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Transmission Modes WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0
Operation
With the help of the FFT-Analysis-Tool look for a SAT-B-C-HSD signal (bandwidth 100 kHz, OQPSK 66
kSymbol/sec) with a lot of traffic.
In the Satellite mode menu choose Inmarsat, SAT-B-C-HSD.
The Session Window displays the start and end of a session. The “MES_ID” displayed is the return MESId
of the MES (Mobile Earth Station); the “Frequency” is a dummy value.
The Session List Window displays the results of the successfully decoded sessions. The decoded data is
saved as “Hsd.txt”.
Additional information:
See “SAT Settings…” on page 44.
See “SAT System” on page 298.
SAT-C-TDM, SAT-C-TDMA, SAT-C-EGC
SAT-C is a satellite based store-and-forward low speed message transmission system operating in the L-
band to (forward direction) and from (return direction) the mobile earth stations (MES) and in the C-band
to and from the land earth stations (LES) and network control stations (NCS).
L-Band (TDM)
C-Band (TDMA)
Broadcast/Duplex FEC/ARQ TDM/TDMA
>15 dB (20 dB recommended)
Mobile stations may be maritime, land based or aeronautical. The channel rate in both directions is 1200
symbols/sec. Error protection is achieved by convolutional encoding with R = 1/2 and k = 7 giving a user
bit rate of 600 bps.
A block or frame of data in the forward direction (TDM) comprises 10368 symbols (8.64 s). Data is highly
interleaved to combat slow fades. It is also scrambled to ensure an even distribution of logical 1s and 0s
for proper bit synchronization. Frame synch is achieved by using an unscrambled unique word at the be-
ginning of the frame.
The coding will correct some errors otherwise ARQ is used.
The forward channels from the LES and NCS are continuous time division multiplex (TDM) channels and
are used for message transmission and signaling.
In the return direction messages are transmitted by the MES on time division multiple access (TDMA)
channels assigned by the NCS. The frame length varies between 2176 symbols and 10368 symbols in
steps of 2048 symbols.
SAT-C TDM
As for the other Inmarsat satellite modes, the Inmarsat C system uses a NCSC (Network Control Station
Channel) for the announcement of new messages for the terminals. At the time of writing these an-
nouncements were transmitted on the following frequencies:
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