臺灣博碩士論文加值系統

本篇論文主要是在研究低密度奇偶檢驗碼（LDPC）應用於快跳頻（FFH）二元頻率鍵移（BFSK）的系統上，通過有部分頻帶雜訊干擾時其系統錯誤率表現。我們使用不同的分集結合技術來計算每個編碼字元的可靠度。在這論文中我們考慮最大可能分集結合技術及二種低複雜的次佳分集結合技術，這二種技術分別為平方率配合適應性增益控制的結合技術及平方率配合等增益結合技術。

模擬結果顯示，我們所建議的系統在結合分集及編碼的增益之後，可以提供非常好的錯誤更正能力來對抗部分頻帶雜訊的干擾。

The performance of low-density parity-check (LDPC) codes is investigated for fast frequency hopping / binary frequency shift keying (FFH/BFSK) in partial-band noise jamming channels. We employ different diversity combining schemes to compute the codeword bit decision reliability. In this paper, we consider the maximum-likelihood (ML) diversity combining scheme and two low-complexity suboptimal diversity combining schemes: square-law with adaptive gain control (AGC) combining and square-law with equal gain combining.

Simulation results show that, by combining both of the diversity and coding gain, our proposed system can provide excellent performance against partial-band noise jamming.

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
Chinese Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . II
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . III
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . VI
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Research Motivation . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Organization of the Thesis . . . . . . . . . . . . . . . . . . .3
2. Spread Spectrum Techniques . . . . . . . . . . . . . . . . . . . 5
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.2 Noncoherent Fast Frequency Hopping . . . . . . . . . . . . . . .6
2.3 Bayes’ Theorem . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4 Likelihood Ratio Test . . . . . . . . . . . . . . . . . . . . . 10
2.5 Maximum A Posteriori Criterion . . . . . . . . . . . . . . . . .11
2.6 Optimum Receiver for M-ary Orthogonal Signals . . . . . . . . . 12
2.7 The Maximum Likelihood Decision . . . . . . . . . . . . . . . . 14
2.8 Diversity Combining Schemes . . . . . . . . . . . . . . . . . . 17
2.8.1 ML Diversity Combining Scheme . . . . . . . . . . . . . . . . 17
2.8.2 AGC Diversity Combining Scheme . . . . . . . . . . . . . . . .19
2.8.3 Equal Gain Diversity Combining Scheme . . . . . . . . . . . . 20
3. Low-Density Parity-Check Codes . . . . . . . . . . . . . . . . . 22
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .22
3.2 Linear Block Codes . . . . . . . . . . . . . . . . . . . . . . .23
3.3 Tanner Graph . . . . . . . . . . . . . . . . . . . . . . . . . .26
3.4 Construction of LDPC Codes . . . . . . . . . . . . . . . . . . .27
3.5 Log-Likelihood Ratios . . . . . . . . . . . . . . . . . . . . . 28
3.6 Iterative SISO Decoding . . . . . . . . . . . . . . . . . . . . 28
3.7 LLR for Variable Node Message . . . . . . . . . . . . . . . . . 30
3.8 LLR for Check Node Message . . . . . . . . . . . . . . . . . . .32
3.9 Sum-Product Algorithm . . . . . . . . . . . . . . . . . . . . . 35
3.10 Boxplus Operator . . . . . . . . . . . . . . . . . . . . . . . 36
4. LDPC for FFH/BFSK Systems . . . . . . . . . . . . . . . . . . . .39
5. Simulation Results . . . . . . . . . . . . . . . . . . . . . . . 42
6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

List of Figure
1.1 A (10,2,4) LDPC code. There are 10 variable nodes
and 5 check nodes, dv is 2 and dc is 4. . . . . . . . . . 2
2.1 Tranmitted signal for an FFH/QFSK spread spec-
trum system. . . . . . . . . . . . . . . . . . . . . . . 7
2.2 FFH/QFSK receiver down-converter output. . . . . . 7
2.3 Demodulation of BFSK signals for noncoherent de-
tection . . . . . . . . . . . . . . . . . . . .. . . . 13
2.4 Block diagram of ML diversity combining scheme. . . 17
2.5 Block diagram of AGC diversity combining scheme. . 19
2.6 Block diagram of EG diversity combining scheme. . . 20
3.1 A Tanner graph for a LDPC codes . . . . . . . . . . 27
3.2 ”Soft-in / soft-out” decoder . . . . . . . . . . . . . . 29
3.3 Update the variable node. . . . . . . . . . . . . . . . 31
3.4 Update the variable node. . . . . . . . . . . . . . . . 32
3.5 Update the check node. . . . . . . . . . . . . . . . . . 33
3.6 Update the check node. . . . . . . . . . . . . . . . . . 34
3.7 Performance compartion between tanh−1 (∗) and box-
plus . . . . . .. . . . . . . . . . . . 38
4.1 Block diagram of the LDPC coded FFH/BFSK system 39
4.2 Partial-band noise jamming. . . . . . . . . . . . . . . 40
5.1 Performance comparison between different diversity
combining schemes: L = 5, = 0.7, SNR = 13.35 dB. 42
5.2 Performance comparison between different diversity
combining schemes: L = 5, = 0.9, SNR = 13.35 dB. 43
5.3 Comparison between AGC and ML scheme with dif-
ferent , where L = 5 ( for BER = 10−3 ). . . . . . . 44
5.4 Performance comparison between different with AGC
diversity combining scheme: SNR = 13.35, L = 7. . . 45
5.5 Performance comparison between different with ML
diversity combining scheme: SNR = 13.35, L = 7. . . 46
5.6 Performance comparison between different diversity
order: = 0.7, ML diversity combining scheme, SNR
= 13.35 dB. . . . . . . . . . . . . . . . . . . . . . . . 47
5.7 Performance comparison between different diversity
order and with ML diversity combining scheme when
BER = 10−3. . . . . . . . . . . . . . . . . . . . . . . 48

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