ele 492 fundamentals of wireless communicationstoker/ele492/1. linkbudgetanalysis.pdf · power...

ELE 492 – Fundamentals of Wireless Communications

Place: E6

Time: Tue. 09:00-12:00

Textbooks:

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

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

Assessment:

Attendance (5 %)

1 Midterm Exam (30 %)

5-6 Popup quiz (25 %)

1 Final Exam (40 %)

Spring 2017 ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS 1

Outline- Link Budget Analysis

- Radio Propagation

- Statistical Description of the Channel

- Wideband Channel Characterisation

- Channel Models

- Demodulation

- Diversity

- Multiple Access

- GSM Air Interface

- Wi-Fi Air Interface


PrerequisitesCurrently there is no official prerequisite of the course, but technically ELE 425 is a prerequisite.

If you haven’t taken or passed ELE 425, I strongly do NOT recommend the course for you.

Furthermore, you should have a very good understanding of

- Probability,

- Wave Propagation,

- Communication Theory,

- Systems Theory


CommunicationsLink Analysis


dB in General


Power (dBW and dBm)


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 power

Amplification and Attenuation


Noise Sources


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 end (amplifiers, filters, etc), channel, etc.

* Sklar, Digital Communications, pg.242


Link Budget AnalysisConsists of the calculations and tabulation of the useful signal power and the interfering noisepower 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.


The Channel Channel is the propagating medium of electromagnetic path connecting the transmitter and thereceiver.

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 surface, mediumcontaining «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 ofthe distance from the transmitter.

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


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 comm. signals, Man-madeinterference

(Consider noise only for the time being.)

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


Bit energy

Noise PSD

SNRAverage noisepower

Average signalpower

Bandwidth

Rate

LOSS HAPPENS HERE ! (HOW ?)

Sources of Signal Loss and Noise1. Bandlimiting Loss

2. Intersymbol Interference (ISI)

3. Local Oscillator Phase Noise

4. AM/PM Conversion (Amplitude variations)

5. Limiter Loss or Enhancement

12. Atmospheric Loss and Noise

13. Space Loss

14. Adjacent Channel Interference

15. Co-channel Interference

16. Intermodulation Noise


6. Multiple-carrier Intermodulation Products (non-linear devices)

7. Modulation Loss (message content power)

8. Antenna Efficiency

9. Radome Loss and Noise

10. Pointing Loss

11. Polarization Loss

17. Galactic or Cosmic, Star and Terrestrial Noise

18. Feeder Line Loss

19. Receiver Noise

20. Implementation Loss

21. Imperfect Synchronization


Sources of Signal Loss and Noise

See Sklar, Figure 5.1, p. 246.


Isotropic Antenna


Dipole Antenna


dBi

Antenna Parameters Antenna (at the transmitter) is a transducer that converts electronic signals into electromagnetic fields.

(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 antenna


Aer: receive antenna

Aet: transmit antenna

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 radiatedby an isotropicradiator

Antenna Parameters Effective Radiated Power wrt. an isotropic radiator (EIRP) (Pt: transmitted power,

Gt: gain of the transmit antenna)


Both meters readthe same power.

For an isotropicradiator

For an antennaWith gain Gt

(Aer for isotropic antennais given in slide 27.)

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

EIRP answers the questions: How much transmit power would we need to feed an

isotropic antenna to obtain the same maximum on theradiated power?

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


Antenna Parameters Antenna gain:

Increasing frequency → Antenna gain increases

Higher antenna dim.s→ more directional antenna

→ narrower beamwidth.


wavelength:

(G was given in slide 23.)

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 is Gt)

Path loss: attenuation of the received power


for the Tx antenna

Received Signal Power (is frequency dependent)

Now, consider a receive antenna with gain Gr

Received signal power:


Ae is a design parameter (dim.s of the antenna). For fixed antennas (Ae: fixed) → Pr↗ as λ↘ For fixed antennas (Ae: fixed) → G↗ as λ↘ → directivity↗

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 actual Pr


Geometric attenuationnot freq. dependent

Effective areafreq. dependent

?

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 end of an 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 bandwidth W is

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


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 Eb/No

For suppressed carrier modulation

(What about a modulation scheme with carrier?)

We have seen that , and , then for a digital receiver Pr/No is

(numerator: gains, denominator: losses).


Receiver figure-of-merit

Bit energy

Noise PSD

SNRAverage noise power

Average received signal power Bandwidth

Rate

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


Link Margin Read Sections 5.4.3 and 5.4.4 from Sklar (discussion about link margin, satellite coverage, link availability).


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


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 35

A reference for Ni is when T0 = 290 oK (reference temperature), i.e.

No = κTo = 1.38 x 10-23 x 290 = 4.00 x 10-21 W/Hz

No = - 204 dBW/Hz @ T0 = 290 oK

An amplifier amplifies the input signalbut also amplifies the input noiseand also introduces additional noise.*

Spring 2017

(Typical value of F: 1 – 10 dB)

Noise Temperature

ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS 36

T0 = 290 oK: reference temperature, TR: effective noise temperature of the receiver (network).

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

Tg: temperature of the source.

Spring 2017

(What percentage of Ni is Nai? [0,∞) )

(Ni @ T0)(Ni @ TR)

Line loss An amplifier amplifies the input signal, but also amplifies the input noise and also introducesadditional noise.

A Lossy Line attenuates the input signal but does not introduce additional noise.

Power Loss:

Gain:

ELE 492 – FUNDAMENTALS OF WIRELESS COMMUNICATIONS 37Spring 2017

Line Noise

Let all components be at temperature Tg.

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 the source andthe 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 input)

Due to thermal equilibrium, noise power of the load is also equal to κTgW.


Line Noise NLi: network noise relative to its input:

Effective noise temperature of the line, TL, is

If the ambient temperature is Tg = T0 = 290 oK (above derivation assumes line temp. is at Tg)

Noise figure for a lossy line is

Then the output noise power is (see pg. 36)


{

Line Loss Example: T0 = 290oK

Tg = 1450oK

Si = 100 pW

W = 1 GHz

L=2

Calculate (SNR)in,

(SNR)out and

TL.


Composite Noise Figure Connect two networks in series:

Noise figure of the composite network is:

Design goal: keep F1 as low as possible & keep G1 as high as possible (conflicting goals!).First stage should be a low-noise-(pre)amplifier (LNA)!

Effective noise temperature of the composite network:

If there is a feed line prior to the amplifier:


composite temperature

System Effective Temperature Apart from the transmission line and pre-amplifier, external noise sources are also present. natural noise sources: lightning, atmospheric noise, cosmic noise, thermal radiation from the ground, etc.

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

They are represented by antenna temperature TA (κTAW).

System temperature is


System Performance (w/o LNA) Example: Receiver without a LNA preamplifier (no line loss)


From source From front-end

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


From source From front-end

Lower noise figurethan F2 only.

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 AnalysisBrackets: (<.>) loss

No brackets: gain

Box: subtotals

Double box: link margin.


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