link budget tutorial xx
TRANSCRIPT
Link Budget Tutorial
CS 401
Full-Duplex Communications
VHF MonopoleReceiving
VHF YagiTransmitting(Command)
UHF DipoleTransmitting
UHF YagiReceiving
Using UHF for spacecrafttransmission and VHFfor command. Most commonamateur radio modes.
Basic HardwareCubesat Ground
Station
Transmitting Dipole Yagi
Transmitting Antenna Gain
0dB 10.2dB
Receiving Antenna
Monopole Yagi
Receiving Antenna Gain
0dB 14.15dB
Transceiver Helio-100 TS-9000
RF output Power
.5-1W 50W
Link Budget Overview• Gains – losses• Done for both sides
– Satellite to ground station (transmit mode)– Ground station to satellite (command mode)
• Gains – Transmitter power (RF output)– Antenna
• Losses– Line loss from cable– Connector losses– Free space loss– Atmospheric loss– Ionospheric loss– System noise loss
Decibel units
• Logarithmic unit• Ratio of power/intensity to a reference value
• P1 and P0 must measure same type and have the same units
• Solving for P1
)0
1(log10 10 P
PLdB
0101 10 PPdBL
• dB’s are easier to add and subtract• 500mW = ? dBm• dBm = 10log10(500/1)• =10log10(500)• ~27dBm• 500mW = ? dBW• =10log10(0.5/1)• =0dBW (don’t show –dBW)
• dB’s are easier to add and subtract• 500mW ~= 27dBm • Examples:• 10mW = 10dB• 100mW = 20dB• 1000mW = 30dB
dB units for RF links
• dBm or dBmW – power relative to 1mWReferenced to a 50ohm load• dBc – noise or peak power relative to carrier
power• dBi – forward gain relative to a theoretical
isotropic antenna. Gain for a ½ wave dipole is 2dBi
• dBd – forward gain relative to a ½ wave dipole so gain for a ½ wave dipole is 0 dBd
Elevation Angle• Angle between ground
station and spacecraft relative to earth
• When spacecraft is directly overhead, elevation angle is 90
• When spacecraft is on horizon, elevation angle is 0
• 0 degrees difficult to communicate, requires full line of sight. Trees, buildings, etc. may obstruct view.
Specs required for link budget
Cubesat Ground Station
Transmitter power 500mW 50W
Antenna Gain 0dB 10.2dB
Cable length (estimate) 19cm (max) 25m
Frequency 434MHz 144MHz
Bandwidth 15000Hz 15000Hz
Modulation/BER
Altitude 800km 800km
Other specs are estimated
Link elements
• XMTR power in Watts – RF output power• XMTR power in dBW – convert Watts to dBW• XMTR system losses in dB
-cable loss – function of frequency and length -connectors -filters -antenna mismatch – see next slide
Antenna Mismatch• Based on VSWR ratio which will be > 1• Calculated for both GS and Spacecraft separatelyLet TX = transmitter output power, V = VSWRPL – power lossPT – power transmittedPLdB – Power loss due to mismatchThen the following are used to compute PLdB
PL = TX*((V-1)2/(V+1)2)PT = TX-PLPLdB = -10*log10(PT/TX)
Antenna Mismatch Examples
PL = TX*((V-1)2/(V+1)2)PT = TX-PLPLdB = -10*log10(PT/TX)
Let TX = 50W and V = 1.5PL = 50((1.5-1)^2/(1.5+1)^2) =
2WPT = 48WPLdB = -10*log(48/50) =
0.18dB
Let TX = 1W and V = 2PL = 0.11WPT = 0.89WPLdB = -10*log(0.89/1) = 0.51 dB
Link Values so farCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1
0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.35
1 - estimates
Antenna Gain – take gain of antenna and add 2dBi. Because we have no attitudecontrol, we are subtracting 3dB to account for pointing losses.Cubesat has gain of 0dB + 2dBi - 3 dB = 0dBiGS uplink antenna has gain of 10.2dB + 2.15dBi = 12.35dB – 3dB = 9.35dBi
EIRPEffective (or equivalent)isotropically radiatedpower (EIRP)
EIRP (dBm) = Pt(dBm)– Lc(dB) + Ga (dBi),
wherePt – transmitted power (dBm)Lc – Line/cable losses (dB)Ga – Antenna Gain (dBi)
Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W)
1W 50W
XMTR Power (dBm)
0 17
XMTR System Losses (dB)1
0.5 2
XMTR Frequency (MHz)
434 144
XMTR Antenna Gain (dBi)
0 9.4
XMTR EIRP(dBm)
-0.5 24.4
Slant Range
d – elevation angle
S -slant rangeRe – radius of the earth, 6376.136kmh – altitude of Cubesat, e.g. 800km
r = h + Re
S
Re
Earth surface
Satellite orbit
h
S = Re[{r^2/Re^2 – cos^2(d)}^1/2-sin(d)]
Slant Range Calculations
)sin(Re*))cos*Re)(Re( 222 hS
S - slant rangeRe – radius of the earthh– mean orbital altitudeΘ – elevation angle
Use whichever formula is easiest to calculate in Excel:
)sin())(cosRe/)(Re(Re* 222 hS
Slant Range Computations• Use Excel and compute
the slant ranges for an altitude of 325km at the elevations given on the chart.
• Use the following constants:
Re – radius of the earth = 6378.14
h – mean orbit altitude = 325km
Slant ranges for mean orbit altitudeof 800km
Elevation Slant Range
(deg) (km)
5 2784
10 2367
20 1769
30 1395
40 1159
50 1006
60 907.2
70 845.1
80 810.9
90 800
Link Budget so far…Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5deg elevation)
2784 2784
The slant range is the same no matter which direction – from space to ground orground to space.
Source: http://www.vetechnet.com/lesson-1.htm
Path Loss (Free Space Loss)• Path loss is a function of distance
and wavelength.• Recall that distance, i.e. the slant
range is a function of elevation• RF often refers to wavelengths
instead of frequency• Note: Cubesat transmits on UHF but
ground station transmits on VHF• Make sure that wavelength and
distance are in the same units• UHF (amateur bands)
– Frequency: 420-450MHz– Wavelength: 70cm
• VHF (amateur bands)– Frequency: 144-148MHz– Wavelength: 2m
]**4
[log*20 10 d
PathLoss
See Diallo link budget for alternative formula.
Using formula above for UHF and elevation angle of 5 degrees:
D= 2783.9 km (slant range at 5 degrees)λ = 70x10-5 (km)
Path loss = 153.97dB
Adding Path Loss Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) 153.97 144.85
Antenna Polarization• Linear polarization –
confines the electrical field vector to a given plane along the direction of propagation
• Circular polarization describes an electrical field that is circular over time. See URL:
• http://upload.wikimedia.org/wikipedia/commons/8/81/Circular.Polarization.Circularly.Polarized.Light_Right.Handed.Animation.305x190.255Colors.gif
Linear polarization
VerticalHorizontal
Circular polarization
Source: http://www.ccrs.nrcan.gc.ca/glossary/index_e.php?id=3089
More Polarization Examples
Circularly polarizedRight-Hand CP
Linearly polarized(Vertical)
Polarization Mismatches
• Antennas transmit and receive in exactly the same way.
• A vertically polarized antenna will not communicate with a horizontally polarized antenna
Polarization Loss Factors• Given two linearly polarized
antennas rotated from each other by angle φ
• Polarization Loss Factor (PLF) = cos2φ
• If they have the same polarization, PLF = 0
• If one is vertically polarized and the other is horizontally polarized, then φ=90 and they will not communicate.
• Given a circularly polarized antenna and a linearly polarized antenna
• The LP antenna will pick up the in-phase component of the CP wave.
• So polarization mismatch will be 0.5 or -3dB no matter what angle the LP antenna is rotated to.
• Since using CP antennas (Yagis) for GS and LP (dipole and monopole) antennas on the Cubesat, PLF = 3dB
Adding Polarization Matching LossCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (km) (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) (dB)
153.97 144.85
Polarization Matching Loss (dB)
3 3
Atmospheric Losses• Power loss due to
absorption, refraction and scattering.
• Lower the elevation, longer the distance in the troposphere
• Major cause of signal attentuation – rain and fog
• Use a look-up table • Source: “Radiowave
Propagation in Satellite Communications” Louis J. Ippolito
ElevationAngle (deg)
Atmospheric Loss (dB)
0 10.2
5 2.1
10 1.1
30 0.4
45 0.3
90 0
Adding Atmospheric LossesCubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (km) (at 5deg elevation)
2784 2784
Path Loss (5deg elevation) (dB)
153.97 144.85
Polarization Matching Loss (dB)
3 3
Atmospheric Losses (dB) (5 deg elev)
2.1 2.1
Isotropic Signal at Received Antenna
• Basically gain – losses• EIRP – Losses which are
the sum of:– Path Loss– Polarization Matching
Losses – Atmospheric Losses
Adding to Link Budget…Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receiver Component
• Received signal at GS (transmit from Cubesat)
• Received signal on Cubesat (command from GS)
• Elements– Receive Antenna Gain– Receive Noise
Temperature– Receive G/T– Receive C/No– Bandwidth– Receive Eb/No– Required Receive Eb/No– Link Margin
Receive Antenna Gain
• Receiving at Cubesat• Recall antenna gain =
0dBi
• Receiving at GS• Antenna gain = 14.15dB• Convert to dBi• =14.15dB + 2.15 dBi =
16.3dBi• Subtract 3dB for
pointing loss• =16.3-3 = 13.3dBi
Cubesat ->Ground Station
Ground Station-> Cubesat
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature• Somewhat complicated• Factors include:
– Antenna Temperature/Sky Temperature
– System Line (physical) Temperature
– Noise temperature of amplifiers
– Computed feedline coefficent
– More• Will use estimates
• 377K – Receive Noise Temperature at GS
• 293K – Receive Noise Temperature at Spacecraft
Cubesat ->Ground StationDownlink
Ground Station-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T
• Receive G/T - Real measure of the receiver’s performance
• Is the “figure of merit”• Receive G/T • = Receive gain in dBi -
10 log10 ( receive noise temperature T ).
• Example• Let RG=receive antenna
gain in dBI, e.g. 13.3• Let RT = receive noise
temperature, e.g. 377• Receive G/T • =RG – 10log10(RT)
• =13.3 – 10log10(377)
• =-12.5
Cubesat ->Ground StationDownlink
Ground Station-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/No (dB-Hz)• Carrier to Receiver Noise Density• C/No = Signal at Rcvr Ant + Received G/T –
Boltzmans Constant(dBW/K/Hz)• Boltzman’s constant = -228.6 dBW/K/Hz• Downlink Example:Iso. Signal at Rcvr Ant (at 5deg elevation) = -159.57Received G/T = -12.5C/No = -159.57 + (-12.5) – (-228.6) = 56.5dB-Hz
Bandwidth
• Need to indicate bandwidth in Hz• Bandwidth – difference between upper and
lower frequency for a range of frequencies• CW < 100Hz• Bandwidth – 15000Hz – frequency range for
Cubesat and GS receivers
Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
Eb/N0
• Eb/N0 (the energy per bit to noise power spectral density ratio) is an important parameter in digital communication or data transmission.
• normalized signal-to-noise ratio(SNR) measure, also known as the "SNR per bit".
• No is the thermal noise density = kT , k – Boltman’s constant in Joules/Kelvin and T is in Kelvin.
• Measure of the signal-to-noise ratio for a digital communications system
• Receive Eb/N0 = C/N0 – 10log10(Bandwidth)• Required Eb/N0 is a function of the modulation scheme and
desired bit error rate (BER)
Modulation/Demodulation Method: CUBE -Sat 2005 July 16
NOTE: Select Here: Choice Made: Result:
UPLINK:
Modulation, Coding & BER Option: 10 GMSK Eb/No:
Command Link Threshold
Option: Modulation Type: Coding: Bit Error Rate Spec: Required Eb/No (dB): 10.6
1 AFSK/FM None 1.00E-04 21.0 dB
2 AFSK/FM None 1.00E-05 23.2
3 G3RUH FSK None 1.00E-04 16.7
4 G3RUH FSK None 1.00E-05 18.0
5 Non-Coherent FSK None 1.00E-04 13.4
6 Non-Coherent FSK None 1.00E-05 13.8
7 Coherent FSK None 1.00E-04 10.5
8 Coherent FSK None 1.00E-05 11.9
9 GMSK None 1.00E-04 8.4
10 GMSK None 1.00E-05 9.6
11 BPSK None 1.00E-05 9.6
12 BPSK None 1.00E-06 10.5
13 QPSK None 1.00E-05 9.6
14 QPSK None 1.00E-06 10.5
15 BPSK Convolutional R=1/2, K=7 1.00E-06 4.8
16 BPSK Conv. R=1/2,K=7 & R.S. (255,223) 1.00E-06 2.5
17 BPSK Conv. R=1/6,K=15 & R.S. (255,223) 1.00E-07 0.8
18 User Defined None 1.00E-05 9.6
Operator Estimate of Implementation Loss
NOTE: Implementation Loss Estimate: 1.0 dB
Required Eb/N0
• From AMSAT chart, required Eb/N0 is 9.6dB + an implementation loss of 1.0dB = 10.6dB
• Receive Eb/N0 (for elevation of 5deg)
C/N0 – 10log10(Bandwidth)
Downlink: 56.5 – 10log10(15000)Uplink: ?
Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
Receive Eb/N0 (dB) 14.74 40.74
Required Eb/N0(dB) 10.6 10.6
Link Margin (dB) 4.14 30.14
Cubesat -> GSDownlink
GS-> CubesatUplink
XMTR Power (W) 1W 50W
XMTR Power (dBm) 0 17
XMTR System Losses (dB)1 0.5 2
XMTR Frequency (MHz) 434 144
XMTR Antenna Gain (dBi) 0 9.4
XMTR EIRP(dBm) -0.5 24.4
Slant Range (at 5° deg elev) 2784 2784
Path Loss (5° elev) 153.97 144.85
Polarization Matching Loss 3dB 3dB
Atmospheric Losses (5° elev) 2.1 2.1
Isotropic Sig at Rcvr Ant (dBW) (5° elev) -159.57 -121.45
Receive Antenna Gain (dBi) 13.3 0
Receive Noise Temperature (K) 377 293
Receive G/T (dB/K) -12.5 -24.7
Receive C/N0(dB-Hz) (5° elev) 56.5 82.5
Bandwidth(Hz) 15000 15000
Receive Eb/N0 (dB) 14.74 40.74
Required Eb/N0(dB) 10.6 10.6
Link Margin (dB) 4.14 30.14
Your assignment• Complete Diallo’s link budget using Excel • Add 5, 20, 30, 45, 60 degree elevation angles for uplink• Add 10 degree elevation angle for downlink• Add formulas to compute slant ranges• Add all needed values/formulas for added elevation angles• Change the mean orbital altitude to 325km• Write a 1-page description of link budget in your own
words emphasizing the key elements. Indicate assumptions: RF power, orbital altitude, antenna gain, etc.
• Link budget due today• Paper due next Wednesday