Net425:Satellite Communications Networks and Communication Department LAB 5

C-Band GEO Satellite - LinkBudget in Clear Air TABLE 4.4a C-band satellite parameters Transponder saturated output power 20 W Antenna gain, on axis 20 dB Transponder bandwidth 36 MHz Downlink frequency band 3.7-4.2 GHz 13-Nov-18 Networks and Communication Department

Signal FM-TV analog signal FM-TV signal bandwidth 30 MHz Minimum permitted overall C/N in receiver 9.5 dB 13-Nov-18 Networks and Communication Department

Receiving C-band station Downlink frequency 4.00GHz Antenna gain, on axis 49.7 dB Receiver IF bandwidth 27 MHz Receiving system noise temperature 75 K 13-Nov-18 Networks and Communication Department

Downlink power budget Pt = Satellite transponder output power, 20 W 13.0dBW Bo = Transponder output backoff -2.0 dB Gt = Satellite antenna gain, on axis 20.dB Gr = Earth station antenna gain 49.7 dB Lp = Free space path loss at 4 GHz -196.5 dB Lant=Edge of beam loss for satellite antenna -3.0 dB La = clear air atmospheric loss -0.2 dB Lm = Other losses -0.5 dB Pr = Received power at earth station -119.5dBw 13-Nov-18 Networks and Communication Department

Figure 4.4 (p. 104) A satellite link. Satellite Communications, 2/E by Timothy Pratt, Charles Bostian, & Jeremy Allnutt Copyright © 2003 John Wiley & Sons. Inc. All rights reserved.

Ex 1 A GEO satellite at a distance of 36,000 km from a point on the earth’s surface Find The received carrier power in dB watts ? The rule : Pr = EIRP + Gr – LP – La – Lta – Lra dBW Where EIRP = effective isotropically radiated power Pt * Gt watt La = attenuation in the atmosphere Lta = losses associated with the transmitting antenna Lra= losses associated with the receiving antenna Rules are in blue color , parameters are in green color 13-Nov-18 Networks and Communication Department

Given Parameters Using the following parameters : Transponder saturated output power which is Satellite transponder output power, (Pt) = 20 W Convert in decibel : 10 log(20) = 13 dB Antenna gain, on axis for Satellite transmitter which is Gt = Satellite antenna gain, on axis 20.dB EIRP = pt+Gt = 13+20= 33 dB Antenna gain, on axis, for Receiving C-band station Gr = Earth station antenna gain = 49.7 dB 13-Nov-18 Networks and Communication Department

Con. Given Parameters path loss Lp= (4πR/λ) 2 It is not a loss in the sense of power being absorbed; it accounts for the way energy spreads out as an electromagnetic wave travels away from a transmitting source in three-dimensional space. Using this parameter Downlink frequency (F) 4.00GHz λ= c/f =3*108 /4000000000=0.075 m 13-Nov-18 Networks and Communication Department

Con. Given Parameters Using the parameter distance of 36,000 km ( R) Lp=(4*3.14*36000000/0.075) 2 =36346429440000000000 watt Convert in decibel : 10 log(36346429440000000000) =196.5 dB Constant Lant=Edge of beam loss for satellite antenna -3.0 dB 13-Nov-18 Networks and Communication Department

Sol. 1 La = clear air atmospheric loss -0.2 dB Lm = Other losses -0.5 dB Loss at transmitter Bo = Transponder output backoff -2.0 dB The equation will be Pr =13+20+49.7-196.5-3.0-0.2-0.5-2.0=-119.5 dBW 13-Nov-18 Networks and Communication Department

A noise power Pn A receiving terminal with a system noise temperature TsK and a noise bandwidth Bn Hz has a noise power Pn referred to the output terminals of the antenna where Pn = kTsBn watts The receiving system noise power is usually written in decibel units as N = k + Ts + Bn dBW 13-Nov-18 Networks and Communication Department

Con. A noise power Pn where k = Boltzmann’s constant = 1.39 × 10^-23 J/K = -228.6 dBW/K/Hz Ts is the system noise temperature in dBK Bn = noise bandwidth in which the noise power is measured (the receiver ), in dBHz 13-Nov-18 Networks and Communication Department

Con. A noise power Pn Note that because we are working in units of power, all decibel conversions are made as 10 log 10(Ts) or 10 log 10 (Bn). The rule : Pn = 10 log(kTsBn )=10 log(k)+10 log (T)+10 log (Bn) Ex2: find the noise power Pn ? 13-Nov-18 Networks and Communication Department

Downlink noise power budget in clear air K = Boltzmann’s constant -228.6dBW/K/Hz Ts = System noise temperature, 75 K 18.8 dBK Bn = Noise bandwidth, 27 MHz 74.3dBHz N = Receiver noise power - 135.5 dBW 13-Nov-18 Networks and Communication Department

Sol.2 Using the following parameters : k = Boltzmann’s constant = 1.39 × 10-23 J/K 10 log (1.39 × 10^-23) = -228.6 dBW/K/Hz Ts = System noise temperature, 75 K 10 log (75)=18.8 dBK Bn = Noise bandwidth, 27 MHz 10log (27*10^6) =74.3dBHz N=-228+18.8+74.3=-135.5dBW 13-Nov-18 Networks and Communication Department

C/N ratio in receiver in clear air The carrier-to-noise ratio, often written CNR or C/N, is a measure of the received carrier strength relative to the strength of the received noise. High C/N ratios provide better quality of reception, and generally higher communications accuracy and reliability, than low C/N ratios. 13-Nov-18 Networks and Communication Department

Ex3 Find carrier-to-noise ratio ? C/N = Pr － N = -119.5 dBW － (-135.5 dBW) = 16.0 dB 13-Nov-18 Networks and Communication Department