Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 - Manual (Page 175)

WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0 Transmission Modes

165
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 45.
See “ SAT System ” on page 219.
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).
Parameter Value
Frequency range L-Band (TDM)
C-Band (TDMA)
Operation modes Broadcast/Duplex FEC/ARQ TDM/TDMA
Symbol rate 1200 Bd
Modulation BPSK
Required SNR >15 dB (20 dB recommended)
Receiver settings BW = 5-10 kHz
Input format(s) IF
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:
Ocean Region NCSC Frequency Ocean Region NCSC Frequency
AOR-W 1537.70 MHz IOR 1537.10 MHz
AOR-E 1541.45 MHz POR 1541.45 MHz
The NCSC frequency is fixed for each ocean region. This ocean region is user selectable through the ‘Sat-
ellite Settings’ panel.
In the frequency offset bar the Inmarsat C mode has a NCSC-Auto check box.
With this checkbox the user is able to select between two operation modes: