Wavecom W61PC V7.5.0 - Manual (Page 167)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  157
This illustration shows a block of eight alphanumeric characters of 6 bits each. The high fading protection
is achieved by transmitting columns rather than rows (interleaving). In this way a burst error affecting 16
bits does not cause a character error. In addition each block contains a checksum computed by binary ad-
dition of the information bits of the other 7 words adding to the error detection capability of the system.
In high capacity systems the GSC makes use of grouping. For this purpose 16 calls are stacked together.
Each stack is preceded by one of 10 copy information blocks that consists of 18 repetitions of a single Go-
lay codeword. In this way all receivers in a system are grouped in 10 header block groups and each re-
ceiver only has to decode the stack that is preceded by its particular header block.
GOLAY also has a facility for optimizing voice calls. A special audio control code is used to separate voice
messages.
GOLAY uses direct frequency modulation. Proper decoding is only possible from the receiver IF output
(455 kHz, 10 MHz or 21 MHz).
G-TOR
G-TOR operates at a radio channel rate of 100, 200 or 300 Bd. The quality of the radio channel deter-
mines the actual adjusted baud rate.
Parameter Value
Frequency range HF
Operation modes Simplex ARQ
Modulation FSK
Symbol rate 100, 200 and 300 Bd adaptive
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ITA-5 with block coding
By clicking the Auto button, the demodulator will automatically adjust to the actual shift and center fre-
quency followed by phasing with automatic baud rate and signal polarity detection.
With some skill the actual baud rate of G-TOR may be easily recognized. Baud rates of 100, 200 and 300
Baud may be manually selected. If so phasing will be accelerated.
After synchronism with a G-TOR signal has been achieved, the software will ensure the baud rate adapta-
tion as is the case in Auto mode. After the end of transmission the software will re-synchronize.
The cycle duration of G-TOR is always 2.4 s. The data frame has a length of 1.92 s, which leaves 0.16 s
for acknowledgement from the remote station. At 300 Baud 69 data bytes are transferred, at 200 Baud 45
bytes and at 100 Baud 21 bytes. After the end of the data block a control byte and a 16 bit CRC sum are
appended.