臺灣博碩士論文加值系統

訊雜比 ( signal-to-noise ratio，SNR ) 估測是無線通訊中重要的研究課題之一，因為許多接收端的演算法藉由訊雜比的資訊可以獲得最佳的性能表現。在本篇論文中提出一個以自相關函數為基礎的訊雜比估測器，其主要是利用符號序列的相關性以及雜訊的無相關性 ( uncorrelated ) 來將訊號功率從接收訊號裡區分出來，其中會使用曲線配適 ( curve fitting ) 的方式來作為一個訊號功率的估測器。
所提出的方法將經由電腦模擬來跟傳統的訊雜比估測器作性能上的比較，在本篇論文的模擬中會考慮在一可加性白色高斯雜訊 ( additive white Gaussian noise，AWGN ) 通道下調變方式為二位元相位鍵移 ( binary phase-shift keying，BPSK )、8-陣列相位鍵移 ( 8-ary phase shift keying，8-PSK )、16-陣列正交振幅調變 ( 16-ary quadrature amplitude modulation，16-QAM ) 以及64-QAM的情形。最後將討論所提出的方法在瑞雷 ( Rayleigh ) 衰減 ( fading ) 通道中的情況。由模擬的結果可以看到所提出的方法可以在平均值與均方誤差上比傳統估測器好。

Signal-to-noise ratio (SNR) estimation is one of the important research topics in wireless
communications. In the receiver, many algorithms require SNR information to achieve optimal performance. In this thesis, an autocorrelation based SNR estimator is proposed. The proposed method utilizes the correlation properties of symbol sequence and the uncorrelated properties of noise sequence to distinguish the signal power from the received signal. Curve fitting method is used for SNR estimator to predict the signal power.
Mean and variance performance of the proposed SNR estimator is compared with that of the conventional SNR estimator by computer simulations. These simulations consider additive white Gaussian noise and multipath Rayleigh fading channel with BPSK, 8PSK, 16QAM and 64QAM modulation schemes. According to the simulation results, the proposed method can provide better performance than conventional methods in both mean and mean-square-error.

誌謝 i
摘要 ii
Abstract iii
目錄 iv
圖索引 vi
第一章 簡介 1
第二章 訊雜比估測演算法 4
2.1 訊雜比估測器的系統模型 4
2.1.1 訊雜比估測器的訊號模型 4
2.2 訊雜比估測器的基本原理 6
2.2.1 最大相似訊雜比估測器 7
2.2.2 動差法訊雜比估測器 10
2.2.3 絕對值動差法訊雜比估測器 11
2.2.4 線性預測法訊雜比估測器 15
第三章 使用訊號相關性的訊雜比估測演算法 18
3.1 系統模型 18
3.2 訊雜比估測器推導 19
3.3 訊雜比估測器在不同調變情況下 27
3.3.1 正交相位鍵移 ( QPSK ) 27
3.3.2 8-陣列相位鍵移 ( 8-PSK ) 27
3.3.3 16-陣列正交振幅調變 ( 16-QAM ) 30
3.3.4 64-陣列正交振幅調變 ( 64-QAM ) 32
3.4 演算法流程 35
3.4.1 離散訊號表示 35
3.4.2 演算法流程化簡 36
3.4.3 演算法參數 37
3.5 結合低通濾波器的訊雜比估測器 38
3.5.1 低通濾波器的考量 39
3.6 訊雜比估測器在瑞雷衰減通道的討論 43
3.6.1 在瑞雷衰減通道的自相關函數 43
第四章 系統模擬 52
4.1 接收端取樣速率與配適係數個數的影響 52
4.2 不同濾波器階數與截止頻率的影響 58
4.3 不同符號數量的性能比較 63
4.4 多種不同調變方式的性能比較 68
4.5 時間同步誤差的影響 76
4.6 在瑞雷衰減通道下的性能 80
4.7 不同傳送波形的影響 89
第五章 結論 94
參考文獻 95

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