I found the item (below) on the SCS web site. Anyone use this "new
class" of packet ?
Robust Packet-Radio (RPR)
Up to now Packet-Radio over shortwave has been basically a
non-starter, it has even been heavily criticized because of the low
effective throughput and repeats. AX.25 is for shortwave not an ideal
protocol, but with automatic FRack-setting and a small MAXFrame value
the protocol should, however, function much better on a shortwave
channel than has previously been the case generally.
One cannot of course expect an asynchrone protocol to reach the same
efficiency as a tight synchrone ARQ protocol (e.g. PACTOR), but for
some applications a multi-user service, with very uncritical
transmit/receive switching, as well as almost zero power holding up a
connection when no data passing, brings a real advantage that
outweighs the lower data throughput.
What finally are the reasons that up to now HF-PR works so poorly, and
apart from "forwarding" is hardly ever used? One finds a simple
answer: The current modulation type for HF-PR namely uncoded 300 Bd
FSK is really unsuitable for normal HF channels. The symbols are much
too short even with moderate "Multi-Path effect" ("delay spread") to
work. Additionally, because no sort of error correction code is used,
even short troughs or "static" will destroy a many seconds long
Packet. Just one missing bit leads to a repeat of the whole packet.
To help cure this problem, SCS has developed a new class of robust
modulations types especially for Packet-Radio. As a special feature
for all the variants of this "Robust PR", a completely new
synchronizations algorithm with "catch" properties that were not
possible before has been realized. Frequency deviations of ±250 Hz are
immediately recognized and without any loss of sensitivity
compensated, and this with signals that are buried deep in the noise.
Because of this it's possible to remove a tuning display. One can say
with good conscience that this is "Plug and Play" for shortwave.
The currently available "Robust PR" modulation types have the
following properties:
Bandwidth: 500 Hz @ -30 dB
Modulation: Pulse-Shaped OFDM (BPSK, QPSK), similar to PACTOR-III
Average Throughput: 200 or 600 Bit/sec
Crestfaktor: 3.0 or 4.2 dB
Delay-Spread: up to ±8 msec is tolerated
Coding: High performance convolutional code, "full-frame interleaved",
rate/2 or rate3/4
Digipeater and APRS Gateway
DB0UAL
Dial Mode Path
3610.0 USB RPR APRS DB0UAL
14102.0 USB RPR APRS DB0UAL
APRS Gateway
XY0XYZ
Dial Mode Path
10147.3 USB RPR FSK300 APXY RELAY WIDE
14103.3 LSB RPR FSK300 APXY RELAY WIDE
DH1TI
Dial Mode Path
10147.3 USB RPR APRS
OE3XMU-4
Dial Mode Path
10147.3 USB RPR FSK300 APRS
OE3KJN
Dial Mode Path
10147.3 USB RPR APRS
ZS1AAZ
Dial Mode Path
10147.3 USB RPR APRS
Note:
To use the following features you need the current Firmware for the SCS DSP-TNC:
Legende:
Recommendation: For transmitting position data with the Tracker/DSP
TNC, we suggest always to use the frequencies as shown in the list
with the respective sideband. The position data can then be
transmitted either only in RPR, or in RPR and FSK alternately (%AH =
1). In both operating conditions all physical channels are then
automatically set in the correct way.
(In case of an alternating transmission, i.e. %AH = 1, the Tracker
automatically uses %F = 2000 Hz, in order to set the correct interval
of 500 Hz between RPR and FSK channels without any user intervention.)
With gateways offering RPR and FSK 300 on one channel simultaneously,
it is assumed that the center audio frequency of the FSK demodulator
(%F-parameter) is 500 Hz higher than the center audio frequency of the
RPR demodulator. The space between the center frequencies of a
simultaneous FSK/RPR channel pair is always 500 Hz.
Basically, gateways receiving RPR and FSK300 simultaneously can also
be reached in FSK300 with the %F standard setting of the Tracker
(center frequency of 1700 Hz) in LSB mode.
In this case, if LSB is actually used, 3.7 kHz have to be added to the
figure shown in USB dial frequency listings. In case of an LSB
channel, 0.3 kHz have to be deducted from the listed frequency.
Gateways shown in the list as 10147.3 kHz USB can hence be reached in
LSB mode with the standard setting of the Tracker (%F = 1700 Hz, %AH =
0) on the standard dial frequency of 10151.0 kHz. Gateways listed as
14103.3 kHz LSB, can be reached in LSB with the default setting of the
Tracker (%F = 1700, %AH = 0) on the standard dial frequency of 14103.0
kHz.
In case of alternating RPR and FSK transmissions (%AH = 1), the
frequencies shown in the list and the respective side bands have to be
programmed. For example, the dial frequencies of 10151.0 kHz LSB or
14103.0 kHz USB MUST NOT be set, as neither the RPR, nor the FSK
channel would be reached correctly.
--
Andy K3UK
www.obriensweb.com
(QSL via N2RJ)
