APPLICATIONS:

• Fixed Radio Communication Services.

• Fixed Satellite Services.

• Mobile Services.

• Broadcasting Services.

• Radio Navigation Services.

• Meteorological Services.

• Radio Astronomy Services.

• M/W systems used to provide communication on major trunk routes with high traffic density and serving long distances are classified as long haul M/W systems. 2, 4, and 6 GHz systems are long haul systems.

• Systems used to provide communication over short distances for trunk routes with light traffic density are classified as short haul system. 7 and 11 GHz systems are short haul systems.

RANGE NAME WAVELENGTH USES

0–30 KHz V.L.F. Up to 10 km. Used for long communication. Has limited

information. Bandwidth require very high

power.

30–300 KHz L.F. 10 km to 1 km

0.3–3 MHz M.F. 1 km to 100 m Radio Broadcast, Marine Power in KW,

ground wave propagation, i.e. follows the

curvature of the Earth.

3–30 MHz H.F. 100 m to 10 m Long haul point to point communication.

Propagation is by one or more reflections

from ionosphere layers and so subject to

variations.

30–300 MHz V.H.F. 10 m to 1 m Line of sight, Tropo-scatter

communication.

0.3–3 GHz U.H.F. 1 m to 10 cm. –––––– do ––––––

3–30 GHz S.H.F. 10 cm to 1 cm. Line of sight, terrestrial M/W and Satellite

communication.

30–300 GHz E.H.F. 1 cm to 1 mm. Experimental.

WPC • In this regard (in the national context) the wireless

planning and co–ordination wing (WPC) of the ministry of communication has allotted m/w frequencies spectrum, on the basis of various wireless users classified as general users and major users. Wireless users who are permitted to plan their services and take action for the development of the required equipment's are major users. BSNL has been nominated as a major wireless user by the WPC in 1981 in the following sub base band of the M/W spectrum for fixed radio communication. Microwave Spectrum Available for BSNL.

CCIR

The CCIR recommends 2 GHz band for 60,120, 300 and 600-1800 channel systems, 6 GHz for 1800 channel system upper 6 GHz band for 960 to 2700 channel system, and 7 GHz band for 60, 120 and 300 channel systems. Taking into account various factors the following gives some of the trends of frequency usage in India.

1. Long-haul wideband systems-4 GHz and 6 GHz 2. Narrowband Long-haul system -2 GHz 3. Narrowband short haul systems -7 GHz and 13 GHz. 4. Wideband short haul systems -11 and 12 GHz. Besides this digital microwave systems are proposed to be used

in the band 2GHz and 13 GHz which is also recommended for digital transmission by CCIR.

Nomenclature Bit rate No. of

chls.

Frequency band

Small capacity 0.704 10 658–712 MHz (UHF)

Small capacity 2.048 30 400 MHz band (UHF)

Small capacity 8.448 120 520–585 MHz (UHF)

622–712 MHz (UHF)

Small capacity 8.448 120 2 GHz band (M/W)(2.0–2.3 GHz)

Medium capacity 34.368 480 7 GHz band (M/W)

(7.425–7.725 GHz)

Medium capacity 34.368 480 13 GHz band (M/W)

[12.75–13.25 GHz band (M/W)]

High capacity 139.264 1920 4 GHz band (M/W)

(3.3–3.8 and 3.8–4.2 GHz)

High capacity 139.264 1920

6 GHz band (M/W)

(5.925–6.425 GHz : Lower)

(6.430–7.110 GHz : Upper)

High capacity 139.264 1920 11 GHz band (M/W)

(10.7–11.7 GHz)

RF channel arrangement

Let us look at a typical RF channel arrangement for a 6 GHz band 5925 to 6425 MHz). This band of 500 MHz is designed for 1800 channel capacity system with 8 pairs of frequencies. The individual channel frequencies are given by

Fn = Fc - 259.45 + 29.65 n

Fn' = Fc-7.41 + 29.65 n

Where Fo = Centre freq. of band= 6175 MHz.

Fn and Fn’ are centre frequencies of nth channel in lower and upper half .

Digital system route

The RF channel occupy 6430–

7110 MHz, accommodating 8

both way RF channels with 40

MHz spacing between adjacent

RF channels.

The radio frequency channels

assignment for Bombay Panjim

route is shown in Fig.3 as an

example. Polarization employed

(V/H) at various stations is also

depicted in the figure.

Lower half band Upper half band

RF CH No. Radio frequency (MHz) RF CH No. Radiofrequency (MHz)

1 6460 1' 6800

2 6500 2' 6840

3 6540 3' 6880

4 6580 4' 6920

5 6620 5' 6960

6 6660 6' 7000

7 6700 7' 7040

8 6740 8' 7080

CCIR Frequency band

The CCIR Upper 6 GHz frequency plan as shown in Fig.2(a) and 2(b) is employed in these systems.

fo : 6770 MHz

Lower half of band : fn = fo–350+40n

Upper half of band : fn' = fo–10+40n

n = 1, 2, 3, 4, 5, 6, 7 or 8

SACFA

• The main objective of the function of the SACFA Board is to investigate the interference possibilities, etc. and allot the frequency and spectrum for new routes. All types of Microwave routes should be cleared by this body as far as the frequency to be used, the location, the height of tower are concerned.

A Microwave Terminal

BLOCK DIAGRAM

MICROWAVE ROUTE

MOD

BB IN

IF

RF

BRANCHING RF IF RF RF IF RF BRANCHING

RF

IF

DEMOD

BB OUT

TERMINAL

STATION REPEATER REPEATER

TERMINAL

Digital System

• 1 x 10–7 BER for more than 1% of any month.

• 1 x 10–3 BER for more than 0.5% of any month.

• HRDP (2500 kms), but greater than 280 kms

• 1 x 10–7 BER for more than (L/2500) x 1% of any month.

• 1 x 10–3 BER for more than (L/2500) x 0.05% of any month

Link is less than 250 kms

• 1 x 10–7 BER for more than (280/2500) x 1% of any month. • 1 x 10–3 BER for more than (280/2500) x 0.05% of any

month. • This takes into account fading, interference and all other

sources of performance degradation. It does not include BER greater than 1 x 10–3 for periods exceeding 10 consecutive seconds. This condition is included in the availability criterion. The high BERs caused by switching operations are included in the above criterion, but not the ones caused by scheduled switching for maintenance). Availability criterion is 1 x 10–3 BER (measured for 10s time interval) not exceeding 0.3% of a year.

Switching Criteria and Switching Priority

• The switching is initiated by the detection of transmission quality degradation or manual control.

• The automatic switching criteria are as follows :

• Bit error rate degradation.

1. Initiation : BER = 1 x 10–4 (1 x 10–4 to 1 x 10–9)

2. Restoration : BER = 1 x 10–6 (1 x 10–4 to 1 x 10–9)

3. Threshold setting can be made on site.

• Loss of frame alignment.

• Mismatch of route identification.

• Loss of data stream.

Switching

• Case A • Forced switching • Automatic switching • Manual switching • Occasional switching • Case B • Forced switching • Automatic switching • Manual switching • Occasional switching

SATELLITE COMMUNICATION

Satellite

Satellites

• The basic component of a communications satellite is a receiver-transmitter combination called a transponder.

• A satellite stays in orbit because the gravitational pull of the earth is balanced by the centripetal force of the revolving satellite.

Satellite orbits about the earth are either circular or elliptical.

Satellite orbits SKG

Satellite orbit altitudes SKG

23 Hrs 56 Min 4 Sec

2000

Orbits of Different Satellites

Earth

10,000 km

35,768 km

15,000 km

LEO (Iridium) GEO (Inmarsat)

MEO

MEO (Intermediate

Circular Orbit )

Not drawn to scale

SKG Satellite categories categories Orbit speed Rotation time Application

Low Earth Orbit (LEO)

0 - 2,000 km 17,000 miles per hour 27,400 km/h

90 minutes Mobile Satellite Services (MSS) Globalstar, Iridium satellite

Medium Earth Orbit (MEO)

2,000 -35,760km R=11400 km

T=201 minutes

Global Positioning System (GPS) 20,200 km

Geosynchronous Orbit (GEO)

35,786 km (22,240 miles).

23 hrs, 56 mins, 4.09 secs

Telecommunications Radio and Television Boradcasting Meteorology

Highly Elliptical Orbit (HEO)

So, an object placed at the orbit approx. 36 000 km above the

equator will be seen at the same position in the sky from Earth.

Important Satellite Classifications

• GEO (Geostationary Earth Orbit) satellites orbit about 36,000 km above Earth’s surface.

• LEO (Low Earth Orbit) satellites are about 500-2500 km above earth’s surface.

• MEO (Medium EO) satellites are about 6000-20,000 km above earth’s surface.

• There are also HEO (Highly Elliptical Orbit) satellites.

Satellites in geosynchronous orbit

Single satellite

gives more than

40% Coverage.

GEO systems are less

complicated to maintain

because fixed location

requires relatively little

tracking capability at

ground.

High orbital altitude allows

GEOs to remain in orbit

longer than systems

operating closer to earth.

Hardware: ground segment

• Antenna

• Receiving/transmitting chain

• Types of connection

• Link budget

August 26, 2001 31

CHOICE OF FREQUENCY Band DOWN LINK UP LINK BANDWIDTH

“C” BAND 5.925 to 6.425GHz

3.7 to 4.2 GHz 500 MHz

Extended “C” Band

5.85 to 5.9 GHz 3.4 to 3.7GHz

6.425 to 7.025GHz

4.5 to 4.8 GHz

“Ku” Band 12.75 to 13.25 GHz

500 MHz

14.00 to 14.5 GHz

10.7 to 11.7 GHz 500 MHz

“Ka” Band 27.00 to 30.00 GHz

18.10 to 20.20GHz

Frequency Bands For Satellite Communication

• C- Band :

• U/L : 5.925 – 6.425 GHz.

• D/L : 3.7 – 4.2 G Hz.

• Total 500 M Hz BW.

• Extended C- Band :

• U/L : 6.725 – 7.025 GHz.

• D/L : 4.5 – 4.8 G Hz.

• Additional 300 MHz BW.

• Ku band :

• U/L : 14.0 - 14.5 G Hz.

• D/L : 10.95 – 11.2 and 11.45 - 11.7 GHz.

• A total of 500 MHz BW in Ku band.

RF Channels

1 2 3 4 5 6 7 8 9 10 11 12

36 MHZ

4 MHZ BEACON SIGNAL IN THE

DOWNLINK FREQUENCY BAND

UPLINK FREQUENCY BAND 5925-6425 MHz.

Receive by satellite and modulated with 2225 MHz

before retransmitted to earth station.

DOWNLINK FREQUENCY BAND 3700-4200

MHz.

500 MHz

Transponder

• Some satellites have (hundreds of) transponders for communication purposes.

• A transponder

1) receives transmissions from earth (uplink);

2) changes signal frequency;

3) amplifies the signal; and

4) transmits the signal to earth (downlink).

Satellite Subsystems

• The main subsystems in a satellite are

– communications;

– power;

– telemetry; tracking, and control (TTC);

– propulsion;

– attitude stabilization; and

– antenna subsystems.

• Power subsystem consists of solar panels, batteries, dc-to-dc converters, and regulators. Solar panels convert sunlight into power to operate all satellite electronics and to charge batteries (used when sunlight is blocked).

Satellite Subsystems (Cont’d)

• The TTC subsystem contains a receiver that picks up commands from a ground station and translates them into control signals that initiate some action on board.

• The telemetry system monitors physical conditions within the satellites and converts them into electrical signals that are transmitted back to earth.

Ground Stations: The Other End

• Satellites in space communicate (transmit/receive radio waves) with ground stations.

• Ground stations consist of subsystems:

– transmit/receive;

– Power;

– Antenna;

– TTC; and

– ground control equipment (GCE).

Satellite Dish • Ground stations feature large parabolic dish

antennas with high gain and directivity for receiving the weak satellite signal.

Satellite signals

The larger the dish is

the higher the received

signal power.

Remote Communication is economic reliable through a

GEO stationary satellite which act as a repeater.

Using inexpensive receive-only satellite dishes, the

university stores the updated material on a server inside

the LAN…

Internet LAN

Wide coverage:-Area irrespective of intervening terrain using

a single satellite. Satellite media is the only alternative for

remote areas inaccessible through terrestrial routes.

REMOTE

COMMUNICATION

•Suitable for both Digital and Analog

Transmission

Same satellite can be used for both digital and

analog communication links. Satellite is

transparent to the type of service being

provided.

•High Quality

Satellite links are designed for high quality of

performance. The links are free from

atmospheric disturbances and fading. As only

one repeater is involved, the reliability is very

high.

•Flexibility

A satellite can be accessed from any point on

the earth from where it is visible. The earth

stations can be relocated and reconfigured

providing complete flexibility of operation

and utilisation of the satellite capacity.

•Quick Provision of Services

Compared to the conventional links, earth

stations can be installed in much shorter

period and, therefore, services can become

available faster.

• Mobile and Emergency Communication

An earth station can be mounted on a vehicle to provide mobile communication services. Using small airlift able earth station terminals, telecommunication services can be extended to any location in emergency.

August 26, 2001 45