Mobile Communication Systems 2Mobile Communication Systems 2 MSc Data Comm MSc Data Comm

Rolando A CarrascoProfessor in Mobile CommunicationsBSc(Hons), PhD, CEng, FIEEr.carrasco@ncl.ac.ukSchool of Electrical, Electronic and Computing EngineeringUniversity of Newcastle upon tyne

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HandoffsHandoffs

If a mobile moves into another cell whilst a transfer is in progress– the RNC transfers the packets to a channel belonging to the new BS– Requires identifying a new BS & data & control signals are allocated to

channels at the new BS

Fixed Networks

PSTN, ISDNBISDN,...

B

A

MSC

3

A

B

RNC1

BS1

BS2

FixedNetworks BS1

BS2

RNC2

Downlink

Uplink

Different Types of HandoffDifferent Types of Handoff Hard Handoff

– Communication is suspended when MS moves from one BS to another

Soft Handoff– The same signal is sent from both

BSs to MS, except for the power control commands

– Macro Diversity combining in the uplink

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Handoff or HandoverHandoff or Handover

Processing handoffs is an important task in any cellular radio system Some handoff strategies

– prioritise handoff requests over call initiation request when allocating unused channels in a cell site.

Handoffs must be– successful, infrequent and imperceptible to the users

System designers specify a signal level at which a handoff is initiated– a slightly stronger signal level is used as a threshold at which a handoff

is made – difference in the levels, such that no unnecessary handoffs take place – A drop in the signal level must not be mistaken for a momentary fade. – BS monitors signal level for a certain period of time

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Handoff in First GenerationHandoff in First Generation

In first generation analogue cellular systems, signal strength measurements are made by the base stations and supervised by the MSC.

Each base station constantly monitors the signal of all mobiles to determine their relative location.

The MSC decides if a handoff is necessary or not.

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Handoff in Second GenerationHandoff in Second Generation

In second generation systems that use digital technology, handoff decisions are mobile assisted

Mobile Assisted Handoff Operation (MAHO)– every mobile measures the received power from

surrounding BSs– continually reports the results to the serving BS– A handoff is initiated when the power received from

another BS begins to exceed the power received from the current base station by a certain level or for a certain period of time.

– The MSC no longer has to monitor the complete process

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Handoff in Third GenerationHandoff in Third Generation

Roam the entire globe Soft handover – connect to >1 BS at a time Mobile Assisted Handoff Operation (MAHO) Power control – very important

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NNOKIAOKIATMTM concept 3G terminals concept 3G terminals

Multimedia applications– Voice– web browsing– e-mail, voice– video conferencing– file transfer– database access

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Standardisation BodiesStandardisation Bodies

ITU

Internet Engineering Task Force, – Request for Comments

http://www.faqs.org/rfcs/

Radio Access TechniquesRadio Access Techniques

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)

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Code

Frequency

Time

Ch

ann

el 1

Ch

ann

el 2

Ch

ann

el 3

Ch

ann

el N

Frequency Division Multiple Access Frequency Division Multiple Access (FDMA)(FDMA)

12

Code

Frequency

Time

Channel 1Channel 2

Channel 3

Channel N

Time S

lots

Time Division Multiple Access Time Division Multiple Access (TDMA)(TDMA)

13

14

15

16

TDMATDMA

Several TDMA schemes have been studied for the third generation air interface

The frame length is 4.615 ms and it can consist of64 1/64 time slots of length 7216 1/16 time slots of length 288

Downlink Uplink

72s 288s Switching point between uplink and downlink

17Capacity and Interference for FDMA and Capacity and Interference for FDMA and TDMATDMA

The Capacity to Interference for FDMA and TDMA is defined by

where Eb is the energy per bit, I0 is the interference power per Hertz, Bc is the radio channel bandwidth in Hertz and Rb is the bit rate.

• In FDMA and TDMA Rb is equal or very similar to Bc.

b

cb

c

bb

R

B

I

E

B

R

I

E

I

C/

00

18Capacity and Interference for FDMA and Capacity and Interference for FDMA and TDMATDMA

0I

Eb

cellper channels ofNumber

32

max

ICM

N

BB

m c

t

• at the base station is always greater than 1

• Radio capacity, m, can be expressed as

where M is the total number of channels and is given byc

t

B

BM

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Macrodiversity

Code

Frequency

Time

Channel 1

Channel 2

Channel 3

Channel N

Code Division Multiple Access Code Division Multiple Access (CDMA)(CDMA)

Power Control

MAI Cancellation

20

21

22

23

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Capacity and Interference in CDMACapacity and Interference in CDMA

13312.3

1

MI

C

S

4444

4

)633.2(6)2(321

RMRMMRRM

R

I

C

S

where M is the number of Traffic channels per cell, R is the radius of the cell and is a constantfactor related to the transmission.

• If power control is applied then the interference to adjacent cells is reduced

controlpower Perfect 1

1

)1( 4

4

MRM

R

I

C

S

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CDMA ClassificationCDMA Classification

CDMA : direct sequence (DS) CDMA : frequency hopping (FH) CDMA : time hopping (TH)

Direct sequence

Frequency hopping

Time hopping

Time

Frequency

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CDMA EvolutionCDMA Evolution

Pioneer Era

Narrowband Era

Wideband Era

1949 John Pierce : time hopping spread spectrum1949 Claude Shannon and Robert Pierce : basic ideas of CDMA1950 De Rosa-Rogoff : direct sequence spread spectrum1956 Price and Green : antimultipath “RAKE” patent1961 Magnuski : near-far problem1970s Several developments for military field and navigation systems

1978 Cooper and Nettleton : cellular application of spread spectrum1980s Investigation of narrowband CDMA techniques for cellular applications1986 Formulation of optimum multiuser detection by Verdu1993 IS-95 standard

1995 - Europe : FRAMES FMA2Japan : Core-AUSA : cdma2000Korea : TTA I, TTA II

2000s Commercialization of wideband CDMA systems

WCDMA

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Basic principles of CDMABasic principles of CDMA

Multiple access capability Protection against multipath

interference

W id eb a nd N a rro w b a n d

D S

F a s tF re q u e n cyH o p p ing

S lo wF re q u e n cyH o p p ing

F H T H

P u re C D M A

D S /F HD S /T HF H /T HD S /F H /T H

T D M A /C D M A M C -C D M AM T -C D M A

H yb rid C D M A

C D M A

Privacy, interference rejection Anti-jamming capability Low probability of interception

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Direct Sequence CDMADirect Sequence CDMA

Directly modulated, discrete time, discrete valued

code signal

Analogue or Digital

Code bits are ‘chips’ (1)

Rate of Code >> Rate of Data

PSK, BPSK, D-BPSK, QPSK or

MPSK Carriergenerator

Codegenerator

Spreadingmodulation

Datamodulator

Data

DS-SS Transmitter

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DS-SS Transmitter & ReceiverDS-SS Transmitter & Receiver

Codegenerator

Carriergenerator

XWidebandmodulator

BinaryData Despreading

Datademodulator

CodeSynchronisation/

tracking

Codegenerator

Carriergenerator

BinaryData

30Generation of BPSK modulated Generation of BPSK modulated signalsignal

Data Signal

Code Signal

Data Signal x Code Signal

BPSK-modulated signal

time

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Frequency Hopped CDMAFrequency Hopped CDMA

Carrier frequency changes periodically, after T secs

Hopping pattern determined by spread code hop-set of frequencies

freq

uenc

y

timetime

freq

uenc

y

FH DS

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FH-SS Transmitter & ReceiverFH-SS Transmitter & Receiver

DataDownconverter

Frequencysynthesiser

Datademodulator

Synchr.tracking

Codegenerator

Data Up converter

Codegenerator

Frequencysynthesiser

Basebandmodulator

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Time Hopped CDMATime Hopped CDMA

Data transmitted in rapid bursts Time intervals determined by code Time axis divided into frames of M slots Uses the whole spectrum as in WCDMA, for short time

periodsfr

eque

ncy

time

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TH-SS Transmitter & ReceiverTH-SS Transmitter & Receiver

Datamodulato

r

Codegenerator

Carriergenerator

Datademodulator

Carriergenerator

Codegenerator

Dataslow in

fast out

fast in

slow out

Buffer

Data

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Improvements Vs DrawbacksImprovements Vs Drawbacks

Cell Splitting

Centralised DCA

Distributed DCA

Power Control

MAI Cancellation

Macrodiversity

Increase number of handoffs

High processing overhead (bottlenecks)

Carrier frequency usage in adjacent cells

No control of out cell interference

Codes use in interfering cells

Additional resources

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ATM Protocol Reference Model

Asynchronous TransferAsynchronous TransferMode (ATM)Mode (ATM)

Different types of services at different traffic rates using the

same unique Universal Network

Common Network Layer for all types of traffic

Intelligent Network that assures QoS

UMTS and Wireless ATM (Mobile)

– connection based,

– fixed size cells

– Service dependent, QoS traffic contracts

– IP over ATMPhysical &

ConvergenceLayer

ATM Layer

ATM Adaptation Layer

HigherLayers

HigherLayers

ControlPlane

UserPlane

Management Plane

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Access Transmission SpeedsAccess Transmission Speeds

Basic second generation (GSM, IS-95, IS-136, PDC)

Evolved second generation (GSM HSCSD and GPRS, IS-95B)10 kbps

144 kbps

2Mbps

384 kbps

GSM EDGE

IMT-2000

Fixed/Low Mobility Wide Area/High Mobility

User Bit Rate

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2G Digital Systems2G Digital Systems

GSM IS-136 IS-95 PDCMultiple access TDMA TDMA CDMA TDMAModulation GMSKa /4-DQPSKb

Coherent /4-DQPSKCoherent 8-PSK

QPSK/0-QPSKc /4-DQPSK

Carrier spacing 200 kHz 30 kHz 1.25 MHz 25 kHzCarrier bit rate 270.833 Kbps 48.6 Kbps (/4-PSK

and /4-DQPSK) 72.9Kbps (8-PSK)

1.2288 Mchip/sd 42 Kbps

Frame length 4.615 ms 40 ms 20 ms 20 msSlots per frame 8/16 6 1 3/6Frequency band(uplink/downlink)(MHz)

880-915 / 935-9601720-1785 /1805-18801930-1990 /1850-1910

824-849 / 869-8941930-1990 /1850-1910

824-849/869-8941930-1990 /1850-1910

810-826 /940-9561429-1453/1477-1501

Speech codec RPE-LTPe 13 KbpsHalf rate 6.5 KbpsEnhanced full rate(EFR) 12.2 kbps

VSELPf 8 KbpsIS-641-A: 7.4 Kbps(ACELP)g

US1: 12.2 Kbps(ACELP)

QCELP 8 KbpsCELP 8 KbpsCELP 13 Kbps

VCELP6.7 Kbps

Maximumpossible datarate

HSCSD:115.2 KbpsGPRS : 115.2 –182.4 Kbps(depending on thecoding)

IS-136+: 43.2 Kbps IS95A:14.4 KbpsIS95B:115.2 Kbps

28.8 Kbps

Frequencyhopping

Yes No N/A No

Handover Hard Hard Soft Hard

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Global System for Mobile, GSMGlobal System for Mobile, GSM

Allocation of a common European frequency band in 1978

Two 25 MHz bands around 900 MHz for mobile In 1990 it was decided that GSM frequency

should be 1800MHz.

GSM radio interface GSM Phase 2+8 channels per carrier Adaptive multirate coder200 – KHz carrier bandwidth 14.4 Kbp data serviceSlow frequency hopping General packet radio service

Enhanced data rates using optimised modulation (EDGE)

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GSM Development Time ScheduleGSM Development Time Schedule

1982 Groupe Special Mobile established within CEPT 1984 Several proposals for GSM multiple access : wideband TDMA,

narrowband TDMA, DS-CDMA, hybrid CDMA/FDMA, narrowband FDMA 1986 Eight prototype systems tested in CNET laboratories in France Permanent nucleus is set up 1987 Basic transmission principles selected : 8-slot TDMA, 200-kHz carrier

spacing, frequency hopping 1987 MoU signed 1988 GSM becomes an ETSI technical committee 1990 GSM phase 1 specifications frozen (drafted 1987 – 1990) GSM1800 standardisation begins 1991 GSM1800 specifications are frozen 1992 GSM900 commercial operation starts 1992 GSM phase 2+ development starts

41GSM Development Time Schedule GSM Development Time Schedule cnt..cnt..

1995 GSM submitted as a PCS technology candidate to the United States

1995 PCS1900 standard adopted in the United States 1996 Enhanced full rate (EFR) speech codec standard ready 1996 14.4-Kbps standard ready GSM1900 commercial operation starts 1997 HSCSD standard ready GSM cordless system (home base station) standardisation started EDGE standardisation started 1998 GPRS standard ready WCDMA selected as the third generation air interface

1 GSM1800 was originally termed DCS1800 (Digital Cellular System 1800).

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3G Air Interface3G Air Interface

Wideband CDMA CDMA has a bandwidth of 5 MHz or more Data rates of 144 and 384 Kbps Even 2-Mbps peak rate Provision of multi-rate services Packet data and complex spreading A coherent uplink using a user dedicated pilot Additional pilot channel in the downlink for beamforming Seamless inter frequency handover Fast power control in the downlink Optional multi-user detection

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Features of Wideband CDMAFeatures of Wideband CDMA

WCDMA Korea TTA II Korea TTA I CDMA2000Chip rate (1.024) / 4.096 /

8.192 /16.384 Mcps

1.024 / 4.096 /(8.192) /16.384 Mcps

0.9216 /3.6864 /14.7456 Mcps

1.2288 / 3.6864 /7.3728 / 11.0593 /14.7456 Mcps fordirect spreadn x 1.2288 Mcps(n=1,3,6,9,12) formulticarrier

Carrier spacing (1.25), 5, 10, 20MHz

1.25, 5, (10), 20MHz

1.25, 5, 20 MHz 1.25, 5, 10, 15, 20MHz

Frame length 10 ms 10 ms 20 ms 20 msInter base stationsynchronisation

Asynchronous Asynchronous Synchronous Synchronous

Coherent detection User dedicated timemultiplexed pilot(downlink anduplink), andcommon pilot indownlink

UL : Pilot symbolstime multiplexedwith power control(PC) bits DL :Common pilotchannel

UL : Pilot symbolstime multiplexedwith PC bits DL :Common pilotchannel

UL : Pilot symbolstime multiplexedwith PC bitsDL : Commoncontinuous pilotchannel andauxiliary pilot

Note : UL=uplink, DL=downlink

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136 HS and GSM EDGE parameters136 HS and GSM EDGE parameters

136 HS (Vehicular/Outdoor) /GSM EDGE

136 HS (Indoor)

Duplex method FDD FDD and TDDCarrier Spacing 200 kHz 1.6 MHz Modulation

B-O-QAMQ-O-QAMGMSK

B-O-QAMQ-O-QAM

Gross bit rate 722.2 Kbps (Q-O-QAM)361.1 Kbps (B-O-QAM)270.8 Kbps (GMSK)

5200 Kbps (Q-O-QAM)2600 Kbps (B-O-QAM)

Payload 521.6 Kbps (Q-O-QAM)259.2 Kbps (B-O-QAM)182.4 Kbps (GMSK)

4750 Kbps (Q-O-QAM)2375 Kbps (B-O-QAM)

Frame length 4.615 ms 4.615 msNumber of slots 8 64 (72 s )

16 (288 s )

Coding Convolutional 1/2, 1/4, 1/3, 1/1ARQ

Convolutional 1/2, 1/4, 1/3, 1/1Hybrid Type II ARQ

Frequency Hopping Optional OptionalDynamic Channel Allocation Optional OptionalNote: the modulation parameters are for the original EDGE and UWC-136 proposals (B-O-QAM and Q-O-QAM), In 1998, a new modulation scheme (8-PSK) replacing the original schemes has been adopted.

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