• 정보보호학회논문지
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• 제16권6호
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• pp.135-149
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• 2006

무선 Ad hoc 네트워크는 통신 채널의 취약성, 노드의 보안 취약점, 기반 구조의 부재, 동적인 위상 변화 등의 특성으로 인해 보안 메커니즘 설계 및 구현이 기존 유선 네트워크에 비해 어려운 것으로 인식되고 있다. 기존의 연구들이 유선 네트워크의 보안을 무선 Ad hoc 네트워크로 적용하는데 많은 노력을 기울여 왔으나, 무선 Ad hoc 네트워크의 본질적인 문제로 인하여 효과적인 성과를 거두지 못하고 있다 본 논문은 무선 Ad hoc 네트워크의 보안 분야 중에서 하나 또는 둘 이상의 협업된 위장노드들의 대량의 위장 패킷 공격으로 인해 네트워크 자체의 생존성 및 가용성에 새로운 문제가 있음을 제기하고 그 결과를 증명한다. 또한 무선 Ad hoc 네트워크의 생존성 및 성능 향상을 위한 접근 방법으로 기존 방식의 기준을 탈피하여 무선 Ad hoc 네트워크의 특성을 반영하는 생존성 강화를 위하여 효율적인 위장 공격 방지 메커니즘을 제안한다.

• ETRI Journal
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• 제37권1호
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• pp.11-20
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• 2015

This paper deals with optimal power allocation for channel estimation of orthogonal frequency-division multiplexing uplinks in time-varying channels. In the existing literature, the estimation of time-varying channel response in an uplink environment can be accomplished by estimating the corresponding channel parameters. Accordingly, the optimal power allocation studied in the literature has been in terms of minimizing the mean square error of the channel estimation. However, the final goal for channel estimation is to enable the application of coherent detection, which usually means high spectral efficiency. Therefore, it is more meaningful to optimize the power allocation in terms of capacity. In this paper, we investigate capacity with imperfect channel estimation. By exploiting the derived capacity expression, an optimal power allocation strategy is developed. With this developed power allocation strategy, improved performance can be observed, as demonstrated by the numerical results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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• pp.229-232
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• 2000

Orthogonal frequency division multiplexing(OFDM) has meanwhile become part of several telecommunicati ons standards, such as satellite and terrestrial digital audio broadcasting(DAB), digital terrestrial TV broad casting(DVB), asymmetric digital subscriber line(ADSL) for high-bit-rate digital subscriber services on twisted-pair channels, and broadband indoor wireless systems. In his paper, we show that OFDM signals contain sufficient structure to accomplish blind channel estimation using second order statistics only. This method doesn't require redundancy as cp in transmitter. And the result is compared with PSAM channel estimation as least square, linear minimum mean square, singular value decomposition.

• 한국항행학회논문지
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• 제11권1호
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• pp.37-42
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• 2007

본 논문에서는 비선택성 페이딩과 주파수 오프셋이 함께 존재하는 채널과 마이크로파 대역의 2경로 Rummer's 채널 환경에서 적응 등화기를 채용한 OFDM 시스템의 성능을 분석하였다. 주파수 비선택성 페이딩과 주파수 오프셋이 함께 존재하는 채널에서 시스템 성능 분석 결과 주파수 오프셋의 증가에 따른 성능이 급격히 열화 됨을 알 수 있다, 그리고 시스템에서 적응 등화기를 채용한 경우에는 일정 범위 내에서 성능 향상이 이루어짐을 확인할 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권11호
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• pp.1976-1996
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• 2011

Cognitive radio (CR) MAC protocol provides access control of unused spectrum resources without causing interference to primary users. To achieve this goal, in this paper a TDMA based cooperative multi-channel cognitive radio MAC (MCR-MAC) protocol is proposed for wireless ad hoc networks to provide reliable protection for primary users by achieving cooperative detection of incumbent system signals around the communication pair. Each CR node maintains transmission opportunity schedules and a list of available channels that is employed in the neighbor discovery period. To avoid possible signal collision between incumbent systems and cognitive radio ad hoc users, we propose a simple but efficient emergency notification message exchanging mechanism between neighbor CR nodes with little overhead. Our simulation results show that the proposed MCR-MAC can greatly reduce interference with primary users and remarkably improve the network throughput.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.259-260
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• 2008

This paper presents fractional frequency reuse (FFR) with sub-channel borrowing to improve spectral efficiency of the wireless broadband (WiBro) system. FFR has constraints on usable sub-channels to balance the interference and cell capacity. Our FFR with sub-channel borrowing allows use of the dedicated sub-channels assigned to neighboring cells. Simulation results show that the proposed FFR with sub-channel borrowing improves the performance of the WiBro system.

• 한국통신학회논문지
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• 제29권3A호
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• pp.257-265
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• 2004

MRC 다이버시티 수신 시스템에서 상호 독립적이고 동일한 전력을 갖는 동일 채널 간섭자들이 존재할 경우, Gray 부호화된 임의 직사각 QAM 신호의 성능을 분석하였다. 본 논문에서는 L개의 수신안테나를 갖는 MRC 수신 다이버시티 시스템에서 N명의 서로 독립적이고 동일한 나카가미 분포를 갖는 동일 채널 간섭자들의 신호가 수신되는 경우의 폐쇄형 (closed-form) 평균 비트 오류 확률 수식을 유도하였다. 이 수식은 수치 계산에 의해 쉽게 계산되는 초기하 함수를 이용하여 표현되었다.

• Journal of Communications and Networks
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• 제17권5호
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• pp.463-472
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• 2015

This paper considers a limited feedback system for two-way wireless relaying channels with physical network coding (PNC). For full feedback systems, the optimal structure with the PNC has already been studied where a modulo operation is employed. In this case, phase and power of two end node channels are adjusted to maximize the minimum distance. Based on this result, we design new quantization methods for the phase and the power in the limited feedback system. By investigating the minimum distance of the received constellation, we present a code-book design to maximize the worst minimum distance. Especially, for quantization of the power for 16-QAM, a new power quantization scheme is proposed to maximize the performance. Also, utilizing the characteristics of the minimum distance observed in our codebook design, we present a power allocation method which does not require any feedback information. Simulation results confirm that our proposed scheme outperforms conventional systems with reduced complexity.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제3권1호
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• pp.18-22
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• 2003

The new realtime applications like multimedia and realtime services in a wireless network will be dramatically increased. However, many realtime services of mobile hosts in a cell cannot be continued because of insufficiency of useful channels. Conventional channel assignment approaches didn't properly consider the problem to serve realtime applications in a cell. This paper proposes a new realtime channel assignment algorithm based on time constraint analysis of channel requests. The proposed algorithm dynamically borrows available channels from neighboring cells. It also supports a smooth handoff which continuously serves realtime applications of the mobile hosts.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.87-88
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• 2006

In this paper, we propose a new selective scanning scheme based on hand-off path information, which can provide an efficient reducing of delay time. This scheme eliminates almost of the scanning delay time by using Selective Scan based on Experience Path Table(SSEPT) algorithm and also completed hand-off within few milliseconds by using the next candidate channel indexing mechanism. Our scheme reduces the total number of scanning channels as well as the delay time on each channel. From the simulation result, we show that the proposed scheme is advantageous over the legacy schemes in terms of the scanning channels and the total delay time.