WINMOR…A Sound Card ARQ Mode for Winlink HF Digital

Messaging

Rick Muething, KN6KB/AAA9WK

PowerPoint Presentation available at www.winlink.org

Overview• 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 itapplies to amateur radio.

Get feedback from you on alternate approaches and suggestionsfor 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 TransformTNC Terminal Node Controller (RF Modem) DSP Digital Signal ProcessingHilbert 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 integratedSCAMP 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 overheadRDFT only changed the RS encoding on it’s 8PSK multi carrier waveform to achieve a 3:1 range in speed/robustness… not enoughRDFT 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.

MotivationWinlink has grown over the years and expanded applications…

Many RVers and Boaters use it for remote E-mail and weatherNow many more adopting it for Emergency Communications:

ARES/RACES EmComm MARS UK CadetHumanitarian 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 hardwareAutomatic connections (no manual tuning)Error-free transmission/confirmationFast lock for reasonable ARQ cyclesAuto adapt to wide range of HF channelsSupport 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 demands200Hz, 500Hz, 2000Hz bandwidthsCompatible with most sound cardsGood bits/sec/Hz ( >.5 target)Efficient Mod/Demod for low latencySelective ARQ and Memory ARQ for throughput & robustnessNear 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 AgilityN

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Comparison of Some Popular Modes in ARQ Environments

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)

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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.

Target For WINMOR

Modulation Schemes Investigated

One of the wish list items was to offer 3 bandwidth modes to be able to operateIn the various (or future?) bandwidth segments of 200Hz, 500Hz and < 3KHz

Current FCC regulations (arguably obsolete) require a maximum HF symbolrate 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 rateMulti carrier OFDM BPSK, QPSK, 16QAM at carrier spacing = 2 x symbol rateSingle 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 throughputand robustness especially when combined with multi-level FEC coding.

Implementation DetailsWINMOR DSP Processing Diagram

Implementation DetailsFrame Leader…Tuning and Frame ID

Phase reversing “Two Tone” Leader 256 ms BPSK

Frame ID DBPSK8,4 Ex Hamm Dmin = 4

Sequential 1024 Point FFTsAlgorithm has good detectionsensitivity and selection @-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)

Soft Decode withdistance threshold

…Data BPSK QPSK 16QAM 4FSK

Non reversed phase frame sync

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) > 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 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 carrierto 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 DetailsFEC, 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 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 assignedto multiple Carriers (allows tradeoff of throughput for robustness). Provides an automatic mechanism for frequency redundancy andprotection from interference on some carriers.

5) Dynamic threshold adjustment (used on QAM modes) helps compensate for fading which would render QAM modes poorin fading channels.

Implementation DetailsThe “Virtual TNC” Concept

In trying to anticipate how WINMOR might be integrated intoapplications we came up with a “Virtual TNC” concept.

This essentially allows an application to integrate the WINMORprotocol by simply treating the WINMOR code as just another TNCand 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 aphysical TNC by “wrapping” the DLL with code that accesses itthrough a virtual serial port or a TCPIP port.

Like a physical TNC WINMOR has a “front panel” with flashinglights. But since operation is automatic with no front panel userinteraction required the WINMOR TNC can be visible or hidden.

WINMOR “Virtual TNC” Screen Capture: 15 Carrier QPSK

“M” recovery after Summation (memory ARQ)

“m” no decode, Good ID (added to summation)

“-” no decode, poor ID match (not added to summation)

“+” decoded OK

QPSK Constellation (heavy fading)Each pixel = 1 symbol

Frame TypeConnection State Bytes Received

2KHz waterfall

WINMOR “Virtual TNC” Screen Capture: 3 Carrier 16QAM

”+” 3 Carriers decoded OK

16QAM Circular Constellation(White Gaussian Noise @ 5dB)Each pixel = 1 symbol Receive Level

Tuning Offset

Relative decode Quality 1 KHz waterfall

Measurement ApproachThe HF Channel Simulator

Station 1Computer & SignaLink USB Sound Card

WINMOR Virtual TNC

Audio In Audio Out

CCIR Channel Options: S/N –5, 0, 5, 10, 15 dB White Gaussian Noise Multi path: Good, Fair, Poor Flat Fading: Moderate, Severe Flutter

Oregon Hardware/Software HF Channel Simulator (used in both directions)

RS232

Station 2Computer & SignaLink USB Sound Card

WINMOR Virtual TNC

SC Out SC Out SC InSC In

The way to get true repeatable comparisons!

(Channels in red wereUsed in simulations)

Preliminary ComparisonsWINMOR 200 Hz vs. Pactor 1

Tests Run 9/2008 by Rick Muething, KN6KBAverage of 4 channels (WGN, CCIR Multipath Poor, Multipath Good, Moderate Flat Fading)Throughput averaged over 5 minute periodWINMOR has Ex Hamm 4,8 on ACK , RS FEC on Data

WINMOR 200 Hz vs Pactor 1

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WINMOR 1 Car QPSK FECWINMOR 1 Car 4FSK FEC

WINMOR 1 Car 16QAM FECPactor 1 SCS PTCII (400 Hz)

10dB 5dB 0dB -5dB

Preliminary ComparisonsWINMOR 500 Hz vs. Pactor 1,2

Tests Run 9/2008 by Rick Muething, KN6KBAverage of 4 channels (WGN, CCIR Multipath Poor, Multipath Good, Moderate Flat Fading)Throughput averaged over 5 minute periodWINMOR has Ex Hamm 4,8 FEC on ACK, RS FEC on Data

WINMOR 500 Hz vs P1, P2

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WINMOR 3 Car QPSK FECPactor 1 (PTC II)Pactor 2 (PTC II)WINMOR 3 Car 16QAM FECWINMOR 3 Car 4FSK FEC

10dB 5dB 0dB -5dB

Preliminary ComparisonsWINMOR 2000 Hz vs. Pactor 2,3

Tests Run 9/2008 by Rick Muething, KN6KBAverage of 4 channels (WGN, CCIR Multipath Poor, Multipath Good, Moderate Flat Fading)15 Car 16QAM points averaged for WGN and Moderate Flat Fading channels onlyThroughput averaged over 5 minute periodWINMOR has Ex Hamm 4,8 FEC on ACK, RS FEC on Data

WINMOR 2000 Hz vs. Pactor 2,3

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WINMOR 15 Car QPSK FEC

WINMOR 15 Car 4FSK FEC

Pactor 2

Pactor 3

10dB 5dB 0dB -5dB

15 Car 16QAM WGN & FLT

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 programsFor 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 SafetyFoundation 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 automaticallyto 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!