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RE: [Discuss-gnuradio] USB latency problem

From: Newman, Timothy
Subject: RE: [Discuss-gnuradio] USB latency problem
Date: Sun, 20 Sep 2009 16:45:08 -0400

It totally depends on where you implement the latency sensitive components.  I 
believe the best USB can do is a minimum of 100us, and that probably the 
theoretical minimum.  If you need 80-120 us latency, you will definitely need 
to move the latency sensitive components to the FPGA.

Here are a couple more references related to latency in GNUradio and the USRP:
G. Nychis, T. Hottelier, Z. Yang, S. Seshan, P. Steenkiste, "Enabling MAC 
Protocol Implementations on Software-Defined Radios", NDIS 2009
K. Tan, J. Zhang, J. Fang, H. Liu, Y. Ye, S. Wang, Y. Zhang, H. Wu, W. Wang, G. 
Voelker, "Sora: High Performance Software Radio using General Purpose 
Multi-core Processors" 


Timothy R. Newman, Ph.D.
Wireless @ Virginia Tech
447 Durham Hall
Blacksburg, VA 24061
Phone: 540-231-2041

From: address@hidden address@hidden On Behalf Of Rushikesh Khasgiwale 
Sent: Sunday, September 20, 2009 5:17 PM
To: gnuradio
Subject: [Discuss-gnuradio] USB latency problem

I tried to use the usrp for implementing rfid protocols, however the USB
latency is causing a bottleneck and I cannot generate and send the reply
packet before the timeout(I need to send the reply within 80-120 us).
upon reading Thomas Schimd's
paper(http://nesl.ee.ucla.edu/document/show/242), it seems that I may have
to do processing on the fpga itself instead of sending data over usb.

Has anyone else faced a similar problem? CTS packets in 802.11 use
functionality similar to mine, so maybe those who implemented it can help


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