arXiv subjects

Seungmo Kim

Publications and source records attributed to Seungmo Kim.

36 records · Page 2Linked to original sources

arXiv2020

Analysis of Human Exposure to Electromagnetic Fields in 5G Uplink and Downlink

Concern has been widely acknowledged about human health---e.g., heating of the eyes and skin--from exposure to electromagnetic fields (EMF) produced by wireless transmitters. Mobile telecommunications rely on an extensive network of base stations (BSs) and handheld devices that transmit signals via EMF. There is chance of aggravation due to two important changes that will be seen in future cellular networks. First, the number of BSs will remarkably grow with the proliferation of small-cell networks, which will expose humans to EMF more often. Second, highly concentrated EMF beams will be generated by employing larger antenna arrays to overcome faster EMF energy attenuation in higher-frequency bands such as millimeter wave (mmW) spectrum, which will increase damage if the main beam points to the human body. However, the two changes can be exploited as leverages for (i) wider selection of alternative BSs and (ii) more precise beamforming to a desired user equipment (UE) with less EMF leakage to other directions, respectively. Harnessing the two changes, we have been investigating the human health impacts of 5G wireless systems. This extended abstract summarizes our findings thus far.

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arXiv2020

Mitigation of Human RF Exposure in Wearable Communications

A major concern regarding wearable communications is human biological safety under exposure to radio frequency (RF) radiation generated by wearable devices. The biggest challenge in the implementation of wearable devices is to reduce the usage of energy to minimize the harmful impacts of exposure to RF on human health. Power management is one of the key energy-saving strategies used in wearable networks. Signals enter the receiver (Rx) from a transmitter (Tx) through the human body in the form of electromagnetic field (EMF) radiation produced during the transmission of the packet. It may have a negative effect on human health as a result of specific absorption rate (SAR). SAR is the amount of radio frequency energy consumed by human tissue in mass units. The higher the body's absorption rate, the more radio frequency radiation. Therefore, SAR can be reduced by distributing the power over a greater mass or tissue volume equivalently larger. The Institute of Electrical and Electronics Engineers (IEEE) 802.15.6-supported multi-hop topology is particularly useful for low-power embedded devices that can reduce consumption of energy by communicating to the receiver (Rx) through nearby transmitted devices. In this paper, we suggest a relaying mechanism to minimize the transmitted power and, as a consequence, the power density (PD), a measure of SAR.

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arXiv2020

Prioritization of Basic Safety Message in DSRC Based on Distance to Danger

Many parties claim the technical significance of Dedicated Short-Range Communications (DSRC) in intelligent transportation system (ITS) for promotion of transportation safety. The main challenge in this key vehicle-to-everything (V2X) standard is high odds of network congestion. Furthermore, in accordance with a V2X network being inherently dynamic in key parameters such as vehicle density and velocity, the networking behavior of a DSRC system is usually highly complicated to analyze. In addition, the United States Federal Communications Commission (US FCC) recently announced the "5.9 GHz band reform," which reduced the dedicated bandwidth for DSRC to 10 MHz from 75 MHz. Motivated from these, the necessity of "lightening" the networking load of a DSRC network has become essential to keep safety-related operations without performance deterioration. To this end, this paper proposes a protocol that prioritizes transmission of a basic safety message (BSM) at a vehicle according to the level of danger that the vehicle experiences. The proposed protocol uses the distance between a danger source and a vehicle as the metric to determine the priority for transmission. Our results show that this protocol prioritizes the transmission opportunity to dangerous vehicles, and hence results in higher performance in terms of key metrics--i.e., average delay, throughput, and inter-reception time ($\mathsf{IRT}$).

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arXiv2020

Adequacy of 5.9 GHz Band for Safety-Critical Operations with DSRC

The recent reform of the 5.9 GHz by the United States Federal Communications Commission (FCC) provoked the need for lightening the load of a vehicle-to-everything (V2X) communications network based on Dedicated Short Range Communications (DSRC). We have collected mathematical analyses and numerical results supporting our proposal of lightening a DSRC network by prioritizing the transmission based on the risk of accident to which a vehicle is exposed.

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arXiv2020

Human Electromagnetic Field Exposure in 5G at 28 GHz

The fifth-generation wireless (5G) has already started showing its capability to achieve extremely fast data transfer, which makes itself considered to be a promising mobile technology. However, concerns have been raised on adverse health impacts that human users can experience in a 5G system by being exposed to electromagnetic fields (EMFs). This article investigates the human EMF exposure in a 5G system and compare to those measured in the previous-generation cellular systems. It suggests a minimum separation distance between a transmitter and a human user for keeping the EMF exposure below the safety regulation level, which provides consumers with a general understanding on the safe use of 5G communications.

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arXiv2020

Reinforcement Learning for Accident Risk-Adaptive V2X Networking

The significance of vehicle-to-everything (V2X) communications has been ever increased as connected and autonomous vehicles get more emergent in practice. The key challenge is the dynamicity: each vehicle needs to recognize the frequent changes of the surroundings and apply them to its networking behavior. This is the point where the need for machine learning is highlighted. However, the learning itself is extremely complicated due to the dynamicity as well, which necessitates that the learning framework itself must be resilient and flexible according to the environment. As such, this paper proposes a V2X networking framework integrating reinforcement learning (RL) into scheduling of multiple access. Specifically, the learning mechanism is formulated as a multi-armed bandit (MAB) problem, which enables a vehicle, without any assistance from external infrastructure, to (i) learn the environment, (ii) quantify the accident risk, and (iii) adapt its backoff counter according to the risk. The results of this paper show that the proposed learning protocol is able to (i) evaluate an accident risk close to optimal and (ii) as a result, yields a higher chance of transmission for a dangerous vehicle.

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arXiv2020

Danger Aware Vehicular Networking

IEEE 802.11p is one of the key technologies that enable Dedicated Short-Range Communications (DSRC) in intelligent transportation system (ITS) for safety on the road. The main challenge in vehicular communication is the large amount of data to be processed. As vehicle density and velocity increases, the data to be transmitted also increases. We proposed a protocol that reduces the number of messages transmitted at a vehicle according to the level of danger that the vehicle experiences. The proposed protocol measures inter-vehicle distance, as the representative of the danger of a vehicle, to determine the priority for transmission. Our results show that this prioritization of transmissions directly reduces the number of transmitters at a time, and hence results in higher performance in terms of key metrics--i.e., PDR, throughput, delay, probabilities of channel busy and collision.

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arXiv2020

Stochastic Analysis on Downlink Performance of Coexistence between WiGig and NR-U in 60 GHz Band

The 60 GHz band (57-71 GHz) has been attracting considerable research interest thanks to the bandwidth abundance and ruling as an unlicensed band. The 60 GHz Wi-Fi (also known as WiGig) and 5G New Radio Unlicensed (NR-U) are among the key access technologies that will operate in the band. This paper inspects the downlink performance of the two technologies under inter-technology interference from each other in 60 GHz band. Based on a dense small-cell setting, this paper finds stochastic models for signal-to-interference-plus-noise ratio (SINR) and data rate. Via simulations, this paper discovers that the downlink SINR and data rate follow Gaussian mixture distributions with three modes representing (i) severely interfered, (ii) mildly interfered, and (iii) not interfered UEs.

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arXiv2020

5G or Wi-Fi for HA/DR in the 60 GHz Band?

This paper studies the feasibility of Wi-Fi and 5G technologies in the unlicensed 60 GHz band for humanitarian assistance and disaster relief (HA/DR) operations. Building a wireless communications system in the 60 GHz band can benefit HA/DR activities for two reasons: (i) no license is needed; (ii) a wide bandwidth is available. Our simulation results show that both of Wi-Fi and 5G can achieve data rates exceeding the requirements for most of the HA/DR missions, which proves the feasibility of the two wireless technologies for operation of high-data-rate HA/DR activities such as real-time video streaming.

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arXiv2020

Mitigation of Civilian-to-Military Interference in DSRC for Urban Operations

Dedicated short-range communications (DSRC) attracts popularity in the military applications thanks to its easiness in establishment, no need for paid subscription, and wide compatibility with any other IEEE 802.11 standards. The main challenge in DSRC is congestion due to existence of only 7 channels, which may not be enough to accommodate the increased number of transmitters expected to be deployed in the near future. Recently, there are a myriad of urban operation scenarios for the military including urban warfare and humanitarian assistance/disaster relief (HA/DR). The key challenge is that the communications among the military vehicles can be interfered by civilian users. It is the desire that the messages transmitted by the military vehicles hold a higher significance so that they can avoid the interference coming from the civilian users, which is not supported in the current version of DSRC. As a remedy, this paper proposes a protocol that prioritizes the military DSRC users while muffling the civilian DSRC users. Our results show that this prioritization method achieves higher communications performances for the military DSRC users.

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arXiv2020

Human EMF Exposure in Wearable Networks for Internet of Battlefield Things

Numerous antenna design approaches for wearable applications have been investigated in the literature. As on-body wearable communications become more ingrained in our daily activities, the necessity to investigate the impacts of these networks burgeons as a major requirement. In this study, we investigate the human electromagnetic field (EMF) exposure effect from on-body wearable devices at 2.4 GHz and 60 GHz, and compare the results to illustrate how the technology evolution to higher frequencies from wearable communications can impact our health. Our results suggest the average specific absorption rate (SAR) at 60 GHz can exceed the regulatory guidelines within a certain separation distance between a wearable device and the human skin surface. To the best of authors' knowledge, this is the first work that explicitly compares the human EMF exposure at different operating frequencies for on-body wearable communications, which provides a direct roadmap in design of wearable devices to be deployed in the Internet of Battlefield Things (IoBT).

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arXiv2019

Human Electromagnetic Field Exposure in Wearable Communications: A Review

The concern on human health is often overseen while wearable technologies attract exploding interests. Mainly due to the extreme proximity or a direct physical contact to the human skin, wearable communications devices are acknowledged to cause higher levels of specific absorption rate (SAR) at the skin surface. Unfortunately, so far, we have found no study encompassing all the aspects that the general public needs to understand about wearable technologies--i.e., the analytical and experimental backgrounds, and report of SAR levels generated from commercial wearable devices. In this context, this paper provides an extensive review on SAR from various commercial wearable devices that are currently sold in the market, as well as the analytical framework and the current measurement methodologies for standard compliance tests. Moreover, considering the present interest in millimeter wave (mmW), this paper sheds light on the SAR evaluated at 60 GHz and also compares the SAR to that measured at 2.4 GHz. We expect that this paper will be of value in informing the general public of the safety in using the currently sold wearable devices, and in igniting further study of the exact biological consequences from electromagnetic field (EMF) exposure due to wearable devices.

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arXiv2019

Spatiotemporal Analysis on Broadcast Performance of DSRC with External Interference in 5.9 GHz Band

Coexistence between the dedicated short-range communications (DSRC) and other wireless technologies needs thorough study since the United States legislative bodies still remain undecided on the shared use of the 5.9 GHz band (5.850-5.925 GHz). If the band is decided to be shared among multiple technologies, the DSRC is expected to experience a performance degradation even in safety-critical application. As such, it is a natural question how much the performance degradation will be. However, it is not trivial to precisely model the behaviors of a vehicular-to-everything (V2X) network since it requires to formulate both spatial and temporal aspects in concert while the network topology keeps dynamic due to the nodes' mobility. Moreover, DSRC relies on broadcast of basic safety messages (BSMs) for supporting safety-critical applications. Most prior work uses performance metrics such as packet delivery rate (PDR) and packet delay, which cannot accurately capture the performance of DSRC broadcasts. To this end, this paper (i) provides a comprehensive analysis framework formulating both spatial and temporal factors in concert and (ii) proposes a new performance metric that can more accurately characterize the broadcast performance of a DSRC network. Based on the new metric, the results present (i) the fundamental performance of a DSRC network under inter-RAT interference from Wi-Fi and C-V2X and (ii) provide suggestions on optimal selection of networking parameters.

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arXiv2018

Mitigation of Human RF Exposure in 5G Downlink

While research on communications at frequencies above 6 gigahertz (GHz) has been primarily confined to performance improvement, their potentially harmful impacts on human health are not studied as significantly. Most of the existing studies that paid attention to the health impacts above 6 GHz focused only on the uplink due to closer contact with a transmitter to a human body. In this letter, we present the human electromagnetic field (EMF) exposure in the downlink of Fifth-Generation Wireless Systems (5G). Moreover, we propose a downlink protocol that guarantees the EMF exposure under a threshold while keeping the data rate above the 5G requirements.

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arXiv2018

Mitigation of Human Exposure to RF Fields in Downlink of Millimeter-Wave Cellular Systems

Out of the very few studies that paid proper attention to the harmful health impacts in millimeter-wave (mmW) communications, most of them are concerned about uplink cases due to closer contact with the human body. Our recent study revealed that even the human exposure to radio frequency (RF) fields in downlink mmW technology is not very minimum to be ignored. There were a few RF exposure mitigation techniques for uplinks, but the downlink scenario is hardly paid any attention. However, this paper proposes a downlink protocol for mmW cellular communications that achieves the maximum data rate while keeping the impacts on human health minimized. Our results show that the proposed technique lowers both power density (PD) and specific absorption rate (SAR) compared to the typical protocol, with only slight sacrifice in data rates.

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arXiv2017

Human Exposure to RF Fields in 5G Downlink

While cellular communications in millimeter wave (mmW) bands have been attracting significant research interest, their potential harmful impacts on human health are not as significantly studied. Prior research on human exposure to radio frequency (RF) fields in a cellular communications system has been focused on uplink only due to the closer physical contact of a transmitter to a human body. However, this paper claims the necessity of thorough investigation on human exposure to downlink RF fields, as cellular systems deployed in mmW bands will entail (i) deployment of more transmitters due to smaller cell size and (ii) higher concentration of RF energy using a highly directional antenna. In this paper, we present human RF exposure levels in downlink of a Fifth Generation Wireless Systems (5G). Our results show that 5G downlink RF fields generate significantly higher power density (PD) and specific absorption rate (SAR) than a current cellular system. This paper also shows that SAR should also be taken into account for determining human RF exposure in the mmW downlink.

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arXiv2017

A Geometric Analysis Method for Evaluation of Coexistence between DSRC and Wi-Fi at 5.9 GHz

Co-channel coexistence between Dedicated Short-Range Communications (DSRC) and Wi-Fi needs thorough study. The reason is that although the 5.850-5.925 GHz (5.9 GHz) band has been reserved for DSRC so far, the U.S. government is moving swiftly on opening the band to be shared with Wi-Fi. However, most prior work lacks sufficient scientific rigor by relying on performance metrics such as packet delivery rate (PDR) and packet delay that cannot accurately measure performance of a vehicular network that primarily uses broadcast in dissemination of packets. Precise analysis of such broadcast operation is essential for rigorous investigation of DSRC-Wi-Fi coexistence because most safety-critical applications of DSRC operate based on broadcast. This paper proposes a new metric that can more accurately characterize the performance of a broadcast-based DSRC network. The new metric is used to (i) characterize coexistence of DSRC with IEEE 802.11ac-based Wi-Fi and (ii) suggest selection of key medium access control (MAC) parameters for DSRC: inter-broadcast interval (IBI) and contention window (CW).

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arXiv2017

Coexistence of Outdoor Wi-Fi and Radar at 3.5 GHz

Coexistence between radar and outdoor Wireless Fidelity (Wi-Fi) needs thorough study since the IEEE 802.11 Working Group (WG) opposed the latest rules in 3550-3700 MHz (the 3.5 GHz band) that require "exclusion zones." This letter proposes a method that suppresses Wi-Fi-to-radar (WtR) interference, in which a Wi-Fi transmitter (TX) is selected to avoid beam angles toward the victim radar. It is distinguished from prior schemes since it ensures that the Wi-Fi remains operable while suppressing the WtR interference.

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