE-A (long term evolution advanced) uplink selected SC-FDMA (single carrier frequency division multiple access) to maintain low PAPR for a low price and tiny terminal. Recently, the application of codebook-based preceding to LIE-A uplink is discussed. This paper shows that PAPR can be increased when various preceding schems are applied to the SC-FDMA as an LTE-A uplink. When, considering nonlinear power amplifier model to the transmitter, BER performances of preceded schemes degrade. But equal gain transmission scheme does show very low PAPR. So the link-level performance of EGT is superior to those of any other preceding schemes. Computer simulations also confirm the anticipated link-level performances.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1B
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• pp.31-38
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• 2012

In this paper, we propose a method to improve cell edge users' performance in HetNet (heterogeneous network) systems by cooperatively transmitting signals using remote radio heads (RRHs) located near coverage boundaries, referred to as edge RRHs. The proposed method locates the edge RRHs in specific locations of the cell boundary and provides an efficient operational strategy by adjusting the duty cycle of the edge RRHs and base stations. The effectiveness of the method is demonstrated by experimental performance based on the system model parameters of the CoMP (coordinated multi-point transmission and reception) scenario, which is discussed in LTE-Advanced (Long Term Evolution - Advanced) standard contributions. When compared with conventional methods, utilization of edge RRHs is especially advantageous for the performance improvement of lower percentile users in terms of average throughput and effectively improves the fairness among users.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.715-717
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• 2014

In recent wireless communication systems such as Long Term Evolution-Advanced (LTE-A) system, to transmit large multimedia data, high order modulations including 64-ary quadrature amplitude modulation (QAM) are adopted. However, performance of the modulation depends on the signal constellation in the same modulation order. Therefore, a symbol error rate (SER) expression of optimal performance is necessary for analyzing the SER performance of various signal constellation. The optimal signal constellation based on error bound has been previously described, but an exact SER expression has not been derived. In this paper, we propose an exact SER expression of optimal signal constellation for 64-ary QAM.

• Journal of Integrative Natural Science
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• v.11 no.4
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• pp.197-203
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• 2018

Long Term Evolution-Advanced (LTE-A) is the next drive in the broadband mobile communication, which allows operators to improve networks performance and service capabilities. LTE-A targets the peak data rates of 1Gbps in the downlink and 500Mbps in the uplink. This requirement is only fulfilled by a transmission bandwidth of up to 100MHz. However the accessibility of such large part of the contiguous spectrum is uncommon in practice. Therefore LTE-A uses some new features on top of the existing LTE standards to provide very high data rate transmission. Some of the most significant features introduced in LTE-A are carrier aggregation, heterogeneous network enhancement, coordinated multipoint transmission and reception, enhanced multiple input and multiple output, and development relay nodes with universal frequency reuse. This review paper presents an overview of the above mentioned LTE-A key features and functionalities. Based on this review, in the conclusion we discuss the current technical challenges for future broadband mobile communication systems.

• Journal of Advanced Navigation Technology
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• v.19 no.6
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• pp.601-606
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• 2015

Recently wireless data services have widely spread on various multimedia devices such as smart phones and tablets. Existing wired data services have been replaced by wireless data services using mobile devices. Especially domestic mobile devices supporting both Wireless-Fidelity (Wi-Fi) and long term evolution (LTE) services have increased steadily. While Wi-Fi network is provided free of charge, LTE network is offered to pay for. Therefore, mobile devices provide smart network switch to support both preferred Wi-Fi and LTE networks. However, such handover and roaming between Wi-Fi and LTE networks can cause data connection stop in spite of charged data services. This paper has proposed the method to overcome data connection stop for guaranteeing seamless data service during handover and roaming procedures between networks.

• Journal of Advanced Navigation Technology
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• v.26 no.2
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• pp.91-98
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• 2022

Unmanned aircraft system traffic management (UTM) service for the safe operation of unmanned aerial vehicles (UAV) such as drones using commercial communication networks such as long-term evolution (LTE) and 5G in low-altitude areas of 150m or less is being studied in several countries. In this paper, whether it is possible to secure three-dimensional (3D) coverage for UTM service using the existing LTE cellular network for terrestrial usersis analyzed through simulations. The practicality in the real environment is confirmed by performing performance analysis in the actual topographical environment and the LTE base station layouts in Korea. According to the analysis results, as the altitude increases, the number of line-of-sight (LOS) interference base stations increases, resulting in a worse signal to interference plus noise ratio (SINR), but coverage is secured except for the limited areas within 150m. was confirmed to be possible. In addition, it is confirmed that a significant proportion of outage areas could be reduced by placing a small number of additional base stations for the outage area.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.219-226
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• 2012

Since OFDM(Orthogonal Frequency Division Multiplexing) technology is applied into LTE(Long Term Evolution)/LTE-Advanced system, it is important to estimate the spectrum sharing and to analyze interference in LTE system based on the characteristics of frequency assignment. Therefore, in this paper, a study on the adjacent channel interference between two operators/systems to provide LTE services. For co-existence of LTE systems, the relative capacity loss and the relative throughput loss in uplink and downlink have been simulated to evaluated ACIR(Adjacent Channel Interference Ratio) values with 5% loss rate. Some parameters such as the location of user, aggressor bandwidth, and the separation offset affect the required ACIR value for spectrum sharing, and these results and interference analysis schemes in this article can provide reliable reference for LTE RF standardization and efficient frequency utilization in future.