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=-2.6 required=5.0 tests=BAYES_00,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 t04JYcwv006340 for ; Sun, 4 Jan 2015 20:34:38 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Y7qqf-0001ix-AF for rs_out_1@blacksheep.org; Sun, 04 Jan 2015 19:28:25 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Y7qqe-0001io-Pg for rsgb_lf_group@blacksheep.org; Sun, 04 Jan 2015 19:28:24 +0000 Received: from mail-oi0-f51.google.com ([209.85.218.51]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.84) (envelope-from ) id 1Y7qqb-00051U-Ij for rsgb_lf_group@blacksheep.org; Sun, 04 Jan 2015 19:28:23 +0000 Received: by mail-oi0-f51.google.com with SMTP id h136so11854432oig.10 for ; Sun, 04 Jan 2015 11:28:19 -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=jKqZyEsRhMfyCQoqzyetkERkFelkstgJ0eRe3zRKlEs=; b=ZIRsDOl8m2CwFSz5T2KH1Oix7V5qiPiAxCRCFr/ZVq0kDCiHBsjtElwXtNrtl4y8mO 5AkUFHKwzlAIXc4KR1S9KDmBhatQfczb3b5xA4XSbxvX02/lFdLNvrQhykJDzVNa9Ay5 YWsdYq79qtTQa+H9u/CLjCAIlISoT/fyyjCnpPAwKjWEdsX6UarUcVkHD0dcRioaHAsu Uiuxq3HTWUdn6kPorX1Zq+2nbBeqIfKutH9/a4tRqXelnn353ngzjcU4yFepxD/Iswbb m1Lj4O/Al8SPWNoSswQOwpzZ3e/X8S94vvT6SofDb0d/qZ9/WhnJWnp+qJZr3oV6pdq1 yogg== MIME-Version: 1.0 X-Received: by 10.60.47.49 with SMTP id a17mr18530167oen.51.1420399699738; Sun, 04 Jan 2015 11:28:19 -0800 (PST) Received: by 10.60.19.67 with HTTP; Sun, 4 Jan 2015 11:28:19 -0800 (PST) In-Reply-To: References: <54A92E4E.2030903@abelian.org> <98BD4CA9E5394486A3D53B80EE042D81@White> Date: Sun, 4 Jan 2015 14:28:19 -0500 Message-ID: From: Warren Ziegler To: rsgb_lf_group X-Scan-Signature: 0ec4100a7eb09b79f89f9c2085e5ddc1 Subject: Re: VLF: Transatlantic messages at 8822Hz Content-Type: multipart/alternative; boundary=001a11c214948ac68e050bd89341 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: 1792 --001a11c214948ac68e050bd89341 Content-Type: text/plain; charset=UTF-8 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 difficulties >> 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 >> an 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 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 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 >> 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 long messages spread to infinite >> bandwidth is >> Eb/N0 = ln(2) = -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 come >> 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 = 10 log(18) - 4 dB = +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. >> >> 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 = 10 log(70) - 5.5 dB = +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 disadvantage >> 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-PSK >> 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 = -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 = 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 --001a11c214948ac68e050bd89341 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I did find some good online material from M.I.T. cour= se notes:
=C2=A0
=C2=A0
=C2=A0
73 Warren
<= div>=C2=A0
=C2=A0

On Sun, Jan 4, 2015 at 2:22 PM, Warren Ziegler <wd2xg= j@gmail.com> wrote:
Paul, Dex, Markus,
=C2=A0
=C2=A0=C2=A0= =C2=A0=C2=A0 First congratulations Dex and Paul !
=C2=A0
Second, it has been many years since my graduate work in mathematics at C= ourant, and then it was oriented toward PDE's, fluid mechanics, complex= variable, and mathematical methods.=C2=A0
What is the best text= for getting up to speed on convolutional coding and Viterbi decoding?
=C2=A0
73 & tnx Warren
=C2=A0
=C2= =A0
=C2=A0
=C2=A0
=

On Sun, Jan 4, 2015 at 10:11 AM, Markus Vester <= markusvester@aol.= com> wrote:
Big congratulations again to Paul and Dex!=20
=C2=A0
What Paul described in unpretentious and=20 matter-of-fact words should really be regarded as a major achievement. It h= as=20 been a well-deserved fruit of several months of effort, and there were a nu= mber=20 of difficulties to be overcome. As I was lucky to be included in the preced= ing=20 email exchange, I had the chance to witness milestones and setbacks during = the=20 process.
=C2=A0
Most members of the LF group will appreciate the= =20 challenges to Dex on the sub-9kHz transmit side, dealing with large coils a= nd=20 high voltage, realizing accurate GPS-derived frequencies and sub-second bit= =20 timing, and last not least being able to leave the signal on air reliably f= or=20 many hours.
=C2=A0
The information processing side handled solely by= =20 Paul surely presented an even higher hurdle: In the first place, he searche= d and=20 found a small handful of "good" FEC codes. The search involved ex= tensive=20 simulations on powerful multicore computers hired from the Amazon cloud. Th= en=20 the soft Viterby decoding of a potential receive signal is also computer=20 intensive, especially for longer messages. There need to be numerous trials= =20 while optimising reference phase evolution, bit timing, and antenna=20 weights.
=C2=A0
Perhaps the most challenging part was guessing=20 appropriate parameters before a transmission, ie. how many characters shoul= d be=20 sent in which amount of time. Although some experience had been gained from= =20 carrier measurements during previous nights, ionospheric and atmospheric=20 variations make it hard to predict SNR accurately enough if you want to exp= loit=20 the channel capacity to the last couple of dBs. In the third round on new y= ear's=20 night, Dex and Paul dared to take a bet, and won. Allow me to cite from the= ir=20 final email exchange on Dec 31st:
=C2=A0
Dex:
Want to test the limits?
=C2=A0
Paul:
Yes please.
Let's go for broke.=
8=20 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 sensitivi= ty=20 close to the theroretical limit. An universal metric for this is Eb/N0, the= =20 ratio of the received signal energy per payload bit (Eb in Joules) and the = noise=20 spectral power density (N0 in Watt/Hertz, equivalent to "noise energy&= quot; in=20 Joules). The Shannon limit for long messages spread to infinite bandwidth i= s=20
=C2=A0Eb/N0 =3D ln(2) =3D -1.59 dB,
which (similar to the speed of = light)=20 cannot be surpassed by any possible encoding scheme. Paul's and Dex'= ; experiments=20 showed that his codes can come within about a dB of this limit in a real=20 long-distance propagation experiment.
=C2=A0
To put that into perspective, let's derive Eb/N0 figures for two p= opular=20 digital modes:
=C2=A0
WSPR-15 transmits 50 information bits in 15 minutes, ie one bit in 18= =20 seconds. The decoding threshold is -38 dB in 2.5 kHz, or -4 dBHz. This give= s=20
=C2=A0Eb/N0 =3D 10 log(18) - 4 dB =3D +8.5 dB,
ie. about 10 dB above= the=20 Shannon limit. Note that although different speed variants (eg WSPR-2) need= =20 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 7= 0=20 seconds. The threshold is about -39.5 dB in 2.5 kHz, (-5.5 dBHz), reference= d to=20 the average power of the 50% dutycycle on-off keying. This gives
=C2=A0E= b/N0=20 =3D 10 log(70) - 5.5 dB =3D +13 dB
or about 14.5 dB above Shannon. Note = however=20 that for LF / VLF transmissions, the limit will often be antenna voltage an= d=20 peak power rather than average power, which can result in a further 3 dB=20 disadvantage for Opera against frequency- or phase-modulated=20 techniques.=C2=A0=C2=A0
=C2=A0
The opds correlation decoder can go about 9 dB lower than Opera. But o= f=20 course it can only find the best match from an a-priori defined list of=20 callsigns, and doesn't attempt to decode any message.
=C2=A0
However we must recognize that the amateur modes spend a significant p= art=20 of their energy to provide a reference for synchronisation, so not all of t= he=20 Eb/N0 difference is due to less efficient encoding. The "nude" FE= C-PSK mode=20 doesn't contain any such overhead. So it can only work when the link ha= s a=20 stable phase (like on VLF), and the decoder has been given accurate informa= tion=20 on carrier frequency and symbol timing.
=C2=A0
All the best,
Markus (DF6NM)=C2=A0



W4DEX achieved another 'first' recently by sendi= ng a series=20 of
messages across the Atlantic at 8822 Hz which were successfully
co= pied=20 at Todmorden UK, range 6194km.

Transmissions used coherent BPSK=20 signalling with ERP of around
150uW.=C2=A0=C2=A0 The modulation encoded = the=20 messages using a rate
1/16 terminated convolutional code with constraint= =20 length 25,
cascaded with an outer error detection code.

The first= =20 message was received at 2014-12-30 03:00, a 4
character message 'EM9= 5'.=C2=A0=20 Eb/N0 was -0.8dB using 9 second
symbols.

A second test the follow= ing=20 night managed 12 characters 'PAUL
HNY DEX' using 14 second symbo= ls giving=20 Eb/N0 of +1.0dB.
Conditions were good and we could have used shorter=20 symbols
and a longer message.

The third test and best result so f= ar=20 was a 25 character message
'8822HZ 2015 JAN 1 TA TEST' sent from= 2015-01-01=20 00:00 using
8 second symbols.=C2=A0 This was received with Eb/N0 =3D=20 -0.1dB.

In the 0.125 Hz bandwidth of a code symbol, the S/N was=20 -13.2dB.
That corresponds to -56dB S/N in a 2.5kHz audio bandwidth
af= ter=20 sferic blanking.=C2=A0 Before the blanker the S/N would be
around=20 -76dB.

The source encoding uses 6 bits per character to produce=20 a
payload of 150 bits.=C2=A0 An outer code adds a 16 bit CRC and=20 the
convolutional encoder expands the message to 3040 signal bits.
Th= e=20 effective code rate is therefore 150/3040 =3D 1/20.27.

Of the 3040 s= ignal=20 bits, 1153 were demodulated incorrectly
but the FEC was able to fix them= all=20 to reveal the message.

Received signal was around 0.12 fT and it was= =20 necessary to
combine H-field and E-field receiver outputs to obtain=20 a
sufficient S/N to decode.

The decoder is a soft Viterbi list=20 decoder.=C2=A0 The signals are too
weak to reveal a reference phase by t= he=20 usual method of summing
the squared complex symbol amplitudes.=C2=A0 Ins= tead=20 the decoder has
to do a brute force trial and error search.

The= =20 information rate in the 3rd test was 24.6 bits per hour
which is 80% of = the=20 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
<= br>=C2=A0
--001a11c214948ac68e050bd89341--