Re: [Openbts-discuss] RX and RX path of a burst

[Thomas T. <tt...@vt...>]

On Mon, Aug 1, 2011 at 11:42 AM, nghia phan <ngh...@gm...> wrote:
> Hello
>
> Does anyone have a good description of the path taken (packetisation, size,
> timing, additional control info) by a ready-to-transmit burst (full encoded
> and interleaved BUT before being modulated into IQ waveform) from the gsm
> core to  transceiver module via UDP socket, to USRP via USB packet. Then
> within USRP from Cypress to FPGA or AD9862?

There isn't much documentation on the OpenBTS specific paths, but
different parts of the USRP have been written about by a couple of
people. For example, "The USRP under 1.5X Magnifying Lens!" by Firas
Abbas Hamza.

http://gnuradio.org/redmine/attachments/129/USRP_Documentation.pdf

> In which module is the burst modulated into IQ?

The GMSK modulator outputs I and Q.

> In which module the intended transmission timestamp of a burst is checked
> against actual time in order to decide whether the burst should be sent or
> not? Or
> At which stage is a burst confirmed for actual transmission?

See Transceiver::pushRadioVector() for timing at the GSM burst level.
Sample level timing is checked in the FPGA.

  Thomas