WINMORA Sound Card ARQ Mode for Winlink HF Digital Messaging

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WINMORA Sound Card ARQ Mode for Winlink HF
Digital Messaging
WINMOR

• Rick Muething, KN6KB/AAA9WK

PowerPoint Presentation available at
www.winlink.org
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Overview
WINMOR

• Todays Objectives
• WINMOR A work in progress Follow-on to SCAMP
• Motivation Why another sound card mode?
• Unique requirements for a message oriented
  protocol
• RF Footprint and Robustness Agility
• Modulation schemes investigated
• Implementation details
• DSP processing diagram
• Tuning, Modulation, Demodulation, Error recovery
  methods
• Screen captures of the WINMOR Virtual TNC
• WINMOR Movies!
• Measurements Using the HF channel simulator
• Preliminary Comparisons with Pactor 1, 2, and 3
• Deployment strategy
• Remaining work to be done

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Todays Objectives
WINMOR
Provide you an update on a promising sound card
mode targeted at message systems. Give some
(within our time limits) of the technical details
on how we are approaching this. Show some
preliminary test results and apples-to-apples
comparisons with the defacto standard
Pactor. Encourage others to learn about and get
competent in DSP as it applies to amateur
radio. Get feedback from you on alternate
approaches and suggestions for implementation and
deployment.
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Acronym Cheat Sheet!
WINMOR
CCIR Consultative Committee on International
Radio (now The ITU-R) WGN White Gaussian
Noise (a simple HF channel model) MPG CCIR
Multipath Good (a standard moderate HF channel
model) MPP CCIR Multipath Poor (a standard
poor HF channel model) OFDM Orthogonal
Frequency Division Multiplexing PSK Phase
Shift Keying (carrier phase is modulated)
BPSK(2), QPSK(4) FSK Frequency Shift
Keying (frequency of the carrier is
modulated) 4FSK FSK using one of 4 tones per
symbol (2 bits per symbol) QAM Quadrature
Amplitude Modulation (phase and amplitude are
modulated) 16QAM Phase and Amplitude modulation
with 16 states (4 bits per symbol) FEC
Forward Error Correcting (use of error correcting
codes) MCA Multiple Carrier Assignment (same
data to multiple carriers) RDFT Redundant
Digital File Transfer (mode by Barry Sanderson,
KB9VAK) ARQ Automatic Retry reQuest
(mechanism to eliminate errors) FFT Fast
Fourier Transform (digital method of a discrete
Fourier Transform) IFFT Inverse Fourier
Transform ( Frequency to Time transform) NCO
Numerically Controlled Oscillator (done in
software) I, Q The In phase and
Quadrature channels of the Fourier
Transform TNC Terminal Node Controller (RF
Modem) DSP Digital Signal
Processing Hilbert Transform A mathematical
transform to generate I and Q
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WINMOR A work in progress
WINMOR
WINMOR WINlink
Message Over Radio An outgrowth of the work
presented on SCAMP at DCC 2004 SCAMP put an ARQ
wrapper around Barry Sandersons RDFT then
integrated SCAMP into a Client and Server for
access to the Winlink message system. SCAMP
proved it COULD be done and it worked in GOOD
channels but Barrys batch oriented DLLs were
slow and required frame pipelining Increasing
complexity and overhead RDFT only changed the RS
encoding on its 8PSK multi carrier
waveform to achieve a 31 range in
speed/robustness not enough RDFT was
inefficient in Partial Frame recovery (no Memory
ARQ) RDFT was a 2.4 KHz modelimited to narrow
HF sub bands. SCAMPs Simple multi-tone ACK/NAK
did not carry Session ID info increasing
chances of fatal cross session contamination.
WINMOR is an ARQ mode generated from the ground
up to address the limitations of SCAMP/RDFT and
leverage on what was learned.
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Motivation
WINMOR
Winlink has grown over the years and expanded
applications Many RVers and Boaters use it for
remote E-mail and weather Now many more adopting
it for Emergency Communications ARES/RACES
EmComm MARS UK Cadet Humanitarian
Missions (IHS, Red Cross, Salvation Army etc)
Emergency applications dictate special
requirements Station Cost is an
issue Limited budgets and resources Seldom
used (often equipment sits idle unless drills,
training, or actual emergency) Consistency
across multiple stations. Training issues. VHF
is used but HF is needed to bridge out of
affected areas. Many with limited budgets get by
with Pactor 1 and accept its throughput and
robustness limitations. What is needed and much
requested is a lower cost plug and
play alternative to Pactor that approaches P2
and P3 performance.
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WINMOR
Requirements for a Message Oriented Sound card
Protocol
Absolute Requirements Standard SSB Radio
hardware Automatic connections (no manual
tuning) Error-free transmission/confirmation Fast
lock for reasonable ARQ cycles Auto adapt to wide
range of HF channels Support true binary with
compression Loose ARQ timing to accommodate
OS and sound card latency. All packets tagged
with session ID
Wish List Modest OS and CPU demands 200Hz,
500Hz, 2000Hz bandwidths Compatible with most
sound cards Good bits/sec/Hz ( gt.5
target) Efficient Mod/Demod for low
latency Selective ARQ and Memory ARQ for
throughput robustness Near Pactor ARQ
efficiency (70) Effective busy channel detection
When you analyze the details and make true
apples-to-apples comparisons you quickly realize
that P2 P3 set the bar pretty high!
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WINMOR
RF Footprint and Robustness Agility
Comparison of Some Popular Modes in ARQ
Environments
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• Assumptions
• 70 ARQ efficiency
• (typical of Pactor)
• Max RAW data rate
• (good channel assumed)
• 200 Hz guard band used in
• bandwidth calculations.
• (allows automatic connections)

Net bits/sec/Hz of BW
Target For WINMOR
(After ARQ overhead)
.5
0
MT63
PSK31
PCALE
Pactor 1
Pactor 2
Pactor 3
HF Packet
A small RF foot print requires maximizing the
net Bits/Sec/Hz BUT. We ALSO must be able
to adapt the modulation for more robustness In
poorer signal conditions. This robustness
agility is why Pactor 2 and 3 perform so well
across a wide range of channel conditions.
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WINMOR
Modulation Schemes Investigated
One of the wish list items was to offer 3
bandwidth modes to be able to operate In the
various (or future?) bandwidth segments of 200Hz,
500Hz and lt 3KHz Current FCC regulations
(arguably obsolete) require a maximum HF
symbol rate of 300 symbols / sec. This eliminates
high symbol rate adaptive schemes. Improved
multipath operation is obtained with lower symbol
rates (lt 100 Hz) The following modes were
investigate in the early development
phases Multi carrier OFDM BPSK, QPSK _at_ carrier
spacing 1 x symbol rate Multi carrier OFDM
BPSK, QPSK, 16QAM at carrier spacing 2 x symbol
rate Single and multiple carrier FSK (2 FSK and
4 FSK) at spacing 1 x symbol rate Recently the
development effort has been focused on 62.5 baud
BPSK, QPSK and 16QAM and 31.25 baud 4FSK using 1
(200 Hz), 3 (500Hz) and 15 (2000Hz) Carriers
spaced at 2 x symbol rate. These appear to offer
high throughput and robustness especially when
combined with multi-level FEC coding.
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Implementation DetailsWINMOR DSP Processing
Diagram
WINMOR
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WINMOR
Implementation DetailsFrame LeaderTuning and
Frame ID
Non reversed phase frame sync
Frame ID DBPSK 8,4 Ex Hamm Dmin 4
Phase reversing Two Tone Leader
256 ms BPSK
Data BPSK QPSK 16QAM 4FSK
Soft Decode with distance threshold
Sequential 1024 Point FFTs Algorithm has good
detection sensitivity and selection _at_-5dB S/N
Frame ID defines Control/Data Function
Modulation Mode FEC Coding level Number of
Carriers Frame length
Leader defines Required NCO freq
(interpolated to .1Hz) Initial Symbol Sync
(Envelope matching) Framing (Frame Sync)
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WINMOR
Implementation DetailsOFDM PSK, QAM DSP
Modulation
The Symbol Data is used to set the Real and
Imaginary Frequency magnitudes for each OFDM
Carrier. e.g. Data 0,1 (QPSK) gt FReal24
0 FImag24 1 (90Deg)
(repeat for each carrier) 128 Point
Inverse FFT (one IFFT per symbol)
Time sample values for all carriers generated
simultaneously!

Shape Envelope (raised cosine) to bound Spectrum
Convert to WAV file for Sound Card
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WINMOR
Implementation DetailsOFDM PSK, QAM DSP
Demodulation
Use 123 point Hilbert Transform, NCO and balanced
LSB Mixing to generate I and Q samples with
signal re centered on 1250.0 Hz Perform 128
point FFT for each symbol using I and Q
values Use the Real and Imaginary frequency
values for each carrier to compute phase and
amplitude for each symbol of each
carrier. Subtract phase values of prior symbol
to get differential PSK symbol For QAM use
dynamic threshold adjustment to track Phasor
amplitude ratios in fading channels. Decode
Phase and Amplitude symbol to corresponding
binary data (BPSK 1bit, QPSK2 bits, 8PSK 3
bits, 16QAM4 bits)
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WINMOR
Implementation DetailsFEC, Selective ARQ

• WINMOR uses several mechanisms for error
• recovery and redundancy
• FEC Data Encoding Currently used
• 4,8 Extended Hamming Dmin 4 (used in ACK and
  Frame ID)
• 16 Bit CRC for data verification
• Two-level Reed-Solomon (RS) FEC for data
• First level Weak FEC e.g. RS 140,116 (corrects
  12 errors)
• Second level Strong FEC e.g. RS 254,116 (
  corrects 69 errors)
• 2) Selective ARQ. Each carriers data contains a
  Packet Sequence
• Number (PSN).
• The ACK independently acknowledges each PSN so
  only
• carriers with failed PSNs get repeated.
• (the software manages all the PSN accounting and
  re-sequencing)

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WINMOR
Implementation DetailsMemory ARQ, MCA, Dynamic
Threshold
3) Memory ARQ. The analog phase and amplitude of
each demodulated symbol is saved for summation
(phasor averaging) over multiple frames.
Summation is cleared and restarted if max count
reached. Reed-Solomon FEC error decoding done
after summation. 4) Multiple Carrier Assignment
(MCA) . The same PSN can be assigned to multiple
Carriers (allows tradeoff of throughput for
robustness). Provides an automatic mechanism
for frequency redundancy and protection from
interference on some carriers. 5) Dynamic
threshold adjustment (used on QAM modes) helps
compensate for fading which would render QAM
modes poor in fading channels.
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WINMOR
Implementation DetailsThe Virtual TNC Concept
In trying to anticipate how WINMOR might be
integrated into applications we came up with a
Virtual TNC concept. This essentially allows
an application to integrate the WINMOR protocol
by simply treating the WINMOR code as just
another TNC and writing a driver for that TNC. A
Virtual TNC Like all TNCs there are some (lt10)
parameters to set up call sign, timing info,
sound card, keying mechanism, etc The WINMOR
Software DLL can even be made to appear as
a physical TNC by wrapping the DLL with code
that accesses it through a virtual serial port or
a TCPIP port. Like a physical TNC WINMOR has a
front panel with flashing lights. But since
operation is automatic with no front panel
user interaction required the WINMOR TNC can be
visible or hidden.
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WINMOR Virtual TNC Screen Capture 15 Carrier
QPSK
WINMOR
QPSK Constellation (heavy fading) Each pixel
1 symbol
Connection State
Frame Type
Bytes Received
decoded OK
M recovery after Summation (memory ARQ)
2KHz waterfall
- no decode, poor ID match (not added to
summation)
m no decode, Good ID (added to summation)
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WINMOR Virtual TNC Screen Capture 3 Carrier
16QAM
WINMOR
16QAM Circular Constellation (White Gaussian
Noise _at_ 5dB) Each pixel 1 symbol
Tuning Offset
Receive Level
Relative decode Quality
3 Carriers decoded OK
1 KHz waterfall
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Measurement ApproachThe HF Channel Simulator
WINMOR
The way to get true repeatable comparisons!
Station 1 Computer SignaLink USB Sound
Card WINMOR Virtual TNC
Station 2 Computer SignaLink USB Sound
Card WINMOR Virtual TNC
SC Out
SC Out
SC In
SC In
CCIR Channel Options S/N 5, 0, 5, 10,
15 dB White Gaussian Noise Multi path
Good, Fair, Poor Flat Fading
Moderate, Severe Flutter
Audio In Audio
Out
Oregon Hardware/Software HF Channel
Simulator (used in both directions)
RS232
(Channels in red were Used in simulations)
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Preliminary ComparisonsWINMOR 200 Hz vs. Pactor
1
WINMOR
10dB
5dB
0dB
-5dB
Tests Run 9/2008 by Rick Muething, KN6KB Average
of 4 channels (WGN, CCIR Multipath Poor,
Multipath Good, Moderate Flat Fading) Throughput
averaged over 5 minute period WINMOR has Ex Hamm
4,8 on ACK , RS FEC on Data
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Preliminary ComparisonsWINMOR 500 Hz vs. Pactor
1,2
WINMOR
10dB
5dB
0dB
-5dB
Tests Run 9/2008 by Rick Muething, KN6KB Average
of 4 channels (WGN, CCIR Multipath Poor,
Multipath Good, Moderate Flat Fading) Throughput
averaged over 5 minute period WINMOR has Ex Hamm
4,8 FEC on ACK, RS FEC on Data
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Preliminary ComparisonsWINMOR 2000 Hz vs. Pactor
2,3
WINMOR
15 Car 16QAM WGN
FLT
10dB
5dB
0dB
-5dB
Tests Run 9/2008 by Rick Muething, KN6KB Average
of 4 channels (WGN, CCIR Multipath Poor,
Multipath Good, Moderate Flat Fading) 15 Car
16QAM points averaged for WGN and Moderate Flat
Fading channels only Throughput averaged over 5
minute period WINMOR has Ex Hamm 4,8 FEC on ACK,
RS FEC on Data
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WINMOR Deployment Strategy
WINMOR
Produce the final Virtual TNC as a DLL (Graphics
display is optional) Integrate the DLL into the
Paclink MP client and RMS Server programs For
full and immediate access to the WL2K system for
beta testing. Offer Wrapper functions to
interface the WINMOR DLL via a virtual serial
port or TCP/IP port. (allows easier access by
other existing applications) These slides and
preliminary WINMOR spec will be posted on the
www.winlink.org web site. No decision to date
as to licensing or open source. WINMOR may be
released through the Amateur Radio
Safety Foundation Inc. a 501C(3) public charity
corporation which supports amateur radio
emergency communications. Estimated start of
beta test (Winlink 2000 system) 3 6 months.
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Remaining Work to be Done
WINMOR
Investigate inner cyclic FEC codes for PSK data
modes (1-2 dB gain?) Optimize gear shifting
algorithm (basic algorithm operational) Integrate
Busy Channel Detector (SCAMP ?) and ID (CW,
Waterfall?) Investigate crest factor
minimization (possible 1-2 dB improvement?) Inves
tigate 15 Car 16QAM mode (2 Kbits/sec) for
VHF/UHF applications. Finalize WINMOR
documentation and release Document DLL interface
and release Build drivers for Paclink MP and RMS
and beta test in Winlink. Complete help and
statistical logging functions
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Summary
WINMOR

• WINMOR looks promising and the testing to date
  confirms
• Sound card ARQ is possible with a modern CPU and
  OS
• while making acceptable CPU processing demands.
• ( CPU Loading of lt 20 on a 1.5 GHz
  Celeron/Win XP)
• 2) Throughput and robustness can be adjusted
  automatically
• to cover a wide range of bandwidth needs and
  channel conditions.
• (101 bandwidth range, 571 throughput range)
• 3) ARQ throughput in excess of .5 bits/sec/Hz is
  possible
• in fair to good channels (.68 - .82 bits/sec/Hz
  measured)
• 4) Good ARQ efficiency .70-75
• 5) Throughput is currently competitive with P2
  and P3 and
• significantly better than P1
• Thank You!