Radio Interface

7/29/2019 Radio Interface

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Rio De Janeiro, October 2005

FPLBRA1TIM

Maria Stella Iacobucci

GSM, GPRS, EDGE radio interface


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GSM/GPRS/EDGE Radio Interface

Maria Stella IacobucciFPLHEL1TIM

Rio De Janeiro,October 2005 3

Divertissement


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Why radiomobile services?

To spread out to mobile users quality and capacity of

telecommunication services generally available to

fixed users To use TLC services wherever through a wireless

terminal and to move during a connection


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Architectural and procedural requirements of aradiomobile cellular system

RADIO ACCESS:

propagation

Cellular coverage

Frequency reuse

MOBILITY MANAGEMENT: User localization

Handover

SECURITY

Access control Cryptography


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Radiomobile systems

Connect mobile users to mobile and/or fixed users through the radio

resource, independently from the user position


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Radiomobile systems

The adoption of a unique illumination point is impossible because:

The used powers would be too high (MW)

the physical resources that could be simultaneously activated would

not be sufficient


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Radiomobile systems

The ground coverage is realized through many radio base stationsthat illuminate contiguous zones that realize service continuity


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Cellular coverage (pictorial)

Oil on Canvas 1995 by Stephen Linhart (New York)


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Main GSM radio parameters

Access FDMA/TDMA/FDD

Channel spacing 200 kHz

No TSs/carrier 8

Modulation GMSK (BT = 0.3)

TCH/F - Gross bit rate 22.8 kbit/s

Modulating bit rate 270.8333 kbps (1625/6 kbps)

CS-Data rates 2.4, 4.8, 9.6, 14.4 kbps (per TS)

Uplink(MHz)

Downlink(MHz)

Duplex spacing(MHz)

Bandwidth(MHz)

P-GSM 900 890 915 935 960 DL = UL + 45 25

E-GSM 900 880 915 925 960 DL = UL + 45 35GSM 900

R-GSM 900 876 915 921 960 DL = UL + 45 39

DCS 1800 1710 1785 1805 1880 DL = UL + 95 75

PCS 1900 1850 1910 1930 1990 DL = UL + 80 60GSM 450 450,4 457,6 460,4 467,6 DL = UL + 10 7,2

GSM 400GSM 480 478,8 486 488,8 496 DL = UL + 10 7,2

GSM 700 GSM 750 747 762 777 792 DL = UL + 30 15

GSM 850 824 849 869 894 DL = UL + 45 25


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Cellular coverage

Given the available resources (voice channels), the

maximum number of users for a given service quality

can be found with the traffic theory

For example, by using an hypothetic cell with 1000telephonic channels, the maximum number of

achievable users would be 40000


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Cellular coverage

In order to increase the number of radio channels, the

frequency reuse is adopted

The same radio channels are used to serve different

areas The reuse areas must be as far as the iso-channel

interference can be neglected


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Cellular coverage


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The cluster

The reuse areas must be as far as the iso-channelinterference can be neglected

The set of cells that can use all the available

frequencies is called cluster

1

8

6 7

23

4 9

5

Example of 9 cells cluster


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1

86

7

2

34

9

5

1

8

67

23

49

5

8

67

3

49

5

1

87

23

9

1

8

67

23

49

51

8

67

23

9

7

75

12

649

51

8

6

2

34

9

5

3

4 6

85

Cellular network

The cellular coverage can be obtained by repeating the cluster in the

space


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Goals

Transmission quality (coverage, performances)

Capacity (available channels)

The frequency reuse produces an increase of the interference

level

In order to increase the system capacity it is necessary to

increase the number of BTS, by reusing the emitted powers

with capillary coverage and link better quality

The main parameter for the performances characterization is the

ratio

PowersignaltInterferen

PowersignalUseful

I

C


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R

42

2

16 R

GGPC

Bmm

Useful signal

The most unfavorable

condition is when

the MT moves near the

hexagon extremity


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4

6

12

2 1)16(

k

Bmm

kd)GG(PI

4

omni 6

1

R

D

I

C

If dk =D (reuse distance)

C/I computation in the omni directional case

R

D

I

C

1

8

67

23

49

5

1

8

67

23

49

5

1

8

67

23

49

5D


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Reuse distanceCluster with 7 cells

7

3

1

6

2

5

4

7

3

1

6

2

5

4

7

3

1

6

2

5

4 7 1

6

2

5

7

3

1

6

2

5

4

7

3

1 2

4

3 4

i=1

j=2

(i2+j2+ij)=7


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Reuse distanceCluster with 21 cells

7

21

14

8

1

16

10

9

15

3

19

6

7

5

21

7

3

13

6

20

5

4 12 19

11

7

5

4

18

1

6

2

17

4

7

3

1 2

4

3 2

i=1

j=4


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Choice of the cluster dimension

By increasing the cluster dimension, the transmission qualityincreases

An higher number of BS is required (higher cost), each with a lowernumber of channels

The cluster dimension must therefore be the lowest that is necessaryfor a given C/I

TACS (C/I)min 18 dB cluster with 21 cells

GSM (C/I)min 9 dB cluster with 9 cells

I

C

R

DDim cluster)(


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Strategies to augment capacity

Sectorization

Cell splitting (tilting)

Micro cells

Underlay-overlay techniquesGSM 1800


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Coverage structures

Omnidirectional coverageDirectional coverageCloverconfiguration


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42

12

2 1

)16(

k

Bmm

kd

)GG(PI

4

2

1

R

D

I

C

sett.

nisett. I

C

I

C

om

3

C/I calculation in the sectorial case

Ifdk=D (reuse distance)

1

8

67

2

3

49

5

1

8

6 7

23

4 9

5

1

8

67

23

49

5

DD


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Is used when cells available channels can not be increased

If the cell is divided into 4 cells, the traffic will be quadrupled

After n split Tn = T0 (4)n

2

1

4

3

3

4

21

Cell splitting


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GSM/GPRS/EDGE Radio InterfaceMaria Stella Iacobucci

FPLHEL1TIMRio De Janeiro,

October 2005 26

Micro cells

Micro cells can be used to serve hot spot locations, that arecoverage-limited zones but with high required capacity

Possibility to satisfy high traffic requirements in very localized

zones

GSM900 Loss (dB)=132.8+38log(d[Km])

GSM1800 Loss (dB)=142.9+38log(d[Km])


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October 2005 27

Overlay/underlay technique (I)

The total assigned radio bandwidth is divided into two channel

blocks

The first uses a canonic cluster (underlay cells )

The second uses cells having a lower area (overlay cells ),

which allows, with the same C/I, a cluster of lower dimension

and therefore a lower normalized distance

Overlay cells share with the underlay:

Sites

Antenna systems

Control channels hand-over control devices


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October 2005 28

Overlay/underlay tecnique (II)

underlay cells overlay cells

Overlay cells allow an higher frequency reuse and therefore anhigher number of available channels

The traffic lost from the overlay cells, if in congestion, is offered as

overflow traffic to the underlay


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October 2005 29

1

1

2

2 3

3 4

4

5

56

7

Different propagation characteristics:

depend on the BS position,

antennas high, terrain characteristics, etc.

Cells dimensions are different

Non uniform traffic and

users distribution

Each cell needs a different

number of carriers

11

22

33

44

55

6

77

(real)(Theoric)

6

Radio cells coverage


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October 2005 30

Real coverage


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October 2005 32

Erlang-B formula

The Erlang-Bformula represents (historically) the first used modelto dimension the GSM cell resources

The model is based on a mono-dimensionalMarkov chain

which describes the resource occupation modalities of the offered load

Define:

N number of channels in the cell

arrival frequency of voice calls (Poisson process)

average duration of voice calls


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FPLHEL1TIM Rio De Janeiro,October 2005 33

Erlang-B formula

A telephone system constituted by N resources can be analized through the

Erlang model where the generic state is described by the number of

occupied channels, that is by the number of users that are in the system

1 Calls frequency of dead

(service times with exponential distribution and parameter )

The dead frequency is proportional to the number of connected users

(i-1) i N2 3 (N-1)

Blocking state

10

2 3 i-1 i

N-1 N


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Loss of a cell with N

channels and an erlang

offered load ofA

The Erlang-B formula

The Erlang-Bformula allows to evaluate the performances of a

GSM cell (loss) equipped with N time slot and an offered load of

A = /

N

i

i

N

N

N

i

A

N

A

N

AAAA

N

A

NB

0

32

!

!

!...

!3!21

!

The loss B(N) goes to zero when Nincreases

The loss B(N) goes to one whenA increases


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...

B1B2B3B4

Bn

The multi service Erlang formula

Multiservice Erlang

Capacity CTOT(number of channels)

...

1 , 1 , C12 , 2 , C23 , 3 , C34 , 4 , C4

N , N , CN

Traffic load of the i-th service: Ai = ii

Required capacity of a connection: Ci

Calls arrival frequency

Average service time

The Markov chain used to evaluate performances is N-dimensionalthe generic state is described by an N-ple of variables which expressthe number of users of each service

TOT

N

i

ii CCn 1

N users can be admitted to the

system if


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1 1 1 11

CTOT/31


Assume:

C1 = 3, C2 = 1 and CTOTmultiple of three

The Markov chain assumes the following form

Blocking states for

both traffic types

Blocking states for

traffic 1

2 22 2

2 2 2 2

2 2 2

1111

1

1

CTOT/3,0

CTOT/3-1,1 CTOT/3-1,2 CTOT/3-1,3

0,CTOT

1,CTOT-31,0 1,1 1,2 1,3 1,4

0,1 0,2 0,3 0,40,0

CTOT/3-1,0

2 22 32 42

2 22 32

4232222


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Application to the GSM case with attivation ofdual rate resource

SR DR SR = DR = CSR = 2 CDR = 1 NTCH= 3

DR DR DR DR DR DR

DR DR DR DR

DR DR

2 3 4 5 6

2 3 4

2

SR SRSR SR

SR SR

SR

SR

SR 3

2

2

2

Blocking states

for both traffic

types

Blocking states

for single rate traffic

TCHDRSR NUU 22

Generic state admission

condition

Number of SR

users

Number of DR

users

0,5

3,0

1,0 1,1 1,2 1,3 1,4

2,22,12,0

0,0 0,1 0,2 0,3 0,4 0,6


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The use of multi service Erlang formula for a GSM cell performance evaluation

implies some assumptions


An half rate channel is assigned if exists a half time slot whichhas remained free afted the other half occupied from aconversation

When an half rate call terminates, an other half rate calloccupies the same time slot if it has to be filled

Each mobile terminal asks for the traffic channel dependig on itsown characteristics, that is a half rate source if is a dual rateterminal and a full rate source if is a single rate terminalThe cell assigns the resource in order to minimizes the whole

occupation


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The multi service Erlang formula: some application examples

30 TCH

4 Erl. off. SR

6 Elr. off. DR

BTOT = 0BSR = 0

BDR = 0

30 TCH

8 Erl. off. SR

12 Erl. off. DR

B = 0BSR = 0

BDR = 0

30 TCH

12 Erl. off. SR

18 Erl. off. DR

B = 0.72%BSR = 1.09%

BDR = 0.48%

30 TCH

16 Erl. off. SR

24 Erl. off. DR

B = 7.76%BSR = 11.06%

BDR = 5.4%

Performances evaluation

20 Erl. off. SR30 Erl. off. DR

BTOT = 0.1%

51 TCH


BTOT = 2%

43 TCH


BTOT = 10%

36 TCH


BTOT = 30%

25 TCH

Dimensioning

Consider that dualrate terminals are the 60% of the total:


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Maria Stella IacobucciFPLHEL1TIM Rio De Janeiro,October 2005 43

Antennas of BS GSM


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Pin = Pr+P0Pt = Poantenna efficiencyp power density (W/m2)

Electrical parameters

Pin

P0 Pt

G(q,f)

p (q,f)

Gmax

pmax

Pr,

20 4/),(

),(rP

pG

fqfq


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Diversity techniques

Create, at the reception side, two radio-electric paths

sufficiently non correlated

By combining the two paths a better signal is obtained

The ratio between the combined signal and the higher singlesignal is called improvement factor


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Rio De Janeiro,

October 2005 48

Space diversity

In presence of multiple reflections the signals that arrive to

spatially separated antennas are sufficiently uncorrelated

The antennas must be horizontally spaced of 15 20

5 m 6,6 m at 900 MHz

2.5 m 3,3 m at 1800 MHz

The attended improvement factor is of 5 dB

5m (900MHz)

Rx 1 Rx 2

2,3 m

0,38 m


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Safety volume

The safety volume is the portion of space out of which are respected the

electromagnetic field exposition limits

People cannot be into the safety volume


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Used to improve the coverage in shadow zones and with low traffic

Repeaters

Service area

Pick-up Antenna

Service Area Antenna


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October 2005 51

Fiber optic repeaters

BTS

O

E

E

O

RF-Rx

RF-Tx

Service area

Fiber optic repeaters are connected with the BTS through aphysical (electro-optical optic) connection


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October 2005 52

Coverage

Powers must be controlled to minimize interferences, and to

assure a good signal level

Radio BTS antennas must be installed such that there are

not obstacles which limit the coverage

Antennas must be installed by respecting electromagnetic

limits.


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Rio De Janeiro,

October 2005 53

GSM network architecture

BSC

BSC

MSC

VLR

MSC/VLR area

GMSC

MSC

MSC

HLR HLRHLR

BSC

BSC area

Other Networks

BTS

MS cell


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Rio De Janeiro,

October 2005 54

Network elements: Mobile Station

MS=ME+SIM

MS=Mobile station

ME=Mobile Equipment

SIM= Subscriber Identity Module

Principal functions

radio transmission Control channels supervision

Cell selection

downlink parameters measurements (BER, received power)

and transmission to the BTS

Execution of access, authentication, hand-over procedures


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Numeration and identity in GSM (II)

TMSI (Temporary Mobile Subscriber Identity)

Temporary identity, alternative to the IMSI and given on

localization area basis

IMEI International Mobile Equipment Identity Univocally identifies the mobile terminal with information

on the type and production establishment


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Base Transceiver Station (BTS)

Executes the following functions:

Radio Transmission

Measures the up-link performances and transmits to

the BSC Free channels supervision

Timing advance calculation

Execution of procedures (paging, broadcasting of

cell parameters)


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Base Station Controller BSC

Typical functions

Control of the BTS included in the BSS

Connection of the traffic channels between BSC and MSC

Radio channel management (allocation and release)

Intra BSC (inter BTSs) hand-over

Optional functions Power control

Pre-elaboration of measurements

Voice transcoding from radio interface coding to standard PCM

Such function is demanded to a dedicated entity named TRC


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Mobile Switching Center MSC

Central office for switching and call control from and to GSM

users Has interfaces with

BSS, MSC, VLR, HLR

Other networks (PSTN, ISDN,..).

Principal functions

Call handling (from and to GSM users) Mobility handling (inter work with VLR and HLR)

Paging

Intra MSC (inter BSSs) Hand-Over

Inter MSC Hand-Over

toll-ticket generation

The VLR is typically associated to the MSC


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Visitor Location Register VLR

Data base associated to the MSC, with information on the visitors in the

MSC area

Semi-permanent data (moved from the HLR)

MSISDN, IMSI

Priority class Service profile

Temporary data

TMSI

LAI (Location Area Identifier)

Authentication and ciphering parameters


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AUC, EIR & OMC

AUC: AUthentication Centre

Generates parameters for user authentication and trafficciphering, sent to the HLR and under require to the VLR

The EIR is a database which allows to the network toverify if the Mobile Equipment (through the IMEI) is

authorized for the network access Operation & Maintenance Centre OMC

Allows supervision and control of MSC, BSS, HLR, VLRentities


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BTS2

BTS1

Cell 1

Cell 2

Handover

Traffic channels

Adiacent cells channels


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Parameters used in handover

Power level in the Uplink and Downlink channel

BER on UL and DL

Base-mobile distance (estimated from the BTS)

Power level relative to adjacent cells Such measures are elaborated and compared to the relative

handover thresholds; on such basis is written an handover

list


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Signaling beacon channels

BTS

Downlink beacon channel Uplink beacon channel

MSMS

CELL

CODE# cella

LAI # LA

PAGING # user

LAUPDATE # user # LA

OUTGOINGCALL # user # destination

Message ID Field 1 Field 2 Message ID Field 1 Field 2


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Location Area

Location area

Is a group of BTS where the VLR localizes the MSfor the incoming calls

The area managed from the same VLR can includemore than one Location Area

Location Area # i

Location Area # j


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Location Area Updating (I)

On the beacon in downlink the location area code istransmitted

The mobile compares the received code with the memorizedone

If the code has varied the mobile communicates to the SRBthe actual location are (through the uplink control channel)

If the new location area belongs to the same VLR, nothing isforwarded to the HLR

If the new location area belongs to another VLR, the old VLRcommunicate to the HLR to update the list and to order tothe old VLR to delete the user


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Forced Location Area Updating

old LA# i new LA#j

LA Updating

old LA# i

new LA#ino action

old LA# i new LA#i

no action


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MSRN Mobile Station Roaming Number

Is a number belonging to the numeration plane of the visited

MSC and assigned to a mobile station when registered to a

certain VLR

L'MSRN is backward transmitted to the VLR and then to the

MSC to route the call to the visited MSC


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Rio De Janeiro,

October 2005

Fixed-Mobile call

MSC

GMSC

HLR

PSTN

BTS

BSC

BTS

BTS

BTS

BSC

LAi

LAj

VLR

VLR2

MSISDN3

1

Asks for MSRN (uses IMSI)

MSRN4

MSRN

5

6

: Send Routing Information2

3 : Provide Roaming Number


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Confidential nature

The client is identified from IMSI and Ki key, memorized in:

SIM (MS side)

HLR (network side)

The authentication key Ki is never sent on the radio interface

IMSI is substituted, in the LA, from a temporary identity called

TMSI which is transmitted to the MS

TMSI substituted IMSI in the LA and goes with LA#

When VLR changes the network can request IMSI


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Authentication (I)

AUC, by using Ki and the casual number RAND, generates,

through A3 and A8 algorithms:

SRES=A3(RAND,Ki) Signed Response

Kc= A8(RAND,Ki) ciphering keys

Through subsequent applications of the algorithm with

different casual numbers, the triplets sent from AUC to VLR

are obtained:

[RAND(128 bit), SRES(32bit), Kc(64bit)]

A th ti ti (II)


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Authentication (II)

RAND is sent to the MS

The MS calculates SRES which is transmitted to the VLR

and then to the MS

If SRES=SRES (which is memorized to the VLR), the

authentication is complete


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October 2005 76

Authentication(III)

IMSIKi

MS

IMSI

[RAND,

SRES, Kc]

IMSI

[RAND,

SRES, Kc]

IMSI

KiVLR HLR

AUC

A3 | A8

Ki RAND

SRES Kc

[RAND, SRES, Kc][RAND, SRES, Kc]

=

A3 | A8

RAND

KiRAND

Kc

OK

SRES

SRES

BS


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Encryption (I)

Is applied on the useful data block (114 bit) contained in the

burst

The A5 algorithm generates a ciphering sequence, different

burst to burst, through the Kc key (64 bit) and the frame number

FN (22 bit)

The ciphering sequence is added in XOR to the informative part

of the bursts and then is transmitted

In Rx the message is deciphered adding in XOR the received

sequence and the ciphering the reconstructed sequence

E ti (II)


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Encryption (II)

A8

Ki

Kc

RAND

SIM-AUC

BTS

A5

Kc

Ciphering

sequence

(114 bit)

MS

+

TDMA FN

Message

(114 bit)

A5

Kc

Ciphering

sequence

(114 bit)

+

TDMA FN

Cipheredmessage

(114 bit)

Deciphered

message

(114 bit)


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Rio De Janeiro,

October 2005 79

User Data Transmission

Because the GSM system was born for the voice service, to each user is

associated a portion of the radio interface the TCH - for the whole call

duration

Two types ofTCH are defined:

TCH/F (Traffic Channel Full Rate) allows the transmission of the

voice coded at 13 kb/s or data at 12.6 and 3.6 kb/s

TCH/H (Traffic Channel Half Rate) allows the transmission of the

voice coded at 7 kb/s or data at 6 and 3.6 kb/s

Si li


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Signaling

Signaling associated to a communication

Each traffic channel is always associated to a channel at low bit rate used for

the signaling transport: the SACCH (Slow Associated Control Channel)

In order to execute urgent procedures, like the call set-up and call release,

the authentication and the handover, a TCH named FACCH (Fast

Associated Control Channel) is used

Non associated signaling Is used to carry network management information, like the location updating

procedure. For that scope a low bit rate channel is used, the SDCCH

(Stand alone Dedicated Control Channel)

C h l


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Common channels

FCCH (Frequency Correction Channel) and SCH

(Synchronization Channel)

Allows the mobile to synchronize with the BTS

BCCH (Broadcast Control Channel) Brings the system information, i.e. the network to which

the cell belongs

PAGCH (Paging and Access Grant Channel)

RACH (Random Access Channel)

Channels of the radio interface: procedure examples


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Channels of the radio interface: procedure examplesLocation Updating (GSM 3.12)

Channel Request (RACH) Channel Assignment (AGCH)

Request per Location Updating (SDCCH)

Authentication Request (SDCCH)

Authentication Response (SDCCH)

Ciphering Command (SDCCH)

Ciphering Complete (da adesso la cifratura in atto)

(SDCCH)

Conferma della location updating, includendo la

assegnazione opzionale della TMSI (SDCCH)

Ack della nuova location e del TMSI (SDCCH)

Channel release dalla rete (SDCCH)

MS Base Station

Mobile-Originated call


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Mobile Originated call

Channel Request (RACH)

Channel Assignment (AGCH) Call establishment Request (SDCCH)

Authentication Request (SDCCH)

Authentication Response (SDCCH)

Ciphering Command (SDCCH)

Ciphering Complete (da adesso la cifratura in atto) (SDCCH) Setup message (indicante il numero desiderato) (SDCCH)

Call Proceeding (la rete instrada verso il numero desiderato)

Assignment di un traffic channel (SDCCH)

Assignment complete (FACCH)

Alerting (il numero chiamato non occupato (ringing)) (FACCH)

Connect (il chiamato risponde) (FACCH)

Connect Ack (FACCH)

Fase di conversazione (TCH)

MS Base Station

L i l h l


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Uplink Downlink

/ PCH + BCCHsystem informationpaging

RACHrandom access

AGCHassignment of dedicated control channel

SDCCH SDCCHsignalling procedure signalling procedure

TCH + SACCH

voice / data traffic orsignalling procedure

(FACCH)

measurements

TCH + SACCH

voice / data traffic orsignalling procedure

(FACCH)

measurements

Logical channels usage


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Frame structure in downlink Frame structure in uplink

Multiframes structures


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Multiframes structures


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8.25

TAIL BITS

GUARDPERIOD

STEALING FLAGSTRAINING SEQUENCE

3 57 1 26 1 57 3

CODEDINFORMATION/SIGNALLING

1 TIME SLOT = 156,25 PERIODI DI BIT (15/26 0.577 ms)

Normal Burst structure
http://images.google.it/imgres?imgurl=http://www.ipixcel.org/picts/news2.jpg&imgrefurl=http://www.ipixcel.org/&h=238&w=348&sz=9&tbnid=zVUX_OeQN_8J:&tbnh=79&tbnw=115&start=11&prev=/images%3Fq%3DGPRS%2Bframe%26hl%3Dit%26lr%3D%26ie%3DUTF-8%26sa%3DG


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Rio De Janeiro,

October 2005 88

TAIL BITS

EXTENDED TAILBITSSYNCHRONIZATION SEQUENCE

8 41 36 68.25EXTENDED

GUARD PERIOD3

CODED SIGNALLINGINFORMATION

1 TIME SLOT = 156,25 PERIODI DI BIT (15/26 0.577 ms)

Access Burst structure

TDMA frame
http://images.google.it/imgres?imgurl=http://www.ipixcel.org/picts/news2.jpg&imgrefurl=http://www.ipixcel.org/&h=238&w=348&sz=9&tbnid=zVUX_OeQN_8J:&tbnh=79&tbnw=115&start=11&prev=/images%3Fq%3DGPRS%2Bframe%26hl%3Dit%26lr%3D%26ie%3DUTF-8%26sa%3DG


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Rio De Janeiro,

October 2005 89

Mobile 1

Mobile 2

Mobile 3

Mobile 8

TDMA Frame (4.6 ms)

Time slot: 577 s

Signal burst: 546 s

TDMA frame


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Rio De Janeiro,

October 2005 90

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4

Reception frame

Transmission frame

Other stations measurements

Transmission and reception

Ti i d


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Rio De Janeiro,

October 2005 91

Timing advance

When the MS is near to the BS its transmission is delayed of three timeslots

When a propagation delay has to be taken into account, the

transmission has to be anticipated (timing advance) respect to the

nominal period of three time slots

The timing advance allows the burst to arrive at the BTS in the correcttime window

Power control


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Rio De Janeiro,

October 2005 92

Power control

The link quality is considered good if:

Pr=Prif The excess power contributes to increment the interference level

The power control varies the mobile station and BTS emitted

power in order to use the lower power that guaranties link

Is actuated at steps of 2 dB in an interval of 20-30 dB for the MS

in an interval of about 30 dB for the BTS

The Power Control in GPRS is more complicate than in GSM because thereis not a continuous bidirectional connection

Ideal Power Control


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Rio De Janeiro,

October 2005 93

Ideal Power Control

Rrr

M

B

R

PT

PM

PR

PRIF

(a)

(a)

(b)

(b)

Step Power Control


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Rio De Janeiro,

October 2005 94

Step Power Control

RPT

r

PR

PRIF

Di ti t i i (DTX)


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Rio De Janeiro,

October 2005 95

Discontinuous transmission (DTX)

It is not transmitted any signal when nothing has to be transmittedLower interference

Higher system capacity

Lower quality

When the user is speaking the voice signal is coded at 13kbit/s

When the user is not speaking the noise characteristics are analyzed and

the parameters are transmitted on the SACCH at 500bit/s and are

updated two times per second

At the reception side such comfort noise is reproduced to maintain the

sensation of connection continuity

Discontinuous reception (sleep mode)


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Rio De Janeiro,

October 2005 96

Discontinuous reception (sleep mode)

Allows the reduction of mobile energy consumption by

periodically switching on and off the MS receiver (in idle mode)

The paging channel is divided into sub-channels whose

organization is described in the BCCH

Paging messages for a given sub-channel are transmitted on a

specific sub-channel (known on IMSI basis)

The mobile station is activated only in correspondence of such sub-

channels (with lower energy consumption)


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Rio De Janeiro,

October 2005 97

Frequency Hopping

During the same connection the carrier is cyclically varied byselecting an hopping frequency code

The carrier

Remains the same during the transmission of an entire burst

Changes in the transmission of the subsequent burst

Such frequency diversityguaranties a quality that is uniform for all

the connections


98/198

GSM radio chain


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Rio De Janeiro,

October 2005 99

GSM radio chain

Source

ChannelEncoder

Interleaver Ciphering

Propagation channel

Output bits

GSMModulator(BB + RF)

Reordering&

Partitioning

TransmitterBurst

Formatter &Multiplexer

RF, IF FiltersCoherent

Demodulation &BB Filters

SynchronizationViterbi Equalizer

GSM BB Demodulator

De-interleaverDe-partition/reordering

Channel Decoder

BurstDe-Multiplexer& De-Formatter

Deciphering

TCH/FS h l di


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Rio De Janeiro,

October 2005 100

VOICE

CODER(13 Kbit/s)

CONVOLUTIONAL

CODE( R = 1/2, LC = 5 )

ADDITION

OF4 TAIL BITS

53 189 37

8

50

(CLASS 1A)

132(CLASS 1B)

CHANNEL ENCODER

260 bits

(20 ms)

456

(22.8 kbit/s)

78(CLASS 2)

REORDERING185

BLOCK

CODE(53,50)

TCH/FS channel coding

Voice coding Full Rate (FR)


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Rio De Janeiro,

October 2005 101

Voice coding Full Rate (FR)

1

10-1

10-3

-5 0

C / I (dB)

Class 2 bit

10-2

5 10 15 20 25

Class 1 bit

BER

Voice codingHalf Rate (HR)


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Rio De Janeiro,

October 2005 102

Class 1 Class 2

Class 1a Class 1b

22 1773

211

Coded bits Class 2

228 bit

Parity bits

c c g ( )

22

Tail bits

17

3 73 6 17

Voice coding and interleaving


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October 2005 103

260 bit 260 bit

456 bit

Voice coder: 260 bits in blocks of 20 ms (13 kbit/s) MS - TRAU

Channel coding: 456 bit in blocks of 20 ms (22.8 kbit/s) MS - BTS

Interleaving: 8 blocks of 57 bits (22.8 kbit/s) MS-BTS

Voice coding and interleaving

57 bit 57 bit 57 bit 57 bit 57 bit 57 bit 57 bit 57 bit

Sub-block

Signal burst formatting ( voice service)


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Rio De Janeiro,

October 2005 104

Signal burst formatting ( voice service)

The sub-blocks are organized in frames, each of 4,6 ms

Each frame contains 16 sub-blocks, belonging to three different blocks following adiagonal interleaving scheme

The burst structure of 0.577 ms is shown (in the control channels the 8 blocks of 57

bits are distributed in 4 bursts)

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

57bit

Frame 4.6 ms

57bit

block A

57bit block B

57bit

block C

8.25

Tail Bits

Guardtime

Signalingindicators

Midamble (for the synchronizationand channel estimate)

3 57 bit 1 26 1 57 bit 3


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Signalling messages coding and interleaving


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October 2005 106

184 bit

456 bit

The signaling message is divided into blocks of 184 bit

Each block is coded (including parity, tail and coded bit) to reach 456 bit (22.8 kbit/s);

40 parity bits are with a Fire code and 4 bit at 0 are added bit before applying theconvolutional code (R = 1/2 and K = 5), non punctured.

g g g g g

Interleaving (block rectangular interleaver): 8 blocks of 57 bits (22.8 kbit/s); MS-BTS

57 bit 57 bit 57 bit 57 bit 57 bit 57 bit 57 bit 57 bit


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GMSK: MSK with Gaussian filtering


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October 2005 108

GMSK: MSK with Gaussian filteringQ

I1 0

GMSK constellation

1 bit per symbol

ttfAts cm 2cos

i

i iTtkt 0

Figure from:

Mouly, Pautet: The GSM System for Mobile

Communications


109/198

Evolution


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October 2005 110

Evolution

GSM

HSCSD

GPRS

EDGE

UMTS

NO

UMTS

GPRS main features


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October 2005 111

GPRS main features

Sharing of radio resources between GPRS and GSM

An MS may be assigned multiple timeslots inside a TDMA

frame

Multiplexing of MSs on the same timeslot

Flexible channel allocation mechanism

Half or full duplex operations

GSM/GPRS network architecture


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Rio De Janeiro,

October 2005 112

GGSN

MSC/VLR

SGSN

HLR

BSC

Abis

PCU

Gb

Gn

Other packet networks(i.e. Internet)Gi

GsGr

A

GMSC

Other networks

Other GPRSnetworks

Gp

GGSN

Um


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Downlink frame structure Uplink frame structure

Example of radio block


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Example of radio block

Radio Blocks


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The radio block is the GPRS main element, which can be retransmitted

The retransmission protocol is window based, and a selective

retransmission of errored received radio blocks is performed

The window is composed of 64 radio blocks

GPRS Downlink Radio Blocks


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Data Block

Control Block

RLC/MAC Control Block

Radio block

MAC HdrControl Header

(optional)

RLC/MAC Signalling

MAC Header

RLC Data Block

Radio block

RLC Header RLC Data

USF S/P RRBPPayload

Type

MAC Hdr

Spare bits

(if any)

GPRS Downlink Radio Blocks

USF: Uplink State Flag

GPRS Uplink Radio Blocks


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October 2005 117

Data Block

RLC Data Block

Radio block

RLC Header RLC Data

Control Block

RLC/MAC Control Block

Radio block

MAC Hdr

MAC Hdr RLC/MAC Signalling

MAC Header

RCountdown

value

Payload

TypeSI

MAC Header

R sparePayload

Type

Spare bits

(if any)

p

USF Uplink State Flag


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October 2005 118

S/P: indicates if RRRBP is valid

RRBP: indicates the period when the MS,

addressed from TFI, sends in uplink a

Packet Control Ack or another message

on PACCH

FBI (Final Block Indicator) indicates the last

RLC data block of the current TBF

TFI (Temporary Flow Identity) indicates the

TBF

PR Power Reduction

BSN Block Sequence Number indicates the

RLC data block sequence number inside

a TBF

FS Final Segment indicates the final segment

of an RLC/MAC control message

SI: indicates if the window can move


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October 2005 119

SI: indicates if the window can move

forward

Contdown value: is transmitted in uplink

and is used to calculate the number ofRLC data blocks left in the current TBF

Payload type: individuates an RLC Data

block or MAC/Control Block and, in this

case, if there is the Control Header

TI indicates if there is a field for TLLI

E (Extension) indicates the presence of

an optional subsequent byte in the RLC

header

M (More) indicates if there are bytes for

another LL-PDU which follows the one

inside the RLC data block


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Radio Block Structure


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October 2005125

USF precoding

4 tail bits

rate 1/2 convolutional codingpuncturing

456 bits

USF BC

S

Payload

Radio Block Structure

Coding Scheme CS-1


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224 bits

456 bits

BC

S

Header & Data181 40

USF3

4 tail bits

rate 1/2 convolutional coding

Coding Scheme CS-1

Coding Scheme CS-2


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USF precoding

4 tail bits

rate 1/2 convolutional coding

Puncturing (132 bits)

444

Punctured bits

5881 2 16 17 18 20 21 22

first last

(except 12 specific bits)15 5872319

287 bits

268 16

Header, Data & Spare BCSUSF

3

1

2

576

12

588 bits

456 bits

Coding Scheme CS-3


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Rio De Janeiro,

October 2005 128

USF precoding

4 tail bits

rate 1/2 convolutional

coding

Puncturing (220 bits)

676 bits

Punctured bits

331 bits

312 16

Header, Data & Spare BCSUSF

3

12

16 22 28 670 672 673 674 675 6761 2

first last

15 17 21 23 27 29 669 671

664

456 bits12 444


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GPRS logical channels


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Packet Common Control Channel (PCCCH):

PRACH: random access (uplink)

PPCH: paging (downlink)

PAGCH: access grant (downlink)

PNCH: PTM-M notification (downlink)

Packet Broadcast Control Channel (PBCCH) (downlink)

Packet Traffic Channels:

PDTCH: data traffic

Packet Dedicated Control Channels:

PACCH: associated control

PTCCH/U: timing advance estimation (uplink))PTCCH/D: timingadvance information(downlink)


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Uplink Transmission


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October 2005 140

Data Block

Packet Uplink Ack/Nack

Data Block (last)

Access and Assignment

MS Network

PDTCH

PACCH

PDTCH

Packet Uplink Assignment (polling)PACCH

Packet Control AcknowledgementPACCH

Data BlockPDTCH

Data BlockPDTCH

Data Block (last in send window)PDTCH

Data Block PDTCH

Data BlockPDTCH

Data BlockPDTCH

Data BlockPDTCH

Packet Uplink Ack/Nack (final, polling) PACCH

Packet Channel Request (or Channel Request)

Packet Uplink Assignment (or Immediate Assignment)

Packet Resource Request

Packet Uplink Assignment

Network

PRACH (or RACH)

PAGCH (or AGCH)

MS

(Optional)

(Optional)

Access

Uplink data transferPacket Control Acknowledgement PACCH


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Resource release


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October 2005 147

The procedure for resource release is generally initiated from the MS, with the

cowntdown procedure of the last sent blocks

The network sends the Packet Uplink Final Ack over the PACCH, in order to

inform the MS of the radio blocks correct reception

The MS sends a Packet Control Acknowledgement in the uplink reserved block,

then releases the TBF, which is also released from the network

The PDCH, the USF and the TFI can therefore be assigned to other MS

In the case of a fast release required from the network which implies the TBF

release, the MS sends a new Packet Channel Request in order to send the RLC

Data Block which are not already sent

PDCH Fast release


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The fast release procedure can be initiated when: The assignments to the PDCH are concluded

Individual notify to each mobile which has an assignment to the

PDCH (over PACCH)

Broadcast notify, over each PDCH to be released


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October 2005 150

http://www.3gamericas.org/English/Statistics/gsm_evolution/edge_launches.cfm
http://www.3gamericas.org/English/Statistics/gsm_evolution/edge_launches.cfmhttp://www.3gamericas.org/English/Statistics/gsm_evolution/edge_launches.cfm


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EDGE


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EDGE is considered as an evolution of GSM/GPRS: the goal

the increase of bit rate through a better spectral efficiency

EDGE adopts the 8 PSK modulation (3 bit per symbol); this

allows to reach 812.5 kbit/s over the radio interface with the

same symbol rate of 270.83 kbit/s;

EDGE defines 9 modulation and coding schemes MCS, from

8.8 kbit/s per Time Slot (MCS-1 with GMSK modulaiton), to

59.2 kbit/s per Time Slot (MCS-9 with 8PSK modulation)


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GERAN reference architecture


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October 2005 154

GSM/UMTSCore Network

GERAN

Gb

A

Iu

MS

Um

Iur-g

BSC

BTS

BTS

BSS

BSS

MS

Iur-g

UTRAN

RNC


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EDGE


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October 2005 156

Moreover

Adoption of the Link Adaption functionality, which, in relation tothe radio channel quality, allows to vary the coding scheme andmodulation (MCS), even for eventual packet retransmissions;

Adoption of the Incremental Redundancy functionality, that isthe software recombination of the wrong received blocks, in order to

increase the codes error correction capacity; EDGE shares radio systems and the core of GPRS network

GPRS and EDGE services are multiplated over the same Time Slot

GPRS RLC/MAC protocols have been enriched for the EDGEservice, in order to allow the increase of user performances

EDGE service requirements

Th ee kind of se ices


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October 2005 157

Service Data rate per slot Peack Data Rate Mobile Speed

EGPRS

ECSD 32 T

48 kb/s

43.2 kb/s

28.8 kb/s

18 kb/s

32 kb/s

384 kbit/s (8 slot)

64 kbit/s (2 slot)

144 kbit/s (8 slot)

3 - 100 km/h

3 - 100 km/h

100- 250 km/h

ECSD 43.2 NT

ECSD 28.8 NT/T

Three kind of services

EGPRS: EDGE GPRS

ECSD NT: EDGE Circuit Switched Data - Non Transparent

ECSD T: EDGE Circuit Switched Data Transparent

The peak data rate is of 64 kbit/s for the ECSD (Enhanced CSD Circuit Switched Data) because the limitation in core networks (Ainterface, with link at 64 kbit/s)

Q(0,1,0)(0 0 0) (0 1 1)

8 PSK modulation

ttfAts 2cos


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October 2005 158

time

0

I

(0,0,0) (0,1,1)

(1,1,1)

(1,1,0)(1,0,0)

(1,0,1)

(0,0,1)

phase shift:

-V

0

V

111 011 010 000

Without Gaussian filter

ttfAts cm 2cos


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Channel coding

-Channel coding adds redundancy and

10-2

k/n=1/2


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October 2005 161

Channel coding adds redundancy and

memory to the information such to reveal

and/or correct errors

-For example, for each k information bits n

coded bits are generated

-The code rate is Rc=k/n

0 2 4 6 8 10 12 14 1610

-12

10-10

10-8

10-6

10-4

Eb/no dB

Pe

uncodedcoded

0 2 4 6 8 10 12 14 1610

-12

10-10

10-8

10-6

10-4

10-2

Eb/n0 dB

Pe

codeduncoded

k/n=1/3


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EDGE Throughput


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October 2005 163


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RLC/MAC Block per EGPRS data


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October 2005 165

E FBI BCS TB37MAC

HeaderMCS-3

EGPRS RLC Data UnitEGPRS RLC Data Block

RLC/MAC Block fordata transmission forEGPRS (DL)

MAC

HeaderMCS-9 E FBI BCS TB37 37 E FBI BCS TB37 37

EGPRS RLC Data Block 1 EGPRS RLC Data Block 2

RLC/MAC Block fordata transmission forEGPRS (DL)

Coding and

puncturing processes

are applied to the

syngol red boxes

A FamilyMCS-6

MAC

HeaderE FBI BCS TB37 37

Basic Unit


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EGPRS Modulation & Coding Schemes

MCS 5

MCS-2MCS-3

MCS 6


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October 2005 167

MCS choice:For initial transmissions, any MCScan be selected based on the current link quality.In case of retransmissions, the MCS is selectedwithin the same Family on the basis of theadopted automatic repeat request mechanism.

28 28 28 28Family B

MCS-7

MCS-5Octets

Family A 37 37 37 37

MCS-6

MCS-9

Octets

22 22Family C

MCS-4

MCS-1Octets

Family

A

padding 34 34 34 34

MCS-8

Octets

34+3 34+3

MCS-6

OctetsMCS-3


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EGPRS MCS


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October 2005 171

MCS-9 A 59.2 57.3

MCS-8 A Padding 54.4 52.6

MCS-7 B 44.8 43.3

MCS-6 A 29.6 28.6


MCS-5 B 22.4 21.7

MCS-4 C 17.6 17.0

MCS-3 A 14.8 14.3


MCS-2 B 11.2 10.8

MCS-1 C 8.8 8.5

Application data rate (Kbps) @

IP packet size = 1500 bytes

8-PSK

GMSK

RLC throughput (bit/S)FamilyMCS Modulation

EGPRS: MCS-1 DL196 bits36 bits3 bits


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Block

code

Rate 1/3

convolutional

Puncturing P1 or P2Puncturing

Rate 1/3 convolutional

588 bits

USFRLC/MAC

headerRLC Data = 22 bytes = 176 bits TB

12 bits 108 bits

372 bits68 bits12 bits4 Extra SF

456 bits

Normal Burst Normal BurstNormal BurstNormal Burst

BCSHCS E FBI

Interleaving



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Block

code

Rate 1/3

convolutional

Puncturing P1 or P2Puncturing


732 bits

USFRLC/MAC


12 bits 108 bits


456 bits


BCSHCS E FBI

Interleaving


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InterleavinInterleavin

Block

code

Rate 1/3

convolutional

Puncturing P1 or P2+ 1 spare bit


1404 bits

USFRLC/MAC


36 bits 99 bits


1392 bits


BCSHCS E FBI



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Rio De Janeiro,

October 2005 177

InterleavinInterleavin

Block

code

Rate 1/3

convolutional

Puncturing P1 or P2+ 1 spare bit


1836 bits

USFRLC/MAC

headerRLC Data

*= 74 bytes = 592 bits TB

36 bits 99 bits


1392 bits


BCSHCS E FBI

* RLC Data: 74 bytes or (68 + 6) bytes68 bytes +6-byte padding for MCS-8 retransmission


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EGPRS: MCS-8 DL

564 bit45 bit3 bit


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October 2005 179

Rate 1/3

convolutional

Puncturing P1 or P2 or P3Puncturin Puncturing P1 or P2 or P3

36 bits 124 bits 8 Extra SF

1392 bits


Rate 1/3 convolutionalBlock

code Rate 1/3 convolutional

1692 bits36 bits 135 bits

564 bits45 bits

TBBCSUSF RLC/MACheader

HCS RLC Data = 68 bytes = 544 bitsE FBI

3 bits

TBBCSRLC Data = 68 bytes = 544 bitsE FBI

564 bits

1692 bits

612 bits 612 bits

Interleavin Interleavin

EGPRS: MCS-9 DL

612 bit45 bit3 bit 612 i


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Rate 1/3

convolutional

Puncturing P1 or P2 or P3Puncturing Puncturing P1 or P2 or P3

36 bits 124 bits 8 Extra SF

1392 bits


Rate 1/3 convolutionalBlock

code Rate 1/3 convolutional

1836 bits36 bits 135 bits

612 bits45 bits

TBBCSUSF RLC/MACheader HCS RLC Data = 74 bytes = 592 bitsE FBI

3 bits

TBBCSRLC Data = 74 bytes = 592 bitsE FBI

612 bits

1836 bits

612 bits 612 bits

Interleavin Interleavin


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Link Adaptation (LA)


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October 2005 184

Re-segmentation

Coding&puncturingInterleavingtransmission

receptionDeinterleavingdecoding

MCS-6 3737 3737!!! NOT OK !!!

MCS-3 37

MCS-3 37

37

37

Higherprotection

New: In the GPRS it is not possible to retransmit with a CS

different from the one used in the first transmission


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Radio Resource (RR) states of a DTM (Rel.6) terminal

Classe A (DTM)

D l

The terminal can effectuate PS and CS traffic


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The terminal has

radio resources

allocated for data

transfer.

PCU, SGSN, HLR

know the position at

cell level; the MSC

at LA level

Classe B

BSC and MSC

know the

terminal

position at cell

level and havean active

signaling

connection to

maintain a

voice

communication

Dual

transfer

Dedicated

CS idle/Packet

transfer

CS Idle/Packet idle

Packet release

Packet request

RR establishment

RR

release

PDCH assignment

TBF(s)

releasePacket access

RR release

RR establishment

The terminal is not attached and the networkhas no infos on the terminal position, which

do not effectuates MM procedures and is not

reacheble with GPRS paging


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Radio Interface

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