FINAL REPORT - Stakeholders - Ofcom

As the new satellite service will support civil aviation world-wide, ICAO SARPS will need
to be developed. It is anticipated that much of the existing AMSS SARPS could be
updated to include SDLS features.
In addition, MASPS and MOPS will need to be developed. A further step will require
standardisation in the avionics industry on equipment form, fit and function
characteristics; this is traditionally the role of the AEEC.
The GES operators will need a more detailed set of technical standards than is provided
in the ICAO SARPS. For the current AMSS this level of detail was contained in the
Inmarsat System Definition Manual (SDM). The SDM is used by GES and avionics
manufacturers to produce equipment. This same level of detail will be required with
SDLS.
The characteristics of SDLS are summarised in Table 5-7 below.
Parameter Value Notes
Service topology Uplink point-to-point,
Downlink point-to-point
ATN compliance Yes Additional specific service also provided.
Frequency band Satellite bands (L-band,
C-band, Ku-band)
RF Channels 867 kHz bandwidth
1545-1555 MHz for the downlink (from satellite to
AES)
1646.5-1656.5 MHz for the uplink (from AES to
satellite)
Modulation scheme QPSK Ground to air: Synchronous CDMA QPSK
Bit rate 6.8 kb/s (4.8 kb/s
vocoder) per channel
Air to ground: Quasi Synchronous CDMA QPSK
SDLS proposes to use a coding scheme using a
convolution code (rate 3/4 and K=5) and, with a
vocoder rate of 4.8 kbps rate (6.4 Kbps with error
protection) leads to a link rate of 6.8 kbps
including synchronisation overhead.
Channel access method CDMA Forward channels are operated as slotted CDMA
by each GES sending information requests to the
controlled AES. A forward channel is allocated to
one GES; this GES sends the information on a
slotted burst, which is received by all AESs. Only
the addressed AES recovers and processes the
message.
Return channels are operated either:
Asynchronously: For the Polling Service
(PS) services, a set of AESs share a CDMA
coded channel for the return link in a slotted
reservation scheme. Each AES has access to the
return channel in a predefined slot burst or frame
according to the message length which is
indicated by the GES in the signalling information
carried in the forward link. For other services, a
set of AESs uses the same CDMA channel using
slotted ALOHA.
Synchronously: A TDMA CDMA channel
is used.
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