propagation emc

Speakers

Mr. Reiner Hoppe

© 2012 by AWE Communications GmbH http://www.awe-communications.comAPAC Distributor: Firespec Engineering (M) Sdn Bhd http://www.firespec.net

www.awe-com.com

Exposure & Electromagnetic Compatibility

© 2012 by AWE Communications GmbH

2012 © by AWE Communications GmbH 2

• Introduction

• Coverage vs. Exposure Analysing the trade off between exposure to electromagnetic waves and deploying optimal (indoor) coverage

• Options for Network Design Examining potential options for network design – determining the suitability of meeting coverage and capacity demands

• Features of EMC module in ProManDefinition of exposure limits for different frequency bands Comparison of predictions to specified exposure limits

• Sample ScenarioDefinition of exposure limits for different frequency bands Comparison of predictions to specified exposure limits

Contents


Introduction

Regulator Requirements for Ensuring Public Safety• To protect humans and nature from electromagnetic hazards, the health and safety legislation

for the deployment of base stations becomes more and more restrictive

• Different public authorities issued recommendations thresholds for exposure

• Different thresholds for controlled and uncontrolled (general public) areas

• Distinction of different zones for exposure:

- Compliance zone: Potential exposure below limits for both controlled and uncontrolled areas

- Occupational zone: Potential exposure below limits for controlled areas, but above limits for uncontrolled (general public) areas

- Exceedance zone: Potential exposure exceeds limits for both controlled and uncontrolled (general public) areas

Compliance zone

Occupational zone

Exceedance zone


Introduction

Regulator Requirements for Ensuring Public Safety• Different thresholds for controlled and uncontrolled (general public) areas

• Different accessibility categories require assessment of different heights:

- Antenna installed on inaccessible tower (with/without neighbouring building)

- Antenna installed on publicly accessible structure (e.g. rooftop)

- Evaluation of ground level

- Evaluation of rooftop level (floor levels)


Occupational General public

Whole body (average SAR) 0.4 0.08

Head and trunk (local SAR) 10 2

Limbs (local SAR) 20 4

Introduction

Regulator Requirements for Ensuring Public Safety• Thresholds for exposure derived based on thermal effects

• Analyzed value: Specific Absorption Rate (SAR) Absorbed power in a human body per mass unit of the body (W/kg)

• ICNIRP thresholds (basic limits) from 10 MHz to 10 GHz (safety factor for public protection):

• Derived reference levels from 400 MHz to 2000 MHz by ICNIRP (average over time):

• Partly lower national margins (e.g. in Switzerland reduction by factor 10)

• Simultaneous exposure to multiple sources: superposition with formula

Occupational General public

Electric field strength (V/m) 3*sqrt(frequency) 1.375*sqrt(frequency)

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87 1.0MHz GHzi i Thresholdi kHz i MHz

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Regulator Requirements for Ensuring Public Safety

Introduction

• Different public authorities issued recommendations thresholds

• These recommendations must be fulfilled for each transmitting antenna

• Site certificate ensures exposure below threshold outside controlled area

Antenna Pattern

Tx Power

few dm

ca. 2-10mEnvironment

Site certificate


**

Example for Determination of Safety Distance

Introduction

*

Radio network GSM1800

Height of transmitter above ground in m 23.7

Azimuth orientation of antenna (north over east) 90

Center frequency f in MHz 1855

Antenna type K 735147

Max. transmitter output power per channel Pa in W 6.3

Number of frequency channels n 3

Loss between transmitter output and antenna input a in dB 1

Antenna gain factor Gi in main direction (18 dBi) 63.1

Total max. power on antenna input P in W 15.01*

Electrical field strength threshold for general public areas 59.00

Safety distance in main beam direction in m 2.86**

1010][a

aPnWP

Threshold

i

EGP

r

30


EMC and the Radiation of Electromagnetic Waves

Introduction

• To protect humans and nature from electromagnetic hazards, the health and safety legislation for the deployment of base stations becomes more and more restrictive

• Different public authorities issued recommendations based on guidelines formulated by the International Committee on Non Ionising Radio Protection (ICNIRP)

• These recommendations must be fulfilled for each new transmitting antenna

• Thresholds for the radiated electrical field strength for different frequency ranges analysis must be carried out before installing a base station or transmitter

• ProMan accurately predicts the radiated electrical field of antennas alternative to costly field strength measurements around each antenna

• ProMan takes into account the detailed geometrical representation of the environment

• Results allow the simple comparison of the superposed radiated field strength levels to the specified exposure limits

• Installation of new antennas on locations where already multiple antennas are mounted is more critical concerning the fulfilment of exposure limits due to superposition


Methods for the Exposure Level Assessment

Introduction

• Field strength prediction based on RF configuration of antenna and environment description lowest effort possible before deployment worst case assumption (far field)

• Measurement of the electrical field strength on specific locations and extrapolation for full power transmission (max. cell load) high effort for measurements depending on individual situation (cell load) limited reproducibility

• Measurement row for grid of locations over larger scenario highest effort covering different scenarios depending on individual situation (cell load) limited reproducibility

Field strength prediction provides most efficient method

http://www.awe-communications.com/Network/EMC/images/ProManEMC_FieldStrength3D.jpg


Inputs for Exposure Level Assessment

Introduction

• Site location and height

• Max. radiated power (EIRP or Tx power at antenna input)

• Carrier frequency / frequency band

• Antenna pattern with gain for each direction (3D or vertical and horizontal)

• Azimuth orientation of antenna

• Antenna downtilt

• Description of the environment (buildings, terrain, …)


Analysing the trade off between exposure to electromagnetic waves and deploying optimal (indoor) coverage

Coverage: Field Strength > Threshold (Receiver sensitivity)

Exposure: Field Strength < Threshold (Health risks)

Summary:

(Receiver sensitivity) (Health risks)Threshold Threshold< Field Strength <

Field Strength

Receiver Sensitivity depending on - thermal noise (bandwidth!)- interference (co-channel, adjacent channel leakage)

Threshold depending on - thermal effects- national margins

Coverage vs. Exposure (1/8)



Coverage: Field Strength > Threshold (Receiver sensitivity)

Receiver Sensitivity depending on - thermal noise (bandwidth!)

wider bandwidths require higher field strengths for reception

P = k * T * B k = Boltzman constant = 1,380 ·10-23 J·K-1

T = absolute temperature (Kelvin)B = bandwidth (Hz)

Examples (T = 300K): GSM 900 (200 kHz): P = -120 dBm

E = 16 dBµV/m UMTS FDD (5 MHz): P = -107 dBm

E = 37 dBµV/m

- interference (co-channel, adjacent channel leakage)

depending on network layout

optimised layout should keep the interference small

in worst cases approx. a few dB above thermal noise



Exposure: Field Strength < Threshold (Health risks)Threshold depending on

- thermal effects

Biology responsible for definition of thresholds

Analysed value: Specific Absorption Rate (SAR): Absorbed power in a human body per mass unit of the body (W/kg)

ICNIRP thresholds:

SAR of 4 W/kg in 30 minutes leads to 1 K increase of temperature in body which is the max.

Safety factor of 50 for public protection

0.08 W/kg

- Thresholds for exposure incl. national margins

Germany / EU / ICNIRP Switzerland

Linear Logarithmic Linear Logarithmic

GSM 900 f = 900 MHz 41 V/m 152,3 dBµV/m 4 V/m 132,0 dBµV/m

GSM 1800 f = 1800 MHz 58 V/m 155,3 dBµV/m 6 V/m 135,6 dBµV/m

UMTS f = 2140 MHz 61 V/m 155,7 dBµV/m 6 V/m 135,6 dBµV/m



(Receiver sensitivity) (Health risks)Threshold Threshold< Field Strength <

Field Strength

40…45 dBµV/m 130 dBµV/mSummary

Indoor Problem

Max. allowed dynamic range of signal :

85 dB (130 dBµV/m – 45 dBµV/m)

Actual dynamic inside buildings due to transmission of walls:

Penetration of walls: Concrete wall: L = 20 dB

max. 4 walls can be penetrated to fulfil coverage and EMC aspects

Due to the wall penetration losses the signal inside the building has a high dynamic range and so it is very difficult to fulfil coverage and EMC aspects simultaneously!


GSM 900 cell, frequency: 948 MHz, Tx power: 43 dBm, Antenna gain: 15 dBi, Antenna height: 15 m

EMC thresholds are no problem…but coverage not sufficient everywhere

Outdoor Coverage (Visualisation of Thresholds)


Computation with propagation models of radio network planning tools

Threshold ICNIRPField Strength: 152,3 dBµV/m

Threshold Switzerland Field Strength: 132 dBµv/m

Threshold ReceiverField Strength: 40..45 dBµV/m


GSM 900 cell, frequency: 948 MHz, Tx power: 43 dBm, Antenna gain: 15 dBi, Antenna height: 15 mPenetration loss: 20 dB

EMC thresholds are no problem…but insufficient indoor coverage

Indoor Coverage (Visualisation of Thresholds)Computation with propagation models of radio network planning tools






GSM 900 cell, frequency: 948 MHz, Tx power: 73 dBm, Antenna gain: 15 dBi, Antenna height: 15 mPenetration loss: 20 dB

Indoor coverage only sufficient if Tx power is so high that EMC problems occur!

Indoor Coverage with increased Tx power (30 dB !)Computation with propagation models of radio network planning tools






Coverage (especially indoor) becomes very often a problem if critical exposure is avoided in outdoor environment (i.e. small Tx power) and if base station density is not very high

Increasing the Tx power is no alternative to guarantee coverage because of exposure thresholds

A detailed planning of the network is mandatory to find a trade off between exposure and (indoor) coverage


Analysing the trade off between exposure due to electromagnetic waves and deploying optimal (indoor) coverage


Options for Network Design (1/8)

Examining potential options for network design – determining the suitability of meeting coverage and capacity demands

Indoor coverage is important in cities (potential users/customers)

Generally, in cities antenna heights are not very high because of traffic (and capacity) requirements

the higher the max. traffic density, the smaller the cell radius (max. number of users per cell reduces cell size with increasing traffic)

the smaller the cell radius, the lower the antenna height (shadowing of buildings increases with decreasing antenna heights)

Results of previous chapter:

Indoor coverage and EMC exposure can only be combined if the distance between base station and buildings is short

Exposure related: 43..50 dBm Tx output power are maximum if combined with sector antennas with 10..20 dBi gain

Indoor coverage related: Distance between site and building below 800 m



the higher the max. traffic density, the smaller the cell radius (max. number of users per cell reduces cell size with increasing traffic)

Thesis 1:

Example:

Assumption: Cell Capacity: 50 user simultaneously, circuit switched traffic (e.g. voice)

Case Study:

Case 1:

10 simultaneous users per km2

Cell Area: 5 km2

Case 2:

50 simultaneous users per km2

Cell Area: 1 km20

1

2

3

4

5

6

10 20 30 40 50 60 70 80 90 100

Cell size [km2]

Size

of

cell

[km

2]

User per km2



the smaller the cell radius, the lower the antenna height (shadowing of buildings increases with decreasing antenna heights)

Thesis 2:

Tx antenna height: 15 m Tx antenna height: 35 m



High traffic and capacity demands can only be achieved with small cells, i.e. low antenna heights

Low antenna heights have problems with indoor coverage

Results:

Increase the number of cells with a homogenous distribution of the sites in the area to be covered with the mobile network

Comparison of two different cell layouts:

• single (central) omni transmitter location (with 20 W Tx power, 0 dBi antenna gain)

• seven (distributed) omni transmitter locations (with 2 W Tx power, 0 dBi antenna gain)

Case Study:

Hints:

Omni instead of sector antennas used to exclude effects of antenna patterns !

GSM network used as example. But key message of results can be transformed to UMTS without significant modifications!



Comparison of Electrical Field StrengthSingle Antenna Configuration Multiple Antenna Configuration

Max. Value = 130 dBµV/m Mean Value = 69 dBµV/m

Max. Value = 125 dBµV/m Mean Value = 64 dBµV/m


Comparison of Coverage Probability Single Antenna Configuration Multiple Antenna Configuration

Bad coverage probability in many buildings (especially at the border)

Coverage Probability > 90% nearly everywhere



Comparison of Required Tx Power in DownlinkSingle Antenna Configuration Multiple Antenna Configuration

Very high Tx power is required to reach mobile stations Exposure problems!

Very low Tx power is sufficient

No exposure problems!




Examining potential options for network design – determining the suitability of meeting coverage and capacity demands

Suggestion: More medium or small power sites should be used instead of a few high power sites to

improve indoor coverage

reduce the exposure to electromagnetic waves

increase the capacity of the network

Problem: Distributed medium or small power sites need more effort in the radio network planning process

highly accurate propagation models required

propagation models should offer the option to analyse indoor coverage in more detail


Features of EMC module in ProMan

EMC Module in ProMan (1/4)

• Based on highly accurate wave propagation models (either deterministic or empirical)

• Unlimited number of antennas can be considered in the project For each antenna the following parameters are used for the EMC analysis:

- Max. radiated power (EIRP or Tx power at antenna input)

- Number of carriers

- Carrier frequency / frequency band

- Antenna pattern incl. azimuth and mechanical downtilt

Path loss prediction (includes influence of antenna pattern)


Features of EMC module in ProMan


• EMC-Specifications (national or international)

- User-defined thresholds (equations) for different frequency ranges / bands

- Predefined specifications for several countries (e.g. Germany, Switzerland,...)

- Open interface to define new specifications or to modify pre-defined specifications

- Threshold within each band defined by following formula (in V/m):

Exp. Limit = Level Factor • (Frequency/MHz)Level Exponent

+ Level Offset

- Definition of constant threshold X possible via

Level Factor a = 0.0

Level Exponent b = 0.0

Level Offset c = X


Features of EMC module in ProMan• Wireless standards (analyzed systems)

- Definition by name and range of the carrier frequencies (min. and max.)

- Predefined standards (GSM900, GSM1800,...)

- Open interface to define new standards or to modify pre-defined standards

- Superposition of all carriers operating on the same standard



Features of EMC module in ProMan• Computed and predicted results:

- Field strength (V/m) for each wireless standard (superposition of all carriers of the same standard)

- Superposition of all wireless standards present in the given scenario by using the following formula with Ei in V/m and individual thresholds per frequency band:

- Resulting exposure plot including all carriers and standards with comparison to overall threshold of 1.0 for superposed exposure limit


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propagation emc

Technology

exposure different thresholds

potential exposure

public safety thresholds

fulfilment of exposure

simultaneous exposure

exposure limits2012

public protection

general public areas59