Propagation emc

Speakers
Mr. Reiner Hoppe

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

Exposure & Electromagnetic
Compatibility

© 2012 by AWE Communications GmbH

www.awe-com.com

Contents

• 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 ProMan
Definition of exposure limits for different frequency bands
Comparison of predictions to specified exposure limits

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

2012 © by AWE Communications GmbH 2

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 Occupational Exceedance
zone zone zone


Introduction

• 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)


Introduction

• 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):

Occupational General public
Whole body (average SAR) 0.4 0.08
Head and trunk (local SAR) 10 2

Limbs (local SAR) 20 4

• Derived reference levels from 400 MHz to 2000 MHz by ICNIRP (average over time):
Occupational General public
Electric field strength (V/m) 3*sqrt(frequency) 1.375*sqrt(frequency)

• Partly lower national margins (e.g. in Switzerland reduction by factor 10)
• Simultaneous exposure to multiple sources: superposition with formula
2
 87 
 i 100kHz  Ei    i 1MHz  Ei EThreshold   1.0
1 MHz 300 GHz 2

 
 f 

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

Environment ca. 2-10m
Tx Power

few dm

Site certificate


Introduction

Example for Determination of Safety Distance

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
a

Total max. power on antenna input P in W 15.01 * * P [W ]  n  Pa 10 10

Electrical field strength threshold for general public areas 59.00

Safety distance in main beam direction in m 2.86** ** 30  P  Gi
r
EThreshold


Introduction

EMC and the Radiation of Electromagnetic Waves

• 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


Introduction

Methods for the Exposure Level Assessment
• 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


Introduction

Inputs for Exposure Level Assessment

• 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, …)


Coverage vs. Exposure (1/8)

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

Coverage: Field Strength > Threshold (Receiver sensitivity)
Receiver Sensitivity depending on
- thermal noise (bandwidth!)
- interference (co-channel, adjacent channel leakage)

Exposure: Field Strength < Threshold (Health risks)
Threshold depending on
- thermal effects
- national margins

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



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



Summary 40…45 dBµV/m 130 dBµV/m
Field
Threshold Strength
< Field Strength < Threshold
(Receiver sensitivity) (Health risks)

Indoor Max. allowed dynamic range of signal :
Problem
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!


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

Threshold ICNIRP
Field Strength: 152,3 dBµV/m

Threshold Switzerland
Field Strength: 132 dBµv/m

Threshold Receiver
Field Strength: 40..45 dBµV/m

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

Indoor Coverage (Visualisation of Thresholds)

Threshold ICNIRP


Threshold Receiver

Penetration loss: 20 dB

 EMC thresholds are no problem…but insufficient indoor coverage

Indoor Coverage with increased Tx power (30 dB !)

Threshold ICNIRP


Threshold Receiver

Penetration loss: 20 dB

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


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

 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


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



Thesis 1: the higher the max. traffic density, the smaller the cell radius
(max. number of users per cell reduces cell size with increasing traffic)

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

Case Study:
Cell size [km2]
Case 1: 6

10 simultaneous users per km2 5

 Cell Area: 5 km2 4

Size of cell [km2] 3

Case 2: 2

50 simultaneous users per km2 1

 Cell Area: 1 km2 0
10 20 30 40 50 60 70 80 90 100
User per km 2



Thesis 2: the smaller the cell radius, the lower the antenna height
(shadowing of buildings increases with decreasing antenna heights)

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



Results: 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

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

Case Study: 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)

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 Strength
Single Antenna Configuration Multiple Antenna Configuration

Max. Value = 130 dBµV/m Max. Value = 125 dBµV/m
Mean Value = 69 dBµV/m Mean Value = 64 dBµV/m


Comparison of Coverage Probability

Bad coverage probability in many Coverage Probability > 90%
buildings (especially at the border) nearly everywhere


Comparison of Required Tx Power in Downlink

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


EMC Module in ProMan (1/4)

Features of EMC module in ProMan
• 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)



• 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



• 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



• 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: 2
 87 
 i 100kHz  Ei   i 1MHz  Ei EThreshold   1.0
1 MHz 300 GHz 2

 
 f 

- Resulting exposure plot including all carriers and standards
with comparison to overall threshold of 1.0 for superposed exposure limit


Propagation emc

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