Monster Media 1993 #2/Image.iso/ham/aprs114.zip/README.APR

Text File | 1993-05-04 | 15KB | 248 lines

                  AUTOMATIC PACKET REPORTING SYSTEM (APRS)

     APRS is the result of my experience over the last 13 years with trying
to use packet radio for real-time communications or public service events.
Packet radio has great potential but so far has been best used for passing
large volumes of message traffic from point to point or into the national
distribution system.  It has been difficult to apply packet to real time
events where information has a very short life time.  Typically, several
steps are involved in preparing and passing message traffic including
decisions about routing and connectivity.

     APRS avoids the complexity and limitations of trying to maintain a
connected network.  It permits any number of stations to participate and
exchanges data just like voice users would on a single voice net.  Any
station that has information to contribute simply transmits it, and all
stations receive it and log it.  Secondly, APRS recognizes that one of the
greatest real-time needs at any special event or emergency is the tracking of
key assets.  Where is the Event Leader?  Where are the emergency vehicles?
Where is the head of the parade?  Where are the VIP's?  Where is the mobile
ATV camera?  Where are the mobiles?  Included on the distribution disk are
several README text files on specific applications of APRS such as for
weather nets, direction finding, plotting satellite contacts, and so forth.

     APRS accomplishes the real-time display of operational traffic via
UI frame broadcasts and map displays.  There are three major display
subsystems and a number of other minor displays as follows:

     LATEST BEACONS - This display maintains a list of the latest UI frame
received from each station.  In effect, this is a multi-station one-line
broadcast message system.  Since the lines contain the LATEST time of
receipt, this display shows if a station is still on line within the last few
minutes.

     POSITIONS - This display maintains a separate list of the positions of
each station.  Each position report can also contain a brief comment.  These
lines retain the time of FIRST receiving a given position report and give an
indication of the latency in the network over unreliable paths such as HF.

     MAPS - Maps to any scale from .5 miles up to 2000 miles can be
displayed. Stations are instantly displayed when they transmit a properly
formatted position beacon.  Stations with a reported course and speed can be
dead-reckoned to their present position.  You can center the map anywhere.

     MESSAGES -  In addition to the BEACON text which is used to broadcast
information to all other stations on the net, there is an operator-to-
operator message capability.  Any station can send a one line message to any
other station.  On receipt, the messages are acknowledged and displayed on
the bottom of the receiving stations screen until the operator hits the K key
to kill them.

     ALL TRAFFIC LOG - This display is a time sequenced log of every new
beacon or one line message sent.  Beacons are logged the first time they are
received.  This is in contrast to the LATEST display which shows the most
recent time of receipt of a beacon text.

     WHEN-HEARD - Since UI frames are redundantly transmitted, this display
maintains a count of the total number of transmissions from each station per
hour.  These statistics are ideal for displaying the connectivity of the
network over varying paths, such as HF, or to see when stations enter and
leave the net.


     STATION TRACKING.  Although the system automatically tracks mobile
packet stations interfaced to GPS or LORAN-C navigation, the graphic
capability of the maps works perfectly well with manual tracking.  Any
station in the network can place an object on his map including himself and
within seconds that object appears on all other station displays.  In the
example of a parade, as each checkpoint with packet comes on line, its
position is instantly displayed to all in the net.  Whenever a station moves,
he just updates his position on his map and that movement is transmitted to
all other stations.  To track other event assetts, only one packet operator
needs to monitor voice traffic to hear where things are.  As he maintains the
positions and movements of all assets on his screen, all other displays
running APRS software display the same displays.


     USING DUMB TERMINALS IN AN APRS NETWORK:  The simplicity and usefulness
of this geographic capability cannot be over stressed.  Stations running APRS
simply move the cursor to where they think they are on the screen and their
LAT/LONG coordinates are automatically transmitted to all other stations.
Even the simplest of portable packet stations with dumb terminals can report
their positions if a pre-printed map is made available to all net
participants which has a LAT/LONG grid reference.  The portable station just
looks at the map and enters his LAT/LONG into his beacon text.  Using the
same map, he can plot with pins the location of all other stations as he sees
their position reports go by.  Eventually, it is hoped that all stations, no
matter how they are using their TNC, will include their LAT/LONG in their
Beacon Text so that their location is immediately available.  See the file
README.DUM for details on APRS formats and help in using dumb terminals in an
APRS network.


     SPACE APPLICATIONS:  APRS could be a solution to the effective
use of orbiting terrestrial style packet radio digipeaters in space such as
on the Shuttle, MIR, AO-21 and ARSENE.  The problem with space digipeaters is
the saturation on the uplink channel which makes the use of a normal
CONNECTED protocol impractical.  For a CONNECTED contact, a total of five
successive and successful packet transmissions are required.  Not only does
APRS reduce this to one packet, but it also capitalizes on the most
fascinating aspect of the amateur radio hobby, and that is the display on a
map of the location of those stations.  If all stations were encouraged to
simply insert their LAT/LONG as the first 19 characters of their beacon text,
everyone within the satellite footprint would see the location of every
successful uplink.  Since the shuttle is a rapidly moving object, the
locations of successful uplink stations will move progressively along the
ground track.  All it would take to implement this capability is a single
AMSAT news bulletin to ask all stations to insert their LAT/LONG in their
beacon text.  No changes onboard the shuttle or MIR would be required.  See
README.SAT for further details.


FOX HUNTING OR DIRECTION FINDING:  APRS is an excellent tool for
triangulating the location of a hidden transmitter, balloon, or interfering
signal.  The X command (cross fiX)has been added to permit displaying the
intersection of bearing lines from a number of reporting stations.  To use
APRS in this manner, each station having a bearing report on the direction of
the target, simply enters that bearing in the COURSE field for his own
station.  His station is now not only reporting his station location, but
also a line of bearing.  All stations running APRS can simply hit the X key
to display the intersection of these bearing lines.  Further, if a DF vehicle
has a GPS or LORAN-C device on board, he can be tracked and directed right to
the location of the target.


     PROTOCOL - Since the objective of APRS is the rapid dissemmination of
real-time information using packet UI frames, a fundamental precept is that
old information is less important than new information.  All beacons,
position reports, messages and display graphics are redundantly transmitted
but at a longer and longer repition rate.  Each new beacon is transmitted
immediately, then 20 seconds later.  After every transmission, an additional
20 second increment is added to the beacon period.  After an hour this
results in one beacon in 6 minutes; after two hours, every 12 minutes, and so
on.  The 20 second nominal increment period is adjusted up or down
automatically by each station depending on channel activity.  This way a few
stations at a special event can get as short as a 10 second cycle times;
whereas a busy channel with dozens of stations transmitting could slow the
increment up to a minute.  A transmission can be forced at any time by
hitting the T key.


     COMMANDS:   In most cases the keyboard is always active.  There is a
mneumonic relationship between all functions and the appropriate key.  For
this reason, the PC function keys are avoided.  The most useful commands are
as follows:

  Space Key           - Display map and all station locations
  H - Help            - Two alternating pages of help
  L - Latest beacons  - Displays the latest BText from each station
  P - Positions       - Displays a list of all stations reporting positions
  C - Controls        - Display a one line status of all control states
  W - When heard      - Displays the number of beacons per hour per station
  S - Send            - Send a directed message to a station

  Alt-C,L,T,R or W    - Cities, Leaders, Tags, Roads or waterways on/off

  Ctrl-L  Load file   - Loads a previously saved file and screen location
  Ctrl-S  Save file   - Saves all positions and Beacons for later restart
  Ctrl-R  Replay      - Replay the recent movements of stations in memory
                        or replay a track history file
  Ctrl-V  Via digi    - Used to change your VIA path for outgoing packets


DEMONSTRATION FILE:  To get an idea of how the APRS system works on an
ordinary packet traffic frequency, use ctrl-L to load the file called FREQ5-
05.BK.  This file contains all the local stations on 145.05 MHz in our area.
To see the tracking of the GPS equiped Army/Navy game football run, load the
file named FBALL.BK and replay the file named FBALL.HST and select to see
only FBALL, or CHASE1.  To see the marathon event we just completed, load
MARTHON.BK and replay the MARTHON.HST file.  See Details in README.1st.


HOOKING STATIONS:  The yellow circular cursor can be moved to select any
station in the system using the arrow keys.  On the MAP display move the
cursor near any station symbol.  Then hit the RETURN key to "hook" the
station.  Detail information on that station will be displayed in the upper
left hand corner.  Alternatively, use the gray + and - keys to step through
each station one by one.  Once hooked, several functions may be performed:

     1.  LIST BEACONS - hitting the L key will list all beacons from that
     station currently in memory.

     2.  POSITION CORRECTION - performed by moving the cursor to the
     desired new location and pressing the Insert key.  You are then
     prompted to enter in a new course, speed, comments or time as needed.

     3.  DELETE - performed by hitting the Del key.  Removes the station
     from the position file.

The hook function also works on the LATEST and POSITION display lists by
using the up/down arrow keys.  If a position exists, you are given the
opportunity to display the map screen with that station centered on the
display.  This is useful for finding a station which is far off the currently
displayed map range.  If a position does not exist, you are given the
opportunity to create one.


REPLAY:  Since all beacons and position reports are retained, the ctrl-R
key may be used to replay the positions of a moving station.  The replay
is performed either from active memory, or from historical files.  Historical
files are automatically saved periodically as shown below.  The replay will
always begin using the existing map and scale.  Alternatively the map
location may be set to automatic so that the map will be recentered whenever
the mobile station moves off the existing screen.  The range scale never
changes.  If there are several widely separated stations in the file, it is
best to either avoid the auto-centering option or to select only one station
at a time for playback so that the screen is not being constantly changed.
During replay, the user has several single key commands available:

      F - Faster.  Speeds up playback
      W - Warp speed.  Skips every other point for still faster playback
      S - Slow.  Slows down playback
      Q - Quit playback.
      Space - Pauses playback.  Toggles on and off


FILES:  There are several files used by the system:

  MAPLIST .map - Contains a list of all map files to be used and also the
                 default LAT/LONG, Range and GMT offset for your location
  USA     .map - large scale map of the east coast
  xxxxxxxx.map - Maps of any area to any scale.  At this writing there is
                 a whole USA map and state maps for most of PA, MD, VA, & NC.
  TKxxxxxx.HST - Track history.  The day and time that the file was saved
                 is indicated by the x's. If the file contains an interesting

                 trip or station movement for later replay, the file should
                 be renamed using DOS to a more descriptive *.HST file
  BACKUP  .BK  - Automatic backup of system every time program is quit.  This

                 file is overwritten every time the program is quit.
  BKxxxxxx.BK  - Backup file of the latest beacons and POSITS heard created
                 whenever Ctrl-S save is commanded.  Usually used to save a

                 file backup of a special event or situation.
  BLxxxxxx.LOG - Log of all new beacons received in chronological order of
                 first receipt.  A good log of text used during an event.


CHESSBOARD:  To demonstrate the flexibility of APRS in reporting the movement
of objects on screens in a net, I have drawn a chessboard map in the center
of the Gulf of Mexico.  Any two stations can play chess easily using APRS by
placing pieces on the map using the alt-A key and updating their positions
using the cursor and INSert keys!  As a start, I have already loaded all the
pieces and saved them in CHESS.BK.  Unfortunately you need to enable each one
for uplinking individually using the X key on the P screen.  Is better to
wait till you move a piece before enabling it for uplink so that channel
loading is minimized.