Transcript WC Lecture 1-2

Wireless Communication
Introduction to Mobile Communication and Cellular
System
bitwali Lecture 1-2
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Mobile Communications-Layered Model
Application layer
Service Location, New/Adaptive Applications
Transport layer
Multimedia, Congestion/Flow Control, Quality of Service
Network layer
Addressing, Routing, Device Location, Hand-over
Data link layer
Authentication, Media Access/Control, Multiplexing,
Encryption
Physical layer
Modulation, Interference, Attenuation, Frequency
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Communication
• Transmitting voice and data using electromagnetic
waves in open space
• Electromagnetic waves
• Travel at speed of light (c = 3x108 m/s)
• Has a frequency (f) and wavelength (l)
c=fxl
1/f  l
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Frequency Carriers/Channels
• The information from sender to receiver is carrier
over a well defined frequency band (range of
frequencies).
• This is called a channel
• Each channel has a fixed frequency bandwidth (in
KHz) and Capacity (bit-rate)
• Different frequency bands (channels) can be used to
transmit information in parallel and independently.
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Example
• Assume a spectrum of 90KHz is allocated over a base
frequency b for communication between stations A and B
• Assume each channel occupies 30KHz.
• There are 3 channels
• Each channel is simplex (Transmission occurs in one way)
• For full duplex communication:
• Use two different channels (front and reverse channels)
• Use time division in a channel
Channel 1
Station A
Channel 2
Station B
Channel 3
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Simplex Communication
• Normally, on a channel, a station can transmit only in one
way.
• This is called simplex transmission
• To enable two-way communication (called full-duplex
communication)
• We can use Frequency Division Multiplexing
• We can use Time Division Multiplexing
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Duplex Communication - FDD
• FDD: Frequency Division Duplex
Mobile
Terminal
M
Forward Channel
Reverse Channel
Base Station
B
Forward Channel and Reverse Channel use different frequency
bands
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Duplex Communication - TDD
• TDD: Time Division Duplex
Mobile
Terminal
M
M
B
M
B
M
B
Base Station
B
A single frequency channel is used. The channel is divided into time
slots. Mobile station and base station transmits on the time slots
alternately.
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What is Mobility
• Initially Internet and Telephone Networks is designed assuming the
user terminals are static
• No change of location during a call/connection
• A user terminals accesses the network always from a fixed location
• Mobility and portability
• Portability describes a radio terminal that can be used by someone at
walking speed (e.g. walkie talkie or cordless telephone at home) Mobility
describes a radio terminal that is attached to a high speed platform (e.g. a
cellular telephone in a fast moving vehicle)
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Degrees of Mobility
• Walking Users
• Low speed
• Small roaming area
• Usually uses high-bandwidth
• Vehicles
•
•
•
•
High speeds
Large roaming area
Usually uses low-bandwidth
Uses sophisticated terminal equipment (cell phones)
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How to realize Ubiquitous Computing
• Small and different sizes computing and communication
devices
• Tabs, pads
• Laptops, Cell-phones
• A communication network to support this
• Anywhere, anytime access
• Seamless, wireless and mobile access
• Need for Personal Communication Services (PCS)
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What is PCS
• Personal Communication Services
• A wide variety of network services that includes wireless
access and personal mobility services.
• Provided through a small terminal.
• Enables communication at any time, at any place, and in
any form.
• The market for such services is tremendously( ‫بہت‬
‫ ) زیادہ‬big
• Eg. cell-phone market
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Several PCS systems
• High-tier(‫ )درجہ‬Systems
• GSM: Global System for Mobile Communications
• The mobile telephony system that we are using
• IS-136
• USA digital cellular mobile telephony system
• TDMA (Time division multiple access ) based multiple access
• Personal Digital Cellular
• IS-95 cdmaOne System
• CDMA (Code division multiple access ) based multiple access
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Several PCS systems
• Wideband wireless systems
• For Internet access and multimedia transfer
• Cdma2000
• W-CDMA (Wideband Code Division Multiple Access) , proposed by Europe
• SCDMA (Synchronous Code Division Multiple Access), proposed by China/Europe
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Several PCS systems
• Other PCS Systems
• Special data systems
• CDPD: Cellular Digital Packet Data
• ARDIS :Advanced Radio Data Information System
• Paging Systems
• Mobile Satellite Systems
• LEO( Low-Earth Orbit ), MEO( Medium -Earth Orbit ) satellites for data/voice
• ISM (industrial, scientific, and medical radio )band systems: Bluetooth,
802.11, etc.
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Teledensity Pakistan
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Cellular Mobile Subscribers
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Paging Systems
• Sending brief messages (numeric, voice messages)
• Message sent to paging subscriber via paging system access
number with telephone keypad or modem
• Wide area paging systems consisting of number of
telephone lines, many base station transmitters and large
radio towers
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Wide Area Paging system
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Cordless Telephone Systems
• Full duplex communication systems using radio to connect a portable
hand set to a dedicated fixed base station
• The base station then connected to a dedicated telephone line with
a specific telephone number on the PSTN
• Limited range and mobility
• Early cordless telephones operate solely ( ‫ محض‬٬‫) سراسر‬as extension
telephones to a transceiver connected to a subscriber line on the
PSTN
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Cordless Telephone Systems
Cellular Telephone Systems
• Why cellular networks?
• To address requirement for greater capacity
• For efficient use of frequency
• To address the poor quality of non cellular mobile networks and increases
coverage
• Replaces a large transmitter with smaller ones in cells
• Smaller transmitting power
• Each cell serves a small geographical service area
• Each cell is assigned a portion of the total frequency
• Why Hexagonal Cell Structure?
• No proper coverage of the area with theoretical circles
• Polygon near to the circle
• Hexagon is selected for further technical simplicity
Description of a Cell
• Approximated to be a hexagonal coverage
• Best approximation of a circular area
• Served by a base station
• Low powered transceiver Antenna system
• May be divided into 6 equilateral triangles
• Different groups of channels assigned to base station
• Area of a cell is:
Area cell
R
3R
 0.87 R
2
R
R 3 3R 2
 6x
3x 
 2.598R 2
2
2
2
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Cellular System Definitions
• Mobile Station
• A station in the cellular radio service intended for
use while in motion at unspecified locations. They
can be either hand-held personal units (portables)
or installed on vehicles (mobiles)
• Base station
• A fixed station in a mobile radio system used for
radio communication with the mobile stations. Base
stations are located at the center or edge of a
coverage region. They consists of radio channels and
transmitter and receiver antennas mounted on top
of a tower.
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Cellular System Definitions
• Mobile Switching Center
• Switching center which coordinates the routing of calls in
a large service area. In a cellular radio system, the MSC
connections the cellular base stations and the mobiles to
the PSTN (Public Switched Telephone Network). It is also
called Mobile Telephone Switching Office (MTSO)
• Subscriber
• A user who pays subscription(‫ )چندہ‬charges for using a
mobile communication system
• Transceiver
• A device capable of simultaneously transmitting and
receiving radio signals
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Cellular System Definitions
• Control Channel
• Radio channel used for transmission of call setup,
call request, call initiation and other beacon(‫ چھوٹاساگھر‬‫ ) روشن مینار‬and control purposes.
• Forward Channel
• Radio channel used for transmission of information
from the base station to the mobile
• Reverse Channel
• Radio channel used for transmission of information
from mobile to base station
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Communication System Definitions
Cellular System
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Types of Mobile Communication Cells
The size of a cell is dictated by capacity demand
• Macro Cell
• Large, covering a wide area
• Range of several hundred kilometers (km) to 10 km
• Mostly deployed in rural and populated areas
• Micro Cell
• Medium cell, coverage area smaller than in macro cells
• Range of several hundred meters to a couple of meters
• Deployed mostly in crowded areas, stadiums, shopping malls
• Umbrella Cell Approach
• Micro cells inside A macro cell.
• Macro cell is defined by high power and lengthy tower
• Micro cells are defined inside the macro cell with less power and less height
towers
• High speed MS are handled by macro cell and low speed subscribers are handled
by micro cell
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Types of Mobile Communication Cells
• Pico Cell
•
•
•
•
•
Small, covering a very small area
Range of several tens of meters
Low power antennas
Can be mounted on walls or ceilings
Used in densely populated areas, offices, lifts, tunnels etc
• Mega Cell
• These cells are formed by LEO and MEO
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Cellular Generations
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Cellular Generations…
• 1G: Analog Voice (FDMA)
• AMPS: Advanced Mobile Phone System
• TACS: Total Access Communication System
• 2G: Digital Voice (TDMA)
• CdmaOne: Qualcomm International Standard (IS-95)
• D-AMPS: (Digital AMPS)
• GSM: Global System for Mobile Communication
• 2.5G: Voice + Data
•
•
•
•
1xEV-DO: Evolution Data Optimized
1xEV-DV: Evolution Data and Voice
General Packet Radio Service (GPRS)
Enhanced Data Rate for GSM Evolution (EDGE)
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Cellular Generations…
• 3G: Voice + High-speed data. All CDMA
• CDMA2000: Qualcomm. International Standard IS-2000
• W-CDMA: Wideband CDMA
• TD-SCDMA: Time Division Synchronous Code Division Multiple Access (Chinese
3G)
• 3.5: Voice + Higher-speed data
•
•
•
•
EDGE Evolution
High-Speed Packet Access (HSPA)
Evolved HSPA (HSPA+)
Ultra Mobile Broadband (UMB)
• 3.9G: High-Speed Data. VOIP. OFDMA
• WiMAX 16e (Worldwide Interoperability for Microwave Access)
• Long Term Evolution (LTE)
• 4G: Very High-Speed Data
• WiMAX 16m
• LTE-Advanced
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Section 1 – GSM Architecture Overview
GSM:A brief background
• At the beginning of the 1980s a problem was that the European
countries were using many different, incompatible mobile phone
systems. These systems are referred to as 1G (first generation) systems.
• In Europe, the most common 1G system was NMT (Nordic Mobile
Telephone) and TACS (Total Access Communications System). In the
United States, as well as in other American countries, AMPS (Advanced
Mobile Phone System) was the most common system.
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Section 1 – GSM Architecture Overview
GSM:A brief background
• With the passage of time, the need for telecom services was remarkably
increased. Due to this, CEPT (Conférence Européenne des Postes et
Télécommunications) founded a group to specify a common mobile
system for Western Europe.
• This group was named “Groupe Spéciale Mobile” and the system name
GSM arose. This abbreviation has since been interpreted in other ways,
but the most common expression nowadays is Global System for Mobile
communications.
• GSM is a 2G (second generation) system.
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Section 1 – GSM Architecture Overview
Expectations From GSM System
• The GSM system must be an open system.
• The system should be able to support several network operators in
each country.
• GSM networks must be built without causing any major changes to the
already existing Public Switched Telephone Networks (PSTN).
• The system must maintain a good speech quality.
• The system must use radio frequencies as efficiently as possible.
• The system must have high / adequate capacity.
• The system must be compatible with ISDN and other data
communication specifications.
• The system must maintain good security both for subscriber and
transmitted information.
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Section 1 – GSM Architecture Overview
Advantages Of GSM
• GSM uses radio frequencies efficiently, and due to the digital radio
path, the system tolerates more inter - cell disturbances.
• The average speech quality is better than in analogue systems.
• Data transmission is supported throughout the GSM system.
• Speech is encrypted and subscriber information security is guaranteed.
• With ISDN compatibility, new services are offered.
• International roaming is technically possible within all countries using
the GSM system.
• The large market increases competition and lowers the prices both for
investments and usage.
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Section 1 – GSM Architecture Overview
Requirement Of Telecom Network
• A connection between two people “a caller and the called person” is
the basic service of all telephone networks.
• To provide this service, the network must be able to set up and
maintain a call, which involves a number of tasks:
•
•
•
•
•
Identifying the called person.
Determining the location.
Routing the call.
Ensuring that the connection is sustained as long as the conversation lasts.
After the transaction, the connection is terminated and (normally) the calling
user is charged for the service he has used.
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Section 1 – GSM Architecture Overview
Requirement Of Mobile Telecom Network
• In a mobile network, however, the
establishment of a call is a far more
complex task, as the wireless (radio)
connection enables the users to move at
their own free will, providing they stay
within the network's service area.
• In practice, the network has to find
solutions to three problems before it can
even set up a call.
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Section 1 – GSM Architecture Overview
Requirement Of Mobile Telecom Network
• In other words, the subscriber has to be LOCATED and IDENTIFIED to
provide him/her with the requested services.
• In order to understand how we are able to serve the subscribers, it is
necessary to identify the main interfaces, the subsystems and network
elements in the GSM network, as well as their functions.
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