• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2323-2340
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• 2012

Recent advances in cognitive radio technology have drawn immense attention to higher layer protocols above medium access control, such as transmission control protocol (TCP). Most proposals to improve the TCP performance in cognitive radio (CR) networks have assumed that either all nodes are in CR networks or the TCP sender side is in CR links. In those proposals, lower layer information such as the CR link status could be easily exploited to adjust the congestion window and improve throughput. In this paper, we consider a TCP network in which the TCP sender is located remotely over the Internet while the TCP receiver is connected by a CR link. This topology is more realistic than the earlier proposals, but the lower layer information cannot be exploited. Under this assumption, we propose an enhanced TCP protocol for CR networks called TCP for cognitive radio (TCP-CR) to improve the existing TCP by (1) detection of primary user (PU) interference by a remote sender without support from lower layers, (2) delayed congestion control (DCC) based on PU detection when the retransmission timeout (RTO) expires, and (3) exploitation of two separate scales of the congestion window adapted for PU activity. Performance evaluation demonstrated that the proposed TCP-CR achieves up to 255% improvement of the end-to-end throughput. Furthermore, we verified that the proposed TCP does not deteriorate the fairness of existing TCP flows and does not cause congestions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권4호
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• pp.1768-1789
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• 2016

In contemporary video streaming systems based on HTTP protocol, video players at the client side are responsible for adjusting video quality to network conditions and user expectations. However, when multiple video clips are streamed simultaneously, an intricate application logic implemented in the video players overlays the TCP mechanism which is responsible for a balanced access to a shared network link. As a result, some video players may not obtain a fair share of network throughput and may be vulnerable to an unstable video bit-rate. Therefore, we propose to simplify the algorithms implemented in the video players, which are responsible for the adjustment of video quality and constrain their functionality only to sending feedback to a server about a state of the player buffer. The main logic of the system is shifted to the server, which is now responsible for bit-rate selection and prioritisation of the video streams transmitted to multiple clients. To verify our proposition, we performed several experiments in a laboratory environment which show that when the server cooperates with the clients, the video players experience fewer quality switches and the system achieves better fairness when allocating network throughput among the video players. However, this comes at the cost of worse utilisation of network bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2081-2101
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• 2016

Successive interference cancellation (SIC) is considered to be a promising technique to mitigate multi-user interference and achieve concurrent uplink transmissions, but the optimal power allocation (PA) issue for SIC users is not well addressed. In this article, we focus on the optimization of the PA ratio of users on an SIC channel and analytically obtain the optimal PA ratio with regard to the signal-to-interference-plus-noise ratio (SINR) threshold for successful demodulation and the sustainable demodulation error rate. Then, we design an efficient resource allocation (RA) scheme using the obtained optimal PA ratio. Finally, we compare the proposal with the near-optimum RA obtained by a simulated annealing search and the RA scheme with random PA. Simulation results show that our proposal achieves a performance close to the near-optimum and much higher performance than the random scheme in terms of total utility and Jain's fairness index. To demonstrate the applicability of our proposal, we also simulate the proposal in various network paradigms, including wireless local area network, body area network, and vehicular ad hoc network.

• 한국정보통신학회논문지
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• 제18권7호
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• pp.1540-1546
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• 2014

인도어 기지국(Indoor BS) 결함으로 인해 발생하는 커버리지홀 문제를 해결하기 위하여, 새로운 프레임 구조와 최적화 기법 기반의 실제적인 알고리즘을 제안한다. 우리의 핵심 공헌은 다음과 같다: 1) 갑작스런 IBS 결함 문제 해결을 위한 힐링(healing) 채널을 가지는 새로운 프레임 구조를 제안하고 2) 최적화 문제의 복잡도 감소를 위한 고정적 IBS 선택에 기반한 효과적인 휴리스틱 자원할당 알고리즘을 제안한다. 시뮬레이션을 통하여 평균 셀 용량과 사용자 공평성 관점에서 기존 알고리즘에 비해 제안 방안이 우수함을 증명한다.

• ETRI Journal
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• 제42권2호
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• pp.175-185
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• 2020

Inter-cell interference (ICI) is a major problem in heterogeneous networks, such as two-tier femtocell (FC) networks, because it leads to poor cell-edge throughput and system capacity. Dynamic ICI coordination (ICIC) schemes, which do not require prior frequency planning, must be employed for interference avoidance in such networks. In contrast to existing dynamic ICIC schemes that focus on homogeneous network scenarios, we propose a novel semi-distributed dynamic ICIC scheme to mitigate interference in heterogeneous network scenarios. With the goal of maximizing the utility of individual users, two separate algorithms, namely the FC base station (FBS)-level algorithm and FC management system (FMS)-level algorithm, are employed to restrict resource usage by dominant interference-creating cells. The distributed functionality of the FBS-level algorithm and low computational complexity of the FMS-level algorithm are the main advantages of the proposed scheme. Simulation results demonstrate improvement in cell-edge performance with no impact on system capacity or user fairness, which confirms the effectiveness of the proposed scheme compared to static and semi-static ICIC schemes.

• 정보처리학회논문지A
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• 제12A권2호
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• pp.117-126
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• 2005

대규모 멀티컴퓨터 시스템에서 단편화를 줄일 수 있는 적응성 있는 프로세서 할당 기법을 제안한다. 큰 크기의 서브메쉬 할당을 요구하는 작업들의 개수가 적을 경우에도 나머지 작업들의 대기 큐의 지연시간이 증가할 수 있다. 이런 상황에서 할당이 불가능한 기존의 기법들과 달리, L-모양 서브메쉬를 할당할 수 있으며, 할당 가능한 L-모양 서브메쉬를 효율적으로 탐색하는 알고리즘을 개발하였다. 그러므로 FCFS로 스케쥴링되어도, 대기 큐의 지연시간을 줄임으로써 평균응답시간을 줄일 수 있다. 시뮬레이션 결과를 통해서 제안하는 기법이 외부 단편화, 작업응답시간, 그리고 시스템의 활용도 면에서 다른 기법들보다 우수함을 보인다.

• 한국통신학회논문지
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• 제30권2A호
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• pp.61-65
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• 2005

본 논문에서는 DVB-RCS (Digital Video Broadcast-Return Channel via Satellite) 망에서 호 수락제어 (CAC)를 위한 Soft-QoS 기반의 borrowing 기법을 제안한다. 제안된 기법은 위성 망에서 사용 가능한 자원이 부족할 때 새로운 호를 받아들이기 위해 서비스 중인 호 중 일부에서 일시적이고 공평하게 대역폭을 가져온다. 각각의 호에서 가져오는 대역폭의 양은 각 사용자의 critical bandwidth ratio에 비례하며 critical bandwidth ratio는 제안된 기법에서 이용하는 QoS 파라메타 중 하나이다. 시뮬레이션 결과는 제안된 기법이 호의 blocking 확률과 대역폭 효율 측면에서 성능의 향상이 있음을 보여준다.

• 한국전자통신학회논문지
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• 제16권4호
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• pp.611-616
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• 2021

본 논문은 상관 관계 중첩 코딩/non-SIC 비직교 다중 접속의 향상된 outage 확률을 고찰한다. 먼저, 기존의 독립 중첩 코딩/SIC 비직교 다중 접속의 outage 확률을 고찰한다. 다음, 모의실험을 통하여, 상관 관계 중첩 코딩/non-SIC 비직교 다중 접속의 outage 확률이 독립 중첩 코딩/SIC 비직교 다중 접속의 outage 확률에 비하여 크게 향상되는 것을 입증한다. 결론으로, 이러한 향상된 outage 확률로 인하여, 상관 관계 중첩 코딩/non-SIC 비직교 다중 접속 기술은 5G 시스템의 유망한 기술이 될 수도 있다.

• ETRI Journal
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• 제45권1호
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• pp.45-59
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• 2023

In this paper, to optimize the average delay and power allocation (PA) for system users, we propose a resource scheduling scheme for wireless networks based on Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) according to the first fifth-generation standards. For delay minimization, we solve a throughput maximization problem that considers CPOFDM systems with carrier aggregation (CA). Regarding PA, we consider an approach that involves maximizing goodput using an effective signal-to-noise ratio. An algorithm for jointly solving delay minimization through computation of required user rates and optimizing the power allocated to users is proposed to compose the resource allocation approach. In wireless network simulations, we consider a scenario with the following capabilities: CA, 256-Quadrature Amplitude Modulation, millimeter waves above 6 GHz, and a radio frame structure with 120 KHz spacing between the subcarriers. The performance of the proposed resource allocation algorithm is evaluated and compared with those of other algorithms from the literature using computational simulations in terms of various Quality of Service parameters, such as the throughput, delay, fairness index, and loss rate.

• Journal of Information Technology Applications and Management
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• 제31권3호
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• pp.149-163
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• 2024

As conversational AI systems such as ChatGPT have become more advanced, researchers are exploring ways to use them in education. However, we need effective ways to evaluate these systems before allowing them to help teach students. This study proposes a detailed framework for testing conversational AI across three important criteria as follow. First, specialized benchmarks that measure skills include giving clear explanations, adapting to context during long dialogues, and maintaining a consistent teaching personality. Second, adaptive standards check whether the systems meet the ethical requirements of privacy, fairness, and transparency. These standards are regularly updated to match societal expectations. Lastly, evaluations were conducted from three perspectives: technical accuracy on test datasets, performance during simulations with groups of virtual students, and feedback from real students and teachers using the system. This framework provides a robust methodology for identifying strengths and weaknesses of conversational AI before its deployment in schools. It emphasizes assessments tailored to the critical qualities of dialogic intelligence, user-centric metrics capturing real-world impact, and ethical alignment through participatory design. Responsible innovation by AI assistants requires evidence that they can enhance accessible, engaging, and personalized education without disrupting teaching effectiveness or student agency.