Home' RTCA Documents for Review : DO-343B Contents 48
© RTCA, 2018
3.3.6 Prioritized IP
The SBB Prioritized IP service is virtually unchanged from the SBB 3G bearer service.
Key differences are:
1. The AES signals the required priority of a PDP context within the PDP context
set up command using the AT commands (the interface is defined in Appendix
5 to ARINC Characteristic 781).
2. The RNS provides priority on the air interface as described in section 3.4.9.
3. There is a private data pipe from the CNP to the GGSN.
In addition the following controls are provided to ensure that only bona fide users can
access priority capability.
1. In an AES, certain physical pins on the ARINC 600 connector are allocated to
priority service. The priority field referred above will only be passed on to the
air interface if it is received on a priority interface (e.g ‘cockpit Ethernet port’).
This is an extension of concepts already embodied in ARINC 741 equipment
for both voice and data Classic Aero service.
2. The prioritized IP data service is only allowed with SIMs provisioned for that
level of priority.
This subsection provides key information on the bespoke air interface known as IAI-2
(Inmarsat Air Interface 2).
3.4.1 Frequency Range
The forward (to aircraft) user link operates in the frequency range 1518-1559MHz.
Some AES and the I4 satellites only support a frequency range of 1525-1559MHz.
Alphasat supports the full frequency range.
The return (from aircraft) user link operates in the frequency range 1626.5-1660.5 and
1668-1675MHz. Some AES and the I4 satellites only support a frequency range of
1626.5-1660.5MHz. Alphasat supports the full frequency range.
Note: ICAO WG-F agreed in March 2013 that use of the Extended L Band (1518-1525
MHz and 1668-1675 MHz) for AMS(R)S operations would require additional study.
Right Hand Circular Polarization is used for both the forward (to aircraft) and return
(from aircraft) user links.
The SBB air interface supports a matrix of carriers and bursts of different modulation
type, symbol rate and code rate. Inmarsat configuration settings and the RAN
determine which bearers and code rate are used on a dynamic basis. In SBB
terminology carriers and bursts are known collectively as bearers.
SBB RF bearers in the forward (to aircraft) direction are a continuous transmission of
time division multiplexed (TDM) carriers shared between a number of users. RF
bearers in the return direction (from aircraft) are based on time division multiple access
(TDMA) between a number of users.
Power efficient QPSK (Quadrature Phase Shift Keying) and bandwidth efficient 16 and
64 QAM (Quadrature Amplitude Modulation) modulation is used, together with a
number of frame burst durations. Symbol rates between 8.4 kilo symbols per second
(kSym/s) and 168 kSym/s are used with each symbol rate being a fraction or multiple
of 33.6 kSym/s. Variable coding rate is used with rates corresponding to 1 dB changes
in C/No. In the main the bearers operate at constant power and as the C/No varies the
coding rate (and hence the user data rate) is adjusted accordingly. Bearers use Raised
Root Cosine (RRC) filtering with roll-off of α=0.13 for T539 and T2.5 bearers and α=0.25
for other bearers. Channel spacing for the 151.2 and 168 kSym/s bearers is 200 kHz.
Other bearers are spaced at fractions of 200 kHz.
The forward and return bearer types are shown in Table 3-5.
15 T5 and T2.5 are bearers with symbol rate of 5 and 2.5 times 33.5kSym/s.
Links Archive Navigation Previous Page Next Page