• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.506-515
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• 2010

In this paper, we compare and analyze the spectral efficiency of representative adaptive MIMO algorithms in indoor environments. We first briefly investigate the modulation and demodulation schemes of MIMO algorithms to be compared and then implement adaptive algorithms by using BPSK and square QAM schemes up to 256QAM. We finally compare the spectral efficiency of adaptive MIMO algorithms employing (2$\times$2) or (4$\times$4) antenna array through the computer simulation in indoor environments.

• The KIPS Transactions:PartC
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• v.11C no.1
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• pp.141-148
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• 2004

Recently, the demand of broadband communications such as high-speed internet, HDTV, 3D-HDTV and ATM backbone network has been increased drastically. For transmitting the broad-bandwidth data using wireless network, it is needed to use ka-band frequency. However, the use of this ka-band frequency is seriously affected to the received data performance by rain fading and atmospheric propagation loss at the Ka-band satellite communication link. So, we need adaptive MODEM to endure the degraded performance by channel environment. In this paper, we will present the structure and design of the 155Mbps adaptive Modem adaptively compensated against channel environment. In order to compensate the rain attenuation over the ka-band wireless channel link, the adaptive coding schemes with variable coding rates and the multiple modulation schemes such as trellis coded 8-PSK, QPSK, and BPSK are adopted. And the blind demodulation scheme is proposed to demodulate without Information of modulation mode at the multi-mode demodulator, and the fast phase ambiguity resolving scheme is proposed. The design and simulation results of adaptive Modem by SPW model are provided. This 155Mbps adaptive MODEM was designed and implemented by single ASIC chip with the $0.25\mu{m}$ CMOS standard cell technology and 950 thousand gates.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.236-239
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• 2001

This paper provides a comprehensive study of the effect of time delay on adaptive transmission methods. By adaptive we mean that the transmission of data is made adaptive according to channel conditions. That is, the modulation level at the transmitter is carefully controlled for maximizing bandwidth efficiency, on the basis of the observation of instantaneous channel characteristics. By making use of the simulator developed for the present work, a large number of channel propagation environments including the models proposed in 3GPP were submitted to the simulator and the performance with respect to both time delay and SNR is observed. The results show that the performance is very sensitive to channel delay and in some cases the performance shows irreducible BER (IBER). A large amount of delay together with a high fading rate greatly affects the performance of adaptive transmission systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.337-342
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• 2001

This paper provides a comprehensive study of the effect of time delay on adaptive transmission methods. By adaptive we mean that the transmission of data is made adaptive according to channel conditions. That is, the modulation level at the transmitter is carefully controlled for maximizing bandwidth efficiency, on the basis of the observation of instantaneous channel characteristics. By making use of the simulator developed for the present work, a large number of channel propagation environments including the models proposed in 3GPP were submitted to the simulator and the performance with respect to both time delay and SNR is observed. The results show that the performance is very sensitive to channel delay and in some cases the performance shows irreducible BER (IBER). A large amount of delay together with a high fading rate greatly affects the performance of adaptive transmission systems.

• 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.

• Proceedings of the Korea Contents Association Conference
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• 2003.11a
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• pp.289-302
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• 2003

In this paper, the performance of a multicarrier CDMA system applying adaptive modulation and adaptive subchannel allocation scheme is analyzed in wireless environment. In case of the proposed system, total subchannels is 4 and data is transmitted over 2 subchannels with the biggest fading, Threshold of each channels is 5.2 ㏈, 9 ㏈, 13.2 ㏈ and 8.4 ㏈, 12.2 ㏈, 16.3 ㏈. The BER of 10-3 is 8.1 ㏈. This is increased 12.9 ㏈ in comparison with the existing system. The BPS according to average channel is needed average E$_{b}$ N$_{o}$ of about 15 ㏈ in 7 bit.t.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.3
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• pp.514-522
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• 2015

In Microwave Radio Link, it is necessary to consider the radio fading to consistently assure the radio link of the high quality as the distance. If the fixed modulation is used for the microwave radio link, it is difficult to keep the high availability of link for the case of the long distance. Adaptive Modulation(AM) provide good quality on microwave link, but the application of the only-AM is not enough to provide the availability assurance due to the fluctuating characteristics of link capacity. Our previous study has proposed the improvement method of transmission in association with the distance, however the previous method needed to make up for the common application. There was no suggestion of a mathematical formula with a variable. In this paper, we propose an optimized Adaptive Transmission Techniques with calculating formula of the priority traffic transmission capacity based on AM in consideration of the fade margin for the availability assurance as the distance and the comparison of the channel bandwidth for Long-distance Radio Link.

• Journal of Satellite, Information and Communications
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• v.5 no.1
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• pp.43-47
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• 2010

In future mobile networks, hybrid/integrated satellite and terrestrial systems will play an important role. Most of the mobile communication systems are focused on the terrestrial systems, in this case, compatibilities between the satellite and terrestrial systems are very important for efficiency of the systems. Terrestrial systems of all the 4G mobile communication adopted the adaptive modulation and coding (AMC) schemes for efficient usage of resources, and the updating interval of resource allocation in an order of msec. However, because of the long round trip delay of satellite systems, we cannot employ the same AMC scheme specified for the terrestrial system, and thus it cannot effectively counteract to short term fadings. In the paper, we propose the method to apply AMC to mobile satellite systems. In addition, in order to effectively counteract to short term fadings, we present the simulation results of the AMC combined with an interleaver.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.130-132
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• 2011

본 논문은 지상파 방송망 내 전계강도가 낮은 지역에 최소한의 데이터 전송률을 보장하기 위한 계층변조와 다중경로 채널 극복 및 수신 성능 향상을 위한 다중 안테나 수신기법을 SFN에 적용하여 제안하였다. 계층변조는 기존의 데이터 스트림에 부가적인 데이터 스트림을 삽입함에 따라 지상파 3D HDTV 방송 서비스는 더 많은 유효 전송률을 확보하고 고품질 비디오 서비스를 제공할 수 있었다. 그러나 기본 서비스의 품질을 유지하면서 부가적인 서비스의 품질을 보장하기 위한 대책이 필요하다. 그래서 송, 수신 안테나의 이득을 올리기 위해 다중 안테나 사용 방식을 채용하고, 그 수신 성능을 다중 안테나 위치에 따라 비교해 보았다. 그 결과, 수신 안테나가 한 쪽의 송신 안테나에 가까워질수록 실질적인 SNR이 증가하여 BER 성능이 향상되는 것을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.1
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• pp.69-82
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• 1993

본 논문에서는 디지틀 이동 통신 시스템의 열악한 페이딩 채널에 적합한 변복조 반식중의 하나인${\pi}$/4-shift QPSK 성능을 논하고, 그 성능 개선을 위한 새로운 TCM(trellis-coded modulation)을 적응하여 trellis-부호화된${\pi}$/8-shift 8SPSK 방식을 제안 한다. 기존의 ${\pi}$/4-shift QPSK변조 방식에 TCM의 도입은 요구된 대역폭과 송신 전력과 전송을 그대로 유지하면서 부호화와 변조를 일체화함으로서 부호화 이득(coding gain)을 얻을 수 있다. 이동 통신 채널에서 trellis-부호화된 ${\pi}$/8-shift 8PSK방식의 시스템 성능을 추정하기 위해서, 가산 백색 가우시안 잡음과 레일레이 페이딩 현상이 존재하는 채널에서, 차량속도 변화에 따른 도플러 효과에 의한 페이딩율이 10Hz와 30Hz인 두 경우에 대해 시스템을 모델링한다. Trellis-부호화된${\pi}$/8-shift 8PSK에 대한 부호화 이득은 비트 에러 확률을 적용하여 분석하고, 기본 시스템과 새롭게 모델링 되어진 시스템의 개선된 성능을 비교하기 위해, TCM의 상태수를 4,8,16으로 선정하여 비교 구현해 본 결과, 상태수가 커질수록 더 좋은 성능을 나타내고, 기존의 ${\pi}$/4-shift QPSK보다 trellis-부호된 ${\pi}$/8-shift 8PSK는 가산 백색 가우시안 잡음채널에서는 3~4dB의 부호화 이득을 얻고, 레일레이 페이티 채널하에서 3~16dB정도의 부호화 이득을 얻음을 알 수 있다.