From: Alexander C. <ale...@gm...> - 2009-09-22 10:08:00
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Hi David, I'm looking for a graduation project around OpenBTS for my student and from all my thinking it seems that GPRS implementation is a pretty good choice: 1) It's not urgently required by community and thus can tolerate delays and even failure. 2) Yet it's a very useful feature and would be great to have. 3) It should be mostly high-level programming (i.e. not DSP), which is best suited to the student's abilities. Are these my thoughts correct? Could you help estimate what should be fixed/implemented to make GPRS working? At least which levels require most of the work. I would also appreciate other ideas for this graduation project. PS Graduation project is for about a year or slightly more. -- Regards, Alexander Chemeris. |
From: Alexander C. <ale...@gm...> - 2009-09-29 19:57:59
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Hi all, Seems something went wrong and David's e-mail hasn't went through. Here it is: ====================================== We have previously estimated the effort to add GPRS to OpenBTS at around 9 labor months. It is a LOT of work. The problem is that GPRS is not so much a new feature within the GSM as a separate service stack, running parallel to GSM. It will not require a new GMSK modem, but will require new L1 FEC and completely new L2 and L3. The radio resource management is also much more complex. When I say "9 labor months", I mean an experienced engineer or developer working on this one project full-time for 9 months. You would know your student and your program well enough to judge if that is a reasonable expectation. Circuit-switched data (CSD) is not quite as exciting as GPRS, but would useful and lot less work. In this bearer service, two peer devices can form a dedicated data link at up to 13 kb/s. This data link interfaces to outside applications on the high side of L1 and can be connected to a public IP network with PPP as its L2. (Functionally, it is like a dial-up modem application and is accessed with the "AT DT" command on standard GSM serial interfaces.) CSD might also be a good intermediate step in the development of GPRS, since it will require similar solutions to IP interfacing problems and similar additions to L1, but with the radio channel management that is already written into OpenBTS. ====================================== -- Regards, Alexander Chemeris. |
From: Alexander C. <ale...@gm...> - 2009-10-04 16:37:56
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Hi David, Could you point to what is a good starting point to read about CSD, i.e. what parts of standards, etc? From your mail I think work should be started from amending L1, right? On Tue, Sep 29, 2009 at 23:57, Alexander Chemeris <ale...@gm...> wrote: > Seems something went wrong and David's e-mail hasn't went through. > Here it is: > > ====================================== > We have previously estimated the effort to add GPRS to OpenBTS at > around 9 labor months. It is a LOT of work. The problem is that GPRS > is not so much a new feature within the GSM as a separate service > stack, running parallel to GSM. It will not require a new GMSK modem, > but will require new L1 FEC and completely new L2 and L3. The radio > resource management is also much more complex. > > When I say "9 labor months", I mean an experienced engineer or > developer working on this one project full-time for 9 months. You > would know your student and your program well enough to judge if that > is a reasonable expectation. > > Circuit-switched data (CSD) is not quite as exciting as GPRS, but > would useful and lot less work. In this bearer service, two peer > devices can form a dedicated data link at up to 13 kb/s. This data > link interfaces to outside applications on the high side of L1 and can > be connected to a public IP network with PPP as its L2. > (Functionally, it is like a dial-up modem application and is accessed > with the "AT DT" command on standard GSM serial interfaces.) CSD > might also be a good intermediate step in the development of GPRS, > since it will require similar solutions to IP interfacing problems and > similar additions to L1, but with the radio channel management that is > already written into OpenBTS. > ====================================== > > -- > Regards, > Alexander Chemeris. > -- Regards, Alexander Chemeris. |
From: David B. <dbu...@ke...> - 2009-10-04 18:59:23
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Alexander - The CSD channels are described in GSM 05.03 sections 3.3-3.8. You will need new convolutional encoders for some of these channels and a lot of new interleavers. The higher rates will be easier because they are more similar to the existing TCH/F. The lower rates my not be worth the trouble. GSM 04.21 describes the "network interface" for the these channels, but it it mostly about adapting the rates to match standard ITU lines. A better approach is probably to treat the high side of L1 just like a serial line and run PPP. -- David On Oct 4, 2009, at 9:37 AM, Alexander Chemeris wrote: > Hi David, > > Could you point to what is a good starting point to read about > CSD, i.e. what parts of standards, etc? From your mail I think > work should be started from amending L1, right? > David A. Burgess Kestrel Signal Processing, Inc. |