衰減通道中進階雙預測器DPCM影像傳輸系統

本研究利用四分樹影像分割法（quadtree segmentation）改善數位影像模式中的非穩定（non-stationary）統計狀態，並使用雙預測器誤差脈波編碼調變（double predictor differential pulse code modulation, DP-DPCM）方式，藉以改善傳統DPCM的量化誤差及增加影像壓縮率和傳輸速度。我們使用四相位鍵移（quadrature phase shift keying, QPSK）調變及加上通道雜訊，來模擬近似現今無線通訊（wireless communication）的系統。通道編碼的部分，我們採用迴旋編碼器，解碼器則使用最大相關威特比硬性決定解碼，使用通道編碼來保護我們的資料在通過衰減通道時能減少錯誤位元發生。我們將探討以此進階雙預測器DPCM影像傳輸在衰減通道的效能。

關鍵字

四分樹影像分割法；統計非穩定狀態；雙預測器誤差；脈波編碼調變；四相位鍵移；通道雜訊；衰減通道

並列摘要

In this study, a given 256x256 digital image is segmented by a quadtree algorithm to form variable blocksize image models, in which the nonstationary statistical characteristics of the given image source can be better exploited. Each variable blocksize sub-image is then applied the double predictor differential pulse code modulation (DP-DPCM) coding scheme to further reduce the quantization error than that in a traditional differential pulse code modulation (DPCM) algorithm. The DP-DPCM algorithm can produce a better data compression ratio than that of a DPCM scheme and can therefore increase the system transmission rate. The transmission medium is modeled as a fading communication channel and quadrature phase shift keying (QPSK) modulation is adopted in the study. To improve the system performance over wireless fading channel, a channel coding algorithm is considered. To simplify the system simulation, we have utilized the convolutional encoder and maximum-likelihood Viterbi hard decision decoder. The channel coding scheme is to protect the transmitted source data and to reduce bit error rate (BER) in fading channel. Performance of this advanced double predictor differential pulse code modulation image transmission system over fading channel is evaluated in this research.

並列關鍵字

quadtree segmentation ； non-stationary statistical ； double predictor differential pulse code modulation ； differential pulse code modulation ； quadrature phase shift keying ； fading channel

國際替代計量

衰減通道中進階雙預測器DPCM影像傳輸系統

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