Download - 3 cellular networks & infarastructure
A Brief Overview By
Engr. Abdul Razzaque Memon
Email: [email protected]
Web: Http://www.uldhdqpia.webs.com
Frequency Carries/Channels
The information from sender to receiver is carrier over a well defined frequency band. 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.
by: Engr. Abdul Razzaque Memon
Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service
by: Engr. Abdul Razzaque Memon
991 992 … 1023 1 2 … 799 991 992 … 1023 1 2 … 799
824-849 MHz 869-894 MHz
Reverse Channel Forward Channel
Channel Number Center Frequency (MHz)
Reverse Channel 1 <=N <= 799 991 <= N <= 1023
Forward Channel 1 <=N <= 799 991 <= N <= 1023
0.030N + 825.00.030(N-1023) + 825.0
0.030N + 870.00.030(N-1023) + 870.0
(Channels 800-990 are unused)
Channel bandwidth is 45 MHz
Frequency & Wavelength of Some Technologies
AMPS Phones: frequency ~= 800 Mhz wavelength ~= 37.5 cm
GSM Phones: frequency ~= 900 Mhz wavelength ~= 33 cm
PCS Phones frequency ~= 1800 Mhz (1.8 Ghz) wavelength ~= 16.6 cm
Bluetooth: frequency ~= 2.4 Gz wavelength ~= 12.5 cm
by: Engr. Abdul Razzaque Memon
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
by: Engr. Abdul Razzaque Memon
Channel 1 (b - b+30)
Channel 2 (b+30 - b+60)
Channel 3 (b+60 - b+90)
Station A Station B
Simplex Communication
Normally, on a channel, a station can transmit only in one way.
This is called simplex transmision
To enable two-way communication (called full-duplex communication)
We can use Frequency Division Multiplexing
We can use Time Division Multiplexing
by: Engr. Abdul Razzaque Memon
Duplex Communication - FDD FDD: Frequency Division Duplex
by: Engr. Abdul Razzaque Memon
Base StationB
Mobile Terminal
M
Forward ChannelReverse Channel
Forward Channel and Reverse Channel use different frequency bands
Duplex Communication - TDD TDD: Time Division Duplex
by: Engr. Abdul Razzaque Memon
Base StationB
Mobile Terminal
M
A singe frequency channel is used. The channel is divided into time slots. Mobile station and base station transmits on the time slots alternately.
M B M B M B
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 means changing point of attachment to the network offline
Mobility means changing point of attachment to the network online
by: Engr. Abdul Razzaque Memon
Degrees of Mobility
Walking Users Low speed Small roaming area Usually uses high-bandwith/low-latency access
Vehicles High speeds Large roaming area Usually uses low-bandwidth/high-latency access Uses sophisticated terminal equipment (cell
phones)
by: Engr. Abdul Razzaque Memon
Very Basic Cellular/PCS Architecture
by: Engr. Abdul Razzaque Memon
Base Station(BS) Mobile Station
Base Station Controller
Mobility Database
Mobile Switching
Center(MSC)
Radio Network
Public SwitchedTelephone Network
Mobile/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.
by: Engr. Abdul Razzaque Memon
Mobile/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 (telephone network). It is also called Mobile Telephone Switching Office (MTSO)
Subscriber A user who pays subscription charges for
using a mobile communication system Transceiver
A device capable of simultaneously transmitting and receiving radio signals
by: Engr. Abdul Razzaque Memon
Mobile/Cellular System Definitions:
Control Channel Radio channel used for transmission of call
setup, call request, call initiation and other beacon and 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
by: Engr. Abdul Razzaque Memon
Mobile/Cellular System Definitions:
Simplex Systems Communication systems which provide only
one-way communication Half Duplex Systems
Communication Systems which allow two-way communication by using the same radio channel for both transmission and reception. At any given time, the user can either transmit or receive information.
Full Duplex Systems Communication systems which allow
simultaneous two-way communication. Transmission and reception is typically on two different channels (FDD).
by: Engr. Abdul Razzaque Memon
Mobile/Cellular System Definitions:
Handoff The process of transferring a mobile station
from one channel or base station to an other.
Roamer A mobile station which operates in a service
area (market) other than that from which service has been subscribed.
Page A brief message which is broadcast over the
entire service area, usually in simulcast fashion by many base stations at the same time.
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
Mobile Communications Network
BS MSC PSTN
PBX
Residence
Mobile Station(Phone)
LandLine
LandLine
Cell Site
Base stationsand other cell
sites
Two- to Three-Mile Radius
BS = Base StationMSC = Mobile Switching Center
WHY NEED CELLULAR SYSTEM FOR MOBILESCapacity Limitationused a single high power radio transmitter to cover a large area.few channels for many people
1976 Bell Mobile Phone service in New York had 12 channels, serving 543 customer, waiting list of 3,700 and market of 10 million!!
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
by: Engr. Abdul Razzaque Memon
Cellular system / Network
Apart from the capacity limitation of these early systems, the other characteristic was that the carrier frequency was only re-used many tens or hundreds of kms away, so that no ‘co–channel’ interference would arise.
[co–channel = same frequency)
Cellular systems
Cellular systems are based on the concept of dividing the geographic service area into a number of cells and placing a low power transmitter in each of these, usually at the geographic centre.
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
Cellular systems – cont. . .
The transmit frequencies are re-used across these cells and the system becomes interference rather than noise limited.
Needs a method for handling the call as the user crosses the cell boundary i.e. call Handover
by: Engr. Abdul Razzaque Memon
Mobile Cellular Telephone System
FrequencyA
FrequencyB
FrequencyC
FrequencyC
FrequencyF
FrequencyE
FrequencyA
FrequencyD
FrequencyA
FrequencyB
BaseStation
Tolloffice
Tolltrunk
Localloop
Landline
CentralOffice
Landline topublic
switchedtelephonenetwork
FrequencyG
FrequencyA
FrequencyF
FrequencyD
FrequencyE
FrequencyG
FrequencyB
FrequencyC
Masterswitching
center(MTSO)
Cellular Telephony
Characterized by High mobility provision Wide-range Two-way tetherless voice communication Handoff and roaming support Integrated with sophisticated public
switched telephone network (PSTN) High transmit power requires at the
handsets (~2W)
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
What is a Cell?
Cellular Telephony meets demand of multiple users in a metropolitan area (called the market) by breaking the whole market into several smaller regions known as CELLS.
Each cell has its own transmission tower and set of assignable communication channels. A Cell is an area covered by a BASE STATION.
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
Figure showing mobile telephone tower
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
Question?
why hexagon is used as a cell? Why not a triangle? a square? a circle?
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
Answer – Yes Hexagonal
Because to avoid gaps between cells.
If a customer is near the boundary of a cell, it can’t be undertaken by the cell next to it,because of the gap between two cells, therefore communication breakdown occurs.
And also to remain equal distance from a base station to a mobile user.
by: Engr. Abdul Razzaque Memon
CELLUAR TELEPHONY
FREQUENCY REUSE
The same frequency is used by many cells (separated by a distance).
Spectral efficiency (or capacity) is greatly increased.
See next slide . . .
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
Example of 2G Digital Cellular
The Global System for Mobile communication . . . .
by: Engr. Abdul Razzaque Memon
Network Architecture
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
Mobile Station (MS)
The Cellular (GSM) committee has introduced an important powerful innovation by using a Smart Card in conjunction with a mobile telephone. Thus GSM subscribers are provided with a Subscriber Identity Module card (SIM-Card) with its unique identification at the very beginning of the service.
"Confidential information -- may not be copied or disclosed without permission".
The Mobile Station (MS) includes radio equipment and the man machine interface (MMI) that a subscriber needs in order to access the services provided by the Cellular (GSM) network.
by: Engr. Abdul Razzaque Memon
Mobile Station (MS)
by: Engr. Abdul Razzaque Memon
Mobile Station (MS)
The mobile station includes provisions for data communication as well as voice.
Each mobile station has an International Mobile Equipment Identity (IMEI) that is permanently stored in the mobile unit. Upon request, the MS sends this number over the signaling channel to the network.
The IMEI is used to identify mobile units that are reported stolen or operating incorrectly.
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
Um Radio-Interface
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon
by: Engr. Abdul Razzaque Memon