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

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

3. Effect of rain on the noise temperature
System temperature
Temperature of the Universe
Temperature of the atmosphere

4. Effect of rain on the noise temperature
Clear sky
Rainy sky
Coupling efficiency
Change in the noise level due to rain

5. Uplink power budget In fixed satellite systems – usually easier
Transmission is to a single location
On the ground - much more power
In mobile systems – usually harder
Small 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:
Ground transmit (PA, antenna requirements)
Satellite receive (linear gain of transponder, antenna requirements)
Propagation path losses (FSPL, elements, margin)
Reliability calculations and margins

6. Combination of C/N At the transponder RX At the transponder TX
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
At the earth station RX
Note: the noise at the RX has a portion that originated at the transponder input

7. Combination of C/N (2) Useful rules of thumb S/N at the receiver
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
S/N at the receiver
Generalization

8. 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
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. Example 4.6.1
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

10. Example 4.5.1
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:

11. Example 4.7.1
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:
C/N = 17dB
C/N = 16.2dB