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PCsat Initial Operational Test



At 1900 on 26 July, PCsat was given an Initial Operational Test consisting
of as many user packets as we could generate.  There were at least 12
invited guests each with his own handheld PCsat user transceiver all in
one room with PCsat.  They represented these professional backgrounds:

   NASA Program Manager
   AMSAT FCC Liason 
   National Disaster Medical Communications System (3)
   AMSAT
   Naval Academy Radio Club (4)
   Professional Engineer
   An ISP provider.

Several tests were conducted with all the users trying to access PCsat as
fast and as much  as they could.

   Transmit Delay,  Random access test,    Timed/periodic test
   Heard-log test,  Full duplex test,      Crossband test
   144.39 Bulletin

Over 2100 Packets were transmitted in about 2 hours representing the full
load to be seen by PCsat during the equivalent of about 8 full
back-to-back USA passes (no oceans in between)....

The first test was with the 12 people "simulating" a pass.  Everyone
trying his best to get in (like ISS).  Success rate was less than 30%.

Second test was with everyone set to a fixed beacon rate.  8 users set to
a 12 second rate,(G) models, and 4 users set to a 30 second rate.  In this
case, the success was better than 50%.  This test would be about the same
as 100 users in a single pass at the PCsat recommended rate of one packet
every 2 minutes.

We do NOT claim that these tests have any semblence to the reality of a
real USA pass, since everyone was in the SAME room and there were no
hidden transmitters.  But it was a fun Packet Radio test anyway to see
what 12 people could do to a channel in a free-for-all.  WOw was it
noisy!    

But since we ALL started our radios at the same time, it did prove that
the radios (on a terrestrial channel) all soon evenly distributed
themselves because with CSMA, they would not transmit on a busy channel...
Thus, users need not fear always coliding with the same person even though
you both start at the same time and have the same rate... They soon
diverge looking for a clear channel...
 
Throughout the first hour of tests, PCsat performed flawlessly.
It relayed all user packets, and sent continuous telemetry.  But during 
one specific test in the second hour, and then later, we did see a
total of two resets on the A side and at least a dozen on the B side.

The test that causes PCsat to reset is not a primary function of bent-pipe
relay, but a feature designed to store-and-forward emergency packets
from distant areas of the planet where there might not be any live ground
stations.   More testing is required to resolve this anomoly.

The good news is that PCsat never crashed, and in all cases, it RESET to
the SAFE mode as it was designed and restarted on its own.  The bad news
is that it will take DAYS to analyze the 2100 packets to figure out at a
detail level the statistics of all the things we can learn from this test.
 
de WB4APR, Bob

PCsat:   http://web.usna.navy.mil/~bruninga/pcsat.html


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