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M.V. RAGHUNADHM.V. RAGHUNADHAssistant Professor, Dept. of ECEAssistant Professor, Dept. of ECE
NIT, Warangal – 506004.NIT, Warangal – 506004.
raghu@nitw.ac.inraghu@nitw.ac.in
INTRODUCTION TO
MOBILE & CELLULAR COMMUNICATIONS
Wireless system
What is a wireless system?
Provides communication without the use of wire
Computing and communication at anytime and anyplace
Small size, portable deviceUses radio wave, to send voice,
data, internet and video signalsGood energy managementAccess to resources
“ Mobile communications is not Cellular communications
but
Cellular communications is Mobile communications ” .
Mobile Com Ex :Public emergency services Police, Fire, Ambulance
Single frequency communications over entire area using one BS
and many mobile vehicular transceiver setsCellular Com
Public com services with frequency reuse over multiple cells in entire area using one BS and many
cellular phones in every cell.
“ Portable communicators are not
mobile but mobile communicators
are Portable ”
Communication devices exhibit followingCharacteristics
a. Fixed & Wired: Typical desktop PC, Telephone large, Data Loggers weight / high power
b. Mobile & Wired: Today’s laptop PCs mobile but connection to company via wired line of PSTN & Modem
c. Fixed & Wireless: WLL last mile in PSTN, in house wireless networks, local net in tradeshows.
d. Mobile & Wireless
Today’s Cell Phones, PDAs, Personal Communicators
Most interesting case, no cable restriction, full mobility, roaming between cities and even different networks
Ex: GSM , CDMA
> 900 million users worldwide
Applications:1.Vehicles:
Cars with
a) Digital Audio Broadcast (DAB) at 1.5 Mbps Music ,news, weather and GPS data
b) UMTS for Wireless Cell Telephony – voice & Data at 384 kbps
c) Adhoc Networks with emergency services Accidents, Maintenance Logistics.
d) Wireless Pico Nets PDA, Laptops, Mobile Phones ,Bluetooth / Wi-Fi.
e) Rail / Air Traffic
2.Emergencies
Ambulance high quality wireless adhoc nets – accidents, natural disasters.
3.Business Sales Database consistency,
wireless LAN hot spots at supermarkets, gas stations, laptop connections via LAN,DSL…
4.Infotainment Up-to-date info over wireless net
i. Travel guideii. Cash paymentiii. Adhoc gaming networks
5. Location Dependent Services
Mobile computing and WLANs applications need to
know the mobile unit location.
a. Follow on Services Call forwarding, e-mail, multimedia conferencing.
b. Location aware Services Printing service from a hotel control room.
c. Privacy Time dependent access/forwarding at the will & wish of user
d. Info. Services Travel guide
e. Support services Caching of data on mobile device via a wireless net access.
Wi-FiStands for “Wireless Fidelity”High-bandwidth category of wireless
communicationsShort range (300-1600ft)Used to connect laptops, PDAs, and
even workstations
Digital Cellular TelephonyCDMA, TDMA, GSMSmart phones and some PDAsLonger range than Wi-Fi
Mobile & Wireless Devices:
a. Sensors : Control state information sources
b. Embeded Controllers: Keyboards, mice, headset, washing machine, TV set,
…..
c. Pager : One or two line message service,
fast replaced by cell phone.
d. Mobile Phones : Vehicular Sets, Cell phones
e. PDA : Personal Communicators, Pocket/Palm Computers
f. Notebook / Laptop : Portable PCs
MOBILE, CELLULAR
&
PERSONAL COMMUNICATIONS
Mobility : Mobility of Talker ( Transmitter ) Mobility of Listener ( Receiver ) Mobility of Both ( TX & RX )
Definition : Communication facility between stationary and mobile or mobile and mobile users ( units )
UserTypes : Walking Pedestrians automobile computers car, bus, train, plane, ship.
What is Mobility?
A device that moves Between different geographical locations Between different networks
A person who moves Between different geographical locations Between different networks Between different communication
devices Between different applications
Device mobility Plug in laptop at home/work on Ethernet Wired network access only Network address changes May want access to information when no network
is available: hoard information locally Cell phone with access to cellular network Continuous connectivity Phone # remains the same (high-level network
address) Network performance may vary from place to
place Can we achieve best of both worlds? Continuous connectivity of wireless access Performance of better networks when available
Laptop moves between Ethernet, WaveLAN and Metricom networks Wired and wireless network access Potentially continuous connectivity Network address changes Radically different network performance on
different networks
Phone available at home or at work Multiple phone numbers to reach me Breaks in my reachability when I’m not in
Cell phone Only one number to reach me Continuously reachable Sometimes poor quality and expensive
connectivity Cell phone, networked PDA, etc. Multiple numbers/addresses for best quality
connection Continuous reachability Best choice of address may depend on
sender’s device or message content
People mobility
Mobility means changesHow does it affect the following? Hardware Lighter More robust
Lower power Wireless communication Can’t tune for stationary access
Network protocols Name changes ; Delay changes ;
Error rate changes Fidelity High fidelity may not be possible
Data consistency Strong consistency no longer
possible Location/transparency awareness Transparency not always desirable
Names/addresses Names of endpoints may change
Security Lighter-weight algorithms Endpoint authentication harder Devices more vulnerable
Example changes Addresses Phone numbers, IP addresses
Network performance Bandwidth, delay, bit error rates, cost,
connectivity Network interfaces PPP, eth0, strip
Between applications Different interfaces over phone & laptop
Within applications Loss of bandwidth triggers change from color
to B&W Available resources Files, printers, displays, power, even routing
Enabling Technologies Software Defined Radios Advanced media access technology to connect
different cores to different access technologies Variable spreading factor ( VSP ) All-IP networks and protocols Ad-Hoc Networking algorithms Ultra Wideband , variable power Hardware
Radio Network-layer mobility protocols Smart antennae MIMO (Multi Input Multi Output) devices Open platform architectures Smart mediation devices for Handsets Smart mediation devices for overlay network
Goal of emerging mobile & PCS systems To enable communication with any person, at any time, at any place (Home office in public in Transit), in any form / device ( Home /normal telephone, cellular/mobile phone , PC phone, PDA, fax, Multimedia terminal).
On the basis of On the basis of ““any time, any where, any one, any any time, any where, any one, any
service”service”
Information Services: Voice, Video, Text, Fax ,Image, Data, Files
Technological Trends
• All Digital Optical Fiber or Satellite media , • Hyper media content• Intelligent Networks• Universal Reachability & Accessibility• User specific & Interactive service • Global Roaming & Interoperability• Mobile ATM and Mobile Internet• Mobile data and computing• Guaranteed Quality of Service (QOS)• Standardized Universal ID Numbers/
Addresses• Personalization
The Electromagnetic Spectrum
ExtremelyLow
VeryLow
Low Medium High VeryHigh
UltraHigh
SuperHigh
Infrared VisibleLight
Ultra-violet
X-Rays
AM BroadcastShort Wave Radio FM Broadcast
Television Infrared wireless LAN
GSM:US ISM: 902-928 MHz
5 GHz802.11a (54 Mbps)
2.4 – 2.4835 GHz802.11b (11 Mbps)802.11g (54 Mbps)
CellularMicrowave
Wireless Network Area Definitions
WAN
WAN-MAN
MAN
Pico-Cell
MAN-LAN MAN-LAN
PAN
LAN-PAN
0km~50km ~2km ~10m
Courtesy of IEEE 802.15 Press Kit. Jan. 2001
BluetoothIEEE802.11HyperLan
GSMGPRSCDMA
Global layer
National layer
Local area layerWireless LANs
DAB and DVB-T
2G, 3G Cellular
Personal network layer
Hierarchical Layers for 4G Hierarchical Layers for 4G
Satellite
Regional layer
Wireless PANs
Vertical Handover
Horizontal Handover
IP-based backbone
The Internet
IP backbone
BillingVHE
Signalling Gateway
WAP Accounting
UMTS
Broadcast Networks (DAB, DVB-T)
Satellite FES
GSM / GPRS
Context-aware informationCentre
IP-based micro-mobility Wireless
LANs
ISPSIP Proxy Server
Inter-WorkingInter-Working
ENABLING CONCEPTS
FOR
MOBILE & PERSONAL COMMUNICATIONS.
These concepts enable us to provide Universal PCS with standardized systems & services at local, regional, national and international levels.
They are :
Terminal Mobility with wireless AccessPersonal Mobility with personal NumberService Portability with Intelligent Network
These are for location independent availability of customized telecom services.
TERMINAL MOBILITY • The terminal mobility systems can locate and identify a mobile terminal as it moves
• Allows a mobile terminal to access telecom services from any location – even in movements
• Uses wireless Access• User must carry wireless terminal and be within a radio coverage area
• Functional parts reside on portable IC / Smart card
• Terminal and User have STATIC Relationship• Terminal and Network have DYNAMIC Relation
• Call delivery and Billing are based on Terminal / Mobile Station Number.
PERSONAL MOBILITY
• Terminal and user have DYNAMIC Relationship. Call Delivery & Billing are based on Personal Identity / Personal Number assigned to the user.
• Locate and identify the end users as they move
• Allows end users to access subscribed telecom services on any terminal, any location
• More broader access whether fixed or wireless
SERVICE PORTABILITY
• Network is capable to provide subscribed services at a terminal or location designated by the user.
• Depends on terminal capabilities• Uses intelligent Network concepts• Maintains User profile in a Database• User can access, query, modify to manage & control subscribed services.
• Intelligent services – seamless international roaming
CELLULAR CONCEPT
&
INITIAL IMPLEMENTATION
Conventional Mobile Tele phone System
A Land mobile system in which available frequency spectrum is divided into mobile radio telephone channels using FDM without reuse facility, serving an area with large size..
A dedicated channel is allocated for each user, whether uses it or not.
Principle of operation is similar to cellular radio telephony
As a result, It has several limitations that are given below.
1. Limited service capability
• Larger coverage area zones• High Power Transmissions• Re-initiation of call in every zone (no auto handoff)• One frequency per channel• No. of active users is equal to No. of channels allocated to zone
2. Poor Service Performance:
• Higher blocking probabilities due the smaller number of radio channels.
3. Inefficient frequency spectrum Utilization
• Smaller Frequency Utilization factor Mo = max. no. of customers/channel at Busy Hour.
• Each channel can serve only one customer at a time in whole area.
SOLUTION
Cellular approach
• Reuse of frequencies
• Multiple Access
• Cell Splitting
• Smaller coverage area (cell)
Principle : Divide large area into cells with 2 to 50 km diameter, each cell allocated with a set of RF channels
Starting point :
AMPS by Bell Labs, 1983, USA
A high capacity land mobile system in which available spectrum is divided into discrete channels, which are assigned in groups to geographic cells covering an area and the frequencies are reused, thus low power transmissions.
Cellular System :
A cellular system: The tower represent base station (BS) which provide radio access between mobile users and the mobile switching center (MSC).
BS BS BSMS
Cellular Advantages:
• Lower Power Transmissions
• Frequency Reusability
• Multiple Access capability
• Lower Antenna Heights
• Unlimited capacity and range
coverage
• Cell splitting & Micro cells
• Automatic hand off transparency
• Multi Level roaming
• Efficient Power control
• Handsets – Light weight, compact, Pocket held
• Digital Communication transceivers
• Value added & intelligent information services
• Mobile Multimedia broadband communication
• Minimal Blocking
• More than one license operator, Competition
• Better propagation models.
CELLULAR SYSTEM
ARCHITECTURE
Basic Cellular system components : 1. Mobile Station / Unit / Site (MS)
2. Cell site / Base station (BS)
3. Mobile Telephone switching office/ Centre
4. Data Links
Mobile Station : (MS)
Mobile station/unit contains a Transceiver, control unit and an Antenna.
Cell Site : (MSC)
Cell site contains a fixed Base station that has a tower antenna, Transceivers (BS) for MS and Fixed links to MTSO
MTSO or MSC
• This is the mobile switching exchange
• The central coordinating system for all the cells
• Contains cellular switch, control computer, mobile management software, user location mobile management software, user location registers, Interfaces and links to BS & PSTN.
• MTSO is the central administrator & Manager
• Cellular switch is Analog or Digital and switches the calls to connect mobile – mobile or mobile – fixed
• Coverage area is partitioned into nearly hexagonal shaped areas called radio cells
• Each cell is served by one Base station for radio coverage of all mobile units in that cell.
• Radio Link carries the VOICE and SIGNALLING information (Channels) between the MS and BS in that cell only.
• Base stations are connected to MSC through fixed circuits (cables or fiber or microwave)
• MSC interacts with a database of subscriber data and location information, to provide dynamic terminal (MS) location to the switching computer.
• MSC is connected to PSTN because majority of calls originate from or terminate at fixed PSTN phones.
• Every cellular system has some number of radio channels for its use, depending on cellular standard and RF band.
• The available radio channels are partitioned into groups of channels, each group being allocated
to an individual cell.
• These individual group of channels can be reused in distant cells without causing interference.
Radio System Planning:
• Cell size design • Cell location identification/assignment • Allocation of group of channels to
each cell • Performance criteria• Handoff mechanism• Propagation modeling
• In each cell, one Radio Channel is set aside permanently assigned to carry signaling information between the cellular network (base station) and all the mobile stations in that cell.
MS BS Signaling Channel Location updating , call set up.Paging response , user data
BS MS Signaling Channel Operating parameters (identities)Paging call, location updating, and control.
Location UpdatingMS always monitors overhead information broadcast by network on the signaling channel
• MS updates the operating parameters as and when necessary
• MS Checks Location information (area identity) broadcast by new cell, if it is in new cell location.
• MS advices the network about its new location
• Then network updates its location registers.
• This location information is used to route / switch the incoming calls or determining paging broadcast area for MS.
Mobile station initialization:
• Whenever a user activates the receiver of Mobile unit, the receiver scans SETUP CHANNEL list designated.
• It selects a strongest one and locks to it
• Each site has one set up channel only. Thus strongest channel selection is the nearest BS (Cell site) selection.
• This process is called SELF LOCATION
• This is done in Idle State also, transparently to user.
• But, it can’t provide location information to BS. Thus BS must search for idle mobile unit by paging.
• In future, registration scheme will be used, in which, the vehicles (MS) must register/update location regularly, as shown above.
Mobile originated call set up:
• Exact procedure depends on particular cellular standard.
• More or less similar in principle
• User places/keys in the called telephoned number into an originating register and checks for correctness in LCD display.
• Then user pushes ‘SEND’ button.
• This call request is sent on the already set up channel on the uplink signaling channel
there is no dial tone at all.
• The BS receives this call request signal and sends a request to MTSO (MSC) via high speed data link.
• BS selects an appropriate voice channel for the call and sends a speech channel (number) allocation message to mobile unit.
• MS now locks on to this allocated radio channel
• Network MSC proceeds now to set up the connection to the called party.
NETWORK ORIGINATED CALL SETUP
(Mobile Terminated Call)• A Landline phone dials a mobile unit number • The PSTN exchange recognizes that the number is a Mobile number
• PSTN exchange forwards this request to MTSO (MSC)
• MTSO first establishes current location area for the called mobile through signaling between Home Location Register (HLR) and Visiting Location Register (VLR).
• This process allows the call to be routed to the current serving MTSO (MSC)
• The serving MTSO initiates a paging message over the downlink-signaling channel toward the cells contained in the paging area, through a cell search algorithm
• Each cell site further transmits this paging signal on its own set up channel.
• If mobile is in ON state, it receives paging message, recognizes its own identification number in it and locks to the strongest set up channel (nearest BS).
• Only the intended mobile now sends back a response to its nearest cell site (BS) on the signaling channel.
• Now the respective BS, sends a speech channel allocation message to the mobile and informs the network so that connection can be established.
• The mobile unit tunes to the assigned voice channel tend initiates user alert of an incoming call
Call Termination:
• When mobile user turns OFF the transmitter, a signaling tone is sent to the BS.
• Both the sides free up the voice channel.
• BS and MTSO recognize this and disconnect the connections and refresh the switch.
• MS resumes monitoring the pages through the strongest setup channel, i.e. expects a paging message from nearest / strongest BS (current cell)
Hand Off:
• During a call, serving BS monitors mobile signal strength
• If signal strength falls below a threshold, Network requests all the neighboring cell BS to measure signal strength from this mobile.
• If any nearest BS indicates better quality and strength than the current serving BS, the MSC commands the current BS to send a signaling message to the mobile, asking it to retune to a free channel in neighboring cell.
• The MS retunes to new channel and network MSC switches call to new BS
Data and Communications Convergence
MediaStreaming videoVideo on demandInteractive video services
TelecommunicationPSTN and cellular servicesVideo telephonyWideband data services
ComputerInternet accessElectronic mailMobile computing
Wireless
Internet
Broadband
Convergence of High Speed Internet & Mobility A major driver of future wireless The Wireless Industry has grown at enormous
pace over the past decade.
More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move.
With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure.
The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective.
First generation (1G): Analog voice systems No standardization
Second Generation (2G): Digital voice systems Currently deployed systems CDMA, GSM (Global System for Mobile
communication) PDC (Japan) D-AMPS (Digital Advanced Mobile Phone System)
PCS Systems Second Generation – advanced (2.5G): Combining voice and data communications Providing enhanced data rate Two basic technologies:
GSM-based (high baud rate) GPRS (General Packet Radio Service) Utilizes voice time slots to send packet traffic An overlay over the existing voice system
Should really be called 2.1G!! Any standards?
Wireless Network Evolution
Third Generation (3G) Two basic proposals to handle voice and data
Ericsson: Universal Mobile Telecommunications systems (UMTS) Compatible with European GSM Backed by ETSI and Japan
Qualcom: CDM2000 Not compatible with GSM Compatible for IS-95 (supported by U.S)
3G Standards 1999 UMTS took over and an agreement was made over setting
some standards Major competing technologies
Bluethood Wireless LAN (IEEE 802.x standards) – also known as WiFi
Short range wireless communications Highly utilized and very popular: offices, airports, coffee
shops, universities and schools Two basic modes of operations:
• Ad-hoc networking: computers send data to one another • Access point:: sending data to the base station
Supporting heterogeneous multitude of systems Includes multiple networks:
Digital video broadband Digital audio broadband Wireless LAB, Bluethood-based networks
Open communication network: infrastructure independent which can access to any services and applications
Complete compatibility between wireless and wired networks through gateways
Supports statistical multiplexing of heterogeneous data over-the-air Latency, noisy environment, unpredictable discontinuities and
loss, etc. High-speed wireless transmission over the air
High performance physical layer 20Mbps (2G: 28Kbps, 3G: 2Mbps)
Scarce bandwidth availability Efficient frequency spectrum utilization Efficient hand off Dynamic bandwidth allocation Advanced digital transmission technology (modulation, low
power devices, etc.)
Fourth Generation (4G)
G-points in Mobile Comms History
1G analog- voice only- inflexible- not optimised- very transparent
2G digital (analog)- voice (data)- inflexible- optimised- transparent
2.5G digital- voice + data- flexible- optimised- transparent
3G digital- data + voice- very flexible- ‘optimisable’- not transparent
3.5G digital- more data (IP)- very flexible- ‘optimisable’- not transparent
4G digital/analog?- even more data- very flexible- ‘optimisable’- transparent
GSM Global System for Mobile Communications Digital cellular system for voice, fax, data >200 million customers >320 networks 137 countries Annual growth rate of 100% - 200% 4 new customers every second
Greater “presence” than MacDonalds!
no GSM
with GSM
Countries with GSMCountries with GSM
Wireless Networks
Motivated by people-on-the-go- PCs availability, Internet usage,
Mobile life
Aimed is to establish wide-area voice data communications
Includes mobile systems (cellular telecommunication systems)
Wireless Network Area Definitions
WAN
WAN-MAN
MAN
Pico-Cell
MAN-LAN
PAN
LAN-PAN
0km~50km ~2km ~10m
Courtesy of IEEE 802.15 Press Kit. Jan. 2001
BluetoothIEEE802.11HyperLan
GSMGPRSCDMA
WLAN Network Architecture
PDA
Laptop
Wired Network
FixedWorkstation
DBMS
FixedWorkstation
FixedWorkstation
Printer
Workstation
MobileAgent
MobileAgent
MobileAgent
Accesspoint
Accesspoint
Accesspoint
Wide Area
Metropolitan Area
Local Area
Personal Area
LAN:collection of secure “hot
spot” connections, providing broadband access to the Internet
PAN:collection of secure
connections between devices in a
“very” local area
WAN:everywhere outside of the hotspots, where wireless Internet connection are
provided
Bluetooth;< 800 Kb/s – < 30 ft, 10 m
802.11b; 802.11a; 802.11g2M > 54Mb/s – > 300 ft, 100 m
GPRS, 3G – UMTS< 400 Kb/s – xx Mls, Kms
MAN:Building to Building
connectionMMDS; LMDS; 802.1610M > 155 Mb/s - Kms
Convergence
Convergence of Cellular Mobile Networks and WLANs
BenefitsFor cellular mobile operators Higher bandwidths. Lower cost of networks and equipment. The use of licence-exempt spectrum. Higher capacity and QoS enhancement. Higher revenue.
For users Access to broadband multimedia services with lower
cost and where mostly needed (e.g. in Central Business
Districts and Business Customer Premises). Inter-network roaming.
These future networks will have the following inherent characteristics :
1. Broadband Internet access.
2. High (guaranteed) QoS.
3. Seamless access – fixed and mobile.
4. Intelligence.
The Internet is the driver
Million 1999 2000 2001 2002 2003 2004
USA 97 118 135 145 148 152
Japan 23 32 38 43 47 50
Asia Pac 32 70 104 120 135 150
W.Europe 54 81 114 145 164 179
ROW 35 72 105 118 130 140
Total 241 373 496 571 624 671
World Internet users (1999 – 2004)
PAN
Mobile Broadband Network Categories
W-LAN
W-WAN
Personal Area Networks
Wireless Local Area Networks
Wireless Wide Area Networks
Wireless Networking StandardsOverview
Reliability,
Power, Cost
Cost,
Convenience
Speed,
Flexibility
Reach quality
Success Metrics
1 - 100+1 - 10+1 - 1001,000+Transmission
Range (meters)
20 - 25072011,000+64 - 128+Bandwidth
(KB/s)
255 / 65,0007321Network Size
100 - 1,000+1 - 7.5 - 51-7Battery Life(days)
4KB - 32KB250KB+1MB+16MB+System
Resources
Monitoring &
Control
Cable
Replacement
Web, Email,
Video
Wide Area
Voice & Data
Application
Focus
ZigBee
802.15.4
Bluetooth
802.15.1
Wi-Fi
802.11b
GPRS/GSM
1xRTT/CDMA
Market Name
StandardUWB
802.15.3a
?
IrDA
Cablereplacement
?
?
1
9.6-115
1-5
Future PAN TechnologiesTechnology Max
SpeedIntroduction AdvantagesDis-
advantagesBottomline
Bluetooth 723.2Kbps 2001 Low cost Interference, security
Replace cables
Infrared 115Kbps In use Very low cost
LOS Replaced by Bluetooth
802.15.1 723.2Kbps 2002 Low cost Interference, security
Formalized Bluetooth
802.15.3 High rate
>20Mbps 2003 High data rates
Expensive, not
backwards compatible
Case not proven yet
Time Modulated Ultra Wideband (UWB)
>20Mbps 2006 High data rates, no dedicated frequency
Not approved, expensive
Under hyped. Potentially
revolutionary technology.
Source: Gartner (2001)
Analogue (1G)
W-WAN Categories• AMPS• N-AMPS
• TACS• NMT
3G
Digital (2G)
2.5G
4G
• GSM• CDPD• PDC
• CDMA/cdmaOne/IS-95A• TDMA / IS-136
• GPRS• HSCSD• EDGE Classic
• EDGE Compact• CDMA / IS-95B• cdma2000 1xMC
• PDC-P
• W-CDMA• cdma2000 3xMC• CDMA 1x EVDV
• CDMA 1 XTREME
• Undefined
Technology
Max Speed
Introduction
Advantages
Dis-advantages
Bottomline
GPRS 171.2Kbps
2001 Packet data for GSM world
Data rates may
disappoint
Will be most
successful technology
through 2005
HSCSD 115Kbps In use Dedicated channels
Low deploymen
t, expensive
Will not be mainstrea
m
EDGE Classic
384Kbps 2003 Higher data rates for
both packet & circuit
Expensive, little
terminal support
Will not be able to
compete with W-CDMA.
EDGE Compact
250Kbps 2002 Higher data rates for
both packet & circuit TDMA
networks
AT&T (main proponent)
has changed direction
Unlikely to be
successful
Transaction - Based
• Mobile Banking• Mobile Stock Trading• Travel Reservation & Payment (Rail, LRT, Bus, Flights, Taxi, Hotel, Insurance)• Entertainment Reservation & Payment (Cinema, Theater, Concerts)• Pre-Paid Voucher Recharge• Vending Machine Purchases• Electronic Cash Download• Payment of Utility Bills (Electricity, Water, Astro, etc)• Other Payments (Restaurant Bills, Takeaways, Parking)• Online Auctions• Online Shopping (eg. CDs, Books)• Music MP3 Downloads
Technology Enabler:
SIMCard
2nd
SmartCard
Dual – Slot Hand Phone
• Customisable with SIM Toolkit• Remote Upgrading
• Credit Card• Debit Card• eCash Card• Pre-Paid Card• Loyalty Card
Mobile Transactions
NEXT GENERATION MOBILE VISION & CONCEPT
Ubiquitous connectivity for slow and fast moving users, accessing high speed internet and related multiple services at affordable cost and reasonable QOS
Cooperation between content providers and Wireless access providers- Virtual operators
Multi-Media, Multi-Environment, Multi-Operator Environment
User Driven, User Controlled, Context Aware Applications
Convergence of services, aggregation and inter-working of existing and emerging technologies and networks
Vertical and Horizontal Seamless Handover
.
80’s 90’s 00’s 10’s
1G
2G
2G evolution
3G
3G evolution
4G
Digital Voice, data
Analog Voice
Packet Data, On
Multimedia messages, multiple services
Cost efficient, Higher Data
Higher Data, Superior Radio Resource Management, Seamless mobility, Aggregation of Generations
Evolution towards better Data rates
and higher mobility
0.1 1 10 100 1000 MB/S
V
P
S
4G Research
Targets
Mobility
CDMA2000, WCDMA 802.11a,g
W-LAN802.11b
1X EV-DV
1X EVDO
CD
MA
1X ,
ED
GE
EVOLUTION
E-Mail 4.2 sec in 2G to 0.002s in 4G
Movie Download 926 hours in 2G to 1minute in 4G
3G E
volv
ed
Syste
ms
Convergence of High Speed Internet & Mobility A major driver of future wireless The Wireless Industry has grown at enormous pace over the past decade.
More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move.
With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure.
The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective.
GENERAL REQUIREMENTS
Handling multimedia TrafficData, Video, Voice
Seamless Services on the moveUser friendly smart devices
Diversified wireless accessUnder One Umbrella, Seamless
access Advanced Mobility ManagementIndependent of the IP versionProactive, always-onIntelligent integrated control
WIRELESS TRANSMISSION
WIRELESS TRANSMISSION
Mobile Radio (Wireless) signals undergo many impairments during transmission / propagation through the radio channel (atmosphere / free space / any medium)
Frequencies • Radio signals are modulated signals with carrier frequency allotted in any of the frequency bonds.
• ITU Region
1. Europe, Middle East, Africa
2. Greenland, North & South America
3. Far East, Australia, New Zealand
• LAND / SATELLITE CELLULAR RADIO BANDS
SIGNALS: Mostly SINUSOIDAL(AM/FM) or its variants (ASK, PSK) spectrum has side bonds or frequencies.
Fundamental + Harmonics
SIGNALS: Mostly SINUSOIDAL(AM/FM) or its variants (ASK, PSK) spectrum has side bonds or frequencies.
Fundamental + Harmonics
f) Ф
Ф = m sinФ 90°Phase
Zero phase
I = m cosФ
xx
zz
yy
ANTENNAS:
Energy Translators /Couplers from TX to CH.
Hence Radiation pattern.
Ideal Isotropic: Equal power in all directions
ANTENNAS:
Energy Translators /Couplers from TX to CH.
Hence Radiation pattern.
Ideal Isotropic: Equal power in all directions
SMART ANTENNAS→ Use DSP
Real Directive: DIPOLE omni directional uniform radiation in one plane fig.of 8 in other two planes
DIRECTIONAL ANTENNA: Main lobe in only one direction
SECTORIZED ANTENNA: Several directed antennas combined on a single pole
Real Directive: DIPOLE omni directional uniform radiation in one plane fig.of 8 in other two planes
DIRECTIONAL ANTENNA: Main lobe in only one direction
SECTORIZED ANTENNA: Several directed antennas combined on a single pole
λ /2λ /2
z
x
xx
yy
z
yy
xx
zz
xx
3 sector3 sector
yy
zz
yy
x
zz
x
zz
8 sector8 sector
Only one direction of transmission unlike wired transmission
Fixed error limited transmission range
Fixed error limited detection range
Interference range
SIGNAL PROPAGATION
d
Free space Loss or Los loss
Squared law pr α 1/d2
- Due to equal distribution of energy Over the surface of energy sphere.
Path Loss : Signal attenuation due to rain,fog,dust,smog,air,snow
Signal penetration medium attenuation frequency
SIGNAL IMPAIRMENTS
- Mobile signal reflects from sky scrapers, Walls, Trucks,Mountains,Towers,Birds.
Reflected signal is not as strong as the original.
Reflection Signal strength
Reflection : When λ < size of obstacle
Blocking or Shadowing :
- due to large obstacles
Scattering : obstace size ≤ λ
Incoming signal is scattered in multiple directions and become weak signals, due to many objects in atmosphere or space .
Diffraction : Similar to scattering Radio waves get deflected at edges signals become weak
Multi Path Effects :
POWER
t
ISI Fading – Short term Long term
Delay Spread
MULTIPLE ACCESS OR MULTIPLEXING :
Means of combining several user signals onto a common channel
Multiple users access and share a common channel with no interference (Hope fully)
Simple ex :1. Athletic tracks / Swimming lanes 2. Many cars/Buses/Trucks share a multiple lane road due to separation of lanes
Space Division Multiplexing
However, needs a special identification and control mechanism for proper MUX & DEMUX.
For Wireless Communication,4 types of Multiplexing
SPACE DIVISION MULTIPLEXING :
Assignment of space to each communication channel i.e., actually a source signal, with minimum
interference and a maximum medium utilization
Assume 3D space represented as shown
k1 k2 k3 k4 k5 k6CH
time t t
frequency fs1 s2 s3f
cccode
Coverage Space is represented via circles
Channels K1, K2, K3 can be mapped into three spaces S1, S2, S3 with clear separation and no overlap
What about K4, K5, K6 ?
Analogous to road traffic separate lanes Analog fixed Telephone Network separate wire pair / local loop
For wireless, SDM implies , a separate sender for each channel with wide space separations.
ex: FM radio stations.
• Problems arise if two or more channels occupy the same space
FREQUENCY DIVISION MULTIPLEXING (FDM / FDMA)
• Subdivision of frequency dimension into several non-overlapping frequency bounds or slots.
• Each channel Ki is allotted its own (dedicated) band
• Sender uses this band continuously
• Guard spaces do exist for no interferences.
Ex:- Am radio stations
f
t
c
S1 S2 S3
• Receivers must TUNE into the specific senders.
• Draw backs : Tremendous wasted frequency as user may not transmit all the time (usually less than 1Hr per day).
TIME DIVISION MULTIPLEXING TDM(A)
• A channel Ki is given whole bandwidth, but only for a fixed period of time
• Time dimension is partitioned into several Time slots
• Each channel is allocated one Time slot.
S1
S2
S3...
t1
t2
t3
f
c
t
• Needs precise synchronization in timings for TX or Rx.
HYBRID-FTDMA:• A channel Ki use a certain frequency band fi for only a
certain amount of time ti
• More robust against frequency selective interference / jamming.
• Better protection against Tapping / Intruder.
• But needs coordination between senders.
t
c
f
All channels use same frequency at the same
time.
Separation through coding each channel with its own code.
Guard space is the distance in code space
CODE DIVISION MULTIPLEXING : CDM(A)
t
c
f
Ex:- ORTHOGONAL CODES
Due to VITERBI.
Ex:- Different telephone calls use same band width but different languages (Codes), at same
time.If language is same, then SDM is needed.
Thus secret codes (Languages) provide security
Code space is huge. Hence better protection against interference and tapping .
However, the intended receiver must know the code and also must synchronize with Tx for correct decoding .
MODULATIONANALOG
DIGITAL
AM
FM
BINARY
M - ary
ASK, PSK, FSK
MSK, QAM, GMSK,
QPSK, DQPSK
Analog
Modulation
Digital
Modulation
Analog Base band
signalDigital Data
101101001
Radio Carrier
SPREAD SPECTRUM MODULATION
Developed for secured communication
Means of transmitting a data sequence that occupies larger bandwidth than the original base
hand
Spreading of bandwidth is through the use of a code that is independent of data
Chief Advantages: 1. Resistance to narrow band interference or
jamming
2. Multiple Access Communication.
Purposeful bandwidth spread to make the signal to possess noise like appearance so as to blend into the back ground noise.
f
Power P
i )
f
P
ii )
f
P
iii )
f
P
iv )
f
P
v )
BPF
STEP i) Narrow band user input data
ii) Tx Spreads the signal into a wide band signal. But energy is same as original.
iii) A Wide band interference and Narrowband interference get added
to wide band signal during transmission
iv) Receiver dispreads the signal into narrowband. Thus narrow band interference gets spread and wide band interference gets left as it is.
v) Receiver uses a BPF to band limit the user signal to original bandwidth and yield high SNR
MOBILE RADIO SIGNAL PROPAGATION & ENVIRONMENT
Mobile radio signals propagating through a communication medium are subjected to many changes or modifications.
Propagation path loss :-
- Due to beam Divergence (Free space Loss) - Proportional to 1/d2
Terrestrial Losses :-
Terrain Dependent (Path Loss)
- Texture, roughness of terrain tends to dissipate propagated energy.
• Scattering and Multipath effects :
- Signal gets scattered at ≤ λ obstacle points and travel in multipaths.
- Result is different delay spreads of signal.
- Thus severe FADING of the received signal (sum total of multipath signals).
- Because of low mobile antenna height and near ground communication.
MS Stationary
MS moving
S(t)
r(t)
m(t)
Local mean
avg Pr
Time or distance
• Instantaneous Signal Strength :
• Depends on whether Mobile station (MS) is in movement or stationary.
• Fading is always present due to multipath effects due to multiple scattering points, reflection points, dissipations.
• Delay spread is the smearing of received signal due to lengthening of time period as a result of different multipath signals arriving with
different phases.
• Short term fading is obtained by
m(t) - r(t) (t)r0 In db
Received Long term fading
• Signal fades about 40 dB
• Nulls around
• Rate of fading α vehicle speed.
m(t) (t)r r(t) 0 Model
2 / λ
(t)r0
- multipath fading
- Rayleigh fading - due to multiple reflections from buildings, structures.
m(t)- Local mean long
term fading due to terrain contour
PROPAGATION PATH LOSS:
• Due to the presence of radio wave scatterers along the path.
• No. of scatterers depend on the contour variations, terrain roughness
▼
▲
▼
)(θ θФ
T BS antenna
Snell’s law
MS antenna
• Therefore changes in the propagation as a result of specular Reflection, Diffuse Reflection and Diffraction.T
Specular Reflection from smooth flat and slopy terrains : • Occurs when radio waves encounter a smooth
interface between two dissimilar media and linear dimension of interface is larger than λ
Ex: Mirror reflection defined by Snell's law.
▼
h1
Elevation
Distance
• Reflected wave at point θ due to reflection of incident wave from BS antenna T can be thought of as originated from a fictitious image antenna TI and passed through the surface without refraction.
h1
Diffuse Reflection: • Occurs when radio waves encounter a rough
textured surface with roughness of order of λ
• Unlike specular reflection, this scatters energy and focus a divergent radio path.
▼
€
d2d1
LOS
LOS
LOSh1
)d1
d1
(λ2
1h
21
p
h2
BS
MS
• Hygen’s principle explains this.
• In tensing of signals is smaller than that of specular reflected wave
• Both these reflections correspond to LOS propagation of reflected signals.
€
▼
l
hp
BS
h2
h1
Elevation
Distance
Diffraction:
• Attenuation depends on whether obstruction extends through the path or protrudes into LOS path.
• Knife edge diffraction modals are used.
• Occurs when the propagation path is obstructed by the features of an intervening terrain between two antennas.
•Thus out of sight propagation.
Path Loss : Propagation frequency distance Path Loss
►
►(Ә2
Ә1(
►
100m
> 2 km
▼3m
Ә1
Ә2
- incident angle / elevation angle
- reflected angle
Propagation path loss is 40 dB / decade or 10 km.
Received carrier powered is inversely proportional to R4.
- For Mobile Radio Channel.
- For Free space Radio Channel.
- For Real Mobile radio model 2 < γ < 5
FADING:
• Antenna height of Mobile unit is less than its surroundings.
• Carrier signal wavelength is smaller than sizes of surrounding structures.
4-R α C
γ- Rα
2- R α
Result : Multipath Fading due to net sum of multiple path arriving signals with different phase.
Fading fluctuation range about 40 dB. (10 dB above, 30 dB below avg / mean).
• Nulls of fluctuation at the base band at about every in space, but not with same levels.
• Rate of fluctuation α vehicle speed.
2
λ
Multi path fading occurs in Three situations :
1.Mobile unit and surrounding scatterers are still / stationary
2.Static Multipath Mobile unit standing still scatterers moving
3.Mobile unit and scatterers moving.
Static Multipath Signal :
Envelope
} i
)-t(f 2 i { 0
0e ) -t ( x s(t)
ai → attenuation factor of ith path.
N signal paths,
N
1i0 i )(ts as(t) i
i f 2 j-i0
0e aax(t)
→ additional relative delay on ith path.
i → Propagation time
i
Case 2 : MS still scatterers
moving cars
i , ai are uniquely different along ith path at any instant.
js}-{Ra e A(t) 0(t) jψ-
t f 2 j-j
00 e e x(t)s(t)
(t) fj2-i i00 e (t)a a x(t)
220 SRa A(t)
RS Tan ψ(t) 1-
Case 3 : MS Moving – a) Scatters are absent b) only one scatterer present c) Many scatterers present near MS. v▼
(t)s0
θ
] ) cosθ vt βφ tω ( j [ Expa s(t) 0 0 0
λ
2π β
X(t)
Voltage
Doppler effect contributes additional frequency due to movement of Mobile
cosθλ
v cosθ f f mdoppler
travel of direction on depending
Thus concept of standing waves is applied to radio signals to understand the multipath effects.
A resultant signal due to an incident signal and a perfect scatterer reflected signal, reaching a mobile of speed V is
The envelope of S(t) looks like a standing wave pattern.
)2
ω - vt (β sin 4a (t) x
0 2 20
2
Fading Frequency → 2V/λ
] ) ω - vt β φ t ω ( j [0
vt] β - φ t ω [ j0
00000 e a - e a s(t)
▼v
Scatterers (Houses)As a mobile unit proceeds in a street, it is passing through an avenue of scatterers as shown.
Highest Doppler Frequency fd is
df
W(f)
λ
v2
)cosθλ
v (max )f (max f dm
λ
v
Why 800 MHz Band?
ITU - T and FCC chose 800 MHz initially because.
- Severe spectral limitations at lower frequency Bands
- Maritime (ship) mobile service at 160 MHz
- Fixed station services from 30 to 100 MHz
- FM and VHF/UHF TV Bands from 80-600 MHz
- No Mobile radio transmission beyond 10 GHz due to propagation path loss, multipath fading and rain loss.
- 800 MHz allocated to educational TV Channels was heavily under utilized.
Even though not an ideal frequency for mobile radio, the 800 MHz band demonstrated the feasibility.
History of 800 MHz spectrum:
1958 -Bell lab proposal for 75 MHz system at 800 MHz.
1974 -FCC allocated 40 MHz spectrum for one cellular operator licensed per market area.
1980 -FCC revised its policy and introduced competition with two licensed carriers per service area of course this resulted in trunk efficiency degradation
Ban Mobile Base System
A 824-835,845-846.5 869-880, 890-891.5 non wire line.
B 835-845, 846.5-849 880-890, 891.5-894 Wire line
1986 – FCC added 5 MHz to each band.
old 333 + new 83 = 416 channels per band with 30 KHz per channel.
FCC assigned frequencies in 20 MHz groups, as
TRUNKING EFFICIENCY:
No. of calls per hour per cell =
Φ = Offered traffic load / average calling time
Trunking efficiency degradation factor
η = {φOne carrier – φ Multi carrier} / φOne carrier
Blocking probability %
30
10
20
0 1 52 10 30
5 career/market
2 career/market
η%
UNIQUENESS OF MOBILE RADIO ENVIRONMENT
Propagation path loss increases with
- Frequency
- distance θ1 elevation angle θ2 incident angle
▼
d
h
Direct pathReflected path
(2θ
1θ (
2 km
30 – 100 m
▼
Cell antenna height: 30 -100 m
Mobile antenna height: 3 m 4-R C Received carrier Power
Difference in Powers
2
1 12
R
R log 40 dB in C - C C
4-
1
2
2
1 )( R
R
C
C
General Rule
=>40 dB/dec path loss
Δc = - 40dB
Free Space- c α R-2
Mobile radio CH- c α R-4
dB/dec 20 R
R log 20 C
2
1
dB/dec 40 R
R log 40 C
2
1
Received signal fading levels:
10 dB above and 30 dB below mean. 2R-e R P(R)CDF
lcr R η2π
βν )(RLevel crossing rate
Average fading duration R
-t
βν
2π (R)
-t afd
η
PATH LOSS MODELPATH LOSS MODEL
• Different, often complicated, models are used for different environments.
• A simple model for path loss, L, is
The path loss exponent = 2 in free space;
2 4 in typical environments.
where Pr is the local mean received signal powerPt is the transmitted powerd is the transmitter-receiver distancef is frequency,
K is a transmission constant.
Pr 1
Pt f2d
= KL =
PATH LOSS LIMITATIONS
• Given the performance requirement SNR SNRo, the path loss imposes limits on the bit rate and the signal coverage.
• The received signal-to-noise power ratio, SNR, is
SNR = = •Pr KPt 1
Pn d NoB
( )B or d
KPt
dNoSNRo
KPt
NoBSNRo
1/
where No is the one-sided noise power spectral density B is the signal bandwidth.
SHADOW FADING• The received signal is shadowed by obstructions such as hills and buildings. • This results in variations in the local mean received signal power,
• Implications – nonuniform coverage – increases the required transmit power
Pr (dB) = Pr (dB) + Gs
where Gs ~ N(0, s ), 4 s 10 dB.2
First order statistics of Fading => Average power CDF, BER
Second order statistics of Fading =>lcr, afd,
word Error Rate
independent of time
time/velocity dependent
Rayleigh Fading :
_LLe1L)P(y
22_AA-e1- A)P(x CDF
NOISE LEVEL IN CELLULAR BANDS:
THERMAL NOISE -129 dBm at B = 30 KHz, T=290K
IGNITION NOISE -124 to –104 dBm at B=30 KHz, T=290K
AMPLIFIER NOISE KTB
G)N(NNF
ai
DELAY SPREAD
• Base station sends an impulse signal to the mobile station.
a0
▼
1 2 3 4 t
4
31
▼
BS Antenna
t
2
4 scatter case Delay spread N=4
s(t)a(t)s 00 error
• Because of multipath scattering, the impulse gets reflected many times and thus many impulses (echo's) arrive at mobile unit at different times.
a0
N>>4
t
N-scatter case delay spread
• Received impulse signal is
t ω j e E(t)
t ω j j 0 e )-δ(taas(t)
• As number of scatterers (N) increases, the received impulse sequence becomes a continuous signal pulse, with a pulse length Δ (called DELAY SPREAD).
Delay envelopes contain multiple peaks.
Shortest path signal need not necessarily produce highest peak as the scatterer could be absorb in nature.
Mean delay time d is the first moment or average.
0
dt E(t) t d
Standard deviation or delay spread Δ is
2
0
22d - E(t)dt t
t=0 → Leading edge of envelope E(t).
DELAY SPREADFREQUENCY DOMAIN INTERPRETATION
Bs = signal bandwidth 1/TH(f)
Bs
12
f
• small flat fadingT
• large frequency-selective fadingT
Parameter Open Urban Suburban Area Area Area
Mean Delay Time d, μs 0.2-0.5 1.5-2.5 0.1-2.0
Path Length, km 20–300 450-750 30-600
Max. Delay Time 0.5-2 5-12 0.3-7 (-30dB)
Path Length, Km 0.5-1 1.5-3.6 0.9-2.1
Range of delay spread 0.1-2.0 1-3 0.2-2 Δi, μs
Mean Delay Spread <0.2 3 0.5
Delay spread is assumed independent of frequency.
DOPPLER SPREADDOPPLER SPREAD
• A measure of the spectral broadening caused by the channel time variation.
• Implications – signal amplitude and phase decorrelates after a time period ~ 1/fD
Example: 900 MHz, 60 mph, fD = 80 Hz5 GHz, 5 mph, fD = 37 Hz
8C32810.87-Cimini-7/98
fD v
COHERENCE BANDWIDTH:
Bandwidth in which either the amplitudes or the phases of two received signals have high degree of similarity or correlated.
• Different delays in two fading signals that are closely spaced in frequency can cause the two signals to become correlated.
• The frequency spacing that allows this condition depends on the delay spread Δ .
• This frequency interval is called coherence or correlation Bandwidth Bc.
Scattered component
Channel input response model
d
E(t)
t
Specular component
Δdt
Coherence bandwidth
Correlation function
f
C(f)
Scattered component
• A typical definition of Bc → ΔΠ 2
1 Bc
AM
or
Δ8
1 Bc
ΔΠ 4
1 PM
FM
NOISE IN MOBILE RADIO CHANNEL:
THERMAL NOISE
WHITE NOISE
WIDEBRAND
GAUSSIAN WHITE NOISE
NARROWBAND
(t)jn(t)nn(t) sc
URBAN
HUMAN MADE NOISE
SUBURBAN
GALACTICSOLAR
EXTERNAL NOISE
ATMOSPHERIC
-10 8642 10 100 1000 105 109
0SOLAR
RURAL QUITE
GALACTIC
RURAL
SUBURBAN
URBAN
INTERNAL RECEIVER
f
NFatmospheric
Mean Noise Figure Fa : 28 db / decade slopes for all.
Automotive Traffic Noise Power increases with traffic density decreases with frequency
ELEMENTS OF CELLULAR MOBILE RADIO SYSTEM DESIGN
GENERAL DESCRIPTION OF PROBLEM:
CONCEPT efficient Spectrum Utilization
Major Elements of System Design
1. Frequency Reuse Channels
2. Co channel Interference Reduction Factor
3. Carrier-Interference Ratio
4. Handoff Mechanism
5. Cell Splitting
Limitation / constraint In system design Frequency Resource
Challenge / goal greatest no. of customers with a specified system quality.
Ex :- Max. no. of calls/hour/cell Q Max. No. of frequency Channels /cell - N
Q depends on
- cell size
- traffic conditions
Ex :- A BUSY Traffic area of 12 Km radius is divided into seven 2 Km cells. Assume a traffic situation with the busiest traffic cell cover 4 freeways and 10 heavy traffic streets, with a total length of
• 64 Km of TWO 8 lane roads
• 48 Km of Two 6 lane freeways
• 588 Km of forty three 4 lane roads
average spacing of cars is 10m during busy periods. One half cars have phones and eight tenths of them make a call (ηc= 0.8) during the busy hour.
28,0000.82
70,000hourbusy in calls No.of
7000010m
700km cars of number Total
700km5884864 roads of length Total
MAX. No. of Frequency Channels per cell (N)
• depends on average calling time T
• depends on maximum calls per hour per cell Qi
• Determined from a plot or Table that shows N,B and A
• OFFERED TRAFFIC LOAD =
Erlangs60
TQA
I
Problems in wireless communicationProblems in wireless communication
• Available unlicensed spectrum allocation
(government regulation)
• Only low transmission power levels allowed
(No brute force possible: strong signal in
narrow band)
• Multi-path propagation echoes
• Interference
• Noise
RADIO ENVIRONMENTRADIO ENVIRONMENT
• Path Loss • Shadow Fading • Multipath • Interference • Infrared Versus Radio
• Path Loss • Shadow Fading • Multipath
Limit the Bit Rate and/or Coverage
BASE STATION
• Frequencies (or time slots or codes) are reused at spatially-separated locations.• Introduces interference system capacity is interference-limited.• Mainly designed for circuit-switched communications• Base stations perform centralized control functions. (call setup, handoff, routing, etc.)
FREQUENCY REUSEFREQUENCY REUSE
• Reuse Distance (D)
– distance between cells using the same frequency, time slot, or code– smaller reuse distance packs more users into a given area, but also increases their co-channel interference
• Cell Radius
– decreasing the cell size increases system capacity, but complicates the network functions of handoff and routing
DESIGN CONSIDERATIONS
History of Mobile Radio &Cellular Communication SystemsHistory of Mobile Radio &Cellular Communication Systems
FCC allots 40 MHz bandwidth in 800-900 MHz band
First cellular system by NTT in Japan First US cellular land mobile phone service in 800-900 MHz band with 40 MHz bandwidth
1974 1979 1981
FCC – 152 MHz duplex radio telephony 1964 Simplex radio telephony system-450 MHz 1956
FCC permitted 4 channels in 30-40 MHz 1933
Police car radio at 2 MHz in Detroit 1921
First radio transmission by Marconi 1897
Initial radio demo by Hertz 1880
Telecom EventTelecom Event YearYear
1984 AMPS cellular system introduced by AT&T in US
1986 FCC added 5 MHz extended band; two operators per market
1988 TDMA digital cellular standard in North America (NA)
1992 GSM operable in Germany D2 cellular system
1993 CDMA chosen as digital cellular standard in NA
1994 American TDMA started in Seattle; PDC in Tokyo, Japan
1995 CDMA in Hong Kong
1996 Six PCS licensed bands at 120 MHz given in US
1997 Broadband CDMA chosen as 3G Technology for UMTS
1999 ITU decides nextG standards- W-CDMA, CDMA2000, TD-SCDMA
2001 First commercial W-CDMA service in Japan
2002 FCC approves additional band for UWB
It is widely believed that the fixed landline telecom network (Telephone, fax, etc) are the largest and most complete integrated systems at present in the world.
The cellular radio has rapidly evolved and had already crossed the size of the fixed land telephone network.
Let us consider the important differences between the conventional landline telephone network and the cellular radio telephone network.
Let us recall the basic features of the plain old land telephone network (Public switched telephone network – PSTN).
Plain old telephone:
DTMF Keypad for number dialing:
i) Telephone Number is registered solely in the local exchange.
ii) Numbers are dialed from DTMF keypad as shown above.
iii)Central Battery supplies power to telephone handset.
iv)Subscriber loop is a 2 wire half duplex circuit.
v) Trunk circuits employ 4 wire circuits with Hybrid coil doing 2/4 wire conversion.
vi)ON/OFF HOOK state of cradle switch is an indication to the exchange about call REQ/ Disconnect signaling information.
vii) subscriber can start dialing (entering telephone no.) only after receiving the dial tone from the exchange.
viii) User must go to instrument to make a land phone call.
Features of land phone:Features of land phone:
Features of mobile/cellular phone:
i) There is no dial tone and cradle switch (i.e. on/off Hookon/off Hook)
ii) User types in/ calls from memory and presses ‘SEND’ button to transmit telephone number of called party
iii)Power comes from the local Battery (LB), not from CB
iv)Local exchange is replaced by a base station (BS) and a mobile switching centre (MSC)
v) Local 2 wire loop is replaced by 2 way HDX radio channel
vi)Cellular user talks on Reverse channel (MS to BS radio link) and listens on forward channel (BS to MS radio link)
vii) signaling information is exchanged via separate set up or control channels in each direction, user transparently
Fundamental principles of cellular Fundamental principles of cellular communications:communications:
Cellular technology had evolved from the mobile radio telephone technology.
Mobile radio telephone (R/T):Mobile radio telephone (R/T):
It is basically a transceiver handset with a 2 way duplex link connecting to a base station and switching centre.
Mobile unit carries its own telephone number in a SIM / smart card, which allows roaming using same number.
BS and MS always keep in touch by handshaking protocols via control channels, transparent to the user.
The following figure depicts the components of a R/T.
Cellular radio phone and its components:
There are many ways of providing wireless and mobile communications
For ex:- cordless phones used at homes employ wireless technology, with a low power transmitter and hence has small coverage area(<100 m)
Such phones used in adjacent homes do not experience any interference, even by operating at same frequency exactly
This is a perfect example for frequency reuse
The same principle of frequency interference avoidance is used in cellular systems also, even with much more transmission powers
Radio Cell Shape:
All users in a cell are served by central BS -gateway of cell !
Ideally all the cells are circular in shape for omnidirectional coverage, with BS located at its centre as shown below.
Cell area and periphery are decided by minimum signal strength, height of BS antenna, presence of hills, tall trees/buildings and atmospheric conditions.
Thus actual shape of cell and coverage area is an irregular zigzag circle, but modeled by a hexagonal building blocks.
Ex:- Bee hives are 3D hexagons
Multiple accessing is employed in cellular systems to allow multiple cellular subscribers to access the same BS in a cell
They are FDMA, TDMA and CDMA
The limited bandwidth allocated to operator is divided into number of radio channels, which are further grouped into subsets, to assign one group of channels to a particular cell
This is the principle of FDMA employed in first generation cellular systems.
Because of unique frequency sets allocated for each cell, it is possible to use the same frequency set in a distant cell, as long as the two transmissions do not interfere with each other.
This is the principle of frequency reuse, a central theme of cellular communications
Radio coverage in a single cell:Radio coverage in a single cell:The fundamental radio cell and parameters that dictate the radio coverage are shown below
Different cellular ranges for mobile radio communications are indicated. The reverse path (MS to BS) limits the radio range, due to limited TX. Power of mobile unit.
The no. of subscribers covered by a single cell depends on the radius or area of the cell, as given in the table.
Cell radius km
Coverage area km2
Number of subscribers
covered 1 3.14 100
3 28.3 900
10 314 10,000
25 1960 60,000
Cell area and number of subscribers coveredCell area and number of subscribers covered
Typical cellular system layout and signal power distribution are shown below. One can see the extensive signal processing required to meet this.
MULTIPLE CEL LAYOUT:MULTIPLE CEL LAYOUT:
The intracellular communication is duplex radio communication between cell site (BS) and mobile unit (MS).
It needs a block allocation of frequencies for the control and voice radio channels
Adjacent cells are not assigned the same frequency sets to avoid the cochannel and adjacent channel interferences.
A handoff mechanism is required to automatically handover an ongoing mobile call from one group to another frequency group used in the next cell, as and when mobile unit is crossing cell boundaries.
That means the cellular phone circuits must be frequency agile to retune to a new frequency without call disconnects.
Basic cellular system architecture:Basic cellular system architecture:
Cellular technology replaced a large coverage area mobile radio system with many smaller cells, with a single BS covering one particular cell only, as depicted in the following figure.
The mobile and wireless devices used by subscribers are cell phones, PDAs, palmtop/laptop PCs, web phones, etc.
All devices are referred to as Mobile Stations/Units (MS)
An MS can communicate only with its nearest BS of a cell in which it is located ( i.e., belongs to).
Hence a BS (with a base transceiver) acts as a gateway switch/router to the rest of the world, to any MS.
Every BS is controlled by one base station controller (BSC), which in turn is connected to a mobile switching centre (MSC) as shown in the following figure.
Several MSCs are interconnected to PSTN and ATM backbone networks.
Cellular system architecture:
Home location register (HLR) and visitor location register (VLR) are two database pointers that support mobility and enable the use of same telephone number worldwide in cellular communications.
HLR is located at the home MSC where MS is registered
VLR stores all the visiting mobiles in that particular area
Authentication centre (AUC) provides authentication for an user attempting to make a cellular call.
This uses a 15 digit unique IMEI number programmed into the MS at registration time and also stored in Equipment identity register (EIR).
Network management and operations control are the functions of the centers NMC and OMC.
BS and MS signaling and voice communication:BS and MS signaling and voice communication:
In any cellular system, four simplex radio channels are needed to exchange synchronization and data between BS and MS, as shown below.
The control channels are used to exchange control messages like, authentication, subscriber identity, call parameter negotiation, power control, etc.
Traffic (information) channels are used to transfer actual data (voice/digital data)
Forward CH/ Downlink BS to MS transmissions
Reverse CH/ Uplink MS to BS transmissions
Control information shall be exchanged before the actual data transfer can take place.
This necessitates the use of handshaking protocols for cellular call setup, maintenance and disconnection.
Handshaking protocols in cellular call setup:Handshaking protocols in cellular call setup:
Simplified handshaking steps for a cellular call setup are illustrated in following figure.
BSBS MSMS
1. Need to establish path1. Need to establish path
2. Frequency/time slot/code assigned2. Frequency/time slot/code assigned
3. Control information acknowledgement3. Control information acknowledgement
4. Start communication 4. Start communication
fig. steps for a call set up from MS to BSfig. steps for a call set up from MS to BS
MSMS BSBS
1. Call for MS # pending1. Call for MS # pending
2. Ready to establish a path2. Ready to establish a path
3. Use of frequency/timeslot/code3. Use of frequency/timeslot/code
4. Ready for communication 4. Ready for communication
steps for a call set up from MS to BS:steps for a call set up from MS to BS:
5. Start communication 5. Start communication
Wireless LANs and PANs:Wireless LANs and PANs:
Mobile wireless networks find extensive use in different facets of human life.
Already we are accustomed to line orientd to Local Area Networks (LAN) and Wide Area Networks (WAN).
Ex:- Internet access, a value added service offered by landline telephone network PSTN
Wireless LANs (WLAN) are being developed to provide mobile access to data users.
Personal access Networks (PAN) cover very small areas referred to as Pico cells using low powers in ISM band.
WLANs and PANs are becoming popular choice and influence the wholesome home and office automation.
It is predicted that the percentage of nonvoice multimedia data traffic is increasing heavily.
Also the digital voice technology is permitting the integration of voice and nonvoice traffic into unified data stream.
Thus convergence of voice and nonvoice networks into a single unified network supporting multimedia communications is the order of the day.
Standards like IEEE 802.11, Bluetooth, HomeRF, HiperLAN etc., are being developed and deployed worldwide.
Adhoc networks are being devised for commercial and military applications.
MOBILE ADHOC NETWORKS (MANNET):MOBILE ADHOC NETWORKS (MANNET):Adhoc networks are basically peer to peer multihop mobile networks for freely moving mobile users and hosts interconnected by nodes (mobile transceivers).
Information packets are transmitted using a store andforward protocol as shown in the fig.
Nodes are very small transceivers with antennas and can be located inside airplanes, ships, trains, trucks, cars, homes, offices, etc.
This adhoc network topology (multihop graph) may change with time as the nodes move or adjust their transmission or reception parameters.
Typical adhoc network is shown below.
Wireless Sensor Networks:Wireless Sensor Networks:
Sensor networks are the newest members of a special class of wireless networks.
A large no. of tiny immobile sensors are planted on the adhoc basis to sense and transmit some physical characteristics of the environment.
An associated BS collects the information reported by the sensors on a data centric basis.
Ex:- Battlefield surveillance of enemy territory/war front by sensors dropped from a low flying aircraft.
Potential commercial uses include machinery prognosis, biosensing and environment monitoring.
Typical wireless sensor network:
WLAN and PAN characteristics and features Type of network
Range of node
Primary function Deployed locations
IEEE IEEE 802.11802.11
30 m30 m Standard for Standard for wireless nodeswireless nodes
Any peer-peer Any peer-peer connectionconnection
Hiper-Hiper-
LANLAN
30 m30 m High speed indoor High speed indoor connectivityconnectivity
Airports, Airports, warehouseswarehouses
Adhoc Adhoc NetworksNetworks
≥ ≥ 500m 500m mobiles, wireless, mobiles, wireless, similar to wired similar to wired connectivityconnectivity
Battlefields, Battlefields, disaster networksdisaster networks
Sensor Sensor NetworksNetworks
2 m2 m Monitor Monitor inaccessible, inaccessible, inhospitable terraininhospitable terrain
Nuclear, Nuclear, chemical plants, chemical plants, oceansoceans
Home RFHome RF 30 m30 m Resource sharing, Resource sharing, device connectionsdevice connections
HomesHomes
BluetoothBluetooth 10 m10 m Avoid wire clutter, Avoid wire clutter, low mobility low mobility provisionprovision
offices, buildingsoffices, buildings
indoorsindoors
HANDOFFHandoff is defined as a process used to allow a call/data transfer to continue uninterrupted as the mobile terminal moves between cells
Hard handoff vs. Soft handoffHard handoff- break before makeSoft handoff – Make before break
Vertical Handoff vs. Horizontal HandoffVertical Handoff- Between Different NetworksHorizontal Handoff- Between Same Networks
Decision to handoff is based on the receivedsignal strength or S/I ratio.
CHANNEL ASSIGNMENTCHANNEL ASSIGNMENT
• Fixed Channel Assignment (FCA) – each cell is assigned a fixed number of channels
– channels used for both handoff and new calls
• Reservation Channels with FCA – each cell reserves some channels for hand off calls
• Channel Borrowing – a cell may borrow free channels from
neighboring cells
• Dynamic Channel Assignment
• Interference Averaging (CDMA)
• Interference Reduction(power adaptation, sectorization)
• Interference Cancellation(smart antennas, multi user detection)
• Interference Avoidance(dynamic resource allocation)
METHODS TO IMPROVESPECTRUM UTILIZATION
PHYSICAL LAYER ISSUES
• Link Performance Measures
• Modulation Tradeoffs
• Flat Fading Countermeasures
• Delay Spread Countermeasures
LINK PERFORMANCE MEASURESPROBABILITY OF BIT ERROR
• The probability of bit error, Pb, in a radio environment is a random variable.
• Typically only one of these measures is useful, depending on the Doppler frequency and the bit rate.
– average Pb, Pb
– Pr [Pb > Pbtarget] outage, Pout=
HOW DO WE OVERCOME THELIMITATIONS IMPOSED BY THE
RADIO CHANNEL?
• Flat Fading Countermeasures – Fade Margin
– Diversity
– Coding and Interleaving
– Adaptive Techniques
• Delay Spread Countermeasures – Equalization
– Multicarrier
– Spread Spectrum
– Antenna Solutions
DIVERSITY
• Independent signal paths have a low probability of experiencing deep fades simultaneously.
• The basic concept is to send the same information over independently fading radio
• Independent fading paths can be achieved by separating the signal in time, frequency, space, polarization, etc.
The chance that two deep fades occur simultaneously is rare.
0
0-20-40-60-80
-1004 8 12 16 dRec
eive
d S
ign
al
Po
wer
(dB
m)
DIVERSITY COMBINING TECHNIQUES
• Selection Combining: picks the branch with the highest SNR.
• Equal-Gain Combining: all branches are coherently combined with equal weights.
• Maximal-Ratio Combining: all branches are coherently combined with weights which depend on the branch SNR.
Combiner Output
1 2 3 M
• • •
THANK THANK YOUYOU
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