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Kurtis Heimerl kheimerl at cs.berkeley.eduComments in line! On Thu, Feb 2, 2012 at 9:17 PM, Alexander Chemeris <alexander.chemeris at gmail.com> wrote: > Hi Kurtis, > > (I'm changing subject to the actual topic of this discussion) Good idea. > > Yes, I quickly looked through your code. Looks like a big hack right > now, but I guess it's meant to be a hack at this point :) And it will remain a big hack into the near future! > > So, your idea is to manipulate Tx power of a BTS to cover only > actually working handsets, if I understand correctly. It's not > possible to do with a normal GSM phone, because phone does not > transmit until it sees a beacon. So you want to create a "wake up BTS" > channel to get around. Am I following your logic correctly? Ah... sorta not really, unless we're using different terminology. We use the existing channel (that the BTS is listening on) and send a RACH over that channel to the BTS. Though the handset can't hear the beacon, the radio is capable of transmitting at that ARFCN without a beacon (thanks Sylvain!) if we tell it to do so. We do so ("wakeup"), causing the handset to RACH at a specific ARFCN and the BTS to hear some discernible noise (however not a RACH as the clocks are not synced) and turn the PA on. Following this, the handset camps normally and makes a call. In writing that, it is awfully hard to describe. I hope that made some sense. I can tell you that it's working in our lab, and it's pretty cool. > > It does look like an interesting idea if could be done dirt-cheap. But > how do you plan to do paging in this system? I see the only way - to > use the same "wake up channel", but in other direction. So basically > you have a network-specific "default" ARFCN which is used when no > active BTS is in range. All communications are first tried on this > ARFCN and only then on other ones. Right? Paging is actually quite simple, as we own the BTS. When we receive a call, we hold it ("please wait for connection") and turn the PA on. We then wait for the HS to camp, and if they do, page them once available. A little delay (much better with SMS), but I think most users would be fine with it. We haven't written this yet. > > On Thu, Feb 2, 2012 at 22:43, Kurtis Heimerl <kheimerl at cs.berkeley.edu> wrote: >> This is part of my thesis work at Cal, yes. Range is not in any way involved. >> >> That's roughly the use case, areas where there are too few users to >> keep a BTS in constant use. Our designs allow the power usage to scale >> with the number of users, rather than sit at a fixed output, as they >> do now. The BTS side is simple; the osmocom side is complicated. We >> have a handset that can wakeup a sleeping tower, or a "wakeup button" >> device which only transmits when a button is pressed. That thing is ~5 >> bucks and can probably be attached to the back of a legacy phone in >> case we can't convince a large manufacturer to incorporate our changes >> into the baseband. >> >> Anyhow, the code is online if you're interested in looking at our >> progress (https://github.com/kheimerl). It's nowhere near ready, but >> you're a very knowledgeable guy, and I'd be happy to hear your >> opinions on any of our designs. >> >> On Thu, Feb 2, 2012 at 10:37 AM, Alexander Chemeris >> <alexander.chemeris at gmail.com> wrote: >>> Is it a part of your TIER university work? >>> I wonder about use cases for this. >>> >>> One use case I see is when you have a BTS which is rarely used, like >>> in a desert and you don't want it to work all the time. What use cases >>> do you plan to use it for? >>> >>> On Thu, Feb 2, 2012 at 22:03, Kurtis Heimerl <kheimerl at cs.berkeley.edu> wrote: >>>> >>>> Yeah, and we have that working. >>>> >>>> On Thu, Feb 2, 2012 at 12:56 AM, Alexander Chemeris >>>> <alexander.chemeris at gmail.com> wrote: >>>> > On Thu, Feb 2, 2012 at 12:08, Kurtis Heimerl <kheimerl at cs.berkeley.edu> wrote: >>>> >> I think I looked at that... I'll give you some context. >>>> >> >>>> >> We've modified osmocom to "wakeup" a specific tower at a specific >>>> >> ARFCN. >>>> > >>>> > Interesting. Do you mean you send some packet to a "sleeping" BTS to wake it up? >>>> > >>>> > -- >>>> > Regards, >>>> > Alexander Chemeris. >>> >>> >>> >>> >>> -- >>> Regards, >>> Alexander Chemeris. > > > > -- > Regards, > Alexander Chemeris.