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Rovers on a planet can communicate to the orbiters and also with other
surface-based vehicles such as the mother ship. With the growing number
of Mars Rovers sent from Mars, the communication between rovers, landers,
orbiters and other vehicle on Mars become important because they can act
as a network of rovers analysing a region of land. Likewise this system
can be employed into our rover system whereby the small rovers and the
mother ship can communicate with one another without the interference
by Earth.
An omni-directional RF system can transmit and receive data from the
rover to and from fast-moving orbiters. This is useful as data can be
sent back to Earth as a much higher rate using the backbone network on
the orbiters and higher volume of information can be transmitted from
Earth to Mars or vice-versa. The radio frequency used will most likely
be Ultra High Frequency (UHF), this will travel at a relatively short
distance and can transmit data through a surface-surface communication
network. As well as an omni-directional antenna, a directional antenna
system can act as a backup link back to Earth. This can be used for sending
out relatively low volume signal such as the status of the rover. Further,
the user on Earth can also take control of the rover itself without going
through the orbiters if there are some faults with the rovers. For proximate
networks between rovers, small volume, power and mass transmitter and
receiver can be used. The X-band, Ka-band and UHF frequencies are often
used for this application. On the orbiter, a focus antenna utilises a
Ka-band (20GHz to 30 GHz) to transmit information between Mars and Earth.
This is ideal for sending relatively large files which are 100kb to a
few megabytes in size. A SiGe RF solid state power amplifier which uses
8.4GHz transfer information between the orbiters and surface links.
CCSDS also formulated a protocol for proximate network within deep space.
This is known as CCSDS Proximity-1 Link Layer Protocol. It is specially
designed for deep-space surface-orbiter links. This protocol allows orbiters
to access more than 1 surface element at a time. This is done by moving
each session to a certain channel.
Concentrating back on the Mars surface Networks, Rovers can transmit
data at a lower data rate than the backbone network, typically at around
a few kbps. With more and more rovers on Mars, the network of rovers can
act as a team of rovers exploring Mars. A rover with weak reception can
use the network as a relay to nearby more capable data gathers to send
the data back to Earth. Many applications can be supported by having a
network of rovers. Sensor webs can provide an analysis of its surrounding
by sensors. Using neighbouring sensors, it can combine the signal to give
a higher SNR. Furthermore, by some local analysis, the rovers can collect
a lot of information about the area and a localise event.
On top of all these, rovers can support interaction between rovers by
stationary relay nodes. This is when the rover drops off a stationary
node as it moves off. By combining all of these communication technologies
for proximity networks, the rovers can engage in team-oriented operations.
Therefore, in designing these systems, they need to be self-organising
and autonomous which are robust to faults. In the future, Rovers will
be able to use low power infered or Bluetooth and IEEE 802.11 with some
modifications to accommodate network dynamics such as faults and ad hac
style handoff for mobile nodes.
Therefore, with these technologies, planetary rovers will later be able
to work in teams and perform much more powerful expedition and give way
to a possible human exploration in the near future.
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