Degree Thesis

Title: Satellite communication channel.

Author: Ahmad Jasim (810406-6330) Fadi Sabah (781101-0870) Mustafa Rauf Mohammed (6905144736) Supervisor: Prof. Sven Nordebo Date: 2012-06-14 Subject: Electrical Engineering Level: Master of Science(M.Sc) Course code: 5ED05E

Contents

Chapters No. Pages

Introduction 1

Chapter 1 1.1 Types of Orbits 2 - Low Earth Orbit (LEO) 2 - Medium Earth Orbit (MEO) 3 - Geostationary Orbit (GEO) 3 - 4

1.2 GEO Satellite 5 1.3 GEO satellite – propagation delay 6

Chapter 2 2.1 Satellite components 7

2.2 Frequency Selection 8

2.3 Satellite dish (Antenna) 9 - 10

2.4 VSAT (Cross-Pol) Feed Assembly 10 Chapter 3 3.1 Azimuth and Elevation angles 11 - 13

3.2 Free Space Loss (FSL) 14 – 15

3.3 Antenna Gain 16 3.4 Uplink and Downlink 17 – 20

Chapter 4 4.1 Programming 21 - 22 4.2 Program application of SVT 23 – 25

Reference 26

1

Figures

Name No. Pages

Figure 1.1 Low Earth Orbit 2

Figure 1.2 Medium Earth Orbit 3

Figure 1.3 Geostationary / Geosynchronous Earth Orbit 4

Figure 1.4 GEO- Satellite 5

Figure 1.5 propagation delays (Uplink and downlink) 6

Figure 3.1 Azimuth and elevation 11

Figure 3.2 Satellite between the Earth and Earth station. 12

Figure 3.3 Downlink 17

Figure 3.4 Received Single Level 18

Figure 3.5 Uplink 19

Figure 3.6 RF Amplifier 19

Figure 4.1 The java program main page 21

Figure 4.2 satellite position and footprint 22

Figure 4.3 Applied program 24

Figure 4.4 The program calculation results 24

Figure 4.5 The PDF file 25

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Tables

Name No. Pages

Table 2.1 Frequency Band 8

3

Introduction

A satellite communication channel is the path the signal takes from earth station

(transmitter) - Satellite- earth station (receiver). The signal is being sent from the earth by very strong transmitters; it is being reinforced inside the satellite and transmitted back to earth.

A communications satellite is an artificial satellite stationed in space for the purposes of telecommunications and it is an independent system floating in space, a satellite can provide customers access to data, video or voice capabilities. It supplies power by solar panels fixed on it, and it attitude.

The equipment inside the satellite needs electricity; this is aroused by solar panels. To keep the satellite in position little rockets are use and that is to be sure that the antennas remain pointed to the earth.

The satellite communications are important because they are anywhere, anytime and anyplace, extremely reliable (99, 9% Uptime) and they are ideally suited for point to- multipoint and large distributed networks. They are also capable of simultaneous delivery of data to an unlimited number of remotes. Two more things make satellite communications important, independence from typical telephone infrastructure and having private network capabilities.

A satellite placed in an orbit by a launch of a space vehicle that can provide a global, on-demand coverage of telecommunications services.

A satellite services can be listed as:  Fixed Satellite Services (FSS).  Broadcasting Satellite Services (BSS).  Mobile Satellite Services (MSS).  Tracking and Data Relay Systems (TDRS). 1

Chapter 1

1.1 Types of Orbits

Every satellite should follow a trajectory, which is the elliptical orbit of the satellite with a maximum extension called apogee and a minimum extension called perigee.

There are several types of orbits:  Elliptical Orbits. - Low Earth Orbit (LEO) - Medium Earth Orbit (MEO)  Circular Orbits. - Geostationary Orbit (GEO) Consider now more about each type of orbits: Low Earth Orbit (LEO) is the region of space around the earth between 500 and 2000 kilometers. Satellite in this ring rotate faster that the earth itself and also faster than MEO satellites. They have an orbital period of 1,5 to 2 hours. It is useful for military observations, metrology, atmospheric studies and for ground studies. Satellite life it is five years and one month. The signal delay approximately 20 ms.

Figure 1.1 Low Earth Orbit

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Medium Earth Orbit (MEO) is the region of space around the earth above low earth orbit (2000 kilometers) and below geostationary orbit GEO (35,786 kilometers). The orbital periods of MEO satellite range from about two to six hours. It is useful for Global Positioning System (GPS). The signal delay approximately 100 ms.

Figure 1.2 Medium Earth Orbit

Geostationary Orbit (GEO) circler with zero inclination and the most favorable is the satellites in this ring around the earth have an orbital period equal to the earth’s period of rotation. This means it takes the satellite 24 hours to finish its rotational period. This makes sense considering the satellite must be locked to the earth’s rotational period in order to have a stationary footprint. This means the satellite has a “fixed spot” above the earth and this can be only achieved at approximately 35,786 km above the equator. Satellites in this ring are used for communication and radio/ television and TV broadcasting. GEO satellites are less useful for telephone and GPS communications because these satellites are highly power consumption. The signal delay approximately 480ms. 3

Figure 1.3 Geostationary / Geosynchronous Earth Orbit

The first two Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) satellites are very useful for mobile communication, like handhelds, GPS and mobile telephones. This is because the satellite is on a lower distance from the earth, and the used power is much lower. The orbital period is less than 24 hours. This means that these satellites have no “fixed spot” above the earth, the satellites in this ring work in a cluster to keep the communication “real- time” without dropping.

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1.2 GEO- Satellite

All Geosynchronous Satellites are considered to be Geostationary which implies that ° that they are orbited into fixed positions over the EQUATOR (0 Latitude). Therefore, a position is determined and reported to the Longitude.

Figure 1.4 GEO- Satellite

From Figure 1.4, we can see that the satellite is never placed on the non–Equatorial or the orbit. Thus, we can see how the entire available satellites are fixed in the orbital plane with the same degree of the longitude. As a matter of fact, all of these satellites are spaced on 2° that reaches 916 Miles or 1.475 Kms.

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1.3 GEO satellite – propagation delay

Propagation delay is considered to be the time the signal takes to travel from the Earth transmitting station to the Earth Receiving station where the signal encounters an uplink and downlink way. In order to calculate the propagation delay, we have to take the light speed of into account. This speed reaches up to 186.282 miles/s or 299.762 Km/s. The speed orbital of the satellite depends on the altitude above the Earth. In particular, the speed of the orbital required to maintain at the orbit is 22.240 miles or 35.790 Kms. In other words, when we divide the orbital speed over the light speed, we can obtain the delay for both uplink and downlink. Uplink delay or downlink delay approximately 0.119 sec and total of delay for both uplink and downlink one way approximately 240. Total round-trip 480ms.

Figure 1.5 propagation delays (Uplink and downlink)

As illustrated from Figure 1.5, the signal moves from the Transmitting Earth station to the satellite and from the satellite to the Receiving Earth station (Uplink and downlink).

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Chapter 2

2.1 Satellite components

Satellite components are divided into two parts.

1. Operational, Guidance and Control Components.

 Power System: A satellite takes its power from the sun’s radiation. (Mainly the light and ultraviolet rays). Solar panels are use to convert the energy from the radiation of the sun to the electrical power.  Propulsion Jets: are engines use to accelerate artificial satellites and spacecraft, the most propulsion jets today are propelled by forcing a gas from the back/rear of the vehicle at a very high speed. These sorts of engine are called the rocket engines.  Guidance System: is a device or a group of devices used to navigate the satellite.

2. Communications Components.

 Antennas: receive the uplink signal and transmit it to the downlink signal where they can be phased array, horn antenna, helical antenna and parabolic antenna.  Transponders: Receive the transmission from earth (the uplink), amplify, convert and retransmit the signal (as the downlink) to the receiving earth stations. In addition, they also include; receiving antenna, broadband receiver and frequency converter, or mixer for frequency translation.  Amplifier- receive: The low Noise Amplifier (LNA) amplifies the received signal.  Amplifier- transmit: The High power Amplifier (HPA) increases the power level of the transmitted signal.  Frequency Converter Mixer (per transponder): is an intermediate step between the receiver and the transmitter that translates the received Uplink frequency into the transmitted Downlink frequency. Furthermore, it utilizes a well-known stabilized frequency source named (Local Oscillator, or L/O). 7

2.2 Frequency Selection

A major concern on the satellite communications design is the selection of the operational frequency. When operating at a high frequency (3GHz), the service quality will be degraded among the transmission path. Earth and satellite station are carefully designed to overcome the problem on which the earth’s atmosphere impairs the signal. L band is used in mobile communications and global positioning systems (GPS) for MSS. On the other hand, S band is used for BBS. In addition, Ku/Ka provides satellite internet and direct TV for BSS and FSS. The W and V bands which are of higher frequencies will open up the spectrum and allow smaller components and throughput through the user devices.

Letter Band Frequency(GHz)

L 1-2 S 2-4 C 4-8 X 7-12 K 12-18 Ku 18-27 Ka 26-40 V 40-75 W 75-111

Table 2.1 Frequency Band.

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2.3 Satellite dish (Antenna)

One of the major components of the satellite which is the satellite dish (Antenna). A satellite dish is a dish-shaped type of parabolic antenna that has been designed to receive microwaves coming from a communicating satellite, which transmits data or broadcasts them, such as, the satellite television.

The operational principle of the dish parabolic shape is that it reflects the signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device that is called a feedhorn. On the matter of fact, this device (feedhorn) is essential in the front-end of a waveguide that gathers the signals at or near the focal point and 'conducts' them to a low-noise block down converter or to an LNB. In particular, the LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the down linked C-band and/or Ku-band to the L-band range. A direct broadcast satellite dish uses an LNBF (low-noise block/feedhorn), which integrates the feedhorn together with the LNB. A new form of Omni directional satellite antenna does not use a directed parabolic dish, but can be used on a mobile platform.

When the frequency increases, the theoretical gain (directive gain) increases as well. The actual gain depends on many factors.  Surface finish.  Accuracy of shape.  Feedhorn matching.

A typical value for a consumer type 60 cm satellite dish at 11.75 GHz is 37.50 dB. With lower frequencies, such as C-band, dish designers have a wider choice of materials. A large size of a dish required for lower frequencies led to the construct those dishes from metal mesh on a metal framework. While at higher frequencies, the mesh type designs are rare, though, some designs have used a solid dish with perforations.

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A common misconception is that the LNBF (low-noise block/feedhorn) of the device at the front of a dish directly receives the signal from the atmosphere. For instance, one BBC News countdown shows a "red data stream" being received by the LNBF directly instead of being beamed to the dish, since its parabolic shape will collect the signal into a smaller area and deliver it to the LNBF.

Modern dishes intended for home television use are generally ranged from 43 cm (18 in) to 80 cm (31 in) in diameter, and are fixed into one position. For Ku- band reception, from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorized C-band dish of up to 3 meters in diameter for receiving channels from different satellites. They are considered to be extremely small dishes that can still cause problems, despite the availability of faded rains and interference from adjacent satellites.

2.4 VSAT (Cross-Pol) Feed Assembly

There are several types of stations; a station for transmission and a station for receiving. In addition, there is a two-way satellite ground station or a stabilized maritime VSAT antenna accompanied with a dish antenna of a diameter smaller than 3 meters. Most of the VSAT antennas are range between 75 cm to 1,2 m. Data rates are typically ranged from 56 Kbit/s to up to 4 Mbit/s.

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 or video).

VSATs can be also used for transportation, on-the-move (utilizing phased array antennas) or mobile maritime communications.

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Chapter 3

3.1 Azimuth and Elevation angles

Azimuth and elevation are angles that are used to define the apparent position of an object in the sky, relative to a specific observation point. The observer is usually (but not necessarily) located on the surface of the earth

Figure 3.1 Azimuth and elevation

The azimuth (az) angle is the compass bearing, relative to the true (geographic) north, of a point on the horizon that is directly beneath an observed object. The horizon is defined as a huge, imaginary circle centered on the observer, equidistant from the zenith (point straight overhead) and the nadir (point exactly opposite the zenith). As seen from Figure 3.1, the observer compass bearings are measured clockwise in degrees from the north. Azimuth angles can thus range from 0 degrees (north) through 90 (east), 180 (south), 270 (west), and up to 360 (north again).

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The elevation (el) angle, also called the altitude, of an observed object is determined by finding the compass bearing on the horizon that is relative to the true north, and then, measuring the angle between that point and the object, from the reference frame of the observer. Elevation angles for objects above the horizon range from 0 (on the horizon) to up to 90 degrees (at the zenith). Sometimes, the range of the elevation coordinate is extended downwards from the horizon to 90 degrees (the nadir). This is assumed to be useful when the observer is located at a particular distance above the surface, such as, in an aircraft.

Figure 3.2 Satellite between the Earth and the Earth station.

From Figure 3.2, it is elaborated that the distance between the satellite and the center of the Earth is 6378Km + 35786Km = 42164Km, besides, between the Satellite and Earth Station it is D. If we know this distance D we can calculate the Elevation and Azimuth angles. 12

Now, the calculation of the Elevation and Azimuth angles is performed as follows, where the Earth station located on longitude, latitude. Satellite located on longitude latitude is alwa s for satellites . et the difference between the latitudes of the earth station and the satellite, and the difference between the longitudes of the earth station and the satellite. In order to calculate the Angle Z, we derive it from cos Z and [2].

cos cos cos (1) Now, use law of cosine. D²= 6378²+ 42164² - 2 * 6378 * 42164 * cosZ (2) D²= 1818481780- 53784398 cosZ (3)

Where, D is measured in kilometers. Use law of cosine again and calculate. 42164² = 6378² + D² - 2D6378 cosΨ (4) cosΨ D² - 1737124012 / 12756 D (5) levation angle Ψ - 9 (6)

To calculate the Azimuth angle, os tan cotZ (7)

Obtain two cases. Azimuth angle 18 + If earth station is at aster than satellite . Azimuth angle 18 - If earth station is Waster than satellite .

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3.2 Free Space Loss (FSL)

A radio wave travelling from a point to any given direction will propagate outwards from that point on the speed of light. Meanwhile, the energy will travel through a straight line forever as there is nothing to prevent them from doing so. To determine Free Space Loss, the ratio of the received power to the transmitted power is [2].

Free Space Loss = (8)

Where Pr is power receive, Pt is power transmitted. This cannot really be considered as loss at all. The energy is conserved, and normally, not all of it is captured at the receiver.

From the equation below, we can simply predict the (FSL). Free Space Loss = 32.45 + 20log (d) + 20log (f) dB, (where d is in km and f is in MHz)

Where, d is the distance between the satellite and the earth in km, and f is the operating frequency in MHz. In order to understand the equation of the (FSL), the received power flux density is.

Pfd = watts / m2 (9)

Now we multiply by the effective area of the antenna to find the received power.

P A ( ) watts (10) r = e

Where, Pr is the receiver power, Pt is the transmitter power, and r is the distance between transmitter and receiver.

The effective area Ae of an antenna is related to its gain as.

A = G m2 (11) e r 14

Now substitute the equation (11) in the equation (10).

. Pr = Gr watts (12)

Rearranging.

Pr = Gr Pt ( ) watts (13)

We refer to the path loss between the isotropic antennas.

(14) Gr = 1, so Pr = Pt ( )

From equation (8) consideration that,

Free Space Loss =

Finally, we obtain.

(15) Free Space Loss = ( )

To useful units of MHz, it is the dB and km.

= (16) FSL = ( ) ( )

_ _ FSL (dB) = 20 log ( ) 20 log (r) 20 log (f) (17)

After putting in the constants and correcting the units in MHz and km, it would be simply to obtain the standard result as. _ FSL = 32.4 + 20 log (f) 20 log (d) (18)

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3.3 Antenna Gain

The gain of an antenna is the ratio of the power radiated or received per a unit solid angle by isotropic antenna fed with the same power. The gain will be at maximum in the direction of a maximum radiation. Antenna gain of a satellite dish can determine as [2].

A (19)

Where A is physical area of the antenna, and R is the diameter of the antenna. Consider the effective area is.

Ae = A ρe (20)

Where, Ae is the effective area, and ρ is aperture efficiency of antenna. Now substitute the equation (19) in the equation (20).

ρ Ae = (21)

The antenna gain of a satellite is.

Ae G = (22)

Now we substitute the equation (21) in the equation (22).

ρ

G= = ρ (23)

ρ approximately 0,55 (For satellite dishes). The antenna gain in dB is.

GdB = 17.8 + 20 Log Rm + 20 Log fGHz. (24)

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3.4 Uplink and Downlink

By considering a communication between an earth station and a satellite, we can explain the uplink and downlink expression. The communication’s link that happened b sending signals from a satellite toward an earth station it is called a downlink, and if it is done by the reverse way (from an earth station to a satellite) it is called an uplink. When an uplink and downlink communication process is happening at the same time it is called a two-way communication, otherwise it is just a one-way. The up and down communication links have several parameters that can be determined. To cover all the parameters we need to consider that we have an uplink and downlink (two-way) communication.

Figure 3.3 Downlink

From figure 3.3 can obtain the Isotropic Receive Level for antenna dish is [1] [3].

IRL= EIRP- FSL- Latm (25) Where, IRL is Isotropic Receive Level, FSL is Free Space Loss, EIRP is Effective

Isotropic Radiated Power and Latmis Loss Atmosphere. .

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Figure 3.4 Received Single Level

From figure 3.4 can obtain the Received Single Level.

RSL= EIRPsat- FSL- Latm+ GR- LTL (26)

Where, RSL Received Signal Level, GR Gain Receiver, and LTL losses in transmission line. The Noise at Receiver is.

N= K Tsys (27)

-23 Where. K Boltzman constant= 1,3805.10 J/K, and Tsys Receiver system noise temperature (k). We can obtain.

(N)dBw= -228,6dBw / Hz + 10 log Tsys (28)

Consider Carrier- to- Noise Ration (C/N) is.

(C/N)dB= RSL dBw- NdBw (29)

Now we substitute the equation (26) in the equation (29).

(C/N)dB = EIRPsat - FSL - Latm + GR- LTL+ 228,6 - 10 log Tsys (30)

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When the communications are going from the ground station to a satellite it called an uplink.

Figure 3.5 Uplink

From figure 3.5 can obtain the Isotropic Receive Level for satellite is.

IRL= EIRP- FSL- Latm, Where, IRL is Isotropic Receive Level, FSL is Free Space Loss, EIRP is Effective

Isotropic Radiated Power and Latmis Loss Atmosphere.

Figure 3.6 RF Amplifire

From figure 3.6 the amplifier output power is.

EIRPdBw= (PRF)dBw - LTL+ GT (31)

Where, PRF amplifier output power and GT Gain transmitted. 19

Consider Received Signal Level for satellite is.

RSL= IRL+ Gsat (32)

Where, Gsa satellite Gain. The Noise is.

N= -228.6 + 10 Log Tsys (33)

We can obtain.

(C/N)dBw= IRL+ Gsat+ 228.6- 10 log Tsys (34)

(C/N)dBw = IRL+ 228,6+ (G/T)sat (35)

The SVT TV they use the Sirius 4 and (G/T)sat (for Sirius 4) approximately 13 dB/k.

(C/N)dB= IRL+ 241.6 (36)

(C/N)dB = (PRF)dBw - LTL + GT – FSL - Latm+241.6 (37)

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Chapter 4

4.1 Programming

To make the mathematical calculations in our project easier and more flexible to be comparable, we made a program to calculate all the satellite communication link’s parameters like,  The distance between satellite and any earth station  Azimuth and elevation angles.  The free space loss for both up and downlinks.  The minimum required antenna diameter.  The minimum amplification for RF.  Up and downlink gain.  Receive system noise level.

Figure 4.1 the java program main page.

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All these parameters can be calculated in just one click. We used java programing language to do all above parameters. The program has also data base for some satellites that included in the program, data base include positions and footprints for these satellites.

Figure 4.2 satellite position and footprint.

To make it perfect practical we took a satellite’s communication parameters (that needed to make all calculations) from SVT television in Växjö, and applied it on our program and compared it with practical realistic parameters that SVT uses.

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4.2 Program application of SVT

The parameters from SVT [6],

Description Parameters 1. Satellite name and position. Sirius 4 (4.8°E) 2. System noise temperature. 199 K 3. Carrier to noise ratio. 87 dB 4. Transmission line loss. 2 dB 5. EIRP. 55 dB 6. Estimated atmospheric loss. 3 dB

7. Uplink frequency. 14122

8. Downlink frequency. 11919 9. Earth station position. Växjö (56.86° N , 14.83° E)

Now apply all these parameters on the program, and by choosing the satellite name it is shows the satellite position and its footprint. Hit “Make the calculations” to get the results. The program has also abilit to save the calculation’s results, time and date in a PDF file.

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Figure 4.3 Applied program

Figure 4.4 The program calculation results

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Figure 4.5 The PDF file

After comparing the results with these that SVT use, found that they are matched except that they use larger antenna dish diameter and more amplified RF power to be sure that the communication work perfectly.

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Reference

[1] Roger L. Freeman, "Radio System Design for Telecommunication", 3rd edition, Wiley-IEEE Press, 2007.ISBN-10: 0471757136.

[2] International Telecommunications Union, Handbook on Satellite Communication, JohnWiley & Sons, 3rd Edtion 2002.

[3] Dennis Roddy, "Satellite Communications", 2nd edition, McGraw-Hill pub., 1996. ISBN-10: 0070533709

[4] Takashi Iida, "Satellite Communications: System and Its Design Technology", IOS Press, 2000.ISBN-10: 4274903796.

[5] L. J. IppolitoJr, Satellite Communications System Engineering: Atmospheric Effects, Satellite Link Design and System Performance, John Wiley & Sons, 2008.

[6] Dan Ejnarsson, Systemutvecklare. Svt Sverrige television AB.

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SE-391 82 Kalmar / SE-351 95 Växjö Tel +46 (0)772-28 80 00 [email protected] Lnu.se/dfm