The Inmarsat-B System; S Y S T E M D E S C R I P T I O N - Nera saturn bp Technical Manual

The INMARSAT-B System

Inmarsat
The INMARSAT-B system offers high quality 16 kbps
voice communication, and 9.6 kbps telefax and data
transmission.
The benefit of the INMARSAT system is its high
capacity, and the rapid and reliable connection
between the land based (fixed) users and the Mobile
Earth Stations (MESs).
The large number of Land Earth Stations (LESs) in
operation allows the operator to select the one giving
the lowest cost to a particular land based subscriber.
Each satellite region is under the control of a Net-
work Coordinating Station (NCS), which controls
and monitors the traffic between the MESs and the
LESs.
See figure 1.
NCS: Network Coordinating Station
LES: Land Earth Station
MES: Mobile Earth Station
(Saturn B terminal)
TELEPHONE
NETWORKS
TELEX
NETWORKS
DATA
NETWORKS
Figure 1.
Overview of the Inmarsat-B system.
6
Services
• Duplex telephone calls – basic telephony services
• Simplex telephone calls – LES-to-mobile only
• Duplex telefax – CCITT Group 3 facsimile servic-
es, 9.6 kbps
• Simplex telefax calls – LES-to-mobile only
• Simplex group ID addressing – to a selected
group of mobiles
• Simplex area addressing – to all mobiles within a
specific geographic area
• Duplex data communication – Hayes compatible
9.6 kbps data service
LES
NCS
MES
MES
System Satellites
The satellites are positioned in a geostationary orbit
above the equator at approximately 35700 km alti-
tude.
In geostationary orbit, each satellite moves at the
same rate as the earth, and so remains in the same
relative position to the earth, above equator, allowing
the antenna to have line-of-sight communication with
the satellite.
The Saturn Bp Portable can communicate via the
four satellites covering one Ocean Region each.
The positions of the system satellites are shown in
figure 2.
Pacific Ocean Region
Atlantic Ocean Region (West)
Atlantic Ocean Region (East)
Figure 2.
Four satellites in a geostationary orbit above the
equator at approx. 35700 km altitude.

S y s t e m D e s c r i p t i o n

S y s t e m D e s c r i p t i o n S y s t e m D e s c r i p t i o n
Transmission frequencies
The INMARSAT-B MESs operate in the following
frequency bands:
Calls from Saturn B terminals 1626.5 MHz — 1646.5 MHz
Calls to Saturn B terminals 1530.0 MHz — 1559.0 MHz
A large number of channels are available (20 kHz
channel separation), offering either 16 kbps voice
communication, or 9.6 kbps duplex data communica-
tion.
Duplex communication uses two channel frequen-
cies, one in each direction.
The LESs provide interface to the international
networks for telephony and data: PSTN (Public
Switched Telephone Networks) and PSDN (Packet
Switched Data Networks).
179°E
Indian Ocean Region
Saturn Bp Portable – Technical Manual