• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.11
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• pp.17-21
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• 2011

In this paper, we propose a pilot symbol assisted low complexity LS channel estimation method for OFDM in fast time varying channels. The proposed method shows low complexity characteristics in terms of memory space and processing time compared with conventional BEM channel model LS estimation methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.27-33
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• 2009

This paper proposes transmit power control techniques with fading channel prediction scheme based on recurrent neural network for high-speed mobile communication systems. The operation result of recurrent neural network which is derived interpretively solves complexity problems of neural network circuit, and channel gain of multiple transmit antenna is derived with maximum ratio combining(MRC) by using the operation result, and this channel gain control transmit power of each antenna. simulation results show that proposed method has a outstanding performance compared to method that is not to be controlled power based on channel prediction. Most of legacy studies are for robust receive technique of fading signals or channel prediction of fading signals limited low-speed mobility, but in open loop Power control, proposed channel prediction method decrease system complexity with removal of fading effect in transmitter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5C
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• pp.556-564
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• 2007

This paper proposes an efficient scheme to track a time variant channel induced by multi-path Rayleigh fading in mobile MIMO-OFDM systems with null sub-carriers. The proposed adaptive channel tracking scheme removes in the frequency domain the interfering signals of the other transmit (Tx) antennas by using a predicted channel frequency response before starting the channel estimation. Time domain channel estimation is then performed to reduce the additive white Gaussian noise (AWGN). The simulation results show that the proposed method is better than the conventional channel tracking method [3] in time varying channel environments. At a Doppler frequency of 300 Hz and bit error rates (BER) of 10-3, signal-to-noise power ratio (Eb/N0) gains of about 2.5 dB are achieved relative to the conventional channel tracking method [3]. At a Doppler frequency of 600 Hz, the performance difference between the proposed method and conventional one becomes much larger.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1863-1868
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• 2006

In this paper we propose the communication system model which improve the performance of OFDM based DSRC system by adopting selective pilot overlay channel estimation scheme. Assuming AWGN and fading channel environment, the performance of OFDM system according to IEEE802.11p physical layer being standardized for OFDM based DSRC is obtained, and the performance of proposed OFDM based DSRC system adopting selective pilot overlay channel estimation scheme is compared with the conventional system. from the simulation results, it is shown that proposed system is superior to conventional one due to reducing channel estimation error.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.222-224
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• 2012

UDT(UDP Data Transfer protocol)는 UDP 기반 전송프로토콜로써 TCP와 같은 전송 신뢰성과 안정성을 보장하면서 우수한 전송성능을 보이고 있다. 성능향상을 위해 다수의 채널을 이용하는 병렬전송 기법이 시도되고 있으나, 이는 네트워크 환경에 최적의 성능을 보이는 채널의 수의 결정이 매우 중요하다. 그러나 데이터를 전송하기 전에 매번 현재의 네트워크 환경에 최적인 채널 수를 결정하는 실험을 하는 것은 불편한 일이다. 본 논문에서는 UDT 기반 병렬전송에서 최적의 채널 수 예측기법을 제안한다. 실험을 통해 네트워크 환경에 따른 채널 수의 추이를 분석하고 최적 채널 수 결정 기법에 대해 논하고자 한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.9
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• pp.1889-1894
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• 2011

Channel allocation is one of the important issues in the multichannel transmission. In the cognitive radio networks, channel allocation scheme should be designed to improve spectrum efficiency without interfering with the transmission of licensed users. In this paper, we propose a spectrum hole prediction based channel allocation scheme. The proposed channel allocation scheme, predicts spectrum hole by using the channel success rate, and limit the transmission of secondary user's data, and it reduces the interference to the primary user. The performance of proposed channel allocation scheme is evaluated by the computer simulation.

• Proceedings of the Korea Information Processing Society Conference
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• 2006.05a
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• pp.1057-1060
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• 2006

본 논문에서는 OFDMA-TDD 환경에서 서비스 사용자들에게 QoS 를 보장해줄 수 있도록 예측 알고리즘을 이용하여 한정된 무선 자원을 효율적이고 공정하게 스케줄링 해주는 알고리즘을 연구하였다. 예측 알고리즘은 각 사용자의 이동 정보와 단말들의 변화해온 채널상태의 history data 를 이용하여 앞으로의 채널상태를 예측하고, 예측된 결과는 사용자의 이동 정보와 함께 무선 자원 스케줄링에 적용한다. 또한 이동단말과 고정단말이 공존하는 환경에서는 QoS 보장에 있어 공정하지 않음을 밝히고, 이와 같은 문제를 해결하는 방안을 제안하였으며, 실험결과를 PF 알고리즘과 비교하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.597-598
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• 2011

In this paper, the spectrum hole prediction scheme was proposed for the cognitive radio networks using the primary user's traffic pattern. Using the channel prediction, the collision probability with primary users can be reduced and the system throuthput can be improved. Simulation result shows that the proposed method can enhance the throughput and reduce the interference to the primary user below the desired threshold.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.757-763
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• 2011

This paper presents a channel reservation scheme using Wiener prediction model in order to reduce the rate of forced termination of cognitive users in cognitive radio networks. The proposed method uses Wiener prediction model to predict the number of radio channel required by the reappearance of primary users, and then calculates and reserves the number of channels that cognitive users demand for their spectrum handoff. Through the simulation we investigate cognitive users' forced termination rate and blocking rate with and without channel reservation. In addition we show the bandwidth utilization efficiency for both cases. The results show that the proposed scheme can reduce the forced termination rate of cognitive users at the cost of slightly increasing in blocking rate. Also it is seen that there is little difference in bandwidth utilization efficiency for both cases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.370-377
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• 2004

In this paper, we present an adaptive modulation technique for orthogonal frequency division multiplexing (OFDM) for broadband wireless communications. Also, using improved channel prediction, we enhance the performance of adaptive OFDM in high mobility environments. Adaptive modulation technique has been shown to achieve reliable high-rate data transmission over frequency-selective fading channel when OFDM is employed. This scheme requires the accurate channel information between two stations for a better performance. In an outdoor high mobility environment, most of adaptive OFDM systems have to be given the channel information transmitted from the receiver. Even if it is possible, there is some delay. Moreover, the channel impulse response between two stations is very rapidly varied. If the channel information is obsolete at the time of transmission, then poor system performance will result. In order to solve this problem, we propose adaptive OFDM with improved channel predictor. The proposed bit allocation algorithm has a lower complexity and the proposed scheme mitigates the effect of channel delay. Robust approach is less sensitive to outdated channel information. Performance results show that the proposed scheme can achieve considerable performance enhancement.