臺灣博碩士論文加值系統

無線多媒體通訊已成為現今行動通訊中的一大熱門議題。對影像傳輸而言，在雜訊嚴重與頻寬有限的無線衰減通道中傳輸，通道編碼是影像傳輸系統中必要的應用。然而，量化後的碼字位元有不同重要性的特性。我們在本論文中，利用位元重要性的不同，利用通道編碼，使接收端能得到最佳的影像品質。

純量編碼量化具有明確的碼字與重建值對應關係與清楚的編碼步驟，因此我們可藉由碼字的位元錯誤率估測接收端在接收此張影像的峰值訊雜比；在通道編碼上，我們選用未來無線通訊中最熱門的錯誤更正碼技術-低密度同位檢測碼，在低密度同位檢測碼上主要影響效能的關鍵在於低密度同位檢測矩陣的設計，在利用效能良好的低密度同位檢測矩陣的門檻值，並結合非均勻功率配置的觀念，給予不同重要性的位元不同的能量，來達到非均勻錯誤保護的目的。此外，因為在實際的無線通訊系統上，必須考慮功率的限制，因此我們在非均勻功率配置上，會調整不同組合的位元的功率來求得較高的峰值訊雜比。

在另一方面本論文也探討文獻上沒有看過的作法，就是利用兩種效能良好的錯誤更正碼，用渦輪結構的方式把其中兩個遞迴式系統迴旋碼換成一個低密度同位檢測碼與遞迴式系統迴旋碼做組合，來分析其效能的好壞。


關鍵字 : 影像傳輸、無線衰減通道、非均勻錯誤保護、通道編碼、
低密度同位檢測

Wireless multi-media communication is one of the most popular topics of today’s wireless communications. For image transmission, channel coding is an essential technique when the channel is noisy and fading. In image transmission, the quantization codeword bits have different degrees of importance. In this thesis, we design an UEP (unequal error protection) channel coding scheme that takes into account the importance of different bits for best image quality at the receiver.

With the codebook for quantization, the bit error rates (BER’s) for bits in a codeword can be converted into the mean squared error (MSE) in the case that transmission errors occur. Therefore, we can estimate the received image peak signal-to-noise ratio (PSNR) at the receiver by using the BER’s in the quantization bits of each codeword. For the channel coding, we choose one recently rediscovered error-correcting technique low-density parity check (LDPC) code, with is considered to be promising for future wireless communication. The key point in the performance on LDPC Codes is designing the low-density parity check matrix. Besides, the threshold effect of LDPC codes should be wisely exploited. Non-uniform power allocation for different importance bits is incorporated to achieve the UEP. Eventually, the goal is to achieve higher PSNR at the receiver.

In this thesis, we also try a new scheme not found in the literature-by using a turbo like interaction between LDPC and turbo codes. We replaced two RSC’s by a new combination of LDPC and RSC. Simulations are conduct to test its performance.

Keywords: image transmission, wireless fading channel, unequal error protection (UEP), channel coding, low-density parity check (LDPC)

第一章 章章 緒論………………………………………………………… 1
1.1 引言…………………………………………………… 1
1.2 研究動機……………………………………………… 2
1.3 本文架構……………………………………………… 4

第二章 低密度同位檢測碼介紹與量化器………………………… 5
2.1 薛農理論極限………………………………………… 6
2.2 低密度同位檢測編碼………………………………… 8
2.3 訊息傳遞演算法……………………………………… 9
2.3.1 以報數法則之訊息傳遞演算法則…………
9
2.4 Tanner 圖…………………………………………… 11
2.5 和積演算法…………………………………………… 13
2.6 低密度同位檢測矩陣設計方式……………………… 22
2.6.1 短迴圈效應………………………………… 23
2.6.2 Gallager LDPC……………………………… 24
2.6.3 EG-LDPC……………………………………… 25
2.6.4 PG-LDPC……………………………………… 28
2.6.5 隨機LDPC…………………………………… 31
2.6.6 IEEE 802.16e LDPC………………………… 32
2.7 Lloyd-Max量化器…………………………………… 34
2.8 無線通道模型………………………………………… 37

第三章 低密度同位檢測編碼與影像傳輸之應用…………………… 39
3.1 以樹狀結構之訊息傳遞演算法………………………… 40
3.2 EG_Gallager_LDPC……………………………………… 42
3.3 影像訊雜比估測………………………………………… 43
3.4 非均勻功率配置………………………………………… 46
3.4.1 同步傳送式非均勻功率配置………………… 47
3.4.2 非同步傳送式非均勻功率配置……………… 50
3.5 渦輪式低密度同位檢測碼……………………………… 53
3.5.1 迴旋碼………………………………………… 53
3.5.2 編碼架構……………………………………… 54
3.5.3 解碼架構……………………………………… 55

第四章 實驗結果與討論……………………………………………… 56
4.1 迴圈-4效應對疊帶次數影響之模擬結果……………果……………… 57
4.2 各種低密度同位檢測矩陣設計方式之模擬結果……… 59
4.3 各種非均勻功率配置之模擬結果……………………… 64
4.2.1 同步傳送式非均勻功率配置之模擬結果…… 64
4.2.2 非同步傳送式非均勻功率配置之模擬結果… 65
4.2.3 實際影像之非均勻功率配置………………… 70
4.4 渦輪式低密度同位檢測碼之模擬結果………………… 78
第五章 結論與未來發展……………………………………………… 79

參考文獻…………………………………………………………………… 81

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