I've finally found enough spare time to work on detailed plans for a GSM development board. The idea here is to have a 100% open hardware design with 100% free software that provides an inexpensive platform for GSM related R&D.
Initially the focus is on having a board that can behave like a GSM cellphone, next steps would be to have a multi-channel frequency-hopping receiver, and finally the option of using it as a BTS.
The idea is fairly simple: Take a commercial off-the-shelf analog baseband and RF circuit for GSM and attach it to a general purpose DSP, add some glue logic and go ahead. But the devil is in the details:
- You want something where you can still find the parts on the market, but which still has sufficient leaked documentation that you can write an open source driver for it.
- The requirements for a MS and a BTS are quite different. A phone never needs to continuously receive and transmit in all timeslots, e.g.
- The requirement for a multi-channel frequency-hopping receiver is mainly a high number of receiver circuits, so the solution needs to scale to a larger number of receivers.
- The analog baseband circuits often have quite obscure control interfaces which need to be driven. Custom peripherals in programmable logic (CPLD/FPGA) are required.
- The TDMA nature has strict timing requirements. Normal processors and software-based mechanisms are not sufficient to trigger the required events and their sequencing at a high enough precision.
Anyway, there is sort of a first plan now, and the next weeks and months will be spent with refining the plans and building a first proof-of-concept prototype. Once that has proven to work, we want to go ahead with finishing the design for a real board, to be manufactured in sufficient quantities for interested parties.
Unless you have worked in GSM phone or base station hardware design or have a similar level of EE and DSP skills, please refrain from contacting me right now about how to join the project. We want to focus on getting things going first, then make a public release at a point where there is something that works sufficiently well that we can support a larger community of developers.