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Frequency Domain Equalization of Modulation Formats with Low Peak to Average Power Ratio

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Frequency Domain Equalization of Modulation Formats with Low Peak to Average Power Ratio Dissertation Frequency Domain Equalization of Modulation Formats with Low Peak to Average Power Ratio Frequenzbereichsentzerrung von Modulationsverfahren mit niedrigem Spitzen- zu Mittelwert Verh¨altnis Der Technischen Fakultaet Fakult¨at der Universit¨at Erlangen-N¨urnberg zur Erlangung des Grades DOKTOR-INGENIEUR vorgelegt von Tufik Buzid, MSc. Erlangen, 2010 2 Als Dissertation genehmigt von der Technischen Fakult¨at der Universit¨at Erlangen-N¨urnberg Tag der Einreichung: 20.07.2009 Tag der Promotion: 16.12.2009 Dekan: Prof.Dr.-Ing.habil.ReinhardGerman Berichterstatter: Prof. Dr. MarioHuemer Prof. Dr. Leonard Reindl Prof. Dr.-Ing. Dr.-Ing. habil. Robert Weigel SC/FDE - Buzid ———————————————————- Zusammenfassung Der Austausch von Informationen mit hohen Datenraten zwischen verschiedenen mo- bilen oder station¨aren Endger¨aten ben¨otigt Techniken, welche die Beschr¨ankungen durch den Funkkanal ¨uberwinden. Ein Funkkanal, ein Kanal mit Mehrwegeausbreitung, wird durch die verschiedenen Signalwege bis hin zum Ziel beschrieben. Zus¨atzlich zum di- rekten Weg, falls dieser ¨uberhaupt existiert, k¨onnen verzerrte Kopien des Signals auch durch Reflexion, Beugung und Streuung zum Empf¨anger gelangen. Eine der gr¨oßten Herausforderungen der Daten¨ubertragung mit hoher Datenrate ist die Uberwindung¨ der durch die Mehrwegeausbreitung verursachten Zeitdispersion. Eine Herangehensweise an das Problem der Zeitdispersion ist die Anwendung des Orthogonal Frequency Division Multiplexing (OFDM). Der Hauptnachteil hierbei ist allerdings der große Dynamikbere- ich des OFDM-Signals. Dieser ist definiert durch das Peak to Average Power Ratio (PAPR). Dies ist ein wichtiges Thema falls der HF-Leistungsverst¨arker durch Nichtlin- earit¨at beeintr¨achtigt wird, was bis zu einem gewissen Maß praktisch immer der Fall ist. Zudem sind Verst¨arker f¨ur Signale mit hohem Spitzen-zu Mittelvert Verh¨altnis meist sehr ineffizient. Eine weitere Breitbandtechnik ist die Eintr¨ager¨ubertragung mit Frequenzbereichsentzerrung (engl. single carrier transmission with frequency domain equalisation, SC/FDE). SC/FDE bringt nachweislich die gleiche Leistungsf¨ahigkeit wie OFDM und weist weniger PAPR auf als dieses. Besondere Beachtung fand SC/FDE in Kombination mit Quadratur-Amplitudenmodulation (QAM), die noch immer ein sub- optimales PAPR aufweist. Allerdings erlaubt SC/FDE im Gegensatz zu OFDM den Einsatz von Modulationsarten mit konstanter Einh¨ullender. Durch Verwendung dieser Modulationsart, welche zur Klasse der nichtlinearen Modulationsverfahren geh¨ort und sich durch kontinuierliche Phaseneigenschaften auszeichnet, kann das PAPR des betra- chteten Systems auf den Wert Eins reduziert werden. Durch den Einsatz der Laurent Darstellung wird eine lineare Form des Signals mit kontinuierlicher Phasenmodulation (CPM) erreicht, die es erm¨oglicht das CPM-Signal linear zu demodulieren. Folglich wird die urspr¨unglich wegen seiner Trellis-Struktur große Komplexit¨at des Empf¨angers deut- lich reduziert. Dar¨uber hinaus k¨onnen Techniken wie z.B. Matched Filtering und lineare Entzerrung, die bereits f¨ur lineare Modulation entwickelt wurden, ohne Schwierigkeiten f¨ur die nichtlineare Modulation verwendet werden. In dieser Arbeit wird die linearisierte Form der CPM auf SC/FDE (CPM-SC/FDE) angewendet. Eine andere Form der Modu- lation mit konstanter Amplitude, die als Tamed Frequenzmodulation (TFM) bekannt ist und vor einem Jahrzehnt eingef¨uhrt wurde, wird ebenfalls auf SC/FDE angewendet. Das resultierende System wird mit OFDM unter dem Aspekt der Nichtlinearit¨at der HF-Stufe iii verglichen. Der Vergleich zeigt, dass die Leistungsf¨ahigkeit der CPM-SC/FDE nicht so stark beeintr¨achtigt wird wie die der OFDM, deren Leistungsf¨ahigkeit dramatisch nachl¨asst. Obwohl das erhaltene System im nichtlinearen Bereich des Verst¨arkers ar- beitet, bleibt seine Fehler Performanz aufgrund der inh¨arenten differentiellen Codierung unbefriedigend. Um diese Fehler-Performanz zu verbessern, wird eine vereinfachte Vari- ante des Laurent Mapping angewendet. Zur Verbesserung der CPM-SC/FDE Band- breiteneffizienz wird die Multiple Input Multiple Output (MIMO)-Technik eingef¨uhrt. Dabei wird vor allem r¨aumliches Multiplexing verwendet, da es die Transmissionseffizienz stark erh¨oht und somit die Systembandbreite linear mit der Anzahl der verwendeten Antennen ansteigt. Dar¨uber hinaus wird SC/FDE mit linearen und nichtlinearen Mod- ulationsarten erweitert f¨ur ”Point to Multipoint”-Anwendungen und mit Spreizcodes (Code Division Multiple Access, CDMA) kombiniert. Schließlich wird SC/FDE-CDMA mit einer Kombination von OFDM und CDMA (MC-CDMA) verglichen und skizziert, dass eine Anwendung der Fourier Spreizcodes auf ein voll ausgelastetes SC/FDE-CDMA zu einem OFDM-System f¨uhrt, w¨ahrend die Kombination von OFDM und CSMA ein SC/FDE-Verfahren erzeugt. SC/FDE - Buzid Abstract High data rates and the exchange of large amounts of information among various mobile or roaming and stationary terminals require techniques that conquer the restrictions imposed by the wireless channels. A wireless channel, known as multipath channel, is modeled by a number of paths that a signal travels to reach its destination. In ad- dition to a direct path, if it exists, distorted copies of the signal may arrive at the receiver through different paths that are formed by reflections, diffractions and scat- tering. One of the most challenging problems in high data rate wireless transmission is to overcome the time dispersion caused by multipath propagation. An approach to overcome the problems of time dispersion is the use of orthogonal frequency division multiplexing (OFDM). A primary drawback is the large dynamic range of the OFDM signal. The signal dynamic range is defined by the peak to average power ratio (PAPR). This is an important topic when RF power amplifiers suffer from nonlinearity, which is in practice always the case to some extent. Another broadband technique is the single carrier transmission with frequency domain equalization (SC/FDE). SC/FDE has been shown to exhibit similar performance as OFDM and shows less PAPR than OFDM. Mainly SC/FDE has been investigated in combination with quadrature amplitude mod- ulation (QAM) formats which still show non-optimum PAPR. But, in contrast to OFDM, SC/FDE also allows the use of constant amplitude type of modulations. By using a con- stant amplitude type of modulation, which is nonlinear and marked by the continuous phase property, the PAPR of the concerned system can be reduced to one. By the deployment of the Laurent representation a linear form of the CPM signals is estab- lished, which enables the CPM signals to be linearly demodulated. Consequently, the receiver complexity which is originally high due to the trellis nature of the structure of the CPM receivers, is significantly reduced. Further, the techniques already developed for linear modulation, e.g. matched filtering and linear equalization can be straightfor- wardly adapted to non-linear modulation. In this work, the linearized form of the CPM is adapted to SC/FDE (CPM-SC/FDE). Another form of modulation with a constant amplitude, that is known as tamed frequency modulation (TFM), introduced a decade ago, is also adapted to SC/FDE. The resulting (emerged) system is compared to OFDM under the constraints of the non-linearity of the RF stage. The comparison shows that the performance of CPM-SC/FDE is not affected as OFDM whose performance deteri- orates dramatically. Although the emerged system is effective in the non-linear region of the amplifier, its error performance remains unsatisfactory because of the inherent differential encoding. To improve the error performance, a simplified approach of Lau- v rent mapping is applied. In order to improve the CPM-SC/FDE bandwidth efficiency, a multiple input multiple output (MIMO) technique is introduced. Spatial multiplexing is particularly applied as it improves the transmission efficiency tremendously. There- fore, the system bandwidth efficiency increases linearly with the number of the deployed antennas. Further, SC/FDE with linear and non-linear modulation formats is extended to ”point to multipoint” applications. It is combined with code division multiple ac- cess (CDMA). Finally, SC/FDE-CDMA is compared to the combination of OFDM and CDMA (MC-CDMA), and it is outlined, that applying Fourier spreading codes to full load SC/FDE-CDMA yields to an OFDM system, whereas, in contrary, the combination of OFDM and CDMA produces an SC/FDE scheme. SC/FDE - Buzid List of Abbreviations ACI Adjacentchannelinterference ACTS Advanced communications technologies and services ADSL Asymmetricdigitalsubscriberline AGC Automaticgaincontrol AMPS Advancedmobilephoneservice ASK Amplitudeshiftkeying AWGN AdditivewhiteGaussiannoise B3G Beyond3G BER Biterrorrate BPSK Binaryphaseshiftkeying BT Bandwidthtimeproduct CDMA Codedivisionmultipleaccess CDPD Cellulardigitalpacketdata COHASK Coherent amplitude shift keying COHFSK Coherent frequency shift keying COHPSK Coherent phase shift keying CPM Continuousphasemodulation DCS1800 Digital cellular system 1800 DECT Digital European cordless telephone DEPSK DifferentialencodedPSK DFT DiscreteFouriertransform DMSK DuobinaryMSK DPSK Differentialphaseshiftkeying DVB-C Digital video broadcasting-Cable DVB-S Digital video broadcasting-Satellite vii DVB-T Digital video broadcasting-Terrestrial EDGE EnhanceddataratesforGSMevolution ETSI European telecommunications standard institute FDM Frequencydivisionmultiplexing FDMA Frequency division multiple access FDOSS Frequency domain
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