Running the BPSK Template
A few windows should appear on your screen after Ptolemy is started,
including the one below. This window contains the Ptolemy facet
init.pal for this design. This facet will automatically
appear whenever Ptolemy is started in this directory.
To close a window type ctrl-D with the pointer over it.
To examine the BPSK template simulation place the pointer over
the far left icon in this window and type "i" for look-inside.
The window below should then appear. It contains the complete
simulation block diagram. In Ptolemy, a complete application like
this BPSK simulation is called an universe.
The BPSK universe contains four galaxies including the BPSK
transmitter galaxy named BPSKxmit. Again, place the pointer
over a galaxy and press "i" to view its contents. Opening the
BPSKxmit galaxy should reveal the window below.
The transmitter galaxy contains two Ptolemy stars named
Table and Repeat. The first is a simple lookup table
that converts the binary values at its input into antipodal signals of
unit amplitude. The source code for this star can be examined by
typing "i" with the pointer over its icon. However, this can
sometimes result in information overload. Pressing the comma (",")
key will instead reveal the function of a particular star. Likewise,
pressing "e" for edit-params will reveal the parameters used by
this star. For instance, the parameters for the Table star
indicate that the bit values 0 and 1 are mapped to +1 and -1
respectively. The Repeat star repeats each input (single value
or block of values) for the number of times specified in its
parameters, basically performing a sampling rate conversion.
Press "R" for run-universe with the pointer over the
BPSK universe. This will present a dialog box like the one
below.
The box "When to stop" specifies the how many iterations the
simulation will run. Clicking the Go button or pressing return will
run the simulation. The cumulative BER is displayed on the control
panel as the simulation runs. After all iterations are complete, the
XMgraph star will plot the transmitted signal and the received
signal for the simulation.
The value of Eb_N0_dB and the sampling rate can be changed by
edit-params while the pointer is over the universe (see below).
Notice that the values of these parameters are passed to the galaxies
in the universe. In fact, the noise variance in the AWGNCh
galaxy is a function of both of them. Examine the effect of the noise
variance on the received signal by running the simulation several
times with a different Eb_N0_dB value and leaving the resulting plot open
for comparison.
John C. Sperandio <sperandi@eng.usf.edu >
Last modified: Thu Oct 9 17:40:20 EDT 1997