| lemay | are there any plans for the milkymist involving GPS? | 01:58 |
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| wolfspraul | lemay: have you worked with namuru or osgps before? | 02:01 |
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| lemay | No - never heard f either | 02:06 |
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| lemay | I've done a lot of work with GPS though | 02:07 |
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| lemay | from the RF front end to the tracking loops | 02:07 |
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| lemay | cool :) | 02:09 |
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| lemay | I'd be happy to chat | 02:09 |
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| kristianpaul | hello lemay ! :) | 02:59 |
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| kristianpaul | lemay: namuru correlator (actually kinda same tp gp2021 from zarlink) is ported now to milkymist | 03:08 |
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| lemay | hah, I have to dust off those memories | 03:14 |
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| lemay | I bumped into wolfspraul | 03:14 |
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| lemay | :) | 03:14 |
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| lemay | well, the tracking loop I've done was pretty much like a PLL as well | 03:15 |
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| lemay | yea, correaltion | 03:16 |
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| lemay | neat gif | 03:16 |
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| lemay | Does the namuru have a complete RF front end? | 03:20 |
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| lemay | what are those sma's for? IF? | 03:21 |
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| kristianpaul | lemay: wich sma's exacly? | 03:22 |
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| lemay | heh, right - http://www.dynamics.co.nz/index.php?main_page=page&id=9 | 03:23 |
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| lemay | I forgot I got there from google and not from you showing me that | 03:23 |
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| kristianpaul | lemay: was your work related to full software processing? | 03:25 |
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| lemay | real time | 03:26 |
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| lemay | you successfully correlated CA code in post-processing? | 03:28 |
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| lemay | uh, heh | 03:29 |
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| lemay | right | 03:29 |
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| lemay | what sort of data are you working with? | 03:30 |
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| lemay | I mean the RF | 03:32 |
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| lemay | gotcha - you already told me that, huh | 03:33 |
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| lemay | :) | 03:33 |
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| lemay | so, since you're working with real samples, your next step is to try to correlate using osgps? | 03:34 |
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| lemay | california | 03:34 |
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| lemay | sounds good | 03:37 |
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| lemay | does the namaru software take care of all of that? | 03:38 |
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| lemay | gotcha. So you're going to interface the FPGA on the milkymist with the RF front end - the SE4162T-EK1 - and use it to track GPS | 03:41 |
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| lemay | this sounds plausible to me | 03:41 |
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| lemay | Yea, I mean the whole thing - the tracking GPS part - that's plausible | 03:42 |
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| lemay | what sort of CPU will you use? | 03:42 |
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| lemay | something in the milkymist - the LatticeMico32? | 03:42 |
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| lemay | haha, I don't know enough about the system architecture :) | 03:43 |
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| lemay | well, I think it will work | 03:43 |
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| lemay | I designed a front end for a system that is very similar | 03:44 |
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| lemay | correlators in FPGAs, and controlled by an x86 running windows, of all things | 03:44 |
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| lemay | its a Dell with a Virtex 4 | 03:44 |
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| lemay | yea, its nifty | 03:45 |
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| wolfspraul | lemay: can you share some sources? :-) | 03:45 |
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| lemay | unfortunately I can't | 03:45 |
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| lemay | but I can try to help you | 03:45 |
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| lemay | I understood the tracking loops pretty well at one point, but it will take me a bit to shake off the dust | 03:46 |
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| lemay | it worked on the early prompt lates from the fpga | 03:47 |
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| kristianpaul | take your time lemay , and hang on here of course | 03:47 |
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| lemay | it updated the phase shift register based on those sums | 03:48 |
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| lemay | and I suppose the code replicators, too | 03:48 |
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| lemay | yea - for the crrelation | 03:49 |
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| lemay | I've got to go afk for a few minutes | 03:50 |
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| lemay | be back in 5 or so | 03:50 |
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| lemay | ok | 03:52 |
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| lemay | nice talking to you | 03:52 |
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| lemay | if you come up with any questions let me know | 03:53 |
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| lemay | I am in #elphel a lot | 03:53 |
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| kristianpaul | okay, nice to meet you too lemay | 03:54 |
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| lemay | Well, your sampling rate will allow you to adjust for doppler | 03:54 |
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| lemay | and you need to tune your tracking loops depending on what dynamics you want | 03:55 |
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| lemay | the satellite motion is part of the doppler estimation | 03:56 |
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| lemay | I mean, that thing is moving at a jillion miles per hour, right? | 03:56 |
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| lemay | so it has a doppler relative to you, even when your stationary | 03:57 |
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| lemay | your tracking loops just care about the combined doppler | 03:57 |
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| lemay | your combined doppler will be fairly insignificant compared with the correlation period | 03:57 |
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| lemay | or, your delta doppler | 03:58 |
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| lemay | I just started spouting gibberish, huh | 03:58 |
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| lemay | so, you can tell what the combined doppler is, in general | 03:58 |
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| lemay | the main issue about tracking is replicating the correct code and carrier | 04:03 |
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| lemay | you look at your early, prompt, and late correlation sums, and it tells you whether or not you are right on the signal, or if you are a little bit off | 04:04 |
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| lemay | based on that, you change the phase of the carrier that you are generating and you move the code forward or backwards | 04:05 |
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| lemay | heh, are you being ironic or not? I can't tell. | 04:05 |
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| lemay | yea, conceptually it is not bad | 04:06 |
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| lemay | so the PLL - phase locked loop - generates a carrier phase based on the early prompt and late sums (if I am remembering all this right.) | 04:06 |
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| lemay | well, you have to correlate for so amount of time to generate your eraly prompt and late sums | 04:07 |
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| lemay | like, 20 milliseconds is standard | 04:07 |
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| lemay | so you get your updates at 50Hz | 04:07 |
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| lemay | you update your tracking loops at 50hz | 04:08 |
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| lemay | sounds right. | 04:08 |
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| lemay | but thats different from the tracking loop | 04:08 |
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| lemay | the tracking loop is adjusting the PLL at 50Hz, based on those correlation times | 04:09 |
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| lemay | the nav data is basically checking the sign of the prompt signal | 04:09 |
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| lemay | well, depends on your implementation | 04:10 |
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| lemay | if Namuru does 1ms that's great | 04:10 |
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| lemay | and maybe that's normal, I haven't thought about this in a while - maybe tomorrow I'll be saying to myself, 'yea, duh, of course its 1 ms....' | 04:11 |
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| lemay | so, narrowband vs wideband - I am not sure I understand the question | 04:12 |
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| lemay | I'm pretty sure that we | 04:18 |
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| lemay | heh, hit enter by accident :) | 04:19 |
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| lemay | o/ | 04:28 |
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| lemay | Yea, that sentence is kind of strange. I'd ignore it. | 04:28 |
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| lemay | Essentially you change modes when you go from acquisition to tracking - in acquisition you are searching the entire code/doppler space, and once you have acquired, you don't need to search the doppler space - just the early prompt lates | 04:30 |
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