Reply by barry_b April 4, 20082008-04-04
Ouch! Let's not get personal.

> >I give you an advice: avoid using the words that you don't understand >and find someone who has a clue. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com > >
Reply by Vladimir Vassilevsky April 3, 20082008-04-03

barry_b wrote:

> According to Matlab for BER = 0.001 > - msk/bpsk/qpsk: Eb/No = 7 dB > - 4-cpfsk h=0.5: Eb/No = 3 dB
This doesn't look right. QPSK/BPSK should perform at Eb/No ~ 7dB, 4-FSK slightly worse than that, and for the MSK it should be about 9dB.
> For 4 bps, carrier = 12 Hz: > - msk: tones (11, 13 Hz); bw = 2 Hz > - bpsk: bw = 4 Hz > - qpsk: bw = 2 Hz > - 4-cpfsk: tones (9, 11, 13, 15 Hz); bw = 6 Hz > > Since I have available bandwidth between 2 and 20 Hz, wouldn't 4-CPFSK > would provide the best use of the available bandwidth, and the lowest > EB/No?
Lowest Eb/No -> maximize the number of states and the bandwidth. However, there is the other important consideration: the carrier and symbol sync accuracy. The more advanced is the signal, the more difficult is maintaining the accurate lock. Hence the performance gets limited by the lock accuracy rather then Eb/No.
> > But, now it seems that we also want bit rates of 1 - 20 bps. > > For example for 12 bps, carrier = 12 Hz: > - msk: tones (9, 15 Hz); bw = 6 Hz > - bpsk: bw = 12 Hz > - qpsk: bw = 6 Hz > - 4-cpfsk: tones( 3, 9, 15 21 Hz); bw = 18 Hz > > Thus, it seems 4-cpfsk is out. Either msk or qpsk is probably a better > bet. > >>I don't have much experience with CPFSK, it's often avoided since it's >>not bandwidth efficient. Are your sims showing the same bandwidth >>occupation for both cases? The filtering applied for each, pulse >>shaping for BPSK and any phase filtering for CPFSK, will be important >>in considering the bandwidth requirements.
I give you an advice: avoid using the words that you don't understand and find someone who has a clue. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by barry_b April 3, 20082008-04-03
According to Matlab for BER = 0.001
- msk/bpsk/qpsk: Eb/No = 7 dB
- 4-cpfsk h=0.5: Eb/No = 3 dB

For 4 bps, carrier = 12 Hz:
- msk: tones (11, 13 Hz); bw = 2 Hz
- bpsk: bw = 4 Hz
- qpsk: bw = 2 Hz
- 4-cpfsk: tones (9, 11, 13, 15 Hz); bw = 6 Hz

Since I have available bandwidth between 2 and 20 Hz, wouldn't 4-CPFSK
would provide the best use of the available bandwidth, and the lowest
EB/No?

But, now it seems that we also want bit rates of 1 - 20 bps.

For example for 12 bps, carrier = 12 Hz:
- msk: tones (9, 15 Hz); bw = 6 Hz
- bpsk: bw = 12 Hz
- qpsk: bw = 6 Hz
- 4-cpfsk: tones( 3, 9, 15 21 Hz); bw = 18 Hz

Thus, it seems 4-cpfsk is out. Either msk or qpsk is probably a better
bet.



>I don't have much experience with CPFSK, it's often avoided since it's >not bandwidth efficient. Are your sims showing the same bandwidth >occupation for both cases? The filtering applied for each, pulse >shaping for BPSK and any phase filtering for CPFSK, will be important >in considering the bandwidth requirements. >
>
Reply by Jerry Avins April 3, 20082008-04-03
Eric Jacobsen wrote:

   ...

> My worry is that the public at large is just going to lose > faith in science in a big way for jerking them around on the topic.
There is very little to lose. About half of Americans polled (I have no reference to cite) think that the King James version of the Bible is accurate, and that supposed mistranslations of earlier texts are in fact a conspiracy to shake their faith. The believe that the Bible contains the last word on creation of species. A significant portion of the rest consult astrologers either directly or through daily publications. Tarot, anyone? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by Eric Jacobsen April 2, 20082008-04-02
On Wed, 2 Apr 2008 15:11:16 -0700 (PDT), clay@claysturner.com wrote:

>On Apr 2, 12:26&#4294967295;pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote: >> On Wed, 2 Apr 2008 07:28:01 -0700 (PDT), c...@claysturner.com wrote: >> >On Apr 1, 3:38&#4294967295;pm, "barry_b" <bbuternow...@gmail.com> wrote: >> >> Can I get some feedback on my thought process below for choosing a >> >> modulation technique? >> >> >> I am in the process of choosing the modulation and coding for the >> >> following system: >> >> - frequency band: 2 - 20 Hz >> >> - bit rate: configurable 2 - 16 bps >> >> - transmitter: battery powered >> >> - receiver: PC based (i.e. lots of processing power) >> >> - channel: some burst noise >> >> - adjacent signals/channels: none >> >> - traffic: 1 direction, single user, bursty, asynchronous >> >> - data in payload: 1 to 150 bits >> >> >> I was considering either bpsk, qpsk, msk or 4-cpfsk. The transmitter can >> >> accomodate psk or fsk. >> >> >> I ranked the modulations as follows: >> >> - bspk/qpsk: good error rate performance curve >> >> - msk: smaller bandwith and same BER as bpsk; thus I can use a narrower >> >> filter and get better performance >> >> - 4-cpfsk (mod index = 0.5): better BER curve than bpsk and msk (according >> >> to Matlab) >> >> >> Given that 4-cpfsk has a better BER curve, does it make sense to use >> >> 4-CPFSK even for low bit rates? I.e which >> >> is better: >> >> 1) bspk/qpsk >> >> 2) msk >> >> 3) 4-cpfsk (mod index = 0.5) >> >> 4) bspk with spreading >> >> 5) msk with spreading >> >> >> From what I know, spreading doesn't provide any coding gain, but only >> >> provides immunity to frequency drop-outs >> >> frequency jamming, thus 3) should be the best. Correct? >> >> >> Given the short payload, I don't think convolutional coding is applicable. >> >> I will be using a reed-solomon >> >> code. >> >> >> In the receiver, I will be implementing a coherent detector. >> >> >> thanks, >> >> barry >> >> >Barry, >> >> >I hope you realize your band is on top of a couple of the Earth's >> >Schumann resonance modes. This is okay if you wish to detect lightning >> >anywhere on the Earth's surface. >> >> >Clay >> >> Clay, >> >> I was also curious about who else might use that band and what the >> regulatory issues might be, but a quick scan of some relevant portions >> of Part 15 suggests that the FCC may not care much about what happens >> below 9kHz. &#4294967295;In any case, I couldn't find any relevant regulations for >> ELF radiators. &#4294967295; If Barry's system interferes with a government system >> he might hear about it, but other than that I don't know if it's >> problematic other than the natural effects you mention. >> >> Eric Jacobsen >> Minister of Algorithms >> Abineau Communicationshttp://www.ericjacobsen.org- Hide quoted text - >> >> - Show quoted text - > >Hello Eric, > >I don't think there is much going on in the way of ELF transmissions >these days. I think the Navy turned off the site in the midwest. I >don't the status of the site in Australia. > >My recent readings were based on a group at MIT who were doing global >lightning detection and correlating that with the Earth's temperature. >Apparently atmospheric temperature and the number of lightning strikes >per second have a very strong positive correlation. So the MIT group >is looking at other ways to verify global warming. > >This as we all know is a very complicated phenomenon. Scientists were >recently suprised to learn that over the last 4 years the oceans have >cooled off. This is from a survey involving 3000 temperature taking >robots travelling in the oceans' currents. > >Clay
Interesting. I've also seen some info where a lot of the "warming" was really just heat-island effects on urbanization around the measuring stations. In other words, measuring stations that used to be rural are now sitting on parking lots measuring the heat off the asphalt. There are enough of these in the data sets that there is now concern that there never has been a warming trend, it's just a change in environment around a number of the monitoring stations. And the number of predictions of imminent global cooling is starting to increase. At some point the trend will change as it becomes more fashionable to go the other way and "global warming" as a concern will go away. My worry is that the public at large is just going to lose faith in science in a big way for jerking them around on the topic. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by April 2, 20082008-04-02
On Apr 2, 12:26&#4294967295;pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
> On Wed, 2 Apr 2008 07:28:01 -0700 (PDT), c...@claysturner.com wrote: > >On Apr 1, 3:38&#4294967295;pm, "barry_b" <bbuternow...@gmail.com> wrote: > >> Can I get some feedback on my thought process below for choosing a > >> modulation technique? > > >> I am in the process of choosing the modulation and coding for the > >> following system: > >> - frequency band: 2 - 20 Hz > >> - bit rate: configurable 2 - 16 bps > >> - transmitter: battery powered > >> - receiver: PC based (i.e. lots of processing power) > >> - channel: some burst noise > >> - adjacent signals/channels: none > >> - traffic: 1 direction, single user, bursty, asynchronous > >> - data in payload: 1 to 150 bits > > >> I was considering either bpsk, qpsk, msk or 4-cpfsk. The transmitter can > >> accomodate psk or fsk. > > >> I ranked the modulations as follows: > >> - bspk/qpsk: good error rate performance curve > >> - msk: smaller bandwith and same BER as bpsk; thus I can use a narrower > >> filter and get better performance > >> - 4-cpfsk (mod index = 0.5): better BER curve than bpsk and msk (according > >> to Matlab) > > >> Given that 4-cpfsk has a better BER curve, does it make sense to use > >> 4-CPFSK even for low bit rates? I.e which > >> is better: > >> 1) bspk/qpsk > >> 2) msk > >> 3) 4-cpfsk (mod index = 0.5) > >> 4) bspk with spreading > >> 5) msk with spreading > > >> From what I know, spreading doesn't provide any coding gain, but only > >> provides immunity to frequency drop-outs > >> frequency jamming, thus 3) should be the best. Correct? > > >> Given the short payload, I don't think convolutional coding is applicable. > >> I will be using a reed-solomon > >> code. > > >> In the receiver, I will be implementing a coherent detector. > > >> thanks, > >> barry > > >Barry, > > >I hope you realize your band is on top of a couple of the Earth's > >Schumann resonance modes. This is okay if you wish to detect lightning > >anywhere on the Earth's surface. > > >Clay > > Clay, > > I was also curious about who else might use that band and what the > regulatory issues might be, but a quick scan of some relevant portions > of Part 15 suggests that the FCC may not care much about what happens > below 9kHz. &#4294967295;In any case, I couldn't find any relevant regulations for > ELF radiators. &#4294967295; If Barry's system interferes with a government system > he might hear about it, but other than that I don't know if it's > problematic other than the natural effects you mention. > > Eric Jacobsen > Minister of Algorithms > Abineau Communicationshttp://www.ericjacobsen.org- Hide quoted text - > > - Show quoted text -
Hello Eric, I don't think there is much going on in the way of ELF transmissions these days. I think the Navy turned off the site in the midwest. I don't the status of the site in Australia. My recent readings were based on a group at MIT who were doing global lightning detection and correlating that with the Earth's temperature. Apparently atmospheric temperature and the number of lightning strikes per second have a very strong positive correlation. So the MIT group is looking at other ways to verify global warming. This as we all know is a very complicated phenomenon. Scientists were recently suprised to learn that over the last 4 years the oceans have cooled off. This is from a survey involving 3000 temperature taking robots travelling in the oceans' currents. Clay
Reply by Eric Jacobsen April 2, 20082008-04-02
On Wed, 02 Apr 2008 11:59:44 -0500, "barry_b" <bbuternowsky@gmail.com>
wrote:

>True. I'm looking to improve the distance and keep the bit rate the same or >higher. > >Can trellis coding be used with 4-CPFSK, or do I have to use PSK? (I just >started reviewing "Intro to TCM".)
You might be able to use trellis coding with 4-CPFSK, sort of, but I don't think it'll be worth the effort. As mentioned previously, you're not going to be able to get much gain from channel coding since your packets are so small. If you can tolerate very low-rate codes you can probably make it work, but your packet transmission time will increase substantially at the rates you're using. Increasing range via coding also requires that the receiver have adequate sensitivity and detection thresholds to exploit the improvement, so that's a consideration as well.
>I haven't seen anyone comment on 4-CPFSK which according to Matlab seems >to have a better BER vs Eb/No curve than MSK/BPSK. Could I not improve the >system by using 4-CPFSK?
I don't have much experience with CPFSK, it's often avoided since it's not bandwidth efficient. Are your sims showing the same bandwidth occupation for both cases? The filtering applied for each, pulse shaping for BPSK and any phase filtering for CPFSK, will be important in considering the bandwidth requirements.
>Frequency band is below 30 Hz (e.g. for bpsk carrier frequency is at 12 >Hz). We sample at 1000 samples/sec, downcovert to baseband, and decode. >There is various filtering as well. >
Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by barry_b April 2, 20082008-04-02
True. I'm looking to improve the distance and keep the bit rate the same or
higher. 

Can trellis coding be used with 4-CPFSK, or do I have to use PSK? (I just
started reviewing "Intro to TCM".)

I haven't seen anyone comment on 4-CPFSK which according to Matlab seems
to have a better BER vs Eb/No curve than MSK/BPSK. Could I not improve the
system by using 4-CPFSK?

Frequency band is below 30 Hz (e.g. for bpsk carrier frequency is at 12
Hz). We sample at 1000 samples/sec, downcovert to baseband, and decode.
There is various filtering as well.


>On Apr 1, 11:43=A0pm, "barry_b" <bbuternow...@gmail.com> wrote: >> The channel frequency band is fixed at 2-20 Hz (maybe up to 30 Hz).
The
>> transmitter works in this range and cannot be changed. We have a
working
>> system that uses bpsk at 12 Hz (bit rate is 4 bps). I am looking into >> improving the performance of the system, thus I am wondering if other >> modulation techniques (msk, 4-cpfsk, etc) may provide a better error
rate.=
> >> The system works outdoors for up to 2 km. >> > > >You have to define IMPROVE.. > >Do you want faster throughput over the same distance... > >or the same throughput over a longer distance > >These are opposite requirments that will impact the choice of >modulation. > >Mark > > > >
Reply by Eric Jacobsen April 2, 20082008-04-02
On Wed, 2 Apr 2008 06:16:03 -0700 (PDT), cb135@hotmail.com wrote:

><snipped.> >> I'll second Vladimir's input on the noise, and also that phase noise >> becomes very problematic at such low bit rates. So phase-modulated >> signals may not be the best choice for such low rates. >> ><snipped> > >Phase noise is problematic at low bit rates? How are the two >related? Not enough pilot symbols available to estimate the phase? >What else am I missing? > >col
As Vladimir mentioned, phase noise is relatable to the 1/f noise, or if you want to look at it another way, the noise that is very close-in to the reference oscillator. This is easily seen on a spectrum analyzer and a very common way of quantifying phase noise is to just measure the noise level close-in to the oscillator, typically within 1kHz or so. If the loop bandwidth of the carrier phase PLL is wider than that it has no problem tracking out the phase noise, since it's in-band wrt to the PLL. Obviously, the carrier recovery PLL loop bandwidth has to be much less than the symbol rate or it won't be able to lock onto the symbols. So, as the symbol rate goes down the 1/f noise, or the oscillator phase noise, becomes a bigger and bigger part of the PLL bandwidth, and, therefore, harder to track out. Symbol rates of a few bps are problematic for that reason. I'd think it would require a different way of looking at the problem. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by Eric Jacobsen April 2, 20082008-04-02
On Wed, 2 Apr 2008 07:28:01 -0700 (PDT), clay@claysturner.com wrote:

>On Apr 1, 3:38&#4294967295;pm, "barry_b" <bbuternow...@gmail.com> wrote: >> Can I get some feedback on my thought process below for choosing a >> modulation technique? >> >> I am in the process of choosing the modulation and coding for the >> following system: >> - frequency band: 2 - 20 Hz >> - bit rate: configurable 2 - 16 bps >> - transmitter: battery powered >> - receiver: PC based (i.e. lots of processing power) >> - channel: some burst noise >> - adjacent signals/channels: none >> - traffic: 1 direction, single user, bursty, asynchronous >> - data in payload: 1 to 150 bits >> >> I was considering either bpsk, qpsk, msk or 4-cpfsk. The transmitter can >> accomodate psk or fsk. >> >> I ranked the modulations as follows: >> - bspk/qpsk: good error rate performance curve >> - msk: smaller bandwith and same BER as bpsk; thus I can use a narrower >> filter and get better performance >> - 4-cpfsk (mod index = 0.5): better BER curve than bpsk and msk (according >> to Matlab) >> >> Given that 4-cpfsk has a better BER curve, does it make sense to use >> 4-CPFSK even for low bit rates? I.e which >> is better: >> 1) bspk/qpsk >> 2) msk >> 3) 4-cpfsk (mod index = 0.5) >> 4) bspk with spreading >> 5) msk with spreading >> >> From what I know, spreading doesn't provide any coding gain, but only >> provides immunity to frequency drop-outs >> frequency jamming, thus 3) should be the best. Correct? >> >> Given the short payload, I don't think convolutional coding is applicable. >> I will be using a reed-solomon >> code. >> >> In the receiver, I will be implementing a coherent detector. >> >> thanks, >> barry > > >Barry, > >I hope you realize your band is on top of a couple of the Earth's >Schumann resonance modes. This is okay if you wish to detect lightning >anywhere on the Earth's surface. > >Clay
Clay, I was also curious about who else might use that band and what the regulatory issues might be, but a quick scan of some relevant portions of Part 15 suggests that the FCC may not care much about what happens below 9kHz. In any case, I couldn't find any relevant regulations for ELF radiators. If Barry's system interferes with a government system he might hear about it, but other than that I don't know if it's problematic other than the natural effects you mention. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org