• Journal of Communications and Networks
• /
• 제10권1호
• /
• pp.44-54
• /
• 2008

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of $10^{-5}$.

• ETRI Journal
• /
• 제33권2호
• /
• pp.155-162
• /
• 2011

The scalable extension of the H.264/AVC video coding standard (SVC) demonstrates superb adaptability in video communications. Joint source and channel coding (JSCC) has been shown to be very effective for such scalable video consisting of parts of different significance. In this paper, a new JSCC scheme for SVC transmission over packet loss channels is proposed which performs two-dimensional optimization on the quality layers of each frame in a rate-distortion (R-D) sense as well as on the temporal hierarchical structure of frames under dependency constraints. To compute the end-to-end R-D points of a frame, a novel reduced trellis algorithm is developed with a significant reduction of complexity from the existing Viterbi-based algorithm. The R-D points of frames are sorted under the hierarchical dependency constraints and optimal JSCC solution is obtained in terms of the best R-D performance. Experimental results show that our scheme outperforms the existing scheme of [13] with average quality gains of 0.26 dB and 0.22 dB for progressive and non-progressive modes respectively.

• 한국방송∙미디어공학회:학술대회논문집
• /
• 한국방송∙미디어공학회 2018년도 추계학술대회
• /
• pp.11-14
• /
• 2018

The aim of this study is to rectify the misclassified image features and enhance the performance of image classification tasks by incorporating a channel- coding technique, widely used in telecommunication. Specifically, the proposed algorithm employs the error - correcting mechanism of convolutional coding combined with the convolutional neural networks (CNNs) that are the state - of- the- arts image classifier s. We develop an encoder and a decoder to employ the error - correcting capability of the convolutional coding. In the encoder, the label values of the image data are converted to convolutional codes that are used as target outputs of the CNN, and the network is trained to minimize the Euclidean distance between the target output codes and the actual output codes. In order to correct misclassified features, the outputs of the network are decoded through the trellis structure with Viterbi algorithm before determining the final prediction. This paper demonstrates that the proposed architecture advances the performance of the neural networks compared to the traditional one- hot encoding method.

• 한국전자파학회논문지
• /
• 제29권4호
• /
• pp.299-307
• /
• 2018

본 논문에서는 X밴드 위성통신을 위해 권고되는 4D-8PSK-TCM(Four Dimensional 8-ary Phase Shift Keying Trellis Coded Modulation) 시스템을 비선형 HPA(High Power Amplifier)와 전치왜곡기를 고려하여 설계하고, 스펙트럼, BER(Bit Error Rate) 성능을 평가 및 분석한다. 위성통신에서는 한정적인 전력으로 인해 전력을 가장 많이 소모하는 HPA의 동작점을 결정하는 비선형 특성 분석이 매우 중요하다. 본 논문에서는 2, 2.25 bits/channel-symbol의 효율을 갖는 4D-8PSK-TCM 시스템을 설계하였다. 시뮬레이션 결과로, 낮은 PAPR(Peak to Average Power Ratio) 특성과, 스펙트럼의 점유 대역폭을 기준으로 SRRC(Square Root Raised Cosine) 필터의 Roll-off 값은 0.35가 효율적이며, 전치왜곡기를 사용하지 않을 경우 HPA에서 약 15~20 dB의 OBO(Output Back-Off)가 요구되며, 전치왜곡기를 사용할 경우 약 1 dB 내외의 OBO가 요구됨을 확인하였다.

• Journal of Communications and Networks
• /
• 제5권2호
• /
• pp.157-166
• /
• 2003

This paper deals with the problem of channel identification for Single Input Multiple Output (SIMO) slow fading channels using clustering algorithms. Due to the intrinsic memory of the discrete-time model of the channel, over short observation periods, the received data vectors of the SIMO model are spread in clusters because of the AWGN noise. Each cluster is practically centered around the ideal channel output labels without noise and the noisy received vectors are distributed according to a multivariate Gaussian distribution. Starting from the Markov SIMO channel model, simultaneous maximum ikelihood estimation of the input vector and the channel coefficients reduce to one of obtaining the values of this pair that minimizes the sum of the Euclidean norms between the received and the estimated output vectors. Viterbi algorithm can be used for this purpose provided the trellis diagram of the Markov model can be labeled with the noiseless channel outputs. The problem of identification of the ideal channel outputs, which is the focus of this paper, is then equivalent to designing a Vector Quantizer (VQ) from a training set corresponding to the observed noisy channel outputs. The Linde-Buzo-Gray (LBG)-type clustering algorithms [1] could be used to obtain the noiseless channel output labels from the noisy received vectors. One problem with the use of such algorithms for blind time-varying channel identification is the codebook initialization. This paper looks at two critical issues with regards to the use of VQ for channel identification. The first has to deal with the applicability of this technique in general; we present theoretical results for the conditions under which the technique may be applicable. The second aims at overcoming the codebook initialization problem by proposing a novel approach which attempts to make the first phase of the channel estimation faster than the classical codebook initialization methods. Sample simulation results are provided confirming the effectiveness of the proposed initialization technique.

• 한국통신학회논문지
• /
• 제27권3A호
• /
• pp.188-195
• /
• 2002

컨벌루셔널 부호의 복호를 위한 M-알고리듬은 복호 트렐리스의 매 단계에서 미리 정해진 개수의 생존 경로를 유지하는 방법으로 구현이 쉽고 고속 데이터의 실시간 처리에 적합하며 최적 복호인 비터비 알고리듬에 비해 복잡도를 크게 감소시킬 수 있다. 반면, 트렐리스 상에서 올바른 경로가 생존 경로에 포함되지 않는 경우 연속된 복호 오류를 생성하는 단점을 가진다. 본 논문에서는 복호 복잡도, 프레임 길이, 부호 구속장의 변화에 따른 M-알고리듬의 성능 분석 결과를 제시하고 구속장을 확장한 부호와 M-알고리듬을 통한 복호를 결합하여 사용 시 얻을 수 있는 성능 이득을 정량화 하였다. 특히 제한된 프레임 길이를 갖는 전송 시스템에 적용되는 경우, 증가된 부호 자유 거리에 의한 성능 이득 효과가 올바른 경로 손실에 의한 성능 감소 효과에 비해 더 큼을 확인하였다. 길이 L=100인 프레임의 오율이 0.01%일 때, 64개의 생존 경로를 갖는 복호를 사용하여 얻어지는 신호 대 잡음비 이득은 구속장을 K=7으로부터 X=9, 11, 15로 증가시킴에 따라 각각 0.6, 0.75, 0.8dB가 된다.