Wireless communication
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Transcript of Wireless communication
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CELLULAR CONCEPTS
By
Syed Mohammed Abrar
III Year-ECE-MEC.
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Transmitting/receiving voice and data using electromagnetic waves in open space.
The information from sender to receiver is carried over a well defined frequency band(channel).
Each channel has a fixed frequency bandwidth & capacity(bit rate).
Different channels can be used to transmit information in parallel and independently.
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Transmitting signalReceived signal
satellite
Transmitting antenna
Receivingantenna
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FM RADIO 88 MHZ
TV BROADCAST 200 MHZ
GSM PHONES 900 MHZ
GPS 1.2 GHZ
PCS PHONES 1.8 GHZ
BLUETOOTH 2.4 GHZ
Wi-Fi 2.4 GHZ
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Freedom from wires.
No bunch of wires running from here and there.
“Auto Magical” instantaneous communication without physical connection setup e.g.- Bluetooth, Wi-Fi.
Global coverage
Communication can reach where wiring is infeasible or costly
e.g.- rural areas,buildings,battlefield,outerspace.
Stay connected,flexiblity to connect multiple devices.
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RADIO TRANSMISSION:- easily generated, Omni-directional , travel long distance , easily penetrates buildings.
PROBLEMS:- frequency dependent , relatively low bandwidth for data communication , tightly licensed by government.
MICROWAVE TRANSMISSION:- widely used for long distance communication , give high S/N ratio , relatively inexpensive.
PROBLEMS:- don’t pass through buildings , whether and frequency dependent.
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INFRARED AND MILIMETER WAVES:-
widely used for short range communication , unable to pass through solid objects , used for indoor wireless LANs , not for outdoors.
LIGHT WAVE TRANSMISSION:- unguided optical signal such as laser , unidirectional , easy to install , no license required.
PROBLEMS:- unable to penetrate rain or thick fog , laser beam can be easily diverted by air.
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CELLULAR SYSTEM
WIRELESS LANs
SATELLITE SYSTEM
PAGING SYSTEM
PANs(BLUETOOTH)
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Definition
Wireless communication technology in which several small exchanges (called cells) equipped with low-power radio antennas (strategically located over a wide geographical area) are interconnected through a central exchange. As a receiver (cell phone) moves from one place to the next, its identity, location, and radio frequency is handed-overby one cell to another without interrupting a call.
Practical
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High capacity is achieved by limiting the coverage of each base station to a small geographic region called a cell.
Same frequencies timeslots/codes are reused by spatially separated base stations.
A switching technique called handoff enables a call to proceed uninterrupted when one user moves from one cell to another.
Neighboring base stations are assigned different group of channels so as to minimize the interference.
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By systematically spacing base stations and the channel groups may be reuse as many number of times as necessary.
MSC
CELLS
PSTN
SUBSCRIBER UNIT
BASE STATIONS
Coverage area
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BSC
BS1
BS2BS3
Connect to Bs1 & start calling
Out of BS1 coverage & connect to BS2
Out of BS2 coverage & connect to BS3
Call ended
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Cellular radio systems rely on intelligent allocation and reuse of channels throughout the coverage area.
Each base station is allocated a group of radio channels to be used within the same geographical area of its cell.
Neighboring base stations are given different channel allocation from each other.
The design procedure of allocating channel groups for all of the cellular BS within a system is called frequency reuse or frequency planning.
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Co channel cells
Co channel cells
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Co channels
60 degree
u
v
D
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Axes u and v intersect at 60 degree.
Unit scale is the distance between center cells.
If cell radius to point of hexagon is R then 2Rcos30=1
Or R = 1/√3. to find the distance of a point P(u , v) from the origin we use x-y to u-v coordinate transformation.
R² = x² + y²
x=ucos30˚
y=u+vsin30˚
r=√(v²+uv+u²)
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Using this equation to locate co-channel cells we start from reference cell and moves i hexagon along u axis then j hexagon along the v axis.
Hence the distance between co-channel cells in
adjacent cluster is given by D = √(i²+ij+j²)
The number of cells in a cluster N is given by
N = √(i²+ij+j²) where i and j are integers.
Hence the possible values of N are 1 , 3 , 4 , 7 , 12……
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Formation of cluster for N=7
Suppose i=2 and j=1 will give co channel cell
Same color showing co-channel cells.
i=2
j-=1
Co channel cells
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Global system for mobile communication is a set of ETSI standards specifying the infrastructure for a digital cellular services.
GSM networks are structured hierarchically it consist of one administrative region which is assigned to a MSC.
Each administrative region is made up of at least one location area (LA). LA is also called the visited area.
An LA consists of several cell groups.
Each cell group is assigned to a base station controller (BSC)
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GSM NETWORK
MSC REGION
LOCATION AREA (LA)
BS CONTROLLER
CELL CELL
LA
LA
BS CONTROLLER
BS CONTR-OLLER
MSC REGION
MSC REGION
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BSC
MSCEIR
AUCHLR VLR
ISDN
PSTN
OTHER NETWORKSBSS
NSS NMS
Mobile station
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Consist of two main elements.
1. The mobile equipment
2. Subscriber identity module(SIM).
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BSS = BSC + BTS
1. RADIO PATH CONTROL
2. AIR INTERFACE SIGNALLING
1. CENTRAL N/W ELEMENT OF BSS
2. CALL ESTABLISHMENT
3. MOBILITY MGMT
4. STATISTICAL RAW DATA COLLECTION
1. SPEECH PROCESSING
2. MODULATION/DEMODULATION
3. TRANSCODER
4. MINIMIZE TRANSMISSION PROBLEM
5. AIR INTERFACE MANAGEMENT
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NSS = MSC + HLR + VLR + AUC + EIR
MANAGECOMMUNICATION B/W USERS
INCLUDEDATABASE TO
STORE INFORMATION OF USER
CALL CONTROL
MOBILITYMGMT
SUBSCRIBERDATA HANDLING
CHECK IDENTITY OF USER
PERMANENT STORAGE OF USER INFORMATION
STORE A COPY OF HLR
CHECK ROAMING
PROVIDE AUTHENTICATION
SECURITY
CHECK IMEI NUMBER OF MOBILE
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1. MONITORING
2. MANAGE
3. OPERATION
4. MAINTANENCE
NMS
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USE TDMA + FDMA
MODULATION USED = GMSK(Gaussian minimum shift keying)
UPLINK FREQUENCY = 890 – 915 MHZ
DOWNLINK FREQUENCY = 935 – 960 MHZ
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WLAN connect local computers
Range (100 m) confined region
Break data into packets
Channel access is shared
Backbone internet provides best service
Poor performance in some application like videos
Low mobility
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Global coverage
Different orbit height
Optimized for good transmission
Expensive base stations.
Voice and data transmission
Telecommunication application
GPS , global telephone connection
TV broadcasting , military , whether broadcasting
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Broad coverage for short messages
Message broadcast from all base stations
Simple terminals
Optimized for one way transmission
Answer back hard
Overtaken by cellular
Pager system
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PSTNPaging control center
Paging terminal
Paging terminal
Paging terminal
Terrestrial link
Terrestrial link
Satellite link
City 1
City 2
City N
Base station
Base station
Base station
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Bluetooth
Cable replacement RF technology
Short range(10m)
2.4 GHz band
TDD duplex scheme
1 Mbps data rate shared b/w 7 devices
Polling based multiple access
Work on frequency hopping spread spectrum technology
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Peer to peer communication
No backbone infrastructure
Routing can be multihop
Topology is dynamic
Fully connected with different link SINRs.
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Ad-hoc network provides a flexible network infrastructure for many emerging applications.
The capacity of such networks is generally unknown.
Transmission , access and routing strategies for these networks are generally ad-hoc.
Cross layer design is very critical and challenging.
Energy constraints impose interesting design for trade offs communication and networking.
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