Re: [Discuss-gnuradio] GSM SoftPhone

[Eric Blossom]

On Thu, Sep 07, 2006 at 12:52:23PM -0700, JoePub wrote:
> 
> Hi All,
> 
> Appologies about the re-post, but the original post wasn't submitted to the
> maililing list.
> 
> I have been looking at the USRB for a work project in implementing a
> softphone.  What are other peoples opinions of using the USRB for developing
> a software based GSM cell phone.  The reason I ask is this.
> 
> Obviously the USRB can handle the channel bandwidth of 200Khz, but these
> physical channels then use TDMA to create another 8 channels within the one
> physical RF channel.  Now GSM has a few timebased counters for
> synchronization to the base station, the lowest timebased counter that are
> involved for synchronization (QN i belive in the GSM spec) is incremented
> every 12/13 of a microsecond.  Would an OS like Linux or Window be able to
> keep up with this level of accuracy, or would a daughterboard need to be
> developed to fulfill this requirment.  In other words, could an OS like
> Windows acuretly send out burst within the requested timeslot within the
> TDMA frame that the base station desires during MS setup.
> 
> Hope that made sense.
> Regards

I don't know about Windows, but Linux is capable of this when the
ultimate timebase is implemented in the FPGA.  This level of timing
resolution is currently in developement and will be implemented in
combination with the upcoming "message blocks".  [Check the archives
for more info on "m-block" and/or "message block"]

Eric