3G Principles

3rd generation of mobile communication

Osman GÜLERCAN16169230356

The evolution

GSM

3G

GPRS

EDGE

HSCSD

Main advantages of 3GComparison to GSM

• increased capacity (4 – 5 times higher)

• datarates up to 2 Mbits/s

• longer call duration (lower TX power)

• improved call establishment

• datarates adjustable as needed

• less dropped calls

3G network architecture• CN

• Core Network (PS or CS)

• UTRAN

• UMTS Terrestrial Radio• Access Network

• UE

• User Equipment

• Iu

• Uu

3G network components

PSTN

A B

Iu-CS

IubUu

IP network

Iu-PS

Gn Gi

NodeBUE RNC

ATM-Module MSC

SGSNGGSN

UTRAN CN

GSM cell structure• Each Base Station (BS) contains of one or more

Base Transceiver Stations (BTS) and serves a certain area

BTS (f2)

BTS (f3)

BS

BTS (f5)

BTS (f1)

BS

BS

BTS (f6)

BTS (f4)

BS

BS

BS

BS BTS (f4)

BTS (f1)

BTS (f2)

BTS (f5)

BTS (f6)

BTS (f1)

BTS (f5)

BTS (f2)

BTS (f3)

BTS (f7)

• In adjacent cells are different

frequencies (f1, f2, …) used

• The same frequencies are reused in distant cells

FDMA(Frequency Division Multiple Access)

• To increase the effiency resp.

capacity, each frequency is splitted into 8 timeslots

TDMA(Time Division Multiple Access)

Node B

3G cell structure

- In FDD each Node B has the same frequency for the downlink and the same frequency for the uplink.- However macrocells, microcells and picocells has their own frequency bands.

Node B

Node B Node B

Node B

macrocell

microcell, FDD (ful = f3, fdl = f4)

picocell, TDD (ful = fdl = f5)FDD (ful = f1, fdl = f2)

UMTS frequency ranges

1900 -1920 MHz : UTRA TDD (4 x 5 MHz bands)

1920 -1980 MHz : UTRA FDD uplink (12 x 5 MHz bands)

2010 - 2020 MHz: UTRA TDD (2 x 5 MHz bands, not licensed)

2110 - 2170 MHz: UTRA FDD downlink (12 x 5 MHz bands)

In future:

1980 - 2010 MHz: MSS uplink

2170 - 2200 MHz: MSS downlink

TDD = Time Division Duplex (uplink and downlink)

FDD = Frequency Division Duplex

MSS = Mobile Satellite Service

f/MHz

1900 2110

TDDFDD

uplink

FDD

downlinkTDDMSS MSS

FDD mode

In FDD mode is for downlink and uplink a separate 5 MHz band used

FDD is used in macro- and microcells

Uplink Downlink

5MHz

f190 MHz

5MHzP

TDD mode

f

t

TDD frame (10 ms)

15 slots, each of them 2/3 ms

5 MHz

In TDD mode is one 5 MHz band used for uplink and downlink. The band is splitted into 15 timeslots.

TDD is mainly used in picocells

Timeslot configuration

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

TDD -Frame, 15 Timeslots, 10 ms

Dow

nlin

k

Dow

nlin

k

Dow

nlin

k

Dow

nlin

k

Dow

nlin

k

Dow

nlin

k

Dow

nlin

k

Upl

ink

Upl

ink

Upl

ink

Upl

ink

Upl

ink

Upl

ink

Upl

ink

Upl

ink

The timeslots can be configured flexible for downlink or uplink

Cell organization and data rates

Macrocell (~ 2 km)

Microcell (~ 1 km)

Picocell(~ 60 m)

Size Datarate Speed

Macrocell 2 km 144 kbits/s 500 km/h

Microcell 1 km 384 kbits/s 120 km/h

Picocell 60 m 2 Mbits/s 10 km/h

Codemultiplexing

Power (P)

Time

Frequency

Subscribers are separated by unique codes and sharing the provided power level

Subscriber 1 (Code1, Power1)

Subscriber 2 (Code2, Power2)

Spreading

Because the RF signal is spread it becomes less sensitive against interferences

GSM

3G

f

f

frequency selective interference

200 kHz

5 MHz

P

P

Transmission principle

ff

ff

User AUser A

User BUser B

DataData Data afterData afterspreadingspreading

P

P

TransmissionTransmissionover the airover the air

Despreadeduser A signalin the receiver

ff

ff

ff ff

The higher the spreading factor, the lower the bitrate and the lower the power level

PP

Usage of the codes

In the Uplink (UE->NodeB), the user data and signalling information is separated by

Channelisation Codes

datasignalling In the Downlink (NodeB->UE),

cells are separated by Scrambling Codes

In the Uplink (UE->NodeB), terminals are separated by

Scrambling Codes

In the downlink (NodeB->UE), user connections are separated by

Channelisation Codes

Dedicated user channel

Channelization codes

Each call respectively data in the UTRAN are coded with an unique code (spreading code)

• To rule out the possibility of interferences, the used codes has to be independent from each other -> orthogonal

Codes are orthogonal to each other, if their scalar product is zero

Example: Code 1 = 1 0 0 1 Code 2 = 0 0 1 1

Code 1 & Code 2 are transformed to NRZ-signals: Code 1‘ = [-1, +1, +1, -1] Code 2‘ = [+1, +1, -1, -1]

-1

+1

+1

-1

+1

+1

-1

-1

= (-1)(+1)+(+1)(+1)+(+1)(-1)+(-1)(-1) = -1+1-1+1 = 0

Spreading factor & Chips

Each bit in the data stream is divided into the number of “chips” according to the spreading factor

Example: Spreading factor = 4

Data: 011

Spreading code: 1001

Coded signal

Scrambling codes

To avoid the interference of asynchronous signals, there is the second code class

Scrambling codes

These codes are „almost“ orthogonal, even if the signals are asynchronous

Quasi orthogonal coding

spreaded signal scrambled signal

scrambling code(38400 chips)

Referances

• Siemens Mobilewww.siemens-mobile.com• Alcatel-Lucentwww.alcatel.com• Motorolawww.motorola.com