On Wed, 2 Apr 2008 15:11:16 -0700 (PDT), clay@claysturner.com wrote:>On Apr 2, 12:26�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�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 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. > >ClayInteresting. 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
choosing the modulation technique
Started by ●April 1, 2008
Reply by ●April 2, 20082008-04-02
Reply by ●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. �����������������������������������������������������������������������
