• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.2
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• pp.161-168
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• 2019

This paper proposes a variable data transfer asymmetric TDD(Time Division Duplex) system for small UAV(Unmanned Aerial Vehicle) data link system. In the proposed method, a turbo decoder with a double buffer controller is proposed to apply turbo decoder with long decoding time to asymmetric TDD system. The proposed method achieves variable data transfer rate and maximum data transfer rate. The advantage of the proposed method is demonstrated by its data transfer rate. The measured data transfer rate is more than 1.8 times than that of symmetric TDD system. In addition, PER(Packet Error Rate) performance is the same and data transfer rate is variable.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.504-511
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• 2016

In this paper, MIMO system based on turbo equalization techniques which LDPC codes were outer code and space time trellis codes (STTC) were employed as an inner code are studied. LDPC decoder and STTC decoder are connected through the interleaving and de-interleaving that updates each other's information repeatedly. In conventional turbo equalization of MIMO system, BCJR decoder which decodes STTC coded bits required two-bit wise decoding processing. Therefore duo-binary turbo codes are optimal for MIMO system combined with STTC codes. However a LDPC decoder requires bit unit processing, because LDPC codes can't be applied to these system. Therefore this paper proposed turbo equalization for MIMO system based on LDPC codes combined with STTC codes. By the simulation results, we confirmed performance of proposed turbo equalization model was improved about 0.6dB than that of conventional LDPC codes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3C
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• pp.215-223
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• 2003

Turbo codes are selected as FEC(Forward error correction) codes with convolution code in 3GFP(3rd generation partnership project) and 3GPP2 standard of IMT2000. Especially, l/3 turbo code with K=4 is employed for 3GPP standard. In this paper, we proposed a hardware structure of a turbo decoder and denveloped the decoder for 3GPP standard turbo code. For its efficient operation, we design a SOVA decoder by employing a register exchange decoding block and new path metric normalization block as a SISO constituent decoder. In addition, we estimate its performance under MATLAB 6.0 and designed the turbo decoder including control block, input control buffer, SOVA constituent decoder with VHDL. Finally, we synthesized the developed turbo decoder under Synopsys FPGA Express and verified it with ALTERA EPF200SRC240-3 FPGA device.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10C
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• pp.923-929
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• 2003

Turbo processing have been known as methods close to Shannon limit in the aspect of wireless multi-input multi-output (MIMO) communications similarly to wireless single antenna communication. The iterative processing can maximize the mutual effect of coding and interference cancellation, but LDPC coding has not been used for turbo processing because of the inherent decoding process delay. This paper suggests a LDPC coded MIMO system with turbo parallel space-time (Turbo-PAST) processing for high-speed wireless communications and proposes a average soft-output syndrome (ASS) check scheme at low signal to noise ratio (SNR) for the Turbo-PAST system to decide the reliability of decoded frame. Simulation results show that the suggested system outperforms conventional system and the proposed ASS scheme effectively reduces the amount of turbo processing iterations without performance degradation from the point of average number of iterations.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.4
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• pp.183-191
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• 2010

In the recent digital communication systems, the performance of Turbo Code used as the error correction coding method depends on the interleaver size influencing the free distance determination and the iterative decoding algorithms of the turbo decoder. However, some iterations are needed to get a better performance, but these processes require a large time delay. Recently methods of reducing the number of iteration have been studied without degrading original performance. In this paper, the new method of combining ME (Mean Estimate) stopping criterion with SDR (sign difference ratio) stopping criterion among previous stopping criteria is proposed, and the fact of compensating each method's missed detection is verified. Faster decoding is realized that about 1~2 time iterations to reduced through adopting this method into serially concatenated both decoders. System Environments were assumed W-CDMA forward link system with intense MAI (multiple access interference).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.2
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• pp.63-70
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• 2016

To increase throughput efficiency and improve performance, FTN(Faster Than Nyquist) method and LDPC(Low Density Parity Code) codes are employed in DVB-S3 system. In this paper, we proposed efficient turbo equalization model to minimize inter symbol interference induced by FTN transmission. This paper introduces two conventional scheme employing SIC(Successive Interference Cancellation) and BCJR equalizer. Then, we proposed new scheme to resolve problems in this two conventional scheme. To make performance improved in turbo equalization model, the outputs of LDPC and BCJR equalizer are iteratively exchange probabilistic information. In fed LDPC outputs as extrinsic informa tion of BCJR equalizer. we split LDPC output to separate bit probabilities. We compare performance of proposed scheme to that of conventional methods through using simulation in AWGN(Additive White Gaussian Noise) channel. We confirmed that performance was improved compared to conventional methods as increasing throughput parameters of FTN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1C
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• pp.81-89
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• 2003

For improving the performance of noise suppression in tactical communication environments, an enhanced MELP vocoder is suggested, in which an acoustic noise suppressor is integrated into the front end of the MELP algorithm, and an FEC code into the channel side of the MELP algorithm. The acoustic noise suppressor is the modified IS-127 EVRC noise suppressor which is adapted for the MELP vocoder. As for FEC, the turbo code, which consists of rate-113 encoding and BCJR-MAP decoding algorithm, is utilized. In acoustic noise environments, the lower the SNR becomes, the more the effects of noise suppression is increased. Moreover, The suggested system has greater noise suppression effects in stationary noise than in non-stationary noise, and shows its superiority by 0.24 in MOS test to the original MELP vocoder. When the interleave size is one MELP frame, BER 10-6 is accomplished at channel bit SNR 4.2 ㏈. The iteration of decoding at 3 times is suboptimal in its complexity vs. performance. Synthetic quality is realized as more than MOS 2.5 at channel bit SNR 2 ㏈ in subjective voice quality test, when the interleave size is one MELP frame and the iteration of decoding is more than 3 times.

• The KIPS Transactions:PartC
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• v.11C no.3
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• pp.353-360
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• 2004

In this Paper, We propose an efficient iteration decoding control method with variable iteration decoding of iteration codes decoding using Cyclic Redundancy Check. As the number of iterations increases, the bit error rate and frame error rate of the decoder decrease and the incremental improvement gradually diminishes. However, when the iteration decoding number is increased, it require much delay and amount of processing time for decoding. Also, It can be observed the error nor that the performance cannot be improved even though increasing of the number of iterations and SNR. So, Suitable number of iterations for stopping criterion is required. we propose variable iteration control method to adapt variation of channel using Frame Error-Check indicator. Therefore, the amount of computation and the number of iterations required for iteration decoding with CRC method can be reduced without sacrificing performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.4
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• pp.165-172
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• 2002

In the next generation mobile communications, powerful channel coding is essential in order to obtain high quality multimedia services. Turbo code can achieve good error performance by iterative decoding, but more iterations result in additional computational complexity and delay. Thus, a method to reduce the number of iterations without additional performance degradation is needed. Turbo code with CRC is known to be the most efficient method to reduce the number of iterations. In this scheme, the performance may be degraded by the edge-effect like the conventional turbo code without CRC. In this paper, a method to eliminate the edge-effect is proposed by adopting D-parameter to the conventional s-random interleaver. As results of simulation, the edge-effect of the turbo code with CRC is shown to be successfully eliminated by using the new interleaver designed with D-parameter.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.45-49
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• 2016

The performance of underwater acoustic communication systems is sensitive to inter-symbol interference caused by delay spread developed from multipath signal propagation. The multipath nature of underwater channels causes signal distortion and error floor. In order to improve the performance, it is necessary to employ an iterative coding scheme. Of the various iterative coding schemes, turbo code and convolutional code based on the BCJR algorithm have recently dominated this application. In this study, the performance of iterative codes based on turbo equalizers with equivalent coding rates and similar code word lengths were analyzed. Underwater acoustic communication system experiments using these two coding techniques were conducted on Kyeong-chun Lake in Munkyeong City. The distance between the transmitter and receiver was 400 m, and the data transfer rate was 1 Kbps. The experimental results revealed that the performance of turbo codes is better for channeling than that of convolutional codes that use a BCJR decoding algorithm.