• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.1313-1336
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• 2020

Cognitive radio (CR) is regarded as an effective approach to avoid the inefficient use of spectrum. However, CRNs have more special security problems compared with the traditional wireless communication systems due to its open and dynamic characteristics. Primary user emulation attack (PUEA) is a common method which can hinder secondary users (SUs) from accessing the spectrum by transmitting signals who has the similar characteristics of the primary users' (PUs) signals, and then the SUs' quality of service (QoS) cannot be guaranteed. To handle this issue, we first design a multiple-phase energy detection scheme based on the cooperation of multiple SUs to detect the PUEA more precisely. Second, a joint SUs scheduling and power allocation scheme is proposed to maximize the weighted effective capacity of multiple SUs with a constraint of the average interference to the PU. The simulation results show that the proposed method can effectively improve the effective capacity of the secondary users compared with the traditional overlay scheme which cannot be aware of the existence of PUEA. Also the good delay QoS guarantee for the secondary users is provided.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.3
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• pp.950-975
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• 2016

Device-to-Device (D2D) communication underlaying cellular networks is a promising add-on component for future radio communication systems. It provides more access opportunities for local device pairs and enhances system throughput (ST), especially when mobile relays (MR) are further enabled to facilitate D2D links when the channel condition of their desired links is unfavorable. However, mutual interference is inevitable due to spectral reuse, and moreover, selecting a suitable transmission mode to benefit the correlated resource allocation (RA) is another difficult problem. We aim to optimize ST of the hybrid system via joint consideration of mode selection (MS) and RA, which includes admission control (AC), power control (PC), channel assignment (CA) and relay selection (RS). However, the original problem is generally NP-hard; therefore, we decompose it into two parts where a hierarchical structure exists: (i) PC is mode-dependent, but its optimality can be perfectly addressed for any given mode with additional AC design to achieve individual quality-of-service requirements. (ii) Based on that optimality, the joint design of MS, CA and RS can be viewed from the graph perspective and transferred into the maximum weighted independent set problem, which is then approximated by our greedy algorithm in polynomial-time. Thanks to the numerical results, we elucidate the efficacy of our mechanism and observe a resulting gain in MR-aided D2D communication.

• ETRI Journal
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• v.37 no.5
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• pp.867-876
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• 2015

This paper proposes an efficient interference control scheme for vehicular moving networks. The features of the proposed scheme are as follows: radio resources are separated into two resource groups to avoid interference between the cellular and vehicle-to-vehicle (V2V) links; V2V links are able to share the same radio resources for an improvement in the resource efficiency; and vehicles can adaptively adjust their transmission power according to the interference among the V2V links (based on the distributed power control (DPC) scheme derived using the network utility maximization method). The DPC scheme, which is the main feature of the proposed scheme, can improve both the reliability and data rate of a V2V link. Simulation results show that the DPC scheme improves the average signal-to-interference-plus-noise ratio of V2V links by more than 4 dB, and the sum data rate of the V2V links by 15% and 137% compared with conventional schemes.

• Korean System Dynamics Review
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• v.5 no.2
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• pp.125-147
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• 2004

System dynamics model has been developed and computer simulation has been peformed for the evaluation of R&D policy. One of the main results of the basecase scenario is as follows. After simulation of nuclear R&D resource allocation strategies, we discovered that their net benefit value was maximum at 130% nuclear R&D budget case. And after simulation of human resource management strategies and policy research program strategies, we confirmed that it is beneficial to allocate budgets in the early phase for human resources management program and research program for the policy.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.205-206
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• 2008

We propose load balancing algorithm based on cross layer designing for MIMO OFDM system. When there are many users using data service, base station(BS) should distribute traffic. Moreover, cross layer design gives benefit managing radio resource and network bandwidth management. Proposed cross layer load balancing technique manages both BS's bandwidth allocation and MS’s power control. One BS request bandwidth to other BSes and other BSes reduce each bandwidth. And BSes reduce power of sub carriers for reserving available bandwidth of backhaul. MSes that didn't get service can be served by obtaining bandwidth from other BSes. The simulation result shows more users can be served and cell throughput was increased

• ETRI Journal
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• v.19 no.3
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• pp.98-115
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• 1997

The architecture of the CDMA mobile system (CMS) is developed based on three function groups - service resource, service control, and service management groups. In this paper, the CMS architecture is discussed from the point of view of implementing these functions. The variable length packets are used for transmission. The synchronization clock signals are derived form the GPS receiver. The open loop and closed loop techniques are used for the power control. The internationally accepted signaling and network protocols are employed. The call control for the primary services in designed to provide efficient mobile telecommunication services. The softer handoff is implemented in one card. The mobile assisted handoff and the network assisted handoff are employed in the soft and hard handoffs. The authentication is based on the secret data which includes random numbers. The management functions, which include the location management, resource management, cell boundary management and OAM management, are implemented to warrant the system efficiency, maximum capacity and high reliability. The architecture ensures that the CMS is flexible and expandable to provide subscribers with economic and efficient system configuration. The dynamic power control, adaptive channel allocation. and dynamic cell boundary management are recommended for future work.

• International conference on construction engineering and project management
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• 2024.07a
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• pp.799-806
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• 2024

Construction planners for hard rock tunnel projects often encounter practical challenges caused by inherent uncertainties in ground conditions and resource constraints. Therefore, planners cannot rapidly generate optimal excavation schedules for the shortest project durations with a given equipment fleet by considering the uncertainties in ground conditions. Although some schedule optimization methods exist, they are not tailored for resource-constrained hard rock tunnel projects. To overcome these limitations, the authors specified a formal Q-learning-based schedule optimization methodology for resource-constrained hard rock tunnel projects. States are defined according to the locations of tunnel faces under excavation. Actions consist of multiple and comprehensive heuristic-based rules, which are efficient methods for resource allocation. Rewards are the time intervals required between current states and next states. After that, the methodology is validated using a case study. The generated Q tables indicate (1) best actions under different states and (2) the shortest remaining durations when the project starts from specific (state, action) pairs. The results demonstrate that the optimal schedules can be obtained by applying the proposed methodology. Furthermore, it is beneficial for planners to rapidly assign optimal rules for each state under one ground condition scenario. The results further show the potential to consider the uncertainties in ground conditions using the information of possible ground condition scenarios provided.

• Smart Media Journal
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• v.13 no.1
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• pp.45-51
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• 2024

Long Range Wide Area Network (LoRaWAN) is a widely adopted Internet of Things (IoT) protocol due to its high range and lower energy consumption. LoRaWAN utilizes Adaptive Data Rate (ADR) for efficient resource (e.g., spreading factor and transmission power) management. The ADR manages these two resource parameters on the network server side and end device side. This paper focuses on analyzing the ADR and Gaussian ADR performance of LoRaWAN. We have performed NS3 simulation under a static scenario by varying the antenna height. The simulation results showed that antenna height has a significant impact on the packet delivery ratio. Higher antenna height (e.g., 50 m) has shown an improved packet success ratio when compared with lower antenna height (e.g., 10 m) in static and mobility scenarios. Based on the results, it is suggested to use the antenna at higher allevation for successful packet delivery.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.593-600
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• 2002

The reverse link signal power required for multimedia traffic in multipath faded single-code (SC-) and multi-code CDMA (MC-CDMA) systems is investigated. The effect of orthogonality loss among multiple spreading code channels is herein characterized by the orthogonality factor. The required signal power in both the CDMA systems is then analyzed in terms of the relative required signal power ratio of data to voice traffic. The effect of varying system parameters including spreading bandwidth, the of orthogonality factor, and the number of spreading codes are examined. Analytical results show that MC-CDMA users transmitting only a single traffic type require significantly more power than SC-CDMA users with only a single traffic type. On the other hand, MC-CDMA users transmitting multimedia traffic require power levels approximately identical to SC-CDMA users with multimedia traffic. The results can be used in the design of radio resource management (e.g., power allocation) scheme for wireless multimedia services.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.140-150
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• 2003

In this paper, we propose a novel code sharing method for downlink transmission of mobile satellite communication systems using a multibeam geosynchronous-orbit satellite. In the proposed system, spreading codes are shared among downlink beams in order to increase the system capacity. We also propose efficient radio resource and transmit power allocation schemes for the proposed system. Simplified analysis and simulation results on the system capacity show the capacity improvement by the proposed scheme. The simulation results show that the capacity of the proposed system is more than 2 times as large as that of a conventional multibeam satellite system. In the frequency-selective fading channel, the capacity improvement increases as the interference between orthogonal spreading codes decrease.