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IFDMA for Uplink Mobile Radio Communication Systems

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An application of interleaved frequency-division multiple-access (IFDMA) for mobile communications has become an active field of r... Weiterlesen
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Beschreibung

An application of interleaved frequency-division multiple-access (IFDMA) for mobile communications has become an active field of research since 1998. The special interest has been given to the uplink of mobile communication since low peak-to-average power ratio makes IFDMA attractive for hand-held mobile devices allowing an application of cheap amplifiers. The IFDMA signal can be generated simply by compression and repetition of the transmit data sequence, without usage of fast Fourier transformation. Due to the periodic nulls in transmit spectrum, other users may utilize the same frequency band allowing multiple access. This work contributes to the state of the art in the field of IFDMA in the following areas: data detection, PAPR reduction of multi-carrier systems, an estimation of frequency offsets in multicarrier uplink, where many users are simultaneously active.

Leseprobe
Chapter 4 (S. 57-58) Frequency Offset 4.1 Introduction The system design of a multi-carrier uplink assumes that the distance between subcarriers of one user is larger than the coherent bandwidth of the transmission channel so that these subcarriers experience non-correlated fading [Kai98]. One of the advantages of IFDMA systems is that the subcarriers of one user are interleaved equidistantly, providing maximum frequency diversity for the received signal. Moreover, the orthogonality of subcarriers enables the BS to avoid MAI, since data symbols of different users are modulated on different subcarriers. However, these advantages come at the cost of sensitivity to frequency offsets. Multi-carrier systems with a block interleaved frequency allocation scheme especially suffer from the performance degradation due to frequency offsets [AS03]. In IFDMA uplink systems, frequency offsets are different for different users. These offsets occur because of a non-zero relative speed between the BS and MT or because of slightly disparate oscillator's frequencies at the receiver and transmitter [Haa03, PSM94]. Since IFDMA is a special case of OFDMA, IFDMA inherits the sensitivity of OFDMA to frequency offsets. The performance of an OFDMA uplink in the presence of frequency offsets is studied in [TLP00, Ste00]. The frequency offsets cause MAI, which leads to the performance degradation. Different methods to combat MAI in an OFDMA uplink can be divided into two groups. The &64257;rst group requires the knowledge of the frequency offsets for each user at the receiver. If the frequency offsets of each user are perfectly known at the BS, interference cancelation schemes can be applied [HL05]. Another possibility is to estimate the frequency offset of each user at the BS. These estimates can be used to correct the sampling time instances at the BS receiver or can be sent back to the MTs where they are used to pre-compensate for the frequency offsets before transmission. A second group of techniques to combat MAI assumes special construction of the OFDMA transmit signal such that the frequency offsets cause a reduced amount of MAI. One promising technique is windowing at the receiver or transmitter, which, however, has been investigated only for the case of an OFDM downlink [Mus96, MW01, SL05, YH03]. Another technique employs a subband frequency allocation scheme, where data of a particular user is transmitted on a speci&64257;c subset of adjacent subcarriers as described in [AS03, LH05]. Unfortunately, the techniques of the second group suffer from a number of drawbacks such as low frequency diversity – as in the case of an adjacent subcarrier allocation scheme – or low bandwidth ef&64257;ciency – as in the case of windowing at the transmitter or receiver. Thus, the techniques which require frequency offset estimation at the BS seem to be only an alternative for a future IFDMA uplink. Generally, frequency offset estimation in the uplink of multi-carrier systems is a complicated task, since the signal received at the BS comprises the received signals from many users each of which can have its own frequency offset. Moreover, received signals from different users are distorted by different transmission channels, which complicates the issue. Several interesting research results for frequency offset estimation in OFDMA uplink have been presented in the literature. Chapter 4 (S. 57-58) Frequency Offset 4.1 Introduction The system design of a multi-carrier uplink assumes that the distance between subcarriers of one user is larger than the coherent bandwidth of the transmission channel so that these subcarriers experience non-correlated fading [Kai98]. One of the advantages of IFDMA systems is that the subcarriers of one user are interleaved equidistantly, providing maximum frequency diversity for the received signal. Moreover, the orthogonality of subcarriers enables the BS to avoid MAI, since data symbols of different users are modulated on different subcarriers. However, these advantages come at the cost of sensitivity to frequency offsets. Multi-carrier systems with a block interleaved frequency allocation scheme especially suffer from the performance degradation due to frequency offsets [AS03]. In IFDMA uplink systems, frequency offsets are different for different users. These offsets occur because of a non-zero relative speed between the BS and MT or because of slightly disparate oscillator's frequencies at the receiver and transmitter [Haa03, PSM94]. Since IFDMA is a special case of OFDMA, IFDMA inherits the sensitivity of OFDMA to frequency offsets. The performance of an OFDMA uplink in the presence of frequency offsets is studied in [TLP00, Ste00]. The frequency offsets cause MAI, which leads to the performance degradation. Different methods to combat MAI in an OFDMA uplink can be divided into two groups. The &64257;rst group requires the knowledge of the frequency offsets for each user at the receiver. If the frequency offsets of each user are perfectly known at the BS, interference cancelation schemes can be applied [HL05]. Another possibility is to estimate the frequency offset of each user at the BS. These estimates can be used to correct the sampling time instances at the BS receiver or can be sent back to the MTs where they are used to pre-compensate for the frequency offsets before transmission. A second group of techniques to combat MAI assumes special construction of the OFDMA transmit signal such that the frequency offsets cause a reduced amount of MAI. One promising technique is windowing at the receiver or transmitter, which, however, has been investigated only for the case of an OFDM downlink [Mus96, MW01, SL05, YH03]. Another technique employs a subband frequency allocation scheme, where data of a particular user is transmitted on a speci&64257;c subset of adjacent subcarriers as described in [AS03, LH05]. Unfortunately, the techniques of the second group suffer from a number of drawbacks such as low frequency diversity – as in the case of an adjacent subcarrier allocation scheme – or low bandwidth ef&64257;ciency – as in the case of windowing at the transmitter or receiver. Thus, the techniques which require frequency offset estimation at the BS seem to be only an alternative for a future IFDMA uplink. Generally, frequency offset estimation in the uplink of multi-carrier systems is a complicated task, since the signal received at the BS comprises the received signals from many users each of which can have its own frequency offset. Moreover, received signals from different users are distorted by different transmission channels, which complicates the issue. Several interesting research results for frequency offset estimation in OFDMA uplink have been presented in the literature.

Inhalt
1;Foreword;8 2;Contents;10 3;Chapter 1 Introduction;14 3.2;1.1 Fourth Generation of Wireless Communication Systems;18 3.3;1.2 State of the Art in the Field of IFDMA;20 3.4;1.3 Goals of the Thesis;23 3.5;1.4 Contents and Important Results;24 4;Chapter 2 Fundamentals of Uplink OFDMA;28 4.1;2.1 Introduction;28 4.2;2.2 Orthogonal Frequency-Division Multiplexing;29 4.2.1;2.2.1 Time and Frequency Domain Properties of an OFDM signal;29 4.2.2;2.2.2 Discrete-Time Signal Processing in OFDM Transmitter;34 4.2.3;2.2.3 Multipath Channel Model;37 4.2.4;2.2.4 Discrete-Time Signal Processing in OFDM Receiver;37 4.2.5;2.2.5 Technical Assumptions;41 4.2.6;2.2.6 Mathematical Notation;42 4.3;2.3 Uplink OFDMA and Its Extensions;44 4.3.1;2.3.1 Uplink Communications;44 4.3.2;2.3.2 OFDMA;44 4.3.3;2.3.3 OFDMA-CDM;46 4.3.4;2.3.4 IFDMA;49 4.3.5;2.3.5 MSK-IFDMA and GOQPSK-IFDMA;50 4.3.6;2.3.6 Spectral Properties;53 4.3.7;2.3.7 M-Modification;54 4.3.8;2.3.8 Remarks on IFDMA system design;56 5;Chapter 3 Peak-to-Average Power Ratio;58 5.1;3.1 Introduction;58 5.2;3.2 PAPR definition;59 5.2.1;3.2.1 PAPR Upper Bound for IFDMA and OFDMA;59 5.2.2;3.2.2 PAPR Distribution;62 5.3;3.3 Simulation Results;62 5.3.1;3.3.1 Simulation Parameters;62 5.3.2;3.3.2 Results and Discussions;63 6;Chapter 4 Frequency Offset;70 6.1;4.1 Introduction;70 6.2;4.2 Simulation Model;72 6.3;4.3 Performance Degradation due to Frequency Offset;75 6.4;4.4 MAI Reduction;77 6.5;4.5 Frequency Offset Estimation in the Frequency Domain;80 6.6;4.6 Frequency Offset Estimation in the Time Domain;83 6.7;4.7 Performance of the IFDMA Uplink System;85 6.7.1;4.7.1 Simulation Parameters;85 6.7.2;4.7.2 System Performance;86 6.7.3;4.7.3 Comparison with Existing Techniques;89 7;Chapter 5 Receiver and Optimum MMSE Equalization;92 7.1;5.1 Introduction;92 7.2;5.2 IFDMA/OFDMA-CDM Receiver;93 7.2.1;5.2.1 Linear Equalizers;94 7.2.2;5.2.2 Despreading;96 7.3;5.3 Self-Interference in Independent Rayleigh Channel;97 7.4;5.4 MMSE Equalizer for OFDM System with Windowing;101 8;Chapter 6 IFDMA Uplink System Evaluation;108 8.1;6.1 Introduction;108 8.2;6.2 System Design;109 8.2.1;6.2.1 System Parameters;109 8.2.2;6.2.2 Nonlinear Power Amplifier Model;110 8.2.3;6.2.3 Out-Of-Band Radiation;112 8.2.4;6.2.4 Scatter Plots;114 8.2.5;6.2.5 BER Performance;117 8.3;6.3 Simulation Results and Discussion;118 9;Chapter 7 Abstract;124 10;Appendix;126 10.1;A.1 DFT Operation at the Receiver;126 10.2;A.2 CFO Coefficients;130 10.3;A.3 Statistical Properties of the Estimate;132 11;Bibliography;134 12;Abbreviations and Symbols;144 12.1;Abbreviations;144 12.2;Symbols;146 12.3;Variables;147 1;Foreword;8 2;Contents;10 3;Chapter 1 Introduction;14 3.2;1.1 Fourth Generation of Wireless Communication Systems;18 3.3;1.2 State of the Art in the Field of IFDMA;20 3.4;1.3 Goals of the Thesis;23 3.5;1.4 Contents and Important Results;24 4;Chapter 2 Fundamentals of Uplink OFDMA;28 4.1;2.1 Introduction;28 4.2;2.2 Orthogonal Frequency-Division Multiplexing;29 4.2.1;2.2.1 Time and Frequency Domain Properties of an OFDM signal;29 4.2.2;2.2.2 Discrete-Time Signal Processing in OFDM Transmitter;34 4.2.3;2.2.3 Multipath Channel Model;37 4.2.4;2.2.4 Discrete-Time Signal Processing in OFDM Receiver;37 4.2.5;2.2.5 Technical Assumptions;41 4.2.6;2.2.6 Mathematical Notation;42 4.3;2.3 Uplink OFDMA and Its Extensions;44 4.3.1;2.3.1 Uplink Communications;44 4.3.2;2.3.2 OFDMA;44 4.3.3;2.3.3 OFDMA-CDM;46 4.3.4;2.3.4 IFDMA;49 4.3.5;2.3.5 MSK-IFDMA and GOQPSK-IFDMA;50 4.3.6;2.3.6 Spectral Properties;53 4.3.7;2.3.7 M-Modification;54 4.3.8;2.3.8 Remarks on IFDMA system design;56 5;Chapter 3 Peak-to-Average Power Ratio;58 5.1;3.1 Introduction;58 5.2;3.2 PAPR definition;59 5.2.1;3.2.1 PAPR Upper Bound for IFDMA and OFDMA;59 5.2.2;3.2.2 PAPR Distribution;62 5.3;3.3 Simulation Results;62 5.3.1;3.3.1 Simulation Parameters;62 5.3.2;3.3.2 Results and Discussions;63 6;Chapter 4 Frequency Offset;70 6.1;4.1 Introduction;70 6.2;4.2 Simulation Model;72 6.3;4.3 Performance Degradation due to Frequency Offset;75 6.4;4.4 MAI Reduction;77 6.5;4.5 Frequency Offset Estimation in the Frequency Domain;80 6.6;4.6 Frequency Offset Estimation in the Time Domain;83 6.7;4.7 Performance of the IFDMA Uplink System;85 6.7.1;4.7.1 Simulation Parameters;85 6.7.2;4.7.2 System Performance;86 6.7.3;4.7.3 Comparison with Existing Techniques;89 7;Chapter 5 Receiver and Optimum MMSE Equalization;92 7.1;5.1 Introduction;92 7.2;5.2 IFDMA/OFDMA-CDM Receiver;93 7.2.1;5.2.1 Linear Equalizers;94 7.2.2;5.2.2 Despreading;96 7.3;5.3 Self-Interference in Independent Rayleigh Channel;97 7.4;5.4 MMSE Equalizer for OFDM System with Windowing;101 8;Chapter 6 IFDMA Uplink System Evaluation;108 8.1;6.1 Introduction;108 8.2;6.2 System Design;109 8.2.1;6.2.1 System Parameters;109 8.2.2;6.2.2 Nonlinear Power Amplifier Model;110 8.2.3;6.2.3 Out-Of-Band Radiation;112 8.2.4;6.2.4 Scatter Plots;114 8.2.5;6.2.5 BER Performance;117 8.3;6.3 Simulation Results and Discussion;118 9;Chapter 7 Abstract;124 10;Appendix;126 10.1;A.1 DFT Operation at the Receiver;126 10.2;A.2 CFO Coefficients;130 10.3;A.3 Statistical Properties of the Estimate;132 11;Bibliography;134 12;Abbreviations and Symbols;144 12.1;Abbreviations;144 12.2;Symbols;146 12.3;Variables;147

Produktinformationen

Titel: IFDMA for Uplink Mobile Radio Communication Systems
Autor:
EAN: 9783831609628
ISBN: 978-3-8316-0962-8
Digitaler Kopierschutz: Adobe-DRM
Format: Kartonierter Einband
Herausgeber: Utz Verlag GmbH
Genre: Elektrotechnik
Anzahl Seiten: 156
Gewicht: 208g
Größe: H205mm x B146mm x T10mm
Veröffentlichung: 01.03.2010
Jahr: 2010

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