ECE 5233 Satellite Communications Prepared by: Dr. Ivica Kostanic Lecture 11: Satellite link design (Section 4.4) Spring 2011

Outline Output power of the transponder Rain effect on the uplink Case study of a Ku satellite link design Important note: Slides present summary of the results. Detailed derivations are given in notes.

Output power of a transponder Two kinds of the transponders Bent pipes Regenerative repeaters For bent pipes the gain is linear (as long as the input is in linear region) For regenerative repeaters, the power output is constant (as long as the input signal to noise ratio is above required threshold) Gain of a bent pipe transponder Note 1: Regenerative transponder operates at the constant power – less restricted on linearity requirements of the HPA Note 2: Backoff of the bent pipe transmitter depends on the type of waveform Note 3: In regenerative repeaters the noise does not accumulate. The overall S/N is the same as the S/N of the last stage Gain of a regenerative transponder

Rain effects on UL Uplink and downlink are effected differently by rain On downlink Signal decreases Noise increases On uplink Negligible impact on noise On uplink noise temperature may vary 270-300K

Satellite Communication Link Design Determine operating frequency Determine communication parameters of the satellite Determine TX and RX parameters of the ground stations Start at the TX side – establish the UL parameters and (C/N)up Find output power of the transponder Establish the downlink power budget and calculate (C/N)down and total (C/N) Calculate S/N (or BER) at the baseband channel Calculate system margins and system reliability (outage times) Iterate through steps 1-8 until the requirements are met

System design example – 4.8.1 Example presented in notes.