• Journal of Communications and Networks
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• v.11 no.2
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• pp.134-147
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• 2009

Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the wellknown Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.189-198
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• 2001

In recent years, the predominant part in telecommunications is mobile communications. The next generation network is extending today's voice-only mobile networks to multi-service networks. ATM Network is possible to carry such multi-media traffic and it will be expect to use wireless ATM for the future mobile access network. One of manly important aspects for the performance of wireless ATM is the Medium Access Control (MAC) protocol. The MAC protocol must be able to satisfyingly handle the different ATM services (CBR, VBR, ABR and UBR) with their radically different performance requirements. Additionally, the MAC protocol must be able to cope with the complex radio environment where fading, multi-path propagation interference and burst-errors further complicate the situation. In this paper, a dynamic slot allocation algorithm in wireless ATM is proposed for an efficient channel sharing/media access at the MAC layer. We use equivalent capacity in the allocation of slots for VBR traffic which is variable along the time. It is simple and effective slot allocation method for VBR service. In particular, we consider the slot allocation of a session consisted of several connections for requirement of multimedia traffic. Simulation shows that the cell loss ratio is reduced by re-allocation of extra slots in Mobile Terminal (MT).

• Journal of IKEEE
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• v.4 no.2 s.7
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• pp.212-224
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• 2000

In this paper, a parallel processing system is proposed for improving the processing speed of image related applications. The proposed parallel processing system is fully synchronous SIMD computer with pipelined architecture and consists of processing elements and a multi-access memory system. The multi-access memory system is made up of memory modules and a memory controller, which consists of memory module selection module, data routing module, and address calculating and routing module, to perform parallel memory accesses with the variety of types: block, horizontal, and vertical access way. Morphological filter had been applied to verify the parallel processing system and resulted in faithful processing speed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.18-38
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• 2017

Infrastructure-as-a-Service (IaaS) clouds provide infrastructure as a pool of virtual resources, and the public IaaS clouds, e.g. Amazon Web Service (AWS) and private IaaS cloud toolkits, e.g. OpenStack, CloudStack, etc. provide their own application programming interfaces (APIs) for managing the cloud resources they offer. The heterogeneity of the APIs, however, makes it difficult to access and use the multiple cloud services concurrently and collectively. In this paper, we explore previous efforts to solve this problem and present our own implementation of an integrated cloud API, which can make it possible to access and use multiple clouds collectively in a uniform way. The implemented API provides a RESTful access and hides underlying cloud infrastructures from users or applications. We show the implementation details of the integrated API and performance evaluation of it comparing the proprietary APIs based on our cloud testbed. From the evaluation results, we could conclude that the overhead imposed by our interface is negligibly small and can be successfully used for multi-cloud access.

• Journal of Communications and Networks
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• v.13 no.4
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• pp.408-417
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• 2011

The stringent performance requirement for the high efficiency of routing protocols on the Internet can be satisfied by exploiting the threaded border gateway protocol (TBGP) on multi-cores, but the state-of-the-art TBGP performance is restricted by a mass of contentions when racing to access the routing table. To this end, the highly-efficient parallel access approach appears to be a promising solution to achieve ultra-high route processing speed. This study proposes a general routing table structure consisting of two-level tries for fast parallel access, and it presents a heuristic-based divide-and-recombine algorithm to solve a mass of contentions, thereby accelerating the parallel route updates of multi-threading and boosting the TBGP performance. As a projected TBGP, this study also modifies the table operations such as insert and lookup, and validates their correctness according to the behaviors of the traditional routing table. Our evaluations on a dual quad-core Xeon server show that the parallel access contentions decrease sharply by 92.5% versus the traditional routing table, and the maximal update time of a thread is reduced by 56.8 % on average with little overhead. The convergence time of update messages are improved by 49.7%.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.279-282
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• 2003

This paper proposes a medium-access control(MAC) protocol designed for wireless multi-hop sensor networks which is used for connecting physical world and cyber computing space. Wireless multi-hop sensor networks use battery-operated computing and sensing device. We expect sensor networks to be deployed in an ad hoc fashion, with nodes remaining inactive for long time, but becoming suddenly active when specific event is detected. These characteristics of multi-hop sensor networks and applications motivate a MAC that is different from traditional wireless MACs about power conservation scheme, such as IEEE 802.11. Proposed MAC uses a few techniques to reduce energy consumption. Result show that proposed MAC obtains more energy sayings.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.911-914
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• 2009

멀티 네트워크는 여러 무선 접속 기술을 동시에 접속할 수 있도록 구성된 시스템으로 정의되며 Ambient Networks(ANs) 프로젝트로 연구가 진행 중에 있다. 우선 ANs은 여러 다른 무선 장치와 Multi-Radio Access(MRA) 기술이 군집된 동적 통신 환경에서의 네트워킹 개념이다. 따라서 3 세대로 불리는 Global System for Mobile communications(GSM), Universal Mobile Telecommunications System(UMTS) 그리고 무선랜(WLAN)등 다양한 네트워크 인터페이스로 구성된 mobile terminal(MT)이 다양한 무선 접속 기술을 지원하는 멀티네트워크에 접속하여 "Always Best Connected" 관점에서 효율적 접속 서비스를 제공 받아야 한다. 본 논문에서는 멀티네트워크 환경에서 단말에 high-performance를 제공하기 위한 자원관리 모델인 MRRM/RARM(Multi-Radio/Radio Access Resource Management)과 GLL(Generic Link Layer)에 대한 기술 요소를 정의하고 분석한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.481-484
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• 2009

멀티 네트워크는 여러 무선 접속 기술을 동시에 접속할 수 있도록 구성된 시스템으로 정의되며 Ambient Networks(ANs) 프로젝트로 연구가 진행 중에 있다. 우선 ANs은 여러 다른 무선 장치와 Multi-Radio Access(MRA) 기술이 군집된 동적 통신 환경에서의 네트워킹 개념이다. 따라서 3 세대로 불리는 Global System for Mobile communications(GSM), Universal Mobile Telecommunications System(UMTS) 그리고 무선랜(WLAN)등 다양한 네트워크 인터페이스로 구성된 mobile terminal(MT)이 다양한 무선 접속 기술을 지원하는 멀티네트워크에 접속하여 "Always Best Connected" 관점에서 효율적 접속 서비스를 제공 받아야 한다. 본 논문에서는 멀티네트워크 환경에서 단말에 high-performance를 제공하기 위한 자원관리 모델인 MRRM/RARM(Multi-Radio/Radio Access Resource Management)과 GLL(Generic Link Layer)에 대한 기술 요소를 정의하고 분석한다.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.374-385
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• 2003

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.

• IEMEK Journal of Embedded Systems and Applications
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• v.15 no.3
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• pp.111-118
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• 2020

We investigate the optimization problem of transmit power control and MMSE Receiver filter for multi access points environment. Previous work showed that increasing the number of access points decreases the transmit power consumption. Accordingly, transmit power control algorithm was developed in such a way that the transmit power is minimized, while each terminal meets Signal to Interference and Noise Ratio Requirement. In this work, we further reduce the transmit power consumption by optimizing the transmit power level and the MMSE receiver filter together. We showed that the proposed joint optimization algorithm satisfies the necessary and sufficient conditions to be standard interference function, which guarantees convergence and minimum transmit power consumption. We observed that the proposed algorithm outperforms the algorithm which only optimizes the transmit power.