Heejung Yu

Korea University | KU · Department of Electronics and Information Engineering

Terahertz (THz) communications will be pivotal in sixth-generation (6G) wireless networks, offering significantly wider bandwidths and higher data rates. However, the unique propagation characteristics of the THz frequency band, such as high path loss and sensitivity to blockages, pose substantial challenges. Reconfigurable intelligent surfaces (RI...

Wireless-powered communications (WPCs) are increasingly crucial for extending the lifespan of low-power Internet of Things (IoT) devices. Furthermore, reconfigurable intelligent surfaces (RISs) can create favorable electromagnetic environments by providing alternative signal paths to counteract blockages. The strategic integration of WPC and RIS te...

As the frequency of jamming attacks on wireless networks has increased, conventional local jamming detection methods cannot counter advanced jamming attacks. To maximize the jammer detection performance of machine learning (ML)-based detection methods, a global model that reflects the local detection results of each local node is necessary. This st...

With the advent of sixth-generation networks, reconfigurable intelligent surfaces (RISs) have revolutionized wireless communications through dynamic electromagnetic wave manipulation, thereby facilitating the adaptability and unparalleled control of real-time performance evaluations. This study proposed a framework to analyze the performance of RIS...

In the sixth-generation (6G) Internet of Things (IoT) networks, the use of UAV-mounted base stations and reconfigurable intelligent surfaces (RIS) has been considered to enhance coverage, flexibility, and security in non-terrestrial networks (NTNs). In addition to aerial networks enabled by NTN technologies, the integration of underwater networks w...

Terahertz (THz) communication is expected to be a key technology for future sixth-generation (6G) wireless networks. Furthermore, reconfigurable intelligent surfaces (RIS) have been proposed to modify the wireless propagation environment and enhance system performance. Given the sensitivity to blockages and limited coverage range, RIS is particular...

In Unmanned Aerial Vehicles (UAVs)-assisted communications, there are two significant challenges that need to be addressed - optimized UAV placement and energy-efficient user association. These challenges are crucial in meeting the quality-of-service (QoS) requirements of users. To overcome these challenges, a reinforcement learning-based intellige...

Wireless powered communication (WPC) involves the integration of energy harvesting and data transmission. This allows devices to communicate without constant battery replacements or wired power sources. Reconfigurable intelligent surfaces (RISs) can dynamically manipulate radio signals. In this paper, we explore the use of active elements to mitiga...

Devices connected to the Internet of Things (IoT) are growing in popularity across multiple industries. IoT links intelligent homes, buildings, businesses, and communities, and also links computers and mobile devices. Cybersecurity in IoT networks remains challenging, although many intrusion detection services for assault avoidance systems have bee...

In this study, physical layer security (PLS) in a dual-hop underwater optical wireless communication (UOWC)-radio frequency (RF) network under the intruding attempts of multiple eavesdroppers via RF links is considered. An intermediate decode-and-forward (DF) relay node between an underwater source and a destination transforms the optical signal in...

Significant challenges are involved in tactical flying ad-hoc network (FANET) missions because network environments are very dynamic. In addition, energy-efficient network operation is important in tactical FANETs owing to the limited capacity of the on-board battery in unmanned aerial vehicles (UAVs). In a slotted-ALOHA (S-ALOHA)-based tactical FA...

This paper introduces an innovative cell-free massive MIMO (CF-mMIMO) architecture integrating a low earth orbit satellite with unmanned aerial vehicles (UAVs) as flying access points (FAPs), referred to as a CF-mMIMO satellite-UAV network, aimed at enhancing uplink spectrum efficiency (SE) for ground users (GUs). Expressions are derived to estimat...

In the sixth-generation (6G) Internet of Things (IoT) networks, unmanned aerial vehicle (UAV)-mounted base stations and reconfigurable intelligent surfaces (RISs) have been considered key technologies to enhance coverage, flexibility, and security in non-terrestrial networks (NTNs). In addition to aerial networks enabled by NTN technologies, the in...

Reconfigurable intelligent surface (RIS)-assisted millimeter wave (mmWave) communication is a promising technology for enlarging the coverage area of millimeter wave systems. Unfortunately, realizing the full potential of these systems requires addressing numerous challenges in channel estimation. In this paper, channel estimation for RIS-assisted...

Network-on-Chip (NoC) has been unfolded as a superior alternative for integrating a considerably greater extent of cores on a single chip. Recently, multi-core systems have become prevalent because of the increased processing demands for high-performance embedded applications. Application mapping techniques play a significant role in enhancing the...

Wireless powered communication (WPC) combines information and energy transmission for energy-constrained nodes. Reconfigurable intelligent surfaces (RISs) are capable of controlling radio signals in a dynamic and goal-oriented manner. This paper investigates the combination of RIS and WPC to enhance the performance of an energy-constrained user. Us...

Reconfigurable intelligent surface (RIS) has recently gained significant interest as an emerging technology for future wireless networks thanks to its potential for improving the coverage probability in challenging propagation environments. This paper studies an RIS-assisted propagation environment, where a source transmits data to a destination in...

Recently, megaconstellations with a massive number of low Earth orbit (LEO) satellites are being considered as a possible solution for providing global coverage due to relatively low latency and high throughput compared to geosynchronous orbit (GEO) satellites. However, as the number of satellites and operators participating in the LEO constellatio...

Internet of Things (IoT) vision has astoundingly transcended environmental sensing with integrated computing systems and smart devices, providing seamless connectivity among humans, machines, and their environment to cooperate for convenience and economical benefits. Apart from all the tremendous benefits of IoT, this paradigm still suffers from ch...

Recently, mega-constellations with a massive number of low Earth orbit (LEO) satellites are being considered as a possible solution for providing global coverage due to relatively low latency and high throughput compared to geosynchronous orbit satellites. However, as the number of satellites and operators participating in the LEO constellation inc...

Sixth-generation (6G) networks pose substantial security risks because confidential information is transmitted over wireless channels with a broadcast nature, and various attack vectors emerge. Physical layer security (PLS) exploits the dynamic characteristics of wireless environments to provide secure communications, while reconfigurable intellige...

Reconfigurable intelligent surface (RIS) has recently gained significant interest as an emerging technology for future wireless networks thanks to its potential for improving the coverage probability in challenging propagation environments. This paper studies an RIS-assisted communication system, where a source transmits data to a destination in th...

In order to meet the demands of diverse services within sixth-generation networks across a range of industries, numerous approaches are being employed to address notable signal degradation resulting from channel obstruction, particularly in the realms of millimeter wave and sub-THz frequencies. One of these solutions is the utilization of reconfigu...

Reconfigurable intelligent surfaces (RISs) have been considered as a promising technology for the sixth-generation (6G) wireless networks that can control wireless channels in a desirable way and significantly enhance the network performance. Simultaneous transmitting and reflecting-RISs (STAR-RISs) can overcome limitation of reflecting-only RISs b...

The data breach and the integrity violation of remote data remain significant issues in the domain of information security. A provably-secure hash function aids in providing solutions to integrity-related issues. Nevertheless, the choice of a provably-secure hash function has to be made with caution from the perspective of security. This research s...

In this study, the performance of intelligent reflecting surfaces (IRSs) with a discrete phase shift strategy is examined in multiple-antenna systems. Considering the IRS network overhead, the achievable rate model is newly designed to evaluate the practical IRS system performance. Finding the optimal resolution of the IRS discrete phase shifts and...

An unmanned aerial vehicle-mounted base station (UAV-BS) is a promising technology for the forthcoming sixth-generation wireless networks, owing to its flexibility and cost effectiveness. Besides, the limited network operation time of UAV-BS networks can be overcome with the concept of tethered unmanned aerial vehicles (TUAVs), which are powered fr...

Predictably, the upcoming six generation (6G) networks demand ultra-massive interconnectivity comprising densely congested sustainable small-to-tiny networks. The conventional radio access network (RAN) will be redesigned to provide the necessary intelligence in all areas to meet required network flexibility, full coverage, and massive access. In t...

Millimeter-wave (mm-wave) and sub-terahertz (sub-THz) communications are expected to be one of the biggest beneficiaries of the emerging reconfigurable intelligent surface (RIS) technology. RISs can compensate for large path loss and blockage inherent to the mm-wave and sub-THz frequency bands to yield enhanced communication performance in these ba...

Advancement in very large scale integration (VLSI) technologies and the ever-shrinking size of the transistors have led the semiconductor designers to create a multiprocessor system on chips. Network on chip (NoC) provides an efficient and flexible communication infrastructure to these systems. One of the most prominent research problems in NoC is...

This paper investigates the reconfigurable intelligent surface (RIS)-empowered dynamic power splitting designs for simultaneous wireless information and power transfer (SWIPT) systems while adopting various practical hardware issues. Specifically, we adopt the physical size of the RIS and the placement of the RIS plane to phase-align the reflected...

Integration of communication and radar functions with a single waveform has been actively investigated in various wireless communication applications, including unmanned aerial vehicles (UAVs). This means that communication frames consisting of a pilot part and subsequent data part can be utilized to transmit information and detect the surrounding...

In this paper, the problem of direction-of-arrival (DoA) estimation for a hybrid array of subarrays is considered in millimeter-wave communication systems. Unlike much prior work using the outputs from the analog subarrays with symbol-wise processing, the proposed framework jointly exploits multiple outputs in time domain for high-resolution DoA es...

Reconfigurable intelligent surfaces (RISs) have been considered as a promising technology for the sixth-generation (6G) wireless networks that can control wireless channels in a desirable way and significantly enhance the network performance. Simultaneous transmitting and reflecting-RISs (STAR-RISs) can overcome limitation of reflecting-only RISs b...

To develop emerging transmission techniques for potential applications of Internet of Things (IoT), the system performance analysis of a cognitive radio (CR)-enabled ambient backscatter (AmBC) system will be studied in this paper with functionality of non-orthogonal multiple access (NOMA). In the proposed scheme, a base station communicates with tw...

The characterization of aircraft in remote sensing satellite imagery has many armed and civil applications. For civil purposes, such as in tragedy and emergency aircraft searching, airport scrutiny and aircraft identification from satellite images are very important. This study presents an automated methodology based on handcrafted and deep convolu...

Through ordinary transmissions over wireless multicast networks are greatly hampered due to the simultaneous presence of fading and shadowing of wireless channels, secure transmissions can be enhanced by properly exploiting random attributes of the propagation medium. This study focuses on the utilization of those attributes to enhance the physical...

Network on chip (NoC) is a promising communication infrastructure for multiple cores on a chip to exchange data efficiently. In such NoC architecture, application mapping is a process of assigning tasks to the processing cores. An optimized application mapping technique enhances the performance of a chip and reduces the entire chip’s energy consump...

In this paper, the problem of training signal design for intelligent reflecting surface (IRS)-assisted millimeter-wave (mmWave) communication under a sparse channel model is considered. The problem is approached based on the Cramér-Rao lower bound (CRB) on the mean-square error (MSE) of channel estimation. By exploiting the sparse structure of mmWa...

In air-to-ground communications, the network lifetime depends on the operation time of unmanned aerial vehicle-base stations (UAV-BSs) owing to the restricted battery capacity. Therefore, the maximization of energy efficiency and the minimization of outage ground users are important metrics of network performance. To achieve these two objectives, t...

Mapping application task graphs on intellectual property (IP) cores into network-on-chip (NoC) is a non-deterministic polynomial-time hard problem. The evolution of network performance mainly depends on an effective and efficient mapping technique and the optimization of performance and cost metrics. These metrics mainly include power, reliability,...

This paper investigates the physical layer security and data transmission for the underlay device-to-device (D2D) networks, and considers a combination of the reconfigurable intelligent surface (RIS) and full-duplex (FD) jamming receiver for the robustness and security enhancements. In the demonstrated spectrum sharing setup, the total power of the...

For Internet of Things (IoT) applications in the sub-1 GHz unlicensed band, the IEEE 802.11ah technology, also called WiFi HaLow, has been standardized. To achieve long-range and low-power features of IoT networks, the physical (PHY) and medium access control (MAC) layer functions in the previous WiFi standards are amended in the IEEE 802.11ah stan...

In this article, channel estimation for millimeter-wave massive multiple-input–multiple-output (MIMO) systems with hybrid beamforming is considered. With a large number of antenna elements, a progressive time delay across antenna elements incurs a change in the beam direction as a function of subcarriers in an orthogonal frequency-division multiple...

In this paper, we consider physical layer security (PLS) of the Internet of Things (IoT) communications based on hybrid automatic repeat request (HARQ) protocols in multiple-input single-output single-eavesdropper (MISOSE) channels. Owing to the reciprocity of wireless channels, a negative acknowledge frame can be used to obtain the channel state i...

Fifth-generation (5G) networks will not satisfy the requirements of the latency, bandwidth, and traffic density in 2030 and beyond, and next-generation wireless communication networks with revolutionary enabling technologies will be required. Beyond 5G (B5G)/sixth-generation (6G) networks will achieve superior performance by providing advanced func...

In this paper, the dimension of artificial noise (AN) and corresponding transmit power in multiple-input multiple-output single-eavesdropper channels are investigated. It is widely known that AN is transmitted in the null space of the channel matrix of a legitimate link between a source and a destination. Here, the secrecy outage probabilities are...

For a secure communication over Radio Frequency-Free Space Optical (RF-FSO) mixed link, a significant enhancement of secrecy capacity (SC) can be achieved via exploiting spatial diversity at the RF path. But besides atmospheric turbulence and pointing error of FSO link, practical multi-antenna systems experience correlation between the antennas at...

With the rapid evolution of communication technologies, high-speed optical wireless applications under the water surface as a replacement or complementary to the conventional radio frequency (RF) and acoustic technologies are attracting significant attention from the researchers. Since underwater turbulence (UWT) is an inevitable impediment for a l...

Non-orthogonal multiple access (NOMA) has gained attention as a promising multiple access scheme for the Internet of Things (IoT). A typical setting of user ordering in NOMA networks with user priority difference allows a service priority for solely low-rate high-priority users. In contrast, the diverse quality of service (QoS) requirements and ser...

In this paper, the problem of training signal design for intelligent reflecting surface (IRS)-assisted millimeter-wave (mmWave) communication under a sparse channel model is considered. The problem is approached based on the Cram$\acute{\text{e}}$r-Rao lower bound (CRB) on the mean-square error (MSE) of channel estimation. By exploiting the sparse...

In this paper, a novel interference free dual-hop device-to-device (D2D) aided cooperative relaying strategy (CRS) based on spatial modulation (SM) (termed D2D-CRS-SM) is proposed. In~D2D-CRS-SM, two cellular users (e.g., a near user (NU) and a relay-aided far user (FU)) and a pair of D2D transmitter (D$_1$)-receivers (D$_2$) are served in two time...

Required throughput for a fronthaul in a cloud-radio access network tremendously increases and becomes a bottleneck in a communication network with wide bandwidth and a large number of antennas. To reduce the fronthaul capacity requirement, more digital function blocks are shifted from a central unit to a distributed unit. In this study, we conside...

Speech emotion recognition (SER) plays a significant role in human-machine interaction. Emotion recognition from speech and its precise classification is a challenging task because a machine is unable to understand its context. For an accurate emotion classification, emotionally relevant features must be extracted from the speech data. Traditionall...

Network-on-chip (NoC) architectures have become a popular communication platform for heterogeneous computing systems owing to their scalability and high performance. Aggressive technology scaling makes these architectures prone to both permanent and transient faults. This study focuses on the tolerance of a NoC router to permanent faults. A permane...

Recent innovation, growth, and deployment of internet of things (IoT) networks are changing the daily life of people. 5G networks are widely deployed around the world, and they are important for continuous growth of IoT. The next generation cellular networks and wireless sensor networks (WSN) make the road to the target of the next generation IoT n...

In this paper, considering a seamless control of an unmanned aerial vehicle (UAV) by a ground base station (GBS), the energy consumption of the UAV is minimized in the downlink communication from the GBS with multiple antennas to the UAV with two antennas. By exploiting the benefit of a space–time line code (STLC) scheme that does not require train...

This paper proposes the application of a space–time line code (STLC) scheme to vehicular-to-roadside unit communication systems. For the STLC encoding, channel state information is estimated before the data transmission. Thus, owing to the channel variation, the discrepancy between the estimated and actual channels degrades the communication perfor...

The Internet of Things (IoT) is a world of connected networks and modern technology devices, among them vehicular networks considered more challenging due to high speed and network dynamics. Future trends in IoT allow these inter networks to share information. Also, the previous security solutions to vehicular IoT (VIoT) much emphasize on privacy p...

In this paper, we investigate a secure dual-hop radio frequency-free space optical (RF-FSO) mixed variable gain relaying framework in the presence of a single eavesdropper. The RF and FSO links are modeled with hyper Gamma (HG) and Gamma-Gamma (ΓΓ) fading channels, respectively. We assume that the eavesdropper utilizes another HG fading channel to...

The integration of unmanned aerial vehicles (UAVs) with a cognitive radio (CR) technology can improve the spectrum utilization. However, UAV network services demand reliable and secure communications, along with energy efficiency to prolong battery life. We consider an energy harvesting UAV (e.g., surveillance drone) flying periodically in a circul...

In 5G, low latency and high reliability have become the most significant issues in addition to ultra-high throughput and support of massive number of devices. To achieve the goal of low latency, the concept of tactile Internet has been introduced. To reduce the latency, the various techniques, which can be applied to from the physical layer to the...