21 Jun
2012
21 Jun
'12
12:07 a.m.
On Wed, Jun 20, 2012 at 12:33 AM, Alexander Chemeris
<alexander.chemeris(a)gmail.com> wrote:
Actually interesting would be to test UmTRX with your
multi-ARFCN code
to see how many channels we could fit into.
I tried this briefly but the transmit output was cutoff by LPF. I'll
try it again with different LMS settings at the end of the week.
I wonder how do you select/measure rx_smpl_offset. My
guess is that
you write both Tx and Rx I/Q streams to files, plot them and try to
align frame starts. Is that how do you do this?
I mainly use two approaches. In the first method, feed the baseband
output to a scope (optionally set the transceiver filler table with
easy to recognizable values). Set one output of a dual function
generator to trigger the scope at the frame rate. Use the second
function generator output (with low duty cycle) to select individual
timeslots and also trigger an RF signal generator that feeds back to
the device. The offset can then be detected using the receiver energy
detector.
The second much quicker (and generally more effective) approach is to
simply measure with a handset. Disable upper layer RACH handling and
average the RACH burst TOA values over a few attempts and different
handsets. This delay value is the effective combined group delay
(relative to the sample counter) of host and device filters, RF
components, feed line, etc.
I rarely use first approach, but sometimes absolutely nothing works
and the test equipment needs to be used to get a better picture.
PS Could you record a short video of making 7 calls
through UmTRX? We
should make some noise or people forget what we're doing.
I could record a (low quality) video with my phone. That is the only
video recorder I have available right now. I can take pretty good
pictures though.
Thomas