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Tech CornerT
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Maximizing Ka-Band Network Uptime by Ground Station Diversity
New growth market applications such as car-
rier grade services, enterprise networks and
mobile backhaul can require significantly
higher network uptime and availability than
traditional “consumer grade” broadband services.
Traditionally, the bulk of fixed satellite communica-
tions have used C-band and Ku-band transmission
frequencies. Today, C/Ku-band orbital positions and
frequencies have become highly congested, creating
demand for use of additional frequency bands includ-
ing Ka-band. Ka-band systems can also offer several
advantages. The available frequency range in the Ka-
band is about 4 times larger than that of traditional-
ly C- and Ku-bands used for Fixed Satellite Services
(FSS). Furthermore, Ka-band transmission is typically
employed with the usage of multiple spot beams, so-
called ‘frequency reuse’ operation. This allows for the
transmission of different signals at the same frequency,
simultaneously to several geographic areas. The high
transmission frequencies of Ka-band allow for highly
focused spot beams and smaller antennas leading to
economically efficient solutions at high data rates. Con-
sequently, state-of-the-art High Throughput Satellites
(HTS) operated in Ka-band can provide data capacities
exceeding 100GBit/s per single satellite, many times
that of conventional satellite systems.
Despite all these advantages, satellite systems oper-
ated in the Ka-band face some challenges. Ka-band
transmission is severely degraded by adverse weather
conditions. In particular additional atmospheric losses
due to rainfall can exceed 50dB for Ka-band satel-
lite transmission systems. With such high atmospheric
losses, conventional fade margin approaches as adap-
tive-waveform and coding/modulation techniques or
adaptive-power control techniques do not always com-
pensate sufficiently for the losses, when it comes to
meeting the needs of high availability services.
Michael Waldow
is business develop-
ment manager DAS -
Systems Engineering
at DEV Systemtech-
nik GmbH & Co. KG,
a Quintech Electron-
ics & Communications
Company.
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Ka-band Site Diversity
Since transmission quality on Ka-band fre-
quencies is heavily dependent on atmospheric
losses dominated by rainfall, suitable system
configurations need to be carefully designed.
Within the ITU rain zone model the world is
mapped into different “rain regions”, in which
the rain rates do not exceed a specific value
during the year. For instance a typical rain
zone for Central Europe would be categorized
as rain “zone F”, meaning that the average
rain rate in this region is below 25mm/h for
0.01percent of the time of a year, whereas
in a tropical rain region, e.g. zone “P”, the
average rain rate does not exceed 145mm/h
for 0.01 percent of the time. Beside other
factors, for example, frequency, earth sta-
tion location, and elevation angle, link losses
scale with these rain rates for Ka-band sat-
ellite systems. Attenuation caused by heavy
rainfall (>70mm/h) can exceed values of 50dB.
Consequently, for 99.99 percent availability,
the satellite system needs to be able to pro-
vide corresponding fade margins in terms of
appropriate system configuration.
To achieve the highest fade margins, and
support higher uptime Ka-band services, Site
Diversity configurations can be used. Figure 1
shows the schematic view of a Ka-band Site
16
at ptc.org/ptc16
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is transmitted and converted by main and
redundant transmitter and receiver mod-
ules. In the case of a malfunction, or loss
of a main transmitter or main receiver mod-
ule, the redundancy switch at the receiver
side switches over to the backup equipment
ensuring a signal transmission with highest
possible quality and uptime.
Conclusion
With a Ka-band Site Diversity configuration,
the signal transmission is redirected from
the Main Site to a Diverse Site in the case of
adverse weather conditions. Site Diversity
configurations, can employ DWDM RF-over-
Figure 3
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Fiber transmission systems and redundancy
switching units, and provide and excellent
way to ensure maximum Ka-band system
reliability and availability, despite the high
level of rain attenuation at Ka-band.
The new RF-over-fiber technology, com-
bined with wider availabil ity of f iber l ines
today allows diverse antenna sites to have
direct RF connectivity to a single data cen-
ter, without installation of all the based band
data center equipment at each antenna site.
This provides cost-savings, and operational
ease compared to the installation of com-
plete antenna or baseband traffic site redun-
dancy configurations. Ka-band networks
can achieve higher resiliency using RF-over-
fiber antenna diversity. If scaled across mul-
tiple gateway sites, this kind of solution can
increase overal l usable satel l i te network
capacity by allowing traffic be routed to less
satellite resource-hungry sites during rain.
This will help Ka-band systems maximize
their competitiveness and ability to address
a broader range of customer needs. VS
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