Power Line Modem with E-meter Platform White Paper Ti Power Line Modem with E-meter Platform White Paper February 4, 2004 ti Copyright © 2004, Texas Instruments Incorporated February 4, 2004 1 Power Line Modem with E-meter Platform White Paper Ti Contents INTRODUCTION .......................................................................................................................................................4 PLATFORM BACKGROUND ..................................................................................................................................5 POWER LINE MODEM APPLICATIONS.........................................................................................................................5 EXISTING POWER LINE MODULATION TECHNIQUES ..................................................................................................6 FSK ......................................................................................................................................................................6 X-10......................................................................................................................................................................6 BPSK....................................................................................................................................................................6 Broadband (HomePlug).......................................................................................................................................6 DESIGN GOALS ..........................................................................................................................................................6 AN INTRODUCTION TO OFDM.............................................................................................................................8 Advantages of OFDM ..........................................................................................................................................8 Fundamentals of OFDM ......................................................................................................................................8 SIGNAL PATH OVERVIEW ..................................................................................................................................10 PACKET FORMAT .....................................................................................................................................................10 TRANSMIT SEQUENCE..............................................................................................................................................10 Transmit Overview.............................................................................................................................................11 Preamble and Synchronization Generation .......................................................................................................11 Data Frame Generation.....................................................................................................................................13 Addition of Cyclic Prefix....................................................................................................................................15 RECEIVE SEQUENCE ................................................................................................................................................17 Overview of Receive Operation .........................................................................................................................17 Data Flow Description of Receive .....................................................................................................................17 SIGNAL PROCESSING OVERVIEW ...................................................................................................................20 SIGNAL SCHEME SELECTION – QPSK.......................................................................................................................20 Signal Scheme Selection.....................................................................................................................................22 Comparing Binary and Quaternary Signaling...................................................................................................23 Channel Coding Error Rate Analysis.................................................................................................................25 OFDM DETAIL ........................................................................................................................................................26 Theoretical Advantage of OFDM.......................................................................................................................27 Advantage of OFDM with Multi-path Interference............................................................................................28 PARITY CHECK BYTES CALCULATION .....................................................................................................................29 DATA SCRAMBLING .................................................................................................................................................32 VITERBI ENCODING .................................................................................................................................................32 MODULATION MAPPING ..........................................................................................................................................33 Advantages to Differential QPSK ......................................................................................................................34 CREST FACTOR AND TRANSMIT TRUNCATION .........................................................................................................34 Study on Transmit Truncation vs. Received SNR ...............................................................................................35 Set Power/Truncation Algorithm .......................................................................................................................36 VITERBI DECODING .................................................................................................................................................36 Choice of Distance Metric for DQPSK..............................................................................................................38 Geometric Distance Metric Computation Simplification...................................................................................39 FREQUENCY EQUALIZATION ....................................................................................................................................41 BER Simulation for Various Frequency Equalization Techniques ....................................................................41 AGC OPERATION .....................................................................................................................................................43 PREAMBLE WAVEFORM AND DETECTION .................................................................................................................44 OFDM Frame Alignment ...................................................................................................................................44 February 4, 2004 2 Power Line Modem with E-meter Platform White Paper Ti SYSTEM BLOCK DIAGRAM AND PARTS SELECTION.................................................................................46 Metering Processor Selection ............................................................................................................................47 DSP Selection.....................................................................................................................................................47 Codec Selection..................................................................................................................................................48 Line Driver Selection .........................................................................................................................................48 MEASURED DATA ..................................................................................................................................................49 Power Line Impedance Measurement................................................................................................................49 Conformance to CENELEC Mask......................................................................................................................51 CONCLUSIONS........................................................................................................................................................52 REFERENCES ..........................................................................................................................................................53 APPENDIX. COMPLETE VITERBI TRELLIS...................................................................................................54 February 4, 2004 3 Power Line Modem with E-meter Platform White Paper Ti Introduction The “Power Line Modem with E-meter Platform” demonstrates communication over a power line using Orthogonal Frequency Division Multiplexing (OFDM) techniques. OFDM spreads the information over several frequencies, reducing sensitivity to impulsive noise, and is able to perform better in a multi-path environment, such as a power line. This