OFDM Transmitter
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APPLICATIONS OF DIGITAL SIGNAL PROCESSING METHODS FOR 4G WIRELESS COMMUNICATION SYSTEMS Anna Torrens Senior Project Report Course: EECE 419 Date submitted: January 10, 2012 Advisor: Dr. Evriclea Voudouri-Maniati Manhattan College ABSTRACT The increasing interest of users in multimedia applications of data communication is growing up very fast; this is the reason why mobile wireless networks are converging to a new generation where the speed is one of the issues. This project, which has been developed in Manhattan College, a University in New York City, evaluates the technique of OFDM. OFDM is used in the current generation of mobile communication as well as in the upcoming generations like 4G and beyond. Specifically, an introduction to the LTE (one of the fourth generation standards) is provided followed by a review of the features of OFDM. A simulation with MATLAB code demonstrates that the transmitted video data can be recovered at the receiver without errors in the presence of indoors and outdoors multipath fading. In addition, as Manhattan College has acquired the Texas Instruments 6713 DSP Starter Kit (DSK), the form of the previous theoretical research has been applied to a practical experiment, in the implementation of the OFDM transmitter. 2 Manhattan College OVERVIEW Nowadays mobile communications are getting a central role in our society. Few years ago a cell phone was used only for voice, but with the introduction of data new directions have been researched to solve the demand of the users. In this report we want to introduce the fourth generation as the new technology of mobile wireless network, and be involved in one of its standards for transmission and reception of data called OFDM. The main goal of this project is to demonstrate the immunity of OFDM to multipath effect by implementing its transmitter and receiver, modeling a probable real channel, and evaluating the system’s performance by recovering the transmitted code without any errors. As we are living a transition from 3G to newer generations, we are going to take advantage of the mobile telephone system of the future, LTE, which uses this kind of modulation. This report can provide future students an overview of new technologies for mobile wireless systems and more efficient techniques of transmission and reception, like OFDM. From this point on, new experiments may be developed originating from the implemented MATLAB simulations and programming of the Texas Instruments TMS320C6713 DSK. They can also witness the fact that it is easier to obtain results via a software simulation compared to trying to do the same thing with hardware. As my period in Manhattan College is limited, only the OFDM transmitter was implemented with the DSP Starter Kit. The project is open to new implementations and investigations. In the first part of the research, there is a review of all generations of mobile wireless that have been existed up to now. We focus in the new one by providing a short description of the standards that have been approved by the ITU-R. As this project has been implemented in the United States, it is based on LTE, which actually big companies like AT&T and Verizon wireless are gradually introducing in some states. Then, there is a description of OFDM presenting its characteristics and its advantages and disadvantages. One of the features of this technique is that can mitigate 3 Manhattan College multipath effect. We explain how the channel produces it, and how good OFDM is in eliminating it. There is also a brief explanation and block diagram of the OFDM transmitter and the OFDM receiver. We comment OFDMA as the way of transmission that the fourth generation uses; it is based on OFDM, the previous technique, but sharing more flexibility to the spectrum of the total bandwidth with other users is accomplished. The next section demonstrates how the theory OFDM system behaves under fading conditions. To accomplish this, we simulate a transmitter and a receiver with the parameters of the LTE standard and we add a channel with multiple paths. Matlab code has been developed for this purpose. Finally, we try to implement the OFDM transmitter with hardware and simulate a real case. The 6713 DSP Starter Kit (DSK) is programmed to generate the video data, apply the IFFT and perform the digital to analog conversion of the signal and radio frequency modulation. As the time was limited, there is only the transmitter implementation. 4 Manhattan College TABLE OF CONTENTS 1. INTRODUCTION ....................................................................................................................................................................... 6 2. REVIEW OF MOBILE NETWORK .................................................................................................................................... 8 3. 4G STANDARDS: LTE AND WIMAX ........................................................................................................................ 12 4. 4G IN US ........................................................................................................................................................................................ 15 5. OFDM .............................................................................................................................................................................................. 17 5.1 DEFINITION ............................................................................................................................................................................ 17 5.2 GENERATION OF SUBCARRIERS USING THE IFFT .................................................................................................. 18 5.3 IMPORTANCE OF ORTHOGONALITY .......................................................................................................................... 19 5.4 ADVANTAGES AND DISADVANTAGES OF OFDM .............................................................................................. 20 5.5 PHENOMENA OF THE MOBILE RADIO ENVIRONMENT-PROPAGATION ...................................................... 21 5.6 HOW OFDM MITIGATES MULTIPATH EFFECT ........................................................................................................ 24 5.7 TRANSMITTER AND RECEIVER OPERATION .............................................................................................................. 25 6. OFDMA ........................................................................................................................................................................................... 30 7. MATLAB SIMULATION ........................................................................................................................................................ 32 7.1 CHANNEL MODEL ............................................................................................................................................................... 32 7.2 SIMULATION RESULTS ........................................................................................................................................................ 38 7.1.1 OFDM transmitter .................................................................................................................................................. 38 7.1.2 OFDM receiver ........................................................................................................................................................ 44 7.1.3 OFDM receiver with multipath channel .................................................................................................... 47 8. THE 6713 DSP STARTER KIT (DSK) ............................................................................................................................ 55 8.1 DSK DESCRIPTION .............................................................................................................................................................. 55 8.2 RESULTS ................................................................................................................................................................................... 59 9. CONCLUSION .......................................................................................................................................................................... 70 10. FUTURE LINES ........................................................................................................................................................................ 71 11. REFERENCES ............................................................................................................................................................................ 72 12. BIBLIOGRAPHY ...................................................................................................................................................................... 75 5 Manhattan College 1. Introduction Since ancient times, mankind has always tried to find ways to communicate, namely to have a process of transmission and reception of information. The purpose of telecommunication network is carry information signals via a media between two or more points that are geographically separate. The basic elements of telecommunication are shown in figure 1. The users that are involved are called source and destination. The information that is transmitted (it can be a photo, voice, data, etc.) has to be transformed into an electrical signal to be sent. That is the reason