• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권6호
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• pp.1996-2013
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• 2015

This paper considers a scenario that more D2D users exist in the cell, they compete for cellular resources to increase their own data rates, which may cause transmission interference to cellular users (CU) and the unfairness of resource allocation. We design a resource allocation scheme for selfish D2D users assisted by cooperative relay technique which is used to further enhance the users' transmission rates, meanwhile guarantee the QoS requirement of the CUs. Two transmission modes are considered for D2D users: direct transmission mode and cooperative relay transmission mode, both of which reuses the cellular uplink frequency resources. To ensure the fairness of resource distribution, Nash bargaining theory is used to determine the transmission mode and solve the bandwidth allocation problem for D2D users choosing cooperative relay transmission mode, and coalition formation game theory is used to solve the uplink frequency sharing problem between D2D users and CUs through a new defined "Selfish order". Through theoretical analysis, we obtain the closed Nash bargaining solution under CUs' rate constraints, and prove the stability of the formatted coalition. Simulation results show that the proposed resource allocation approach achieves better performance on resource allocation fairness, with only little sacrifice on the system sum rates.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권7호
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• pp.2650-2667
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• 2021

In this paper, we derive the expression of the cache hitting probability with random caching policy and propose the joint optimization algorithm based on difference of convex algorithm (DCA) in the three-tier caching heterogeneous cellular network assisted by macro base stations, helpers and users. Under the constraint of the caching capacity of caching devices, we establish the optimization problem to maximize the cache hitting probability of the network. In order to solve this problem, a convex function is introduced to convert the nonconvex problem to a difference of convex (DC) problem and then we utilize DCA to obtain the optimal caching probability of macro base stations, helpers and users for each content respectively. Simulation results show that when the density of caching devices is relatively low, popular contents should be cached to achieve a good performance. However, when the density of caching devices is relatively high, each content ought to be cached evenly. The algorithm proposed in this paper can achieve the higher cache hitting probability with the same density.

• 한국컴퓨터정보학회논문지
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• 제22권9호
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• pp.41-47
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• 2017

In this paper, we consider the case where D2D users and the cellular user share the uplink of the cellular system. We propose an iterative power control algorithm that converges to the optimum power value. Each user iteratively updates its transmit power level according to the interference function. Finally, all D2D users and cellular user that participate in the transmission get the optimum transmit power level. We first investigate the interference structure and define the interference function. Then, we show that the considered interference function belongs to the standard interference function that converges the unique transmit power level. Through numerical examples, the convergence of the proposed power control algorithm is examined in the various transmission scenarios.

• 한국위성정보통신학회논문지
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• 제9권2호
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• pp.101-106
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• 2014

최근 전 세계적으로 전자가격 표시기 시스템이 매장 및 유통업체에서 활성화됨에 따라 2.4GHz의 동일 대역을 사용하는 무선단말기의 Wi-Fi 통신과 간섭현상이 발생하게 되었다. 무선단말기에 의한 전자가격표시기 시스템의 간섭영향을 분석하기 위해 간섭시나리오와 확장된 하타 전파모델을 설정하였다. 심캣을 적용하여 시뮬레이션을 수행하여 무선단말기 간섭으로부터 전자가격표시기 시스템의 태그를 보호하기 위한 이격거리를 도출하였다.

• 한국컴퓨터정보학회논문지
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• 제24권7호
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• pp.79-85
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• 2019

We investigate the D2D utility maximization in the cellular system. We focus on the non cooperative game theoretic approach to maximize the individual utility. Cellular system's perspective, interference from the D2D links must be limited to protect the cellular users. To accommodate this interference issue, utility function is first defined to control the individual D2D user's transmit power. More specifically, utility function includes the pricing which limits the individual D2D user's transmit power. Then, non cooperative power game is formulated to maximize the individual utility. Distributed algorithm is proposed to maximize the individual utility, while limiting the interference. Convergence of the proposed distributed algorithm is verified through computer simulation. Also the effect of pricing factor to SIR and interference is provided to show the performance of the proposed distributed algorithm.

• 한국컴퓨터정보학회논문지
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• 제24권5호
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• pp.19-26
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• 2019

In this paper, we consider the D2D Transmitter(Tx) and Receiver(Rx) pair assignment problem in the cellular system. Sharing the resource of the cellular system, D2D users may cause interference to the cellular system, though it is beneficial to improve the D2D user Capacity. Therefore, to protect the cellular users, D2D transmit power should be carefully controlled. Previously, optimal Tx-Rx assignment to minimize the total transmit power of users was investigated. Accordingly, the iterative algorithm to find the optimum Tx-Rx asignment was obtained. In this work, we consider the case where Tx group users becomes Rx group users, and Rx group users become Tx group users. We prove that the Tx-Rx assignment problem has the duality property. We present the numerical examples that show the duality between U-link and D-link.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 춘계종합학술대회 A
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• pp.237-242
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• 2008

A number of wireless technologies have been implemented, but each technology has its limitation in terms of coverage and bandwidth. WLAN and 3G cellular network has emerged to be a complementary platform for wireless data communications. However, the mobility of roaming terminals in heterogeneous networks poses several risks. To maintain secure communications in universal roaming, the effective authentication must be implemented. The focus of this paper is on analysis of authentication architecture involved in integrated WLAN/3G networks.

• 한국통신학회논문지
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• 제19권3호
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• pp.560-572
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• 1994

본 논문에서는 셀룰라 CDMA 이동통신 시스팀에서 다중 경로의 페이딩 채널을 보상하기위한 레이크 수신기를 설계한다. 다중 경로 페이딩 환경에서의 임펄스 응답을 측정하기 위해 기지국에서 파일롯 채널을 통해 전송되는 short PN 부호의 부분상관함수 특성을 이용하였다. 약 10 s의 다중 경로 퍼짐을 보상하기위해 12개의 역확산 경로를 사용하였으며 보상 방법에 대한 앨고리듬을 제시하였다. 디지틀 변환되어 입력되는 수신신호를 처리하기위해 전 디지틀화된 회로를 제시하고 컴퓨터 시뮬레이션 및 타이밍 시뮬레이션에 의해 회로의 타당성을 검증한다.

• 한국통신학회논문지
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• 제37권7C호
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• pp.584-591
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• 2012

Distributing a Certificate Revocation List (CRL) quickly to all vehicles in the system requires a very large number of road side units (RSUs) to be deployed. In reality, initial deployment stage of vehicle networks would be characterized by limited infrastructure as a result in very limited vehicle to infrastructure communication. However, every vehicle wants the most recent CRLs to protect itself from malicious users and malfunctioning equipments, as well as to increase the overall security of the vehicle networks. To address this challenge, we design and implement a nomadic device based CRL acquisition method using nomadic device's communication capability with cellular networks. When a vehicle could not directly communicate with nearby RSUs, the nomadic device acts as a security mediator to perform vehicle's security functions continuously through cellular networks. Therefore, even if RSUs are not deployed or sparsely deployed, vehicle's security threats could be minimized by receiving the most recent CRLs in a reasonable time.

• 한국통신학회논문지
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• 제25권10A호
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• pp.1480-1485
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• 2000

본 논문은 디지틀 셀룰러 이동전화를 위한 효과적인 동기시퀀스 설계에 대하여 기술하였다. 논문에서 연구된 동기시퀀스의 종류는 시프트 되지 않은 시퀀스와 가운데로 지연 시프트된 시퀀스에서 극성이 반대이고 크기가 같은 두 개의 피크값을 갖고, 그 외 다른 모든 지연에서 가장 낮은 자기상관함수값을 갖는다. 이들 동기시퀀스들은 동기 타이밍을 이중점검하고 동기탐색시간을 줄이기 위해서 이용될 수 있다.