Challenges of Data Over HF Radio

Presented to

The Radio Club of America

Technical Symposium

By Alan Spindel

Senior Electrical Engineer

HAL Communications

Champaign, IL

The Many Challenges of HF Data

● Nature is against you

● Your fellow man is against you

● The planet is not your friend

● Everything else is against you

U.S. Department of the Interior/Hallie Larsen, National Park Service/Facebook

Nature is Against You

● Limited bandwidth channel (~3KHz)

● Shannon's Law

– The maximum attainable error-free data speed, in bits per second (bps), is a function of the signal-to-noise ratio and bandwidth.

● Ionospheric radio is challenging

– Sun spots, fades, dropouts, selective fading

– Lightning, solar cycles

– Impulsive noise

• Fluctuating signal to noise ratio (SNR)

https://www.space.com/28857-aurora-photos-northern-lights-2015.html

Your Fellow Man is Against You

Tom and Jerry are a trademark of Metro-Goldwyn-Meyer

Your Fellow Man is Against You

● Welders, electric fences, chargers

● DC-DC converters, dimmers, and drives

● Plasma TVs, AC power distribution

● Broadband over Power Line (BPL)

● Broadcasters

● High-power military and sovereign stations

● Electro-Magnetic Pulse (EMP)

The Planet is Not Your Friend

● Propagation Modes

● Ground wave

● Near Vertical Incident Skywave (NVIS)

● E-Layer skip skywave

● Back-scatter

● All combine to create multi-path distortion

● Earth’s own magnetic field flux has a value around 500 milligauss

Everything Else is Against You

Everything Else is Against You

● Component tolerances

● Natural laws of filter design

● Processor power

● International regulation

● Peak-average ratio of radios

● Narrow-band interference

● Inter-symbol interference

Modem Design Theory

Courtesy HALComm

Communication Channels

Modulator Channel Demodulator

Noise

Modulation Schemes

● OOK -- On-Off Keying (CW)

● ASK -- Amplitude Shift Keying

● FSK – Frequency Shift Keying

● PSK – Phase Shift Keying

● QPSK – Quadrature Phase Shift Keying

● OFDM – Orthogonal FDM

● Serial-Tone

● QAM – Quadrature Amplitude Modulation

HF Data Packet Format

Synchronization Preamble Payload + Redundancy Postamble

Data Modem Accessories

● Coding and interleaving

● Bit scrambling

● Adaptive equalization

● Echo canceling

● AFC – Automatic frequency control

● ALC, AGC – Automatic level and gain control

● ARQ – Automatic Repeat reQuest

● Encryption

Data Rates

• Data Rates

Data signaling rate (bps) = t k x modulation rate (Bd)

Where k = log2M is the number of binary digits per modulation symbol,

M is the number of modulation symbols,

and t is the number of tones.

• Throughput

Throughput rate (bps) = Data rate / (Beta + Tp)

Where Beta = coding (redundancy) overhead and

Tp is the channel probe and preamble overhead .

Coding Conundrum

• More Data Reliability

• More coding redundancy

• Less data throughput

• Longer interleave

• Less Data Reliability

• Less coding redundancy

• More data throughput

• Shorter interleave

Automatic Repeat reQuest (ARQ)

https://image.slidesharecdn.com/ch-11-090721210444-phpapp02/95/ch-11-7-728.jpg?cb=1248210318

ARQ Conundrum

● Smaller Blocks (Stop-and-Wait ARQ)

– Less costly retry, low SNR

– Less throughput, high SNR

● Bigger blocks

– More costly retry, low SNR

– More throughput, high SNR

● Adaptive ARQ (Go-Back-N ARQ)

– More complex implementation

HF Technology Generations

● Legacy

● Solid state technology

● First Generation

● Dedicated digital hardware

● Second Generation

● Current technology (FSK PSK)

● Automated encrypted voice talk groups

● Leverages TCP/IP networking

● Groupware applications – email and chat

● Third Generation

● Wider bandwidth, faster data

● More automated

● Faster call setup times

● Lower SNR (PSK + QAM)

● Multiple access

2G HF Technology

Courtesy Barrett Radio

2G Communications System

https://www.mathworks.com/help/comm/examples/defense-communications-us-mil-std-188-110b-baseband-end-to-end-link.html

MIL-STD-188-141 Layers

1. Network coordination and management

2. Message store and forward

3. Automatic message exchange – STANAG 5066

4. Link Quality Analysis and channel selection

5. Connectivity exchange

6. Polling

7. Sounding - ALE

8. Scanning - SELCAL

9. Selective calling and handshake

10. Baseline system (plain vanilla radio)

Automatic Link Establishment (ALE)

● Simplified user interface

● Familiar, telephone-type call experience

● ALE uses sounding for channel estimation

● Builds and maintains an almanac of propagation data

● Estimates the best frequency at call time

http://www.hflink.net

Automatic Link Establishment (ALE)

Courtesy US Army MARS

ALE Generations

● First Generation ALE – No longer used

● 2G ALE

– Widely deployed, expensive

– Can be bulky, complicated, slow call setup time

– FSK restricts ALE use in low SNR environments

● 3G ALE under early deployment

– Uses PSK

– Designed for tactical nets

– Shorter call setup time

– PSK works better in lower SNR applications

• Other Commercial Link Management Implementations

HFLINK – HF Propagation Map

http://hflink.com/propagation/

Automatic Link Maintenance

● ALM – Automatic Link Maintenance

– Nailed Up HF connections between stations

• 3G ALE – Connection Management (CM)

• Relink

• Link negotiation

• Coordinated departure to new channel

• Waveform/data rate negotiation

Channel Sharing

● Holy Grail of HF Data - Channel Sharing

● Multiple Access Carrier – CSMA, CDMA

● Token passing schemes

● UWB schemes

● Correlated Hopping Spread Spectrum (CHESS)

● Time Slot Broadcast

Software Defined Radio

Courtesy Barrett Radio

Commercial Aviation / Marine

● HFDL – ACARS

● HF SELCAL

● SITOR-A for GMDSS and SOLAS

● SITOR-B is FEC broadcast for USCG SafetyNet

● DSC Automated voice/data is also part of GMDSS

● WEFAX Weather facsimile broadcasts

Amateur Radio Digital Modes

● Classic TNC modes

– RTTY

– G-TOR

– PACTOR

– AMTOR

– CLOVER

Amateur Radio Digital Modes

● PSK31 PSK63

● SSTV

● HF HD SSTV

● MFSK

● MT63

● Hell

● HF Packet

● THOR

● JT65

● JT6M

● THROB

● OLIVIA CONTESTIA

● DRM

● DOMINO

● PAX, PAX2

Amateur Radio Digital Modes

● New, Exciting Amateur Modes

– WSPR - Sounding beacon

– 25 mW signal gives 450,000 Km/W

– WSJT - Weak signal

– ROS - Super low SNR work

– RSID - Auto ID for digimodes

–Reed-Soloman IDentifier

– VIDEO ID - Latest Gadget

http://blog.g4ilo.com/2010/03/show-your-id.html

Military Standard Waveforms

● QAM rediscovered for HF data

● Serial tone PSK waveforms

● MIL-STD-188-110B

● STANAG 4539

● ARQ schemes / network layer stacks

● FED-STD-1052

● STANAG 5066

● MIL-STD-188-141

Military Standard Waveforms

From “Third-Generation and Wideband HF Radio Communications”, Johnson, et al.

3G Military Waveforms

● MIL-STD-188-110D

● Up to 24KHz

● Wideband

● Worldwide HF video, command and control

● Burst waveforms

● Highly adaptive communication systems

Emergency Communications

● SHARES

● MARS

● ARRL ARES

● RACES

● Winlink

● fldigi MT63 HF / VHF

● ARRL NTS

● Red Cross

● SATERN

● SouthBEARS

● LDS

● INTERCON

● MMSN

EasyPal SSTV EmComm Reporting

Courtesy commacademy.org

Challenges of Data Over HF Radio

Presented to

The Radio Club of America

Technical Symposium

By Alan Spindel

Senior Electrical Engineer

HAL Communications

Champaign, IL

Glossary2G - 2nd Generation technology era as in “2G ALE”.3G - 3rd Generation technology.AFC - Automatic Frequency Control, see ALC.ALC - Automatic Level Control, a less aggressive form of AGC.ALE - Automatic Link EstablishmentALM - Automatic Link MaintenanceARQ - Automatic Repeat reQuestASK - Amplitude Shift KeyingBaud - The actual physical symbol rate in symbols per secondBPL - Broadband Over Power LinesBPS - Bits Per SecondBPSK - Binary PSKCDMA - Code Division Multiple Access, a channel sharing scheme, see CSMA.CM - Connection Management, a feature of 3G ALE.CSMA - Carrier Sense Multiple Access, see CDMACW - Continuous Wave, a synonym for Morse code transmission.EMP - Electromagnetic Pulse; Satan’s workshop.FIPS - Federal Information Processing Standards

GlossaryFSK - Frequency Shift Keying, arguably the most popular data modulation technique.HF - High Frequency (Radio), usually agreed on as 3-30 MHz radio operation.ISI - Inter-Symbol Interference, primary cause of data loss in HF data transmission.Legacy - A technological era of less practical application to modern applications. MIL-STD - Prefix to a specification document from the US military.NVIS - Near Vertical Incident Skywave, a HF radio propagation mode.OFDM - Orthogonal Frequency Division MultiplexingOOK - On Off Keying, the simplest form of data modulation.PSK - Phase Shift Keying, a very popular and effective modulation scheme.QAM - Quadrature Amplitude ModulationQPSK - Quadrature Phase Shift KeyingSELCAL - Selective Calling, an annunciator scheme, also an ITU standard for aviation radio.SELCALL - A synonym for SELCAL, both are pronounced “sell-call”.SNR - Signal to Noise Ratio, high is good, low is bad. STANAG - STANdards Agreement, a specification document for a NATO standard.UWB - Ultra-WideBand, a very wide spread spectrum modulation scheme.