在正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM)系統下，能量負載問題是非常重要的議題。因此我們主要探討在固定的傳輸能量下，如何降低位元錯誤率(Bit-Error Rate , BER)。並且我們也針對在固定位元錯誤率下，如何使系統容量提升。在本論文中，我們提出新的能量分配演算法分配傳輸能量，使位元錯誤率降低，系統效能提高。在我們的演算法中，利用接收端回傳通道狀態訊息，使得傳送端可以使用我們所提出的演算法計算新的能量分配，因此通道效能較好的子載波會搭配較低的能量進行資料傳輸，反之通道效能較差的子載波會分配較高的傳輸能量。為了使位元錯誤率能有效改善，我們將設定一個門檻值，去選擇效能較好的子載波來傳輸資料。
最後我們探討位元錯誤率與系統容量之間的平衡，主要針對限制不同的位元錯誤率，觀察系統容量的效能。我們利用系統子載波使用率來配置我們提出的能量分配方法，使系統的位元錯誤率和系統容量之間得到平衡，達到提升整體系統效能的目的。

The problem of power loading in Orthogonal Frequency Division Multiplexing (OFDM) systems that provide minimization of the bit-error rate (BER) performance under a fixed transmit power (or equivalently minimization of the transmit power under a fixed value of the BER) is addressed in this work. We also discuss how to upgrade the system capacity in a fixed bit error rate. In this thesis, we propose a new algorithm for allocation of transmission power to reduce the bit error rate and increase system efficiency. In the transmitter, we use channel state information from the receiver to compute the new power allocation algorithm. Hence subcarriers will be well performance with lower power to transmit; otherwise worse performance of subcarrier will be assigned a higher transmission power. In order to effectively improve the bit error rate, we will set a threshold value and choose the well performance of subcarriers to transmit.
Finally, we will discuss the trade-off between the bit error rate and capacity of the system in different limits of bit error rate. The selection of subcarriers is used to configure our proposed method of power allocation so that it can achieve the trade-off between bit error rate and system capacity to improve overall system performance. Therefore, with efficient power allocation, the performance of OFDM systems can be improved.

摘要　 .....................................I
Abstract　....................................II
致謝 .....................................III
目錄　 .....................................IV
表目錄　 .....................................VIII
圖目錄　 .....................................IX
第一章 緒論....................................1
1.1　研究背景..................................1
1.2　研究動機與目的............................4
1.3　論文架構..................................4
第二章 系統架構................................6
2.1　正交分頻多工系統簡介......................6
2.2　正交分頻多工系統優點......................7
2.3　正交分頻多工系統架構......................8
2.3.1 正交分頻多工調變技術.....................11
2.4　通道模型介紹..............................12
2.4.1　訊息的回授機制..........................14
2.4.2　通道狀態消息............................15
第三章 資源配置機制介紹........................17
3.1 系統模型..............................17
3.1.1　AWGN通道................................18
3.2　相同能量配置機制介紹......................19
3.3　模擬結果..................................21
3.4　小結 ......................................26
第四章 動態子載波配置衍伸機制..................27
4.1　定義新的變數..............................28
4.2　動態子載波配置衍伸機制之步驟..............28
4.3　子載波使用機制............................30
4.4　模擬結果..................................32
4.5 小結..................................44
第五章 通道配置之系統容量......................45
5.1　模擬環境參數..............................45
5.1.1　子載波使用率和錯誤率....................46
5.1.2 Shannon –Hartley Capacity..............47
5.1.3　位元錯誤率和系統容量平衡................48
5.2　模擬結果..................................48
5.3　小結 ......................................60
第六章　結論...................................61
參考文獻.......................................62
附錄...........................................65
表目錄
表3.1　多載波OFDM系統模擬參數..................23
表4.1　多載波OFDM系統模擬參數..................33
表5.1　通道門檻值和子載波使用率參數表..........46
表5.2 選擇多載波OFDM系統模擬參數..............49
圖目錄
圖1.1 OFDM資源配置機制方塊圖...................3
圖2.1 OFDM基本架構圖...........................8
圖2.2連續時間OFDM發射器模型....................9
圖2.3 OFDM符元時域架構圖.......................10
圖2.4 離散時間OFDM發射器模型...................11
圖2.5 (a)BPSK (b)QPSK (c)16QAM調變.............12
圖2.6 多重路徑傳輸環境.........................13
圖2.7 瑞利衰減和子載波相對關係圖...............14
圖2.8 回授機制基本示意圖.......................15
圖3.1 相同能量配置機制方塊圖...................17
圖3.2 可加性白高斯雜訊通道.....................19
圖3.3 4QAM-OFDM位元錯誤率曲線圖................24
圖3.4 8QAM-OFDM位元錯誤率曲線圖................24
圖3.5 16QAM OFDM位元錯誤率曲線圖...............25
圖3.6 16QAM OFDM位元錯誤率曲線圖...............26
圖4.1 新能量配置機制方塊圖.....................29
圖4.2 選擇子載波的流程圖.......................31
圖4.3 4QAM-OFDM使用通道門檻值為0的位元錯誤率曲線圖......34
圖4.4 8QAM-OFDM使用通道門檻值為0的位元錯誤率曲線圖......35
圖4.5 16QAM-OFDM使用通道門檻值為0的位元錯誤率曲線圖.....35
圖4.6 4QAM-OFDM使用通道門檻值為1的位元錯誤率曲線圖......36
圖4.7 8QAM-OFDM使用通道門檻值為1的位元錯誤率曲線圖......37
圖4.8 16QAM-OFDM使用通道門檻值為1的位元錯誤率曲線圖.....37
圖4.9 4QAM-OFDM使用通道門檻值為1.5的位元錯誤率曲線圖....38
圖4.10 8QAM-OFDM使用通道門檻值為1.5的位元錯誤率曲線圖...39
圖4.11 16QAM-OFDM使用通道門檻值為1.5的位元錯誤率曲線圖..39
圖4.12 4QAM-OFDM使用通道門檻值為2的位元錯誤率曲線圖.....40
圖4.13 8QAM-OFDM使用通道門檻值為2的位元錯誤率曲線圖.....41
圖4.14 16QAM-OFDM使用通道門檻值為2的位元錯誤率曲線圖....41
圖4.15 4QAM-OFDM使用通道門檻值為0, 1, 1.5和2的位元錯誤率曲線圖.......42
圖4.16 8QAM-OFDM使用通道門檻值為0, 1, 1.5和2的位元錯誤率曲線圖.......43
圖4.17 16QAM-OFDM使用通道門檻值為0, 1, 1.5和2的位元錯誤率曲線圖.......43
圖5.1 通道門檻值選擇子載波系統架構圖...................47
圖5.2 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為2.7的位元錯誤率曲線圖...50
圖5.3 通道門檻值2.7的系統容量..........................50
圖5.4 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為2.2的位元錯誤率曲線圖...51
圖5.5 通道門檻值2.2的系統容量..........................52
圖5.6 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為1.65的位元錯誤率曲線圖...53
圖5.7 通道門檻值1.65的系統容量.........................53
圖5.8 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為1.23的位元錯誤率曲線圖...54
圖5.9 通道門檻值1.23的系統容量.........................55
圖5.10 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為1.1的位元錯誤率曲線圖...56
圖5.11 通道門檻值1.1的系統容量.........................57
圖5.12 4QAM , 8QAM和16QAM-OFDM使用通道門檻值為0的位元錯誤率曲線圖.....58
圖5.13 通道門檻值0的系統容量...........................60

[1] IEEE Std 802.11g-2003: “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, Nov. 2003.
[2] IEEE Std 802.16g-2004: “Air Interface for Fixed Broadband Wireless Access System”, Mar. 2004.
[3] Cheong　and　J.　M. Cioffi, “Discrete　Wavelet Transforms　in　Multi-carrier　Modulation”, Proc. of IEEE Global Telecommunications Conference (GLOBECOM). vol. 5, pp. 2794-2799, Nov. 1998.
[4] J. G. Proakis, Digital Communications. Fourth Edition, McGraw-Hill, 2001, Chapter 14.
[5] Y. F. Chen and J. W. Chen, “A Fast Subcarrier, Bit, and Power Allocation Algorithm for Multiuser OFDM-Based Systems,” IEEE Transactions on Vehicular Technology, vol. 57, no. 3, pp. 873-881, Mar. 2008.
[6] Digital Video Broadcasting (DVB): “Transmission System for Hand-Held Terminals (DVB-H),” ETSI EN 302 304 v1.4.1, Proc. of European Telecommunication Standards Institute (ETSI), Nov. 2004.
[7] H. Lin and G. Li, OFDM-Based Broadband Wireless Networks: Design and Optimization. Wiley, 2005.
[8] T. J. Wang, J. G. Proakis and J. R. Zeidler, “Performance Analysis of High QAM OFDM System over Frequency Selective Time-varying Fading Channel ,” Proc. of 14th IEET Proceedings on Personal Indoor and Mobile Radio Communications(PIMRC), vol. 1, pp. 793-798, Feb. 2003.
[9] W. Stallings, Wireless Communications and Networks. Prentice Hall, 2005.
[10] H. Moon and C. D. Cox, “Efficient Power Allocation for Coded OFDM Systems,” IEEE Transactions on Communications, vol. 6, no. 4 pp. 4366-4370, Apr. 2004.
[11] A. Rosenzweig, Y. Steinberg and S. Shamai, “On Channels with Partial Channel State Information at the Transmitter,” IEEE Transactions on Information Theory, vol. 51, no.5, pp. 1817-1830, May 2005.
[12] Z. Hasan, G. Bansal, E. Hossain, and V. Bhargava, “Energy-efficient Power Allocation in OFDM-based Cognitive Radio Systems: A Risk-return Model,” IEEE Transactions on Wireless Communications, vol. 8, no.12, pp. 6078-6088, Dec. 2009.
[13] Y. H. Zhang and C. Leung, “Performance of Equal Power Subchannel Loading in Multiuser OFDM Systems,” Proc. of IEEE Pacific Rim Conference on Communications Computers and Signal Processing(PACRIM), pp. 1820-1824, Sept. 2006.
[14] D. Dardari, “Ordered Subcarrier Selection Algorithm for OFDM-based High-speed WLANs,” IEEE Transactions on Wireless Communications, vol. 3, no.5, pp. 1452-1458, 2004.
[15] K. Cho and D. Yoon, “On The General BER Expression for One-and Two-domensional Amplitude Modualation,” IEEE Transactions on Communications, vol. 50, no.7, pp. 2422-2427, Nov. 2002.
[16] N. Y. Ermolova and B. Makarevitch, “On Subchannel Inversion for Improvement of Power Efficiency in OFDM-based Systems,” Proc. of IET on Communications, vol. 1, no. 6, pp. 1263-1266, Jan. 2007.
[17] C. H. Cheng, C. Y. Lee and Y. F. Huang, “The Power Allocation of Subcarriers for Multicarrier OFDM Systems,” Proc. of Information Technologies Applications and Management Conference (ITAMC), Kaohsiung, Taiwan, Jun. 2010.
[18] M. Yoshida, E. Ishizu, Y. Asano and T. Saito, “High-rate OFDM Codes for Peak Envelope Power Reduction and Error Correction in MQAM Systems,” , Proc. of IEEE on Vehicular Technology Conference (VTC), vol. 3, pp. 1148-1153, Aug. 2000.