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Lehrstuhl fr Rechnernetze und InternetWilhelm-Schickard-Institut fr Informatik Universitt Tbingen

UMTS Networks

Leo Petrak, Dr. Christian Hoene und Prof. Georg Carle

Course OverviewMotivation Standardization issues UMTS architecture basics UMTS radio linkPhysical layer Signaling

UE, UTRAN, PS Domain, CS Domain Basic functionalities:Accessing the network Transferring data Detaching from the network Information storage

Mobility QoS Security

Charging UMTS Evolution: from R99 to Rel7 Beyond UMTS

UMTS Networks and Internet Telephony Sommersemester 2006

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UMTS Radio Link Physical Layer

Radio Communication Fundamentals Dividing Radio Resources Frequency Licensing

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Radio Communication Fundamentals

ModulationQPSK Modulation used in UMTS

Fourier Analysis Wave Propagation Scarcity of Radio Resources

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Radio Communication Fundamentals IRadio communication uses electromagnetic waves as the transmission mediumUEs / Base Stations emit and receive waves of the carrier frequency f

Signal strength of a wave P(t) = P0 cos (2ft - )

P(t) P00

-P0 UMTS Networks and Internet Telephony Sommersemester 2006

2ft

5

Radio Communication Fundamentals II - Modulation

Information is encoded by modulating (change midway) a wave of the carrier frequency f

P(t) = P0 cos (2ft + )Phase - Phase Shift Keying Frequency f - Frequency Shift Keying modulate Amplitude P0 - Amplitude Shift Keying

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Modulation in UMTS: QPSKUMTS uses Quaternary Phase Shift Keying (aus 4-er bestehende)Four possible sequences of two bits are coded: 0 0 - phase shift of 1/4 1 0 - phase shift of 3/4 1 1 - phase shift of 5/4 0 1 - phase shift of 7/4

P(t)

0

t

phase shift: Bit sequence:

1/4 00

3/4 10

5/4 11

7/4 017

UMTS Networks and Internet Telephony Sommersemester 2006

Radio Communication Fundamentals III - Fourier AnalysisSignal 0 1 1 0 0 0 1 0 1 0 1 0 1 2 3 4 5 6 7 8 9 1011 1 2. Harm. 0 1 2 3 4 5 6 7 8 9 1011 1 4. Harm. 0 1 2 3 4 5 6 7 8 9 1011 1 0 1 2 3 4 5 6 7 8 9 1011 8. Harm. T

Harmonics n

Fourier Analysis: Each signal can be described as an integral (sum) of sine waves

1 2 3 4 5 6 7 8 9 1011 1. Harm.

P(t ) =

n =1

Pn sin(2 nf t+ n)

The modulated wave is a superposition of many waves of different frequencies of a frequency band f It can be shown that f r (bandwidth data rate)

Density D(f) 2/r

Bandwidth f

f0 (f0 +1/2r) f Carrier Frequency

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Radio Communication Fundamentals IV - Wave Propagation The intensity of electromagnetic waves emitted by a point source (e.g. antenna) decreases with distance Electromagnetic waves add linearlyInterference of waves emitted by different sources When waves of same frequency interfere, extraction of information difficult Because a modulated wave occupies a frequency band of bandwidth f , interference may be a problem in mobile communications

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Radio Communication Fundamentals V - Scarcity of radio resources

Radio spectrum is a scarce resourceShared by many systems

It is necessary to clearly separate radio resources used by different entities, e.g.- Technologies - Users of the same technology "Multiple Access" - "user -> network" (uplink) from "network -> user" (downlink): "Duplex"

it is necessary to efficiently use radio resources Possibilities for separating radio resourcesFrequency division Time division Space division Code division Combinations thereof

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UMTS Radio Link Physical Layer

Radio Communication Fundamentals Dividing Radio Resources Frequency Licensing

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Dividing Radio Resources

Frequency division Time division Space divisionCellular networks

Code division Examples: GSM and UMTS

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Frequency Divisionfrequency Frequency band 3Guard band

Radio Spectrum is divided into frequency bands Power emitted outside these bands must be strictly below a certain level To be on the safe side, unused guard bands limit interference between frequency bands Receivers use filtering to receive carrier frequency of interest Already introduced in 1900 to organize usage of radio transmitters, e.g. on ships Usually used in combination with other division techniques

Frequency band 2Guard band

Frequency band 1

time

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Time Divisionfrequency Radio Spectrum usage is divided into time slotsEach sender is assigned a time slot Guard time

Time slot 2

Time slot 3

Time slot 1

UMTS Networks and Internet Telephony Sommersemester 2006

Guard time

To avoid collisions, all participating entities need to be synchronizednetwork needs to periodically synchronize terminals need to consider finite traveling time of synchronization signal, depending on distance between terminal and synchronizing entity!

time

Guard times between slots prevent collisions due to imperfect synchronization Usually used in combination with other division techniques

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Space DivisionUsage of radio resources restricted to certain geographic areas (cells) Transmission power is limiteddue to decrease of power with distance to sender, interference is limited

Re-use of same radio resource only at appropriate distance In combination with e.g Frequency Division, very large areas can be coveredreuse frequency band only in distant cells

New antenna techniques (adaptive antenna arrays / MIMO) allow forming "beam" towards specific mobile

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Space Division - The Cellular ConceptSpace Division is today the technique of choicepatented in 1972 by Bell Labs

Instead of each antenna illuminating an area as big as possible (1G Systems), each antenna covers only small arealower transmission power more efficient use of the spectrum => better coverage higher infrastructure costs need technique for switching moving users from cell to cell: "Handover"

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Code Division I Several signals are sent in the same (wide) frequency band and the same time slot Each signal is created by spreading a narrowband signal through the use of a unique user code to a multiple of the original bandwidth (spreading) [Spreizung] The receiver correlates the sum of the received signal with the (time-shifted) user code, and thereby re-obtains the original narrowband signal (de-spreading) power level of different signal needs to be aligned codes need to be uncorrelated, otherwise interference replanning cells becomes easier with this technique

code

frequency

Code 1 Code 2 Code 3

time

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Code Division II - What are these codes?Sequences S of 1 and -1 (chips) S = {S1, S2 , ... , Sn}, Si Correlation: C(j) =

i

Si Ti+j

measures how "different" two codes S and T are uncorrelated codes result in little interference e.g. S = {-1, 1, 1, 1, -1, -1, 1, -1} T = {-1, -1, 1, -1, 1, -1, -1, -1} C(0) = 0, C(1) = 2, C(3) = 0,... but Autocorrelation A(j) e.g. of S: A(0) = 8, A(1) = 0, A(2) = 4,... Autocorrelation only high if synchronized!

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{-1,1}

Code Division III - Coding and DecodingData D(t) Code S(t)-1 1 1 1 -1 -1 1 -1

Coding at sender

D(t) S(t)

Decoding at receiver with correct code

Decoding at receiver with wrong code

Code T(t - )-1 -1 1 -1 1 -1 -1 -1

D(t) S(t) S(t - ) = D(t)

D(t) S(t) T(t - ) = no data signalUMTS Networks and Internet Telephony Sommersemester 2006 19

Code Division III - SpreadingChip rate greater bit rate therefore bandwidth becomes higher after spreading [Spreizung]

Data D(t)TD

D(f) 1/TD

Bandwidth f

f0

f0+TD

f

D(t) S(t)

TDS

D(f) Bandwidth f f0 f0+TDS f

1/TDS

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Code Division IV- near-far effectDe-spreading at receiver works best when power levels of different signals are aligned. However: When senders A and B emit with same power, the signal of B at the Antenna is stronger power control is applied constantlyAntenna Controller tells sender with what power to send

B AUMTS Networks and Internet Telephony Sommersemester 2006 21

Dividing Radio Resources: SummaryUplink / downlink FDD TDD Different users FDMA TDMA CDMA SDMA

(D Duplex)

(MA Multiple Access)

Frequency Division (FD) Time Division (TD) Code Division (CD) Space Division (SD)

The different techniques for dividing radio resources can be combined, e.g. pick one technique for separating uplink / downlink pick one technique for separating different users

e.g. FDD - CDMA

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GSM: FDD + T