May
2015
Oilfield Technology
|
11
such as the mast and funnel can block the antenna’s view to the
satellite. So a second antenna positioned on the other side or end
of the ship can take over connectivity duties if the first antenna is
‘blocked’ from the satellite. The dual antenna approach also works
when a vessel is operating in a congested area, or near oil platforms,
that may also block line of sight to the satellite.
The satellite services have full resilience coupled with the ability
to operate out of normal trading routes, as seismic operations do not
generally follow conventional maritime routes where VSAT coverage
is nearly always guaranteed. These operations include routes into
the polar region where Ku‑band is insufficient and a large antenna
(C‑band) is therefore required to stabilise the satellite link. The
Sealink VSAT allows for the highest quality broadband connectivity
and stability ensuring a reliable service.
However, regardless of the satellite band, VSAT coverage is
not 100% global when considering operations in the far North and
South, i.e. a vessel passing through the Northeast Passage around
the North Pole. Throughout this seismic passage, the vessel was
able to maintain its communications system up until the point
where the satellite could no longer be tracked. This was due to
the satellite going beyond the horizon. Foreseeing this obstacle,
Marlink had provided the vessel with the low‑orbit satellite system,
Iridium OpenPort, which allowed for continued communications
albeit on a lower bandwidth. So for certain kinds of vessel and
operation, a third, smaller L‑band antenna may be thrown into the
mix, to provide complete global coverage.
Dual networks
One of the biggest challenges in designing a fully redundant
network with two complete sets of hardware, is to ensure that the
back‑up system comes on line as quickly as possible should the
primary network have a problemmaintaining its connection. With
a configuration that uses a single router/switch, changing antennas
is automatic and almost instant. But when designing a new dual
redundant network for another offshore client, the challenge was to
switch between the separate networks quick enough. By employing
a MPLS protocol, which is a solution used for creating hybrid
networks combining different communication channels, switchover
was achieved quick enough to avoid significant disruptions in ship
operations.
This clients’ network became even more complex, with the
addition of a further two modems, operating on the single channel
per carrier (SCPC) dedicated capacity protocol. These were
introduced over the primary iDirect modems operating on the time
division multiple access (TDMA) shared capacity protocol to ready
the network for future temporary speed boosts that may be required
by clients. The solution can on request, handle bandwidths greater
than 15 Mbps, Marlink has however already provided temporary
bandwidth increases over 12 Mbps to other seismic vessels.
Futureservices
So far Marlink has deployed dual redundant network solutions
for three offshore vessel owners. The approach represents the
pinnacle in high bandwidth, reliable connectivity on board.
Compared to a traditional dual antenna solution that uses a single
router and switch, the addition of a complete second set of below
deck equipment (the on board network) is relatively inexpensive.
However, any extra expense can be justified by ship owners, as
offering full redundancy and stronger SLAs to clients is a more
attractive market proposition. Clients can be guaranteed more
uptime because if equipment fails, IP connectivity will simply
switch to the secondary network. There will be a loss of connectivity
counted in seconds, but once back online, the bandwidth and
functionality experienced before will be available. So intelligent
operations can continue as planned.
The dual antenna networks developed in the examples above
are based on C‑band and Ku‑band VSAT antennas and services,
with in some case, L‑band services to ensure connectivity, albeit
on lesser bandwidth) even outside of normal VSAT coverage. The
choice of services will expand over the next few years though, with
the introduction of high throughput satellite services, initially from
Inmarsat (Global Xpress) and Intelsat (Epic
NG
).
More satellite capacity, greater coverage and the potential for
even higher average connectivity speeds will support even greater
operational efficiency based on intelligent operations. So it is
expected that more ubiquitous VSAT coverage on traditional Ku‑ and
C‑band, and Ku‑ and Ka‑band HTS services will drive further the
development of smart software and hardware for E&P. The challenge
will be for service providers to combine all available services into
a transparent, technically feasible, cost-effective solution that
can offer the levels of reliability and redundancy that today’s and
tomorrow’s high‑end offshore satcom consumers require.
This integrated approach is already in place at Marlink,
supporting its pioneering dual antenna networks and dual
redundant solutions for offshore vessels. The company’s
satcom services are based on a multi‑network portfolio called
AuroraGlobal, developed by parent company Airbus Defence and
Space. AuroraGlobal offers services on all available commercial
maritime satcom bands and has already been prepared for
forthcoming HTS services. So come 2016, Marlink will be ready
to support its offshore shipowner partners when they look to
develop their already complex dual antenna networks further by
throwing HTS into the mix. The technicalities are challenging but
the experience of working with the best offshore shipowners to
create the most reliable on board networks will help bring HTS to
intelligent operations on the oilfield.
Figure 3.
Dual antennaapproach.
