6567822 Gsm Presentation

8/6/2019 6567822 Gsm Presentation

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Wireless Networks-- Cellular phone perspective

A presentation onGlobal System for Mobile

Communication

Abu Hena Md. Imrul Kayser



Wireless Systems

Wireless systems

GSM WCDMA SDRCDMA AMPS

GSM= Global System for Mobile CommunicationCDMA= Code Division Multiple AccessWCDMA= Wide-band CDMAAMPS= Advanced Mobile Phone SystemSDR= Software Dependent Radio



1

7

6

5

2

3

4

T ypical Cell Pattern

Neighboring frequency is 3 channel (600 kHz) separated

1

7

6

5

2

3

4

1

7

6

5

2

3

4

1

7

6

5

2

3

4

r D

D / r = 3N N= frequency reuse factor



89 0 915 9 35 9 60

25

MHz 25

MHz

GSM- 9 00 Frequency Band

Uplink

MS to BT

S

Downlink

BT S to MS



Channel bit rate : 270. 8 33 kb/s

Multiple access : T DMA and FDMA

Number of channels : 1 24 / 2 99 / 374

Users per channels : 7

Channel spacing : 200kHzModulation : GMSK

GSM / PCS / DCS Specification



MSC : Mobile Switching Center

BSC : Base Station Controller

BT S : Base T ransceiver Station

MS : Mobile Station / Handset

PST N : Public Switched T elephone Network

Some Definitions



MSC

BSC

BSC

BSSBase Switching Sub System

NSS

Network SwitchingSub System

PSTN

OMC-S

OMC-R

EIR

HLR VLR AuC

GSM Network

BTS



BSS - Base Sub System1

7

6

5

2

3

4

9 00 MHz

Radio link

15 GHzMicrowave link

BSC

BaseStation

Controller

BaseT ransceiver

Station

1 3GHzMicrowave link



BT S and Signal Propagation

3 sectored B T S3 sectored

Radiation patter 1 sector

Radiation pattern

OmniRadiation pattern

Down link 9 35 -9 60 MHZ

Uplink 89 0-915 MHZ

TX

R X

R X

1 0PTo

BSC



Direct

wave

Reflectedwave

Signal Propagation

Receive Sensitivity ± 1 02 dBmBT S T ransmit power = 43 dBmMS T ransmit power = 33 dBm



MSC

BSC

BSC

BSSBase Sub System

NSS Network Sub System

PSTN

OMC-S

OMC-R

EIR

HLR VLR AuC

GSM Network



HLR Home Location Register

VLR Visitor Location Register

AuC Authentication Center

EIR Equipment IdentificationRegister

MSC - Mobile Switching Center

OMC-R Operation / MaintenanceCenter - Radio

OMC-S Operation / Maintenance

Center - Switch

MSCOMC-S

HLR

VLR EIR AuC

BSS

PSTN

OMC-R



1

7

6

5

2

3

4

FDMAFrequency DivisionMultiple Access

FDMA and T DMA in GSM / PCS

Frequency Hopping andT

ime slot hoppingT

DMA frame length = 4.615

ms /8

T

ime slot

0 1 2 3 4 5 6 7 0

0 1 2 3 4 5 6 7 0

T DMAT ime DivisionMultiple Access

T DMA Frame



T DMA Frame ± Down link ( B T S to MS )

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

TDMA frame = 4.6

15ms

1 Channel (One way)

T ime slot / T CH

9 35 MHz

9 60 MHz

T S ³ 0 ´ for signaling and synchronization

Speech rate 24.7 kb/s Max Subscriber is 7 / sector



SpeechBits

57 Bits

T rainingBits

26 Bits

Stealing Flag1 Bit

StopBits

3 Bits

StartBits

3 Bits

5 77 micro Seconds / 15 6.2 5 bits

GuardBits

8 .25 bits

SpeechBits

57 Bits

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

T DMA frame = 4.6 15 msT ime slot / T CH

9 60 MHz

9 35 MHz



T DMA Frame ± Up link ( MS to B T S )

T S ³ 0 ´ for signaling and synchronization

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

Propagation delay 3 T S89 0 MHz

915 MHz

200 KHz Channel Spacing T CH



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

T DMA frame = 4.6 15 msT ime slot

9 35 MHz

9 60 MHz

7th

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

Propagation delay 3 T S89 0 MHz

915 MHz

200 KHz Channel Spacing

7th

TDMA FrameUplink / Down link



BT S-1

BT S-2

BT S-3

BT S-4

BT S-5

BSC- 1

BSC-2

MSC

PS T N

HLR

VLR

Handover

BTS-1 ± BSC-1 ± MSC ± PSTN



BT S-1

BT S-2

BT S-3

BT S-4

BT S-5

BSC- 1

BSC-2

MSC

PS T N

HLR

VLR

Handover




Limitations of GSM- 9 00Small Bandwidth of only 2 5 MHz

Limited number of Channel

InterferenceCo channel interference

Neighboring channel interference

Handover call drop / hard hand off



CDMA

CDMA

Code Division Multiple Access



CDMA

185 0 191 0 19 30 199 0

60 MHz 60 MHz

25

25

50

25

25

25

25

25

Channel spacing = 5 0 KHz

T otal Channels = 302

Career spacing = 1 .25 MHz

CDMA



CDMASingle frequency in all the base station

2525

50

25

25

2525

25

Unique Pilot signal ( PN )is transmitted from all the base station.

Each sector of base station is assigned a specifictime (or phase ) offset of these PN sequence.

CDMA



Benefits of CDMAIncreased capacity

Improved coverage / fewer cell sites

Improved call quality / few drop calls

Enhanced privacy

Bandwidth on demand

CDMA



Features of CDMA

System capacity depends on

Interference level

System coverage depends on

Interference level

Dynamic power management

CDMA



Limitations of CDMA

Co channel Interference

Data rate only 9 .6 kbps

Network coverage prediction iscomplicated

CDMA



Research on CDMA

Keep interference minimum

Develop Better power managementalgorithm

CDMA

Improve MS sensitivity

6567822 Gsm Presentation

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