Earticle

As mobile traffic is growing, the demand for spectrum is increasing but the deficiency of spectrum becomes serious as the supply is restricted essentially. For resolving the issue, spectrum sharing system is discussed from the technical and regulatory point of view, where multiple radio users occupy same frequency. In this paper, the policies and adoptions of spectrum sharing system in some countries are analyzed with a focus on TV white space and licensed shared access, which are based on unlicensed and licensed spectrum usage respectively. Some legal and regulatory plans to adopt and activate spectrum sharing in the Radio Waves Act system of Korea are proposed as well.

최근 차량 교통 시스템은 스마트 센서 및 외부와의 소통을 통해 교통의 효율성과 안정성을 향상시키는 교통 체계를 의미하는 지능형 교통시스템(Intelligent Transport Systems : ITS)의 형태로 진화하고 있다. 이러한 발전 추세에 반하여 국내의 ITS 서비스는 다른 주요 통신 서비스에 비해 많이 낙후되어 있다. 이러한 현상의 원인은 현재 국내에서는 국제적으로 배정된 ITS 주파수 대역 내에 방송용 주파수가 할당되어 있으며, 국내에서 ITS로 사용되고 있는 DSRC(Dedicated Short Range Communications) 방식의 주파수도 ISM(Industrial, scientific and medical) 대역을 사용하고 있기 때문에 그것의 활용에 있어서 제한적일 수밖에 없다. 본 논문에서는 국내 ITS의 기술적 현황을 분석하여 다음과 같은 ITS 활성화 방안을 제안하였다. 첫째, 기존의 DSRC방식을 포용하는 WAVE(Wireless Access in Vehicular Environments)방식의 ITS 관련 표준을 시급히 확정하여 표준 설치 사양을 마련해야 한다. 둘째, ITS 표준을 완성하기 위한 주파수 배정이 시급히 시행되어야 한다.

Recently, automobile traffic systems are evolving toward Intelligent Traffic Systems(ITS) with smart sensor technology and collaboration between traffic systems and external ones. On the contrary, Korean ITS services have little improvement comparing with other communication services. The main causes of this phenomenon are due to already allocation of ITS recommended frequency band to broadcasting services, and also dedication of DSRC frequency band over ISM band resulting in interferences. This paper provides the analysis of current Korean ITS technology status, and two suggestions to activate the ITS industry. First, need to fix the ITS standard combining WAVE and DSRC specifications soon. Second, ITS frequency allocation to complete its standard implementation in near time frame.

In this letter, we propose a game-theory based heuristics for assigning frequency resources in communication systems. We suggest an algorithm that combines centralized and distributed behavior under the consideration of net filter discrimination (NFD) which leads to efficient usage of frequency resources. We show that by applying the heuristics, (because we applied a distributed algorithm that uses local information only) we can do the following: maximize the sum of users’ signal-to-interference-noise-ratio (SINR), minimize the standard deviation of SINRs between users, and also reduce the computational complexity. All of these achievements concern crucial issues in, for example, military communications where users need high-quality communication, less probability of isolation, rapid action corresponding to rapidly-varying military situations.

In this letter, we propose graph theory-based heuristics for jointly assigning frequency and antenna polarization in a cluster-based tactical communication environment (e.g., military communications). In addition to considering the frequency assignment problem (which is an NP-hard problem), we also consider the polarization assignment issue. A practical antenna and a 3D ray tracing-based simulator are exploited to measure the interference. We show that the suggested heuristics are nearly optimal in terms of chromatics and their low complexity makes them suitable for practical usage.

무선 이동 통신 시장의 증가에 따라 신규 기지국을 설치해야 하며 이를 위해 기존 기지국에 대한 주파수 재배치가 필요하다. 신규 기지국에 주파수를 할당하기 위해 기존 기지국의 주파수를 재할당해야 하는 경우 기존 기지국의 주파수 변경을 최소화하는 것이 중요하다. 또한 이동통신 서비스를 제공하기 위해서는 주파수 재배치가 완료된 시점에서, 모든 기지국에 주파수가 할당되어야 하며, 인접 기지국간 간섭을 피하기 위해 각 기지국간 주파수 최소 이격거리를 만족해야만 한다. 본 연구에서는 주파수 이격 조건을 만족하고 기존 기지국의 주파수 변경을 최소화하면서 새로운 기지국에 주파수를 할당하는 알고리듬을 개발하였다. 알고리듬을 위해 먼저 문제를 해결하기 위한 IP 모형을 제시하였고 빠른 시간에 문제를 해결하기 위한 휴리스틱 알고리듬을 개발하였다.

A frequency assignment problem on time division duplex system is considered. Republic of Korea Army (ROKA) has been establishing an infrastructure of tactical communication (SPIDER) system for next generation and it will be a core network structure of system. VHF system is the backbone network of SPIDER, that performs transmission of data such as voice, text and images. So, it is a significant problem finding the frequency assignment with no interference under very restricted resource environment. With a given arbitrary configuration of communications network, we find a feasible solution that guarantees communication without interference between sites and relay stations. We formulate a frequency assignment problem as an Integer Programming model, which has NP-hard complexity. To find the assignment results within a reasonable time, we take a genetic algorithm approach which represents the solution structure with available frequency order, and develop a genetic operation strategies. Computational result shows that the network configuration of SPIDER can be solved efficiently within a very short time.

This study investigates generational differences in the tonal realization of English loanwords in North Kyungsang Korean (NK), focusing on how structural and lexical factors jointly shape ongoing prosodic change. Production data were collected from forty NK speakers and the stimuli were grouped by syllable number, lexical frequency, and borrowing period. The results show that younger speakers produce fewer double high accents and more penult and final accents, with the strongest generational divergence observed in quadrisyllabic items. Lexical frequency and borrowing period further modulate these patterns. Mid-frequency and integrated loanwords exhibit relatively stable tonal realizations across age groups, whereas low frequency and recently borrowed items show substantial reductions in the representative pattern among younger speakers. These findings suggest that tonal change in NK loanwords proceeds in a gradient, lexically conditioned fashion, driven by the interaction of prosodic structure, usage frequency, and diachronic entrenchment.

The design problem of partial pole assignment (PPA) in two classes of frequency-domain MIMO models by constant gain feedback is investigated in this paper. Its aim is to design a constant gain feedback which changes only a subset of the open-loop eigenvalues, while the rest of them are kept unchanged in the closed-loop system. A near general parametric expression for the feedback gain matrix in term of a set of design parameter vectors and the set of the closed-loop poles, and a simple parametric approach for solving the proposed problem are presented. The set of poles do not need to be previously prescribed, and can be set undetermined and treated together with the set of parametric vectors as degrees of design freedom provided by the approach. An illustrative example shows that the proposed parametric method is simple and effective.

The tactical communications network has to be deployed rapidly at military operation area and support the communications between the military command systems and the weapon systems. For that, the frequency assignment is required for backbone wireless links of tactical communications network without frequency interferences. In this paper, we propose a frequency assignment method using net filter discrimination (NFD) and graph coloring to avoid frequency interferences. The proposed method presents frequency assignment problem of tactical communications network as vertex graph coloring problem of a weighted graph. And it makes frequency assignment sequences and assigns center frequencies to communication links according to the priority of communication links and graph coloring. The evaluation shows that this method can assign center frequencies to backbone communication links without frequency interferences. It also shows that the method can improve the frequency utilization in comparison with HTZ-warfare that is currently used by Korean Army.

본 논문에서는 주파수 할당의 최적화를 위하여 제약만족문제의 모델링과 백트랙킹 탐색의 경험적 알고리즘을 제안한다. 연구의 목적은 주어진 서비스 영역에서 공동체 라디오 방송국의 개수를 최대화하면서 동시에 필요주파수를 최소화시키는 제약조건을 만족하는 주파수 할당이다. 본 연구는 효과적으로 해를 찾기 위하여 경험적 알고리즘을 제안하는데, 이것은 제한된 시간 안에 해를 찾는데 필요한 백트랙킹 횟수를 최소화하는 변수 순서와 값 순서에 관한 방법이다. 백트랙킹에서 불일치성을 늦게 발견하는 문제를 보완하기 위해서 일관성 강화기술 또는 제약 전파 방법을 사용한다. 백트랙킹 탐색과 일관성 강화 기술을 함게 사용함으로써 제약만족문제에 관한 보다 강력하고 효과적인 알고리즘을 얻을 수 있다. 본 논문은 또한 계산된 해와 이론적인 하한 값을 비교함으로써 제안된 알고리즘의 성능 비교를 수행한다.

We present a modeling of constraint satisfaction problems and provide heuristic algorithms of backtracking search to optimize the frequency assignment. Our research objective is to find a frequency assignment that satisfies all the constraints using minimum number of frequencies while maximizing the number of community radio stations served for a given area. In order to get a effective solution, some ordering heuristics such as variable orderings and value orderings are provided to minimize the backtracking in finding all solutions within a limited time. To complement the late detection of inconsistency in the backtracking, we provide the consistency enforcing technique or constraint propagation to eliminate the values that are inconsistent with some constraints. By integrating backtracking search algorithms with consistency enforcing techniques, it is possible to obtain more powerful and effective algorithms of constraint satisfaction problems. We also provide the performance evaluation of proposed algorithms by comparing the theoretical lower bound and our computed solution.

데이타 및 음성 등의 통신에서 무선 통신의 비중은 날로 증가하고 있다. 그러나 무선 통신에서는 유선통신에 비해 여러 가지 자원의 제약을 받는다. 컴퓨터, PDA, 이동통신기기 등 급격히 증가하는 무선 단말기의 증가에 따른 통신량 수요를 충족하기위해 제한된 자원을 보다 효율적으로 사용해야 한다. 무선 통신에 있어 효율성이 필요한 자원중의 하나가 주파수 이다. 효율적 주파수 사용을 위한 주파수 할당 문제에 관한 연구는 현재 활발히 진행되고 있다. 그러나 대부분의 주파수 할당 문제가 NP-Complete의 어려운 문제로 실험적 연구를 통한 접근과 함께 이에 대한 이론적 이해 또한 필요하다. 주파수 할당 문제의 이론적 연구 중 셀룰러 위상구조에서의 크로마틱 대역폭 문제의 하한 값이 $O(k^2)$로 알려져 있다. 본 논문에서는 셀룰러 위상구조에서의 크로마틱 대역폭 주파수 할당 문제의 하한 값으로 기존에 알려진 $O(k^2)$보다 향상된 하한 값 $O(k^3)$을 제시하여, 주파수 할당 문제의 보다 정확한 이론적 이해를 제시하였다.

Because of its exponential growth of data and voice transmissions through wireless communications, efficient resource management became more important factor when we design wireless networks. One of those limited resources in the wireless communications is frequency bandwidth. As a solution of increasing reusability of resources, the efficient frequency assignment problems on wireless networks have been widely studied. One suitable approach to solve these frequency assignment problems is transforming the problem into traditional graph coloring problems in graph theory. However, most of frequency assignments on arbitrary network topology are NP-Complete problems. In this paper, we consider the Chromatic Bandwidth Problem on the cellular topology wireless networks. It is known that the lower bound of the necessary number of frequencies for this problem is $O(k^2)$. We prove that the lower bound of the necessary number of frequencies for the Chromatic Bandwidth Problem is $O(k^3)$ which is tighter lower bound than the previous known result.

본 연구는 우리나라 출연금 제도 중 하나인 “주파수 할당 대가”를 중심으로 동태적인 제도화 및 제도 변화 과정을 분석했다. 분석 결과 우리나라 정보통신산업의 출연금의 하나인 주파수 할당대가의 제도화 과정은 국가라는 단일의 행위자에 의해 일방적인 결정이 이루어지는 것이 아닌 다수의 이해관계자들의 상호작용을 통해 자생적 질서로 전개되어 왔으며, 시행착오 및 학습 결과 한계적 조정과 변이를 통해 점진적인 제도화를 거쳐 왔다. 이러한 변화는 무작위적으로 이루어졌다기보다는 이전 사례의 오차를 수정, 학습하고, 외국사례를 모방, 적용해 나가는 과정으로 볼 수 있다. 또한 주파수 할당대가의 제도화 과정은 제도의 효율성이나 객관성에 대한 고려보다 제도에 대한 정당성을 부각시키거나 시장 기제를 수용하 는 등 사회적으로 인정된 관례나 상징 기제를 활용해 왔다.

This study analysed the process of frequency assignment institutionalization such as method, criteria, and price in Korea. Especially this work studied new-entry process of mobile telecommunication sector Cellular, PCS, IMT-2000 business since the late 1980's. The major finding of this study is that the institutionalization process of frequency allotment in Korea has been evolved gradually over time affected by diverse causes such as historical institution or diverse social, political environment change. In particular, frequency allotment method and criteria have continuity and change aspect that descent with modifications that showed learning process by trial-and-error and adaptation over changing environments. The institutionalization process showed evolutionary characters such as path-dependency, variations and fluctuations, bounded rationality, endogenous innovation, emergent properties and indeterminacy. Complete or global rational calculation was ruled out and thus rationality was bounded. Agents made use of given routines of 'rule of thumb', deeply embedded in institutions. Therefore evolutionary process did not result in profitable and just showed the process of learning and adaptation to changing environment.

본 논문에서는 대용량 셀룰러 이동통신 시스템에 있어 새로운 채널할당 알고리듬을 제안하였다. 새로 제안된 채널할당 알고리듬은, 고정배치된 채널이 모두 사용중인 Cell에 요구된 Call의 서비스를, Idle한 채널이 있는 인접 Cell에서 대행하도록 하였으며, 채널의 순서적인 할당, 채널의 재할당 및 지향성 안테나의 사용등의 기법을 이용하였다. 49개의 Cell로 구성된 시스템에 본 알고리듬을 Simulation 한 결과 고정채널 할당방식에 비해 18~38%의 높은 채널이용율을 나타내었다.

A new algorithm for frequency channel assignment in high capacity cellular mobile communication systems is proposed. The algorithm is the advanced type of the fixed channel assignment scheme. It enables calls having all nominal channels busy to be served by adjacent cells have idle channels. Thus, it considerably reduces the blocking probability compared with the fixed channel assignment. Simulation has been performed for a 49-cell system having uniform traffic density hexagonal array as a representative system lay out. Results showed that new algorithm is better than the fixed channel assignment scheme in high capacity cellular mobile communication systems.

The frequency band differs a quality, so 800MHz frequency bands monopolized by SK Telecom are higher the effectiveness than 1.8GHz frequency bands of PCS business owners. The advantage to under securing does the extraordinarily many mobile telephone member from mobile communication market, and is able to create the enormous profit. The marketing strategy which it applies to under forming does that SK Telecom goes over 50% of mobile communication market. Finally the market lop-sided competitive composition in compliance with a frequency difference is little by little fixed. But the radio wave is a important resources of the national possession, and accomplishes the foundation of information communication industry. Consequently we must pay attention in the point which is a limit resources that it will not be able to be sufficient the demand which is satisfied economically in development of IT techniques. Conclusively, it will be able to discuss frequency joint use, frequency refarming, and the actual levy of electronic rental fee to improve the efficient use of frequency at the Radio Law. Korea as IT powerful country must prepare a perfection in the radio wave management policy and legal and institutional maintenances of information communication field for Dynamic u-Korea time. Namely, it should integrate the Radio Law and the Telecommunication Organic Law and the Telecommunication Enterprising Law, and convergence communication and broadcasting, so it will be able to solve IP television problems of the regulative organization which is integrated and maintenance of the legal system. Also the government have to be propelling continuously u-Korea basic plans in base on IT839 strategy, and to respect this, which must prepare to the support plan of IT industry and R&D expense of a area of study.