[USRP-users] [ANNOUNCE] OpenBTS USRP2 support

Thomas Tsou ttsou at vt.edu
Wed Nov 17 18:17:30 EST 2010


On Wed, Nov 17, 2010 at 2:20 PM, Josh Blum <josh at joshknows.com> wrote:
>
>> *Operation in the upper bands (1800, 1900MHz) requires an external
>> reference for reliable operation. This is true to a lesser extent in
>> the lower bands as well.
>>
>
> I wonder if this will be necessary for the USRP-N210 since that has a 10MHz
> TCXO for an "internal" reference.

I'm thinking that it will suitable to hold calls on all bands; but it
depends on the requirements of application. I'm sure there are some
people who won't be happy with anything but carrier grade rubidium.

> In another note. I am considering modifying the old USRP classic FPGA code
> to get receive timestamps (secs and ticks) for the USRP1 + UHD support. What
> is needed for in terms of timestamps with transmit for OpenBTS? Basically,
> does it a timestamped send_at() capability?

The transmit samples go out in a continuous stream so the critical
timing points are the start and resync period after an interruption
(underrun). For the latter, the underrun and late packet arrival
behaviour is the main factor. The USRP2 will still transmit packets
that arrive late, so they're checked and dropped at the host.
Otherwise, we get a constant shift in the transmit slots compared to
those on the receive side.

  Thomas




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