ADVANCED SATELLITE COMMUNICATION (ASC) CASE STUDY DESIGN OF SYSTEM LEVEL CONCEPT FOR A SATELLITE LINK. 29 February 2016

Transcription

1 HOCHSCHULE BREMEN UNIVERSITY OF APPLIED SCIENCES FACULTY OF ENGINEERING AND COMPUTER SCIENCE ADVANCED SATELLITE COMMUNICATION (ASC) CASE STUDY DESIGN OF SYSTEM LEVEL CONCEPT FOR A SATELLITE LINK 29 February 2016 INSTRUCTOR : Prof. Dr. S. Peik RISHABH CHIKKER MSC-EE STUDENT MAT. # RCHIKKER@HS-BREMEN.DE NAVANEETHA CM MSC-EE STUDENT MAT. # NMANJAPPA@HS-BREMEN.DE

2 Contents 1. Introduction 3 2. Orbital Calculations 3 3. Link Budget Power Budget Conclusion Appendix References.. 20 List of Figures 1. Latitude and Longitude of sub-satellite point as a function of time Plot of satellite Latitudes and Longitudes to show the first exemplary pass Elevation angle of the satellite as a function of time Distance of the satellite as a function of time Azimuth of the satellite as a function of time Elevation for one exemplary overpass of the satellite as a function of time Distance for one exemplary overpass of the satellite as a function of time Azimuth for one exemplary overpass of the satellite as a function of time Plot of time slots when the satellite is visible for one exemplary overpass Doppler shift for one exemplary overpass of the satellite as a function of time Satellite link design for NOAA Bit error ratios graph for different modulation schemes Antenna noise temperature as a function of Zenith angle and Frequency.. 13 List of Tables 1. Link Budget Calculations for NOAA 19 satellite 9 2. Power Budget Calculations for NOAA DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 2

3 1. Introduction The task at hand was to track the NOAA 19 satellite and to design the link for a connection time during its first exemplary pass over our Ground Station which is located at Mumbai, India. In the following pages of our report we have broken down the task at hand by calculating the: Orbital Calculations Link Budget Power Budget In order to do the these calculations, it is necessary to first state the assumptions: It is assumed that the date of tracking is taken as 24 th December The Ground Station is assumed to be in Mumbai (Bombay), India. The Latitude & Longitude of Mumbai is & respectively. The lifetime of satellite is assumed to be for 5 years. The battery used within the power sub-system of the satellite is assumed to be Lithium ion battery with charge/kg as 165Wh. In order to achieve this task and to perceive the situation visually we have done a simulation of tracking on Python. In order to enhance calculations and simplify the mathematics involved in Link Budget and Power Budget, MS Excel was used. The codes for generating this visualization are attached in an appendix at the end. 2. Orbital Calculations To locate a satellite in space we need to find some orbital elements for the satellite. A Two-Line Element set (TLE) is a set of orbital elements that describe the orbit of an earth satellite. A computer program called a model can use the TLE to compute the precise position of a satellite at a particular time. The TLE of NOAA-19 is NOAA U 09005A DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 3

4 By using the TLE of the satellite we compute the sub-satellite point to locate the satellite. The point at which a line between the satellite and the center of the Earth intersects the Earth's surface is called the sub-satellite point. It is defined by Latitude & Longitude. The orbital period of the satellite NOAA 19 is 102 minutes. The path traced by the satellite in 24 hours is obtained by computing latitudes and longitudes for each minute and plotting on map which roughly covers the entire phase of Earth. The satellite tract is geographically widespread. The latitude and longitude of the sub-satellite point as a function of time is plotted on the world map below: Figure 1: Latitude and Longitude of sub-satellite point as a function of time Figure 2: Plot of satellite Latitudes and Longitudes to show the first exemplary pass i.e. for the 6 th orbital period. Note: Large blue dots indicate the current position of ground station and the satellite. DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 4

5 The elevation, distance and azimuth angles of the satellite with respect to the ground station as a function of time are plotted. To get the first exemplary pass of NOAA 19 satellite over Mumbai we need to consider the 6 th orbital period, i.e. up to 612 minutes. Figure 3: Elevation angle of the satellite as a function of time with respect to ground station Mumbai Elevation is the angle above the horizon; azimuth is the angle from a reference in North direction to the right or to the left. Figure 4: Distance of the satellite as a function of time with respect to ground station Mumbai DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 5

6 Figure 5: Azimuth of the satellite as a function of time with respect to ground station Mumbai The distance, elevation and Doppler shift for one exemplary overpass of the satellite as a function of time can be seen in the map below: The below plot shows that the satellite is visible to the observer between 518 minutes to 531 minutes i.e., for about 13 minutes. Figure 6: Elevation for one exemplary overpass of the satellite as a function of time with minimal elevation angle of DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 6

7 As the elevation angle increases, the distance from the satellite to ground station decreases. At the largest elevation, the satellite is very close to the ground station and maximum data reception is possible at this point. Figure 7: Distance for one exemplary overpass of the satellite as a function of time Figure 8: Azimuth for one exemplary overpass of the satellite as a function of time DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 7

8 The connection time can be found by using Figure 6, that is when the satellite is visible to the ground station as shown in the below map. The connection time is. Figure 9: Plot of time slots (Red Dots) when the satellite is visible for one exemplary overpass Doppler Shift is a shift of frequency in an electromagnetic wave due to the movement of the transmitter or receiver. It can be calculated using the formula: Where f is the central frequency 8450 MHz and c is the speed of light in vacuum = Figure 10: Doppler shift for one exemplary overpass of the satellite as a function of time DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 8

9 3. Link Budget In the Link Budget section we calculate the required data bit rate and symbol rate for 500Mbytes of data using.the Bandwidth is calculated for the BPSK, raised cosine modulation scheme and filtering using symbol period. Figure 11: Satellite link design for NOAA 19 All the calculations were done on the spread sheet and the results are as show below: Bit Error Rate Modulation BPSK Bits per symbol m 2 Amount of data 4.00E+09 bits Connection Time Tcon 780 seconds Bit rate Rc 5.13E+06 bits/second Symbol Rate Rs 5.13E+06 symbols/sec Symbol Duration Ts 1.95E-07 Filter Raised Cosine Roll-off Factor α 0.3 Bandwidth required B 6.67E+06 Hz Energy per noise E/n0(dB) 10.5 db DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 9

10 SNR Receiver Path Loss Ground Station & Transmitter SNR (Rc*E/n0)/B 8.63E+00 SNR(in db) db Boltzmann k 1.38E-23 J/K Noise Figure F 2.00E+00 db 1.58E+00 Equivalent Noise temperature Te K Antenna noise temperature Ta 30 K Output Noise N0 1.84E-14 Output Noise(in db) dbw Output Signal S0 1.59E-13 W Output Signal(in db) dbw Receiver Gain G db Received Power Pr(Si) 7.93E-14 Pr in dbw dbw Distance R m Center Frequency f Hz Wavelength λ m Path Loss Lp 1.01E+19 Path Loss(in db) db Receiver Antenna Gain Gr Receiver Antenna Gain(in db) dbi G/T G/T /K Received noise at antenna Ni 2.67E-14 W Ni(in db) dbw EIRP EIRP W dbw Transmitter Gain Gt dbi Transmitter Power Pt W Transmitter Power(in db) dbw Power Flux Density S E-15 W/m dbw/m 2 Effective Area Ae m 2 DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 10

11 Antenna Efficiency ɳ 0.6 Physical Area Aphy m 2 Antenna Diameter at Ground D m Transmitter Antenna Diameter D_sat m For 30% efficiency Antenna Efficiency_changed ɳ_change 0.3 Physical Area_changed Aphy m 2 Antenna Diameter_changed D_changed m Transmitter Antenna Diameter D_sat_changed m Table 1: Link Budget Calculations for NOAA 19 satellite The required SNR, which is an important parameter, is calculated for a bit error rate of. For this an appropriate value of is chosen from the standard bit error ratios graph for different modulation schemes as shown below. Figure 12: Bit error ratios graph for different modulation schemes DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 11

12 For the worst case scenario of elevation of, the distance of satellite from ground station is 9000kms, we can calculate EIRP value by taking antenna noise temperature for frequency of 8450MHz and Appropriate value of antenna noise temperature is chosen from below graph and comes out to be about 30K. Figure 13: Antenna noise temperature as a function of Zenith angle and Frequency We need to assume Receiver antenna gain(about 52.3dBi), transmitter gain(about 26.5dBi) in such a way that we obtain desired SNR, with the ground station antenna of 3 meter diameter. If we consider the antenna efficiency of 30%, it results in a ground station antenna diameter of about 4.25 m. The satellite is equipped with matching transmitter antenna of diameter 0.44 meters for 30% efficiency. As the receiver has high gain, transmitted power of 10.5 mw is received efficiently. DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 12

13 4. Power Budget In the Power Budget section we calculate the required solar cell area and the battery capacity. We know that NOAA19 satellite orbit is a Sun synchronous orbit with altitude of 870 kms (below Van Allen belts). Satellite circles around the Earth in ±1.7 hours. Max. Eclipse duration => 35 minutes Typical lifetime of 5 years thermal cycles. The calculations for the solar cell area and battery capacity are done on the spread sheet below: Power Budget Orbital Period Tu 102 mins Eclipse time period Tecl 35 mins Time period in Sun Tsun 67 mins Payload Power Ppl 10 W Other Power (RFF + DB + Telemetry) Pother 20 W Total Power Psum 30 W Total Orbital Power Porbit W Charge of Battery Ebat 17.5 Wh Power from Sun Psolar 1367 W/ End of Life of Li-ion Battery EOL 0.2 Area of solar cells Asg Depth of discharge of Li-ion battery DOD 0.3 Battery Capacity Cbat Wh For Li-ion battery Charge/kg(assumed) 165 Wh/kg Mass of Battery m_battery kg Table 2: Power Budget Calculations for NOAA 19 RF Front end Power is assumed to be 5W. When the satellite is in eclipse, Lithium-ion batteries of capacity 58.3 Wh are used. DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 13

14 5. Conclusion In this project we located the satellite NOAA 19 by computing the sub-satellite points with respect to ground station Mumbai and found the visible time of the satellite for one exemplary overpass by tracing the path for 24 th December, Then the satellite communication link is designed by computing the below mentioned parameters: Bit rate 5.13 Mbits/sec Symbol Rate 5.13 Mbits/sec SNR 9.36 db Bandwidth 6.67 MHz Received Power 7.93E-14W (-131 dbw) Effective Isotropic Radiated Power 4.7 W (6.75 dbw) Transmitted Power 10.5 mw ( dbw) Ground station Antenna diameter ( ) 3 m Ground station Antenna diameter ( ) 4.25 m We can receive the maximum data at an elevation angle of approximately satellite is about 2000 kms above the ground station. when the The power subsystem of satellite uses total solar cell area of 0.11 and Lithium ion batteries with capacity of 58 Wh. Total mass of the battery required is 0.35kg. From the above calculations, we can expect the Satellite to have a life time of 5years and run its mission successfully. DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 14

15 6. Appendix Formulas Used for the Calculations: Bit rate Symbol Rate (in symbols/s) Bandwidth B (in Hz) SNR Effective noise temperature Output Noise Output signal Input Noise Received Power Wavelength (in meters) Path Loss Transmitter Antenna Gain ( ) ( ) EIRP Power flux Density Transmitted Power Effective Area Physical Area Charge of Battery Battery Capacity Total Power Area of Solar cell Mass of Battery DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 15

16 Python Code: DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 16

17 DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 17

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20 7. References [1] S. Peik, Satellite Communication Lecture Notes ASC. Hochschule Bremen, [2] I. T. Union and I. T. Union, ITU Handbook on Satellite Communications. Wiley- Interscience, 3 ed., [3] G. Maral and M. Bousquet, Satellite Communications Systems. Wiley-Blackwell (an imprint of John Wiley & Sons Ltd), 5 ed., [4] Brandon Craig Rhodes, PyEphem, [Online] Available: [5] NOAA Satellite Information System, NOAA s Geostationary and Polar-Orbiting weather satellites, [Online] Available: [6] U.S. DEPARTMENT OF COMMERCE, User's Guide for Building and Operating Environmental Satellite Receiving Stations, February 2009, [Online] Available: f DESIGN OF SYSTEM LEVEL CONCEPT FOR NOAA 19 LINK (WS ) Page 20