https://scholar.dgist.ac.kr/handle/20.500.11750/866 Sat, 04 Apr 2026 17:29:38 GMT 2026-04-04T17:29:38Z https://scholar.dgist.ac.kr/handle/20.500.11750/56365 Title: Heterogeneous Cellular Networks With LoS and NLoS Transmissions-The Role of Massive MIMO and Small Cells Author(s): Zhang, Qi; Yang, Howard H.; Quek, Tony Q. S.; Lee, Je Min Abstract: We develop a framework for downlink heterogeneous cellular networks with line-of-sight (LoS) and non-line-of-sight (NLoS) transmissions. Using stochastic geometry, we derive tight approximation of average downlink rate that enables us to compare the performance between densifying small cells and expanding BS antenna arrays. Interestingly, we find that adding small cells into the network improves the downlink rate much faster than expanding antenna arrays at the macro BS. However, when the small cell density exceeds a critical threshold, the spatial densification will lose its benefits and further impair the network capacity. To this end, we provide the optimal small cell density that maximizes the rate via numerical results for practical deployment guidance. In contrast, expanding macro BS antenna array can always benefit the capacity until an upper bound caused by pilot contamination, and this bound also surpasses the peak rate obtained from deployment of small cells. Furthermore, we find that allocating part of antennas to distributed small cell BSs works better than centralizing all antennas at the macro BS, and the optimal allocation proportion is also given numerically for practical configuration reference. In summary, this work provides a further understanding on how to leverage small cells and massive MIMO in future heterogeneous cellular networks deployment. IEEE Thu, 30 Nov 2017 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/56365 2017-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/46612 Title: Precoding Design for Ensuring Data Freshness in Multi-user MISO Networks Author(s): Kim, Minsu; Lee, Jemin; Huang, Kaibin Abstract: The existing multiple-input single-output (MISO) design to transmit data reliably to multiple mobile users (MUs) has become insufficient as MUs require fresh data, not just data. Therefore, in this paper, we consider multi-user MISO networks, where a base station (BS) equipped with multiple antennas serves MUs that want to maintain data freshness. To analyze the data freshness in this network, we first define the age-of-information (AoI) violation ratio, which is the ratio of duration that the AoI is larger than the AoI violation threshold to a sensing period. We then obtain the upper bound on the AoI violation ratio using the smooth maximum/minimum unit. We consider an optimization problem that minimizes the AoI violation ratio of multiple MUs. We propose a generalized power iteration (GPI) precoding algorithm to find a principal precoding vector that satisfies a first-order optimality condition of the optimization problem. Furthermore, for the scenario where the BS has the imperfect channel state information (CSI) of MUs, we provide the upper bound on the AoI violation time using the lower bound on the ergodic spectral efficiency, and also design the GPI precoding algorithm. Simulation results show proposed methods outperform baseline methods and demonstrate the effect of network parameters on the AoI violation probability. © 2023 IEEE Thu, 29 Feb 2024 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/46612 2024-02-29T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/17158 Title: EC-SVC: Secure CAN Bus In-Vehicle Communications with Fine-grained Access Control Based on Edge Computing Author(s): Yu, Donghyun; Hsu, Ruei-Hau; Lee, Jemin; Lee, Sungjin Abstract: In-vehicle communications are not designed for message exchange between the vehicles and outside systems originally. Thus, the security design of message protection is insufficient. Moreover, the internal devices do not have enough resources to process the additional security operations. Nonetheless, due to the characteristic of the in-vehicle network in which messages are broadcast, secure message transmission to specific receivers must be ensured. With consideration of the facts aforementioned, this work addresses resource problems by offloading secure operations to high-performance devices, and uses attribute-based access control to ensure the confidentiality of messages from attackers and unauthorized users. In addition, we reconfigure existing access control based cryptography to address new vulnerabilities arising from the use of edge computing and attribute-based access control. Thus, this paper proposes an edge computing-based security protocol with fine-grained attribute-based encryption using a hash function, symmetric-based cryptography, and reconfigured cryptographic scheme. In addition, this work formally proves the reconfigured cryptographic scheme and security protocol, and evaluates the feasibility of the proposed security protocol in various aspects using the CANoe software. IEEE Mon, 31 Jan 2022 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/17158 2022-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/15478 Title: Base Station Coordination Scheme for Multi-tier Ultra-dense Networks Author(s): Mukherjee, Sudanshan; Kim, Dongsun; Lee, Jemin Abstract: In this paper, we consider a relative received link power (RRLP)-based coordinated multi-point (CoMP) joint transmission (JT) in the multi-tier ultra-dense networks (UDN). In this CoMP scheme, we identify the cooperating base stations (BSs) by comparing the average received link power (ARLP) of the neighbouring BSs with respect to the BS having the strongest ARLP (i.e., the main link BS) to a user. To analyze the performance of this CoMP scheme in the downlink multi-tier UDN, we first approximate the received signal power distribution, and derive the coverage probability using stochastic geometry. After revisiting the area spectral efficiency (ASE) to make it more suitable for CoMP transmission in UDN, we also analyze the ASE and the network energy efficiency (NEE). Using simulations, we validate the derived coverage probability, and investigate the CoMP performance in multi-tier UDN. Our simulations show that the RRLP-based CoMP scheme can outperform the fixed number of strongest BS-based CoMP scheme in the high BS density regime. Our study of the NEE performance reveals that not only the RRLP-based CoMP scheme is more efficient than conventional non-CoMP transmission scenario, but also its NEE performance improves with the average number of cooperating BSs. © 2002-2012 IEEE. Sun, 31 Oct 2021 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/15478 2021-10-31T15:00:00Z