06_gsm-umts

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Prof. Dr. Claudia Linnhoff-Popien

Moritz Kessel, Kevin Wiesner

http://www.mobile.ifi.lmu.de

Wintersemester 2010/2011

Praktikum Mobile und Verteilte Systeme

GSM & UMTS - Introduction

http://www.mobile.ifi.lmu.de/

http://www.mobile.ifi.lmu.de/

7/29/2019 06_gsm-umts


Prof. Dr. C. Linnhoff-Popien, M. Kessel, K. Wiesner - Praktikum Mobile und Verteilte Systeme

Wintersemester 2010/2011, GSM & UMTS - Introduction

GSM & UMTS - Introduction

Today:

• GSM – Global System for Mobile Communication

– System architecture

– Addressing and location management

– Air interface

• UMTS – Universal Mobile Telecommunications System

– System architecture

– Air interface

Next week:

•

Mario Jaritz: Mobilfunk in der Praxis

Note:

Some slides originate from the lecture Mobile Communications.

By courtesy of Axel Küpper

2

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Evolution Path: From GSM to LTE

3

GSM speech

Short Message

Service (SMS)

Data services

(circuit switched)

2G

General Packet Radio

Service (GPRS)

Multimedia Messaging

Services (MMS)Wireless Application

Protocol (WAP)

High-Speed Circuit

Switched Data

(HSCSD)

Location-based

Services (LBS)

Enhanced Data Rates

for GSM Evolution

(EDGE)

Global System for

Mobile Communications

(GSM)

High-Speed

Downlink/Uplink

Packet Access

(HSDPA/HSUPA)

Long Term Evolution

(LTE)

Universal Mobile

Telecommunications

System (UMTS)

Streaming (Audio/

Video)

Video Telephony Mobile Internet

Push Email

Push-to-Talk

Over-Cellular

(PoC)

2.5G 3G 3.5G 4G

1990 2010

Network technologies/services

High-level services

Service functionalityData rate

Quality of transmission

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GSM

• 1982: Groupe Spécial Mobile established by Conférence Européenne des

Administrations des Postes et de Télécommunications (CEPT)• 1987: Elements of wireless transmission are specified based on prototype evaluation

• 1989: GSM becomes a Technical Committee of the new European TelecommunicationStandards Institute (ETSI)

• 1990: GSM 900 specifications are frozen. Adaption to DCS 1800 (Digital Cellular Systemat 1800 MHz) commences

• 1991: First GSM networks launched. DCS 1800 specification finalized and frozen

• 1993: First roaming agreements in operation. 32 networks in 18 countries areoperational

• 1994: Data transmission capabilities launched. 69 networks in 43 countries

• 1995: First PCS 1900 (Personal Communications System at 1900 MHz) network islaunched in the US

• Data and SMS roaming starts; Video transmitted by GSM for demonstration

•

1998: 320 GSM networks in 118 countries with 135 million subscribers worldwide• 1999: Wireless Application Protocol; 130 countries, 260 million subscribers

• 2000: 362 million subscribers; Introduction of General Packet Radio Service (GPRS)

• 2004: 1 billion subscribers; 200 countries

• 2007: 2 billion subscribers

4

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GSM – Architecture

AUC Authentication Center ISDN Integrated Services Digital Network

BSC Base Station Controller MSC Mobile Switching Center

BTS Base Transceiver Station OMC Operation and Maintenance Center

EIR Equipment Identity Register PSTN Public Switched Telephone Network

GGSN Gateway GPRS Support Node SGSN Serving GPRS Support Node

GMSC Gateway Mobile Switching Center SMSC Short Message Service Center

HLR Home Location Register VLR Visitor Location Register

5

BSC

BTS

BTS BSC

BTS

MSC

VLR

MSC

VLR

HLR EIR OMC

AUC GMSC

PSTN /

ISDN

SMSC GGSNInternet

SGSN

SGSN

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Components – Mobile Station

Mobile Station (MS)

• Used by mobile service subscribers for

access to services, e.g., voice telephony,

SMS, or browsing the Internet

• Contains the mobile equipment (transceiver,

mechanisms for media access, coding, ...)

and the SIM

Subscriber Identity Module (SIM)

• Personalization of mobile stations

• Provides separation of personal from

terminal mobility (e.g., enabling international

roaming independent of mobile equipment

and network technology)

• Contains cryptographic algorithms to support

authentication and user data encryption

• Storage of charging information,SMS, and telephone book

• Protection with a PIN againstunauthorized access

• Network specific data (organizationof air interface)

• SIM Application Toolkit (SAT):execution environment for operator specific functions

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Components – Base Station Subsystem

Base Station Subsystem (BSS)

• Consists of a Base Station Controller

and one or more Base Transceiver

Stations

Base Transceiver Station (BTS)

• Defines a single radio cell with a radius

of between 100m and 35 km

(depending on the environment)

• Each BTS is allocated a set of

frequencies (Cell Allocation, CA)

• Contains radio antenna, radio

transceiver, and link to a base station

controller

• Signal and protocol processing is

limited to error protection, encryption,

and link level signaling

Base Station Controller (BSC)

• Controls one or multiple BTS units

and hence multiple cells

• Performs essential control functions

and coordination between BTSs, e.g.

• Reservation of radio frequencies

• Management of handover from

one cell to another within the

same BSS

• Control of paging

• ...

BTS

BTS

BSC

BTS

BSC

BTS

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Components – Switching Centers

Mobile Switching Center (MSC)

• Performs all switching functions of a

fixed-network switching node, e.g.

routing path search, signal routing,

service feature processing)

• Difference between conventional fixed

network switch and MSC: allocation

and administration of radio resourcesand mobility of subscribers (supports

location registration, handover

between different BSCs, ...)

• Support of service features like call

forwarding or conference calls

• Signaling between MSCs andbetween MSCs and other logical

entities by the Signal System No. 7

Gateway MSCs

• Passing of voice traffic between

fixed and mobile networks

• Required as access to GSM

network, because fixed network is

unable to connect an incoming call

to the local target MSC (due to its

inability to interrogate the HLR)

MSC

VLR

MSCVLR

HLR EIR OMC

AUC GMSC

PSTN /

ISDN

SMSC GGSNSGSN

SGSN

Internet

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Components – Databases, Operation and Maintenance

Home Location Register (HLR)• Central database, stores permanent

and temporary information about eachof the subscribers associated with thenetwork

Visitor Location Register (VLR)•

Database containing distributednodes, each being responsible for acertain coverage area

• Contains information aboutsubscribers currently physicallystaying in the associated coveragearea

•

Usually combined with an MSC

Other components• SMS gateway

• WAP gateway

• ...

MSC

VLR

MSCVLR

HLR EIR OMC

AUC GMSC

PSTN /

ISDN

SMSC GGSNSGSN

SGSN

Internet

Components for Operation andMaintenance

• Operation and Maintenance Center

(OMC): controls and monitors all

network entities (traffic and status

reports, accounting and billing,...)

• Authentication Center (AuC):Protects user identity and data

transmission

• Equipment Identity Register (EIR):

Stores all device identification

registered for this network

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Components – GPRS Infrastructure

• GSM was initially designed for circuit-

switched voice telephony• MSCs operating in circuit-switched

mode cannot be used for packet-switching

• Introduction of the packet-switchedGeneral Packet Radio Services(GPRS) for offering packet-switched

data services• Reuse of existing access networks

• Introduction of a new core network

Serving GPRS Support Node• Internet router with mobility support

•Counterpart of MSC

Gateway GPRS Support Node• Gateway to the public Internet

• Counterpart of GMSC

MSC

VLR

MSCVLR

HLR EIR OMC

AUC GMSC

PSTN /

ISDN

SMSC GGSNSGSN

SGSN

Internet

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GSM – Medium Access

• Combination of TDMA and FDMA

11

124

…

…

…

…

…

...1

124

…

……

…

…

2

1

960 MHz

959,8 MHz

935,2 MHz

935 MHz

915 MHz

914,8 MHz

890,2 MHz

890 MHz

200 KHz

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

3 Time slots delay

Data burst = 576,9 µs

Downlink

Uplink

Modulation: G(MSK)

Data rate: 270,83 kbps per physical channel

BTS

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GSM – Impact of Propagation Delay

12

Mobile

Station A

Downlink

Uplink

Base Station

Propagation

delay

Mobile

Station B

Round trip propagation delay BSMS B

Propagation

delay

1 21

2 Round trip propagation delay BSMS A

Downlink

Uplink

Downlink

Uplink

!!! Collision !!!

Problem: As the distance between a mobile and a base station usually varies, the

signal propagation delays between them also vary adjacent channel interference

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GSM – Guard Intervals

• Guard times between time slots avoid co-channel interference caused by

different propagation delays

• Example:

– Distance between MS and BS: 35 km

– Synchronization signal from BS arrives after

– Necessary guard time: 234 µs

Problem: guard times decrease capacity

234 µs guard time lowers capacity by 40 %!

Solution: Adaptive frame spacing

– Guard time can be reduced down to 30 µs

13

117μsm103

m10358

3

s

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GSM – Data Bursts

10 2 3 4 6 75

4,615 ms

Data DataTraining

sequence

57 5726

3 Tail bits 1 Signaling bit 1 Signaling bit 3 Tail bits

Burst (148 bits)

Time slot (156,25 bits)

0,577 ms

Guard

time

8,25

•

Each time slot of a TDMA frame lasts 0,577ms, which corresponds to the duration of

156.25 bit periods

• 156.25 bits are assigned according to a

well-defined structure known as a data

burst

•

GSM defines five different kinds of databursts used for different purposes:

• Normal burst (shown in this figure)

• Synchronization burst

• Frequency Correction Burst

• Access Burst

• Dummy Burst

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GSM – Dummy and Access Bursts

Dummy Burst

• Transmitted on one frequency of the cell allocation, when no other bursts are to be

transmitted

• Enables the mobile station to perform signal power measurements (quality

monitoring)

• Access Burst

• Initial signal sent by the mobile station

• Increased guard period is necessary as adaptive frame alignment could not have

been established yet

• Long guard duration of the guard period compensates propagation delay if a mobilestation sends an access burst from the boundary of a cell of 70 km diameter

326 bit training

sequence

3 8.25

336 data bits41 bit training

sequence8 68.25

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GSM – Physical Channels

16

GSM 900 GSM 1800

Frequencies Uplink: 890-915 MHzDownlink: 935-960 MHz

Uplink: 1710-1785 MHzDownlink: 1805-1880 MHz

# Carriers 124 374

# Duplex Channels 992 (Full rate)

1984 (Half rate)

2976 (Full rate)

5925 (Half rate)

Duplex distance 45 MHz 95 MHz

Max. BS power 320 W 20 W

Max MS power 8 W 1 W

Max MS velocity 250 Km/h 130 Km/h

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GSM – Logical Channels

MS BSSFull rate TCHTCH/F

MS BSSHalf rate TCHTCH/H

MS BSSStand-alone dedicated controlSDCCH

MS BSSSlow associated controlSACCH

MS BSSFast associated controlFACCH

MS BSSBroadcast controlBCCH

MS BSSFrequency correctionFCCH

MS BSSSynchronizationSCH

Access grant MS BSS AGCH

Paging MS BSSPCH

Notification MS BSSNCH

Random access MS BSSRACH

Traffic channel

(TCH)

Broadcast

channel

(BCH)

Common control

channel (CCCH)

Dedicated

control

channel (DCCH)

Traffic channel

(TCH)

Control

channel

(CH)

Group Channel Function Direction

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GSM – System Hierarchy

GSM network consists of

at least oneadministrative region,

which is assigned to a

Mobile Switching Center

(MSC)

Administrative domain is

made up of at least one

location area (LA)

An LA consists of several

cell groups

A cell group is assigned

to Base Station

Controller (BSC)

For each LA there exists

at least one BSC, but

cells of one BSC may

belong to different LAs.

GSM network MSC region Location Area BSC Controller Cell

Cell

.....

BSC Controller

BSC Controller

BSC Controller

Location Area

BSC ControllerLocation Area

MSC region

MSC region

..........

.....

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GSM – Addressing and Location Management

• Permanent numbering

– Numbering of subscribers

• IMSI International Mobile Subscriber Identity

• MSISDN Mobile Subscriber ISDN

– Numbering of devices

• IMEI International Mobile Station Equipment Identity

• Temporal Numbering

• MSRN Mobile Station Roaming Number

• TMSI Temporary Mobile Subscriber Identity

• LAI Location Area Identifier

• CI Cell Identifier

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GSM – Permanent Subscriber Addresses

International Mobile Subscriber

Identity (IMSI)• Uniquely identifies the subscriber and is

stored in the SIM, HLR, and AuC

• Hierarchical addressing (example:

MCN=262 for Germany, MNC=01,02,03,07

for T-Mobile, Vodafone, Eplus, O2)

• Used, e.g., for billing

Mobile Subscriber ISDN Number

(MSISDN)

• Real telephone number of a subscriber

• Subscriber can have several MSISDNs, e.g.,

to distinguish several services (voice, data,

fax,...)

• Thus, automatic activation of service-

specific resources is already possible

during setup of connection

• Stored centrally in the HLR and in the SIM

Mobile Country

Code (MCC)

Mobile Network Code

(MNC)

Mobile Subscriber Identification Number

(MSIN)

Country Code

(CC), max. 3 places

National Destination Code

(NDC), max. 3 places

Subscriber Number

(MSIN), max. 10 places

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GSM – Temporary Subscriber Addresses

Mobile Station Roaming Number

(MSRN)• Temporary location-dependent ISDN

number

• Required to make routing decisions and toidentify the responsible MSC

• Assigned by the locally responsible VLR to

each mobile station in its area and passed tothe HLR

• Generated at each registration or when theHLR requests it for call setup (on a call-by-call basis)

VCC VNDC MSIN

Addresses the

responsible MSC

Addresses the

subscriber

Temporary Mobile Subscriber Identity

(TMSI)• Used in place of the IMSI for the definite

identification and addressing of the mobilestation

• Avoids to determine the identity of thesubscriber by listening to the radio channel

• Assigned during the mobile station’spresence in the area of one VLR (by that VLR)and can be changed during this period (IDhopping)

• Is stored by the mobile station on the SIMcard

• Is stored on the network side only in the VLR,

not in the HLR• Is assigned in an operator specific way and

consists of 4x8 Bits

• Subscriber can be uniquely identified; IMSI isreplaced by (TMSI, LAI)

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GSM – Other Addresses

International Mobile Station Equipment

Identity (IMEI)• Uniquely identifies mobile stations

internationally

• Allocated by the manufacturer, registered by thenetwork operator and stored in the EIR

• Characterizes a mobile station and gives cluesabout the manufacturer and the date of

manufacturing

Location Area Identity (LAI)• Internationally unique identification of a location

area

• Regularly broadcasted by the base station

• “Heard” by the mobile station in order to decide

whether or not a new LA has been entered

Cell Identifier (CI)• Uniquely identification of cells within an LA

• Length of CI: 2x8 bits

• Internationally unique identification with theGlobal Cell Identity (LAI+CI)

Type Approval Code (TAC),centrally assigned

Finally Assembly Code (FAC),

assigned by the manufacturer

Serial Number (SNR),assigned by the man.

Spare (SP),

not used

Country Code (CC)

Mobile Network Code (MNC)

Location Area Code (LAC)

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IMSI RAND SRES Ki Kc

IMEI

IMSI MSISDN MSRN

IMEI

IMSI, MSISDN, TMSI

MSRN IMSI TMSI MSISDN LAI

GSM – Overview of Addresses

BTS

CI, LAI

EIR

VLR

HLR

AUC

CI Cell IdentifierBSIC Base Transceiver Station Identity Code

LAI Location Area Identifier

IMSI International Mobile Subscriber Identity

MSISDN Mobile Subscriber ISDN Number

TMSI Temporary Mobile Subscriber Identity

MSRN Mobile Station Roaming Number

IMEI International Mobile Station Equipment Identity RAND Random Number

SRES Session Key

Ki Subscriber Authentication Key

Kc Cipher/Decipher Key

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ISDN

GSM – Mobile Terminated Call

24

MSISDN Mobile subscriber ISDN number

CC Country code

NDC National destination code

MSRN Mobile station roaming number

TMSI Temporary mobile subscriber identity

HLR

MSC

BTS

BSC

MSC

SS7

HLR

BTS

VLR

VLRGMSC

4

1

MSRN

2

3

5

6

8

7

7

7

Forwarding to

responsible GMSC

(based on CC and

NDC of MSISDN)

Request and

delivery of routingaddress

Forwarding to

the local MSC

Request and

delivery of

TMSI for

paging

Paging request

Paging response

MSRN

MSISDN

TMSI

MSISDN

TMSI

TMSI

TMSI

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UMTS – Release 99

25

BSCBTS

RNCNode B

MSCVLR

HLR EIR OMCAUC

GMSCPSTN /

ISDN

GGSNInternet

SGSN

AUC Authentication Center ISDN Integrated Services Digital Network

BSC Base Station Controller MSC Mobile Switching Center

BTS Base Transceiver Station PSTN Public Switched Telephone Network

EIR Equipment Identity Register RNC Radio Network Controller

GMSC Gateway Mobile Switching Center SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node VLR Visitor Location Register

HLR Home Location Register

GSM/EDGE Radio Access Network

Universal Terrestrial

Access Network

(UTRAN)

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UMTS – UTRAN-FDD

• Primarily used for speech transmission and forservices with data rates of up to 384 kbps in macroand micro cells

• A physical channel is defined by its carrierfrequency, a channelization code (OVSF), and therelative phase

• Frame structure with 15 slots for timing andsynchronization (no time multiplex)

• Variable data rates are achieved by varyingspreading factors

• Spreading factors: 1, 2, 4, ..., 256

• Depending on the number of physicalchannels used and their data rate, thenumber of available channelizationcodes varies

• The number of voice channels percarrier can be approximated to 250(256 available orthogonal codes, minussome control channels)

• Multicode and multirate users

5.0 MHz

Multicode users

Multirate user

1 frame = 10 msUTRAN-FDD mode:

Code

Frequency

Time

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UMTS – UTRAN-TDD

• Primarily used for services with data rates of up to 2 Mbps in indoor/pico cells

• A physical channel is defined by its carrierfrequency, access code, and time slot

•

Frame structure with 15 slots for timemultiplex

• Multicode, multirate, and multislot users

• Two options for combined TDMA/CDMAoperation: multicode and single codetransmission

• Multicode with fixed spreading• Each user in a time slot gets assigned a

different spreading code and up to 8 different

codes can be allocated per time slot

• Spreading factor is fixed (=8)

• Single code with variable spreading• Each user gets one code but employs a

different spreading factor depending on the

required data rate

• Spreading factors: 1, 2, 4, 8 ,16

1 frame = 15 slots = 10 ms

5.0 MHz

Multicode user

Multirate user

Multislot user

Multislot/multicode user

UTRAN-TDD mode:

Code

Frequency

Time

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UMTS – Principles of Wideband-CDMA

Principle of WCDMA

• All users are simultaneously transmitting in

the same frequency bands

• Each user interferes with each other

• Cluster size is 1, i.e., adjacent cells use the

same frequencies

• Cells, users (terminals), and physical channels

are separated by code

Codes

• Channelization codes for separation of

physical channels in the uplink and

separation of users in the downlink

•

Scrambling codes for separation of users/terminals in the uplink and

cells/sectors in the downlink

3,84 MHz

5 MHz

f

Guard Guard

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Excurs – Cross-Correlation

Cross-Correlation

Two codes have a low cross-correlation if their product is low for all shift combinations

Low cross-correlation between a sequence and noise is useful to the receiver in filtering out

noise

Low cross-correlation between two sequences is useful to the receiver to discriminate

among signals generated by different users

If the cross-correlation between two sequences is 0, the sequences are said to be full

orthogonal

Cross-correlation between c1 and c2 is

c3 and c4 are orthogonal, because their cross-correlation is

c1: +1 +1 +1 +1 −1 +1 +1 −1

c2: −1 +1 −1 +1 +1 −1 −1 +1

−1 +1 −1 +1 −1 −1 −1 −1 =4

c3: −1 −1 −1 +1 +1 −1 +1 +1

c4: −1 −1 +1 −1 +1 +1 +1 −1+1 +1 −1 −1 +1 −1 +1 −1 =0

5.08

40

2,1

08

00

4,3

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1

1,1

1,-1

1,1,1,1

1,1,-1,-1

1,-1,1,-1

1,-1,-1,1

1,1,1,1,-1,-1,-1,-1

1,1,1,1,1,1,1,1

1,1,-1,-1,1,1,-1,-1

1,1,-1,-1,-1,-1,1,1

1,-1,1,-1,1,-1,1,-1

1,-1,1,-1,-1,1,-1,1

1,-1,-1,1,1,-1,-1,1

1,-1,-1,1,-1,1,1,-1

C1,1

C2,1

C8,5

C8,4

C8,3

C8,2

C8,1

C4,4

C4,3

C4,2

C4,1

C2,2

C8,8

C8,7

C8,6

UMTS – Channelization Codes

• Orthogonal Variable SpreadingFactor (OVSF): method toobtain variable lengthorthogonal codes thatpreserve orthogonalitybetween different rates andspreading factors

• Recursive generation of variable orthogonal codesusing a tree structure

• A node adopts the code fromits predecessor andconcatenates it either with acopy of this code (firstsuccessor) or with its inverse(second successor)

• Codes of the same layer are

orthogonal• Any two Codes of different

layers are orthogonal exceptfor the case that one of thetwo codes is a mother code of the other

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UMTS – Channelization Codes(II)

Example:

C4,2 is assigned to a user

Codes C8,3 and C8,4 generated from this code cannot be assigned to other users requesting lower bit rates

Mother codes C1,1 and C2,1 cannot be assigned to users requesting higher rates

bit rate * spreading factor = 3.84 Mcps

1

1,1

1,-1

1,1,1,1

1,1,-1,-1

1,-1,1,-1

1,-1,-1,1

1,1,1,1,-1,-1,-1,-1

1,1,1,1,1,1,1,1

1,1,-1,-1,1,1,-1,-1

1,1,-1,-1,-1,-1,1,1

1,-1,1,-1,1,-1,1,-1

1,-1,1,-1,-1,1,-1,1

1,-1,-1,1,1,-1,-1,1

1,-1,-1,1,-1,1,1,-1

C1,1

C2,1

C8,5

C8,4

C8,3

C8,2

C8,1

C4,4

C4,3

C4,2

C4,1

C2,2

C8,8

C8,7

C8,6

Spreading factorBit rate

8480 kb/s

4960 kb/s

16240 kb/s

5127.5 kb/s

25615 kb/s

12830 kb/s

6460 kb/s

32

Chip rate

3.84 Mcps

3.84 Mcps

3.84 Mcps

3.84 Mcps

3.84 Mcps

3.84 Mcps

3.84 Mcps

3.84 Mcps120 kb/s

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UMTS – Drawbacks of Channelization Codes

Problem 1

•

Networks based on WCDMA haveusually a cluster size of 1

• Thus, access to the code tree must becoordinated between adjacent cells oreach cell needs its own code tree

Problem 2

• Propagation delay of users withdifferent distances to the node B coulddestroy the orthogonality of the usedcodes (see example)

• Codes are received asynchronously

Scrambling codes

• Sector and cell separation in the

downlink• Terminal and cell separation in the

uplink

• Codes remain nearly orthogonal if received asynchronously

NBx m

x+78 m

1 1 -1 -1 1 1 -1 -1 1 1 -1 -1

1 -1 -1 1 1 -1 -1 1 1 -1 -1 1Propagation delay

A

B t

User B:

C4,4User A: C4,2

Orthogonality is lost!

Example for (2):

Two users A and B use channelization codes

C4,2 and C4,4

Difference in the distance to the node B is 78 m,

which is covered by the signal in 0,26s

(corresponds to the duration of 1 Chip)

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GSM & UMTS – Practical Courses

33

Set up of

Android

project

Cell-ID

positioning

Reading of Cell

related

information

Documents

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