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Wire less Technologies
Employ FDMA/TDMA/CDMA/WCDMA technique
High capacity systems and better suited for urban areas
E.g.: GSM, PCS, D-AMPS, PDC, IS-95, cdma2000, UMTS etc.
Wireless Technologies
1982 - USA has standardised the AMPS
1982 - ETSI has setup GSM
1987 - TDMA selected for GSM
1989 - Validation of GSM
1992 - Coverage of Capital Cities & Airports
1993 - Coverage of Main Road & other cities
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Examples:
Mobile Generations
Better service quality
Support Voice and Data
Advance mobility management and power control
GSM & IS-95 are examples
Integration of services like speech, data, image, video, fax etc.
Provides better QoS than 2G
Lesser call set up time
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Seamless Network Architecture
Digital Mobile Systems
Easier integration of computer technology
Hand-over, Subscriber authentication, Roaming and Billing
Better co-existence with emerging IN services
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of European Post and Telecommunications)
The aim was to design a uniform pan-European mobile
system to replace the existing incompatible analog systems
Later on the ETSI (European Telecommunications
Standards Institute) was made responsible for GSM
standardization
1986 - Field Test of GSM
1987 - TDMA selected for GSM
1989 - Validation of GSM
1992 - Coverage of Capital Cities & Airports
1993 - Coverage of Main Roads & other cities
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CDMA IS-95
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Introduced in 1994
Like GSM, it is based on the TDMA access technology
Personal Handy phone System (PHS)
A digital system used in Japan, launched in 1995
Between a cellular and a cordless technology
Limited usage in moving vehicles
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Integrated system with international roaming
Create large single market
Better security functions
Accommodation of new services
Objectives of GSM System
Frequency Spectrum
ARFCN : 124
ARFCN : 374
ARFCN : 299
spectral allocation
spectral allocation
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124 channels (of 200 kHz each) in each band
Each channel has a TDMA structure with 8 timeslots
TDMA structure of each channel
935 MHz
960 MHz
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Introduction to Mobile Systems
Cell : Service area of a Base Station (BTS) having a number
of RF channels. Usually Hexagonal shape is used for
representing cells, but actually having irregular shape
Coverage Area : Each Cell covers a limited geographical area
within the Cell boundaries to serve a number
of subscribers
Cell Principles
Cell Size :
Remote areas
Coastal regions
Urban areas
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Introduction to Mobile Systems
GSM has a total of 124 frequencies (900 MHz) for use
If 4 operators are allowed, each will get only 31 frequencies
The max cell radius is only 35 Km
Moreover each frequency can support a maximum of 7 or 8 calls simultaneously
So 31 frequencies are insufficient to cover whole area & support millions of subscribers
Hence frequency re-use is must
So the need to adopt “Cellular Principle”
Frequency Reuse & Cellular Principle
Geographical locations
to cover given area
Able to serve large number of subscribers with limited RF
Frequency re-use introduces two types of interferences
Co-channel Interference
Frequency Reuse Pattern
transmitted in close proximity to each other
Transmission from one ARFCN interferes with the other
Adjacent Channel Interference
This occurs when an RF source of a nearby frequency
interferes with the RF carrier
Effect of Co-channel Interference
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4 --------------- 3.46 Higher N
12 --------------- 6.00 Less Traffic handling capacity
LOWER - Q
Challenge in planning: Compromise between speech quality & system capacity
Co-Channel Interference
Use of Sectored Cell reduces Interference from 6 to 2
Cell with
Omni Antenna
Cell with
Directional Antennas
Cell Sectorisation
Increasing in number of subscribers
Sectored sites are required in densely populated areas
Sectorisation splits a single site into a number of cells
Each sector cell has its own antenna
Each sector behaves as an independent cell
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S/I > 12 dB for Digital Cellular Mobile System
Q = 4.6 , N-7 , S/I = 14 dB (Omni) S/I = 24.5 dB (Three Sectored)
S/I = 29 dB (Six Sectored)
3 Sectored Cell
6 Sectored Cell
7/21 : 7 Cell Pattern, each with 3 Sectors
CDMA - 1/3 : 1 Cell Pattern, each with 3 Sectors
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Introduction to Mobile Systems
Better Signal - Radio propagation energy is concentrated in a smaller area 60, 120, 180 degrees instead of 360 degrees. So much stronger signal benefits for in-building coverage
Less Interference - Same frequencies can be used in a much closer areas
More Capacity - More cells in a geographic area support more subscribers
Less cost - 3 cells implementing in the same location
Advantages of Sectored Sites