2g cellular networks - gsm and is95

7/30/2019 2G Cellular Networks - GSM and IS95

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2G Cellular Networks

GSM and IS95

April 15, 2013


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Classification Of ExistingSystems

Technologies

TDMA/FDMA CDMA

GSM (European Standard)

IS 136 (U.S Standard)

PDC (Japnese Standard)

IS 95 (U.S Standard)

The Next Generation Mobile Networks2


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Evolution Chart

Years

Service type

Multi

media

VoiceAnalog

AMPS

Digital

IS 95

IS 136

GSM

IMT

2000

WirelessInternet

Mobile

system

~ 24kbps ~64kbps ~2Mbps ~20Mbps

1980 1990 2000 2010

1G 2G 3G

4G

Narrow Band Wide Band

Broad Band

The Next Generation Mobile Networks 3


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Access technology

Time Time Time

Freq Freq Freq

PN Code

FDMA TDMA CDMAThe Next Generation Mobile Networks

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ComparisonBetweenTechnologies

Digital

Mobile

technology

Users

Dec-02

Users

Dec-03

Growth

in2003

% Growth Share Of

Growth

CDMA 145.2 181.0 35.4 24.3% 15.6%

GSM 790.5 970.8 180.3 22.8% 79.5%

PDC 60.1 63.1 3.0 5.0% 1.3%

TDMA 107.4 113.0 5.5 5.1% 2.4%

3 GSM

(W CDMA)

0.2 2.8 2.6 1708.5% 1.2%

GLOBAL

USER

BASE

1103.7 1330.6 226.9 20.69% 100%

The Next Generation Mobile Networks

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GSMAn Overview


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Services provided by GSM

Telephony Basic Teleservice

Other Services Emergency calling

Voice Messaging


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Services provided by GSM

Bearer Services

Low Speed data transfer (upto 9.6 Kbps)

Group 3 Fax and Sms

Suplementary Services call offering , call forwarding, call restriction,

call waiting, call hold.

Multiparty teleconferencing, special schemes


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Architecture of GSM

ME

SIM

BTS

BTS

BSC

BSC

MSC

VLR

EIR

HLR

AuC

AUm

Abis

PSTN,

ISDN

Mobile

station

Base Station

Subsystem

Network

Subsystem

MS BSS NS


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OAM

S ervice carrie r

CM

MM

RR

Subsc riber

Tran smissi on

Function Layers of GSM


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11

CM

MM

RR

LAPDm

MS

RR

LAPDm

Um

LAPD

BTSM

LAPD

Abis

RR

BTSM SCCP

MTP3

BSSAP

BTS BSC

MTP2

SCCP

MTP3

BSSAP

MTP2

CM

MM

MSC

A

Protocol Stack Structure of GSM


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GSM

Mobile Station (MS): Two Blocks Mobile Equipment (ME)

Subscribers Identity Module (SIM)

Function of Mobile Station:

1. Personal Mobility


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GSM

Mobile Station (MS): Two Blocks Mobile Equipment (ME)

Subscribers Identity Module (SIM)

Function of Mobile Station:

1. Personal Mobility

2. IMEI (International Mobile

Equipment Identity)3. IMSI (International Mobile

Subscriber Identity)


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GSM

Base Station Subsystem (BSS) Base Transceiver Station (BTS)

Base Station Controller (BSC)

BSC


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GSM

BSC

BSC: Base station Controller

1. It manages radio resources for

one or more BTS.

2. Allocation and Deallocation ofchannels.

3. Transmitter power control.

4. Handoff control

BTS : Base Tranceiver station1. It defines the cell .

2. It handles the radio link protocol with the mobile station


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GSM

Network Subsystem

MSC: Mobile Switching Center

HLR: Home Location Register

VLR: Visitor Location register

AuC: Authentication Center

EIR: Equipment Identity Register

BSC MSC

VLR

EIR

HLR

AuC

PSTN,

ISDN


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GSM

Mobile Switching center:(MSC) call set up/supervision/release

call routing

billing information colllection mobility management

paging, alerting, echo cancellation

connection to BSC, other MSC and otherlocal exchange networks

Access to HLR and VLR


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GSM

Home Location Register (HLR)

One HLR per GSM operator

Contains permanent database of allthe subscribers in the network

contains MSRN(mobile station routing

no.)

It is reffered for every incomming call


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GSM

Visitor Location Register(VLR) Temporary visitors database

One VLR per MSC

Authentication Center(AuC) Provides security

Authentication and encryption

Equipment Identity Register: Contains IMEI


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GSM

BSC

BSC

MSC

MSC

VLR

VLR

HLR GMSC

PSTN.

ISDN

Location Update


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GSM

Mobile call originating

BSC

BSC

MSC

MSC

VLR

VLR

HLR GMSC

PSTN.

ISDN


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GSM

Mobile call terminating

BSC

BSC

MSC

MSC

VLR

VLR

HLR GMSC

PSTN.

ISDN


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GSM

Handoff

BSCBSC BSC

MSC MSC

GMSC Handoff is of

3 types

1. Intra BSC

2 Inter BSC

3. Inter MSC


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GSM

GSM Radio Aspects : Uplink(Mobile to base)

890-915 MHz (Total 25 MHz)

Downlink ( Base to Mobile) 935-960 MHz (Total 25 MHz)

Total 45 MHz spacing for duplex operation

GSM uses TDMA and FDMA


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GSM

GSM Using FDMA

Uplink Freq890MHz 915Mhz

200KHz

1 2 3 4 5 124

Total Frequency range(Uplink)=25Mhz

Spacing between two carriers= 200kHz

No. of Carriers=25MHz/200KHz = 124The Next Generation Mobile Networks

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GSM

GSM Using TDMA TDMA Frame is divided into 8 time slots.

0 71 2 4 5

03 3 3 5 6 7

Time

Freq

Down

Link

carrier

Up Link

carrier

45MHz

200 KHz

Time slots

4.6 ms0.57ms

3 6

5421


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GSM

Classification of channels in GSM Two types

Traffic channels (TCH)

Control channels (CCH)

Channels are used to carry speech , data

and control information.

Traffic Channels are defined using 26 TDMAframe multiframe.


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28

0 1 765432

8 9 151413121110

16 17 232221201918

The physical channel adopts FDMA and TDMA techs.

On the time domain, a specified channel occupies the

same timeslots in each TDMA frame, so it can be

identified by the timeslot number and frame number.

Physical Channel

Ch l T S


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channel

TCH

CCH

Voice CH

Data CH

FR Voice Traffic Channel (TCH/FS)

HR Traffic Channel (TCH/HS)

4.8Kbit/s HR TCH (TCH/H4.8)

9.6Kbit/s FR TCH(TCH/F9.6)

4.8Kbit/s FR TCH (TCH/F4.8)

BCH

FCCH (down)SCH (down)

BCCH (down)

CCCH

RACH (up)

AGCH (down)

PCH (down)

DCCH

SDCCH

FACCH

SACCH

14.4Kbit/s FR TCH (TCH/F14.4)

Enhanced FR Traffic Channel (TCH/EFR)

Channel Type-Summary


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GSM

2 Control (CCH) Broadcast (BCCH)

Freq correction (FCCH)

Synchronization (SCH)

Common (CCH) Paging (PCH)

Access grant (AGCH)

Random Access (RACH)

Dedicated (DCCH)

Fast Associative (FACCH) Slow Associative (SACCH)

Stand alone (SDCCH)


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GSM

Length of 26 TDMA frames = 120msec

Length of 1 TDMA frame =120/26

= 4.615 msec

1 TDMA frame consists of 8 burstframes

Length of 1 burst frame = 0.577msec

Out of 26 frames

24 are TCH used for traffic

1 is SACCH used for controlThe Next Generation Mobile Networks

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GSM Timeslot and Frame structure

time

Frequency

BP

15/26ms

200KHz

interval


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0 2045 2046 2047321 2044

3210 4947 48 50

0 24 251

1 super high frame = 2048 super frame = 2715648 TDMA frame

1 super frame = 1326 TDMA frame6.12s

0 1 2524 504910

1 multiplex frame = 26 TDMA frames120ms 1 multiplex frame = 51 TDMA frame

0 1 765432

1 TDMA frame = 8 timeslot120/26 = 4.615ms

BCCH

CCCH

SDCHSACCH/TCHFACCH

Timeslot and Frame structure


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GSM

0 1 2 653 7

1 2 2524

4

0 10

3 57 57261

Data DataTraining

Tdma Frame

Frame Multiframe

Format of a single Burst

Duration=120ms

Duration=4.615ms

Duration=0.577ms

25


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GSM

Speech coding

Speech is digitized by PCM, o/p of PCMis 64Kb/s

It is further reduced by Regular pulseexcited-Linear predictive coder, bit rateachieved 13kb/s for full rate (260 bits in20 msec)

Further encoded for error correction,456 bits per 20 msec, bit rate = 22.8Kb/s

456 bits are divided into 8 blocks andtransmitted during 8 burst periods.


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GSM

Classification of Channels

1 Traffic (TCH) Speech

Full rate 22.8 kb/s

Half rate 11.4 kb/s

Data

9.6kb/s 4.8kb/s

2.4kb/s


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GSM

GSM Security

A3 A8 A3 A8

EqualSRES

Kc

Ki KiRandom no

Ki Ki

SRES Kc

MS NETWORK


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Code Division Multiple

Access

(IS 95)

An Overview


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CDMA

Classification of CDMA Systems

CDMA

oneCDMA

2000

IS95 IS95B JSTD 008

Narrow Band

Wide Band

CDMA SYSTEMS


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CDMA

Multiple Access in CDMA: Each user is assigned a unique PN code.

Each user transmits its information by

spreading with unique code. Direct Sequence spread spectrum is used.

Users are seperated by code not by time

slot and freq slot.


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CDMA

Concept of CDMAUsers share same

bandwidth

User axis showscumulative signal strength

of all usersCode 1

Code2

Code 3

Code 4

Freq

User


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CDMA

Spread Spectrum and Multiple Access: Spread Spectrum

In Spread spectrum data is transmitted with BW in

excess to minimum BW necessary to send it.

Spread spectrum is achieved by spreading with PN

code at transmitter . Same code is used to

despread the received signal at reciever

How do we get increased spectrum

XNarrow band

inputsignal

Wide band

code seq

Wide band

Spreaded seq


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CDMA

Advantages of spread spectrum: Multipath Rejection

Immunity to interference and jamming

Multiple access

Code 1

Code2

Code 3

Code 4

Freq

User


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CDMA

Comparison between CDMA and

TDMA/FDMA: In TDMA Band width available for transmission is

small which leads to compromise in quality oftransmission. Whereas in CDMA systems entire

spectrum is used which enhances voice quality.

In TDMA/FDMA, cell design requires more frequency

planning which is tough job. Whereas in CDMAfrequency planning is minimal.

TDMA is Band limited system. CDMA is Power

limited systemThe Next Generation Mobile Networks

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CDMA

Types of Codes used in CDMA: Walsh code

Orthogonal codes

In IS 95A and IS 95B 64 Walsh codes are used

In CDMA 2000 128 Walsh codes are used

Short PN code(16 bit) Used to identify the BS and hence the cell

Long PN code(42 bit code) Used to identify mobile station on reverse link


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IS-95 CDMA

Direct sequence spread spectrum signaling onreverse & forward links

Each channel occupies 1.25 MHz

Fixed chip rate 1.2288 Mcps

Variable user data rate - depends on voice activity

Universal frequency reuse

fast power control to overcome near-far problem RAKE receiver to take advantage of multipath

Soft handoffs


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CDMA IS95 Channels & Frequencies

CDMA frequencies assigned through a 11-bit CDMAChannel number, N

At Mobile

MHz

MHz

At Base Station

MHz

MHz

825)1023(030.0

825030.0

10231013

7771

N

N

N

N

870)1023(030.0

870030.0

10231013

7771

N

N

N

N


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CDMA Channel & Frequency

1.25MHz 1.25MHz

Reverse

CDMA Channel

Forward

CDMA Channel

45 MHz

FrequencyCDMAChannel

Frequency 847.74 MHz 892.74 MHz


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Frequency Reuse CDMA

D

E

F

G B

C

D

E

F

BC

G

DE

F

C

D

E

B

C

GA

B

C

F

B

AA

7 cell Freq Reuse Plan Freq Reuse Plan in CDMA

AA

A

A

A

A

A

A

A

A

AA

A

A

AA

A

A

A

A

A

A

A

AA

A

A

A


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Spreading Codes in IS-95 CDMA

Two types of spreading codes are

used in IS-95

Walsh codes of length 64 are used on

the forward link (base-to-mobile link)e.g., c1 = 0 0 0 0

c2 = 0 1 0 1

c3 = 0 0 1 1

c4 = 0 1 1 0

used to separate one user from another

PN codes are used on both forward

and reverse (mobile-to-base) links

jikckc ji ,0)()(


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CDMA

Formation of channels (IS 95)

PN Code( Chip code) has rate of 1.23

MHz

Chip rate = 1.23 MHz (spread BW)

Link

Forward Link(BS to MS)

Reverse link(MS to BS)


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CDMA

Forward Link (BS to MS)

Forward CDMA Channels

PILOT SYNC PAGE PAGE TRAFFIC TRAFFIC

TRAFFIC

DATA

POWER

CNTRL

SUB CH

W0 W32 W1 W7 W9 W0


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IS-95 CDMA Forward Link

Pilot Channel(Code Channel 0) provides phase reference for coherent demodulation

pilot strength measurement for handoffs

Paging Channel(up to 7 channels - Code Channels 1 to 7) sends control messages and page messages

Walsh Code Channels 1 through 7

Sync Channel(Code Channel 32) broadcasts system timing messages

Traffic Channel(up to 63 channels - remaining code channels) supports variable data rates at 9600, 4800, 2400, or 1200 bps


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Forward Link Channel Structure

Forward CDMA Channel

(1.25 MHz Chl. Tx by Base Stn

Pilot

Chl

W0

Sync

Chl

W32

Paging

Chl. 1

W1

Paging

Chl. 7

W7 W8 W9 W63

Traffic

Chl. 1Traffic

Chl. 2

Traffic

Chl. 55

Traffic dataPower Control

Sub channel


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CDMA

Reverse Link Channel (BS to MS) Here CDMA ch does not follow strictly orthogonal

rule.

It consists of 242 logical channels. 42 bit long PN

code is used to distinguish between channels.

Reverse CDMA Channels

Access

Ch 1

Access

Ch n

Traffic

Ch 1

Traffic

Ch m

m mobiles tryin to gain access

to system

m mobiles engaged in calls


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IS-95 CDMA Reverse Link

Reverse CDMA Channel

(1.25 MHz Chl. Rx by Base Stn

Access

Chl. 1

Access

Chl. 2Access

Chl. n

Traffic

Chl. 1Traffic

Chl. 2

Traffic

Chl. mTraffic

Chl. 3

Addressed by long code PNs


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IS-95 CDMA Reverse Link

Access Channels enables mobile to communicate non-traffic information (e.g.,

call request) in random access mode

fixed data rate at 4.8 kbps

identified by a distinct access channel long code sequenceoffset

a paging channel number is associated with access channel

Traffic Channels

identified by long distinct

user code offset

data rate 9.6, 4.8, 2.4, 1.2 Kbps

data is convolutionally encoded, block interleaved, 64-ary

orthogonal modulated, and direct sequence spread before

transmission


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CDMA

Other key Factors Diversity

Time diversity

Frequency diversity

Space(Path) diversity

Power Control

Handoff: It supports Soft Handoff


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Power Control in IS-95

At 900 MHz Carrier frequency and 120 km/h mobile speed,Doppler = 100 Hz

In IS-95A, closed loop power control is operated at 800 Hz

update rate

Power control bits are punctured into the traffic data stream

Closed loop power control step size is +/- 1 dB

Power control bit errors do not affect performance much

Coding and interleaving has effect on CLPC performance

Both open (outer) and closed (inner) loops drive the

transmit power to ensure a target FER of 1%


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RAKE Receiver

4 RAKE fingers are used in the Mobile Receiver

3 fingers for tracking and demodulating multipath

components of the FL CDMA channel

1 finger is used for searching and estimating the

signal strength on different pilots

used to select the desired (strongest) base station in idle

mode

for generating pilot strength information messages

during traffic mode to enable Handoff


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Handoffs in IS-95 CDMA

Types of Handoff Soft Handoff

Mobile commences commun with a new base station without

interrupting commun with old base station

same freq assignment between old and new base station

provides different site selection diversity

Softer handoff

Handoffs between sectors in a cell

CDMA-to-CDMA Hard Handoff

Mobile transmits between two base stations with different

frequency assignment


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Soft Handoff Architecture

Mobile

BSC BSC

BTS BTSBTSBTS

New LinkOld Link

RR

MSCTo other switch

R

R - Handoff request sent to theold cell on the degrading link Energy measurements are made at

the mobile

Switch Diversity:

MSC selects the bit stream with

lower error rate


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CDMA

Soft Handoff

Signal

strength

DistanceThe Next Generation Mobile Networks

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Handoff Procedure

Pilot Sets

Active Set

Pilot associated with FL traffic channels assigned to the

mobile

Candidate Set

Pilots that are not in Active Set but are received by the mobilewith sufficient strength

Neighbor Set

Pilots not in Active or Candidate Set but are likely candidates

for handoff

Remaining Set

Set in the current system on current freq assignment,

excluding the above 3 sets


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Handoff Example

Time

PilotStrength

(1)

T_ADD

T_DROP

(2) (3) (4) (5) (6) (7)

Neighbor

Set

Candidate

Set Active Set

T_TDROP

Neighbor

Set


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Handoff Example

(1) Pilot strength exceeds T_ADD. Mobile sends a PilotStrength Measurement Message (PSMM) to base station

and transfers pilot to the Candidate Set

(2) Base station sends a Handoff Direction Message (HDM)

(3) Mobile transfers pilot to Active Set and sends s Handoff

Completion Message (HCM)

(4) Pilot strength drops below T_DROP. Mobile starts handoff

drop timer

(5) Handoff drop timer expires. Mobile sends a PSMM

(6) Base station sends a HDM

(7) Mobile moves pilot from Active Set to Neighbor Set and

sends a HCM


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END

2g cellular networks - gsm and is95

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