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ECE 5233 Satellite Communications Prepared by: Dr. Ivica Kostanic Lecture 11: Satellite link design (Section 4.4) Spring 2014.

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Presentation on theme: "ECE 5233 Satellite Communications Prepared by: Dr. Ivica Kostanic Lecture 11: Satellite link design (Section 4.4) Spring 2014."— Presentation transcript:

1 ECE 5233 Satellite Communications Prepared by: Dr. Ivica Kostanic Lecture 11: Satellite link design (Section 4.4) Spring 2014

2 Florida Institute of technologies Page 2  Rain attenuation and system noise temperature  Uplink link budget calculations Outline Important note: Slides present summary of the results. Detailed derivations are given in notes.

3 Florida Institute of technologies Effect of rain on the noise temperature Page 3 System temperature Temperature of the Universe Temperature of the atmosphere

4 Florida Institute of technologies Effect of rain on the noise temperature Page 4 Clear sky Rainy sky Change in the noise level due to rain Coupling efficiency

5 Florida Institute of technologies Uplink power budget  In fixed satellite systems – usually easier oTransmission is to a single location oOn the ground - much more power  In mobile systems – usually harder oSmall transmit power from the ground (usually ~1 watt)  Various trade offs involved with the uplink are examined through proper power budget  Four sections of the budget: oGround transmit (PA, antenna requirements) oSatellite receive (linear gain of transponder, antenna requirements) oPropagation path losses (FSPL, elements, margin) oReliability calculations and margins Page 5

6 Florida Institute of technologies Combination of C/N  Bent pipe transponder amplifies both signal and noise  As the signal travels through the chain the noise is accumulated  On board processing transponder removes input noise Page 6 At the transponder RX At the transponder TX At the earth station RX Note: the noise at the RX has a portion that originated at the transponder input

7 Florida Institute of technologies Combination of C/N (2) Useful rules of thumb  If two C/N values are equal output C/N is 3dB lower  If two C/N differ by 10dB, output C/N is 0.4 below the lower of the two  If C/N differ by 20dB, output C/N is essentially the same as the lower of the two Page 7 S/N at the receiver Generalization

8 Florida Institute of technologies Side-lobe envelope of the transmit antenna  Specification on side-lobe of ground antenna that minimizes interference on the UL  Adopted by ITU-R to allow 2 degree spacing in the geo-stationary arc Page 8 Note: maximum antenna gain towards the neighboring satellite space is 21.5dB This is still significant gain and coordination is frequency coordination may be required between operations in adjacent slots

9 Florida Institute of technologies Example Consider a transponder in Ku band with linear gain of 127dB and nominal power at saturation of 5W. The satellite’s antenna has a gain of 26dB on axis. Calculate output power required from a ground PA if following data are known: frequency of operation 14.45GHz, Earth station gain of 50dB, antenna feed losses -1.5dB, atmospheric losses of 0.5 dB, rain margin 7dB, off axis satellite antenna losses - 2dB. Answers: Required power at the satellite: -127dBW Environmental losses: dB Transmit power: 44.15dBm (26W)(review attached spreadsheet) Note: the power requirement at the satellite are relatively low. Assuming noise temperature of 300K, and noise bandwidth of 27MHz, the maximum theoretical bandwidth efficiency would be 1.5bps/Hz Page 9

10 Florida Institute of technologies Example Estimate decrease in C/N at the receiver if the atmospheric losses due to rain increase by 3dB. In clear sky the atmospheric losses are 0.4dB and the equivalent system noise temperature is 145K. The coupling efficiency is 0.95 Answers: Page 10

11 Florida Institute of technologies Example Thermal noise at the earth station results in S/N is 20.0dB. A signal is received from a bent pipe transponder with C/N of 20dB. What is the value of the overall C/N at the earth station? If the C/I ratio of the IM distortion at the transponder is 24dB, what is the overall C/N ratio at the earth station? Answers: 1.C/N = 17dB 2.C/N = 16.2dB Page 11


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