The document provides an overview of cellular mobile concepts and GSM radio interface. It discusses the history and growth of mobile communications from 1G analog to 2G and 3G digital systems. It describes key cellular concepts like frequency reuse, interference reduction techniques, and trunking efficiency which allow efficient use of limited radio spectrum. It also summarizes GSM specifications including frequency bands, channel structure, access methods, modulation, voice coding and bit rates used in the radio interface.

1. 1
PART I A Brief History
PART II Cellular Concepts
PART III GSM- Radio Interface
CELLULAR MOBILE RADIO

2. 2
MOBILE COMMUNICATION
• REVOLUTION IN TELECOM.
• MOBILE COMMUNICATION IS A VERY RAPIDLY
GROWING AND A POPULAR SERVICE.
• MORE THAN 40 FOLD INCREASE IN LAST 10 YEARS
• IT HAS BECOME A BACKBONE FOR BUSINESS
SUCCESS AND EFFICIENCY
• CHANGED THE LIFE STYLE ALL OVER THE
WORLD.

3. 3
History
• First mobile service started in 1946 in St.
Louis, Missouri, USA.
– Manually operated service, restricted area of
service, only few lucky subscribers.
• Between 1950-60, it evolved to be
automatic with decreased cost.
• Mobile telephony service appeared in its
useful form in 1960s.

4. 4
Mobile Communications: 1980s
Analog systems: 1st Generation
• AMPS: Advanced mobile phone service
USA: 800 MHz band
• TACS: Total Access communication system
UK : 900 MHz band
• NMT: Nordic Mobile telephone service
• Scandinavian: 450 MHz & 900 MHz band

5. 5
Mobile Communications:1990s
Digital systems: 2nd Generation
• DAMPS: Digital AMPS
• USA: 800 MHz band, IS-54, IS-136
• CDMA: Code division multiple access
system: US: 900 MHz band :IS-95
• GSM: Global system for mobile comm.
Europe: 900/1800 MHz

6. 6
• Any time Anywhere
• Mobility & Roaming
• High capacity & subs. density
• Efficient use of radio spectrum
• Seamless Network Architecture
• Low cost
• Flexibility
• Innovative Services
• Standard Interfaces
MOBILE COMMUNICATION
OBJECTIVES

7. 8
MOBILE COMMUNICATION
• 1 G -analog (cellular revolution)
- only mobile voice services
WIRELESS GENERATIONS
• 2 G - digital (breaking digital barrier)
- mostly for voice services & data delivery
possible
• 3 G - Voice & data ( breaking data barrier)
- Mainly for data services where voice services
will also be possible

8. 9
CELLULAR MOBILE CONCEPTS

9. 10
CELLULAR MOBILE CONCEPTS
•RADIO IN LOCAL LOOP
•LIMITED AVAILABILITY OF RF SPECTRUM
•INTERFERENCE PROBLEM
•INTERFERENCE AND SYSTEM CAPACITY
•FREQUENCY REUSE PATTERN
•TRUNKING EFFICIENCY
•CELLULAR PRINCIPLE
•CELLULAR ENVIRONMENT
•CAPACITY CONSIDERATIONS
•FUTURE TRENDS

10. 11
Propagation loss
L in dBs
Transmit power PT
and antenna gain GT
Voice
Channels
Or
control
channels
Lines to
MSC
Site
noice
MS
Operating distance d
Planned cell radius R
Cell radio range - radius R max
Radio Cell Parameters

11. 12
Fundamental problems
• Radio range, or coverage
• no. of channels, or voice circuits
• Full, seamless service coverage
• Large no. of subscribers in the range
of millions

12. 13
•
FERQUENCY SCARCITY PROBLEM
Tel
Ex.



WIRED NETWORK
100,000  50 Khz = 5 Ghz (NOT POSSIBLE)
Hence Individual RF Loop is not extended
But a Common group of channels is shared
CELLULAR MOBILE CONCEPTS
BW forTelephony speech: 3KHz increases to 25 KHz with FM for Radio Trans.

13. 14
CELLULAR MOBILE CONCEPTS
CELL
RADIUS
(KM)
COVERAGE
AREA(KM2
)
No. Of
SUBS.
No. of
CHANNELS
REQD.
1 3.14 100 8
3 28.3 900 38
10 314 10,000 @ 360
25 1960 60,000 @ 2,000
ASSUMPTIONS Traffic /User = 30 mE , GOS = 1%

14. 15
CELLULAR MOBILE CONCEPTS
• 360 * 25 KHz * 2 = 18 000 KHz = 18 MHz
FOR A CELL OF 10 KM RADIUS ONLY
• WHICH IS IMPOSSIBLE TO BE ALLOCATED
• HENCE FREQUENCY REUSE IS A MUST TO
COVER THE TOTAL SERVICE AREA WITH
A LIMITED AVAILABLE RF RESOURCES
• HENCE THE NEED FOR A CELLULAR PRINCIPLE

15. 16
CELLULAR MOBILE CONCEPTS
WHAT IS A CELL ?
• A base station (transmitter) having a number of RF
channels is called a cell
• Each cell covers a a limited number of mobile subscribers
within the cell boundaries ( Coverage area)
• Typical Cell Radius Aprrox = 30 Km (Start up), 1 KM
(Mature)

16. 17
A CLUSTER OF CELLS
4
5
6
7
2
3
1
1 2 3 4 5 6 7
GIVEN FREQ.
RESOURCE
CELLULAR MOBILE CONCEPTS

17. 18
1
4
2
1
3
5
6
7 2
6
3
4
5
7
D
R
CELLULAR PRINCIPLE N=7
1 2 3 4 5 6 7
Frequency Reuse Pattern “N”=7
Given Freq Resource
CELLULAR MOBILE CONCEPTS

18. 19
CELLULAR MOBILE CONCEPTS
CO-CHL INTERFERENCE :Interference caused by
another cell/mobile using the same frequency
R
Co Chl Interference is
a Function of “Q”
the re-use ratio:
Q =D / R
Lower Q Increased Co-Chl Interference 
Higher Q Reduced Co-Chl Interference 

19. 20
CELLULAR MOBILE CONCEPTS
CO - Chl Interference
Q = D /R = 3N
N =Cluster Size
R = Size (Radius of Cell)
D = Distance between
two Co- Chl Cells
N Q=D/R
1 1.73
3 3.00
4 3.46
7 4.58
9 5.20
12 6.00
Higher Q Less Interference 
Higher N
More Cluster Size
Less RF freq/cell
Less Traffic Handling
Capacity of the system

LOWER Q Higher Interference 
Increased System
Handling Capacity 
Higher Q Less Interference 
Higher N
More Cluster Size
Less RF freq/cell
Less Traffic Handling
Capacity of the system

20. 21
CELLULAR MOBILE CONCEPTS
Co- Chl Interference Reduction Technique
• Antenna Front to Back Coupling Reduces Potential Interference
• Use Directional Antennas Instead of Omni Directional Antennas
• Receives interference from lesser directions
*
1
2
3 f1
f2
f3
Three Sectored Cell
Omni Directional

21. 22
CELLULAR MOBILE CONCEPTS
Improvement in Co- Chl Interference
*
1
2
3 f1
f2
f3
Three Sectored Cell
Q= 4.6 ,N=7 , S/I=14 db (Omni) S/I= 24.5 dB (Three Sectored)
Q= 4.6 ,N=7 , S/I=14 db (Omni) S/I= 29 dB (Six Sectored)

22. 23
CELLULAR MOBILE CONCEPTS
FREQUENCY REUSE PATTERN
*
1
2
3 f1
f2
f3
Three Sectored Cell
CDMA = 1/3 ; 1 Cell Pattern & each cell with 3 sectors
GSM = 4/12 ; 4 Cell Pattern & each cell with 3 sectors
DAMPS = 7/21 ; 7 Cell Pattern & each cell with 3 sectors

23. 24
CELLULAR MOBILE CONCEPTS
FREQUENCY REUSE PATTERN
4/12
7/21

24. 25
CELLULAR MOBILE CONCEPTS
Extract from Traffic Table - Erlang B Model
Number
of Access
Channels
GoS
0.5% 1.0% 2 %
5 1.13 1.36 1.66
10 3.96 4.46 5.08
20 11.1 12.0 13.2
33 21.5 22.9 24.6
50 36.0 37.9 40.3
56 41.2 43.3 45.9
99 80.0 84.1 87.0
100 80.9 85.0 88.0

25. 26
CELLULAR MOBILE CONCEPTS
TRUNKING EFFICIENCY
• More The Number Of Access Channels In A Cell
Further Increase In The System Handling Capacity
• The Number Of Users Served In A Cell Are Directly
Proportional To The Access Channels Allocated In A Cell
TRUNKING EFFICIENCY
• It is better to have a single cell than to split into two
with half the number of access channels
20
10
10
132 Subs
50 subs
50 subs

26. 27
Cellular Environment
• Cellular Environment is quite different from fixed radio
systems
-Cellular approach
-MOBILITY of the user
-Dynamically changing surrounding terrain conditions
•  RF Signal attenuates, RF  d-  =4 (generally)
• Multipath Fading  Distortions
• Signal fluctuations due to mobility of the user

27. 28
CELLULAR ENVIRONMENT
•  Techniques
• Power Control
• Channel Coding
• Interleaving
• Equalization
• Slow Frequency Hopping
• Antenna Diversity

28. 29
GSM
CAPACITY CONSIDERATIONS
1
1
1
1
2
8 8 Access Channels
1--Signaling
7- Voice
With 2 % GoS

2.94 E

2.94E/25mE=120 Subs
120 Subs/Sector  3 = 360 Subscribers

29. 30
MOBILE COMMUNICATION
WORLD CELLULAR MARKET 1N 2004
• ASIA -PACIFIC 35% 225 M
• WESTERN EUROPE 30 % 192.85 M
• NORTH AMERICA 17 % 109.25 M
• LATIN AMERICA 8 % 51.5 M
• EASTERN EUROPE 5 % 32.25 M
• AFRICA 3 % 19.25 M
• MIDDLE EAST 2 % 12.5 M

30. 31
Public Land Mobile Network
• INDIA has adopted GSM standard for PLMN.
• Digital Cellular System.
• Operates at 900 MHz.
• International Roaming facility.
• Power class 0.8 to 20W.
• Cell Radius upto 35 Kms.
• Maximum mobility speed 250 Km/hr.

31. 32
GSM - RADIO INTERFACE

32. 33
Communication - Mobile
Telephone
Exchange
Subscriber
Line
(2W)
Inter-Exchange
Junction
Mobile Switching
Centre (MSC)
BSC BTS
MS

33. 34
GSM
RADIO INTERFACE
• Most Important Interface
• Full Compatibility between mobile stations of various
Manufacturers & Networks of different vendors to help
roaming
• To increase spectral efficiency
-- Large number of simultaneous calls in a given
bandwidth
-- Frequency Reuse
-- Interference
-- Use of Interference Reduction Techniques

34. 35
GSM
Specifications - II
• Frequency Bands -
Mobile to Cell (UP-LINK) - 890 to 915 MHz
Cell to Mobile (DOWN -LINK) - 935 to 960 MHz
• Channel Bandwidth - 200 KHz
• Access Method - TDMA/FDMA
• Modulation - GMSK

35. 36
GSM
Specifications - III
• Number of Channels - 124
• Voice Channel Coding - ( 13 Kbps)
RPE-LTP
RPE-LTP - Regular Pulse Excitation Long
Term Prediction
FULL RATE - 13Kb/s ; HALF RATE - 6.5 Kb/s
• Bit Rate - 270.833 Kbps

36. 37
GSM - MULTIPLE ACCESS
• GSM uses both FDMA & TDMA
Freq
Mhz.
890.2
0
890.4
1
890.6
2
890.8
3
891.0
4 5
915
124
• FDMAAccess along Frequency axis
• Each RF carrier 200khz apart
• Total 124 RF Channels available.
One or more carrier assigned to each base station
• Absolute Radio Freq Carrier Number (ARFCN) 0 & 124 not used
untill it is co-ordinated with Non -GSM operators in adjacent freq. bands.
• In most cases 124 RF Channels are used
……...

37. 38
GSM
FDMA
25 MHz 25 MHz
Mobile to Base
0 1 2
890.2 890.4 890.6
(MHz)
Base to Mobile
0 1 2
935.2 935.4 935.6
200 kHz
45MHz
Channel layout and frequency bands of operation
890 935 960
915
200 kHz

38. 39
GSM
TDMA
8
7
6
5
4
3
2
1
8
7
6
5
4
3
2
1
45 MHz
Frequency
F2’
F1’
(Cell transmit)
F2
F1
(Cell Rx)
Amplitude
Typical TDMA/ FDMA frame structure