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 USES0–30 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 km0.3–3 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 equipments 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.
CCIRThe 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 GHz2. Narrowband Long-haul system -2 GHz3. 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 Frequency band chls. Small capacity 0.704 10 658–712 MHz (UHF) Small capacity 2.048 30 400 MHz band (UHF) 520–585 MHz (UHF) Small capacity 8.448 120 622–712 MHz (UHF) Small capacity 8.448 120 2 GHz band (M/W)(2.0–2.3 GHz) 7 GHz band (M/W)Medium capacity 34.368 480 (7.425–7.725 GHz) 13 GHz band (M/W)Medium capacity 34.368 480 [12.75–13.25 GHz band (M/W)] 4 GHz band (M/W) High capacity 139.264 1920 (3.3–3.8 and 3.8–4.2 GHz) 6 GHz band (M/W) High capacity 139.264 1920 (5.925–6.425 GHz : Lower) (6.430–7.110 GHz : Upper) 11 GHz band (M/W) High capacity 139.264 1920 (10.7–11.7 GHz)
RF channel arrangementLet 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 nWhere 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.
CCIRFrequency bandThe CCIR Upper 6 GHz frequency plan as shown in Fig.2(a) and 2(b) is employed in these systems. fo : 6770 MHzLower half of band : fn = fo–350+40nUpper 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.
MICROWAVE ROUTEBRANCHING RF IF RF RF IF RF BRANCHING RF RF IF TERMINAL IF REPEATER REPEATERMOD STATION DEMOD TERMINALBB IN BB OUT
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.
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.
Orbits of Different SatellitesLEO (Iridium) GEO (Inmarsat) Earth 10,000 km MEO (Intermediate Circular Orbit ) 15,000 kmMEO 35,768 km Not drawn to scale
SKG Satellite categories categories Orbit speed Rotation time Application Low Earth 0 - 2,000 km 17,000 90 minutes Mobile Satellite Services (MSS) Orbit (LEO) miles per Globalstar, Iridium satellite hour 27,400 k m/h Medium 2,000 - Global Positioning System Earth Orbit 35,760km T=201 (GPS) 20,200 km (MEO) R=11400 km minutes Geosynchron 35,786 km 23 hrs, 56 Telecommunications ous Orbit (22,240 mins, 4.09 Radio and Television (GEO) miles). secs 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 GEO systems are less complicated to maintain because fixed location requires relatively little tracking capability at ground.High orbital altitude allows Single satellite GEOs to remain in orbit longer than systems gives more than operating closer to earth. 40% Coverage.
Hardware: ground segment• Antenna• Receiving/transmitting chain• Types of connection• Link budgetAugust 26, 2001 31
CHOICE OF FREQUENCYBand DOWN LINK UP LINK BANDWIDTH“C” BAND 5.925 to 3.7 to 4.2 GHz 500 MHz 6.425GHzExtended “C” 5.85 to 5.9 GHz 3.4 to 3.7GHzBand 6.425 to 4.5 to 4.8 GHz 7.025GHz“Ku” Band 12.75 to 13.25 500 MHz GHz 14.00 to 14.5 10.7 to 11.7 GHz 500 MHz GHz“Ka” Band 27.00 to 30.00 18.10 to GHz 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 ChannelsUPLINK FREQUENCY BAND 5925-6425 MHz.Receive by satellite and modulated with 2225 MHz before retransmitted to earth station. DOWNLINK FREQUENCY BAND 3700-4200 MHz. BEACON SIGNAL IN THE 4 MHZ DOWNLINK FREQUENCY BAND 36 MHZ 1 2 3 4 5 6 7 8 9 10 11 12 500 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 aGEO 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 usinga single satellite. Satellite media is the only alternative forremote areas inaccessible through terrestrial routes.
•Suitable for both Digital and AnalogTransmissionSame satellite can be used for both digital andanalog communication links. Satellite istransparent to the type of service beingprovided.•High QualitySatellite links are designed for high quality ofperformance. The links are free fromatmospheric disturbances and fading. As onlyone repeater is involved, the reliability is veryhigh.•FlexibilityA satellite can be accessed from any point onthe earth from where it is visible. The earthstations can be relocated and reconfiguredproviding complete flexibility of operationand utilisation of the satellite capacity.•Quick Provision of ServicesCompared to the conventional links, earthstations can be installed in much shorterperiod and, therefore, services can becomeavailable 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