USRP2 (gpslocked) openbts dowlink transmission works, uplink timing issue .

[evertverduin]

Hi All,

I am trying to get openBTS 5 to work with the USRP2, but i am unable to get the uplink working. The USRP2 is gps locked.
I cannot see any immediate assignments coming from openBTS ( log files ) caused by the RACH burst from the mobile. I can see the mobile transmitting ( on my analyser ), but there is no SDCCH immediate assignment from openBTS. I see the network, sim card is properly configured. There is no interference on the channel -> checked ( private GSM ). I assume the RACH is never heard by openbts due to timing issues. How can this be resolved, or what am i doing wrong?
EDIT: I see a lot of T3101 timer expiry and that is expiry of immediate assignment after RACH burst from mobile. So my theory is correct. The rach burst is received by OpenBTS, but somehow the mobile keep sending RACH bursts because it misses the immediate assignment command from OpenBTS. ( I see 4 SDCCH channels opened and closed due to T3101 expiry ).

Evert