Download WINMOR…A Sound Card ARQ Mode for Winlink HF

WINMOR…A Sound Card ARQ
Mode for Winlink HF Digital
Messaging
Rick Muething, KN6KB/AAA9WK
PowerPoint Presentation available at www.winlink.org
Overview
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Today’s 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
Today’s Objectives
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.
Acronym Cheat Sheet!
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
WINMOR… A work in progress
WINMOR
=
WINlink Message Over Radio
An outgrowth of the work presented on SCAMP at DCC 2004:
SCAMP put an ARQ “wrapper” around Barry Sanderson’s 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…
Barry’s batch oriented DLLs were slow and required frame pipelining…
Increasing complexity and overhead
RDFT only changed the RS encoding on it’s 8PSK multi carrier
waveform to achieve a 3:1 range in speed/robustness… not enough
RDFT was inefficient in Partial Frame recovery (no Memory ARQ)
RDFT was a 2.4 KHz mode…limited to narrow HF sub bands.
SCAMP’s 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.
Motivation
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
it’s 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.
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 ( >.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!
RF Footprint and Robustness Agility
1
Assumptions:
1) 70% ARQ efficiency
(typical of Pactor)
2) Max RAW data rate
(good channel assumed)
3) 200 Hz guard band used in
bandwidth calculations.
(allows automatic connections)
Target For WINMOR
.5
Pactor 3
Pactor 2
Pactor 1
HF Packet
PCALE
PSK31
0
MT63
(After ARQ overhead)
Net bits/sec/Hz of BW
Comparison of Some Popular Modes in ARQ Environments
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.
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 < 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 (< 100 Hz)
The following modes were investigate in the early development phases:
Multi carrier OFDM BPSK, QPSK @ 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.
Implementation Details
WINMOR DSP Processing Diagram
Implementation Details
Frame Leader…Tuning and Frame ID
Non reversed phase frame sync
Phase reversing “Two Tone” Leader
256 ms BPSK
Frame ID DBPSK
8,4 Ex Hamm Dmin = 4
…Data
Sequential 1024 Point FFTs
Algorithm has good detection
sensitivity and selection
@-5dB S/N
Leader defines:
Required NCO freq (interpolated to .1Hz)
Initial Symbol Sync (Envelope matching)
Framing (Frame Sync)
Soft Decode with
distance threshold
BPSK
QPSK
16QAM
4FSK
Frame ID defines:
Control/Data Function
Modulation Mode
FEC Coding level
Number of Carriers
Frame length
Implementation Details
OFDM 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) > 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
Implementation Details
OFDM 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, QPSK=2 bits, 8PSK= 3 bits, 16QAM=4 bits)
Implementation Details
FEC, Selective ARQ
WINMOR uses several mechanisms for error
recovery and redundancy:
1) 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 carrier’s 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)
Implementation Details
Memory 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.
Implementation Details
The “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 (<10) 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.
WINMOR “Virtual TNC”
Screen Capture: 15 Carrier QPSK
Connection State
Frame Type
Bytes Received
“+”
“M” recovery after Summation
(memory ARQ)
“m” no decode, Good ID
(added to summation)
QPSK Constellation
(heavy fading)
Each pixel = 1 symbol
decoded OK
2KHz waterfall
“-” no decode, poor ID match
(not added to summation)
WINMOR “Virtual TNC”
Screen Capture: 3 Carrier 16QAM
Tuning Offset
Receive Level
”+” 3 Carriers
decoded OK
16QAM Circular Constellation
(White Gaussian Noise @ 5dB)
Each pixel = 1 symbol
Relative decode Quality
1 KHz waterfall
Measurement Approach
The HF Channel Simulator
The way to get true repeatable comparisons!
Station 1
Station 2
Computer & SignaLink USB Sound Card
WINMOR Virtual TNC
Computer & SignaLink USB Sound Card
WINMOR Virtual TNC
SC Out
SC In
SC Out
SC In
CCIR Channel Options:
Audio In
Audio Out
Oregon Hardware/Software
HF Channel Simulator
(used in both directions)
RS232
S/N –5, 0, 5, 10, 15 dB
White Gaussian Noise
Multi path:
Good, Fair, Poor
Flat Fading:
Moderate, Severe
Flutter
(Channels in red were
Used in simulations)
Preliminary Comparisons
WINMOR 200 Hz vs. Pactor 1
WINMOR 200 Hz vs Pactor 1
WINMOR 1 Car QPSK FEC
WINMOR 1 Car 4FSK FEC
WINMOR 1 Car 16QAM FEC
Pactor 1 SCS PTCII (400 Hz)
800
ARQ Trhoughput (bytes/min)
700
600
500
400
300
200
100
0
10dB
5dB
S/N (3 Khz Bw)
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
Preliminary Comparisons
WINMOR 500 Hz vs. Pactor 1,2
WINMOR 500 Hz vs P1, P2
WINMOR 3 Car QPSK FEC
Pactor 1 (PTC II)
Pactor 2 (PTC II)
WINMOR 3 Car 16QAM FEC
WINMOR 3 Car 4FSK FEC
3500
ARQ Throughput (bytes/min)
3000
2500
2000
1500
1000
500
0
10dB
5dB
S/N (3 KHz Bw)
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
Preliminary Comparisons
WINMOR 2000 Hz vs. Pactor 2,3
WINMOR 2000 Hz vs. Pactor 2,3
12000
WINMOR 15 Car QPSK FEC
WINMOR 15 Car 4FSK FEC
ARQ Throughput
(bytes/min)
10000
8000
Pactor 2
15 Car
16QAM
WGN &
FLT
Pactor 3
6000
4000
2000
0
10dB
5dB
0dB
-5dB
S/N (3 KHz Bw)
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
WINMOR Deployment Strategy
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.
Remaining Work to be Done
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?)
Investigate 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
Summary
WINMOR looks promising and the testing to date confirms:
1) Sound card ARQ is possible with a modern CPU and OS
while making acceptable CPU processing demands.
( CPU Loading of < 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.
(10:1 bandwidth range, 57:1 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!