Overview of new technologies

Jørgen Bach Andersen, Aalborg University, Denmark

Sven Kuhn, Rasmus Krigslund, Troels B. Sørensen

GSM + UMTS

Gausssian Minimum Shift Keying (GMSK)

Constant envelope modulation, all the information is in the phase

GSM

Time domain Frequency domain

No higher frequencies in the case of GSM (except for EDGE)

WCDMA (UMTS) 3G

• multiple access is controlled by code division• rapid power control at 1500 Hz• non-constant envelope modulation

Uplink. Browsing with a handset

T=64 ms (0-5 kHz) T=0.5 ms (0-4 MHz)

Chip rate

Measured spectrum from WCDMA base station

0-10 kHz 0-50 kHz

Note the dominant 15 kHz common pilot signal, different from the 1500 Hz power control component. Also a weak 100 Hz.

By coding the signal is spread over a larger bandwidth with the consequence of having a processing gain equal to the bandwidth ratio. For speech the gain is large, for high data rates it is small.

Rapid power control ensures low as possible transmit powers.

WCDMA (UMTS) 3G

GSM1800

GSM900

3G UMTS

Handset transmit Handset receive

From Gati et al, Duality between uplink local and downlink whole-body exposures in operating networks, IEEE Transact EMC, 2010,52,no4,829-836

LTE 3.9 G

‘Long Term Evolution’ system is the answer to high data rates, for 4G theoretically 1 Gb/s in downlink (from base to user).It is basically different from 3G in access method and modulation. A flexible bandwidth scheduling with bandwidths up to 20 Mb/s. In the OFDM system the bandwidth is divided up into many narrowband subcarriers.Voice is just another type of narrowband data, voice over IP..

Distribution of subcarriers for data and control

Power vs time. Note non-constant envelope, 1 ms pulsing and deep nulls

LTE is more like GSM than UMTS what power concerns.

Multiple antennas is another new feature in LTE.

WiFi exposurefrom access points

Exposure from handheld devices will be much smaller than from a phone due to the larger distance.

WiFi

2.45 GHz. Uploading a file, two different time resolutions

T=1 s T=1 ms

Absorbing people

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without passengerswith passengersdifference

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diffuse theoryexperiment HRLOS theoryexperiment AR

Measuring whole-body-absorption by real people

Incident power density determineswhole-body SAR . The closest takes all!

RFID

Radio-frequency identification (RFID) is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, through a reader for the purpose of identifying and tracking the object.

Some RFID tags can be read from several meters away and beyond the line of sight of the reader. The application of bulk enables an almost-parallel reading of tags.

RFID: Background 1/2

• Usage: Automatic identification– Facilitates mapping from the physical world

(objects) to the digital world

Picture from: http://www.rfideducationlabs.com/Portals/0/Inbound%20RFID%20Solution04f.jpg

RFID: Background 2/2

• Equipment:– Tags: Cheap transceivers holding a unique ID

• Passive: no internal power source• Semi-passive: Internal power source for processing• Active: Internal power source for processing and transmission

– Reader: Identifies and interrogates tags

Picture from: http://www.impinj.com/Speedway_Revolution_Reader.aspx

RFID: Operation 1/2

• Reader <-> Tag: Reader-Talks-First– Reader initiates session by informing about #available

slots– A tag chooses a slot to reply in at random

• Tag makes aware of itself in chosen slot• Reader acknowledges (Hand-shake)

– Tag replies with ID + potential application specific data• The reader implements an anti-collision protocol

for when tags replies in the same slot

RFID: Operation 2/2

• Reader transmits a continuous carrier wave– Passive tags are powered up by the current

induced in their antenna• Commands to tags: Special AM modulation of

carrier

• Tag reply to reader: Backscattered carrier wave

Pulse Interval Encoding, PIE

RFID: Typical Signal

• Frequency: UHF (865-868 MHz in EU)• Transmission power: 30 dBm (1 Watt,

maximum in EU for indoor use)• Tag type: Passive• Ensuring continuous power to tag:

– Mod. index of 90%– Pulse Interval Encoded (PIE) symbols

• Number of slots per session: 16

Conclusions

1. In terms of average power from mobile phone at head exposure UMTS is widely to be preferred compared with GSM and LTE, orders of magnitude smaller. Most phones accept both 2G and 3G, user may choose.

2. For WIFI exposures are weak due to the distance factor, which also means that the person(s) closest to access point will receive most of the power.

3. RFID is also away from the head, but relatively high power and continuous radiation.