Impact of VoIP Services on the Level of Head Exposure to Radiation from 3G Smartphones

Impact of VoIP Services on theLevel of Head Exposure to

Radiation from 3G Smartphones

Hayat Abdulla and Renny E. Badra

Departamento de Electrónica y Circuitos - Universidad Simón Bolívar

Caracas, Venezuela

Why Voice over IP (VoIP)? So far, all studies considering head emissions from cell

phones are referred to circuit-switched voice services.

However, the use of packet-switched voice-over-IP(VoIP) speech connections is becoming increasinglyattractive for cellular users, given its advantages interms of cost and connectivity.

Moreover, there is consensus around the fact that in thenext decade or so VoIP will be the dominant protocolfor voice services across all segments of a cellularnetwork, including its radio interface.

Skype is the dominant commercial VoIP services (over700 million subscribers worldwide).

Why a system-level study? So far, prevention efforts have been focused on

controlling the maximum output levels of cell phones.Only a small fraction (less than 10%) of mobiles in atypical cell transmit at maximum power.

Little attention has been paid to the impact of systemparameters, such as voice technology and quality ofcoverage, on other relevant statistics of the emissions.

Overwhelming evidence indicates that cell phone useshould not be a reason for generalized public healthconcern.

However, the scence on this is not fully settled, as seenfrom a number of recent studies on the subject…

50 minutes of cell phone use significantly alterbrain glucose activity

USA2011

No correlation found between cell phone useand brain tumors

4 scandinaviancountries

2009

Brain tumor incidence on british populationfound to have grown only marginally from1998 to 2007 (0.6 cases per 100.000 inhab.)

UK2011

50% increase in risk of parotid glande tumorsamong cell phone users

Israel2008

In some cases, long-term use and glioma foundto be possitively correlated. In other cases,regular use and several types of tumors foundto be negatively correlated.

13 countries

(INTERPHONE)

2007

no link between cell phone use and braintumor risk in long-term users (10 years

Denmark2006

Summary of ResultsCountryYear

WHO, june 2011

The WHO/International Agency for Research on Cancer(IARC) has classified radiofrequency electromagneticfields as possibly carcinogenic to humans (Group 2B),based on an increased risk for glioma, a malignant typeof brain cancer, associated with wireless phone use.

This conclusion is based on the analysis of previousresearch and not in any new research.

The Group 2B list of possible carcinogenic include over200 items, including coffee!

SAR and transmit power

Effect of non-ionizing radiation over organic tissue isheat dissipated from EM emissions.

SAR (Specific Absortion Rate) is defined as the amountof power dissipated per unit mass of tissue [W/kg].

For regulatory purposes, SAR is obtainedexperimentally.

Maximum FCC tolerated head SAR level is 1.6 W/kg(source: ANSI).

This work asumes a linear relationship between SAR andaverage transmit power:

!

SAR = Pt"K

SAR

Experiment Design

Determine statisticsof transmit power

Obtain statistics ofSAR

Evaluate impact ofsystem parameters

Monte Carlo Simulations (approx.260.000 trials per cell).

Link power budget obtained usingstatistical propagation models.

Power control algorithms applied.

Parameter KSAR obtained for each cellphone model under study.

Linear relationship between SAR andaverage power applied.

Effect of system parameters on twoindicators (average SAR throughoutcell and percentage of trials above0.16 W/kg) is evaluated.

W-CDMA uplink traffic scenarios

Parameter Circuit-

Switched

Voice

VoIP using

Standard

Protocols

VoIP using

SKYPE®

Voice Codec GSM-EFR GSM-EFR iSAC

Vocoder rate 12.2 kbps 12.2 kbps 32 kbps

Bit rate at MAC

level

15.7 kbps 18..2 kbps 50 kbps

Transmission Time

Interval (TTI)

20 ms 20 ms 30 ms

RLC mode Transparent Unacknowledged

Channel coding CRC + Rate-1/3 Convolutional

Voice Activity

Factor

0.67 0.67 1.00

BLER 1% 1% 5%

Required Eb/No 5 dB 5dB 1.5 dB

Link Budget Analysis

!

Pmin

= Rsen + Lp + Lii

" # Gi

i

"

!

Pt= Power_Control (Pmin )

Minimum RequiredTransmit Power

ReceiverSensitivity

Radio ChannelPropagation Loss

Other power lossesalong signal path

Power gains alongsignal path

Actual Transmit Power Application of power control algorithm

Link Budget Parameters

Parameter Value

UE max transmit power 22 dBm

UE ant. gain + cable loss 0 dB

Receiver Noise Figure 4.0 dB

Receiver Sensitivity Service-dependent (see Eq. (5))

NodeB Antenna Type Sectorized, 90° beamwidth

NodeB Antenna Max Gain 16.1 dBi

NodeB Cable losses 2 dB

Uplink CDMA Load Factor 3.0 dB (50% cell load)

NodeB antenna diversity

gain Included in (Eb/No)req

Radio Channel Model

Street-level locations with 1/3 probabilityIn-building locations with 2/3 probability

Indoor / Outdoor locations

COMPONENT MODEL

Distance-dependent propagation loss COST 231 Extension of Hata Model for the1900 MHz band

Shadowing loss Zero-mean log-normal random variable withstandard deviation of 8 dB (outdoors) or 11 dB

(indoors)Small scale fading Rayleigh amplitude distribution

Structure penetration loss Fixed: 12 dB (indoor locations only)

Human body loss Fixed: 3 dB

LOS/NLOS discrimination All locations NLOS (non-Line of Sight)

Power Control ParametersParameter R’99 W-CDMA

Maximum Power 23 dBm

Minimum Power -50 dBm

Granularity 1 dB

Transmit Power

CallBegins

Max Transmit Power

Call Time

Minimum requiredtransmit power

Smartphone Parameters andSimulation Scenarios

Device SAR [w/Kg] <Pt>

[dBm]

KSAR [Kg-1

]

1 1.19 22.2 7.17

2 0.906 21.9 5.85

3 1.41 22.3 8.30

Simulation

Scenario

Street-level cell

area coverage

confidence

Cell radius

A 90% 1350 m.

B 95% 1020 m.

Results: Average SAR

Results: Fraction of trials withSAR > 0.16 w/kg.

Other Results

When compared to CS voice, VoIP cell area coverage isslightly lower (2-3% for standard VoIP and 5-6% for Skype).

When compared to CS voice, average transmit power risesby about 0.2 dB (standard VoIP) and by 2.0 dB (Skype) Fraction of mobiles transmitting at maximum power

increases by 5-6% (standard VoIP) and 10-12% (Skype).

Big differences among devices in average SAR and fractionof trials with SAR>0.16 w/kg.

Conclusions

We have quantified the level of head emissions fromcellular phones operating under the three major voicetechnologies, as a function of system parameters. Novel methodology based on linearly relating SAR and

transmit power.

SAR levels depend on coverage confidence levels of thecell more strongly than on any other system parameter Higher confidence reduce SAR levels. Improving the reverse link budget design margins translates

not only into higher coverage reliability but also into lowertransmit power levels and lower head emissions.

Conclusions

The use of VoIP always carries an increase of averageemissions as well as other relevant statistics. Increase when stadard protocols are used is small, but with

proprietary service Skype, it may be as high as 60% in termsof average SAR.

Rise in emissions linked to the fact that under Skype,average mobile transmit power increases by about 2 dBwith respect to circuit switched voice services. Power increase is related to substantially higher bit rates

required by the Skype application. More research on traffic generated by Skype VoIP client is

requiered.

Conclusions

Cell area coverage shrinks under VoIP protocols, ascompared to CS voice. Reduction is only about 2-3% for standard VoIP and 5-6% for

Skype.

Significant differences in average SAR can be observedamong devices (up to 42%). Such differences are linked to differences in KSAR among

devices.

Additional Results: Skype Codectype and WCDMA BLER analysis

0 20% 40% 60% 80% 100%

A ScenarioB Scenario

BLER=10%

G.7

29 BLER=1%

BLER=10%

iSAC BLER=1%

BLER=10%

SVO

PC BLER=1%

Increase in average SAR with respect to CS voice

Additional Results: Skype Codectype and WCDMA BLER analysis

BLER=10%G.7

29 BLER=1%

BLER=10%

iSAC BLER=1%

BLER=10%SVO

PC BLER=1%

0 10% 20% 30% 40% 50% 60%

A ScenarioB Scenario

CS voice

Fraction of Monte Carlo trials with average SAR of 0.16 watt/Kg or more

Additional Conclusions

Setting BLER in the W-CDMA to lower values reducesSAR levels BLER around 1% prevents packet retransmissions and

drastically reduces over-the-air bit rate

Strong influence of the voice CODEC type used by Skype G.729 induces the lowest emissions, while SVOPC induces

the highest iSAC and SVOPC preferred for end-to-end Skype calls, while

G.729 is typically chosen for SkypeOut calls Codec choice can be controlled by user to a certain extent

Hayat Abdulla and Renny E. Badra

Departamento de Electrónica y Circuitos - Universidad Simón Bolívar

Caracas, Venezuela

Impact of VoIP Services on theLevel of Head Exposure to

Radiation from 3G Smartphones