Wavecom W74PC V8.7.0 - Manual (Page 186)

176

Transmission Modes WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V8.7.0
pressed emails and/or several commands. If the processed data packets yield evaluable data, the follow-
ing information is shown:
 Transmitting station information
 If emails are found and extraction is successful (possibly with a CRC-Error): Data transmission in-
formation and the extracted emails are printed
 If emails are found but extraction fails, the cause for the failure is printed
 Otherwise if only commands are found, they are printed
In addition to the decoded output, several files are generated in the Global Data (RW) directory. In the
subdirectory “GWOFDM[SN]”, all decoded emails are stored, either as text file (OutFileTXT) or in a folder
as .SSP-file (OutDir). The .SSP files can be opened with any standard text editor. The subdirectory
RAW_DATA saves for every transmission a log file with all detected packets and – if a transmission con-
tains data packets – a data file with the decoded data packets put together is created. These files can be
used for advanced examination of the transmission. In the subdirectory TRANSMISSION_DATA data pack-
ets of aborted transmissions are saved, which are used in case of a continuation of the transmission. Files
in the RAW_DATA and TRANSMISSION_DATA directory are deleted after two hours, or when the mode is
closed.
As the GW-OFDM-signal contains no redundancy, sufficient reception quality is important: every DATA
packet must be received at least one time without corruption. In the case of packet repetition, the decoder
can handle multiple received packets. It should be noted that the decompressor has no error correction -
even one wrong bit can produce a completely false decoded output.
GW-PSK
GW-PSK is used by Globe Wireless on the Maritime Data Network of the company. The network works with
several digital modes in an adaptive system. GW-FSK is always used for opening a connection. Depending
on propagation conditions, it may switch to GW-PSK or other digital modes.
Parameter Value
Frequency range HF
Operation modes Simplex ARQ
Modulation DQPSK, D8PSK
Symbol rate 200 Bd
Bandwidth 400 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ASCII
GW-PSK is DQPSK and D8PSK modulated with a bandwidth of 400 Hz. The bit rate is 400 bits/s or 600
bits/s with a fixed symbol rate of 200 Baud.
A GW-PSK frame consists of 288 or 432 bits. Each frame contains 25 characters or data bytes. For error
detection a 16 bit CRC-checksum is required. For smaller packets, a filler ‘U’ for traffic or ‘<’ for last pack-
ets is used.
A GW-PSK signal is tuned in the same way as a PACTOR-II signal. The precision of the center frequency is
very important and influences directly the performance of the decoding.
Most of the traffic is compressed. From time to time uncompressed GPS position data in NMEA format is
transmitted on ship frequencies. GW-PSK stations can be found on all maritime bands and also in the fixed
service bands. More Information is available on http://www.globewireless.com.
HC-ARQ
HC-ARQ is a simplex system operating at a symbol rate of 240 Bd on the radio link.