mobile basics
TRANSCRIPT
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Mobile Communication Systems
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Course Outline
Introduction Mobile communication systems issues, system
structure, safety
Wireless communication fundamentals
Propagation, Modulation and Coding, Frequencyreuse.
Intersystem Operation + Mobility Management
Location tracking and Paging, Handoff, Trunkingtheory.
Second Generation Cellular (2G) :
GSM
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Outline
2.5G Cellular: Wireless Data Services
GPRS (General Packet Radio Service)
EDGE (Enhanced Data GSM Evolution)
3G Cellular: Structure, protocols and advance services
UMTS (Universal Mobile Telecom.Services)
Cdma 2000 1x EV-DO (Evolved DataOptimized)
Location Based Systems/Services
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Mobile vs. Wireless Wireless Communication System:
Any electrical communication system that uses anaturally occurring communication channel, such as air,water, earth.
Mobile wireless communication systems focus
Communicate over the air via radio-waves
Support some form of user mobility
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Wireless Issues
Wireless link implications
communications channelis the air
poor quality: fading, shadowing, weather, etc.
data rate and coverage vary
regulatedby governments
frequency allocated, licensing, etc.limited bandwidth
low bit rate, frequency planning and reuse, interference
power issues
Power levels regulated (safety issue), conserve mobile
terminal battery lifesecurity issues
wireless channel is a broadcastmedium!
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Mobility Issues
Mobility Types
User mobility : user can access network while mobile
must handoff calls/connections in progress as user moves
track users as they move so they can receive info/calls
Service mobility: users services follow them
Need to have authentication and services follow user Degree of Mobility
Geographic range
ranges from a house/apartment to worldwide
Speed
ranges from stationary to bullet train cordless phone vs. cell phone
Mobility portable device
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Device Issues
Mobile Device Issues
Portability
Device and accessories size and weight
Usability
User characteristics (size, dexterity, knowledge, etc.)
Environment characteristics (Temperature, degree of mobility,etc)
Device Characteristics
startup time
data integrity and security
cpu speed and memory size power supply
user interface (keypad, voice, etc.)
Functionality (standalone, network dependent)
Connectability (always, partial, never)
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Mobile devices
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Wireless Networks
Wireless Wide Area Networks (WWANs)
Cellular Networks :
GSM, cdmaone (IS-95), UMTS, cdma2000 EVDO
Satellite Networks:
Iridium, Globalstar, GPS, etc.
Wireless Metro Area Networks (WMANs)
IEEE 802.16 WiMAX
Wireless Local Area Networks (WLANs)
IEEE 802.11, a, b, g, etc. (infrastructure, ad hoc, sensor)
Wireless Personal Area Networks (WPANs)
IEEE 802.15 (Bluetooth), IrDa, Zigbee, etc.
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Wireless Networks
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Licensed vs. Unlicensed
Licensed Spectrum
need to buy right to use spectrum allocation in aspecific geographic location from the government
(e.g., AM/FM radio)
Prevents interference licensee can control signalquality
Unlicensed spectrum
Anyone can operate in the spectrum (e.g. ISM
band for WLANs) but must maintain proper behaviorin spectrum (max power level and frequencyleakage, etc.)
Can have interference problems
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Mobile Phone Systems
Mobile phone systems
Support communication to mobile users via wirelessradio channel
Variety of systems and standards:
Analog 1G : NMT, AMPS, TACS
Digital 2G: GSM, IS-95b (cdmaone),
3G: UMTS, cdma 2000
Scope of services and coverage areas growing
SMS, MMS, laptop data, etc.
Focus now on wireless data and location awareservices
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Trends in cellular systems
2G(second generation) is the current generation ofmobile phones, and includes such standards as GSM,TDMA and CDMA, which primarily transmit voice
over a circuit switched network. Data service is possiblesuch as SMS in GSM
2.5Gis a bridge between 2G and 3G. The term 2.5G(second and a half generation) describes systems thatprovide faster services than 2G, but not quite as fast or
advanced as newer 3G systems. 2.5G provides some ofthe benefits of 3G (i.e. it is packet-switched) and usessome of the existing 2G infrastructure.
GPRS is an example of a 2.5G cellular standard.
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Trends in cellular systems
3G is the next (third) generation of mobile
telephony that will require a different
infrastructure than 2G. It is packet-switched(faster and more efficient) rather than circuit-
switched (slower and less efficient), and can
transmit both voice (telephone calls) and non-
voice data (such as email, video, and otherlarge files).
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Trends in cellular systems
CDMA2000: CDMA2000 is an upgrade to the originalCDMA (Code Division Multiple Access) network and isan evolving standard with several phased
implementations. CDMA2000 1xhas the capability ofusing up to three separate 1.25 MHz channels for datatransmission.
EDGE (Enhanced Data Rates for GSM Evolution): EDGEuses the same TDMA (Time Division Multiple Access)
frame structure, logic channel and 200 kHz carrierbandwidth as todays GSM networks, which allowsexisting cell plans to remain intact. EDGE provides ashort-term upgrade path for GSM operators anddirectly competes with CDMA2000.
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Migration to 3G3G2.75G
MultimediaIntermediateMultimedia2.5G
Packet Data2GDigital Voice1G
Analog VoiceGPRS W-CDMA
GSM(UMTS)EDGE
115 Kbps
NMT 9.6 Kbps 384 Kbps Up to 2 Mbps
GSM/TD-SCDMA
GPRSTDMA
(Overlay)2 Mbps?TACS 115 Kbps
9.6 Kbps
iDEN iDEN9.6 Kbps PDC (Overlay)
9.6 Kbps
AMPS cdma2000CDMA 1xRTTCDMA 1X-EV-DV
PHS14.4 Kbps Over 2.4 Mbps
(IP-Based) 144 Kbps/ 64 Kbps
64 KbpsPHS 2003 - 2004+2003+
2001+ Source: U.S. Bancorp Piper Jaffray1992 - 2000+1984 - 1996+
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Future Generations
Other Tradeoffs:Rate Rate vs. Coverage
Rate vs. Delay4G
Rate vs. Cost802.11b WLAN 3G Rate vs. Energy
2G
2G Cellular
Mobility
Fundamental Design Breakthroughs Needed
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Spectrum Regulation
PTA regulates the spectrum allocation inpaksitan
PTA auctions spectral blocks for set applications.
Some spectrum set aside for universal use
Worldwide spectrum controlled by ITU-R
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Standards
Interacting systems require standardization
Companies want their systems adopted as
standard- Alternatively try for de-facto standards
Standards determined by TIA/CTIA in US -
IEEE standards often adopted- Process fraught with inefficiencies and conflicts
Worldwide standards determined by ITU-T
- In Europe, ETSI is equivalent of IEEE
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Main Points
The wireless vision encompasses many exciting systemsand applications
Technical challenges transcend across all layers of thesystem design.
Cross-layer design emerging as a key theme in wireless.
Existing and emerging systems provide excellent qualityfor certain applications but poor interoperability.
Standards and spectral allocation heavily impact theevolution of wireless technology
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Future Wireless Networks
Ubiquitous Communication Among People and DevicesWireless Internet access
Nth generation CellularWireless Ad Hoc Networks
Sensor NetworksWireless EntertainmentSmart Homes/SpacesAutomated HighwaysAll this and more
Hard Delay Constraints
Hard Energy Constraints
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First-Generation Analog
Advanced Mobile Phone Service (AMPS)
In North America, two 25-MHz bands allocated to
AMPS
One for transmission from base to mobile unit
One for transmission from mobile unit to base
Each band split in two to encourage competition
Frequency reuse exploited
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Frequency Division Multiple Access
Definition - FDMA is a multiple access
method in which users are assigned
specific frequency bands. The user hassole right of using the frequency band
for the entire call duration. (Qualcomm, 1997)
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FDMA
Frequency Division Multiple Access
F
requency
Time
Chan A
Chan B
Chan C
Chan D
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Differences Between First and
Second Generation Systems Digital traffic channelsfirst-generation systems are
almost purely analog; second-generation systems aredigital
Encryption
all second generation systems provideencryption to prevent eavesdropping
Error detection and correctionsecond-generationdigital traffic allows for detection and correction,
giving clear voice reception Channel accesssecond-generation systems allow
channels to be dynamically shared by a number ofusers
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Time Division Multiple Access
Definition - TDMA is an assigned frequency
band shared among a few users. However,
each user is allowed to transmit in
predetermined time slots. Hence,channelization of users in the same band is
achieved through separation in time.(Qualcomm, 1997)
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TDMA
Time Division Multiple Access
F
requency
Time
Chan A
Chan B
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Mobile Wireless TDMA Design
Considerations Number of logical channels (number of time slots in
TDMA frame): 8
Maximum cell radius (R): 35 km
Frequency: region around 900 MHz Maximum vehicle speed (V
m):250 km/hr
Bandwidth: Not to exceed 200 kHz (25 kHz perchannel)
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Paging & SMS
Evolution of Paging
Tone Boy, early 1960s
Tone-Voice, late 1960s
Digital Pagers, 1970s
Numeric Paging Systems
Alpha/Numeric Paging Systems
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Paging
Larger coverage area in each site
Signal, Numeric, Alpha-numeric
Marketed by coverage area. Features--Web messaging, modem
messaging
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Paging
Current Applications
Fax Forwarding
E-Mail Forwarding
Voice Mail Notification
Automated Problem Notification
Two-way Paging
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Wireless Local Loop
Wired technologies responding to need for reliable,high-speed access by residential, business, andgovernment subscribers
ISDN, xDSL, cable modems
Increasing interest shown in competing wirelesstechnologies for subscriber access
Wireless local loop (WLL)
Narrowband
offers a replacement for existing telephonyservices
Broadbandprovides high-speed two-way voice and dataservice
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WLL Configuration
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Advantages of WLL over Wired
Approach Costwireless systems are less expensive due to cost
of cable installation thats avoided
Installation timeWLL systems can be installed in a
small fraction of the time required for a new wiredsystem
Selective installationradio units installed for
subscribers who want service at a given time
With a wired system, cable is laid out in anticipation of
serving every subscriber in a given area
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Propagation Considerations for
WLL Most high-speed WLL schemes use millimeter wave
frequencies (10 GHz to about 300 GHz)
There are wide unused frequency bands available above 25
GHz At these high frequencies, wide channel bandwidths can be
used, providing high data rates
Small size transceivers and adaptive antenna arrays can be
used
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Propagation Considerations for
WLL Millimeter wave systems have some
undesirable propagation characteristics
Free space loss increases with the square of the
frequency; losses are much higher in millimeterwave range
Above 10 GHz, attenuation effects due to rainfalland atmospheric or gaseous absorption are large
Multipath losses can be quite high
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Atmospheric Absorption
Radio waves at frequencies above 10 GHz are
subject to molecular absorption
Peak of water vapor absorption at 22 GHz
Peak of oxygen absorption near 60 GHz
Favorable windows for communication:
From 28 GHz to 42 GHz
From 75 GHz to 95 GHz
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Effect of Rain
Attenuation due to rain
Presence of raindrops can severely degrade the reliabilityand performance of communication links
The effect of rain depends on drop shape, drop size, rain
rate, and frequency
Estimated attenuation due to rain:
A = attenuation (dB/km)
R = rain rate (mm/hr)
a and b depend on drop sizes and frequency
baRA
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Effects of Vegetation
Trees near subscriber sites can lead to multipath
fading
Multipath effects from the tree canopy are diffraction
and scattering Multipath effects highly variable due to wind
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Multipoint Distribution Service
(MDS) Multichannel multipoint distribution service (MMDS)
Also referred to as wireless cable
Used mainly by residential subscribers and small
businesses Local multipoint distribution service (LMDS)
Appeals to larger companies with greater bandwidth
demands
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Advantages of MMDS
MMDS signals have larger wavelengths andcan travel farther without losing significantpower
Equipment at lower frequencies is lessexpensive
MMDS signals don't get blocked as easily by
objects and are less susceptible to rainabsorption
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802.16 Standards Development
Use wireless links with microwave or millimeter
wave radios
Use licensed spectrum
Are metropolitan in scale
Provide public network service to fee-paying
customers
Use point-to-multipoint architecture with stationaryrooftop or tower-mounted antennas
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802.16 Standards Development
Provide efficient transport of heterogeneous traffic
supporting quality of service (QoS)
Use wireless links with microwave or millimeter
wave radios Are capable of broadband transmissions (>2 Mbps)
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IEEE 802.16.1 Services
Digital audio/video multicast
Digital telephony
ATM
Internet protocol
Bridged LAN
Back-haul Frame relay
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IEEE 802.16.3 Services
Voice transport
Data transport
Bridged LAN
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LAN Extension
Wireless LAN linked into a wired LAN onsame premises
Wired LAN
Backbone Support servers and stationary workstations
Wireless LAN
Stations in large open areas
Manufacturing plants, stock exchange trading floors,and warehouses
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Wireless LAN Applications
LAN Extension
Cross-building interconnect
Nomadic Access
Ad hoc networking
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Ad Hoc Networking
Temporary peer-to-peer network set up to meet
immediate need
Example:
Group of employees with laptops convene for a
meeting; employees link computers in a temporary
network for duration of meeting
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Wireless LAN Requirements
Throughput
Number of nodes
Connection to backbone LAN
Service area Battery power consumption
Transmission robustness and security
Collocated network operation
License-free operation
Handoff/roaming
Dynamic configuration
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Sensor Networks
Specialized wireless networks to gather data from a specific system,usually no mobility of sensor nodes
APPLICATIONS:
Military, Environmental, Health, Home, Space Exploration,Chemical Processing
SENSOR TYPES:
Seismic, Low Sampling Rate Magnetic, Thermal, Visual,
Infrared, Acoustic, Radar
SENSOR TASKS:
Temperature, Humidity, Vehicular Movement, LightningCondition, Pressure, Soil Makeup, Noise Levels, Presence or
Absence of Certain Types of Objects, Mechanical StressLevels on Attached Objects, Current Characteristics (Speed,Direction, Size) of an Object .
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Example Sensor Network
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Applications of WPAN