Spark Final GSM All

8/18/2019 Spark Final GSM All

1/123

Karim Tawfik

GSM Global System for Mobile Telecommunications


2/123

2PRIVATE AND CONFIDENTIAL ©

www.sparkeg.com

Training Program Title

Instructor Name

Mobile Technology Evolution

Speech

1G

GSM

13 kbps

HSCSD

57.6 kbps

Circuit Switched

GPRS

115 kbps

Packet Switched

EDGE

384 kbps

Time

WCDMA

(UMTS)

2 Mbps

HSDPA

3.6 Mbps

HSUPA

5.76 Mbps

Circuit Switching Packet Switching

2G

2.75G

2.25G

2.5G

3G

3.5G

1G


3/123


www.sparkeg.com


Instructor Name

Basic communications Block Diagram

Transmitter

Carrier

Information to

be transmitted(Baseband signal)

Transmitted

signal

Channel

Received

signal

Receiver

Recovery ofinformation


4/123


5/123


www.sparkeg.com


Instructor Name

Why Wireless?

•The kinds of transmission medium :

1- Twisted-pair:

It is very low bandwidth and it is easily tapped either physically orby monitoring its electromagnetic radiation

2- Coaxial cable:

It is greater bandwidth than twisted-pair but it is very expensive.

3- optical fibers:

It is very high bandwidth , very high bit rate.

4- Radio (wireless):

It is greatly depending on the particular frequency of the

electromagnetic wave and Some of their advantages are:a- They are very flexible.

b- Portable system can be installed very quickly

c- There are often the most cost-effective solution


6/123


www.sparkeg.com


Instructor Name

Types of communication

TX RX

TX+RX TX +RX

TX+RX TX +RX


7/123

Radio Coverage


8/123


www.sparkeg.com


Instructor Name

Cell Geometry

Problem of omni Directional antennas

Dead Spots


9/123


www.sparkeg.com


Instructor Name

Cell Geometry Shape

R R

To solve the dead spot problem

• The number of cells required to cover a given area.

• The cell transceiver power.

Tradeoffs

R


10/123


www.sparkeg.com


Instructor Name

Transceiver Antenna

Omni-Directional AntennaSectorial Antenna


11/123


www.sparkeg.com


Instructor Name

Sectorial antenna

- The cells will take the form of overlapping circles.

- Due to the obstacles in the coverage area the actual shape of the

cells would be Random.

Sectorial Antenna


12/123


www.sparkeg.com


Instructor Name

GSM Coverage Plan

• To provide coverage for a large service area of a mobile network we

have two Options:

(A) Install one transceiver with high

radio power at the center of the

service area

Drawbacks

• The mobile equipments used in this

network should have high output

power in order to be able to transmit

signals across the coverage area.

• The usage of the radio resources

would be limited.

Advantages

• Each cell as well as the mobile

handsets will have relatively small

power transceivers.

• The frequency spectrum might be“reused” in two far separated cells.

This yields:

Unlimited capacity of the system.

Good interference characteristics

(B) Divide the service area into

smaller areas (cells)


13/123


www.sparkeg.com


Instructor Name

Radio Access Methods

• Frequency Division Multiple Access (FDMA)


14/123


15/123


www.sparkeg.com


Instructor Name


• Hybrid TDMA/FDMA


16/123


www.sparkeg.com


Instructor Name


• Code Division Multiple Access


17/123


www.sparkeg.com


Instructor Name

Spectrum allocations:

UHF band found to be the most suitable one for GSM as antenna lengthrequired for hand sets must be few cm. and that according to the rule.

Lα (1/f)


18/123


www.sparkeg.com


Instructor Name

Frequency spectrum


19/123


www.sparkeg.com


Instructor Name

Frequency spectrum


20/123


www.sparkeg.com


Instructor Name

GSM standards used in Egypt

• Spectrum Allocation (GSM 900)

GSM 900 Frequency Allocation

F (MHz) 915 890

Uplink 1 2 3 4 121 122 123 124

F (MHz)

Downlink

960 935

1 2 3 4 121 122 123 124

890.2

890.4

890.6

935.2

935.4

935.6

200 KHz

1

1

121

121

Downlink 935 – 960 MHz

Uplink 890 – 915 MHz

ARFCN Absolute Radio Frequency Channel Number


21/123


www.sparkeg.com


Instructor Name

GSM standards used in Egypt

• Spectrum Allocation (GSM 1800)

GSM 1800 Frequency Allocation

F (MHz) 1785 1710

Uplink 1 2 3 4 371 372 373 374

F (MHz)

Downlink

1880 1805

1 2 3 4 371 372 373 374

1710.2

1710.4

1710.6

1805.2

1805.4

1805.6

200 KHz

Downlink 1805 – 1880 MHz

Uplink 1710 – 1785 MHz


22/123


www.sparkeg.com


Instructor Name

Frequency reuse concept

• Why do we need frequency reuse?

Total no of channels (frequencies) = 124

Every channel can be shared between a maximum of 8 subscribers.

Maximum no of simultaneous calls = 8 X 124 = 992 !!

The group of frequencies allocated to a given cell must not be

used in the adjacent cells.

Enough distance between the cells where the same group offrequencies are reused.

GSM F B d


23/123


www.sparkeg.com


Instructor Name

GSM Frequency Bands

System P-GSM 900 E-GSM 900 GSM(DCS) 1800 GSM(PCS) 1900

Uplink (MS BS) Downlink(BS MS)

890 – 915 MHz935 – 960 MHz

880 – 915 MHz925 - 960 MHz

1710 – 1785 MHz1805 - 1880 MHz

1850 – 1910 MHz1930 - 1990 MHz

Wavelength 33 cm 33 cm 17 cm 16 cm

Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz

Duplex distance 45 MHz 45 MHz 95 MHz 80 MHz

Carrier separation 200 kHz 200 kHz 200 kHz 200 kHz

No. of carriers 124 174 374 299

Channel rate 270.8 kbps 270.8 kbps 270.8 kbps 270.8 kbps


24/123


www.sparkeg.com


Instructor Name

Frequency Reuse Concept

N = i^2 + j^2 + ijN:number of cells/cluster

i and j are integers.

3 / 9 Cluster 3/9 cluster in which the available frequencies are divided into


25/123

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

3 / 9 Cluster 3 /9 cluster in which the available frequencies are divided into9 groups and distributed between 3 sites

4 / 12 Cluster 4/12 cluster in which the available frequencies are divided into


26/123

4 / 12 Cluster

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

4/12 cluster in which the available frequencies are divided into

12 groups and distributed between 4 sites

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2A1

B3

B2B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

7 / 21 cluster in which the available frequencies are divided7 / 21 Cluster


27/123

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

7 / 21 cluster in which the available frequencies are divided

into 21 groups and distributed between 7 sites7 / 21 Cluster


28/123


www.sparkeg.com

Training Program TitleInstructor Name

Which Cluster Size to use?

Carrier to interference ratio

It’s the difference in power level between the carrier in a given

cell and the same carrier received from the nearest cell that reuses

the same frequency.

Number of frequencies

per site

Traffic ChannelsC/I Ratio

3/9 High High Low

4/12 Medium Medium Medium

7/21 Low Low High


29/123

29PRIVATE AND CONFIDENTIAL ©www.sparkeg.com


Cellular System Concepts “Frequency reuse

Reuse Pattern(Cluster):

- Cells are grouped into Clusters- Available Band is distributed among the cells of the cluster

- “N” is the number of cells in a cluster .

- Each frequency is reused after the same distance “D”

- Reuse Plan = >> (D/R)²= 3N

Where R is the cell radius

5

23

4

7

1

6

5

N=7 Cell Cluster N=7 Cell Cluster

7 Cell Reuse Plan7 Cell Reuse Plan

2

3

4

7

1

6

5

2

3

4

7

1

6

5

2

3

4

7

1

6

5

2

3

4

7

1

6

5

D


30/123



Co-channel Interference:

• Cells that have the same set of frequencies called co-

channel cells and the interference between them is calledco-channel interference.

• We can't remove co-channel interference by increasing thecarrier transmitter power as it will increase the interferencewith the neighboring cells. To solve co-channel interference,we must separate the co-channel cells by a minimumdistance to provide sufficient isolation due to propagation.

• In the case of each cell has the same size and transmittedpower, the co-channel interference ratio is independent ofthe transmitted power and depend on the radius of the cell(R) and the distance between the centers of the nearest co-

channel cell (D). As the ratio D/R increased, the interferencewill be reduced as the distance between the co-channelcells will increase.


31/123


32/123



Configure ARFCN


33/123



Allocate ARFCN to TRX


34/123



Erlang B Clculator


35/123



Traffic and coverage analysis

• A = n x T / 3600 Erlang

Where, A = offered traffic from one or more users in the systemn = number of calls per hour

T = average call time in seconds

Where,

P is the probability of blocking

m is the number of resources such as servers or circuits in a group

E is the total amount of traffic offered in erlangs


36/123



GSM Capacity analysis


37/123



Capacity calculations

1. Up link BW = down link BW = (Total BW (MHZ) =50)/2=25 MHZ.

2. No. of frequencies = (uplink bw (MHZ) =25/ch.spacing (MHZ))=0.2=125.3. Traffic channels/cell= (no. of frequencies=125/cluster size=21) =6.

. No. of traffic channels= (traffic channels/cell=6)*8-2=46.

5. Traffic/subscriber= (Expected call/hour/user=1/3600)*(Average call/user (second)

=90) =0.025.

6. Using erlang b table B=2%Traffic channels=46

So traffic/cell=36.53

7. Subscriber/cell= (traffic/cell=36.53)/ (traffic/subscriber=0.025)=1462.

8. No. of cells= (No. of subscribers=300000)/(subscriber/cell=1462)=206.

9. No. of BTS’s = (no. of cells= 206)/3=69.•


38/123

Thank You

www.sparkeg.com


39/123

Network architecture


40/123



Basic GSM Nodes

AUC: Authentication Center

BGW: Billing GateWay

BSC: Base Station Controller

BSS: Base Station Subsystem

BTS: Base Transceiver Station

DTI: Data Transmission Interworking

EIR: Equipment Identity RegisterGMSC: Gateway MSC

HLR: Home Location Register

ISDN: Integrated Services Digital Network

MS: Mobile Station

MSC: Mobile services Switching Center

PLMN: Public Land Mobile Network

PSTN: Public Switched Telephony Network

SMSC: Short Message Service Center

SS: Switching Subsystem

TRC: Transcoder Resources ControllerVLR: Visitor Location Register

SS SS

D T I

BTS BTS

ISDN

PLMN

PSTN

ISDN ISDN

PLMN PLMN

PSTN

SMSC

B G W H L R

E I R

GWMSC GMSC

MSC/VLR MSC/VLR

MS

Air I/f

BSC/TRC BSC/TRC

BSS BSS

AUC


41/123



Mobile stations

The SIM Card contains:

A processor and memory.

that stores:

- The international mobile subscriber Identity IMSI

- The Authentication and ciphering keys.

The Mobile Equipment is said to be a Mobile Station if the Subscriber

Identity Module ( SIM Card ) is added to it

+

Mobile Station (MS)

=


42/123



SIM Card

Stores user addresses

IMSI,MSISDN,TIMSI, rooming, etc

Personalization

SIM stores user profile (subscribed services)

RAM available for SMS, short numbers, user’s

directory, etc Protection codes PIN ,PUK

authentication and encryption features

subscriber’s secret authentication key (Ki)

Authentication algorithm (“secret” algorithm - A3 – not

unique)

Cipher key generation algorithm (A8)


43/123



GSM Identities

• Mobile Station ISDN Number (MSISDN)

CC : Country Code

NDC : Network Destination Code

SN : Subscriber Number

VodaFone Egypt MSISDN

20

CC

10

NDC

1100477

SN

VodaFone UK MSISDN

44

CC

385

NDC

196099

SN


44/123



GSM Identities

• International Mobile Subscriber Identity (IMSI)

MCC : Mobile Country Code

MNC : Mobile Network Code

MSIN : Mobile Station Identification Number

Vodafone UK IMSI

234

MCC

15

MNC

1234567890

MSIN

Vodafone Egypt IMSI

602

MCC

02

MNC

1234567890

MSIN


45/123



GSM Identities

• International Mobile Equipment Identity (IMEI)

IMEI

6 Digits

TAC

2 Digits

FAC

6 Digits

SN

TAC: Type Approval Code, The first two

digits are the code for the country approval

SN: Serial Number

Final Assembly Codes (FAC)

01,02 AEG

07,40 Motorola

10,20 Nokia

30 Ericsson40,41,44 Siemens

47 Optional International

50 Bosch

51 Sony

51 Siemens

51 Ericsson60 Alcatel

70 Sagem

75 Dancall

80 Philips

85 Panasonic


46/123



Temporary Mobile Subscriber Identity Number (TMSI)

• The TMSI can be allocated to the mobile subscriber

in order to be used instead of his IMSI during all radiocommunications. The purpose is to keep subscriber

information confidential on the air interface.

• The TMSI is relevant on the local MSC/VLR level onlyand is changed at certain events or time intervals.

Each local operator can define its own TMSI

structure.


47/123



Cell Basic Attributes


48/123



Base Transceiver Station (BTS)

Consists of the radio transmitters, receivers and the antenna system required

to provide the coverage area for one cell.

Converts the GSM radio signals into a format that can be recognized by the

BSC.

Records and passes to the BSC the periodic power measurement reports.

Performs the network end function for the ciphering/encryption process.


49/123



Base station controller

• Paging

• Channel allocation

• Dynamic power control in MS and BTS

• Locating the MS

• Handover

• Frequency Hopping


50/123



The Mobile Services Switching Center (MSC)

Administers its Base Station Controller(s) BSC(s).

Switches calls to/from mobile subscribers.

Records charging and accounting details.

Provides the gateway functionality to other networks.


51/123



Split architecture


52/123



Home Location Register (HLR)

The HLR is a centralized network database that stores and manages allmobile subscriptions. Permanent information

• IMSI, MSISDN

• Services subscribed

• Service restrictions (e.g. roaming restrictions)

• Parameters for additional services

• info about user equipment (IMEI)

• Authentication data

Temporary information

Link to current location of the user:

• Current VLR address (if avail)

• Current MSC address (if avail)

• MSRN (if user outside PLMN)


53/123



Visitor Location Register (VLR)

MSC/VLR


54/123



Equipment Identity register (EIR)

•Database that validates Mobile Equipments

usage. It contains White list for normal

handsets, Gray list for faulty or non-type

approved handsets & Black list for stolen

handsets.


55/123



Short Message Service Center (SMSC)

Receives and stores short messages from mobile subscribers.

Forwards short messages to mobile subscribers.

If the delivery of short messages fails (due to mobile absent or fullmemory condition), it starts a retry schedule to deliver the message .

Generates charging data for the short messages delivered.


56/123




57/123



Security Feature

Authentication: to secure network against unauthorized access.

Ciphering: to protect subscriber data sent over the radio path against

eavesdropping.

Subscriber identity confidentiality.

Equipment Identity Check: to prevent fraudulent usage of mobile

handsets.


58/123



Triplets

Authentication Center

Triplet

RAND SRES Kc

Home Location Register

Triplet

RAND SRES Kc

Visitor Location RegisterRAND SRES Kc


59/123



Producing Triplets

Ciphering

Algorithm

A8

IMSI

Ki

Authentication

Algorithm

A3

Random

Number

Generator

SRES

RAND

Kc

SRES

RAND

Kc

RANDKi

RAND

Ki


60/123



The Authentication procedures

Visi tor Locat ion Register

Rand SRES AUC Kc

SRES AUC SRES MS

Barred

Base Stat ion Subs ystemKc

SIM Card

A8

SRES MS

= Access

Kc

SRES MSRand

Rand

A3 KiRand


61/123



The Ciphering Procedures

Base Transceiver StationDecryptionAlgorithm

Encryption

Algorithm

Mobile Station

TDMA

Frame Number

DATA

E n c r y p t e d

D A T A

DATA

E n c r y p t e d

D A T A

Encryption

Algorithm

Decryption

Algorithm

Kc

TDMA

Frame Number

DATA DATA

Kc

Air Interface


62/123

Thank You

www.sparkeg.com

GSM Transmission Process


63/123



Segmentation

Speech Coding

Channel Coding

Interleaving

Ciphering/Encryption

A/D Conversion

Burst Formatting

Modulation and

Transmission



64/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Analog to Digital Conversion

Analog to digital conversion takes place in

3 steps:

1. Sampling

2. Quantization

3. Coding

1. Sampling

Telecommunication systems use Sampling rate = 8 Kbit/s



65/123



2. Quantization

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission


Within common



66/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission


Coding involves converting the quantized values into binary.

Every value is represented by a binary code of 13 bits (2 13 = 8192).

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

The output rate of the A/D Conversion process is:

8000 Samples/Sec x 13 bits/Sample = 104 Kb/s

If one frequency will be used for 8 calls, then thebit rate will be 8 x 104 kb/s = 832 kb/s this will not

fit in the 200 KHz channel allocated for one

frequency. Coding should be used to reduce the

rate.

3. Coding



67/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

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

160 sample in 20 ms = 1 Segment

1 2 3 4 . . . . . . . . . . . . . . . 160



68/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

GSM Speech Coding

Instead of using 13 bits per sample as in A/D conversion, GSM speech coding uses

260 bits to encode one segment.

This calculates as 260 bits / 20 ms = 13 kb/s. This provides a speech

quality which is acceptable for mobile telephony and comparable with

wire line PSTN phones.Many types of speech coders

are available. Some offer better

speech quality, at the expense

of a higher bit rate (waveform

coders). Others use lower bit

rates, at the expense of lowerspeech quality (vocoders).

The hybrid coder used by GSM

provides good speech quality

with a low bit rate, at the

expense of speech coder

complexity.



69/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Channel Coding

speech coding does not consider theproblems which may be encountered on the radio transmission path.

The next stages in the transmission process, channel coding and

interleaving, help to overcome these problems.

I n p

u t i s 2 6 0 b i t s r e p r e s e n t i n g 1 s e g m e n t

Channel coding


70/123



Channel coding

o Mobile channel is error-prone.o Compressed speech is sensitive to errors.o Error correction is necessary.o Channel coding adds extra bits to help in

error correction.

o GSM uses:1. Block code2. Convolutional code

Channel coding


71/123



o The 260 b are split into 3 blocks:

o Block 1 (class 1a) 50 very important bits. Sent to block code to get 53 bits. If erroneous, (BFI) is sent.

o Block 2 (class 1b) 132 important bits. 53 b + 132 b + 4 tail bits are 1:2 Convolutional coded. 4 tail bits will set the register.

o Block 3 (class 2) 78 not so important bits.

These are not protected at all.o This results in 456 bits/20 mseco This gives 22.8 kb/sec

Channel coding

Types of channels


72/123



• Types of Traffic channels

1. Full rate

- 13 Kbps data rate

2. Enhanced full rate

- 12.2 Kbps data rate

3. Half rate

- increase network capacity

13 Kbps 9.8 Kbps

12.2 Kbps 10.6 Kbps

5.6 Kbps 5.8 Kbps

11.4 Kbps

22.8 Kbps

Data

Redundancy

Types of channels

Interleaving


73/123

• Interleaving

- First level :Block interleaving 1

9

17

25

.

.

.

449

2

10

18

26

.

.

.

450

3

11

19

27

.

.

.

451

8

16

24

32

.

.

.

456

4

12

20

28

.

.

.

452

5

13

21

29

.

.

.

453

6

14

22

30

.

.

.

454

7

15

23

31

.

.

.

455

57 bits

Interleaving

Radio Transmission Problems


74/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Interleaving

1. First Level Interleaving1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24

25 26 27 28 .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

429 430 431 432

433 434 435 436 437 438 439 440

441 442 443 444 445 446 447 448

449 450 451 452 453 454 455 456

5 7 Bi t s

8 Groups



75/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Ciphering and Encryption

The purpose of ciphering is to encode the

burst so that it cannot be interpreted by any other

device than the intended receiver.

The ciphering algorithm in GSM is called the A5algorithm.

It does not add bits to the burst, meaning that the

input and output

to the ciphering process is the same as the input: 456bits per 20 ms.



76/123



Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Burst Formatting

Every transmission from an MS/BTS mustinclude some extra information such as the training sequence.

The process of burst formatting is to add these bits (along with some

others such as tail bits) to the basic speech/data being sent.

In GSM, the input to burst formatting is the 456 bits received from

ciphering. Burst formatting adds a total of 136 bits per block of 20 ms,

bringing the overall total to 592.

Now, the 592 bits will be sent on 4 bursts, each containing 2 x 57 bits

+ 136 / 4 = 148 bits.

However, each time slot on a TDMA frame is 0.577 ms long.

This provides enough time for 156.25 bits to be transmitted (each bit

takes 3.7 us),

The rest of the space, 8.25 bit times, is empty and is called the Guard

Period (GP). This time is used to enable the MS/BTS “ramp up” and

“ramp down”.

Calculations


77/123



Calculations

– -Bit rate of the radio carrier is 270.833 Kbps

– -Bit duration =1/270.833=3.69 µsec

– -One time slot =148 bits+8.25 guard bits=156.25 bits

– -Time slot duration =156.25x3.69 µsec= 0.577 msec

– -Frame duration=0.557x8= 4.615 msec



78/123

78PRIVATE AND CONFIDENTIAL ©www.sparkeg.comTraining Program TitleInstructor Name

To ramp up means to get power fromthe battery/power supply for transmission.

Ramping down is performed after each transmission to ensure

that the MS is not transmitting during time slots allocated to other

MSs.

The output of burst formatting is a burst of 156.25 bits or 625 bitsper 20 ms. When it is considered that there are 8 subscriber per

TDMA frame, the overall bit rate for GSM can be calculated to be

270.9 kbits/s.

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Burst Formatting

Guard

Period

Tail

BitsEncrypted Bits

Training

SequenceEncrypted Bits

Tail

Bits

8.253571261573

TDMA Frame

76543210

156.25 bits in 577 u Sec

Modulation


79/123


modulator

- Gaussian minimum shift keying


80/123

Air Interface

Air Interface


81/123


Physical Channels

Time

GSM band is divided into 124 RF channels, and each channel is divided into 8time slots using TDMA. These time slots are called “physical channels”.

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

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

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

CH 124 0 1 2 3 4 5 6 7 0 1 2 3 4 5

Air Interface


82/123

82PRIVATE AND CONFIDENTIAL ©www.sparkeg.com Training Program TitleInstructor Name

Logical Channels

Logical Channels

A physical channel may be occupied by a traffic channel or a control channel,both of them are classified as “logical channels”.

Traffic Channels

Half Rate Full Rate

Control Channels

SCH

BCCH

FCCHPCH

RACH

ACGCH

SDCCH

SACCH

FACCH

CBCCH

BroadcastCommon Dedicated

Air Interface


83/123


Traffic Channels

Carries either encoded speech or user data up and down link between a singlemobile and a single BTS.

Full Rate = 13 Kbit/S

Half Rate = 6.5 Kbit/S

Enhanced Full Rate = 15.1 Kbit/S

Common Control Channel


84/123


Common Control Channel

Paging CHannel (PCH)

At certain time intervals the MS listens to the PCH to check if the networkwants to make contact with the MS. The reason why the network may want

to contact the MS could be an incoming call or an incoming short message.

The information on PCH is a paging message, including the MS’s identity

number (IMSI) or a temporary number (TMSI). PCH is transmitted downlink

only.

Random Access CHannel (RACH)

The MS listens to the PCH to determine when it is being paged. When the

MS is paged, it replies on the RACH requesting a signaling channel. RACH

can also be used if the MS wants to contact the network. For example,

when setting up a mobile originating call. RACH is transmitted uplink only.

Access Grant CHannel (AGCH)

The networks assigns a signaling channel (Stand-alone Dedicated Control

Channel (SDCCH)) to the MS. This assignment is performed on the AGCH.

AGCH is transmitted downlink only.

Broadcast Channels


85/123



Instructor Name

Broadcast Channels

Frequency Correction Control CHannel (FCCH)

On FCCH, bursts only containing zeroes are transmitted. This serves two purposes.

First to make sure that this is the BCCH carrier, and second to allow the MS to

synchronize to the frequency. FCCH is transmitted downlink only.

Synchronization CHannel (SCH)

The MS needs to synchronize to the time-structure within this particular cell, and

also ensure that the chosen BTS is a GSM base station. By listening to the SCH,

the MS receives information about the frame number in this cell and about BSIC ofthe chosen BTS. BSIC can only be decoded if the base station belongs to the GSM

network. SCH is transmitted downlink only.

Broadcast Control CHannel (BCCH)

The MS must receive some general information concerning the cell in order to start

roaming, waiting for calls to arrive or making calls. The needed information is

broadcast on the Broadcast Control CHannel (BCCH) and includes the Location

Area Identity (LAI), maximum output power allowed in the cell and the BCCH

carriers for the neighboring cells on which the MS performs measurements. BCCH

is transmitted on the downlink only.

Dedicated Control Channels


86/123



Instructor Name

Dedicated Control Channels

Standalone Dedicated Control Channel (SDCCH)

The MS as well as the BTS switches over to the assigned SDCCH. The call set-up procedure

is performed on the SDCCH, as well as the textual message transmission (short message andcell broadcast) in idle mode. SDCCH is transmitted both uplink and downlink. When call set-up

is performed, the MS is told to switch to a TCH.

Slow Associated Control Channel (SACCH)

The SACCH is associated with SDCCH or TCH (i.e. sent on the same physical channel). On

the uplink, the MS sends averaged measurements on its own BTS (signal strength and quality)

and neighboring BTSs (signal strength). On the downlink, the MS receives informationconcerning the transmitting power to use and instructions on the timing advance. SACCH is

transmitted both uplink and downlink.

Fast Associated Control Channel (FACCH)

If a handover is required the FACCH is used. FACCH works in stealing mode meaning that

one 20 ms segment of speech is exchanged for signaling information necessary for the

handover. Under normal conditions the subscriber does not notice the speech interruptionbecause the speech coder repeats the previous speech block.

Cell Broadcast Channel (CBCH)

CBCH is only used downlink to carry Short Message Service Cell Broadcast (SMSCB) and

uses the same physical channel as the SDCCH.


87/123



Instructor Name

Chapter 4 : Radio Transmission Problems

Effects on Radio Communication


88/123



Instructor Name



89/123



Instructor Name


Effects on Radio


90/123



Instructor Name

- Path lossPr α Pt

Rβ

β = 3 ~ 4

Signal

level (dB)

Distan

e

Effects on RadioCommunication



91/123



92/123


www.sparkeg.com


Instructor Name

2. Rayleigh Fading (Multi-path Fading):

t1 t

2

t3


The difference in paths leads to a difference in paths of the received

components.



93/123


www.sparkeg.com


Instructor Name

Fading Problems



94/123


www.sparkeg.com


Instructor Name

• To overcome multipath fading we use :

- Microscopic diversity and combining techniques

- Frequency hopping

- Interleaving technique



95/123


www.sparkeg.com


Instructor Name

Fading Problems Solutions

1. Increase the fading Margin



96/123


2. Antenna Diversity (Space Diversity)


97/123



98/123


4. Interleaving (time Diversity)


99/123



100/123

- Time dispersion

- Due to multipath fading

- To overcome this we use1. delay equalizer (Viterbi Equalizer)2. Increase the Carrier to reflection

ratio 1 2 3 4 65

1 2 3 4 65

Path 1

Path 2



101/123


www.sparkeg.com


Instructor Name

Time dispersion problem

There would be an Inter-Symbol Interference between the a bit in the reflected

ray and 1 bit later in the direct way .

Bit Rate = 270.8 Kb/s

One BIT Duration = 3.7 sec

Bit stream is moving with

the velocity of light which equals

3 x 10 Km/sec

Then, when bit 2 is transmitted,

bit one will

cut a distance

= 3.7 x 10 -6 x 3 x 10 5 = 1.1 km



102/123


www.sparkeg.com


Instructor Name

The C/R ratio is defined as the difference in signal strength between the signal

received from the RBS and the strongest reflected signal .

C/R Relative position to the BTSResultPlanner should choose the proper position of the site to make the C/R

maximum everywhere in the coverage area of the site.

Time dispersion problem Solution

1. Increase the Carrier to reflection ratio


103/123



104/123


www.sparkeg.com


Instructor Name

If a mobile subscriber is located far from the site,then its transmitted bursts will arrive at the cell

transceiver with a significant delay that may lead to

overlapping with the bursts sent on the next time slot.

Solution to time delay problem

The site will send a “Timing Advance” value to the mobile station that is moving

away, telling it to send its bursts with a certain amount of time ahead of the

synchronization time.The timing advance has values from 0 to 63 depending on how far the mobiles

located. The size of a cell is limited by this parameter to a maximum radius of 35

Km.

Time Delay problem


105/123

Traffic Cases

Location update


106/123


www.sparkeg.com


Instructor Name

Why do we need to update our location data ?

Actually, the location update process is invited in aim to exactly identify your

location within the network so that any incoming call goes directly to the called

subscriber.

To fulfill this aim, one can say that we may update the system with the cell IDeach time the subscriber changes his serving cell.

The MSC/VLR will now know the exact cell you are roaming in.

This will result in a huge amount of location update messages.

An extreme is never to make a location update and to be paged in all the

network. This will cause huge amount of paging messages.

Do you have a compromising solution ?

Traffic Cases


107/123


www.sparkeg.com


Instructor Name

Location area is a part of the MSC/VLR coverage area. Each group of adjacent cells isassigned a universal unique location area identity.

The mobile subscriber is only required to update the network with its new location everytime it changes its Location Area.

Introducing the concept of Location area enables us to make an approximate estimationof your location.

Location Area

MSC Coverage Area


108/123


www.sparkeg.com


Instructor Name

Location Area Identity (LAI)


109/123


www.sparkeg.com


Instructor Name



LAC : Location Area Code

Vodafone Egypt LAI

602

MCC

02

MNC

1607

LAC

Cell Global Identity (CGI)


110/123


www.sparkeg.com


Instructor Name



LAC : Location Area CodeCID : Cell ID

Vodafone Egypt CGI

602

MCC

02

MNC

1607

LAC

781

CID

Types of Location update


111/123


www.sparkeg.com


Instructor Name

1. Normal Location update within same MSC/VLR service area

2. Normal Location update between 2 different MSC/VLR service areas

3. IMSI attach/detach

4. Periodic Location Update


112/123

Normal Location Update between 2 different MSC/VLRservice areas


113/123


www.sparkeg.com


Instructor Name

Old MSC/VLR New MSC/VLR

NEW BSCOld BSC

LA 1

LA 2

1. The mobile sends a locationupdate request to the MSC.

2. The new MSC/VLR receives the IMSI

and conclude the MGT.

IMSI to MGTtranslation

3. The MSC/VLR sends a subscriber

information request with the IMSI

to the proper HLR

4. The HLR stores the address of

the new MSC/VLR

VLR Address

=

Old MSC

VLR Address

=

New MSC

5. The HLR sends the data to the

new MSC/VLR and it is kept there

6. The HLR sends a location

cancellation message to the old

MSC/VLR to remove the data

HLR

7. The new MSC/VLR sends a location

updating confirmation message to

the mobile

service areas

IMSI Detach


114/123


www.sparkeg.com


Instructor Name

1. At power off, the MS asks for a signalingchannel.

2. The MS uses this signaling channel to

send the IMSI detach message to theMSC/VLR.

3. In the VLR, an IMSI detach flag is set for

the subscriber. This is used to reject

incoming calls to the MS.

IMSI Attach


115/123


www.sparkeg.com


Instructor Name

IMSI attach is a complement to the IMSI detach procedure. It is used by

the mobile subscriber to inform the network that it has re-entered an

active state and is still in the same location area. If the MS changes

location area while being switched off, a normal location update takesplace.

1. The MS requests a signaling channel.

2. The MSC/VLR receives the IMSI attach message from the MS.

3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now

ready for normal call handling.

4. The VLR returns an acknowledgment to the MS.

MSC/VLRBSC

1

2 3

4

Periodic Location Update


116/123


www.sparkeg.com


Instructor Name

Periodic location update is a routine task performed by thenetwork if the MS doesn’t make any location update ( any of

the previous 4 types) during a predefined period.If the MS doesn’t respond to this periodic location update, it will

be marked as implicitly detached. ( Temporarily out of service )

Handover


117/123


www.sparkeg.com


Instructor Name

- Handover is to keep continuity of the call when the subscriber is roaming along

the network moving from one cell to another and moving between different

nodes in the network.

- During call, the MS is continuously measuring transmission quality of

neighboring cells and reports this results to the BSC through the BTS.

- The BSC, being responsible on supervising the cells, is responsible of

handover initiation.

- Good neighbor relations between cells is an important factor in keeping the

network performance in the accepted level.

Types of Handover


118/123


www.sparkeg.com


Instructor Name

1. Intra BSC Handover:

When the cell to which the call will be handed over belongs to the sameBSC of the serving cell.

2. Inter BSC / Intra MSC Handover:

When the cell to which the call will be handed over belongs to the differentBSCs but to the same serving MSC.

3. Inter MSC

When the cell to which the call will be handed over belongs to the different BSCand different MSC.

Handover between Cells Controlled by the Same BSC


119/123


www.sparkeg.com


Instructor Name

When performing a handover between two cells controlled by the same BSC,

the MSC/VLR is not involved. However, the MSC/VLR will be informed when

a handover has taken place. If the handover involves different LA’s, location

updating is performed once the call is finished.

1. The BSC orders the new RBS to activate a TCH.

2. The BSC sends a message to the MS, via the old RBS, containing

information about the frequency and time slot to change to and also the

output power to use. This information is sent to the MS using FACCH.

3. The MS tunes to the new frequency, and transmits handover access burstsin the correct time slot.

4. the new RBS detects the handover bursts.

5. The MS sends a Handover Complete message to the BSC via the new RBS

6. The BSC tells the old RBS to release the old TCH.

Mobile Originated Call


120/123


www.sparkeg.com


Instructor Name

1. The mobile sends a call request along with its

IMSI to its serving MSC/VLR which will mark themobile as busy.

2. Authentication is performed by the MSC to

verify the mobile access to the network, and

then ciphering is initiated in order to protect the

mobile call on the radio path.

3. The mobile sends a call setup message to the

MSC with information about the call type,services required and the dialed number.

4. MSC checks the categories of the mobile

subscriber to verify that he is authorized to use

the required services, and then a link is

established between the MSC and BSC.

5. BSC checks the mobile serving BTS for an idletraffic channel and then orders that BTS to seize

this channel for a call.

6. The BSC informs the MSC when the traffic

channel assignment is complete, and then the

MSC/VLR starts to analyze the dialed number

and sets up a connection to the called

subscriber.

PSTN

BSC

MSC

IMSI ATTACH while Roaming


121/123


www.sparkeg.com


Instructor Name

When an MS is roaming internationally, the following occurs:

1. The MS is switched on and scans all GSM frequencies within

one frequency band (e.g. GSM 900). It is searching for a BCCH carrier. The MS tunes to theBCCH carrier that has the strongest signal strength and reads its system information. This

includes the identity of the network operator.

2. The MS compares this network identity with the list of

forbidden PLMN’s in the SIM memory. This list contains all network identities, which the

subscriber’s home operator does not have an international roaming agreement with. If the

network, which the MS has tuned to, is a forbidden network, the MS continues to scan for apermitted network.

3. If the MS does not find a permitted network, but has identified a forbidden network, it displays

the message “Emergency Calls Only”. If the MS finds a permitted network, it tunes to it and

sends an IMSI attach message.

4. The remainder of this traffic case is identical to that of the normal IMSI attach case, with the

only difference being that the subscriber’s HLR is located in another country.

Roaming: Location Update

Traffic Cases


122/123


www.sparkeg.com


Instructor Name

HLR

Attached

VLR ADD=

Egypt Airport

Roaming & Int.

Allowed

Detached

Roaming & Int.

Allowed

MSC/VLR

Is a roaming agreement present ?IMSI60202..

I s r o a m i n g a n d I n t .

c

a l l s a l l o w

e d ?

Attached

VLR ADD=

Stock. Airport

Roaming & Int.

Allowed

Copy of the HLR Profile will

be stored in Stock. VLR


123/123

Thank

You

Spark Final GSM All

Documents