Lecture 10: Link Budget Analysis and Design Eytan Modiano AA Dept
Lecture 10: Link Budget Analysis and Design Eytan Modiano AA Dept. Eytan Modiano Slide 1
Signal attenuation TX Channel RX R n The signal suffers an attenuation loss l Received power PR= PT/L Received snr=E,/No, Eb=Pr/Rb Antennas are used to compensate for attenuation loss Capture as much of the signal as possible L=(4d T Rx→PR=P1G1GL T R L= free space loss, d-distance between Tx and rx n= signal wavelength
Signal attenuation Channel PT + Rx n(t) PR L • The signal suffers an attenuation loss L – Received power PR = PT/L – Received SNR = Eb/N0, Eb = PR/Rb • Antennas are used to compensate for attenuation loss – Capture as much of the signal as possible GT GR Tx PT L = (4πd/λ)2 Rx PR = PT GTGR/L L = free space loss, d = distance between Tx and Rx Eytan Modiano Slide 2 λ = signal wavelength Tx
Antenna Gains R ARI/2 r is the effective area of the antenna For Parabolic antenna Ar=Tn D2/4 m=illumination efficiency factor, 0.5<n<0.6 d= dish diameter GR n(D/n)2 PR=PTGTD2n/(4d)
Antenna Gains GR = AR4π/λ2 AR is the effective area of the antenna For Parabolic antenna AR = πηD2/4 η = illumination efficiency factor, 0.5 < η < 0.6 D = dish diameter => GR = η(πD/λ)2 => PR = PTGTD2η/(4d)2 Eytan Modiano Slide 3
Antenna beamwidth Beamwidth is a measure of the directivity of the antenna Smaller beamwidth concentrated power along a smaller area Free space loss assumes that power is radiated in all directions An antenna with a smaller beamwidth concentrates the power hence yields a gain For parabolic antenna, 0: -70ND Gain(G)s proportional to(e8)-2 Hence a doubling of the diameter D increases gain by a factor of 4
θ λ θ Antenna Beamwidth θB • Beamwidth is a measure of the directivity of the antenna – Smaller beamwidth concentrated power along a smaller area • Free space loss assumes that power is radiated in all directions • An antenna with a smaller beamwidth concentrates the power hence yields a gain – For parabolic antenna, θB ~ 70λ/D – Gain (GT) s proportional to (θB )-2 – Hence a doubling of the diameter D increases gain by a factor of 4 Eytan Modiano Slide 4
Example(GEO Satellite d=36,000km=36,000000 meters f=4GhZ→>=0.075m P1r=100w,G=18dB Receiver antenna is parabolic with d=3 meters A)What is PR? B)Suppose(E/Norea=10 dB, what is the achievable data rate Rb?
Example (GEO Satellite) d = 36,000 km = 36,000,000 meters fc = 4 Ghz => λ = 0.075m P T = 100w, G T = 18 dB Receiver antenna is parabolic with D = 3 meters A) What is PR? B) Suppose ( E b/N 0)req = 10 dB, what is the achievable data rate R b? Eytan Modiano Slide 5