• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권5호
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• pp.1682-1701
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• 2015

In this paper, we propose an intergraded unified imperfect CSI model and investigate the joined effects of feedback delay and channel estimation errors (CEE) for two-hop relaying systems with transmit beamforming and relay selection. We derived closed-form expressions for important performance measures including the exact analysis and lower bounds of outage probability as well as error performance. The ergodic capacity is also included with closed-form results. Furthermore, diversity and coding gains based on the asymptotic analysis at high SNRs are also presented, which are simple and concise and provide new analytical insights into the corresponding power allocation scheme. The analysis indicates that delay effect results in the coding gain loss and the diversity order loss, while CEE will merely cause the coding gain loss. Numerical results verify the theoretical analysis and illustrate the system is more sensitive to transmit beamforming delay compared with relay selection delay and also verify the superiority of optimum power allocation. We further investigate the outage loss due to the CEE and feedback delays, which indicates that the effect of the CEE is more influential at low-to-medium SNR, and then it will hand over the dominate role to the feedback delay.

• ETRI Journal
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• 제43권3호
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• pp.561-570
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• 2021

This paper presents master key identifier based protocol steganography (MKIPS), a new approach toward creating a covert channel within the Secure Real-time Transfer Protocol, also known as SRTP. This can be achieved using the ability of the sender of Voice-over-Internet Protocol packets to select a master key from a pre-shared list of available cryptographic keys. This list is handed to the SRTP sender and receiver by an external key management protocol during session initiation. In this work, by intelligent utilization of the master key identifier field in the SRTP packet creation process, a covert channel is created. The proposed covert channel can reach a relatively high transfer rate, and its capacity may vary based on the underlying SRTP channel properties. In comparison to existing data embedding methods in SRTP, MKIPS can convey a secret message without adding to the traffic overhead of the channel and packet loss in the destination. Additionally, the proposed covert channel is as robust as its underlying user datagram protocol channel.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권5호
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• pp.2362-2378
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• 2017

To mitigate the performance degradation caused by performance anomaly, a number of channel assignment algorithms have been proposed for multi-rate wireless mesh networks. However, network conditions have not been fully considered for routing process in these algorithms. In this paper, a joint scheme called Multi-rate Dijkstra's Shortest path - Rate Separated (MDSRS) is proposed, combining routing metrics and channel assignment algorithm. In MDSRS, the routing metric are determined through the synthesized deliberations of link costs and rate matches; then the rate separated channel assignment is operated based on the determined routing metric. In this way, the competitions between high and low rate links are avoided, and performance anomaly problem is settled, and the network capacity is efficiently improved. Theoretical analysis and NS-3 simulation results indicate that, the proposed MDSRS can significantly improve the network throughput, and decrease the average end-to-end delay as well as packet loss probability. Performance improvements could be achieved even in the heavy load network conditions.

• Journal of Communications and Networks
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• 제11권5호
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• pp.464-472
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• 2009

In this paper, we propose a packet scheduling algorithm for cellular relay networks by considering relay selection, variation of channel quality, and packet delay. In the networks, mobile users are equipped with not only cellular but also user relaying radio interfaces, where base station exploits adaptive high speed downlink channel. Our proposed algorithm selects a user with good cellular channel condition as a relay station for other users with bad cellular channel condition but can get access to relay link with good quality. This can achieve flexible packet scheduling by adjusting transmission rates of cellular link. Packets are scheduled for transmission depending on scheduling indexes which are calculated based on user's achieved transmission rate, packet utility, and proportional fairness of their throughput. The performance results obtained by using computer simulation show that the proposed scheduling algorithm is able to achieve high network capacity, low packet loss, and good fairness in terms of received throughput of mobile users.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권1호
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• pp.18-34
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• 2014

It is widely believed that cognitive radio (CR) networks have an opportunistic nature and therefore can only support best-effort traffics without quality-of-service (QoS) guarantees. In this paper, we propose a centralized CR network that adopts interference averaging techniques to support QoS guaranteed traffics under interference outage constraints. In such a CR network, a CR user adaptively adjusts its transmit power to compensate for the channel loss, thereby keeping the receive signal power at the CR base station (BS) at a constant level. The closed-form system capacity of such a CR network is analyzed and derived for a single cell with one CR BS and multiple CR users, taking into account various key factors such as interference outage constraints, channel fading, cell radius, and locations of primary users. The accuracy of the theoretical results is validated by Monte Carlo simulations. Numerical and simulation results show promising capacity potential for deploying QoS-guaranteed CR networks in frequency bands with fixed primary receivers. Our work can provide theoretical guidelines for the strategic planning of centralized CR networks.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.38-41
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• 1998

Due to the increasing demand to multimedia services over wireless communication network, LMDS(Local Multipoint Distribution Service) has been proposed as an alternate approach for broadband wireless access network. But LMDS, Which uses the mmwavelength radio spectrum, has been limited for unknown microwave frequency characteristics. In this paper, we analyze the parameters related to the system design on 28GHz frequency: Propagation path loss and rainfall attenuation. Based on these analytical results, the proper cell size in Korea is determined. We also analyze the bit error rate and frame loss rate for various kinds of digital modulation schemes(QAM 4, 16, 64, 256). Finally, we apply to ㅍ service to evaluate a call blocking rate, efficiency and channel capacity.

• 한국음향학회지
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• 제32권4호
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• pp.294-300
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• 2013

본 논문에서는 간략화된 차 주파수의 신호대잡음비을 이용하여 수중 AWGN 환경하에서 파라메트릭 배열 통신 시스템의 성능을 비트오류확률과 MIMO 채널용량 관점에서 분석한 결과를 제시한다. 분석을 위해 사용된 차주파수의 신호대잡음비는 전달손실, 잡음준위 그리고 비선형성이 고려된 차 주파수의 음원준위로 계산된다. 1차 주파수 210 kHz와 190 kHz, 차 주파수 20 kHz, 트랜스듀서 직경 0.1 m, 잡음준위 50 dB, 요구되는 비트오류 확률을 $10^{-4}$으로 가정할 때, 담수 환경과 해수 환경에서의 1차 주파수 통신 거리 대비 파라메트릭 배열의 통신거리 이득을 각각 59.11 km와 5 km를 얻었다. 또한, 10 bps/Hz의 채널용량 조건을 위해 SISO 및 ($2{\times}2$) MIMO 파라메트릭 배열을 사용할 경우, 담수에서는 38.84 km와 46.38 km 거리이득을 해수에서는 3.88 km 4.381 km의 거리이득을 얻었다.

• 한국인터넷방송통신학회논문지
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• 제13권4호
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• pp.1-7
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• 2013

차세대 이동통신 시스템에서는 새로운 주파수 대역에서 다중 안테나 사용이 높은 데이터 전송률과 용량을 가능하도록 만들 것이다. 본 논문에서는 국내 전파 특성 측정을 통해 도출된 채널 파라미터(경로 손실, 지연 확산, 각 확산, K-factor) 간에 상관도를 분석하였다. 측정은 DTV 방송과 혼신을 피하기 위하여 제주도에서 채널 사운더와 $4{\times}4$ 안테나로 측정하였다. 채널 파라미터 간에 상관도 분석은 유사한 환경에서 통신 시스템을 설계하는데 있어서 많은 도움을 줄 것이다.

• 전기학회논문지P
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• 제63권2호
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• pp.61-68
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• 2014

Function of battery bank stores energy for DC load in general, and DC power system of the nuclear power plant is used to supply DC loads for safety- featured instrumentation and control such as inverter, class 1E power system control and indication, and station annunciation. Class 1E DC power system must provide a power for the design basis accident conditions, and adequate capacity must be available during loss of AC power and subsequent safe shutdown of the plant. In present, batteries of Class 1E DC power system of the nuclear power plant uses lead-acid batteries. Class 1E batteries of nuclear power plants in Korea are summarized in terms of specification, such as capacity, discharge rate, bank configuration and discharge end voltage, etc. This paper summarizes standards of determining battery size for the nuclear power plant, and analyzes duty cycle for the class 1E DC power system of nuclear power plant. Then, battery cell size is calculated as 2613Ah according to the standard. In addition, this paper analyzes performance test results during past 13 years and shows performance degradation in the battery bank. Performance tests in 2001 and 2005 represent that entire battery cells do not reach the discharge-end voltage. Howeyer, the discharge-end voltage is reached in 14.7% of channel A (17 EA), 13.8% of channel B (16 EA), 5.2% of channel C (6 EA) and 16.4% of channel D (19 EA) at 2011 performance test. Based on the performance test results analysis and size calculation, battery capacity and degradation by age in Korearn nuclear power plant is discussed and would be used for new design.

• 한국전자파학회논문지
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• 제23권11호
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• pp.1288-1296
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• 2012

최근 기존의 MSS(Mobile Satellite Service) 대역에 지상망과 위성망의 하이브리드 형태인 ATC(Ancillary Terrestrial Component) 서비스 도입이 추진되고 있다. 새로운 MSS/ATC 서비스 주파수 할당을 위해서는 기존의 지상망에 의한 인접 채널 간섭뿐만 아니라 시스템 자체 내의 인접 채널 간섭 분석이 중요하다. 이에 본 논문에서는 인접 채널 간섭에 의한 ACIR(Adjacent Channel Interference Ratio), 지상 이동국 및 위성 이동 지구국의 수를 파라미터로 하여 업링크에서는 지상 기지국 최소 허용 전력 및 시스템 용량(capacity) 손실, 다운링크에서는 1 빔(beam) 당 1 셀(cell)을 가정하여 MSS/ATC 시스템 용량 손실에 대한 시스템 성능을 평가하였다. MSS/ATC 서비스 주파수 배치에 따른 주파수 공유를 위해 두 가지 시나리오 즉, 5 MHz 및 10 MHz 주파수 간격에 대한 ACIR 기준값을 평가하였으며, 향후 이 기준값에 따른 ATC 서비스 커버리지 및 수신 필터 설계 등이 요구된다.