LinkBudget Analysis

8/16/2019 LinkBudget Analysis

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ELE 492 – Fundamentals of Wireless Communica

Place: E6

Time: Wed. 13:00-16:00

Textbooks:

1. Molisch, Wireless Communications, 2nd Ed., Wiley

2. Sklar, Digital Communications: Fundamentals and Applications, 2nd Ed., Prentice

Assessment:

1 Midterm Exam (40 %)

1 Final Exam (60 %)

Spring 2015 ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS


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CommunicationsLink Analysis



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dB in General



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Power (dBW and dBm)



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Power


Sensitivity level of GSM receiver: 6.3x10-14 W = -132 dBW or -102 dBm

Bluetooth transmitter: 10 mW = -20dBW or 10dBm

GSM mobile transmitter: 1 W = 0 dBW or 30 dBm

GSM base station transmitter: 40 W = 16 dBW or 46 dBm

Vacuum cleaner: 1600 W = 32 dBW or 62 dBm

TV transmitter: 1000 kW ERP = 60 dBW or 90 dBm ERP

Nuclear powerplant: 1200 MW = 91 dBW or 121 dBm

ERP: effective radiated p


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Amplification and Attenuation



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Amplification and Attenuation



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Noise Sources



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Noise Sources



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Communications Link

The link contains/covers the entire communications path

From the information source to the information sink

Contains modulator/demodulator, encoder/decoder, pulse/matched filter, analog front e

filters, etc), channel, etc.

* Sklar, Digi



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Link Budget Analysis

Consists of the calculations and tabulation of the useful signal power and the interfpower present at the receiver.

It is a balance sheet of gains and losses on the link

Available power at the transmitter

Tx + Rx antenna gains

Propagation/channel losses

Performance loss due to noise and natural/man-made interference

Ultimately gives us the system requirements for a desirable performance of the link.



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The Channel

Channel is the propagating medium of electromagnetic path connecting the transmreceiver.

Physically a channel can be For wired communications: Wire, coaxial cable, fiber optic cable,

For wireless (RF) communications: empty space, waveguide, the atmosphere, earth’s surfcontaining «buildings, trees, vehicles, etc…»

Free space: A channel free of all impairments to RFpropagation Absorption, reflection, refraction, diffraction

Energy arriving at the receiver is only a function of the distance from the transmitter.

We will consider the free space as the ideal channel!.



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Error-Performance Degradation

Main causes:

1. Noise: thermal noise, impulsive noise, galactic noise, etc.

2. Interference: Inter-Symbol Interference (ISI), Multi-User Interference (MUI), Other cominterference

(Consider noise only for the time being.)

Error performance depends on the received Signal-to-Noise Ratio per bit (SNR/bit


Bit energy

Noise PSD

SNRAverage noise

power

Average signal

power

Bandwidth

Rate

LOSS HAPPENS HERE ! (HO


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Sources of Signal Loss and Noise1. Bandlimiting Loss

2. Intersymbol Interference(ISI)

3. Local Oscillator PhaseNoise

4. AM/PM Conversion(Amplitude

variations)

5. Limiter Loss orEnhancement

12. Atmospheric Loss andNoise

13. Space Loss

14. Adjacent ChannelInterference

15. Co-channel Interference

16. Intermodulation Noise


6. Multiple-carrierIntermodulation

Products (non-linear devices)

7. Modulation Loss (messagecontent

power)

8. Antenna Efficiency

9. Radome Loss and Noise

10. Pointing Loss

11. Polarization Loss

17. Gand T

18. Fe

19. R

20. Im

21. ImSynch


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Sources of Signal Loss and Noise

S


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Isotropic Antenna


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Dipole Antenna


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Dipole Antenna


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dBi


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Antenna Parameters

Antenna

(at the transmitter) is a transducer that converts electronic signals into electromagnetic f

(at the receiver) converts electromagnetic fields into electronic signals.

Hypothetical antenna: isotropic radiator

Omnidirectional RF source: radiates uniformly over 4π steradians,

Power density p(d) on the sphere of radius d is

W/m2 (4πd2 = ?)

Receiver side: In the far field (d >> λ)

Ae: effective area of the an antenna


Aer: receive antenna

Aet: transmit antenna


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Relation between the effective area (Ae) and the physical area (Ap) of an antenna

efficiency parameter of an antenna η

Dish antenna η = 0.55, horn antenna η = 0.75.

Directive gain

(If there is no loss or impedance mismatch, the antenna gain is equal to the directive

Gain, which is the assumption here.)


Antenna Parameters

in a direction

Power radiated

by an isotropic

radiator


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Antenna Parameters

Effective Radiated Power wrt. an isotropic radiator (EIRP) (Pt : transmitted power,Gt : gain the trans


Both meters read

the same power.

For an isotropic

radiatorFor an antenna

With gain Gt

( Aer for

is given


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EIRP and the Link Budget

EIRP = Transmit power (fed to the antenna) + antenna gain

EIRP answers the questions:

How much transmit power would we need to feed anisotropic antenna to obtain the same maximum on theradiated power?

How strong is our radiation in the maximal direction of theantenna?



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Antenna Parameters

Antenna gain:

Increasing frequency → Antenna gain increases

Higher antenna dim.s→ more directional antenna

→ narrower beamwidth.


(G was given in slide 22.)

h l ( )


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Path loss (Free-space Loss)

What is Ae for an isotropic receive antenna?

Gr=1 →

Received power Pr for an isotropic receive antenna (gain of the transmit antenna

Path loss: attenuation of the received power


for the Tx antenna

R i d Si l P


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Received Signal Power (is frequency dependen

Now, consider a receive antenna with gain Gr

Received signal power:


Ae is a design param

For fixed antennas (

For fixed antennas (

P h L


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Path Loss (is frequency dependent)

Path loss (free-space loss):

One may express the received power in the logarithmic scale:

It is sometimes useful to calculate Pr for «d = 1 m» and then scale d to find the act


Geometric attenuation

not freq. dependent

Effective area

freq. dependent

?

Th l N i P


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Thermal Noise Power

Originates from the random motion of electrons in a conductor. PSD of this noise is hypothetically flat (constant) at all frequencies of interest.

The maximum thermal noise power N that could be coupled observed at the front

amplifier is

κ : Boltzmann’s constant (1.38x10-23 W/K-Hz=-228.6 dBW/K-Hz)

T: ambient temperature (o K)

W: bandwidth (Hz)

Max. single-sided noise PSD No available at the amplifier input is:

and the noise power contained in a bandwidt

No is dependent on the ambient noise (thermal noise) T . Similarly, the terminology effectivecan be use for noise with non-thermal origin (galactic, atmospheric, man-made noise, etc).


E /N


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Eb/No SNR at the receiver input : C/N (Carrier-to-noise ratio)

SNR at the predetection point: Pr/N (or S/N) ← this SNR term is used to calculate E

For suppressed carrier modulation

(What about a modulation scheme with carrier?)

We have seen that , and , then for a digital receiver Pr/N

(numerator: gains, denominator: losses).


Receiver figure-of-merit

Bit energy

Noise PSD

SNRAverage noise power

Average received signal power Bandwidth

Rate

Li k M i


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Link Margin

Required SNR for a target BER is

«to be on the safe side» add a couple of dBs for thereceived SNR

«safety margin» -> link margin

Remember that , then

or


Li k M i


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Link Margin

Read Sections 5.4.3 and 5.4.4 from Sklar (discussion about link margin, satellite coavailability).


Noise Figure


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Noise Figure

Noise figure, F, relates the SNR at the input of a network to the SNR at the output o


Noise Figure


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Noise Figure

Si : signal power at the amplifier input port

Ni : noise power at the amplifier input port

Na: noise power introduced at the amplifier

Nai : amplifier noise referred to the input port

G: amplifier gain.

ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS

A reference for Ni is when T 0 = 290oK (refe

No = κ T o = 1.38 x 10-23 x 290 = 4.00 x 10-21 W/

No = - 204 dBW/Hz @ T 0 = 290oK

An amplifier amp

but also amplifies

and also introduc

*

Spring 2015

(Typical valu

Noise Temperature


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Noise Temperature

ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS

T 0 = 290oK : reference temperature, T R: effective noise temperature of the receive

For the output of an amplifier, we can write the output noise power as

T g: temperature of the source.

Spring 2015

(What percentag

(Ni @ T 0)(Ni @ T R)


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Line Noise


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Line Noise

Let all components be at temperature T g.

There is thermal equilibrium -> no current flows due to noise.

Assume that the impedances of the input and output of the network is matched with tthe load.

The total output noise power Nout flowing from the network to the load:

Ngo: noise at the output due to the source

GNLi : noise at the output due to the lossy network (NLi : network noise relative to its inp

Due to thermal equilibrium, noise power of the load is also equal to κ T gW.

ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONSSpring 2015

Line Noise


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Line Noise

NLi : network noise relative to its input:

Effective noise temperature of the line, T L, is

If the ambient temperature is T g = T 0 = 290oK (above derivation assumes line temp

Noise figure for a lossy line is

Then the output noise power is (see pg. 34)


{

Line Loss


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Line Loss

Example:

T0 = 290oK

Tg = 1450oK

Si = 100 pW

W = 1 GHz

L=2

Calculate (SNR)in,

(SNR)out and

TL.



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System Effective Temperature


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System Effective Temperature

Apart from the transmission line and pre-amplifier, external noise sources are also

natural noise sources: lightning, atmospheric noise, cosmic noise, thermal radiation from

man-made noise sources: automobile ignition, electrical machinery, other radio signals, e

They are represented by antenna temperature T A (κ T AW).

System temperature is


System Performance (w/o LNA)


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System Performance (w/o LNA)

Example: Receiver without a LNA preamplifier (no line loss)


From source From front-end

System Performance (w LNA)


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System Performance (w LNA)

Example: Receiver with a LNA preamplifier (no line loss)


From source From front-end

Sky Noise Temperature


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Sky Noise Temperature

When the antenna points towards the sky:

Up to 1 GHz, galactic noise is dominant.

After 10 GHz atmospheric noise is dominant.

There is an available window in between with low

natural noise.

(Observe variation wrt. elevation.)

(Study Example 5.7 and Sections 5.4.4 and 5.5.6.1 for satellite comm.s)


Sample Link Analysis


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Sample Link Analysis

Brackets: () loss

No brackets: gain

Box: subtotalsDouble box: link margin.


LinkBudget Analysis

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