Earticle

디지털 위성 통신 시스템은 다양한 서비스를 제공하기 위하여 지상망과 통합되어 사용되는 경우가 많다. 이 경우에 위성 통신 시스템은 지상망에서 정의한 성능 목표를 만족시켜야 한다. ITU-R 권고서 S.1062 에서는 15GHz 이하의 디지털 위성 통신 시스템의 오류 성능 목표를 명시하고 있다. 권고에서는 오류 버스트 내의 평균 오류의 개수를 로 정의 하고 비트 오류 확률 나누기 를 오류 성능 목표로 제시하고 있다. 본 논문에서는 이러한 오류 성능 목표를 분석하는데 있어서 오류 버스트 내의 평균 오류 개수인 값을 이론적으로 구하는 방법을 제시한다. 이를 토대로 길쌈 부호의 이론 값 및 이에 바탕을 두고 있는 DVB-RCS 터보부호의 값에 대한 이론값을 구하고 시뮬레이션 값과 비교하여 의 이론적인 계산식을 증명해 보일 것이다.

Digital satellite communication systems are usually integrated with terrestrial systems to provide various services. In these cases, they should satisfy the performance objectives defined by the terrestrial systems. Recommendation ITU-R S.1062 specifies the error performance objectives of digital satellite communication systems operating below 15 GHz. The error performance are given in terms of bit error probability divided by the number of the average bit errors in the burst (). This paper presents a theoretical method to estimate that is a very important parameter in the satellite communication systems to analyze the error performance objectives. We show performance estimation result of DVB-RCS turbo code using the presented method, and verify them by comparing to the simulation results.

In 1997, the US National Science Foundation recognized the need to unite research communities together to solve mutual problems, overcome challenges, future development and practical applications of cryptography and error correction coding. Recent works in this area are connected with turbo codes, which have a special ability to provide error correction characteristics of the information transmission close to theoretically obtained values. Besides, they are used for television (DVB-RCS, DVB-RCT), wireless local networks (WiMAX), software-defined radio systems, mobile (3G, 4G, Inmarsat) and space (CCSDS) communications etc. In this article is presented the crypto coding system based on turbo codes with secret keys used by interleavers. All calculations are performed during data encoding, which reduces the computational complexity of data pre-encryption. The necessary mathematical apparatus was presented, the security level of the communication system was estimated, a simulation of the error correction characteristics was performed, and multimedia information was processed. The working characteristics of the classical and proposed turbo codecs do not differ statistically. The results can be used in communication systems for various functional purposes.

계층적 부호화 방식은 멀티미디어 방송 및 멀티캐스팅 서비스(multimedia broadcasting and multicasting services; MBMS)등과 같이 단방향의 서비스에서 신호 품질에 대한 피드백 정보의 활용이 어려울 경우 사용할 수 있는 적응형 수신 기법 중의 하나이다. 이 기술은 계층적 변조 방식과 결합하여 사용함으로써, 부호화율과 변조 방식을 적절하게 결합하여 사용할 수 있는 방식이다. 또한, 터보부호와 결합된 시공간부호를 이용하여 멀티미디어 방송 서비스 제공에 있어서 위성-지상 통합망에서 효과적으로 다이버시티 이득을 얻을 수 있음이 보여왔다. 본 논문에서는 계층적 터보 부호와 결합된 시공간 부호화 방식을 위성-지상 통합 망에 적용하는 방안을 제시한다. 먼저, 시스템 구조 및 동작 원리를 설명하고, 실제 적용 예제들을 제시한다.

A layered coding scheme is one of the adaptive receiving techniques for unidirectional services such as multimedia broadcasting and multicasting services (MBMS), where we cannot utilize feedback information. The layered coding scheme can be used with hierarchical modulations by combining suitable code rates and modulation orders of each. In addition, it has been reported that hybrid and/or integrated satellite systems can effectively achieve transmit diversity gains by appropriate utilization of space time coding combined with turbo codes. This paper proposes a layered turbo coding schemes for hybrid and/or integrated satellite systems. We first introduce the system architecture and operational principle of the proposed scheme, and discuss the applicability.

본 논문에서는 반복 복호 과정에서 연판정 정보값들의 변화로 인하여 성능이 개선되는 상황을 분석하기 위하여 사용되는EXIT(extrinsic information transfer) 차트를 LDPC 부호와 터보 부호에 대하여 생성하는 기법을 소개하고, EXIT 차트 생성과정에서 비트 오류를 제외하였을 경우 나타나는 효과에 대해 살펴보기로 한다. 본 논문에서 제시된 시뮬레이션을 이용한 EXIT 챠트생성 기법은 매우 간단한 방법으로 반복 복호를 사용하는 오류정정부호의 정보흐름을 파악할 수 있는 효율적인 방법이다. 시뮬레이션 결과 분석을 통하여 비트 오류를 제외할 경우 지나치게 정보량이 높은 구간에서만 EXIT 챠트가 생성된다는 사실을 확인할수 있었다.

In this paper, we present two simulation methods to investigate the effect of excluding bit errors on generating the extrinsic information transfer (EXIT) chart for low density parity check (LDPC) and turbo codes. We utilized the simulation methods including and excluding bit errors to generate EXIT chart which was originally proposed for turbo codes. The generated EXIT charts for LDPC and turbo codes shows that the presented methods appropriately demonstrates the performance behaviours of iterative decoding for LDPC and turbo codes. Analysis on the simulation results demonstrates that the EXIT chart excluding the bit errors shows only a small part of the curves where the amount of information is too large.

In order to improve safety and reliability of secure communication system, we propose a joint encryption error correction coding scheme. In this scheme, a conflict-free interleaver parallel decoding method of Turbo codes is used, which is known simply as” efficient Turbo codes”, and it is combined with chaotic encryption together. This scheme makes the information encryption and efficient Turbo coding step be completed at the same time, and explain the encryption/decryption process through the efficient parallel decoding method, and verify the feasibility of the scheme through the application of Turbo code in image transmission as an example. The Matlab simulation results show that, the scheme performance is more excellent and effective in security and reliability than the existing joint encryption and error correction coding scheme. Our proposed scheme may provide an excellent encoding candidate scheme for secure communication system.

Shortened turbo product codes (TPCs) have already been adopted in many standards, especially in multimedia field. Generally, the realizations of shortening turbo codes are based on designing specific interleavers with variable interleaving span; or using shortened–extended Hamming codes as the component to obtain different encoding block sizes. In this paper, we propose a very simple method to realize the shortening. This method is based on a parallel concatenated convolutional code (PCCC) and their inherent characteristic of unequal error protection. Sample simulation results are presented confirming the efficiency of the proposed scheme.

In multimedia transition systems, data usually is divided into levels according to their different importance. For these systems, unequal error protection (UEP) techniques are the powerful methods to guarantee lower BER for the more important classes. Puncturing patterns are very important for turbo codes to produce different code rates. Also, different puncturing patterns can give different BER distributions so that UEP can be obtained. In this paper we will study the affection of puncturing pattern to the BER distribution and present a new scheme of designing the puncturing patterns for turbo codes so that the strong unequal error protection is obtained. In this scheme the puncturing is only carried on the two parity check sequences and an idea of “gradually sparsing” is employed. Simulation results show that, compared with other puncturing schemes, this scheme can provide strong error protection for some bits without apparent degradation for other bits.

A method for bitwise energy optimization of turbo codes with large size is developed. Unlike earlier methods, which relied on searching for minimum-weight codewords, the proposed method finds the required parameters using two bit error rate (BER) distributions obtained via simulation. Therefore, this method can be used not only for the codes with small codeword length, but also for the codes with large codeword length. Simulation results show BER improvements for turbo codes. Though the method is applied to turbo codes in this letter for concreteness, it can also be used for other kinds of error control codes because it does not rely on the code’s structure.

In this paper, we propose an efficient technique for an iterative soft input soft output (SISO) decoding algorithm of block turbo codes with constituent Hamming codes. Pyndiah’s iterative decoding algorithm for block turbo codes supports various code rates by using concatenation, and shows high bit error rate (BER) performance in an additive white Gaussian noise channel (AWGN) environment as the iterative decoding progresses. However, one disadvantage of this code is that the delay increases during decoding with an increasing number of iterations. By employing syndrome-based iterative SISO decoding and iterative SISO decoding using an alpha value, we could obtain high BER performance. In addition, we propose a SISO-hybrid maximum likelihood decoding (SISO-H-MLD) algorithm which achieves almost the same performance as SISO decoding while reducing the number of iterations.

Complexity and energy-efficiency are viewed as two main factors of design error correct coding for the wireless sensor networks. First of all, this paper presents a Weighted Hard-Input Hard-Output (WHIHO) iterative decoding algorithm with the low complexity when the required bit error rate (BER) is satisfied for wireless sensor nodes. A reliability matrix from four different aspects of the decoding process, properly weighs and combines their respective reliability measures, and then employs the combined measure to make a judgment with regard to whether each received bit is correct or not. Next, the energy efficiencies of turbo product codes using HIHO and WHIHO decoding algorithm are analyzed. Simulation results in a BER curve indicating that the WHIHO decoding algorithm can achieve a better tradeoff between reliability and complexity, which compared with conventional HIHO and soft-input and soft-output (SISO) decoding algorithms. The simplicity and effectiveness of WHIHO decoding algorithm makes it a promising candidate for the application for wireless sensor network.

본 논문에서는 지상파 3D HDTV 방송 서비스를 제공하기 위하여 기존의 유럽형 HDTV 방송 서비스인 DVB-T2 전송 시스템의 채널 부호군 중 외부부호로 쓰이는 BCH 부호를 연판정 복호가 가능한 Block Turbo Code로 대체함으로써 생기는 성능 이득과 높은 부호율을 달성하기 위한 방법을 제안하였다. 기존의 DVB-T2 시스템에서 외부부호로 쓰이는 BCH 부호의 부호율의 경우 0.994정도의 높은 부호율을 가진다. 따라서 이에 준하는 높은 부호율을 가지면서 연판정 복호가 가능한 BTC 부호를 제안하고, 기존의 BTC 보다 더 높은 부호율을 가지는 BTC 부호를 설계한다. 모의 실험을 통하여 새롭게 제안된 BTC 에서도 반복복호의 이득이 생기는 것을 확인하고 기존 DVB-T2 시스템의 BCH 부호보다 성능이 우수함을 확인하였다.

This paper presents an efficient carrier recovery algorithm combined with a turbo-coding technique in a mobile communication system. By using a block turbo code made up of independently decodable block codes, we can efficiently recover the fast time-varying carrier phase as well as correct channel errors. Our simulation results reveal that the proposed scheme can accommodate mobiles with high speed, and at the same time can reduce the number of iterations to lock the phase.

본 논문은 다중 입력을 가진 터보 코드 구조에 대한 연구로서 tail-biting 기법에서 효율적으로 Latency를 줄이는 터보 부호 알고리즘 및 하드웨어를 제안하였다. Mobile WiMAX 및 DVB-RCS 등에 적용된 이중 입력 터보 부호기의 고유 특성을 이용, 병렬 처리 하드웨어로 구현한 결과 tail-biting 기법을 위해 필요한 Latency를 기존 대비 약 47%로 줄이는 동시에 파워 소모량도 감소를 시켰다.

The low latency encoder for high data rate duo-binary turbo codes with tail biting trellises is considered. Encoder hardware architecture is proposed using inherent encoding property of duo-binary turbo codes. And we showed that half of execution time as well as the energy can be reduced with the proposed architecture.

This paper introduces an efficient iterative decoding method for high-dimensional block turbo codes. To improve the decoding performance, we modified the soft decision Viterbi decoding algorithm, which is a trellis-based method. The iteration number can be significantly reduced in the soft output decoding process by applying multiple usage of extrinsic reliability information from all available axes and appropriately normalizing them. Our simulation results reveal that the proposed decoding process needs only about 30% of the iterations required to obtain the same performance with the conventional method at a bit error rate range of $10^{-5}\;to\;10^{-6}$.

In this article, we introduce a new class of product codes based on convolutional codes, called convolutional product codes. The structure of product codes enables parallel decoding, which can significantly increase decoder speed in practice. The use of convolutional codes in a product code setting makes it possible to use the vast knowledge base for convolutional codes as well as their flexibility in fast parallel decoders. Just as in turbo codes, interleaving turns out to be critical for the performance of convolutional product codes. The practical decoding advantages over serially-concatenated convolutional codes are emphasized.

In this paper, turbo codes with the DC-free trellis codes based on partition chain as constituent codes are presente. And efficient methods to design the DC-free turbo codes are introduced. An iterative decoding with the MAP algorithm is used for the decoding of the turbo codes designed by various methods. As results of simulations, the presented DC-free turbo codes show better error performances than the DC-free trellis codes.

시공간 블록부호는 송신단에서 여러 개의 안테나를 사용하여 무선 통신의 신뢰도를 높인다. 그런데 4개의 송신안테나를 사용하는 시공간 블록부호는 다이버시티 차수 4와 전송률 1을 동시에 얻을 수 없다. 직교 시공간 블록부호는 다이버시티 차수 4를 유지하지만 전송률에서 손해를 보는 반면, 준직교 시공간 블록부호는 다이버시티 이득에서 손해를 보면서 전송률 1을 유지한다. 본 논문에서는 준직교 시공간 블록부호의 복호기에서 최대 우도 복호 방법으로 비트별 연성결정값을 출력하고, 터보부호와 연접하여 다양한 전송률에서 직교 및 준직교 시공간 블록부호의 성능을 비교하였다.