• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.782-790
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• 1999

In this paper, we propose an adaptive trellis-coded Multiple Quadrature Amplitude Modulation(ATCMQAM) applying MQAM as the modulation scheme in the conventional ATCMPSK (Adaptive trellis-Coded Multiple Phase Shift Keying) for slowly varying Rayleigh fading channels. The proposed system adaptively controls the coding rate combined with modulation level of pragmatic approach to trellis-coded modulation according to the instantaneous fading channel conditions, and employs MQAM as modulation scheme.Results by computer simulation show that the proposed adaptive model using MQAM can realize higher quality transmission with the improvement more than 0.5 ~ 1bit in average bit rate. And there is a coding gain of 2-5dB, depending on the high SNR value, compared with the conventional adaptive model employing MPSK.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.411-416
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• 2003

In this paper, We analysed performance of adaptive modulation system with STTD. Transmission error of system is increased by ISI according to delay wave in wireless channel environment. Therefore, We analysed performance that it is applied adaptive modulation system with STTD to reduce ISI's effect. As a results, Data transmission of high speedㆍhigh quality could know possible by applying adaptive modulation system with STTD. Because of selected high modulation mode in low SNR.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.73-76
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• 2001

A key requirement for packet based wireless communication systems is to provide a high data rate packet service and improved throughput. To achieve a high throughput, adaptive methods for adjustment of the modulation and coding can be used. In this paper, we propose and analyze a scheme which is a combination of an adaptive modulation and coding(AMC) and transmit diversity(TD). Two different TD schemes are analysed: STTD and STD. Proposed system provides significant improvement in the average throughput.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.5
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• pp.893-898
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• 2003

This paper proposes a Truncated Type-II Hybrid ARQ scheme and coding techniques using an adaptive modulation system to achieve high throughput data transmission systems for wireless multimedia communication systems. In this paper, the adaptive modulation system analyzed in Nakagami (m-distribution) fading channel environment. The adaptive modulation system controls the modulation level and symbol rate according to the Nakagami fading parameter(m). When the received Eb/No is high or the Nakagami fading parameter m is high, the propose system selects higher modulation level and higher symbol rate to increase throughput. On the other hand, this system selects lower modulation level and lower symbol rate to prevent throughput performance degradation when the received Eb/No is low. The modulation method have been adopted QPSK(Quadrature Phase Shift Keying), 16QAM(Quadrature Amplitude Modulation), 64QAM, 256QAM. Therefore, adaptive modulation systems with truncated type-II hybrid ARQ scheme is proper for wireless multimedia communication system that require high reliability and delay-limited applications.

• Journal of Digital Convergence
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• v.11 no.12
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• pp.401-406
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• 2013

In this paper, the optimum transmission method is proposed to save the energy and to increase the throughput of the adaptive modulation mobile radio system with frame length control. Traditionally, adaptive modulation has been used to improve the throughput using the power margin of the system design. Considering the frame length vs energy saving and adaptive modulation, the optimum transmission method is proposed for hub and mobile station each.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.282-291
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• 2011

Adaptive modulation(AM) is an important technique to increase the system efficiency, in which transmitter selects the most suitable modulation mode adaptively according to channel state in the temporary and spatially varying communication environment. Fixed modulation on channels with varying signal-to-noise ratio(SNR) is that the bit-errorrate(BER) probability performance is changing with the channel quality. An adaptive modulation scheme can be designed to have a BER which is constant for all channel SNRs. The correct as well as fast and simple SNR estimation is required essentially for this adaptive modulation. In order to operate adaptive modulation system effectively, in this paper, we analyze the effect of SNR estimation performance to it through the average BER and data throughput. Applying SNR estimation based on auto-correlation of decision feedback signal and others to adaptive modulation system, we also confirm performance degradation or improvement of its which is decided by SNR estimation error at each transition point of modulation level. Since SNR estimation based on auto-correlation of decision feedback signal shows stable estimation performance for various quadrature amplitude modulation(QAM) comparatively, this can be reduced degradation than others at each transition point of modulation level.

• Journal of Digital Contents Society
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• v.12 no.3
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• pp.355-360
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• 2011

In this paper, the performance of OFDM (Orthogonal Frequency Division Multiplexing) was assessed by using computer simulations performed using Matlab. We analyzed channel estimation algorithm for adaptive modulation techniques and effect of system using designed simulator in Multimedia wireless communication multipath fading channel environment. Also, we analyzed performance of adaptive OFDM systems that apply adaptive equalizer using guided result through BER. In result, in case of adaptive modulation OFDM systems that modulation mode changes according to channel state, we knew that adaptive modulation OFDM systems have gains of about 7dB performance than general system (BER=$10^{-1}$). Thus we know that adaptive OFDM propose systems is required for efficient transmission in the high speed Multimedia wireless communication channel environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.2
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• pp.501-506
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• 2010

The proposal set out in this paper, is the Adaptive-MCM(Modulation, Coding and MIMO) system, which results from the combination of adaptive modulation and coding (AMC) and multiple input multiple output (MIMO) schemes. The performance of this system is analyzed through computer simulation. By using the MIMO scheme adaptively as well, the proposed Adaptive-MCM system, presents a better improvement of data rate and error performance compared to the AMC system. The throughput performance of the Adaptive-MCM system is analyzed and compared with the throughput performance of Non-Adaptive-MCM Systems. As a result of the simulation, we can infer that, at a fixed MCM level, there is an improvement of the trade-off between secure Signal to Noise Ratio (SNR) and a high data rate. Consequently, this trade-off improvement results in a better average data rate.

• Journal of information and communication convergence engineering
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• v.9 no.2
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• pp.183-186
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• 2011

In this work, we consider imperfectness of feedback channels in the adaptive transmission scheme which was previously studied with an assumption of error-free feedback channels. New method of mapping the modulation index into the feedback channel symbols and quantifying feedback error over fading channels are proposed. The presented method and results are expected to offer valuable tools for the system designer to efficiently implement adaptive diversity schemes to compensate for the performance degradation due to feedback error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.810-816
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• 2001

This paper proposes a Truncated Type-II Hybrid ARQ scheme using an adaptive modulation system to achieve high throughput data transmission systems for mobile communication systems. In this paper, the adaptive modulation system analyzed in Nakagami (m-distribution) fading channel environment. The adaptive modulation system controls the modulation level and symbol rate according to the Nakagami fading parameter(m). When the received $E_bN_0$ is high or the Nakagami fading parameter m is high, the propose system selects higher modulation level and higher symbol rate to increase throughput. On the other hand, this system selects lower modulation level and lower symbol rate to prevent throughput performance degradation when the received $E_bN_0$ is low. The modulation method have been adopted QPSK(Quadrature Phase Shift Keying), 16 QAM(Quadrature Amplitude Modulation), 64 QAM, 256 QAM. Therefore, Adaptive Modulation Systems with Truncated Type-II Hybrid ARQ Scheme is proper for mobile and radio for mobile and radio data communication system that require high reliability and delay-limited applications.