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Wireless Digital Communications: Design and Theory

by: Tom McDermott, N5EG
334 pages. ISBN: 0-9644707-2-1

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Preface
Amateur radio communication has progressed in many ways since its beginning in the early 1900's. General communications progressing from spark to CW and voice from AM to FM and SSB. Similarly, data communications as a mode of amateur communications has progressed from using on-off keying (OOK) to FSK, and from RTTY to more modern modes of communications (synchronous and error-correcting). There has been a lack of good technical background material in amateur radio literature on the principles and design of synchronous digital modems.

The wealth and quality of literature in the professional world in the subject area is astounding, but much of it may not be readily accessible to the radio amateur, whether for reasons of advanced mathematics, or simple lack of availability.

In writing this book, the aim has been to bring a concise group of topics covering a broad spectrum of amateur synchronous digital communications subjects to print in one place, and to make it readily accessible to the radio amateur. This text aims to present the information in a clear and straight-forward manner, with the maximum use of graphical and computer-assisted aids, and with a minimum of rigorous mathematical theory. However, digital communications deals with the application and solution of statistical phenomenon, and a minimum background is necessary. Where practical, the appendices provide short summaries of some of the important mathematical concepts that will be needed in understanding certain areas.

Overall, the field of digital communications could be generally broken into two categories: bandwidth-limited communications and power-limited communications. Much of the professional literature focuses on the former, while in practice the amateur is many times concerned with the latter. This text focuses more on the subject of power-limited communications and emphasizes, through examples, the circuits and problems of the latter category of applications.

With time and the increasingly more crowded HF bands, however, the radio amateur will adopt more sophisticated data modems, offering higher throughput and narrower bandwidth operation under the demanding propagation conditions of the HF medium. This trend has already started and should accelerate as the cost of technology, particularly Digital Signal Processing, continues to decrease. So, this text includes information on the subject areas of DSP-based modem filters, and on forward-error-correcting codes, whose use by the radio amateur will become dominant within a few short years. While the data rate of VHF and UHF communications will increase, it is expected that, for the radio amateur, these will remain power-limited applications for some time.

In the preparation of this text, I have relied on the study of a number of exceptionally well written textbooks, and to the IEEE literature in the area, and these should be consulted whenever more depth or broader interest is desired. I would like to thank the reviewers of the text for many helpful comments, related both to the readability of the material, ...

(more in the book!)

    Thomas C. McDermott, N5EG

    Dallas, Texas August 25, 1995


Tom's first book signing party!
(January 5th, 1997)

Tom McDermott, N5EG, Greg Jones, WD5IVD, Lon Cecil, WB5PKJ, Bob Stricklin, N5BRG, and John Koster, W9DDD (left to right)


Chapter 1 - Introduction

  • Definition of Information
  • Source Entropy
  • Fundamental Data Capacity
  • Signal to Noise ratio - Eb/No
  • Block Diagram of the Communication System
  • Review / Definition of Some Key Concepts
  • Eye Pattern
  • Signal Constellation Diagram
  • Chapter 1 - References

Chapter 2 - Additive White Gaussian Noise (AWGN)

  • Definition of AWGN Noise
  • Gaussian Distribution
  • Calculating the BER given AWGN
  • Generating a BER Curve
  • Relation of Power Spectrum and AWGN
  • Computing Noise and Signal Magnitudes
  • Chapter 2 - References

Chapter 3 - Antipodal, Orthogonal, and Non-orthogonal Signaling

  • Antipodal Signaling
  • Orthogonal Signaling
  • Non-orthogonal Signaling
  • Analysis of FSK signaling
  • Orthogonal Waveforms
  • Orthogonal FSK Demodulators
  • Chapter 3 - References

Chapter 4 - Carrier Transmission

  • FSK - Frequency Shift Keying
  • FFSK - Fast Frequency Shift Keying
  • mFSK - m-ary FSK
  • PSK - Phase Shift Keying
  • mPSK - m-ary Phase Shift Keying
  • OQPSK - Offset QPSK
  • Received Phase Ambiguity
  • Performance of PSK modulation in the presence of AWGN
  • ASK - Amplitude Shift Keying
  • MSK - Minimum Shift Keying
  • OFDM - Orthogonal Frequency Division Multiplexing
  • OFDM based on m-ary FSK
  • OFDM based on ASK
  • AFSK - Audio Frequency Shift Keying
  • Summary
  • Chapter 4 - Reference

Chapter 5 - Frequency and Impulse Response of Optimum Modem Filters

  • Optimum filter criteria
  • Raised-Cosine Filter Responses
  • Filter Response Partitioning
  • Filter Impulse Response
  • Filter Response to an Isolated Data Bit
  • Eye Pattern Generation
  • Equivalent Noise Bandwidth
  • Some Frequency Response Defects
  • Impulse-Response Length Truncation
  • Detailed Step-by-Step Procedure
  • Dolph-Chebychev Transmit Pulses
  • Chapter 5 - Reference

Chapter 6 - Matched Filters

  • Matched filter for Rectangular Pulses
  • Matched filter for Square-Root Raised-Cosine Transmit Pulses
  • Use of the Matched Filter Symmetry to Equalize a Channel
  • Chapter 6 - Reference

Chapter 7 - Data Codes

  • Basic Data Codes
  • DC-Balance (One's Density) of the Code
  • Scrambling
  • Forward Error Correcting (FEC) Codes
  • Linear Block Codes
  • AWGN Performance of Linear Block Codes
  • Statistical Performance of Linear Block Codes
  • Other Properties of FEC Codes
  • Interleaving the Codewords
  • Golay Codes
  • Longer Codes
  • Reed-Solomon Codes
  • Convolutional Codes
  • Decoding the Convolutional Code
  • Convolutional Decoders
  • Viterbi's Algorithm
  • Summary of Viterbi Decoder
  • Chapter 7 - Reference

Chapter 8 - Data Slicer and the Slicing Level

  • Slicing Level Determination
  • Source Statistics
  • Non-Scrambled Data
  • NRZI-Coded HDLC Calculations
  • Scrambled Data Calculations
  • Binomial Distribution
  • Fixed Slicing-Level Methods
  • DSP-Based Slicing-Level Determination

Chapter 9 - Clock Recovery

  • The Importance of Accurate Clock Position
  • Methods to Recover the Clock
  • Closed-Loop Clock Recovery
  • Clock Recovery Filters
  • Filter Transfer Function
  • Modulation-Based Clock Recovery
  • Chapter 9 - Reference

Chapter 10 - Carrier Recovery

  • Deriving a Carrier Reference
  • Carrier Generation by Rectification
  • Carrier Generation by Multiplication
  • Other Methods of Carrier Generation
  • 2PSK Carrier Recovery - Costas Loop
  • Chapter 10 - Reference

Chapter 11 - Phase Locked Loops for Carrier and Clock Recovery

  • Closed Loop Response
  • Open Loop Response
  • Lead Lag Filter
  • Higher Order Loop Filter
  • Parasitic Poles
  • PLL Loop Lock time
  • PLL Noise Bandwidth
  • Types of Phase Detectors, Lock-in Range
  • Control Loop Dynamic Range
  • Chapter 11 - Reference

Chapter 12 - Frame Alignment and Data Carrier Detect

  • General Data Carrier Detect (DCD) Acquisition
  • DCD and Frame Alignment based on Message Content
  • Median Time to False Frame Declaration
  • Maximum Average Reframe Time
  • Going Out of Frame
  • Other Message Content
  • Framing on Short Transmissions
  • Chapter 12 - Reference

Chapter 13 - Propagation Channel Models

  • VHF and UHF Channel Models
  • Minimum-Phase and Non-Minimum-Phase Fades
  • Rayleigh fading
  • Circular Polarization
  • Wideband Data Channels
  • Rules of Thumb
  • HF Channel models
  • Signaling Rate Bounds
  • HF Channel Simulation
  • Coefficient Properties
  • Bit Error Rate Performance of Rayleigh Faded Path
  • Diversity Reception
  • Approaches to HF Modem Design
  • RTTY - Live With the Errors
  • AMTOR - Simple Error Detection and Re-transmission
  • AX.25 Packet Transmission - 300 baud HF
  • More Recent Developments
  • GTOR
  • Pactor II
  • Clover II
  • Future Improvements
  • Chapter 13 - Reference

Chapter 14 - Automatic Request for Repeat (ARQ)

  • Simple ARQ
  • Hybrid ARQ
  • Performance of ARQ

Chapter 15 - Testing Considerations

  • Bit Error Rate vs. Received Signal Level
  • Baseband BER Test
  • Butterworth Calibration Filter
  • Radio Characterization for Data
  • Radio-based Test
  • FSK - Transmitter Characterization
  • Other Transmitter Characterization
  • FSK - Receiver Characterization
  • System Characterization
  • Theoretical Eb/No vs. Received Signal Level (RSL)
  • Pseudo-Level Error Detection Margin
  • Adjustment Aid - 'Click' box
  • Bit Error Rate Test Statistics
  • Chapter 15 - Reference

Appendix A - Some Useful Probability Distributions

  • A.1 Probability of Events.
  • A.2 Histograms, Probability Density, Cumulative Density
  • A.3 Uniform Distribution
  • A.4 Binomial Distribution
  • A.5 Gaussian Distribution
  • A.6 Poisson Distribution
  • A.7 Rayleigh Distribution

Appendix B - Pseudo-Random Binary Sequence (PRBS) Generators

  • B.1 Properties of a PRBS
  • B.2 Construction of the PRBS Generator.
  • B.3 Autocorrelation Properties
  • B.4 Self Synchronization
  • B.5 Self Synchronous Scrambler and Descrambler
  • B.6 Binary Polynomial Arithmetic
  • Appendix B - Reference

Appendix C - Discrete Fourier and Inverse Discrete Fourier Transforms & Complex Numbers

  • C.1 The Fourier Transform and the Impulse Response
  • C.2 Complex Number Representation
  • C.3 Description of a Signal using Complex Notation
  • C.4 Complex Conjugate
  • C.5 Discrete Fourier Transform
  • C.6 Power Spectral Density (PSD)
  • C.7 Symmetry Requirement for Frequency Response
  • Appendix C - Reference

Appendix D - Correlation, Convolution, and Laplace Notation for Filters

  • D.1 Convolution and Multiplication
  • D.2 Convolution
  • D.3 Frequency and Impulse Response
  • D.4 Correlation
  • D.5 Cross Correlation
  • D.6 Autocorrelation
  • D.7 Complex Signals
  • D.8 Laplace Notation for Complex numbers
  • Appendix D - Reference

  • TAPR Information
  • Index
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