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研究生:鄧光超
研究生(外文):Guang-Chao Deng
論文名稱:子載波和位元分配在正交分頻多工系統
論文名稱(外文):A Sub-carrier and Bit Allocation Base on OFDM System
指導教授:蔡木金
指導教授(外文):Mu-King Tasy
學位類別:碩士
校院名稱:國立中央大學
系所名稱:通訊工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:英文
論文頁數:58
中文關鍵詞:子載波位元分配
外文關鍵詞:sub-carrierbit allocation
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通訊技術不斷地朝向高傳輸速率和高移動性的目標前進,正交分頻多工系統是一套有效率的方式,能同時傳輸高速率並且對抗碼際干擾,其具有多個載波,當通道為頻率選擇性衰減時,系統必須要有一套有效率的方法來分配資源。
傳統的分頻多路存取,是將子載波以固定的方式分配給用戶,有別於此,若我們能夠依照通道的狀況和使用者的需求,將子載波和位元適應地分配給使用者,必能減少所需的功率輸出。
將功率最小化的問題,其解決方式太過於複雜,所以陸續有次佳的方法提出,本論文提出一套方法來分配子載波和位元,並求此方法的改善,最後我將分析這套方法的複雜度和表現的情況。
The communication technology is forward to the target of high data rate and high mobility. Orthogonal frequency division multiplexing (OFDM) system is an efficient system. It can transmit high data rate and combat intersymbol interference (ISI). It has many sub-carriers. When channel is the frequency selective fading channel, the system must have an efficient algorithm to allocate resource.
Traditional OFDM allocate sub-carriers and bits to users statically. If we can allocate sub-carriers and bits to users according to channel gain and the need of users, it can decrease the power that we need.
It is too complex problem to minimum the power in all system. Some paper propose the sub-optimal allocation algorithm continually. This thesis proposes a bit allocation algorithm for sub-carrier and improves this algorithm. I will show their complexity and performance finally.
Contents

Abstract I
Contents II
List of Figures V
List of Tables VII

Chapter 1 Introduction 1

1.1 Motivation and Objective………………………………………1
1.2 Structure of the Thesis………………………………………….3

Chapter 2 Basic Principles of OFDM 5

2.1 Introduction to OFDM…………………………………………..5
2.2 Generation of Sub-carriers using the IFFT……………………...6
2.3 Guard Interval…………………………………………………..10
2.4 Choice of OFDM Parameters…………………………………..12
2.5 Channel Estimation…………………………………………….14

Chapter 3 Sub-carrier Allocation and Bit Loading 19

3.1 System Model…………………………………………………..19
3.2 Optimal Bit Allocation Algorithm for Single User Channel…...23
3.3 Optimal Sub-carrier Allocation (OSA) Scheme for Multiuser…27
3.4 Dynamic Modulation…………………………………………...31

Chapter 4 The Improved Sub-carrier Allocation
Scheme…………………………………..35

4.1 Multi-Rate Allocation (MRA)…………………………………36
4.2 A Fast Sub-carrier Allocation Scheme (FSA)…………………40

Chapter 5 Simulation Results 43

5.1 the complex degree for sub-carrier allocation………………….43
5.2 The Performance of Symbol Error Rate to SNR……………….50
5.2.1 The Performance of Symbol Error Rate to SNR for Single User……………………………………………………….50
5.2.2 The Performance of Multi-user with Multi-rate User……...51
5.2.3 The Performance of MRA and FSA……………………….53

Chapter 6 Conclusions 55

References 57

















List of Figures

Figure 2.2-1 OFDM modulator…………………………………………..7
Figure 2.2-2 Spectrum of OFDM……………...………………………...8
Figure 2.2-3 Spectrum of traditional FDM………………………………9
Figure 2.3-1 OFDM symbol with cyclic extension……………………..11
Figure 2.3-2 Example of an OFDM signal……………………………..11
Figure 2.5-1 Base-band model of OFDM system with pilot insertion…16
Figure 2.5-2 Block diagram of OFDM transmitter……………………..18
Figure 2.5-3 Block diagram of OFDM receiver………………………..18
Figure 3.1-1 Block diagram of a multiuser OFDM system with subcarrier bit and power allocation…………………………………...20
Figure 3.2-1 Frequency selective fading channel………………………26
Figure 3.3-1 An example of initial subcarrier allocation……………….29
Figure 3.4-1 The flow chart of subcarrier allocation…………………...34
Figure 4.1-1 An example of initial sub-carrier allocation by multi-rate user………………………………………………………...38
Figure 4.1-2 The flow chart of sub-carrier allocation by multi-rate users………………………………………………………..39
Figure 4.2-1 Every user’s channel gain in frequency domain…………..40
Figure 5.1-1 The 4 users’ iterative number for normal power………….44
Figure 5.1-2 The 4 users’ iterative number for normal power with initial sub-carrier allocation and no initial sub-carrier allocation...44
Figure 5.1-3 The 8 users’ iterative number for normal power………….45

Figure 5.1-4 The 8 users’ iterative number for normal power with initial sub-carrier allocation and no initial sub-carrier allocation...45
Figure 5.1-5 The 16 users’ iterative number for normal power………...46
Figure 5.1-6 the 16 users’ iterative number for normal power with initial sub-carrier allocation and no initial sub-carrier allocation...46
Figure 5.1-7 The numbers of accumulative iteration for 4users………...47
Figure 5.1-8 The numbers of accumulative iteration for 8users………...48
Figure 5.1-9 The numbers of accumulative iteration for 16users……….48
Figure 5.2-1 Symbol error rate probability to average SNR per sub-carrier for single user……………………………………………...50
Figure 5.2-2 Symbol error rate probability to average SNR per sub-carrier for 4 user、8 user、16 user and data rate=128…………….51
figure 5.2-3 symbol error rate probability to average SNR per sub-carrier for 4 user、8 user、16 user, data rate=256………………..52
Figure 5.2-4 The performance with MRA and without MRA, data rate=128……………………………………………………53
Figure 5.2-5 The performance of FSA and OSA………………………..54









List of Tables

Table 3.2-1 Bit loading in one user……………………………………...27
Table 3.3-1 Sub-carrier orders…………………………………………..28
Table 3.4-1 Threshold Levels For Different Modulation Schemes……..32
Table 4.2-1 average channel gains in each region (1)…………………..41
Table 4.2-2 average channel gains in each region (2)…………………..41
Table 4.2-3 average channel gains in each region (3)…………………..42
Table 5.1-1 The complexity for 4 users、8 users、16 users……………49
Reference

[1]. C. Y. Wong, R. S. Cheng, K. B. Letaief, and R. D. Murch, “Multiuser OFDM with adaptive sub-carrier, bit, and power allocation,” IEEE J. Select. Areas Commun., vol. 17, pp. 1747-1758, Oct. 1999.

[2]. W. Rhee and J. M. Cioffi, “Increase in capacity of multiuser OFDM system using dynamic sub-channel allocation,” in Proc. IEEE Vehicular Technology Conf. (VTC’2000), 2000, pp. 1085-1089.

[3]. J. M. Cioffi. Lecture Notes for Advanced Digital Communication, Stanford, Fall 1997.

[4]. Richard van Nee, Ramiee Prasad, “OFDM for Wireless Multimedia Communication”

[5] Blahut, R. E., “Fast Algorithms for Digital Signal Processing”, Reading, MA: Addison-Wesley, 1985

[6] Yuping Zhao and Aiping Huang, “A Novel Channel Estimation Method for OFDM Mobile Communication Systems Based on Pilot Signals and Transform-Domain Processing”, Vehicular Technology Conference, IEEE, 1997

[7] J.Rinne and M. Renfors, “Channel estimation in OFDM systems utilizing pilots”, Espoo, Finland, 1996

[8] D.Hughes-Hartogs, “Ensemble modem structure for imperfect transmission media,” U.S. PatentsNos. 4679227, July 1987; 4731816, Mar. 1988; and 4833796, May 1989.

[9] S.K. Lai, R. S. Cheng, K. Ben Letaief, and R. D. Murch, “Adaptive trellis coded MQAM and power optimization for OFDM transmission,” in Proc. IEEE Vehicular Technology Conf. (VTC’ 99), Houston, TX, May 1999.

[10] John G. Proakis “Digital Communications” the third edition, Singapore: McGraw Hill, 2001
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