Communication System Design Using DSP Algorithms. with Laboratory Experiments for the TMS320C6713 DSK

Transcription

1 Communication System Design Using DSP Algorithms with Laboratory Experiments for the TMS320C6713 DSK

2 Information Technology: Transmission, Processing, and Storage Series Editors: Robert Gallager Electrical Engineering & Computer Science Massachusetts Institute of Technology Cambridge, Massachusetts Jack Keil Wolf Electrical & Computer Engineering University of California at San Diego La Jolla, California

3 Communication System Design Using DSP Algorithms with Laboratory Experiments for the TMS320C6713 DSK Steven A. Tretter University of Maryland College Park, MD 1 3

4 Steven A. Tretter Department of Electrical Engineering University of Maryland College Park, MD, 20742, USA Series Editors Robert Gallager Electrical Engineering & Computer Science Massachusetts Institute of Technology Cambridge, Massachusetts Jack Keil Wolf Electrical and Computer Engineering University of California at San Diego La Jolla, California ISBN: e-isbn: Library of Congress Control Number: Springer Science+Business Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. The following are trademarks of Texas Instruments: Code Composer Studio, TMS320C30, C6000, C6x, TMS320C5000, TMS320C3x, TMS320C40, C67x, C2x, C24x, C5x, C8x, C54x, C55x, and TMS320C67x. MATLAB is a registered trademark of MathWorks. Printed on acid-free paper springer.com

5 To Teresa, Anne, Jeffrey, Max, Norah, and in memory of David

6 Preface The first edition of this book began in January 1993 when I was elected by Dr. William Destler, who was then Chairman of the Electrical Engineering Department at the University of Maryland and is now President of the Rochester Institute of Technology, to set up and write experiments for a new senior elective laboratory course, ENEE418c Communications Laboratory, scheduled to be given for the first time in the Fall 1993 semester. At that time, we chose to use the state-of-the-art Texas Instruments TMS320C30 EVM (evaluation module) DSP board. In January 2001 we upgraded the lab to use the new state-of-the-art Texas Instruments TMS320C6701 EVM DSP board which is now no longer supported by TI. Starting with the Fall 2007 semester, we will use TI s TMS320C6713 DSK which is relatively inexpensive and connects conveniently to a USB port of a modern PC. The lab s PC s are all connected to the campus network. Each lab group is given a private workspace on a departmental server. Students are given only read/execute privileges for the standard utility and development software on the PC s so they do not inadvertently alter these files. In 1993, books for hardware based laboratory courses with standard digital signal processing and filter design experiments existed, but no book focusing on analog and digital communications techniques was available. This is still largely true. Laboratories in the Department of Electrical and Computer Engineering at the University of Maryland are separate courses. Each week they have a one hour lecture given by a regular faculty member to introduce the theory and explain the experiments followed by a three hour laboratory period run by a graduate teaching assistant. Students in this lab work in pairs. We have found that this works well because both group members actively participate. With groups of three or more, some members just sit and watch. Students have card key access to the laboratory from 8:00 AM to 11:00 PM seven days a week and so they can work outside of regular class hours if they wish. One section of the lab was first offered in the Fall 1993 semester and two in the Spring 1994 semester. Then five sections a week were offered for several years until a couple of years ago when a new communications capstone design course was offered in addition. The students have been highly enthusiastic and often spend extra hours working on the experiments because they find them to be very interesting and challenging. They also have realized that this course will help them get jobs and provide them with the skills required to perform well in their future jobs. The lab was designed for seniors, but 1/4 to 1/3 of the class is now graduate students who want to learn some real-world practical skills in addition to the purely theoretical concepts presented in the typical graduate communications and signal processing courses. When asked why they are taking this senior class, the graduate students often say they think it will help them get jobs. vii

7 viii Preface The goal of this set of experiments is to explore the digital signal processing and communication systems theoretical concepts presented in typical senior elective courses on these subjects by implementing them with actual hardware and in real time. In the process, students will gain experience using equipment commonly used in industry, such as, oscilloscopes, spectrum analyzers, signal generators, error rate test sets, digital signal processors, and analog-to-digital and digital-to-analog converters. They will also learn about typical software development tools. In addition, they will learn that there is a big step in going from an equation on paper to a real working system. This book differs from any others on the market in that its primary focus is on communication systems. Fundamental digital signal processing concepts like digital filters and FFT s are included because they are required in communication systems. Approaches that are particularly useful for DSP implementations are presented. While the experiments, particularly the earlier ones, are described for the TMS320C6713 DSK, they can be easily modified for any DSP board with an A/D and D/A converter. There are several books on digital signal processing experiments for stable software packages like MATHCAD and MATLAB. In my view, one of the purposes of a laboratory course is to help prepare students for industrial jobs. Off-line software simulation is no substitute for making actual hardware work in real-time. It does not present students with the strange unexpected and often frustrating things that occur when using actual hardware in real-time which can not be explained by nice equations, nor does it teach them how to use standard lab equipment. The prerequisites for this course are an understanding of linear systems and transform methods at a level that is often presented in a junior required course on Signals and Systems and a working knowledge of PC s and C programming. Students who have programmed in other languages like BASIC, PASCAL, or FORTRAN can quickly learn enough C to do the experiments if they are willing to make the effort. Corequisite are a senior level elective course in Digital Signal Processing and/or Communication Systems. Ideally, both courses should be taken before the Communications Laboratory. However, this is not usually possible for our seniors. We wanted our students to have the opportunity to take this lab, so we made just one of them a corequisite. With the engineering background of a senior, the presentation of the necessary theory in the text, and the one hour lab lecture to explain the theory, students have quickly learned the signal processing and communication system concepts required for the experiments. In addition, it can be argued that a lab course should help prepare students for the work world where they will have to figure out new things for themselves so the experiments should have some uncertainty and require students to fill in some of the details. There is a large initial hurdle for the students to get over while learning the details required to use the lab s hardware and software tools. Chapters 1 and 2 gradually introduce them to these tools and the architecture of the TMS320C6713 floating-point DSP. An attempt has been made to reduce this hurdle by including some basic programs on the program disk for initializing the DSK that can be used as a starting point for the experiments. FIR and IIR filter design and implementation are explored in Chapter 3. Filters are required in many communication system signal processing algorithms. Experiments comparing the relative merits of C and assembly language implementations are performed. In particu-

8 Preface ix lar, TI s linear assembly is briefly discussed. Modern DSP applications in industry are often written primarily in C with only numerically intensive critical functions written in assembly to reduce development time and improve portability to new platforms. TI s optimizing C compiler generates relatively efficient software pipelined executable code that is adequate for the experiments in this course. Therefore, assembly programming is not emphasized. Chapter 4 investigates the FFT and power spectrum estimation. A simple spectrum analyzer is made. Chapters 5 through 8 explore the classical analog communication methods of amplitude modulation, double-sideband suppressed-carrier amplitude modulation, single-sideband modulation, and frequency modulation. Transmitters and receivers are built using DSP techniques. Noncoherent receivers using envelope detectors and coherent receivers using phase-locked loops are implemented. The use of Hilbert transforms and complex signal representations in modulation systems are explored. Chapters 9 through 16 introduce some digital communication techniques. These experiments focus on methods used in high-speed wire-line data modems where DSP s have been extensively used. Topics covered include linear shift register scramblers, the RS232C interface, pulse amplitude modulation (PAM), variable phase interpolation, and quadrature amplitude modulation (QAM). The experiments lead up to building almost a complete V.22bis transmitter and receiver. Symbol clock recovery and tracking, carrier tracking, and adaptive equalizer receiver functions are implemented. The echo canceling technique used in V.32, V.34, V.90, and V.92 modems is studied in Chapter 16. Enough details are included so that this set of experiments could form a good practical guide to engineers in industry interested in wire-line modem design. I learned many of these techniques while consulting since 1970 for companies that build high-speed wire-line modems and have seen them employed in hundreds of thousands of modems. Multi-carrier modulation has become popular in a variety of systems. It is employed in several types of Digital Subscriber Line (DSL) systems which use copper telephone lines where it is called Discrete Multi-Tone (DMT) modulation. It is a popular choice for wireless systems transmitting over fading channels where it is called Orthogonal Frequency Division Multiplexing (OFDM). These include existing HF radio and Wi-Fi systems as well as soon to be deployed WiMax systems. The European cellular 3GPP committees are working to finalize a multi-carrier system called LTE. Multi-carrier modulation is explored in Chapter 17. Chapter 18 briefly presents some ideas for additional projects related to high-speed wireline modem design, error-control coding, and speech codecs. These ideas can be expanded to satisfy the capstone design project requirements of the ABET accrediting committee. Appendix C contains a complete list of the equipment used for this laboratory at the University of Maryland. It has been included as a guide to others setting up a similar lab and is not intended to be an endorsement of any specific manufacturer. Clearly, any equipment with equivalent capabilities can be substituted for items in the list. There are many more experiments in this book than can be performed in one semester. Based on our experience, an ambitious goal is to have all students do Chapters 1, 2, and 3 followed by a choice of any three additional experiments. In some semesters, we have limited the choice to three of the classical analog modulation chapters and in others to three of the

9 x Preface digital communication chapters. It would be nice if students could continue in the lab for a second semester for additional credit and build on their earlier experiments. Utility programs, software updates, text corrections, lab lecture slides, and supplementary material can be found on my web site Steven A. Tretter

10 Acknowledgements I would like to thank Mark Kohler and Sonjai Gupta for helping to unpack equipment and install and debug hardware and software in the PC s during the Spring 1993 semester when the lab was initially being set up. The students in the original Communications Laboratory section offered in the Fall 1993 semester as well as their Teaching Assistant, Yifeng Cui, deserve a great deal of thanks for being extremely patient and enthusiastic Guinea pigs. They helped correct and significantly improve the first few experiments. In particular, I want to thank Mike Barr who, with his partner Brian Silverman, forged well ahead of the rest of the students and was so enthusiastic by the end of the semester that he asked about helping with the lab in the Spring 1994 semester. The Electrical Engineering Department was able to make an exception and assign Mike as a senior to be the TA for one section and he did an outstanding job. Mrs. Tahereh Fazel was also an excellent Graduate TA for a second lab section in the Spring 1994 semester. I also want to thank those who have been TA s for the lab since that time and have all done excellent jobs, as well as Dr. Adrian Papamarcou and Dr. Jerome Gansman who have shared in teaching the lab. Jay Renner of the University of Maryland ECE staff also deserves thanks for laying out and getting manufactured the RS232/TTL daughter cards, and for securing the TMS320C6713 DSK s inside the PC cases. Dr. Brian Evans of the University of Texas at Austin also deserves thanks for reviewing preliminary versions of the previous edition of this book and making good suggestions for improvements. I would also like to thank my friends from RIXON (which was in Silver Spring, MD, but has long since dissipated in a chain of corporate take-overs), from Penril Datability Networks (which was in Gaithersburg, MD, and was bought by Bay Networks, which was in turn bought by Nortel Networks, became the Signal Processing Group of Nortel in Germantown, MD, and is now gone), and at Texas Instruments in Germantown, MD (which was formerly Telogy Networks) for helping me stay at the state-of-the-art in DSP applications to wire-line and wireless modems by using me as a consultant. I also want to thank Texas Instruments for designating our lab as one of ten Elite Digital Signal Processing Labs in the country. TI has been very generous in supporting our lab with TI hardware and software tools. In particular, Torrence Robinson, formerly in charge of University Programs at TI in Houston, and now Cathy Wicks deserve many thanks for their constant and cheerful support. xi

11 Contents 1 Overview of the Hardware and Software Tools Some DSP Chip History and Typical Applications The TMS320C6713 Floating-Point DSP The C6000 Central Processing Unit (CPU) Memory Organization for the TMS320C6713 DSK Enhanced Direct Memory Access Controller (EDMA) SerialPorts Other Internal Peripherals Brief Description of the TMS320C6000 Instruction Set Parallel Operations and Pipelining The TMS320C6713 DSP Starter Kit (DSK) The Audio Interface Onboard the TMS320C6713 DSK Software Support for the DSK Board and C6x DSP s The Board Support Library (BSL) The Chip Support Library Code Composer Studio Project Files and Building Programs The Optimizing Compiler and Assembler TheLinker Building Programs from Command Line Prompts TheArchiver Additional Code Composer Studio Features OtherSoftware Digital Filter Design Programs Commercial Software Introductory Experiments Learning to Use the Hardware and Software Tools Getting Started with a Simple Audio Loop Through Program A Linker Command File and Beginning C Program PropertiesoftheAIC23Codec Creating a CCS Project for dskstart32.c Experiment 2.1: Building and Testing dskstart32.c More Details on the McBSP Serial Ports and Codecs xiii

12 xiv Contents Basic McBSP Transmitter and Receiver Operation Example C Code for Reading from and Writing to the Codec The C6000 Timers Generating a Sine Wave by Polling XRDY Experiment 2.2: Instructions for the Polling Experiment Generating a Sine Wave Using Interrupts TheCPUInterruptPrioritiesandSources InterruptControlRegisters What Happens When an Interrupt Occurs TI Extensions to Standard C Interrupt Service Routines Using the dsk6713bsl32 Library for Interrupts Experiment 2.3: Generating Sine Waves by Using Interrupts Generating a Sine Wave with the EDMA and a Table EDMAOverview EDMA Event Selection RegistersforEventProcessing The Parameter RAM (PaRAM) Synchronization of EDMA Transfers Linking and Chaining EDMA Transfers EDMAInterruptstotheCPU Experiment 2.4: Generating a Sine Wave Using the EDMA Controller 62 3 Digital Filters Discrete-Time Convolution and Frequency Responses Finite Duration Impulse Response (FIR) Filters Block Diagram for Most Common Realization Two Methods for Finding the Filter Coefficients to Achieve a Desired Frequency Response Using Circular Buffers to Implement FIR Filters in C Circular Buffers Using the C6000 Hardware How the Circular Buffer is Implemented Indirect Addressing Through Registers Interfacing C and Assembly Functions Responsibilities of the Calling and Called Function Using Assembly Functions with C Linear Assembly Code and the Assembly Optimizer A Linear Assembly Convolution Function that Uses a Circular Buffer and Can be Called from C Infinite Duration Impulse Response (IIR) Filters Realizations for IIR Filters A Program for Designing IIR Filters TwoMethodsforMeasuringaPhaseResponse Laboratory Experiments for Digital Filters Experiment 3.1: FIR Filters Entirely in C... 96

13 Contents xv Experiment 3.2: FIR Filters Using C and Assembly Experiment 3.3: Implementing an IIR Filter Additional References The FFT and Power Spectrum Estimation The Discrete-Time Fourier Transform Data Window Functions TheDiscreteFourierTransformanditsInverse TheFastFourierTransform UsingtheFFTtoEstimateaPowerSpectrum Laboratory Experiments Experiment 4.1: FFT Experiments Experiment 4.2: Making a Spectrum Analyzer Additional References Amplitude Modulation Theoretical Description of Amplitude Modulation Mathematical Formula for an AM Signal Example for Single Tone Modulation TheSpectrumofanAMSignal Demodulating an AM Signal by Envelope Detection Square-Law Demodulation of AM Signals Hilbert Transforms and the Complex Envelope Laboratory Experiments for AM Modulation and Demodulation Experiment 5.1: Making an AM Modulator How to Capture DSK Output Samples with CCS for Plotting Experiment 5.2: Making a Square-Law Envelope Detector Experiment 5.3: Making an Envelope Detector Using the Hilbert Transform Additional References DSBSC Amplitude Modulation and Coherent Detection Mathematical Form for a DSBSC-AM Signal The Ideal Coherent Receiver The Costas Loop as a Practical Approach to Coherent Demodulation Exercises and Experiments for the Costas Loop Theoretical Design Exercises Hardware Experiments Additional References Single-Sideband Modulation and Frequency Translation Single-Sideband Modulators Coherent Demodulation of SSB Signals Frequency Translation Laboratory Experiments

14 xvi Contents Experiment 7.1: Making an SSB Modulator Experiment 7.2: Coherent Demodulation of an SSB Signal Additional References Frequency Modulation TheFMSignalandSomeofitsProperties Definition of Instantaneous Frequency and the FM Signal Single Tone FM Modulation Narrow Band FM Modulation The Bandwidth of an FM Signal FM Demodulation by a Frequency Discriminator An FM Discriminator Using the Pre-Envelope A Discriminator Using the Complex Envelope Using a Phase-Locked Loop for FM Demodulation Laboratory Experiments for Frequency Modulation Experiment 8.1: Measuring the Spectrum of an FM Signal Experiment 8.2: FM Demodulation Using a Frequency Discriminator Experiment 8.3: Using a Phase-Locked Loop for FM Demodulation Additional References Pseudo-Random Binary Sequences and Data Scramblers Using Shift Registers to Generate Pseudo-Random Binary Sequences The Linear Feedback Shift Register Sequence Generator The Connection Polynomial and Sequence Period Properties of Maximal Length Sequences Self Synchronizing Data Scramblers The Scrambler The Descrambler Theoretical and Simulation Exercises Exercises for a Shift Register Sequence Generator with a Primitive Connection Polynomial Exercises for a Shift Register Sequence Generator with an Irreducible but not Primitive Connection Polynomial Exercises for a Shift Register Sequence Generator with a Reducible Connection Polynomial Additional References The RS-232C Protocol and a Bit-Error Rate Tester The EIA RS-232C Serial Interface Protocol Error Rate for Binary Signaling on the Gaussian Noise Channel TheNavtelDatatest3BitErrorRateTester Bit-Error Rate Test Experiment Additional References

15 Contents xvii 11 Digital Data Transmission by Pulse Amplitude Modulation Description of a Baseband Pulse Amplitude Modulation System Baseband Shaping and Intersymbol Interference TheNyquistCriterionforNoISI Raised Cosine Baseband Shaping Filters Splitting the Shaping Between the Transmit and Receive Filters EyeDiagrams Implementing the Transmit Filter by an Interpolation Filter Bank Symbol Error Probability with Additive Gaussian Noise SymbolClockRecovery Simulation and Theoretical Exercises for PAM Generating Four-Level Pseudo-Random PAM Symbols Eye Diagram for a PAM Signal Using a Raised Cosine Shaping Filter Eye Diagram for a PAM Signal Using a Square-Root of Raised Cosine Shaping Filter Theoretical Error Probability for a PAM System HardwareExercisesforPAM Generating a PAM Signal and Eye Diagram Testing the Square-Law Symbol Clock Frequency Generator OptionalTeamExercise Additional References Variable Phase Interpolation ContinuouslyVariablePhaseInterpolation Computing the Least-Squares Fits Quantized Variable Phase Interpolation ClosingtheTrackingLoop Changing the Sampling Rate by a Rational Factor Experiments for Variable Phase Interpolation Experiment 12.1: Open Loop Phase Shifting Experiments Experiment 12.2: Making a Symbol Clock Tracking Loop Additional References Fundamentals of Quadrature Amplitude Modulation ABasicQAMTransmitter Two Constellation Examples The Point Constellation A 4-Point Four Phase Constellation A Modulator Structure Using Passband Shaping Filters Ideal QAM Demodulation QAM Modulator Experiments StepstoFollowinMakingaTransmitter TestingYourTransmitter Generating a Startup Sequence

16 xviii Contents 13.6 Additional References QAM Receiver I Clock Recovery and Other Front-End Subsystems Overview of a QAM Receiver Details About the Receiver Front-End Subsystems AutomaticGainControl The Carrier Detect Subsystem SymbolClockRecovery Experiments for the QAM Receiver Front-End Additional References QAM Receiver II Equalizer and Carrier Recovery System The Complex Cross-Coupled Passband Adaptive Equalizer The LMS Method for Adjusting the Equalizer Tap Values Theoretical Behavior of the LMS Algorithm Adding Tap Leakage to the LMS Algorithm The Phase-Splitting Fractionally Spaced Equalizer Decision Directed Carrier Tracking Blind Equalization Blind Equalization with the Complex Cross-Coupled Equalizer Blind Equalization with the Phase-Splitting Equalizer Complex Cross-Coupled Equalizer and Carrier Tracking Experiments Implementing the Slicer Making a Demodulator and Carrier Tracking Loop Making a Complex Cross-Coupled Adaptive Equalizer Bit-ErrorRateTest Optional Experiment Receiving the 16-Point V.22bis Constellation Optional Experiment Ideal Reference Training Optional Phase-Splitting Fractionally Spaced Equalizer Experiment Optional Blind Equalization Experiment Additional References Echo Cancellation for Full-Duplex Modems The Echo Sources in a Dialed Telephone Line Circuit The Data-Driven, Nyquist, In-Band Echo Canceler General Description The Near-End Echo Canceler The Far-End Echo Canceler Far-End Frequency Offset Compensation Echo Canceler Experiments Making a Near-End Echo Canceler Making a Far-End Echo Canceler with Frequency Offset Correction Additional References

17 Contents xix 17 Multi-Carrier Modulation History and Implementation of Multi-Carrier Modulation Asymmetric Digital Subscriber Line (ADSL) System Architecture Components of a Simplified ADSL Transmitter The Cyclic Redundancy Check Generator The Scrambler The Reed-Solomon Encoder TheConvolutionalInterleaver The Map and IFFT Modulator Blocks Some Signals Used for Initialization and Synchronization A Simplified ADSL Receiver Demodulation and Frequency Domain Equalization Sample Clock Acquisition and Tracking Symbol Alignment Acquisition and Tracking Remaining Blocks Making a Simplified ADSL Transmitter and Receiver Makinga64-PointIFFTanda64-PointFFT Making a Scrambler, Constellation Point Mapper, and Their Inverses Measuring the Channel Impulse Response Duration Completing the Transmitter Making the Receiver Additional References Suggestions for Additional Experiments Elementary Modem Handshake Sequence Make an ITU-T V.21 Frequency Shift Keyed (FSK) Modem Fast Equalizer Training Using Periodic Sequences Trellis Coded Modulation Reed-Solomon Encoder and Decoder TurboCodes Low Density Parity Check Codes V.34 Constellation Shaping by Shell Mapping Nonlinear Precoding for V Speech Codecs A Generating Gaussian Random Numbers 313 A.1 The C6713 C Compiler Pseudo Random Number Generator A.2 A Better Uniform Random Number Generator A.3 Turning Uniformly Distributed Random Variables into a Pair of Gaussian Random Variables A.4 Limit on the Peak of the Simulated Gaussian Random Variables B A TTL/RS-232C Interface for McBSP0 319 C Equipment List for Each Station 323

18 xx Contents References 325 I.ListofManuals II. Selected Reference Books and Papers A.DSPLaboratoryBooksUsingDSPHardware B.DSPLaboratoryBooksUsingSoftwareSimulation C.BooksandPapersonDigitalSignalProcessing D. Books and Papers on Communications E. References for Wireline and Wireless Multi-Carrier Modulation F.BooksandPapersonErrorCorrectingCodes III.InterestingWebSites Index 335