• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.826-829
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• 2007

본 논문에서는 HDR-WPAN 시스템의 신뢰성을 향상시키는 방안으로 STTC 기법과 STTC 기반 STBC 기법을 제안하였고, 그 성능을 슬로우 페이딩 환경에서 분석하였다. 제안한 두 기법은 부가적인 대역폭의 증가 없이 부호화 이득과 다이버시티 이득을 갖는다. 그러나 시스템의 신뢰성 측면에서 STTC 기반 STBC 기법이 STBC의 추가적인 다이버시티 이득 때문에 STTC 기법보다 $BER=10^{-3}$에서 약 4dB정도 우수하였다. 이 결과를 통해 HDR-WPAN 시스템에 더 좋은 통신 신뢰성 확보, 채널용량의 증가를 위해서는 STTC 기반 STBC 기법의 적용이 STTC 기법을 적용하는 것이 보다 바람직함을 알 수 있었다.

• Journal of Communications and Networks
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• 제10권1호
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• pp.71-78
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• 2008

We propose a sub-band spreading technique for adaptive modulation (AM) in orthogonal frequency division multiplexing (OFDM) systems in order to reduce signaling overheads and to average frequency selective fading channels causing different signal-to-noise ratio (SNR) values for subcarriers in each subband. The conventional sub-band based AM schemes can also reduce signaling overheads and complexity for allocating a resource per sub-band at a time. However, they may suffer from the channel variation in a sub-band when the sub-band size is larger than the channel coherence bandwidth (BW). The sub-band spreading at the transmitter enables the received symbols in each sub-band to have an identical reliability even in a frequency selective fading channel. We rigorously analyze the averaged SNR value at the receiver of the sub-band spreading system and the analyzed average SNR in a sub-band is used for an adaptation criterion. The proposed AM scheme outperforms the conventional sub-band based OFDM scheme without spreading, and it can yield better throughput performance than the conventional subcarrier based AM schemes when we consider the signaling overheads.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.1805-1824
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• 2013

Recently, the use of wireless body area networks (WBAN) has been increasing rapidly in medical healthcare applications. WBANs consist of smart nodes that can be used to sense and transmit vital data such as heart rate, temperature and ECG from a human body to a medical centre. WBANs depend on limited resources such as energy and bandwidth. In order to utilise these resources efficiently, a very well organized medium access control (MAC) protocol must be considered. In this paper, a new, adaptive and energy-efficient MAC protocol, entitled isMAC, is proposed for WBANs. The proposed MAC is based on multi-channel communication and aims to prolong the network lifetime by effectively employing (i) a collision prevention mechanism, (ii) a coordinator node (WCN) selection algorithm and (iii) a transmission power adjustment approach. The isMAC protocol has been developed and modelled, by using OPNET Modeler simulation software. It is based on a networking scenario that requires especially high data rates such as ECG, for performance evaluation purposes. Packet delay, network throughput and energy consumption have been chosen as performance metrics. The comparison between the simulation results of isMAC and classical IEEE 802.15.4 (ZigBee) protocol shows that isMAC significantly outperforms IEEE 802.15.4 in terms of packet delay, throughput and energy consumption.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.302-309
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• 2004

The transmission capacity of wireless communication systems may become dramatically high by employ multiple transmit and receive antennas with space-time coding techniques appropriate to multiple transmit antennas. For large number of transmit antennas and at high bandwidth efficiencies, the receiver may become too complex whenever correlation across transmit antennas is introduced. Reducing decoding complexity at receiver by combining array processing and space-time codes (STC) helps a communication system using STC to overcome the big obstacle that prevents it from achieving a desired high transmission rate. Multi-carrier CDMA (MC-CDMA) allows providing good performance in a channel with high inter-symbol interference. Antenna array, STC and MC-CDMA system have a similar characteristic that transmit-receive data streams are divided into sub-streams. Thus, there may be a noticeable reduction of receiver complexity when we combine them together. In this paper, the combination of array processing and STC in MC-CDMA system over slow selective-fading channel is investigated and compared with corresponding existing MC-CDMA system using STC. A refinement of this basic structure leads to a system design principle in which we have to make a trade off between transmission rate, decoding complexity, and length of spreading code to reach a given desired design goal.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.265-266
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• 2006

In this paper, we propose an efficient rate control scheme based on the received power level to overcome a quality degradation of video under time varying channel condition caused by the movement of mobile devices. First, we statistically obtain the relation between the PLR and the received power level. With this information and the sequences of received power level, we calculate the transition probability for the Markov Channel Model. Then, with using Markov chain rule, we obtain the probability where the channel condition remains in a good state and finally find the efficient target bit rate by multiplying it by the offered bandwidth when the network access has begun. We use TMN8 to adjust the bit rate to our proposed outcome. Experimental results show that the proposed method can efficiently enhance the video quality and provide better PSNR performance than with only using TMN8 rate control method.

• 전기학회논문지
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• 제65권5호
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• pp.831-835
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• 2016

In this paper, a dual-channel feed-forward transimpedance(TIA) array is realized in a standard $0.18-{\mu}m$ CMOS technology which exploits automatic gain control function to provide 40-dB input dynamic range for either detecting targets nearby or sensing imminent danger situations. Compared to the previously reported conventional feed-forward TIA, the proposed automatic-gain-control feed-forward TIA(AFF-TIA) extends the input dynamic range 25 dB wider by employing a 4-level automatic gain control circuit. Measured results demonstrate the linearly varying transimpedance gain of 47 to $72dB{\Omega}$, input dynamic range of 1:100, the bandwidth of $${\geq_-}670MHz$$, the equivalent input referred noise current spectral density of 6.9 pA/${\surd}$HZ, the maximum sensitivity of -26.8 dBm for $10^{-12}BER$, and the power consumption of 27.6 mW from a single 1.8-V supply. The dual-channel chip occupies the area of $1.0{\times}0.73mm^2$ including I/O pads.

• ETRI Journal
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• 제26권5호
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• pp.375-383
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• 2004

This paper proposes a common interleaving method associated with independent channel-encoding among transmitter antenna branches in orthogonal frequency and code division multiplexing based on multiple-input multiple-output (MIMO) multiplexing to achieve an extremely high throughput such as 1 Gbps using a 100 MHz bandwidth. This paper also investigates the average packet error rate performance as a function of the average received signal energy per bit-to-background noise power spectrum density ratio $(E_b/N_0)$. We found that the loss in the required average received $E_b/N_0$ of the proposed method is only within approximately 0.3 dB in up to a 12-path Rayleigh fading channel, using 16QAM and Turbo coding with a coding rate of 5/6. We also clarify that even for a large fading correlation among antenna branches, 1 Gbps is still possible by increasing the transmission power. Therefore, the proposed method reduces the processing rate to 1/4 in the turbo decoder with only a slight loss in the required average received $E_b/N_0$.

• 한국산업정보학회논문지
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• 제6권2호
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• pp.31-37
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• 2001

본 연구에서는 WLL 다중채널 수신단말기 RF-모듈을 제작하였다. 그리고 WLL 다중채널 RF-모듈의 실질적인 성능을 수신감도, 인접채널 선택도, 스퓨리어스 응답제한 등의 파라미터를 이용하여 평가하였다. 실제로 WLL 다중채널용 RF-모듈을 제작하여 측정한 결과, 입력전력이 -90 dBm에서 -30 dBm까지 변화할 때 -30 dBm의 일정한 출력전력이 유지되어 약 60 dB의 동작범위를 가졌다. WLL 단말기 RF 출력단의 통과대역내의 평탄도가 약 2 dB 이내를 유지하여 대역화산신호의 전력제어가 정확히 이루어지고 있음을 확인하였다. 그리고 WLL RF 수신 전단의 전송대역폭은 10 MHz으로 본 연구의 설계목표와 정확히 일치하였다.

• 한국정보통신학회논문지
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• 제2권3호
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• pp.401-408
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• 1998

최근 들어서 실시간 제어, 오디오/비디오 회의, Medical image등의 실시간에 관한 다양한 응용들이 출현하고 있으며 이들은 하부 통신 서브 시스템 (Underlying communication subsystem) 에서 각기의 일정한 QoS (Quality of Service)를 요구한다. 이 경우 통신 서브시스템은 각각의 응용들에 관한 QoS 요구를 만족시키는 실시간 통신 서비스를 제공하여야 하며 동시에 최적의 트래픽을 유지하기 위한 성능을 제공하여야 한다. 본 논문에서 고려하는 단대 단 망은 고 대역폭과 확장성을 내재하고 있음으로 인하여 분산 시스템에 대하여는 자연 적인 플랫폼을 제공하는 것으로 볼 수 있다. 본 논문에서는 QoS를 만족하는 단대 단 망에서의 실시간 프로토콜에 대해 살펴보고, 효율적인 실시간 채널의 디자인 요소(Design Factors)를 제안한다.

• 한국멀티미디어학회논문지
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• 제20권1호
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• pp.1-9
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• 2017

Explosive deployment of smart mobile devices such as smart phones, and tablets along with expansion of wireless internet bandwidth have enabled the deployment of mobile video streaming such that video traffic becomes the most important service in wireless networks. Recently, for more efficient video streaming services, the ISO MPEG group standardized a protocol called DASH (Dynamic Adaptive Streaming over HTTP) and the standard has been quickly adopted by many service providers such as YouTube and Netflix. Despite of the convenience of mobile streaming services, users also suffer from low QoE(Quality of Experience) due to dynamic channel fluctuations and unnecessary downloading due to high churning rates. This paper proposes a noble efficient video rate selection algorithm considering user buffer level, channel condition and churning rate. Computer simulation based performance study showed that the proposed algorithm improved the QoE significantly compared to a method that determines the video rate based on current channel conditions. Especially, the proposed method reduced the rebuffering rate, one of the most important performance factors of the QoE, to a nonnegligible level.