OFDM RECEIVER SYNCHRONIZATION FOR A DVB-H SYSTEM _______________ A Thesis Presented to the Faculty of San Diego State University _______________ In Partial Fulfillment of the Requirements for the Degree Master of Science in Electrical Engineering _______________ by Ramprasad Rao Vasudeva Rao Summer 2010 iii Copyright © 2010 by Ramprasad Rao Vasudeva Rao All Rights Reserved iv DEDICATION To my father Vasudeva Rao For all the unconditional love and support And in loving memory of my mother Shashikala For the person I am today v ABSTRACT OF THE THESIS OFDM Receiver Synchronization for a DVB-H System by Ramprasad Rao Vasudeva Rao Master of Science in Electrical Engineering San Diego State University, 2010 DVB-H (Digital Video Broadcasting – Handheld) technology is based on ETSI (European Telecommunications Standards Institute) standard designed to bring the broadcast services to battery-powered handheld receivers such as mobile phones and PDA’s. The system is defined based on the existing DVB-T (Terrestrial) system allowing for lower power consumption, lower signal strengths and fast movements. DVB-H system uses Orthogonal Frequency Division Multiplexing (OFDM) technique to deliver multimedia services in any of the three bandwidth modes i.e. 6, 7 and 8 MHz. OFDM has been successful in numerous wireless applications, where its superior performance in multi-path environments is desirable. It is a multicarrier system where the data is transmitted in parallel sub channels by using several subcarriers. All the data carriers in one OFDM frame can be modulated using either QPSK, 16-QAM or 64-QAM. In this thesis, DVB-H (Physical layer) system is simulated using 4096 FFT mode and the signal transmitted is in accordance with the specification of ETSI TR 102 377. Multipath Rician and Rayleigh channel conditions are considered. The main emphasis is on the receiver; concentrating mainly on the Squelch detection, symbol timing synchronization, correcting the coarse frequency offset and channel estimation for the DVB-H system. Various stages of the signal recovery process are also discussed. vi TABLE OF CONTENTS PAGE ABSTRACT ...............................................................................................................................v LIST OF TABLES ................................................................................................................... ix LIST OF FIGURES ...................................................................................................................x ACKNOWLEDGEMENTS ................................................................................................... xiii CHAPTER 1 INTRODUCTION .........................................................................................................1 1.1 Mobile TV: A New Reality................................................................................2 1.2 Mobile TV Using Terrestrial Broadcasting Networks .......................................2 2 A LITERATURE REVIEW ON ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING ..........................................................................................................4 2.1 OFDM is Bandwidth Efficient ...........................................................................4 2.2 Advantages and Disadvantages of OFDM .........................................................6 2.3 Importance of Orthogonality in an OFDM System ...........................................7 2.4 OFDM System Model ........................................................................................8 2.5 Guard Interval and Cyclic Prefix .....................................................................12 2.6 Multipath Fading Channel ...............................................................................14 2.7 Doppler Shift ....................................................................................................16 2.8 Doppler Spread (BD) ........................................................................................16 2.9 Coherence Time (TC) .......................................................................................17 2.10 Rayleigh Fading .............................................................................................17 2.11 Ricean Fading Distribution ............................................................................17 2.12 Synchronization .............................................................................................18 2.13 Synchronization Issues with OFDM ..............................................................19 2.14 Effect of Symbol Timing Offset ....................................................................19 2.15 Effect of Frequency Offset .............................................................................21 2.16 Synchronization Using the Cyclic Prefix .......................................................22 2.17 Channel Estimation ........................................................................................23 vii 3 DIGITAL VIDEO BROADCASTING- HANDHELD DESCRIPTION ....................24 3.1 Scope of DVB-H Standard ...............................................................................26 3.2 Basic Aspects of DVB-H Networks ................................................................27 3.3 Principle of MFN (Multi Frequency Networks) ..............................................28 3.4 Principle of SFN (Single Frequency Network) ................................................28 3.5 Time Slicing .....................................................................................................30 3.6 MPE-FEC .........................................................................................................31 3.7 Main Issues in DVB-H .....................................................................................32 3.8 How Time Slicing and MPE-FEC Provides a Solution ...................................32 3.9 Delta-T Method ................................................................................................33 3.10 Burst Size and Off-Time ................................................................................34 3.11 Physical Layer Specifications for DVB-H .....................................................36 3.12 Transmitter Input Signal ................................................................................37 3.13 Channel Coding .............................................................................................39 3.14 Outer Coding and Outer Interleaving ............................................................40 3.15 Inner Coding ..................................................................................................42 3.16 Inner Interleaving ...........................................................................................42 3.17 Bit-Wise Interleaving .....................................................................................42 3.18 Symbol Interleaver .........................................................................................45 3.19 Modulation .....................................................................................................46 3.20 4K Mode in DVB-H .......................................................................................46 3.21 OFDM Frame Structure .................................................................................47 3.22 Reference Signals ...........................................................................................49 3.23 Definition of Reference Sequence .................................................................49 3.24 Location of Scattered Pilots ...........................................................................50 3.25 Location of Continual Pilot Carriers ..............................................................51 3.26 Transmission Parameter Signalling (TPS) .....................................................51 3.27 Scope of the TPS ............................................................................................52 3.28 TPS Transmission Format..............................................................................52 3.29 Number of RS-Packet per OFDM Super-Frame ............................................54 3.30 Useful Bitrate .................................................................................................54 viii 4 IMPLEMENTATION AND SIMULATION OF THE PHYSICAL LAYER FOR A DVB-H SYSTEM ...........................................................................................56 5 CONCLUSION AND FUTURE WORK ....................................................................76 REFERENCES ........................................................................................................................78 ix LIST OF TABLES PAGE Table 3.1. Guard Interval Lengths for all Modes .....................................................................37 Table 3.2. Frequency Domain Parameters for 4K Mode in 8 MHz, 7MHz and 6 MHz Channels .......................................................................................................................48 Table 3.3. Time Domain Parameters for 4K Mode in 8MHz, 7MHz and 6MHz Channels .......................................................................................................................48 Table 3.4. Carrier Indices for Continual Pilot Carriers. ...........................................................51 Table 3.5. Carrier Indices for TPS Carriers in 4K Mode .........................................................51