Hi all, I am currently trying to measure delays on the USRP and found some interesting things. I wanted to see if others have similar results:
- First I measured the round trip time of my IEEE 802.15.4 implementation. I have to computers, one runs a ping application, the other one a pong. The average delay in this case is 26.8ms. - Next, I measured the round trip time of my FSK implementation (also based on packets). Here, the mean RTT is 14.9ms. - Next, I tried to find out the one way delay, i.e., how much time does it take between generating one sample at the computer, until that sample gets sent out at the USRP output. For this, I changed the code of the sig_gen class such that it generates a square wave instead of a cosine and I added code that toggles the parallel port pins according to the state of the square wave. Then I used an oscilloscope to measure the delay between the two signals, i.e., the one generated at the parallel port and the one from the USRP (LFTX). The signal is at 2 Hz. The delays in this case depend a lot on what I choose for the decimation (while keeping a constant square wave frequency). If I use decimation=500, then I find an average delay of 65.8ms. When I change the decimation to something else, I get values ranging from 30ms up to 150/200ms (I didn't do exact measurements for these yet). What I am wondering is, why is there such a huge difference? Is it because of the GNU Radio scheduler? Or is there some other problems? Thomas _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
