Earticle

최근 데이터 처리용량 증대에 대한 수요를 만족시키기 위해서, 전파 자원을 효율적으로 사용하고 네트워크 용량을 증대시키는 연구가 진행되고 있다. 현재 차세대 5G 이동통신망의 핵심적인 기술로서 소형 셀 네트워크, 밀리미터파대역 그리고 빔포밍이 존재한다. 그러나 밀리미터파대역의 전파특성이 기존에 사용되고 있는 대역의 것과 상이하기 때문에, 기존 대역을 사용하는 무선통신시스템이재설계되어야 할 필요가 있다. 본 연구에서는 실외환경에서 60GHz의 셀 네트워크에 대한 3D 시뮬레이션 모델을 논의한다. 거리협곡 시뮬레이션 환경 등을 포함한 일반적인 도심 환경에서 소형 셀 시스템에 대한 커버리지와 시스템 성능을 분석한다. 또한, 데이터 처리용량의 개선을 분석하기 위해 빔포밍의 적용을 고려하였다. 시뮬레이션 결과, 밀리미터파 소형 셀 기반의 시스템이 데이터전송속도 측면에서 5G의 요구사항을 충족시킬 수 있는 주요 후보 기술 중의 하나가 될 것으로 기대된다.

In an effort to compensate the rising of the data throughput demand nowadays, there have been many research works to optimize the radio resource and increase the capacity of the network. At the present, small cell network, mmWave band and beamforming technology are leading the trend and becoming the core solutions of the fifth generation (5G) cellular networks. Since the propagation characteristics of radio wave in the mmWave band is quite different from the conventional bands, the communication systems which work in these bands have to be redesigned. In this paper, a 3D simulation model is discussed for cellular network at 60 GHz in outdoor environments. Coverage analysis and system performance is carried out for a small cell system in the typical urban environment including street canyon simulation scenario. In addition, the beamforming technique is considered to evaluate the throughput improvement. Simulation results show that the mmWave small cell systems is expected to be one of the major candidate technologies to satisfy the requirements of 5G in terms of data rate.

최근 UHD, AR, VR 등 초고화질 미디어 데이터 전송에 대한 요구가 증가함에 따라 이를 위한 다양한 기술들이 활발하게 개발되고 있고, 그 중 IEEE 802.11ad 표준의 상용화가 진행 중에 있다. 본 논문에서는 초고주파(mmWave)를 기반으로 근거리 통신을 지원하는 IEEE 802.11ad 표준 기반 모듈을 이용하여 실내 무선 환경을 분석하기 위해 테스트 베 드를 구축하고 다양한 실내 무선 환경에 대한 측정 실험 결과를 소개하고 분석한다. 모듈로 데이터 전송을 통해 SNR(Signal to Noise Ratio), Throughput 등의 데이터를 수집하는 방법으로 비교하며, 모듈의 빔 패턴과 폭을 측정하여 복도 및 사무실의 실내 환경에서 미치는 영향을 비교하였다. 이를 통해 벽의 신호 반사로 더 높은 SNR 값을 보여 실외보다 실내에 더 적합하다는 것을 확인하였고, LoS(Line of Sight)가 아닐 때의 손실을 벽면의 반사된 신호가 보완할 만큼 충분 하지 않다는 것을 확인하였다. 결론적으로 초고주파 무선랜의 실내 사용에 적합하다고 판단되며 차후 추가적인 실험 구성 에 유용하게 활용될 수 있다.

Recently, as the demand for transmission of ultra-high quality media data such as UHD, AR, and VR increases, various technologies for this have been actively developed and IEEE 802.11ad standard have been commercialized. In this paper, a test bed is constructed to analyze the indoor wireless environment using the IEEE 802.11ad standard based on mmWave, and the experimental results of various indoor wireless environments are introduced and analyzed. We compared the data from the module by data transmission, such as signal to noise ratio(SNR) and throughput. And we measured the beam pattern and width of the module and compared the effects on the indoor environment of the corridor and the office. This shows that the signal reflection of the wall shows higher SNR values and is more suitable to use for indoor than outdoor. It is confirmed that the loss when not in line of sight(LoS) is not enough to compensate the wall reflected signal. As a result, it is judged to be suitable for the indoor use of the mmWave LAN and can be usefully used for further experiments.

실내 고속 데이터 전송을 목표로 하는 밀리미터파 무선통신 시스템은 고 품질의 무선 링크에 대한 요구 사항이 매우 중요하다. 그러 나, 이러한 주파수 대역에서 전자기파는 상대적으로 작은 파장으로 인하여 발생하는 높은 전파 손실을 감수해야 한다. 이러한 상황에 서 방사전력을 특정 방향으로 집중하여 링크 품질을 향상시킬 수 있는 빔포밍 기법은 밀리미터파 대역 무선통신에서 가장 중요한 기법 중의 하나가 되었다. 최근 몇 년간, 무선 시스템의 성능을 향상시키기 위한 빔포밍 관련 연구가 많이 이루어지고 있다. 본 논문 에서는 다중절차와 3상 빔 선택을 기반으로 한 단순화된 코드북 기반의 빔포밍 기법의 성능을 평가한다. 이 단순화된 기법은 전수검 색, IEEE 802.15.3c 표준이 적용된 2-레벨 검색 및 기존의 멀티레벨 기법과 비교하여 빔포밍 준비에 필요한 시간 감소를 달성할 수 있음을 보여준다.

Millimeter wave wireless communication systems, especially those targeting indoor high rate data transfer, have a strong requirement for high quality wireless link. Unfortunately, in this frequency band, the electromagnetic wave has to sustain the high propagation loss caused by the smaller wavelengths. In this scenario, beamforming technique, which enhances the link quality by focusing the radiation power on a direction, becomes one of the most important techniques in millimeter wave band wireless communication. In recent year, there been conducted many research on beamforming to improve the performance of wireless system. In this paper, we evaluate the performance of a simplified codebook-based beamforming scheme which is based on multiple-procedure and three-state beam selection. The simplified scheme significantly reduces beamforming setup time, comparing to the exhaustive searching, two-level searching adopted in IEEE 802.15.3c standard, and also conventional multi-level scheme.

In this paper, we present the channel measurement and cell coverage result around 2018 Pyeong Chang Alpensia sky resort area at 28GHz frequency band. A channel sounder system is used to measure the characteristics of 28GHz frequency band. Consequently, path loss and channel model parameters are obtained by analysis of the measurement results. Furthermore, expected 5G cell coverage analysis results are presented by conducting simulation based on real 3D digital elevation models and base-station sites.

In this paper, we will consider the problem of multi-unmanned aerial vehicles (UAVs) deployment among users’ hotspots. UAVs carry reconfigurable intelligent surface (RIS) boards to strengthen millimeter wave (mmWave) coverage at these hotspots. UAVs should maximize hotspots’ sum data rates while minimizing their flights’ cost, i.e., hovering and flying energy consumptions. Moreover, collisions should be avoided among UAVs, i.e., one hotspot should be served by only one UAV at a time. In this paper, this problem is considered as a multi-player multi-armed bandit (MP-MAB) game with budget constraint and collision avoidance. In this context, budget constraint Thompson sampling (TS) with collision avoidance MAB algorithm (BTSCA-MAB) is proposed to efficiently implement the formulated MP-MAB game. Numerical analysis confirms the superior performance of the proposed BTSCA-MAB over other benchmarks.

Mmillimeter-wave (mmWave) massive multiuser multiple-input multiple-output (MU-MIMO) system usually utilizes hybrid precoding to reduce complex hardware and high energy consumption. However, most hybrid precoding scheme consider the fully connected architecture, which may result in a significant loss of energy efficiency. In this paper, we propose a hybrid precoding scheme based on the overlapped subarray architecture (OSA), where the analog part of the MU-MIMO system is realized by a OSA network. Based on the OSA architecture, a modified generalized low rank approximation of matrices (GLRAM) based hybrid precoding scheme is designed to maximize the achievable sum-rate, where the analog precoding algorithm apply the phase alignment technology and GLRAM approach to obtain RF precoder/combiner with high array gain provided by massive MIMO system. Then, the block diagonalization (BD) technology is performed to obtain the digital precoding matrix for the multiplexing gain. Simulation results show that the modified GLRAM based hybrid precoding algorithm for OSA architecture can reduce the number of iterations. Compared with the existing hybrid precoding algorithm, it achieves higher spectral efficiency and lower complexity.

With the growing interest in both public and private 5G services based on millimeter wave (mmWave) communication for indoor usage scenarios such as smart factories, site design specialists are seeking sophisticated methods and tools for simulating indoor radio coverage based on highly accurate path loss prediction models. Although machine learning approaches can be used in path loss modeling thanks to the highly accurate prediction capability, their performance can be limited by the size of available measurement data set used for training. In this paper, we propose new approaches to train path loss models in the few-shot learning scenarios of smart factories. The proposed approaches are based on meta-learning with slight modifications to perform fine-tuning over an entire train data set rather than a meta-test data set. It is shown that the indoor path loss models based on convolutional neural networks (CNNs) trained by meta-learning based on three different meta-train task assignment schemes outperform both a conventional CNN model and an empirical model.

Identity-aware activity recognition is a key enabler for customized services. However, joint modeling of activity recognition and user identification from wireless signals remains underexplored. This work presents a dual-task graph model for millimeter-wave (mmWave) frequency-modulated continuous-wave (FMCW) radar point-cloud sequences. We construct directed graphs that capture a user’s spatial structure and motion over time. A shared graph neural backbone processes these graphs and produces node embeddings that encode local spatial features and short-term dynamics. Each task-specific head first aggregates node embeddings into a graph-level representation and then performs activity or identity classification. Experiments on two public datasets demonstrate that the proposed scheme achieves classification performance comparable to single-task baselines for both activity recognition and user identification while maintaining low-latency inference. Codes are available at?https://github.com/junyongeom/mmActId/.

In this paper, we propose deep learning-based channel estimation and pilot reduction for mmWave point-to-point multi-input multi-output systems. The proposed scheme consists of a two-step approach where the first step is applying a denoising autoencoder for channel estimation. With the denoising characteristic of autoencoder, sparse channel estimation can be conducted although the orthogonality of pilot sequences is not guaranteed due to shorter pilots. The second step is exploiting the temporal correlation of the channel, using the previous estimate to extract information for the current estimate. Through simulation, the proposed scheme shows superior performance with reduced pilots.

Beamforming training (BFT) is a critical process for establishing directional links in millimeter-wave (mmWave) wireless local area networks. However, its performance significantly degrades due to frequent slot collisions. This paper proposes a non-orthogonal multiple access (NOMA)-based exhaustive search (NES) scheme, which allows multiple stations (STAs) to perform BFT concurrently by independently selecting predefined transmit power levels. We integrated the NOMA-based technique into a time-based beam collision avoidance (TBCA) scheme, named NOMA-TBCA (NTBCA). The proposed NES and NTBCA schemes are analytically modeled and evaluated through simulations. The results confirm that the combined approach effectively enhances the association probability and the throughput.

In this paper, we propose a reflection pattern design scheme for reconfigurable intelligent surface (RIS) assisted vehicular platoon communications in millimeter wave (mmWave) channels. We focus on optimizing the reflection pattern of a RIS that is installed in a roadside unit to maximize the broadcast information rate from the lead vehicle in a platoon to each following member vehicle. We show that this problem can be effectively solved using semidefinite programming. Next, we propose a reflection pattern design scheme for the RIS that maximizes its reflection gain by exploiting the angle of departure, angle of arrival, and path loss information between each vehicle and the RIS in mmWave channels. Finally, we present numerical results that demonstrate the effectiveness of our proposed reflection pattern design scheme.

In millimeter wave communication, the beamforming technique with accurate angle information plays a key role to overcome the high path-loss and mitigate the interference. Particularly with multiple mobile stations (MSs), accurate multi-beam tracking without any knowledge of dynamic model is challenging. In this regard, we propose the model-free multi-beam tracking algorithm combining the Q-learning with auxiliary beam pair-based angle estimation in multi-MS environment. The proposed scheme benefits from low pilot overhead and high-resolution angle estimation. Simulation results show that the proposed scheme outperforms the conventional schemes in terms of the effective sum-rate.

The increasing demand for high-speed, low-latency applications, especially with 5G mmWave technology, has led to challenges in TCP performance due to signal blockages, small buffers, and high Packet Error Rates (PERs). Existing congestion control algorithms (CCAs) struggle to fully utilize available bandwidth under these conditions. This paper proposes MSS-TCP, a novel congestion control algorithm designed for mmWave networks. MSS-TCP dynamically adjusts the congestion window (cwnd) based on the maximum segment size (MSS) and round-trip time (RTT), improving bandwidth utilization and congestion adaptability. The simulation results using the ns-3 network simulator show that MSS-TCP outperforms state-of-the-art CCAs, including NewReno, HighSpeed, CUBIC, and Bottleneck Bandwidth and Round-trip propagation time (BBR), and Fuzzy Logic-based (FB-TCP), particularly when the buffer matches the bandwidth-delay product (BDP), achieving a 24.26% to 45.43% improvement in throughput compared to BBR while maintaining low latency. These findings demonstrate that MSS-TCP enhances TCP performance in 5G mmWave networks, making it a promising solution for next-generation wireless communication.

One of promising transmission technologies for beyond-5G wireless communication is cell-free massive MIMO where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs). Based on the benefits from massive MIMO, the novel notion of cell-free network architecture is adequate to overcome the inter-cell interference limitation in ultra-dense network (UDN) environments, owing to the full cooperation among ANs. In this paper, we develop synergetic operations between the cell-free massive MIMO and mmWave ultra-wide frequency band, which is able to provide a genuine high-quality and robust wireless pervasive service by fully utilizing the basic three pillars for wireless capacity, such as bandwidth, spectral efficiency and network densification. For this goal, we study the impacts of analog precoding schemes to be combined with zero-forcing digital precoding on cell-free mmWave massive MIMO UDN systems. In addition, we investigate the effect of correlated shadowing and pilot assignment strategies on the average spectral efficiency performance for the proposed hybrid precoding schemes in both outdoor and indoor UDN environments.

최근 무선 통신의 발전으로 정확한 위치인식이 요구되는 다양한 응용 어플리케이션이 개발되고 있으며, 사람들은 실내 활동 시간의 증가 및 산업적 발전으로 인하여 위치기반 서비스에 의존성이 증가하게 되었다. 하지만 무선통신기 반 위치인식은 실내환경의 공간의 크기에 따라 벽이나 기둥과 같은 장애물에 의해 신호 감쇠가 발생하여 정확하게 추 정할 수 없다. 따라서 이 문제를 해결하기 위해 mmWave Radar기반 공간 인식을 이용한 클러터신호 제거 알고리즘을 제안한다. 제안한 알고리즘은 전처리시 공간에 대한 정보를 입력하는 방식이 아닌 자동으로 추출할 수 있도록 지도학 습기반의 ANN을 활용하며, 연산량을 감소시키고 정확도를 향상하기 위해 PCA를 이용하여 특징을 추출한다. 또한, 타 당성을 검증하기 위해 실내 공간 인식 성능 차이를 분석하였다.

Recently, development of a cryogenic fluids storage tank for storing or transporting liquid hydrogen is actively in progress. In cryogenic fluids storage tanks, hydrogen evaporates due to the extreme temperature difference inside and outside the tank. As the mass of the cryogenic fluids changes with continuous vaporization, the fluids level also changes. Therefore, there is need for a method of accurately measuring the level change in the storage tank. In the case of general cryogenic fluids, it is difficult to accurately measure the level because the dielectric constant is very low. As a method of measuring cryogenic fluids level with low dielectric constant, it can be used an Millimeter wave (MM wave) FMCW radar sensor. However, the signal sensitivity is very weak and the level accuracy is poor. In this paper, the signal sensitivity is improved by designing the horn lens antenna of the existing 80 GHz FMCW radar sensor. Horn lens antenna is fabricated by FDM/SLA type 3D printer according to horn and lens characteristics. The horn is used to increase the signal gain and the lens improves the signal straightness. This makes it possible to measure the level of cryogenic fluids with a low dielectric constant.