• 한국항행학회논문지
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• 제10권1호
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• pp.1-6
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• 2006

본 논문에서는 터보 코드 기법을 사용하여 무선 CDMA 망에서 WAP의 전송 시간을 분석하였다. 이러한 WAP의 전송 능력을 향상시키기 위한 한 방법으로 WTP(Wireless Transaction Protocol)에서 SAR(Segment And Re-assembly) 기능을 사용하여 상위 계층에서 내려온 전체 메시지를 분할하고, RLP(Radio Link Protocol) 타임 슬롯에서 패킷을 전송한다. 이 터보 코드 기법을 사용하여 RLP에서 전송하는 WAP 패킷의 시간을 감소시킨다. 결과로부터 라이시안 페이딩 환경에서 무선 CDMA망 WAP의 효율적인 WTP 패킷 크기와 전송 시간을 구할 수가 있었다.

• Journal of Communications and Networks
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• 제12권4호
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• pp.334-345
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• 2010

In this paper, we study optimal tradeoffs of achievable throughput versus consumed power in wireless ad-hoc networks formed by a collection of multiple antenna nodes. Relying on adaptive modulation and/or dynamic channel coding rate allocation techniques for multiple antenna systems, we examine the maximization of throughput under power constraints as well as the minimization of transmission power under throughput constraints. In our examination, we also consider the impacts of enforcing quality of service requirements expressed in the form of channel coding block loss constraints. In order to properly model temporally correlated loss observed in fading wireless channels, we propose the use of finite-state Markov chains. Details of fading statistics of signal-to-interference-noise ratio, an important indicator of transmission quality, are presented. Further, we objectively inspect complexity versus accuracy tradeoff of solving our proposed optimization problems at a global as oppose to a local topology level. Our numerical simulations profile and compare the performance of a variety of scenarios for a number of sample network topologies.

• IEIE Transactions on Smart Processing and Computing
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• 제3권4호
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• pp.212-220
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• 2014

The current cellular communications are optimized for low mobility users, meaning that their performance is degraded at high speed. Therefore, passengers in a high-speed train experience very poor radio link quality due to the significantly large number of simultaneous handovers. In addition, wireless data traffic is expanding exponentially in trains, subways and buses due to the widespread use of smartphones and mobile devices. To solve the inherent problem of cellular communication networks and meet the growing traffic demand, this paper proposes the mobile hotspot network of a millimeter-wave communication system as a mobile wireless backhaul. This paper describes the physical layer design of uplink and downlink in the proposed system, and the performances of uplink and downlink are evaluated under Rician fading channel conditions. The implemented baseband prototype of the proposed millimeter-wave communication modem is presented. This system can provide a Gbps data rate service in high-speed trains carrying hundreds of wireless Internet users.

• 한국통신학회논문지
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• 제30권8C호
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• pp.754-761
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• 2005

본 논문에서는 나카가미-n(라이시안) 페이딩 채널 상에서 그레이 부호화된 직사각 QAM(Rectangular-QAM) 신호를 최대비 합성(maximal ratio combining) 다이버시티로 수신하는 경우 비트노율(Bit Error Rate, BER)을 계산하는 수식을 다양한 채널에 적용할 수 있도록 일반적 형태로 유도하고 그 성능 분석을 실시한다. 유도된 BER 수식은 휘태커 함수)Whittaker function)와 초기하 함수(confluent hypergeometric)로 표현된다. 또한 M-PSK와의 성능 비교를 통하여 나카가미-n 페이딩 채널의 특성을 확인한다. BER 수식이 일반적인 형태로 유도되었기 때문에 가시 경로(line-of-sight)를 가지는 통신채널이나 위성통신 채널의 성능분석에 본 논문에서 유도한 BER 수식을 쉽게 적용할 수 있다.

• 한국통신학회논문지
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• 제32권9B호
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• pp.604-611
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• 2007

본 논문에서는 AFH 알고리즘을 사용하는 블루투스로 이루어진 피코넷이 WLAN과 공존할 때 피코넷 패킷 간의 충돌을 다중 경로 페이딩 채널을 고려하여 수학적으로 분석하였다. AFH에 의해 줄어든 블루투스의 홉 수와 패킷 주변의 피코넷의 신호 세기에 따라 패킷의 충돌 확률에 영향을 줄 수 있음을 알 수 있다. 또한 본 논문에서는 AFH이 갖는 한계를 인식하고 이를 극복하고자 AAFH 알고리즘을 제안하였다. AAFH은 계속적인 채널 사용 여부에 따라 채널 상태의 확인 여부(scanning)를 결정하게 되는데 AFH 와 비교했을 때 collision와 waste 양에서 큰 차이를 보이지 않으면서도 채널 scanning 수가 최대 50% 감소하게 되어 블루투스의 에너지 낭비가 줄어들게 됨을 보였다.

• 전자공학회논문지A
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• 제31A권4호
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• pp.11-20
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• 1994

The error rate equation of DS-CDMA/DQPSK skgnal adopting ARQ scheme has been derived in indoor radio channel which is characterized by AWGN, multi-user interference (MUI) and Rician fading, Using the derived equation the error performance has been evaluated and shown in figures as a function of direct to diffuse signal power ratio(KS1rT), the number of active users (K), PN code sequence length (N), the number of parity bit of linear code (b), forward channel BER, and ES1bT/NS1OT. From the results it is known that in severe fading environments (KS1rT=6) the performance of DS-CDMA/DQPSK system is not reliable so it is needed to adopt techniques for improvement. When an ARQ scheme is adopted, as a method for improving error performance, the performance improves compared with that of non-ARQ scheme and the degree of improvement is proportional to the number of parity bits of linear code. As increasing the number of parity bits, system performance is improved vut system throughput efficiency must be considered. In severe fading channel Hybrid ARQ scheme is more effective than ARQ scheme. As a result, ARQ scheme is appropriate for the high-reliability data communication systems over the radio channel in which the real time processing is not required.

• Journal of information and communication convergence engineering
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• 제4권2호
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• pp.71-74
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• 2006

A basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size Also, a time of packet transmission delay increases and efficienty is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (A WGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2003년도 추계종합학술대회
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• pp.133-136
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• 2003

초광대역(Ultra-WideBand) 시스템은 1nsec 이하의 매우 짧은 펄스폭을 갖는 가우시안 모노펄스를 이용하여 전송한다. 따라서, 전송 신호는 매우 낮은 전력의 수 GHz에 이르는 초광대역 스펙트럼을 갖게 되며, 기존의 통신 시스템에 거의 간섭을 미치지 않는 것으로 알려져 있다. 반송파를 사용하지 않는 초광대역 시스템에서 다중 경로 전파의 충돌은 일반적인 무선 통신시스템과는 매우 다르다. 이 논문은 다중 경로 채널하에서 BPSK, QPSK, 16-QAM 변복조 기술들을 적용한 초광대역 시스템을 컴퓨터 시뮬레이션을 이용하여 BER(Bit Error Rate) 성능을 비교 분석하고자 한다.

• 한국통신학회논문지
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• 제21권8호
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• pp.2063-2076
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• 1996

In this thesis, in order to apply a punctured convolutional codes to the trellis coded modulation(TCM), an efficient punctured trellis coded modulation(PTCM) based on the decomposition of the metric into orthogonal components is presented. Also, a simulation is performed in an additive white Gaussian noise(AWGN) and a rician fading channel modeling the mobile satellite channel. The PTCM combines punctured convolutional coding with MPSK modulation to provide a large coding gain in a power-limited or bandwidth-limited channel. However, in general the use of the punctured convolutional code structure in the decoder results in a performance loss in comparison to trellis codes, due to difficulties in assigning metrics. But, the study shows no loss in performance for punctured trellis coded MPSK in comparison to TCM, and what is more, the punctured convolutional codes results in some savings in the complexity of Viterbi decoders, compared to TCM of the same rate. Also, the results shows that the punctured trellis coded .pi./8 shift 8PSK is an attractive scheme for power-limited and band-limited systems and especially, the Viterbi decoder with first and Lth phase difference metrics improves BER performance by the mobile satellite channel.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권12호
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• pp.4432-4450
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• 2014

It is widely observed that in practical wireless cooperative communication systems, different links may experience different fading characteristics. In this paper, we investigate into the outage probability and channel capacity of two-way amplify-and-forward (TWAF) relaying systems operating over a mixed asymmetric Rician and Rayleigh fading scenario, with different amplification policies (AP) adopted at the relay, respectively. As TWAF relay network carries concurrent traffics towards two opposite directions, both end-to-end and overall performance metrics were considered. In detail, both uniform exact expressions and simplified asymptotic expressions for the end-to-end outage probability (OP) were presented, based on which the system overall OP was studied under the condition of the two source nodes having non-identical traffic requirements. Furthermore, exact expressions for tight lower bounds as well as high SNR approximations of channel capacity of the considered scenario were presented. For both OP and channel capacity, with different APs, effective power allocation (PA) schemes under different constraints were given to optimize the system performance. Extensive simulations were carried out to verify the analytical results and to demonstrate the impact of channel asymmetry on the system performance.