I'm interested in knowing what it would take at a minimum to enable GSM cellphone to cellphone comms among a limited number of phones in the absence of a traditional cell-site structure. ie add your own cell-site if necessary. That could be tightened up somewhat to say GSM 2G platform or better and could be just SMS, just voice, and ideally SMS and voice and data. Either all phones involved need to be capable of peer to peer communications, or a cell site / base station "cellphone tower" is needed. Has anyone here any experience in this area or can comment on the feasibility of using existing in-phone GSM hardware to meet this need. Assume regulatory issues are not of concern (even though in many cases they will be). A hypothetical example application might be a "flying cell site" that is used in look-down mode from high altitudes to provide search and rescue radio communications in rugged terrain allowing the use of cellphones by ground parties - which would otherwise be ineffective in cell-site-less valleys. If you can talk to the cellphone equipped hiker lying incapacitated with a broken leg, so much the better. (An extremely experienced wilderness veteran died some years ago in NZ after lying incapacitated for several weeks after a fall and not being found until too late. He should have been carrying a locator beacon, but with a flying cellsite a $25 phone would have saved his life. This example would easily support the basic "$1000 solution" below (although it would usually done for even more in that application) but some applications would benefit from lowest possible cost. Russell "Resources:" The minimum arrangement that I'm currently aware of is to implement a cell site (or "cellphone tower") using a SDR (Software defined radio) and a computer of some sort. Almost any linux box can be used and I've recently read of people doing it with a Raspberry Pi. The probably most accessible, but not necessarily the best, solution is the use of Open BTS (Open Base Transceiver Station) free software (refs below) with a suitable SDR (Software Defined Radio). The usual hardware starting point is the open source USRP1 - User Software Defined Radio transceiver. A version of this, the USRPB100 can be bought fully assembled from Ettus Research for $US650 retail. Various Ettus Research SDR's here https://www.ettus.com/product/category/USRP_Bus_Series Add an eg Raspberry Pi and probably a GPS timing source, basic power supply and aerial(s) and you have a workable base for around $US1000 (assuming your time is worth zilch). That's a good start , but cheaper still would be better. _____________________ Android SDR anyone :-) Agh: That opened up a whole new line of thought. eg Realtek RTL2832U DVB stick gives you an SDR control core for under $20. Looks like it could handle the receive size OK. Transmit? http://wiki.spench.net/wiki/RTL2832U http://www.hamradioscience.com/forum/discussion/88/setting-up-your-rtl2832u= -dongle-for-sdr-use/p1 http://sdr.osmocom.org/trac/wiki/rtl-sdr http://dx.com/p/rtl2832u-r820t-mini-dvb-t-dab-fm-usb-digital-tv-dongle-blac= k-170541 __________________ Open BTS - Wikipedia http://en.wikipedia.org/wiki/OpenBTS OpenBTS (Open Base Transceiver Station) is a software-based GSM access point, allowing standard GSM-compatible mobile phones to be used as SIP endpoints in Voice over IP (VOIP) networks. OpenBTS is the first free software implementation of the lower three layers of the industry-standard GSM protocol stack. It is written in C++ and released as free software under the terms of version 3 of the GNU Affero General Public License (AGPL). Good GSM / Open BTS video 5m:34 http://www.youtube.com/watch?v=3DZoWKYJ1ATeE&feature=3Dplayer_embedded USRP Wikipedia http://en.wikipedia.org/wiki/Universal_Software_Radio_Peripheral USRP1 circuit diagram http://code.ettus.com/redmine/ettus/attachments/download/209/usrp1.pdf http://www.tcmaker.org/wiki/doku.php?id=3Dhamradio:ettus_research_u= srp1 USRP1 for sale $700 https://www.ettus.com/product/details/USRP-PKG The USRP1 is the original Universal Software Radio Peripheral=99 hardware (USRP) that provides entry-level RF processing capability. It is intended to provide software defined radio development capability for cost-sensitive users and applications. The architecture includes an Altera Cyclone FPGA, 64 MS/s dual ADC, 128 MS/s dual DAC and USB 2.0 connectivity to provide data to host processors. A modular design allows the USRP1 to operate from DC to 6 GHz. The USRP1 platform can support two complete RF daughterboards. This feature makes the USRP ideal for applications requiring high isolation between transmit and receive chains, or dual-band dual transmit/receive operation. The USRP1 can stream up to 8 MS/s to and from host applications, and users can implement custom functions in the FPGA fabric. _____________________________ 25C3 - Running your own GSM network. Excellent 44 minute video. http://www.youtube.com/watch?feature=3Dendscreen&NR=3D1&v=3De_9hPRF5fzA http://events.ccc.de/congress/2008/wiki/GSM/ Harald Welte This presentation will mark the first public release of a new GPL licensed Free Software project implementing the GSM fixed network, including the various minimal necessary functionality of BSC, MSC, HLR. It will introduce the respective standards and protocols, as well as a short demonstration of an actual phone call between two mobile phones registered to the base station. On the Ethernet/IP based Internet, we are used to Free Software and general-purpose hardware. The worlds second largest communications network GSM couldn=92t be any more different. Even though the protocols are standardized and publicly available at the ETSI, all implementations are highly-guarded proprietary secrets of a few major players in the industry. The hardware is even more closed, as there is not a single GSM subscriber or base station chipset with even the least bit of publicly known information. Nonetheless, in recent years there are a number of different projects working on driving a wedge of Openness into this world. You might have heard about other projects like the THC GSM sniffer project (pure wireshark-like functionality) and OpenBTS (a software defined radio based GSM base station interfacing with the Asterisk VOIP server). This presentation is about yet another new GSM related Open Source project. A project that follows the GSM specs more closely and actually aims at interoperability with existing equipment such as hardware BTS hooked up via S2M =85 _____________ Raspberry Pi Used To Replace A 30-Foot GSM Base Station And Create A Working Mobile Network Uses Open BTS and a Ettus SDR Excellent links in discussion http://techcrunch.com/2012/12/21/raspberry-pi-used-to-replace-a-30-foot-gsm= -base-station-and-create-a-working-mobile-network/ Open BTS source forge redirect page http://wush.net/trac/rangepublic This Trac is the home of the OpenBTS public release, a FOSS version of Range Network's self-contained SDR/GSM/VoIP stack. GNU Radio http://gnuradio.org/redmine/projects/gnuradio/wiki/OpenBTS Freeswitch http://en.wikipedia.org/wiki/FreeSWITCH FreeSWITCH is free and open source communications software for the creation of voice and messaging products. It is licensed under the Mozilla Public License (MPL), a free software license. Its core library, libfreeswitch, is capable of being embedded into other projects, as well as being used as a stand-alone application. Open BTS =96 superb You tube intro video for Open BTS Uses Ettus Research SPR USRP N210, ($US 1500 list) BUT could use eg USRPB100 at $US650 list. Software Radio / OpenBTS - The Well Tempered Hacker Ep 4 16m 20s http://www.youtube.com/watch?v=3DpTb1_v8M6iA Range Networks http://www.rangenetworks.com/ -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .