Classic Aero GES Channel Unit Subsystem

The Inmarsat Classic Aero system provides voice, low-speed data and safety communications services to end users via Aircraft Earth Stations (AESs) installed on airborne platforms and Ground Earth Stations (GESs) which provide the interface between the satellite and terrestrial networks. Classic Aero services are used by most of the world's airlines and corporate jet operators, as well as governments for VIP aircraft, coast guard and defence agencies. Inmarsat’s worldwide coverage is complemented by the Japanese Civil Aviation Bureau (JCAB) MTSAT satellite, which also provides Classic Aero services.

A new generation of GESs has been installed by Inmarsat, using Square Peg Communications Inc.’s Multi-Channel Platform (MCP) to provide the modems.

The Inmarsat Classic Aero Channel Unit Subsystem (CUS) is an application of the MCP that provides up to 192 P/R/T or C-channels in a single 7U rack mount chassis. The modems implemented in the CUS are based on those in Square Peg’s Inmarsat Aeronautical Ground Data Unit (GDU), the “gold brick” reference used for type approval of AESs for operation on the Inmarsat network.

The architecture of the MCP is based on the use of a common LAN protocol for communication both within an MCP chassis and with other system elements. This provides a high degree of flexibility in configuring the system. The cards comprising a system can be distributed among multiple synchronized MCP chassis. All elements can be redundant for fault tolerance and high availability. This architecture makes it ideal for GES applications requiring fault tolerance, high availability and fully compliant performance in a compact implementation.

    • High availability
    • Hot swappable elements
    • Ease of maintenance
    • Up to 6 Channel Units (CUs) per chassis
    • Up to 16 transmit and 16 receive channels per CU
    • Integrated voice codecs
    • Common CU hardware and software for all channel types
    • Redundant Ethernet interface
    • Built-in dual polarization support
  • Channel Unit Subsystem


    19” / 7U PICMG® 2.16, rack mount


    Front to back

    Power supplies

    N+1, 115/230V AC or 48V DC

    Shelf managers

    Dual redundant per PICMG® 2.9
    RCMP, CLI, GUI, SNMP interfaces
    Alarm dry contact relays

    Ethernet switches

    Dual redundant 10/100 + 2 x 1G

    Channel Units

    1 to 6 front / rear card pairs

    Maximum channels per CUS

    96 Tx + 96 Rx

    Channel Unit Functionality

    Composite channels

    4 Tx/Rx (independently tuneable)

    Composite channel bandwidth

    500 kHz

    Bearer channels per composite channel


    Operational bearer channel types


    Test bearer types

    CW, unframed, random data, random symbols

    Voice codecs

    4.8 kb/s AMBE for C8400
    9.6 kb/s LPC for C21000

    Max. data channels per CU

    16 P-channel Tx
    16 P/R/T-channel Rx

    Max. C-channels per CU

    8 C-channel Tx/Rx


    Ethernet interface

    Auto-switching between Switch A, Switch B and front panel

    Monitor and control, data

    Proprietary over TCP/IP

    PCM samples

    RTP over UDP

    Tx/Rx IF frequency range

    50 to 90 MHz

    Max. total power per Tx feed

    –17 dBm

    Max. per-carrier Tx power

    –29 dBm

    Tx phase noise density

    @ 100 Hz:   ≤ –70 dBc/Hz
    @ 1 kHz:     ≤ –80 dBc/Hz
    @ 10 kHz:   ≤ –90 dBc/Hz
    @ 100 kHz: ≤ –100 dBc/Hz

    Tx spurious

    < –86 dBm for carrier at –29 dBm

    Tx 3rd order intermodulation

    < –55 dBc (2 carriers at –20 dBm)

    Tx I/Q imbalances


    Typical Rx dynamic range

    –65 to –25 dBm
    –10 dBm max total

    Reference input

    10 MHz

  • Aero CUS Data Sheet

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