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1.
Radio Communication
Service
Frequency Band (uplink /
downlink) GHz
Terminology
Fixed Satellite Service
(FSS)
6 / 4 C band
8 / 7 X band14 / 11 – 12 Ku band
30 / 20 Ka band
50 / 40 V band
Mobile Satellite Service
(MSS)
1.6 / 1.5 L band
30 / 20 Ka band
Broadcasting Satellite
Service (BSS)
2 / 2.2 S band
12 Ku band
2.6 / 2.5 S band
FSS
Above 30 GHz is for technology development
20 – 30 GHz has little interference, large bandwidth
12 – 14 GHz for Satellite broadcasting for MEASAT 3a
7 – 8 GHz reserved by agreement between administrators or governmental use
4 – 6 GHz TV broadcasting service such as ASTRO
The services implement Point to Point communication and network via
satellite between fixed Stations and utilize C-Band and lower power portion of Ku-
Band spectrum. Very Small Aperture Terminal (VSAT) is an application for fixed
Satellite Services. VSAT services provide wide area coverage, offers borderless
communication within the satellite coverage area and reachable to remote areas with
digital transmission such as oil rig far out at sea and a station in a dense tropical
jungle. VSATs are most commonly used to transmit narrowband data (point of sale
transactions such as credit card), or broadband data (for the provision of Satellite
Internet access to remote locations, VoIP or video).
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MSS
The Services implement Point to Point communication and network via
satellite between mobile stations. Services are available to the maritime users and
land users in any locations that require long distance portable telephony, fast and
instantaneous communications setup. Satellite phone is a type of mobile phone that
connects to orbiting satellites instead of terrestrial cell sites. Depending on the
architecture of a particular system, coverage may include the entire Earth, or only
specific regions.
The mobile satellite service makes use of the following bands:
a. VHF (very high frequency, 137 – 138MHz downlink and 148 – 150MHz uplink)
and UHF (ultra high frequency, 400 – 401MHz downlink and 454 – 460MHz
uplink). These bands are for non-geostationary systems only.
b. About 1.6GHz for uplinks and 1.5GHz for downlinks, mostly used by
geostationary systems such as INMARSAT; and 1610 – 1626.5MHz for the
uplink of non-geostationary systems such as GLOBALSTAR.
c. About 2.2GHz for downlinks and 2GHz for uplinks for the satellite component
of IMT2000 (International Mobile Telecommunications).d. About 2.6GHz for uplinks and 2.5GHz for downlinks.
e. Frequency bands have also been allocated at higher frequencies such as Ka
band.
BSS
Broadcasting Satellite system is the services for distribution of video and
audio streams through satellite. Usually utilize Ku-Band and propagate circular
polarization wave pattern; however there is a trend for Ka-Band for broadband
application. Astro is a subscription-based direct broadcast satellite (DBS) or direct-to-
home satellite television and radio service initially in Malaysia and is broadcast high-
power Ku-band transmissions utilizing the transponders of the MEASAT satellite
system.
The broadcasting satellite service makes use of downlinks at about 12 GHz.The uplink is operated in the FSS bands and is called a feeder link.
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Typically, there are four types of base station as follows.
i. Macrocell
- Macrocell provides radio coverage served by a power cellular base
station. It is suitable to be deployed in location where no existing
coverage. The coverage is approximately 6km while the area is 80km2.
- The antennas for macrocells are mounted on ground-based masts,
rooftops and other existing structures, at a height that provides a clear
view over the surrounding buildings and terrain. Macrocell base
stations have power outputs of typically 10 watts.
ii. Microcell
- To improve signal strength or increase capacity in a smaller area then a
microcell may be used. This has a range of approximately 300 meters
in the best conditions.
- Several microcell base stations can also be used as an alternative to a
single macrocell. Microcells can also be used temporarily at big public
events where the existing local system is insufficient.
iii. Picocell
-
Picocells are used in places like airports, offices or shopping centreswhere call numbers can be very high. They have a range of somewhere
between 50 and 100 meters.
iv. Femtocell
- Femtocell has the least area of coverage which is normally
implemented for home or small office. The range of coverage is 10
meters.
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2. i.
Geosynchronous Orbit
A geosynchronous orbit is also known as geostationary orbits, because
satellites in these orbits circle the Earth at the same rate as the Earth spins. The
satellite takes 23 hours, 56 minutes, and 4.09 seconds to make one full revolution at
approximately 35,790 km above the Earth. The satellites are located near the equator
since at this latitude, there is a constant force of gravity from all directions.
Geosynchronous orbits allow the satellite to observe almost a full hemisphere
of the Earth. These satellites are used to study large scale phenomenon such as
hurricanes, or cyclones. Since these satellites are very far away, they have poor
resolution. The disadvantage is that these satellites have trouble monitoring activities
near the poles.
LEO and MEO Orbit
As technology has progressed, low-altitude earth orbits (LEOs; less than 600
mi or 1000 km) and medium-altitude earth orbits (MEOs; less than 8000 mi or 14,400
km) have acquired some distinct advantages for mobile services. The lower-altitude
satellites have much shorter paths from base stations and mobile earth terminals as
compared with satellites in geostationary orbit. Thus RF power requirements and path
delay are much smaller. The consequence is that the mobile earth terminals can use
low-gain antennas that need little or no tracking while still using low-power
transmitters and the system does not degrade from delay with multiple hops.
Molniya Orbits
Another orbit use in communication satellite is Molniya orbit which is highly
inclined to guarantee good elevation over selected positions during the northern
portion of the orbit. A satellite at the horizon has zero elevation and a satellite directly
overhead has elevation of 90 degrees. Furthermore, the Molniya orbit is designed so
that the satellite spends the great majority of its time over the far northern latitudes,
during which its ground footprint moves only slightly. Its period is half day, so that
the satellite is available for operation over the targeted region for nine hours every
revolution. Therefore, three Molniya satellites can provide uninterrupted coverage.
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ii.
F = Gravitational Force
√
But,
√
√
Where
r is the radius from center of earth,
m is the mass of earth, 5.97 x 1024
G is gravitational constant, 6.67 x 10-11
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iii.
using the equation derived in ii,
√
√
r = 42,227 km
h = r – radius of earth
h = r – 6378
h = 35,849 km
iv.
Apply the formula derived in ii,
Given h = 500 km
r = h + radius of earth
r = 500 km + 6378 km
= 6878 km
√
√
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Antenna Gain
To calculate Gtransmitter,
Gtransmitter = η (πD/λ 2)
For efficienct of 55%,
Gtransmitter (dBi) = 20 log (D/λ) + 7.3
Transmit Power
To calculate Ptransmit,
SNR = Preceiver – Pnoise
but,
Preceiver = Ptransmit + Gtransmitter + Greceiver – Losses
Therefore,
SNR = Preceiver – Pnoise
Ptransmit = SNR – Gtransmitter – Greceiver + Losses + Pnoise
but
Pnoise = 10 log (K Tsystem B) where Tsystem = Treceiver + Tantenna
Therefore,
Ptransmit = SNR – Gtransmitter – Greceiver + Losses + 10 log (K Tsystem B)
Free Space Loss
LFS = 20 log [4πR/λ]
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3. Given that, SNR = 10 dB, E= 15°, f=10GHz, Gr=30dBi
λ = c/f, = 3mm
Assumption:
a. Diammeter of antenna is 2m
b. Efficiency of antenna is 55%
Gtransmitter (dBi) = 20 log (D/λ) + 7.3
= 20 log (2/3mm) + 7.3
= 43.78 dBi
Referring to table 30, at 10GHz,
Tantenna = 85K, Treceiver = 75K
Tsystem = Tantenna + Treceiver
Tsystem = 160K
Pnoise = 10 log (K Tsystem B)
Pnoise = – 106.56 dBW
LFS = 20 log [4πR/λ]
Since the height of the satellite from the earth surface is 35849 km,
LFS = 20 log [4π(35849km)/3mm]
= 223.53 dB
Accoding to Figure 5.30,
The Elevation of 15° produces atmospheric loss of 0.2 dB
Ptransmit = SNR – Gtransmitter – Greceiver + Losses + 10 log (K Tsystem B)
= 10 – 43.78 – 30 + 223.53 + 0.2 – 106.56
= 53.39 dBW
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4. R=500km, f=1.5GHz, E=60°, G=3dBi
λ = c/f, = 200mm
Assumption:
a. Diammeter of antenna is 2m
b. Efficiency of antenna is 55%
Gtransmitter (dBi) = 20 log (D/λ) + 7.3
= 20 log (2/200mm) + 7.3
= 27.30 dBi
Referring to table 30, at 1.5 GHz,
Tantenna = 35K, Treceiver = 35K
Tsystem = Tantenna + Treceiver
Tsystem = 70K
Pnoise = 10 log (K Tsystem B)
Pnoise = 10 log [K (70) (1.5GHz)]
Pnoise = – 118.39 dBW
LFS = 20 log [4πR/λ]
Since the height of the satellite from the earth surface is 500 km,
LFS = 20 log [4π(500km)/200mm]
= 149.94 dB
Since the frequency is less than 10 GHz, the atmospheric attenuation is negligible.
Ptransmit = SNR – Gtransmitter – Greceiver + Losses + 10 log (K Tsystem B)
= 10 – 27.30 – 3 + 149.94 – 118.39
= 11.25 dBW
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http://www1.orange.co.uk/about/phone_masts/base_station.html
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