1 part i a brief history part ii cellular concepts part iii gsm- radio interface cellular mobile...
TRANSCRIPT
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PART I A Brief History
PART II Cellular Concepts
PART III GSM- Radio Interface
CELLULAR MOBILE RADIO
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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.
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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.
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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
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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
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• 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
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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
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CELLULAR MOBILE CONCEPTS
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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
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Propagation lossL in dBs
Transmit power PT
and antenna gain GT
Voice Channels Coverage area
Forward path
Reverse path
Or control
channels
Lines toMSC
Site noice
MS
Operating distance d
Planned cell radius R
Cell radio range - radius R max
Radio Cell Parameters
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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
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•
FERQUENCY SCARCITY PROBLEM
TelEx.
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.
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CELLULAR MOBILE CONCEPTS
CELLRADIUS(KM)
COVERAGEAREA(KM2)
No. OfSUBS.
No. ofCHANNELS
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%
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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
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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)
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A CLUSTER OF CELLS
4
5
6
7
2
3
1 1 2 3 4 5 6 7
GIVEN FREQ. RESOURCE
CELLULAR MOBILE CONCEPTS
18
14
2
13
5
6
7 2
6
3
4
5
7DR
CELLULAR PRINCIPLE N=7
1 2 3 4 5 6 7Frequency Reuse Pattern “N”=7
Given Freq Resource
CELLULAR MOBILE CONCEPTS
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CELLULAR MOBILE CONCEPTS
CO-CHL INTERFERENCE :Interference caused by another cell/mobile using the same frequency
D
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
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CELLULAR MOBILE CONCEPTS
CO - Chl Interference
Q = D /R = 3N N =Cluster SizeR = Size (Radius of Cell)D = Distance between two Co- Chl Cells
N Q=D/R
1 1.733 3.004 3.467 4.589 5.2012 6.00
Higher Q Less Interference Higher NMore Cluster SizeLess RF freq/cellLess Traffic HandlingCapacity of the system
LOWER Q Higher Interference Increased System Handling Capacity
Higher Q Less Interference Higher NMore Cluster SizeLess RF freq/cellLess Traffic HandlingCapacity of the system
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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
23 f1
f2
f3
Three Sectored CellOmni Directional
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CELLULAR MOBILE CONCEPTS
Improvement in Co- Chl Interference
*1
23 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)
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CELLULAR MOBILE CONCEPTS
FREQUENCY REUSE PATTERN
*1
23 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
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CELLULAR MOBILE CONCEPTS FREQUENCY REUSE PATTERN
4/12 7/21
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CELLULAR MOBILE CONCEPTS
Extract from Traffic Table - Erlang B Model
Numberof AccessChannels
GoS
0.5% 1.0% 2 %
5 1.13 1.36 1.6610 3.96 4.46 5.0820 11.1 12.0 13.233 21.5 22.9 24.650 36.0 37.9 40.356 41.2 43.3 45.999 80.0 84.1 87.0100 80.9 85.0 88.0
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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
201010
132 Subs50 subs50 subs
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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
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CELLULAR ENVIRONMENT
Techniques• Power Control • Channel Coding• Interleaving• Equalization• Slow Frequency Hopping• Antenna Diversity
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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
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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
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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.
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GSM - RADIO INTERFACE
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Communication - Mobile
TelephoneExchange
SubscriberLine (2W)
Inter-ExchangeJunction
Mobile SwitchingCentre (MSC)
BSC BTSMS
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GSMRADIO 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
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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
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GSMSpecifications - 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
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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
• FDMA Access 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
……...
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GSMFDMA
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 kHz45MHz
Channel layout and frequency bands of operation
890 935 960915
200 kHz
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GSMTDMA
8765
43
21
8765
43
21
45 MHz
Frequency
F2’F1’(Cell transmit)
F2F1(Cell Rx)
Amplitude
Typical TDMA/ FDMA frame structure