Re: rrc filter in generic mod demod


Sent a my mobile…Dqe

----- Reply message -----
From: “Ian B.” [email protected]
To: “Dan CaJacob” [email protected]
Cc: “[email protected][email protected]
Subject: [Discuss-gnuradio] rrc_filter in generic_mod_demod
Date: Wed, Jun 12, 2013 07:52
Dan, Any chance you can attach those pictures in a different way and
resend, I couldn’t find a way to view them and I’m curious to see
On Jun 11, 2013, at 10:12 PM, Dan CaJacob [email protected]
wrote:There are two parameters that will affect your TX power: digital
amplitude and RF gain. The digital amplitude sets the amplitude of your
signal going into the DAC. UHD expects a signal between 0 and 1.0, but
to keep your output nice and linear, keep your signal amplitude belw
0.2. Conversely, 0.02 seems pretty low. RF gain is applied in the
aughtercard once your signal has been up converted. My practice is to
keep the signal amplitude at 0.2 max amplitude, then adjust RF gain to
control power. You’ll end up getting less than the max rated power
output (e.g. 20 dBm for WBX, but you’ll have a clean RF signal.

I very recently characterized a WBX across the full range of amplitude
and gain settings. Here’s the result. Note that the non linearity belw
a gain of about -10 dB is due to the signal power being belw the bottom
range of the power sensor.

And here’s a plot for just the 0.2 amplitude curve.

On Tuesday, June 11, 2013, yeran wrote:

Dear all,

I am doing channel estimation in gnu radio narrow-band. I’m collecting
data at the receiver side after the time_recov block. It has been
through the gr.firdes.root_raised_cosine in the time_recov. But the
plot I get is as the figures in the attachment. It looks like the
fluctuation of the channel amplitude has some pattern, it looks like
signal pulse shaping in there. But doesn’t the
gr.firdes.root_raised_cosine works as the rrc matched filter, and
already take off the pulse shaping?

Also, when I do experiment, I found out something strange. According to
my understanding, the --tx-amplitude on the transmitter benchmark sets
the transmission power. So the bigger the amplitude is, the better
performance it should be, since the SNR will be bigger. But in actual
experiment, it is totally the opposite way! The amplitude of 0.02, or
even 0.002 works better than the default 0.25. Has anyone come across
the same problems?

Highly appreciate if anyone can give me some suggestions on this! Thanks
in advance!!


Very Respectfully,

Dan CaJacob