• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.577-586
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• 2011

Modem digital communication systems are required to use forward error correction (FEC) codes to combat inevitable channel impairment. Turbo codes or low density parity check (LDPC) codes, using iterative decoding with soft decision detection (SDD) information, are the most common examples. The excellent performance of these codes should be conditioned on accurate estimation of soft decision detection information. In order to use FEC codes with iterative decoding for Multi-Input Multi-Output (MIMO) system, reliable soft decision channel gain should be provided. In this paper, we investigate efficient SDD methods for turbo-coded MIMO system, and derive the corresponding formulas of SDD for various MIMO detection schemes. We present simulation results of the derived SDD schemes for turbo-coded MIMO systems, and show that the presented results almost approximate to maximum likelihood detection performance with much less computational load.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.4
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• pp.712-720
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• 1994

In digital mobile communication systems, the convolutional coding is considered as the optimum error correcting scheme. Recently, the Viterbi algorithm is widely used for the decoding of convolutional code. Most Viterbi decoder has been proposed in conde rate R=1/2 or 2/3 with memory components (m) less than 3. which degrades the error correcting capability because of small code constraints (K). We consider the design method for typical code rate R=1/2, K=7(171,133) convolutional code with memory components, m=6. In this paper, a novel construction method is presented which combines maximum likelihood decoding with a state transition double detection and comparison method. And the designed circuit has the error-correcting capability of random 2 bit error. As the results of logic simulation, it is shown that the proposed Viterbi decoder exactly corrects 1 bit and 2 bit error signal.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.405-409
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• 2009

In this paper, the effects of LLR (Log-Likelihood Ratio) approximation on LDPC (Low-Density Parity-Check) decoder performance are analyzed, and optimal design conditions of LDPC decoder are derived. The min-sum LDPC decoding algorithm which is based on an approximation of LLR sum-product algorithm is modeled and simulated by MATLAB, and it is analyzed that the effects of LLR approximation bit-width and maximum iteration cycles on the bit error rate (BER) performance of LDCP decoder. The parity check matrix for IEEE 802.11n standard which has block length of 1,944 bits and code rate of 1/2 is used, and AWGN channel with QPSK modulation is assumed. The simulation results show that optimal BER performance is achieved for 7 iteration cycles and LLR bit-width of (7,5).

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.83-86
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• 2007

In the blind Maximum-likelihood (ML) detection for Orthogonal Space-Time Block Codes (OSTBC), the problem of ambiguity in determining the symbols has been a great concern. A solution to this problem is to apply semi-blind ML detection, i.e., the blind ML decoding with pilot symbols or training sequence. In order to increase the performance, the number of pilot symbols or length of training sequence should be increased. Unfortunately, this leads to a significant decrease in system spectral efficiency. This work presents an approach to resolve the aforementioned issue by introducing a new method for constructing transmitted information symbol. Thus, by transmitting information symbols drawn from different modulation constellation, the ambiguity can be easily eliminated in blind detection. Also, computer simulations are implemented to verify the performance of the proposed approach.

• Journal of information and communication convergence engineering
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• v.6 no.2
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• pp.150-153
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• 2008

In the blind Maximum-likelihood (ML) detection for Orthogonal Space-Time Block Codes (OSTBC), the problem of ambiguity in determining the symbols has been a great concern. A possible solution to this problem is to apply semi-blind ML detection, i.e. the blind ML decoding with pilot symbols or training sequence. In order to increase the performance, the number of pilot symbols or length of training sequence should be increased. Unfortunately, this leads to a significantly decrease in system spectral efficiency. This work presents an approach to resolve the aforementioned issue by introducing a new method for constructing transmitted information symbols, in which transmitting information symbols drawn form different modulation constellations. Therefore, the ambiguity can be easily eliminated. In addition, computer simulation is implemented to verify the performance of the proposed approach.

• ETRI Journal
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• v.45 no.6
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• pp.952-962
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• 2023

In this study, a space-time transmission scheme is proposed to tackle the limitations of channel estimation with orthogonal pilot information in colocated multiple-input multiple-output systems with several transmitting and receiving antennas. Channel information is obtained using orthogonal pilots. Channel estimation introduces pilot heads required to estimate a channel. This leads to bandwidth insufficiency. As a result, trade-offs exist between the number of pilots required to estimate a channel versus spectral efficiency. The detection of data symbols is performed using the maximum likelihood decoding method as it provides a consistent approach to parameter estimation problems. The moment-generating function of the instantaneous signal-to-noise ratio is used to drive an approximate expression of the symbol error rate for the proposed scheme. Furthermore, the order of diversity is less by one than the number of receiver antennas used in the proposed scheme. The effect of the length of a pilot sequence on the proposed scheme's performance is also investigated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.45-52
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• 2004

This Paper presents a modified hard decision Viterbi decoder with an error prediction circuit enhancing performance for the burst error inputs. Viterbi decoder employs the maximum likelihood decoding algorithm which shows excellent error correction capability for the random error inputs. Viterbi decoders, however, suffer poor error correction performance for the burst error inputs under the fading channel. The proposed error prediction algorithm increases error correction capability for the burst errors. The algorithm estimaties the burst error data area using the maximum path metric for the erroneous inputs, It calculates burst error intervals based on increases in the maximum values of a path metric. The proposed decoder keeps a performance the same as the conventional decoders on AWGN channels for the IEEE802.l1a WLAN system. It shows performance inproving 15% on the burst error of multi-path fading channels, widely used in mobile systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3C
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• pp.304-310
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• 2009

This paper proposes a successive MAP (maximum a posteriori probability) detection scheme with SoIC(soft interference cancellation) to reduce the receiver complexity of hierarchical M-ary QAM system. For the successive MAP detection, modulation symbols generated from the other data streams are treated as Gaussian noise or eliminated as the soft interference according to their priorities. The log-likelihood ratio of the a posteriori probability (LAPRP) of each bit is calculated by the MAP detector with an adjusted noise variance in order to take the elimination and Gaussian assumption effect into account. By separating the detection process into the successive steps, the detection complexity is reduced to increase linearly with the number of bits per hierarchical M-ary QAM symbol. Simulation results show that the proposed detection provides a small performance degradation as compared to the optimal MAP detection.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.66-76
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• 2016

In this paper, we propose a new hierarchical modulation scheme for DVB-NGH to improve the performance of LP (Low-Parity) signals by applying a conventional constellation-rotation method to the LP signals without virtually a loss of performance of a HP (High-Parity) signals. The improvement of the LP signals is mainly due to the increased divesity gain caused by the constellation-rotation method which barely affect the performance of the HP signals. For the new scheme, we also propose a hardware-efficient ML (Maximum-Likelihood) detection algorithm that first decodes the HP signals by using a conventional HP receiver, and then simply decodes the precoded LP signals based on the pre-detected HP signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.10
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• pp.858-866
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• 2013

In the DVB-S2, which is the technical specification of the second generation digital video broadcasting via satellite, APSK modulation scheme along with LDPC coding schemes are defined. APSK is a multi-lelvel PSK modulation scheme and decoding of LDPC coded signal requires soft decision information. Therefore, the APSK demodulator at the receiver should have capability of estimating soft information. In this paper, we introduce a method to estimate soft information by using simple distance estimation, and show that this method overestimates the soft information. Subsequently, this overestimated soft information leads to performance degradation. In order to overcome this problem, we propose a scaling method to improve the performance at the receiver In addition, we show that the proposed scaling scheme enables us to estimate the soft information with linear order complexity and produce the performance close to the maximum likelihood detection.