• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.147-151
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• 2010

In this paper, we propose network-coding based two-way relay communication using adaptive modulation scheme for satisfying relay QoS(Quality of Service) according to channel environment between user and relay. Two-way relay communication is bidirectional cooperative communication that users exchange own signal with help of relay. Network-coding based two-way relay communication can achieve high throughput compared to conventional scheme through reducing time slots. we propose adaptive M-QAM modulation scheme in network-coding based two-way relay communication for satisfying QoS of relay. Simulation result shows that the proposed scheme satisfies goal QoS of system.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.6
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• pp.66-74
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• 2010

Recently distributed video coding (DVC) is spotlighted for the environment which has restriction in computing resource at encoder. Wyner-Ziv (WZ) coding is a representative scheme of DVC. The WZ encoder independently encodes key frame and WZ frame respectively by conventional intra coding and channel code. WZ decoder generates side information from reconstructed two key frames (t-1, t+1) based on temporal correlation. The side information is regarded as a noisy version of original WZ frame. Virtual channel noise can be removed by channel decoding process. So the performance of WZ coding greatly depends on the performance of channel code. Among existing channel codes, Turbo code and LDPC code have the most powerful error correction capability. These channel codes use stochastically iterative decoding process. However the iterative decoding process is quite time-consuming, so complexity of WZ decoder is considerably increased. Analysis of the complexity of LPDCA with real video data shows that the portion of complexity of LDPCA decoding is higher than 60% in total WZ decoding complexity. Using the HDA (Hard Decision Aided) method proposed in channel code area, channel decoding complexity can be much reduced. But considerable RD performance loss is possible according to different thresholds and its proper value is different for each sequence. In this paper, we propose an adaptive HDA method which sets up a proper threshold according to sequence. The proposed method shows about 62% and 32% of time saving, respectively in LDPCA and WZ decoding process, while RD performance is not that decreased.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.826-833
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• 2007

In this paper, we present an adaptive transmission system model to establish the baseline for wireless adaptive transmission using CR (Cognitive Radio) systems, and propose an adaptive transmission scheme based on IT (Interference Temperature) cognition for CR systems in the presented system environment. The proposed CR adaptive transmission scheme is the method that provides the CR user with the maximum transmit power in the range of not causing any interference to the incumbent user and guaranteeing the optimal throughput by applying CR-AMC (CR-Adaptive Modulation and Coding) in the given channel state. Simulation results show that in case of using the proposed CR adaptive transmission scheme, there is little degradation of BER performance, while causing no interference to the incumbent user. At the same time, the proposed scheme guarantees the optimal throughput to the CR user in the given channel state.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.3 s.303
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• pp.81-90
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• 2005

When we transmit signals, which are quantized by the vector quantizer (VQ), through noisy channels, the overall performance of the coding system is very dependent on the employed quantization scheme and the channel error effect. In order to design an optimal coding system, the source and channel coding scheme should be jointly optimized as in the channel-optimized VQ. As a suboptimal approach, we may consider the robust VQ (RVQ). In RVQ, we consider developing an index assignment function for mapping the output of quantizers to channel symbols so that the effect of the channel errors is minimized. Recently, a VQ, which can reduce the encoding complexity and is called the sample-adaptive product quantizer (SAPQ), has been proposed. SAPQ has very similar quantizer structure as to the product quantizer (PQ). However, the quantization performance can be better than PQ. Further, the encoding complexity and the memory requirement for the codebooks are lower than the regular full-search VQ case. In this paper, SAPQ is employed in order to design an RVQ to channel errors by reducing the vector dimension. Discussions on the codebook structure of SAPQ and experiments are introduced in an aspect of robustness to noisy channels.

• Journal of Satellite, Information and Communications
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• v.4 no.1
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• pp.28-35
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• 2009

We investigate the adaptive channel attenuation compensation of satellite OFDMA downlink users for minimum PAR (Peak to Average power Ratio), which is one of the main challenging issues in satellite OFDMA application. First, we analyze and compare PAR performances of two main different channel attenuation compensation schemes for OFDMA, i.e., PC-OFDMA (power control OFDMA) and AMC-OFDMA (Adaptive Modulation and Coding). While AMC-OFDMA maintains the constant transmission powers through entire user data subcarriers, PC-OFDMA has non-uniform subcarrier transmission powers because subcarrier powers are separately controlled to compensate each user's sub-channel attenuation. We newly found the fact that non-uniform subcarrier power in PC-OFDMA achieves rather reduced PAR compared to AMC-OFDMA and the amount of reduction becomes larger as the power differences among subcarriers increase. Also, there is an additional PAR reduction in PC-OFDMA by optimizing subcarrier grouping scheme for user's sub-channelization.

• Journal of Communications and Networks
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• v.1 no.2
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• pp.99-110
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• 1999

The adaptive coded modulation (ACM) is a promissing way to provide a substantial improvement in spectral efficiency for slow fading channels. The basic idea is to adapt system functional-ity such as modulation, coding, information rate, and transmission power to varying channel conditions. In this work, the potential of adaptive coded modulation is investigated using cut-off rate anal-ysis in a unified way and using computer simulation. The anal-ysis includes various effects of fading channels such as feedback delay and channel prediction error. It was shown that the adaptive coded modulation can provide several folds of increase in spectral efficiency compared to a fixed coded-modulation system employing QPSK when channel varies slowly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.6
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• pp.669-676
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• 2008

The adaptive resource optimization problem in multi-input multi-output orthogonal frequency division multiple access (MIMO-OFDMA) systems is addressed. This paper, adaptive modulation and coding(AMC) and power control algorithms is proposed with SFC(Space-Frequency Coding), which aims to maximize the system capacity based on the CQI(Channel Quality Information). Firstly, power level is decided to each sub-channels with received feedback signal to noise ratio(SNR). In the second step, sub-carriers are allocated according to modulation type. Simulation results show that the proposed algorithm achieves a better performance than conventional algorithm in terms of capacity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.140-146
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• 2004

In this paper we proposed the reducing method of feedback information for transmitting of adaptable data rate in multi-user OFDMA/FDD systems. In order to transmit downlink channel information to Base-Station(BS) through the limited uplink control channel, the proposed algorithm exploits the channel variation level which describes the similarity among the adjacent clusters and uses just one modulation and coding scheme(MCS) level representing channel information of all clusters'. We investigated the performance in single cell environment. It has a similar overhead for feedback information with conventional algorithm and has better performance in that bandwidth efficiency and outage probability than the conventional algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3C
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• pp.338-347
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• 2007

In this paper, a weighted block adaptive channel estimation (WBA-CE) for a space-time block-coded (STBC) single-carrier transmission with a cyclic-prefix is proposed. In operation of the WBA-CE, a STBC matrix-wise block for filter input symbols is first formulated. Applying a weighted a posteriori error vector-based least-square (LS) criterion for this block, the coefficient correction terms of the WBA-CE are then computed. An approximate steady-state excess mean-square error (EMSE) of the WBA-CE for the stationary optimal coefficient is also analyzed. Simulation results show in a time-varying typical urban (TU) channel that the proposed channel estimator provides better bit-error-rate (BER) performances than conventional algorithms such as the NLMS and RLS channel estimators.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.251-258
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• 2002

In this paper, an adaptive convolutional coding method in multicarrier direct sequence code division multiple access (DS/CDMA) systems is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate compatible punctured convolutional (RCPC) code. To achieve maximum data throughput, an adaptive rate system based on the channel state information (the SINR estimate) is proposed. We show that the proposed adaptive rate convolution coded multicarrier DS/CDMA systems can enhance spectral efficiency and provide frequency diversity.