COBHAM Sailor 250 FleetBroadband, Training Manual, Page: 24 / 270

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1
Chapter 1
Inmarsat Network
Admission Control:
The RNC performs admission control when deciding whether to
allow a new connection onto a bearer control. If a connection can
be added without violating the quality of service of the existing
connections, it is permitted. If capacity is not available then the
RNC requests extra capacity from the GRM. If there is no extra
capacity then the connection must be rejected.
FleetBroadband Terminal reporting to RNC:
The FleetBroadband RRM centralises all resource handling
intelligence at the RNC. The FleetBroadband Terminals simply
follow the RNC’s instructions. The FleetBroadband Terminal RRM
is relatively simple and is primarily concerned with complying
with contention slot usage rules, measuring and reporting the
queue size of the data awaiting return transmission and making
and reporting link quality measurements of the received forward
direction bearer. The RNC instructs the FleetBroadband Terminal
how frequently it should make these measurements and takes all
the decisions on the basis of them.
Multiplexing:
The approach BGAN network used, uses to group traffic from
many FleetBroadband Terminals onto bearers, is complex. To
provide an overview of this mechanism we will discuss in basic
terms how capacity is allocated in the narrow beams since this
is where the user traffic is carried. In this section we discuss how
bearers are managed and how multiple users share bearers. As
we have described, narrow beams are illuminated with bearers
only when there is traffic to send or receive. When traffic increases
bearers are added to the beam. When traffic reduces, bearers
are removed. There is no pairing of forward and return bearers
– if there is more forward demand than return demand then more
forward bearers will be added to the beam.
Link Adaptation:
The BGAN network air interface uses link adaptation to increase the
capacity of BGAN bearers. Rather than fixing the data rates for all
FleetBroadband Terminals, link adaptation gives higher data rates
to those FleetBroadband Terminals with a better radio link. Thus
larger FleetBroadband Terminals and those with good pointing,
perhaps located in the centre of a beam can take advantage of
favourable link conditions to send or receive at a higher data rate.
The receiver (either the RNC or the FleetBroadband Terminal
depending on the direction of transmission) constantly measures
the received link quality and periodically reports this information
back to the sender. If the average link quality rises above the level
required to achieve a packet error rate of 0.1% (10-3), the sender
increases the transmission rate. If the average error rate falls
below 0.1% then the sender reduces the transmission rate. The
sender adjusts its transmission rate by selecting one of a range of
puncturing matrices to apply each turbo-coded block of data prior
to sending it.