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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