Communications using the high frequency spectrum (2-30 MHz) have experienced a considerable resurgence. In recent years, powerful microcomputers and VLSI technology have greatly enhanced the prospects of overcoming many of the unique problems that formerly afflicted the HF systems More...designer. The aim of this book, therefore, is to provide a firm foundation for the design, evaluation and operational use of HF communications, with systems issues as the primary perspective. The approach provides an understanding of the way in which various elements of the system contribute to the overall HF communications link performance. Mathematics is introduced only where needed to clarify or illustrate key issues. The book will be vital to the professional communications engineer, already familiar with many of the problems but requiring a consolidated systems view of the subject; to the engineering student and research worker as a reference text which demonstrates how modern technology can be used to solve problems posed to the HF user; and to non- specialists and consultants within the communications industry.
Preface
1 HF Radio: Past and Present
Early Developments
Origins of long-range communications
Experiments with the short waveband
HF gains the upper hand
Changes in Fortune
The reliance upon the operator
The fall from favour
A resurgence of interest
Percent Usage
HF spectrum allocation
Non-military users
Military users
Evolving technology
2 System Considerations
Concepts
The systems approach
System characteristics
Design considerations
Radio Communications Systems
System definition
System decomposition
Open systems interconnection
Transmitting sub-system
Channel sub-system
Receiving sub-system
Design considerations
HF Communications Systems
Propagation characteristics
A unique role for HF
System design overview
The power level diagram
3 Ground Wave Propagation
Propagation over a Plane Earth
Free space propagation
Electrical characteristics of the ground
Ground wave components
The Surface Wave
General principles
Zonal relationships
Effect of antenna height
The Space Wave
Zonal relationships
Effect of antenna height
Deviations from Simplified Model
General considerations
Ground conductivity
Terrain irregularities
Shadowing
Mountainous terrain
Vegetation
Field Strength Computation
The prediction problem
Field strength values
Variability of ground conditions
Mixed propagation paths
Sea state
Obstacles
Vegetation
4 Sky Wave Propagation
The Ionosphere
Structure
Ionisation
D-region
E-region
F-region
Ionospheric disturbances
Wave Propagation in the Ionosphere
Physical processes
Reflection at oblique incidence
Ray paths
Virtual height
Lowest usable frequency
Maximum usable frequency
Effect of the Earth’s magnetic field
Variation of the Critical Frequency
Typical values
Solar cycle dependence
Annual, seasonal and diurnal variations
Characteristics of the Received Signal
Components
Multipath propagation and time dispersion
Fading
Frequency dispersion
Delay distortion
Nearly Vertically Incident Sky Waves
The need for short-range sky wave links
Selecting the frequency
Signal strength
Dependence upon range
Mode structure and multipath
Wave polarization
Summary of attributes
5 Noise and Interface
Noise
Sources
Noise power
Atmospheric noise
Man-made noise
Galactic noise
Statistical variations
Condition for external noise limitation
Interference
Sources
Magnitude of effects
Variation with time and frequency
Variation with bandwidth
Local Noise and Interference Effects
Sources
Precipitation static
Local electromagnetic interference
Electromagnetic compatibility
Magnitude of effects
Audio Noise
Sources
Effects upon speech transmission
Effects upon speech reception
6 System Performance Assessment
Antenna Considerations
Matching
Gain and directivity
Polarization
Arrival angles
Transmitting antennas
Receiving antennas
Diversity operation
Signal-to-Noise Ratios
The received signal-to-noise ratio
The required signal-to-noise ratio
The median signal-to-noise
Variability of signal-to-noise ratio
Circuit Performance Criteria
Ground wave variability
Sky wave variability
Sky wave availability
Circuit reliability factor
Effect of signal-to-noise on reliability
Ground Wave Performance
Field strength and received power
Baseline assessment
The range factor
Effect of short antennas
Sky Wave Performance
Representative example
Monthly signal-to-noise ratios
Frequency dependence
Assessment of reliability improvement
7 Air-Ground Communications
The Mobile User
Comparison with point-to-point circuits
Parameters critical to the mobile user
Characteristics of the Airborne Terminal
Antenna radiation efficiency
Antenna radiation patterns
Aircraft generated noise
Flight paths and frequency selection
Impact upon System Performance
Effect of antenna efficiency
Effect of aircraft noise
Effect of frequency choice
Effect of flight path
Communications with Small Aircraft
Summary of system problems
Performance predictions
Air-to-ground links
Advantage of multi-ground station usage
Ground-to-air links
Guidance for the System Designer
Criteria
Frequency management
Antennas
Aircraft noise
8 Frequency Management
Techniques
Ionospheric Predictions
Predicting the frequency window
MUF prediction
LUF prediction
Example format of long-term predictions
Limitations of long-term predictions
Short-term predictions
Sounding
Types of technique
Pulse sounding and ionograms
Comparison of sounding techniques
Linear sweep sounding (chirpsounding)
Channel sounding
Real Time Channel Evaluation (RTCE)
The need for RTCE
The nature of RTCE
Automation of system control
Matching the channel to the medium
An air-ground link example
Potential advantages of RTCE
9 Data Communications
General Considerations
Digital Modulation Techniques
Terminology
Phase discontinuous schemes
Phase continuous schemes
Primary modulation schemes for HF systems
Error Rate Performance
Error probability
Non-fading signals
Fading signals
Use of diversity reception
Non-ideal receivers
Effect of non-Gaussian noise
Multipath and interference considerations
High Data Rate Transmissions
Types of technique
Parallel data modulation methods
Equalisation techniques
Comparison of techniques
Wide Bandwidth Techniques
General limitations
Channel dispersion effects
Matched filter/wideband correlation
Matched filter/signal gating
Direct sequence spread spectrum
Narrowband interference
Principles of Error Control Coding
Causes of data errors
Types of coding
Block coding, with hard decision
Convolutional coding, with hard decision
Detection and correction of error bursts
Sort decision decoding
Performance of Error Control Coding
Effect of error probability
Coding gain
Analysis of examples
Some practical considerations
Time delays
Interleaving
Erasure decoding and soft decision decoding
10 Impact of Modern Technology
Overview
Hardware Evolution
Receivers
Transceivers
Power Amplifiers
Synthesisers
Transmitting antennas
Receiving antenna
Signal Processing
Lincompex
Digital receive modules
Signal detection
Signal identification
Transmit processing
Interference Reduction
Interference nulling at the antenna
Interference nulling at the receiver
Frequency agility
Spread spectrum processing
Interference cancellation
Interference blanking
Adaptive Techniques
Adaptive channel evaluation
Adaptive detection processes
Adaptive receive array processing
Adaptive modulation and coding
Speech Processing
Voice digitisation
Vocoders
Speech recognisers
Benefits of speech processing
Future trends
References
Index
Biography
Nicholas M Maslin
