Hi, I've been running some experiments to quantify the delay involved in USRP + GNU Radio (ex. round trip time). I downloaded UCLA's 802.15.4 implementation on GNU Radio from the SVN server on acert.ir.bbn.com However, I got some results which I cannot explain. I hope someone here can shed some light on this. :-)
When both transmitter and receiver are USRP + UCLA 802.15.4 on GNU Radio, sometimes I found that a packet is finished decoded by ucla_ieee802_15_4_packet_sink long after a packet is received by USRP. To be more precise, the packet is sent to the message queue (to upper layer) after the next packet (which can be half a second later than the first packet) is transmitted by the transmitter. My guess is that USRP does not have enough samples to form a USB packet and transmit to the host side, so it waits until the next packet arrives. Is this correct? Does this ever occur to anyone who is experimenting with packet radio? Is there anyway to flush the buffer in USRP so the delay is reduced? http://rafb.net/p/tJZuIQ76.html The above URL is a trace of my experiment. Most of the lines marks the time of the entry and exit time stamps of the blocks using gettimeofday(). From line 414 to 438, you can see that the packet is almost done, but it waits until line 512, which is when the next packet arrives, to insert the packet to the queue. Thanks for reading this long post. I'm looking forward to the reponses. Sincerely, -Michael -- Hsin-Mu (Michael) Tsai Ph.D. Student Electrical and Computer Engineering Department Carnegie Mellon University _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
