FINAL REPORT - Stakeholders - Ofcom

Live TV content and pushed web page content (most popular web pages) are multicast to
aircraft. The web content is cached in an onboard server for rapid availability to
passengers.
The satellite links will only be used to convey content that is not available from the
onboard server. All e-mail will be received and transmitted in real-time over the satellite
links.
5.9.2.4 Downlink
As on the uplink, the system uses a direct sequence spread spectrum (DSSS). The
system downlink uses demand assigned multiple access (DAMA) to adjust the transmit
data rate from the aircraft (16 Kbps to 1.5 Mbps) to match the aircraft demand.
Figure 5-4: Data downlink via transponders (carriers) in Boeing Connexion system
The number of DSSS chips per bit is adjusted to maintain a nearly constant chipping rate
of 90% of the transponder bandwidth. Multiple aircraft simultaneously access each return
link transponder using different pseudo noise (PN) code phases (similar to CDMA). The
system experiences some loss of performance (about 1 dB) due to self-interference from
asynchronous aircraft transmissions.
Airborne antenna design
Boeing will initially offer airlines an electronically scanned phased array antenna that
mounts flat on the crown of the aircraft. The antennas cause some additional
aerodynamic drag to the aircraft.
The antennas will be mounted on top of the aircraft fuselage and separated from each
other by approximately 1.25 meters to prevent self-interference. Prototype transmit
antennas are currently being fabricated by Boeing, and receive antennas have been flight
tested for a number of years.
Both phased array antennas can be electronically scanned to about 70 °. This scan angle
performance is sufficient for initial operation but is inadequate for busy higher latitude air
routes in North America, Europe and the North Atlantic.
A different antenna design that can scan down to the horizon is required for operation at
latitudes above 60°. Such antennas typically protrude more above the top of the aircraft
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