emc analysis and engineering

7/27/2019 EMC Analysis and Engineering

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EMC Analysis and Engineering

Mr. Wang Jian

Spectrum Engineering Division

State Radio Monitoring [email protected]

+86-10-6835 5711


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Monitoring

Planning & allocating

Spectrum Engineering

Rules Regulations &associated standards

FrequencyCoordinating

Licensing &

Billing

Inspection

Law &Enforcement

National Spectrum Management


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The Questions:

1. Will new frequency assignment causeinterference to existing stations ?

2. Will the new frequency receiveinterference from existing stations


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Why we need EMC

Operators need clear spectrum

All the system need co-exist peacefully

Use Spectrum efficiently an effectively


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Overview

Interference Model

Culling

PropagationInterference Analysis


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What is interference

Unwanted energy Receiver

Performance degradation,

Misinterpretation,

Loss of information


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Interference Model

Co-Channel (Co-frequency) Interference

Adjacent Channel Interference

Intermodulation

Transmitter Noise

Receiver Desensitization


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Co-Channel Interference

Interference falls on frequency withinthe receivers pass band

Can only be eliminated at its source

CH1 CH2 CH3 CH4


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Frequency Reuse

Increase the efficiency of frequency usage

Co-channel Cell


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Frequency Reuse

Minimum distance separation to providesufficient isolation between co-channelstations

In cellular mobile systems, Co-channel reuseratioQ= D/ R

where D:minimum distance separation

R: radius of cell


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What about CDMA

Same frequency,but different code

Spread Spectrum exchange for better

performanceSelf-interference system


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What about CDMA

Interference effect:

Capacity Loss

Coverage Loss


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Adjacent Channel Interference

In-band energy from adjacent Channel

CH1 CH2 CH3 CH4


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Proposed Receiver RF Pass Band

Signal from strong

nearby transmitter

within RF

passband of the

Proposed Receiver


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Automatic Gain Control (AGC) :

Undesired Signal Gain

Undesired signal force receiver to reduce itssensitivity

When Gain 0, receiver was blocked


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How to eliminatetransmitter noise

Install a band-pass filter at thetransmitter output

Increase geographical separationSelecting another frequency


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Intermodulation (IM) Analysis

Where does it come from?

For Transmitter IM

2 or more transmitters stand nearby and intermodulated

Final output amplifier turns non-linearity

New frequencies radiate out

For Receiver IM

Strong RF Signals nearby

Victim receiver being saturated

IM product falls in to a transmitters pass band


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Intermodulation

InterferersDesired

Channel

f ff1 f2 f1 f22f1-f2 2f2-f1


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Intermodulation interference

Transmitter

B

Transmitter

C

Proposed

Receiver

Receiver

Intermodulation


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Intermodulation interference

TransmitterB

Transmitter

A

Proposed

Receiver

Transmitter Intermodulation


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Intermodulation Mathematics

Intermodulation Formula

Second Order Fa Fb

Third Order

2Fa Fb, Fa 2Fb|FaFbFc|


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EXAMPLE

Third Order IM

Example 1

F1=154.350MHz

F2=143.875MHzFim= 2F1-F2= 2*154.350-143.875=164.825 MHz

Example 2

F1=154.625MHz

F2=279.2875MHz

F3=279.2125MHz

Fim= F1-F2+F3

=154.625+279.2875-279.2125=154.7MHz


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IM Product Fa Fb 2Fa-Fb 2Fb-Fa

Im Product 1 165.240 165.150 165.330 165.100

Im Product 2 165.240 163.500 166.980 161.760

Im Product 3 165.240 165.330 165.150 165.420

Im Product 4 165.240 164.370 166.110 163.500

Im Product 5 165.150 163.500 166.800 161.850

Im Product 6 165.150 165.330 164.970 165.510

Im Product 7 165.150 164.370 165.930 163.590

Im Product 8 163.500 165.330 165.670 167.160

Im Product 9 163.500 164.370 162.630 165.240

Im Product 10 165.330 164.370 166.290 163.41

Table 5, Receiver IntermodulationDetermination of Intermodulation Products


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Newly assigned Freq

EXISTING SYSTEM EXISTING SYSTEM

IM make EMC more Complicated


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Content

Interference Model

Culling



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Why perform a cull

In a frequency congested environment, theSpectrum Manager must use a valid and reliable

means to identify potential interference problemswhich can occur between thousands of assignedfrequencies in the area.

Which assignments need detailed analysis?


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Culling


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How to cull

Frequency criteria (frequency separation)

Distance between interfering transmitter

and victim receiverLocal environment consideration

An accurate,comprehensive DATABASE is necessary


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After considering distance separation


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Culling example

In land mobile service:

CHANNEL DISTANCE

FROM THEPROPOSED

MINIMUM CULL

DISTANCE (Km)

MAXIMUM CULL

DISTANCE (Km)

CO-CHANNEL 120 240

ADJECENT 30 60


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Distance separation between

Radionavigation & FM Stations

55

50

45

40

35

30

25

20

15

300

100

30

10

3

1

0.300

0.100

0.030

125

75

40

25

20

20

20

20

20

210

120

65

40

2020

20

20

20

20

400

230

125

70

40

25

20

20

20

500

340

190

105

60

35

20

20

20

500

500

310

180

95

55

30

20

20

500

500

500

380

210

120

65

40

20

500

500

500

500

500

370

200

115

65

dBW KW Distance (Km)

Frequency ofBC

stations(MHz)

100 102 104 105 106 107 107.9


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Culling example

Earth station coordination area

Coordination area

B

A

EARTHSTATION

Receiving

earth station

Stations using the same

frequency band within thecoordiation area are likely to

receive interference from the

earth station or to cause

interference to the earthstation


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Question :

How to cull for very large area?


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Solution for Large Culling area

Typical Radio Stations

Test Points


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Frequency band and usage

Band Frequency Propagate Range Usage

VLF 3 - 30 kHz several 1000 kmlong range Radio navigation and

strategic communications

LF 30 - 300 kHz several 1000 km

Long range radio navigation and

strategic communications

MF 0.3 - 3 MHz a few 1000 kmMedium range pt. to pt. broadcasting

&maritime mobile

HF 3 - 30 MHz up to several 1000 kmLong and short range pt. to pt.,

global broadcasting, mobile.

VHF 30 - 300 MHz up to a few 100 km

Short and medium ptp, mobile, LAN,

audio & video broadcasting,

personal communications


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Propagation

Transmitter Power: P0

Radius of the sphere: R

Power density on the sphere:

Receivers antennaeffective area : Aeff

R

2

0/ 4D

R D eff

P P R

P P A

P ti h i


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Propagation mechanisms

Line-of -sight


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Below 30MHz, Ionosphere propagation dominate

Sky-wave


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The requirement for spectrum manager

Analyze Propagation mechanisms

Make right choice

Calculate the BASIC path loss

You can NOT expected to predict thepath loss accurately !


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Free space Path Loss

Loss = 32.44+ 20 log d (km) +20logF(MHz) dB

Line-of-sight transmission

Simple

the most optimistic


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EIRP: 10dBw

Transmitter Carriers frequency: 250MHz

Transmitting distance: 20 kilometers

QUESTION:

Calculate the Power at receiver antenna

Transmitter

A

Receiver

A

Question


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Loss = 32.44+ 20logd(km) +20logF(MHz)

= 32.44+ 20log20+20log250=104 (dB)

Power at receiver antenna= 10- 104 = -94 (dBw)

Answer


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In Land Mobile Service

OKUMURA-HATA

Egli model

ITU-R Recommendation P.1546

Formulas and curves are based on statistical Analysis ofexperimental data


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OKUMURA-HATA model Loss

L= 69.5526.16lgf13.82lghte(hre)44.96.55lghblgdWhere:

f: frequency (150MHz1500MHz)

hte=equivalent height of transmitters antenna (30-200m)

hre= equivalent height of receivers antenna (1-10m)

d=distance between antennas of transmitter & receiver(


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Egli model loss

Lp=88.1+40lgd+20lgf-20lg(h1h2) h2>10mLp=88.1+40lgd+20lgf-20lgh1-10lgh2 h2


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LVF

Location variability factor (LVF) (takeinto account effects on propagation

from terrain and local ground: Buildings,terrain feature,foliage)

No absolute value

Local Knowledge is very important


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ITU-R Recommendations

See document ITU-R Recommendation P.1144


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Content

Interference Model

Culling



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Interfering

transmitter

Receiver

A

Wanted

Transmitter

S

I

Basic Concept


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Interference Analysis

Compare C/I or S/I with criteria or

standards---->Margin

If Margin is enough, favorable findingOr un favorable finding

For digital system, criteria or standardsderive from expected BER


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Other Standards and Criteria

I/N for frequency sharing andcoordination, e.g. I/N


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S = EIRPS PL+ GRX+LRX+LVF (dBw)

Where:

EIRPS: EIRP of the interfering transmitter (dBw)

PL: path loss (dB)

GRX: gain of the receive station antenna gain (dBi)

LRX: total loss of receiver (filter,cable) (dB)LVF: Location variability factor (dB)



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I = EIRPI PL+ GRX+LRX-OCR+LVF (dBw)Where:

EIRPI: EIRP of the interfering transmitter (dBw)

PL: path loss (dB)

GRX: gain of the receive station antenna gain (dBi)

LRX: total loss of receiver (filter,cable) (dB)

OCR: off-channel rejection(dB)LVF: Location variability factor (dB)


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OCR

Off-Channel rejection (OCR) isdetermined by a formula based on the

frequency difference between the victimor no-channel and the potentiallyinterfering or off-channel frequency.


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Exercise

Co-channel interference

Desensitization/transmitter noise

Receiver Intermodulation


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Summary

Interference Model

Culling

Propagation



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Technology used in sharing

Frequency separation (FDMA)

Spatial separation

Time separation (TDMA)

CDMA


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System Evaluation


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Content of Application

Applicant information

Location of station

Technical characteristics of proposedequipment and accessories


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Technical characteristics

Frequency(ies)

Transmitter power

Receiver sensitivityAntenna:location,gain,structure,gain,azimuth,height,

Ancillary device : loss


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Application information

Become parts of spectrum management

database

Some will appear on the license


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Purpose of Evaluation

Evaluate application submitted for authorizing aradio communication station or system

Ensure requested system performance (e.g.coverage area) is practical

Ensure proposed technical parameters arenot in excess of those required to perform the

requested communication service.


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Case Study in Land Mobile Service

Two way communication:

Base station to Mobile

Mobile to Base station


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Frequency Configurations

Simplex:

Two frequency Simplex:


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System Coverage Area

Meet the coverage requirements of theApplicant and economically designed

Meet the objectives and policies of theSpectrum Management Authority:

No interference,permit frequency reuse


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Coverage Balance

Max Mobile talkback range

Coverage

area basedon EIRP ofBS

BS

Excess systemcoverage


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Potential Interference

Interference Zone

Range of coveragedue to excessivepower


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Conclusion

Maximum distance that a mobile stationcan hear the systems base station shall

be balanced with the distance that thebase station can reliably hear themobile station.

How to determine what EIRP is necessary ?


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Calculate Required EIRP

Required information:

Transmitter frequency (MHz)

Effective height of transmitter and receiver

antenna(m)Gain of transmitter and receiver antenna(dBd)

Required coverage area (Km)

Required minimum signal level (dBw)

Location Variability Factor (LVF) (dB)


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Calculate Required EIRP

EIRP=PL-G+Pmin+LVF (dBw)

Where:

PL:Path loss in dBG: Gain of receive antenna (dBi)

Pmin: Required Signal level (dBw)

LVF: local variability factor (dB)


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Exercise:EIRP=?

Parameter ValueTransmitter Effective height 15m

Receiver Effective height 2m

Frequency 150MHzRequired Coverage (radius) 50Km

Receiver Antenna Gain 0 dBi

Receiver System Loss 0 dB

LVF 4dB

Required Signal level Pmin- -137dBw (0.65V)

Propagation Model Egli


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Mobile Talk-back Distance

Use Egli Model:

d=10exp((EIRP+Gb-TL- Pmin-LVF-88.1-20Logf+20Logh1h2)/40)

Where:

d:Distance which mobile can talk back to base station (km)

h1,h2: Antenna height of mobile and base station (m)

f: Mobile station transmitting frequency (MHz)

EIRP: EIRP of mobile station (dBw)

Gb: Base station receiving antenna gain(dBi)

Pmin: Minimum required Signal level at base station receiver(dBw)LVF: local variability factor (dB)

TL: base station receiver total losses (dB)


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