wireless technology and network convergence 1224574383734501 8
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A Brief History
Wireless communications originated withthe demonstration by Tesla in 1893,followed by the invention of wirelesstelegraph by Marconi in 1896
Advances in wireless communicationshave led to radio, television, mobiletelephones, and communication satellites
Development of wireless networks: LAN,
MAN, and WAN Trend continues: Voice Data
Broadband Need to support mobility
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Trends
Revenue for wireless communicationindustry has surpassed that of wiredtelephony industry
Wireless applications span both local areaand wide area for: voice-oriented services, and
data-oriented services
Global cellular networks are providing veryconvenient communication infrastructure
Broadband wireless networks areevolving: Wireless LANs are very popular
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Licensed and Unlicensed Bands
Licensed: Cellular/PCS
Expensive (PCS bands in US were sold for around $20B)
Time consuming to deploy new applications rapidly at
low costs Unlicensed:
Industrial, Medical, and Scientific (ISM) Bands
Free, component costs are also low
New applications such as WLAN, Bluetooth are easily
developed With the increase in frequency and data rate, the
hardware cost increases, and the ability topenetrate walls also decreases
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Duplexing
Duplexing facilitates communications inboth directions simultaneously: basestation to mobile and mobile to basestation
Duplexing is done either using frequencyor time domain techniques: Frequency division duplexing (FDD)
Time division duplexing (TDD) FDD is suitable for radio communication
systems, whereas TDD is more suitable forfixed wireless systems
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Multiple Access Techniques
Frequency Division Multiple Access
Time Division Multiple Access
Spread Spectrum Multiple Access Space Division Multiple Access
Packet Radio
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Frequency Division Multiple Access(FDMA)
The frequency spectrum is divided intounique frequency bands or channels
These channels are assigned to users on
demand Multiple users cannot share a channel
Users are assigned a channel as a pair of
frequencies (forward and reversechannels)
FDMA requires tight RF filtering to reduceadjacent channel interference
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Channel-1
Channel-6
Channel-5
Channel-7
Channel-8
Channel-9
FDMA
TIME
FREQUENCY
Channel-2
Channel-3
Channel-6
Channel-4
Channel-5
Channel-7
Channel-8
Channel-9
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Time Division Multiple Access-TDMA
TDMA systems divides the radio spectruminto time slots, and in each time slot onlyone use is allowed to either transmit orreceive
Transmission for any user is non-continuous
In each TDMA frame, the preamblecontains the address and synchronization
information TDMA shares a single carrier frequency
with several users
TDMA could allocate varied number of
time slots per frame to different users
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TDMA
TIME
FREQUENC
Y
Channel-7
Channel-10
Channel-8
Channel-9
Channel-6
Channel-5
Channel-4
Channel-3
Channel-2
Channel-1
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Spread Spectrum Multiple Access(SSMA)
SSMA uses signals that have atransmission bandwidth several orders ofmagnitude greater than the minimumrequired RF bandwidth
SSMA provides immunity to multipathinterference and robust multiple accesscapability
SSMA is bandwidth efficient in multi-user
environment SSMA techniques:
Frequency hopped (FH) multiple access Direct sequence (DS) multiple access
Also known as code division multiple access (CDMA)
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FHMA
Carrier frequencies of individual users are variedin a pseudorandom fashion within a widebandchannel
Data of each user is broken into uniform size
bursts that are transmitted on different channelsat different time instants based on their pseudo-noise (PN) code sequence
In the FH receiver, a locally generated PN code isused to synchronize the receivers instantaneous
frequency with that of the transmitter FHMA provides inherent security, and guard
against erasures through error control coding andinterleaving
Use: Bluetooth and HomeRF
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CDMA The narrowband message signal is multiplied by a very
large bandwidth signal called spreading signal The spreading signal has a pseudo-noise code sequence
that has a chip rate which is orders of magnitudes greaterthan the data rates of the message
All users use the same carrier frequency and can transmitsimultaneously
Each use has its own pseudorandom codeword that isorthogonal to the others
The receivers need to know the codeword of thecorresponding sender
Power control is used to combat the near-far problem Near-far problem:
When many mobile users share the same channel, thestrongest received mobile signal will capture thedemodulator at a base station. Thus a nearby subscribercould overpower the base-station receiver by drowningout the signals of far away subscribers.
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CDMA Features
Many users of CDMA share the same frequency either TDD or FDD may be used
CDMA has soft capacity limit systemperformance is inversely proportional to the
number of users Multipath fading is reduced because of the signal
spread
Channel data rates are very high
Prone to self-jamming and near-far problem Self-jamming: when the spreading sequences ofdifferent users are not exactly orthogonal
Near-far problem occurs at a CDMA receiver if anundesired user has a high detected power
compared to the desired user
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Space Division Multiple Access(SDMA)
SDMA controls the radiated energy foreach user and serves different users byusing spot beam antennas
Different areas covered by antenna beammay be served by same or differentfrequencies
Reverse links present difficulty:
Transmitted power from each subscriber mustbe controlled to prevent any single user fromdriving up the interference level
Transmit power is limited by batteryconsumption at the subscriber unit
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Packet Radio
In Packet Radio (PR) access techniques,many subscribers attempt to access asingle channel in an uncoordinatedmanner
Collisions from simultaneoustransmissions from multiple transmittersare detected at the base station receiver,in which case an ACK or NACK signal isbroadcasted by the base station to alertthe user
PR subscribers use a contention techniqueto transmit on a common channel
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Carrier Sense Multiple AccessProtocols (CSMA)
In CSMA protocols, each terminal onthe network is able to monitor thestatus of the channel before
transmitting information
Variations:
1-persistent CSMA
non-persistent CSMA
p-persistent CSMA
CSMA/CD
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Convergence of Public Network
Carriers now use converged technologyprimarily in core, backbone portion of theirnetworks to carry customer traffic moreefficiently
Although carriers increasingly add IPequipment when they replace their voiceswitches, the majority of voice traffic isstill carried in circuit switched networks
A circuit is a physical path for thetransmission of voice, image or data.
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ITU defines circuit switching as :
The switching of circuits for the exclusiveuse of the connection for the duration of acall
When a person or modem dials a call, the
network sets up a path between the callerand the dialed party Circuit switching is an example of a
connection-oriented system
The path is maintained exclusively for theduration of the call and not shared This causes wasteful utilization of network
capacity
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Other Switching Technique-Message Switching
Message switching transfers arbitrarysized messages from a source to adestination using one or more
message switches Each switch stores the complete
message before forwarding it
Normally messages are stored foronly a short time, but they may bestored for days in some cases
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A message being sent using oneintermediate message switch.
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The telex network is an example of amessage switched network
Since the messages are stored in eachmessage switch, message switching is
suitable for the transfer of electronic mailand is used to send email to isolated partsof the world using connections providedby modems over the telephone network
Since there is no direct connectionbetween the sender and the recipient, it isnot possible to use message switching tologin to a remote computer
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Rationale for Convergence
The Internet Protocol (IP) does not have thislimitation The Internet is a connection-less packet-switched
network. Packets from other sources fill pauses in one
conversation Eg. when a call is on hold, network capacity is
used for other traffic Moreover, technical advances have improved the
quality of voice and video carried on packet
networks In addition, costs for routers, hard drives and
fiber optics have decreased The capability to deploy and maintain a single
network for voice, data and video
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As VoIP protocols becomeincreasingly standardised, custominterfaces between switches and
applications will increasingly becomeunnecessary
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Softswitches
Process calls (issue commands onsetting up and ending calls)
Communicate with billing systems
Acts as an overall network controlpoint
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Media Gateways
Switch calls and translate protocolsbetween different networks andbetween public network trunks such
as T-1 and T-3 trunks and IPnetworks
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Media Servers
Generate touch-tone
Play announcements
Generate voice over IP packets from
voice mail application Convert voice mail messages to
digital IP packet and vice versa
Record voice mail messages Generate ring tones, busy signals,
dial tone
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Application Servers
Contain complex applications
Eg.
unified messaging (capability to receivevoice mail, e-mail, and fax messages onpersonal computers)
Large audio conferencing systems
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Peer-to-Peer Services
P2P services operate in adecentralised mode withoutsoftswitches to control signaling and
communication Napster, Gnutella, KaZaA enable
sharing of free music over theInternet
Skype introduced P2P architecturefor VoIP without central servers
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Calling 911-VoIP vs Circuit switched
The Wireless Communication and Public SafetyAct (1999) establishes 911 as the emergencynumber throughout the US.
The first emergency number was 999 used inLondon
The act mandated all carriers to connect 911 callto appropriate local emergency dispatch centre
It also mandated FCC to develop a plan forwireless providers to transition to enhanced 911(E911)
Under E911, the agent who answer 911 calls isable to receive the callers phone number andlocation
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Mobile Services
Competition between mobile networkoperators, and the desire for morerobust networks have led to the
implementation of third generationdigital networks by major mobileoperators
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Evolution from 1G, 2G, 2.5G to 3G
The 1st G of cellular service usedanalog equipment in the early 1980s
The 1st service in US is AMPS
The 2nd G started in 1990s whencarriers upgrade their analog todigital networks to gain more
capacity These include GSM, CDMA, TDMA
and iDEN (Motorola)
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2.5 G
Provides transition to WCDMA Most GSM operators implemented GPRS
and EDGE before WCDMA for the followingreasons:
WCDMA equipment was not stable until 2004 Small, lightweight 3G handset were not widely
available prior to 2004 Installing GPRS and EDGE delayed the large
expenses to upgrade to WCDMA
Handset for GPRS and EDGE were readilyavailable
GPRS and EDGE operate on the samefrequencies as GSM
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3G
Transition from 2G CDMA TO 3GCDMA2000 is less costly and complex thantransition from GSM networks to WCDMA
The major incentive for upgarding is theincreased voice capacity as well as thedesire for a network capable of handlingadvanced application
Because it is easier to implement,CDMA2000 has more subscriberscompared to WCDMA
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CDMA2000 1xEV-DO (dataoptimised- high data rate)
Network providers already have the1st stage CDMA2000 can upgrade tohigher data speeds by adding
software and channel cards to theirbase stations for high data rate
HDR service is a data-onlyenhancement with higher downlinkspeeds
No capacity is gained for voice traffic
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WCDMA
Release FeaturesWCDMA(Release 4)
Enables operators to prioritisedata services per customer
subscriptionWCDMA(Release 5)
HSDPA (high speed downlinkpacket access)
IP voice and data
WCDMA(Release 6)
HASUPA (high speed uplinkpacket access)
Doubles the uplink speed
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MobileFi
802.20: IP Mobile Broadband Wireless Access
In 2002, the IEEE stated its intention to providemobility in vehicles such as trains traveling up to150mph or 250kmph, and to support higher data
rates and more users than currently available Flarion uses a form of orthogonal FDM (OFDM) in
equipment called FLASH-OFDM.
Flash is short for Fast, Low-latency Access withSeamless Handoff
FLASH-OFDM spreads signals over a widerfrequencies and at faster rate than OFDM
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Flarion service includes handoffs betweenWi-Fi and FLASH-OFDM networks so thatusers use Wi-Fi when it is availabale andFlarion when it is not
Flarion supports VoIP and able to prioritisetraffic It is not expected to be available until
2008
T-Mobile, Vodafone and TIME dotCOM (inMalaysia) are conducting trials of Flarionequipment
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Wi-Fi, Wireless broadband, SensorNetworks and PANs
Wi-Fi IEEE 802.11
Wireless broadband - WiMax
Zigbee and IEEE 802.15 PANs
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Evolution of Wireless LAN
Early experiences (1970-72): IBM, HP, Motorola Abandoned due to limited performance and
unavailability of frequency bands
Early challenges: Complexity and cost
Bandwidth Coverage Interference Frequency administration
Emergence of unlicensed bands
Release of Industrial, Scientific and Medical (ISM) bandsin 1985
Applications: military, home and enterprisenetworks, mobile networks, teetherless access
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Wi-Fi is based on 802.11 technology
It is originally intended tio provide wirelesscomputing for staffs within businesses andcommercial organisations
However, residential customers adopted Wi-Fifaster than enterprises because of its simplicity,fewer concerns about security and the benefit ofavoiding the expenses for cabling
Its advantage is low equipment cost and easierinstallation
Benefits were also immediately noticed forhealthcare, education, retailing and warehousing
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Logical link control
Point coordination function(PCF)
Distributed coordination function (DCF)
2.4-Ghz
frequency-hoppingspread
spectrum1Mbps2Mbps
2.4-Ghz
directsequence
spreadspectrum1Mbps2Mbps
Infrared
1Mbps2Mbps
5-Ghz
orthogonalFDM 6, 9.12. 18, 24,36, 48, 54
Mbps
2.4-Ghz
directsequence
spreadspectrum5.5 Mbps11 Mbps
Contention-free service
Contentionservice
MAClayer
IEEE 802.11 Protocol Architecture
IEEE 802.11 IEEE 802.11a IEEE 802.11b
802 11 hi h d ll
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802.11a higher speeds, smallercoverage, more channels
Wi-Fi is also sold to hotspot operators particularlyhotel, convention centres, cafes, airports
Hotspots offer higher-speed Internet access thanmost cellular networks data offering and costless to build than cellular base station
802.11 wireless standards are based on Ethernetprotocols
802.11a is the only 802.11 standard thatoperates at 5 GHz
The use of 5 GHz band avoids interference frommicrowave ovens, Bluetooth equipments andcordless phones that operate at 2.4 GHz
Disadvantage is the signal fade faster
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802.11b
When they were first available,802.11 equipments were equippedwith only 802.11b chips
Now most use b and g which aredesigned to interoperate
Because home broadband
connections are slower than 802.11networks, no advantage is gained
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802.11g
Support higher data rates than802.11b
Use 2.4 gHz bands
The higher speeds and capacity of gand a are required to support voiceover IP on WLANs
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802.11n
Backward compatibility with a, b andg
Improve coverage by overcoming a
certain amount of interference
Increase speeds and supports moreusers per access point
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Broadband wireless access
Wimax and universal mobile telecommunicationsystem time division duplex (UMTS TDD) may inthe future provide mobile wireless broadbandservice for pedestrian, people in moving vehiclesand within buildings
However, most current implementations are forless complex wireless service between fixedlocations or for wireless service with Internetaccess and portability within a service providers
coverage area Currently no portability is provided within
buildings (therefore, Wi-Fi is still needed)
Wimax is based on 802.16
WCDMA M difi d f Wi l
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WCDMA Modified for WirelessLocal Loop
SOMA Networks provide a packetized wirelesslocal loop service to replace broadband cable andDSL service
The service is designed for circuit-switched voice,fax and high-speed data
The equipments operate in the 1.9, 2.3 and 2.6GHz licensed frequency bands SOMA is used in developing countries where
cabling to residential or rural areas is rare SOMA modified 3G WCDMA to provide end-to-end
QOS and multimegabit data speed SOMA is not portable or mobile However, it is rolling out integrated Wi-Fi handset
for portable voice within home Jaring uses SOMA equipments
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Sensor Networks An emerging technology to monitor condition in
buildings, control manufacturing systems, etc Until recently, large-scale sensor networks are
expensive because sensors require wiredconnection to each other and the LAN
The new sensor network is able to send infowirelessly
2 topology can be deployed Full-mesh: each sensor is connected to every
other device
Partial-mesh: some nodes are connected to eachother, others only to the nodes they exchangethe info most
Based on 802.15.4 which is slow speed (20-250kbps), non line-of-sight (LOS)
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IEEE 802.15.4 and ZigBee
Home Applications
Internet connectivity, multi-PC connectivity,audio/video networking
[broadband, always-on, relatively expensive] Home automation, security, devicemanagement
[low-throughput, power-constraint, low-cost]
IEEE 802.11 and Bluetooth do not satisfythe requirements of the second set
Evolution of IEEE 802.15.4 and ZigBee in2000
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ZigBee
Based on 802.15.4 standard, developed byZigBee Alliance
Defined higher-level protocols that will operateover network using 802.15.4
ZigBee 1.0 was announced in Dec 2004 It is a lightweight routing protocol for mesh
network that adds security and additional meshnetworking function to 802.15.4
It has potential to control alarms, monitorelectricity, provide status from smoke detectors,thermostat, and hot water tanks in commercial orresidential buildings
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Protocol Stack
APPLICATIONS
APPLICATION FRAMEWORK
NETWORK/SECURITY LAYERS
MAC LAYER
PHY LAYER
User Defined
ZigBee Alliance
IEEE 802.15.4
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It can monitor windows to determineif they are closed or not
Its target application include remote
controls (now using infrared thatrequires LOS)
However, it receives competitionfrom companies providing alarmservices like ADT
Has potential for future use
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PANs Bluetooth- widely used (not discussed here) Ultra-Wideband (802.15.3a) Is high-speed, short range wireless tech that
works by transmitting low-power signals over awide range of frequencies
Does not require spectrum license It is designed not to interfere with conventional
radio It can penetrate walls and do not drain batteries
quickly
It is faster than Bluetooth and Wi-Fi Can be used to link electronics for home
entertainment network and asset tracking However, lack of uniform standard is holding its
sales
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RFID
A non-LOS wireless tech used to control,detect and tract objects
RFID system is made up of Interrogator readers
Transponder with integrated antenna on chips Active transponder has battery, larger in
size, more costly than passive one.However can be read at further distance
from reader Passive one has no battery, size of a 5cent coin, are woken up by magneticinduction from reader, also known as tag
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A middleware is required to reformatinformation gathered by readers to makeit compatible with database
RFID tags have electronic product codes(EPC)
Super RFID can be used for sensornetwork requires intelligent tags andreaders that record conditions beingmonitored and set off alarms if thethresholds are exceeded
Operates in low frequency (30-500KHz)- shorter range High frequency (850-950KHz/2.4-2.5GHz)
range up to 90 feet- may interfere with Bluetooth and Wi-Fi gear