root/vtcross/trunk/src/cross-examples/python/gnuradio-examples/README @ 416

benchmark_dsa.py - GNUradio Dynamic Spectrum Access example script

Summary:
This script implements a extremely simple DSA algorithm and 
rendezvous protocol.  When two nodes are running this script, they
will dynamically change frequencies  until they rendezvous and begin
communication.  

Operation:
In order to run this script several GNUradio utilities scripts must be
located in the same directory as the benchmark_dsa.py script.  The 
easiest way to do this is to copy benchmark_dsa.py into the following
GNUradio source directory:

<gnuradio_top_srcdir>/gnuradio-examples/python/digital/


General Information:
The purpose of this script is to demonstrate simple dynamic spectrum
access.  In our case we do a simple probe using the gr.probe_avg_mag_sqrd_cf
component to get a ROUGH estimate of the energy.  An energy threshold is
used to determine if another signal is present in the channel.  This
threshold can be set from the command line using the --threshold arg.
By default it is set to 1.5e8.  We calibrated this using the following:

USRP1
RFX400 USRP daughterboard
Standard 2-way FRS radios

The threshold should be set accord to your specific environment and will
most likely be different for everyone.

If a primary user is detected, the script will change channels to avoid 
causing interference.  The channel selection is the fun part.  By default
the script simply picks a random channel from the STATICLY available 
channel list that we've hardcoded in.  Also available is intgration into
our open source cognitive engine system which uses a case-based reasoning
system to select a channel based on previous environments.  

For example, the CROSS system, when requested, will query it's database
and observe that channel A has previously seen a primary user, in this
case the probability that channel A is selected as the next channel to
hop is will be small compared to other channels that have seen seen primary
users.  To use the CROSS system, CROSS must be built and installed 
(https://cornet.wireless.vt.edu/trac/wiki/Cross/BuildGuide) and you must
supply the --cross argument.  DSA algorithms are ongoing research items
at many institutions and this is just a VERY SIMPLE implementation to get
others started.

Also worth noting is the rendezvous method.  To get the full functionality
two of these nodes must be running. Each node decides on it's own which
channel to move to next if scanning for other nodes or if a primary
user is detected.  At each channel hop, a beacon is transmitted.  This 
beacon is used by other nodes in the channel to identify each other. 
If a beacon is seen on a channel, an ACK beacon is sent and both nodes
settle on the current channel and begin communication.  

Again this is still a work in progress but hopefully others can gain 
some insight into spectrum sensing and DSA using GNUradio, the USRP, or
the Virginia Tech Cognitive Radio Open Source System.

For questions or comments related to CROSS: 
cross-discuss@listserv.vt.edu
or
trnewman@vt.edu