Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=5.0 tests=BAYES_00,HTML_50_60, HTML_MESSAGE autolearn=unavailable version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id t04LaltF006624 for ; Sun, 4 Jan 2015 22:36:48 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Y7skj-0002qV-MX for rs_out_1@blacksheep.org; Sun, 04 Jan 2015 21:30:25 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Y7ski-0002q5-SJ for rsgb_lf_group@blacksheep.org; Sun, 04 Jan 2015 21:30:24 +0000 Received: from mail-ob0-f178.google.com ([209.85.214.178]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.84) (envelope-from ) id 1Y7skf-0005S1-He for rsgb_lf_group@blacksheep.org; Sun, 04 Jan 2015 21:30:23 +0000 Received: by mail-ob0-f178.google.com with SMTP id gq1so58564617obb.9 for ; Sun, 04 Jan 2015 13:30:19 -0800 (PST) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=TXZ/avqfFPQVAKsamQVF6qXKjeULyD9bEiq70W/pPSE=; b=MAraxCotfnf2gUHjKhibsONHGJExeIrFWG+g5Z64VCE+S3prmQ3LbCPV4hXNhCFYr1 u1Jsd3cySkbfpwc9qcI7ceZy0uoeQ+6PTrzySUue+40TDlflVnpM5anwWNuOsblA5RLr aPDJ8fw69h2VDmbMUPLDh5rUjetC3r5PKjeh52plXIF8O6WjYwShUF/1Olh0+goVvzwk X98IY0u3Q3jwlIYNLc4dcp7/HdHYxko05rspkvSm8KvBOBFdct6ZG/f8OIDu9G8hCzH5 9g62OGQoPbrbEzIvqEnPKKmWDfCTPeU4SEqPKs2BP7HA3MJc9EXmpAuZQXXRvD0Q505x X1WQ== MIME-Version: 1.0 X-Received: by 10.202.230.145 with SMTP id d139mr49168454oih.8.1420407019406; Sun, 04 Jan 2015 13:30:19 -0800 (PST) Received: by 10.60.19.67 with HTTP; Sun, 4 Jan 2015 13:30:19 -0800 (PST) In-Reply-To: References: <54A92E4E.2030903@abelian.org> <98BD4CA9E5394486A3D53B80EE042D81@White> Date: Sun, 4 Jan 2015 16:30:19 -0500 Message-ID: From: Warren Ziegler To: "rsgb_lf_group@blacksheep.org" X-Scan-Signature: c8e6a610b8081fa324d8057b79d67afa Subject: Re: VLF: Transatlantic messages at 8822Hz Content-Type: multipart/alternative; boundary=001a1141745ad40cb5050bda4705 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 1800 --001a1141745ad40cb5050bda4705 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Thank you David! Warren On Sunday, January 4, 2015, David Weinreich wrote: > Warren, > > > > A good general book on coding theory, that also covers convolutional > codes, is =E2=80=9CError Control Coding=E2=80=9D by Lin and Costello or = =E2=80=9CPrinciples of > Digital Communications and Coding=E2=80=9D by Viterbi and Omura. The latt= er is now, > I believe available from Dover Books. > > > > My congratulations also to Dex and Paul; a very impressive feat. > > > > 73, > > David Weinreich > > WA2VUJ/8 > > > > *From:* owner-rsgb_lf_group@blacksheep.org > > [mailto:owner-rsgb_lf_group@blacksheep.org > ] *On > Behalf Of *Warren Ziegler > *Sent:* Sunday, January 04, 2015 2:28 PM > *To:* rsgb_lf_group > *Subject:* Re: VLF: Transatlantic messages at 8822Hz > > > > I did find some good online material from M.I.T. course notes: > > > > http://web.mit.edu/6.02/www/f2010/handouts/lectures/L8.pdf > > > > http://web.mit.edu/6.02/www/f2010/handouts/lectures/L9.pdf > > > > 73 Warren > > > > > > > > On Sun, Jan 4, 2015 at 2:22 PM, Warren Ziegler > wrote: > > Paul, Dex, Markus, > > > > First congratulations Dex and Paul ! > > > > Second, it has been many years since my graduate work in mathematics at > Courant, and then it was oriented toward PDE's, fluid mechanics, complex > variable, and mathematical methods. > > What is the best text for getting up to speed on convolutional coding and > Viterbi decoding? > > > > 73 & tnx Warren > > > > > > > > > > > > On Sun, Jan 4, 2015 at 10:11 AM, Markus Vester > wrote: > > Big congratulations again to Paul and Dex! > > > > What Paul described in unpretentious and matter-of-fact words should > really be regarded as a major achievement. It has been a well-deserved > fruit of several months of effort, and there were a number of difficultie= s > to be overcome. As I was lucky to be included in the preceding email > exchange, I had the chance to witness milestones and setbacks during the > process. > > > > Most members of the LF group will appreciate the challenges to Dex on the > sub-9kHz transmit side, dealing with large coils and high voltage, > realizing accurate GPS-derived frequencies and sub-second bit timing, and > last not least being able to leave the signal on air reliably for many > hours. > > > > The information processing side handled solely by Paul surely presented a= n > even higher hurdle: In the first place, he searched and found a small > handful of "good" FEC codes. The search involved extensive simulations on > powerful multicore computers hired from the Amazon cloud. Then the soft > Viterby decoding of a potential receive signal is also computer intensive= , > especially for longer messages. There need to be numerous trials while > optimising reference phase evolution, bit timing, and antenna weights. > > > > Perhaps the most challenging part was guessing appropriate parameters > before a transmission, ie. how many characters should be sent in which > amount of time. Although some experience had been gained from carrier > measurements during previous nights, ionospheric and atmospheric variatio= ns > make it hard to predict SNR accurately enough if you want to exploit the > channel capacity to the last couple of dBs. In the third round on new > year's night, Dex and Paul dared to take a bet, and won. Allow me to cite > from their final email exchange on Dec 31st: > > > > Dex: > Want to test the limits? > > > > Paul: > Yes please. > Let's go for broke. > 8 seconds is close to the limit, which is what I'd like to see. > > > > > The ultimate goal of this work has been to take decoding sensitivity clos= e > to the theroretical limit. An universal metric for this is Eb/N0, the rat= io > of the received signal energy per payload bit (Eb in Joules) and the nois= e > spectral power density (N0 in Watt/Hertz, equivalent to "noise energy" in > Joules). The Shannon limit for long messages spread to infinite bandwidth > is > Eb/N0 =3D ln(2) =3D -1.59 dB, > which (similar to the speed of light) cannot be surpassed by any possible > encoding scheme. Paul's and Dex' experiments showed that his codes can co= me > within about a dB of this limit in a real long-distance propagation > experiment. > > > > To put that into perspective, let's derive Eb/N0 figures for two popular > digital modes: > > > > WSPR-15 transmits 50 information bits in 15 minutes, ie one bit in 18 > seconds. The decoding threshold is -38 dB in 2.5 kHz, or -4 dBHz. This > gives > Eb/N0 =3D 10 log(18) - 4 dB =3D +8.5 dB, > ie. about 10 dB above the Shannon limit. Note that although different > speed variants (eg WSPR-2) need different power, the minimum energy per b= it > has to remain the same. > > > > Opera-32 carries 28 information bits in 32.6 minutes, ie. one bit in 70 > seconds. The threshold is about -39.5 dB in 2.5 kHz, (-5.5 dBHz), > referenced to the average power of the 50% dutycycle on-off keying. This > gives > Eb/N0 =3D 10 log(70) - 5.5 dB =3D +13 dB > or about 14.5 dB above Shannon. Note however that for LF / VLF > transmissions, the limit will often be antenna voltage and peak power > rather than average power, which can result in a further 3 dB disadvantag= e > for Opera against frequency- or phase-modulated techniques. > > > > The opds correlation decoder can go about 9 dB lower than Opera. But of > course it can only find the best match from an a-priori defined list of > callsigns, and doesn't attempt to decode any message. > > > > However we must recognize that the amateur modes spend a significant part > of their energy to provide a reference for synchronisation, so not all of > the Eb/N0 difference is due to less efficient encoding. The "nude" FEC-PS= K > mode doesn't contain any such overhead. So it can only work when the link > has a stable phase (like on VLF), and the decoder has been given accurate > information on carrier frequency and symbol timing. > > > > All the best, > Markus (DF6NM) > > > > *From:* Paul Nicholson > > > *Sent:* Sunday, January 04, 2015 1:13 PM > > *To:* rsgb_lf_group@blacksheep.org > > > *Subject:* VLF: Transatlantic messages at 8822Hz > > > > > W4DEX achieved another 'first' recently by sending a series of > messages across the Atlantic at 8822 Hz which were successfully > copied at Todmorden UK, range 6194km. > > Transmissions used coherent BPSK signalling with ERP of around > 150uW. The modulation encoded the messages using a rate > 1/16 terminated convolutional code with constraint length 25, > cascaded with an outer error detection code. > > The first message was received at 2014-12-30 03:00, a 4 > character message 'EM95'. Eb/N0 was -0.8dB using 9 second > symbols. > > A second test the following night managed 12 characters 'PAUL > HNY DEX' using 14 second symbols giving Eb/N0 of +1.0dB. > Conditions were good and we could have used shorter symbols > and a longer message. > > The third test and best result so far was a 25 character message > '8822HZ 2015 JAN 1 TA TEST' sent from 2015-01-01 00:00 using > 8 second symbols. This was received with Eb/N0 =3D -0.1dB. > > In the 0.125 Hz bandwidth of a code symbol, the S/N was -13.2dB. > That corresponds to -56dB S/N in a 2.5kHz audio bandwidth > after sferic blanking. Before the blanker the S/N would be > around -76dB. > > The source encoding uses 6 bits per character to produce a > payload of 150 bits. An outer code adds a 16 bit CRC and the > convolutional encoder expands the message to 3040 signal bits. > The effective code rate is therefore 150/3040 =3D 1/20.27. > > Of the 3040 signal bits, 1153 were demodulated incorrectly > but the FEC was able to fix them all to reveal the message. > > Received signal was around 0.12 fT and it was necessary to > combine H-field and E-field receiver outputs to obtain a > sufficient S/N to decode. > > The decoder is a soft Viterbi list decoder. The signals are too > weak to reveal a reference phase by the usual method of summing > the squared complex symbol amplitudes. Instead the decoder has > to do a brute force trial and error search. > > The information rate in the 3rd test was 24.6 bits per hour > which is 80% of the channel capacity. > > -- > Paul Nicholson > http://abelian.org/ > -- > > > > -- > > 73 Warren K2ORS > WD2XGJ > WD2XSH/23 > WE2XEB/2 > WE2XGR/1 > > > > > > > -- > > 73 Warren K2ORS > WD2XGJ > WD2XSH/23 > WE2XEB/2 > WE2XGR/1 > > > --=20 73 Warren K2ORS WD2XGJ WD2XSH/23 WE2XEB/2 WE2XGR/1 --001a1141745ad40cb5050bda4705 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Thank you David!
Warren


On Sunday, January 4, 2015, D= avid Weinreich <David.= Weinreich@globalstar.com> wrote:

Warren,

=C2=A0

A good general book on co= ding theory, that also covers convolutional codes, is =E2=80=9CError Contro= l Coding=E2=80=9D by Lin and Costello or =E2=80=9CPrinciples of Digital Com= munications and Coding=E2=80=9D by Viterbi and Omura. The latter is now, I believe ava= ilable from Dover Books.

=C2=A0

My congratulations also t= o Dex and Paul; a very impressive feat.

=C2=A0

73,<= /p>

David Weinreich=

WA2VUJ/8

=C2=A0

From: owner-rsgb_lf_group@blacksheep.org [mail= to:owner-rsgb_lf_group@blacksheep.org= ] On Behalf Of Warren Ziegler
Sent: Sunday, January 04, 2015 2:28 PM
To: rsgb_lf_group
Subject: Re: VLF: Transatlantic messages at 8822Hz

=C2=A0

I did find some good online material from M.I.T. cou= rse notes:

=C2=A0

=C2=A0

=C2=A0

73 Warren

=C2=A0

=C2=A0

=C2=A0

On Sun, Jan 4, 2015 at 2:22 PM, Warren Ziegler <<= a href=3D"javascript:_e(%7B%7D,'cvml','wd2xgj@gmail.com');"= target=3D"_blank">wd2xgj@gmail.com> wrote:

Paul, Dex, Markus,

=C2=A0

=C2=A0=C2=A0=C2=A0=C2=A0 First congratulations Dex a= nd Paul !

=C2=A0

Second, it has been many years since my graduate wor= k in mathematics at Courant, and then it was oriented toward PDE's, flu= id mechanics, complex variable, and mathematical methods.=C2=A0

What is the best text for getting up to speed on con= volutional coding and Viterbi decoding?

=C2=A0

73 & tnx Warren

=C2=A0

=C2=A0

=C2=A0

=C2=A0

=C2=A0

On Sun, Jan 4, 2015 at 10:11 AM, Markus Vester <<= a href=3D"javascript:_e(%7B%7D,'cvml','markusvester@aol.com'= ;);" target=3D"_blank">markusvester@aol.com> wrote:

Big congratulations again to Paul and Dex!

=C2=A0

What Paul described in unpretentious and matter-of-fact wo= rds should really be regarded as a major achievement. It has been a well-de= served fruit of several months of effort, and there were a number of difficulties to be overcome. As I was lucky to be included in = the preceding email exchange, I had the chance to witness milestones and se= tbacks during the process.

=C2=A0

Most members of the LF group will appreciate the challenge= s to Dex on the sub-9kHz transmit side, dealing with large coils and high v= oltage, realizing accurate GPS-derived frequencies and sub-second bit timing, and last not least being able to leave the signal on air relia= bly for many hours.

=C2=A0

The information processing side handled solely by Paul sur= ely presented an even higher hurdle: In the first place, he searched and fo= und a small handful of "good" FEC codes. The search involved extensive simulations on powerful multicore computers hired from the Amazo= n cloud. Then the soft Viterby decoding of a potential receive signal is al= so computer intensive, especially for longer messages. There need to be num= erous trials while optimising reference phase evolution, bit timing, and antenna weights.

=C2=A0

Perhaps the most challenging part was guessing appropriate= parameters before a transmission, ie. how many characters should be sent i= n which amount of time. Although some experience had been gained from carrier measurements during previous nights, ionospheric and a= tmospheric variations make it hard to predict SNR accurately enough if you = want to exploit the channel capacity to the last couple of dBs. In the thir= d round on new year's night, Dex and Paul dared to take a bet, and won. Allow me to cite from their final e= mail exchange on Dec 31st:

=C2=A0

Dex:
Want to test the limits?

=C2=A0

Paul:
Yes please.
Let's go for broke.
8 seconds is close to the limit, which is what I'd like to see. =

=C2=A0


The ultimate goal of this work has been to take decoding sensitivity close = to the theroretical limit. An universal metric for this is Eb/N0, the ratio= of the received signal energy per payload bit (Eb in Joules) and the noise= spectral power density (N0 in Watt/Hertz, equivalent to "noise energy" in Joules). The Shannon limit for l= ong messages spread to infinite bandwidth is
=C2=A0Eb/N0 =3D ln(2) =3D -1.59 dB,
which (similar to the speed of light) cannot be surpassed by any possible e= ncoding scheme. Paul's and Dex' experiments showed that his codes c= an come within about a dB of this limit in a real long-distance propagation= experiment.

=C2=A0

To put that into perspective, let's derive Eb/N0 figur= es for two popular digital modes:

=C2=A0

WSPR-15 transmits 50 information bits in 15 minutes, ie on= e bit in 18 seconds. The decoding threshold is -38 dB in 2.5 kHz, or -4 dBH= z. This gives
=C2=A0Eb/N0 =3D 10 log(18) - 4 dB =3D +8.5 dB,
ie. about 10 dB above the Shannon limit. Note that although different speed= variants (eg WSPR-2) need different power, the minimum energy per bit has = to remain the same.

=C2=A0

Opera-32 carries 28 information bits in 32.6 minutes, ie. = one bit in 70 seconds. The threshold is about -39.5 dB in 2.5 kHz, (-5.5 dB= Hz), referenced to the average power of the 50% dutycycle on-off keying. This gives
=C2=A0Eb/N0 =3D 10 log(70) - 5.5 dB =3D +13 dB
or about 14.5 dB above Shannon. Note however that for LF / VLF transmission= s, the limit will often be antenna voltage and peak power rather than avera= ge power, which can result in a further 3 dB disadvantage for Opera against= frequency- or phase-modulated techniques.=C2=A0=C2=A0

=C2=A0

The opds correlation decoder can go about 9 dB lower than = Opera. But of course it can only find the best match from an a-priori defin= ed list of callsigns, and doesn't attempt to decode any message.

=C2=A0

However we must recognize that the amateur modes spend a s= ignificant part of their energy to provide a reference for synchronisation,= so not all of the Eb/N0 difference is due to less efficient encoding. The "nude" FEC-PSK mode doesn't contain any such o= verhead. So it can only work when the link has a stable phase (like on VLF)= , and the decoder has been given accurate information on carrier frequency = and symbol timing.

=C2=A0

All the best,
Markus (DF6NM)=C2=A0

=C2=A0

Sent:= Sunday, January 04, 2015 1:13 PM

Subje= ct: VLF: Transatlantic messages at 8822Hz<= /u>

=C2=A0


W4DEX achieved another 'first' recently by sending a series of
messages across the Atlantic at 8822 Hz which were successfully
copied at Todmorden UK, range 6194km.

Transmissions used coherent BPSK signalling with ERP of around
150uW.=C2=A0=C2=A0 The modulation encoded the messages using a rate
1/16 terminated convolutional code with constraint length 25,
cascaded with an outer error detection code.

The first message was received at 2014-12-30 03:00, a 4
character message 'EM95'.=C2=A0 Eb/N0 was -0.8dB using 9 second
symbols.

A second test the following night managed 12 characters 'PAUL
HNY DEX' using 14 second symbols giving Eb/N0 of +1.0dB.
Conditions were good and we could have used shorter symbols
and a longer message.

The third test and best result so far was a 25 character message
'8822HZ 2015 JAN 1 TA TEST' sent from 2015-01-01 00:00 using
8 second symbols.=C2=A0 This was received with Eb/N0 =3D -0.1dB.

In the 0.125 Hz bandwidth of a code symbol, the S/N was -13.2dB.
That corresponds to -56dB S/N in a 2.5kHz audio bandwidth
after sferic blanking.=C2=A0 Before the blanker the S/N would be
around -76dB.

The source encoding uses 6 bits per character to produce a
payload of 150 bits.=C2=A0 An outer code adds a 16 bit CRC and the
convolutional encoder expands the message to 3040 signal bits.
The effective code rate is therefore 150/3040 =3D 1/20.27.

Of the 3040 signal bits, 1153 were demodulated incorrectly
but the FEC was able to fix them all to reveal the message.

Received signal was around 0.12 fT and it was necessary to
combine H-field and E-field receiver outputs to obtain a
sufficient S/N to decode.

The decoder is a soft Viterbi list decoder.=C2=A0 The signals are too
weak to reveal a reference phase by the usual method of summing
the squared complex symbol amplitudes.=C2=A0 Instead the decoder has
to do a brute force trial and error search.

The information rate in the 3rd test was 24.6 bits per hour
which is 80% of the channel capacity.

--
Paul Nicholson
http://abelian.org/ --



--

73 Warren K2ORS
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XGJ
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XSH/23
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WE2XEB/2
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WE2XGR/1

=C2=A0




--

73 Warren K2ORS
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XGJ
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XSH/23
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WE2XEB/2
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WE2XGR/1

=C2=A0



--
73 Warren K2ORS
=C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XGJ
=C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 WD2XSH/23
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 WE2XEB/2
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 WE2XGR/1

=C2=A0
--001a1141745ad40cb5050bda4705--