CPET 565 Mobile Computing Systems Lecture 2 Introduction to Wireless Communication and Networking Hongli Luo Indiana University-Purdue University Fort.

CPET 565 Mobile Computing SystemsCPET 565 Mobile Computing Systems

Lecture 2Lecture 2

Introduction to Wireless Communication Introduction to Wireless Communication and Networkingand Networking

Hongli Luo Hongli Luo Indiana University-Purdue University Fort WayneIndiana University-Purdue University Fort Wayne

Wireless NetworkingWireless Networking WAN : Wide Area NetworkWAN : Wide Area Network MAN: Metro Area NetworkMAN: Metro Area Network LAN: Local Area NetworkLAN: Local Area Network PAN: Personal Area NetworkPAN: Personal Area Network

Wireless Networking TechnologiesWireless Networking Technologies

Satellite (WAN)Satellite (WAN) Microwave (MAN)Microwave (MAN) WiMax - Broadband Wireless (MAN)WiMax - Broadband Wireless (MAN)

• 802.16 standard802.16 standard Cellular (WAN)Cellular (WAN) Wireless LANs (WLAN) – Wi-FiWireless LANs (WLAN) – Wi-Fi

• 802.11 standards802.11 standards Bluetooth (Wireless PAN)Bluetooth (Wireless PAN) IrDA (Infrared Data Association)IrDA (Infrared Data Association)

• Wireless point-to-point PANWireless point-to-point PAN RFIDRFID Sensor NetworkSensor Network

• 802.15.4 Standard802.15.4 Standard• ZigBee – a protocol for sensor networkZigBee – a protocol for sensor network

Wireless NetworksWireless Networks

IEEE 802.11 or WiFiIEEE 802.11 or WiFi Wireless LANs – up to 100 metersWireless LANs – up to 100 meters

IEEE 802.15IEEE 802.15 Bluetooth technology over short distanceBluetooth technology over short distance

IEEE 802.16 or WiMaxIEEE 802.16 or WiMax WiMax – World Interoperability for Microwave AccessWiMax – World Interoperability for Microwave Access Provide wireless broadband service over longer distanceProvide wireless broadband service over longer distance Aimed at support mobility at speeds at 70-80 miles per Aimed at support mobility at speeds at 70-80 miles per

hourhour Wireless WANsWireless WANs

Cellular telephone networksCellular telephone networks Satellite networksSatellite networks

Characteristics of selected wireless link Characteristics of selected wireless link standardsstandards

Indoor10-30m

Outdoor50-200m

Mid-rangeoutdoor

200m – 4 Km

Long-rangeoutdoor

5Km – 20 Km

.056

.384

1

4

5-11

54

IS-95, CDMA, GSM 2G

UMTS/WCDMA, CDMA2000 3G

802.15

802.11b

802.11a,g

UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellularenhanced

802.16 (WiMAX)

802.11a,g point-to-point

200 802.11n

Dat

a ra

te (

Mbp

s)

data

From Figure 7.17 of Data Communications and Networking by Forouzan, 4th

Electromagnetic spectrum for Electromagnetic spectrum for wireless communicationwireless communication

Figure 14.14 Industrial, scientific, and medical (ISM) band


Wireless: ProblemsWireless: Problems Typically much slower than wired networksTypically much slower than wired networks

• ““State of the art” wireless LAN: 54Mb/secState of the art” wireless LAN: 54Mb/sec• Wired LAN: 10000Mb/sec+Wired LAN: 10000Mb/sec+

Higher transmission bit error rates (BER)Higher transmission bit error rates (BER) Uncontrolled populationUncontrolled population Difficult to ensure Quality of Service (QoS) Difficult to ensure Quality of Service (QoS) Asymmetric bandwidthAsymmetric bandwidth Limited communication bandwidth Limited communication bandwidth

aggravates the problem of limited battery aggravates the problem of limited battery lifelife

SatelliteSatellite Altitude of satellites is classified asAltitude of satellites is classified as

• GEO, MEO, LEOGEO, MEO, LEO Used for TV broadcasting, telephone, Used for TV broadcasting, telephone,

internet accessinternet access GEO (Geosynchronous/Geostationary)GEO (Geosynchronous/Geostationary)

• Remains "stationary" relative to equatorRemains "stationary" relative to equator• Deployed at around 36,000 km above the earthDeployed at around 36,000 km above the earth• Need only 3 to cover earthNeed only 3 to cover earth• High latency (1/4 sec or so round trip)High latency (1/4 sec or so round trip)• Need high-power transmitter to reach satelliteNeed high-power transmitter to reach satellite• TV programTV program

Satellite (2)Satellite (2) LEO (Low Earth Orbit)LEO (Low Earth Orbit)

• Much lower orbits—less than 1000 kmMuch lower orbits—less than 1000 km• Must have handoff mechanism from one satellite Must have handoff mechanism from one satellite

to anotherto another don't appear stationary to earthbound base stationsdon't appear stationary to earthbound base stations

• Lower power transmitter than GEOLower power transmitter than GEO• Lower latency, but needs handoff delayLower latency, but needs handoff delay

MEO (Middle Earth Orbit)MEO (Middle Earth Orbit)• ~10,000 km, between LEO and GEO~10,000 km, between LEO and GEO• Application: GPS (Global Positioning System)Application: GPS (Global Positioning System)

Satellite: DirecPC/DirecWAYSatellite: DirecPC/DirecWAY

Now as HughesNet,Now as HughesNet, Provides satellite broadband Internet Provides satellite broadband Internet

accessaccess ~400Kb/sec downlink from GEO~400Kb/sec downlink from GEO Previously, only upload link with a dial-Previously, only upload link with a dial-

up modem connection, but now 2-wayup modem connection, but now 2-way Dish must see the sky (typical of Dish must see the sky (typical of

satellite)satellite) HUGE latency compared to DSL or HUGE latency compared to DSL or

cable modemscable modems

MicrowaveMicrowave

Common type of antenna – parabolic dishCommon type of antenna – parabolic dish Range: 20 miles or more, typically lessRange: 20 miles or more, typically less To achieve long-distance transmission, a To achieve long-distance transmission, a

series of microwave relay towers is used.series of microwave relay towers is used. Line of sight Line of sight onlyonly Rain causes problems, because rain Rain causes problems, because rain

absorbs microwave energyabsorbs microwave energy Bandwidth: 12 Mbps ~ 200 MbpsBandwidth: 12 Mbps ~ 200 Mbps Used for voice and television transmission, Used for voice and television transmission,

or short point-to-point linksor short point-to-point links

Cellular Phone NetworkCellular Phone Network Mobile Cellular Phone Communication Mobile Cellular Phone Communication

InfrastructuresInfrastructures• 1G1G• 2G2G• 2.5G2.5G• 3G3G

Cellular Phone SystemCellular Phone System

Base Station Mobile

Station

Mobile Switching

Center

Public Switched

Telephone Network

Base Station

Cell Phone

List of Mobile Network Operators, List of Mobile Network Operators, http://en.wikipedia.org/wiki/List_of_mobile_network_operators

Mobile Network OperatorsMobile Network Operators

T-Mobile (Germany)T-Mobile (Germany)• GSM, GPRS, EDGE, UMTS, HSDPA (High GSM, GPRS, EDGE, UMTS, HSDPA (High

Speed Downlink Packet Access)Speed Downlink Packet Access) Cingular (U.S.)Cingular (U.S.)

• GSM, GPRS, EDGE, UMTS, HSDPA (TDMA)GSM, GPRS, EDGE, UMTS, HSDPA (TDMA) Verizon (U.S.)Verizon (U.S.)

• CDMA, CDMA2000 1x, EV-DO (Evolution-CDMA, CDMA2000 1x, EV-DO (Evolution-Data Optimized data standard)Data Optimized data standard)

Sprint/Nextel (U.S.)Sprint/Nextel (U.S.)• CDMA, CDMA2000 1x, EV-DO, iDEN CDMA, CDMA2000 1x, EV-DO, iDEN

(Integrated Digital Enhanced Network)(Integrated Digital Enhanced Network)

Mobile Communication InfrastructuresMobile Communication Infrastructures Mobile Communication InfrastructuresMobile Communication Infrastructures

• 1G Analog FM1G Analog FM• 2G TDMA-FDMA/ CDMA (Code Division Multiple 2G TDMA-FDMA/ CDMA (Code Division Multiple

Access)Access)• 2.5 G – extend 2G system by adding packet-switched 2.5 G – extend 2G system by adding packet-switched

connectionconnection GPRS (General Packet Radio Service; for data packet GPRS (General Packet Radio Service; for data packet

service on GSM network) service on GSM network) EDGE (Enhanced Data GSM Evolution, up to 384 Kbps) - a EDGE (Enhanced Data GSM Evolution, up to 384 Kbps) - a

transition to 3G by Cingular that used TDMA for 2Gtransition to 3G by Cingular that used TDMA for 2G Support WAP, search, directory services, etcSupport WAP, search, directory services, etc

• 3G3G

The Mobile Telephone SystemThe Mobile Telephone System 1 1 G Mobile PhoneG Mobile Phone

• Analog voiceAnalog voice 2 Generation Mobile Phone2 Generation Mobile Phone 2.5 G2.5 G 3 G3 G Reference: Wikepedia, the free encyclopedia,Reference: Wikepedia, the free encyclopedia,

http://en.wikipedia.org/wiki/Digital_AMPShttp://en.wikipedia.org/wiki/Digital_AMPS

11stst Generation Cellular Phone System Generation Cellular Phone System

Advanced Mobile Phone Service (AMPS)Advanced Mobile Phone Service (AMPS)• Invented by Bells Labs and first installed in the U.S. in 1982Invented by Bells Labs and first installed in the U.S. in 1982• Analog FDMA (Frequency Division Multiple Access)Analog FDMA (Frequency Division Multiple Access)• ISM 800-MHz bandISM 800-MHz band

Base Station Base Station → Mobile Station: forward communication → Mobile Station: forward communication channels channels (824-849 MHz: 25 MHz band)(824-849 MHz: 25 MHz band)

Base Station Base Station ← Mobile Station: reverse communication ← Mobile Station: reverse communication channels channels (869-894 MHz: 25 MHz band)(869-894 MHz: 25 MHz band)

Voice channel – Frequency modulation (30 kHz)Voice channel – Frequency modulation (30 kHz) Control Channels - FSK (Frequency Shift Keying) – 10 kbps/30 kHz Control Channels - FSK (Frequency Shift Keying) – 10 kbps/30 kHz

signalsignal• No of ChannelsNo of Channels

832 channels: 25 MHz / 30 kHz, can be shared by two providers832 channels: 25 MHz / 30 kHz, can be shared by two providers Each provider: 416 channels in eachEach provider: 416 channels in each cell , 21 channels for control, 395 cell , 21 channels for control, 395

channels for voicechannels for voice Frequency Reuse FactorFrequency Reuse Factor

• Each cell uses some set of frequencies not used by any of its neighborsEach cell uses some set of frequencies not used by any of its neighbors• Reuse factor 7Reuse factor 7

Cellular bands for AMPS


AMPS reverse communication band


Frequency Reuse Factor 4Frequency Reuse Factor 4

1

2

3

4

1

2

3

4

1

2

3

4

Frequency Reuse Factor 7Frequency Reuse Factor 7

6

7

5

1

2

3

4

6

7

5

1

2

3

4

6

7

5

1

2

3

4

22ndnd Generation Cellular Telephone System Generation Cellular Telephone System D-AMPS (Digital AMPS)D-AMPS (Digital AMPS)

• IS-136IS-136• TDMA-FDMATDMA-FDMA

GSM (Global System for Mobile GSM (Global System for Mobile Communication)Communication)• TDMA-FDMATDMA-FDMA

IS-95 CDMA (Code Division Multiple IS-95 CDMA (Code Division Multiple Access)Access)• CDMA-FDMACDMA-FDMA

Digital Advanced Mobile Telephone System Digital Advanced Mobile Telephone System (D-AMPS)(D-AMPS)

D-AMPS (Digital AMPS)D-AMPS (Digital AMPS)• Backward compatible with AMPS: FDMABackward compatible with AMPS: FDMA• First defined by IS-54 (Interim standard 54) and later First defined by IS-54 (Interim standard 54) and later

revised by IS-136revised by IS-136• TDMA (Time Division Multiple Acceess)/IS-136TDMA (Time Division Multiple Acceess)/IS-136

Added to each sub-bandAdded to each sub-band Triple the no. of channels Triple the no. of channels

• ISM 800 MHz bandISM 800 MHz band• 824-849 MHz range: Base station 824-849 MHz range: Base station → Cellular phone → Cellular phone

(forward channels)(forward channels)• 869-894 MHz range: Cellular phone →Base station 869-894 MHz range: Cellular phone →Base station

(reverse channels)(reverse channels)

D-AMPS D-AMPS (continue)(continue)

Voice Signal DigitizationVoice Signal Digitization• Digitizing: PCM (Pulse Code Modulation) and Digitizing: PCM (Pulse Code Modulation) and

compressioncompression• 3 kHz 3 kHz → PCM Digitized →→ PCM Digitized →7.95 kbps digital 7.95 kbps digital

voice channelvoice channel TDMATDMA

• 1 slot – 7.95 kbps1 slot – 7.95 kbps• 3 slots: 48.6 kbps digital data: 3 x 7.95 kbps3 slots: 48.6 kbps digital data: 3 x 7.95 kbps• Combined using TDMACombined using TDMA• TDMA Frame [ 1 2 3 1 2 3]TDMA Frame [ 1 2 3 1 2 3]

D-AMPS D-AMPS (continue)(continue) Digitized Voice Signal TransmissionDigitized Voice Signal Transmission

• 25 frames per second25 frames per second• 1944 bits per frame1944 bits per frame• Each frame last 40 ms (1/25) and is divided into 6 Each frame last 40 ms (1/25) and is divided into 6

slots shared by three digital channels: TDMA [ 1 2 3 slots shared by three digital channels: TDMA [ 1 2 3 1 2 3]1 2 3]

• Each channel: 2 slotsEach channel: 2 slots• 324 bits per slot: 159 bits digitized voice, 64-bits 324 bits per slot: 159 bits digitized voice, 64-bits

control, 101-bits for error correctioncontrol, 101-bits for error correction QPSK Modulation (Quadrature Phase-Shift Keying) QPSK Modulation (Quadrature Phase-Shift Keying)

• 48.6 kbps 48.6 kbps → QPSK Modulation → 30 kHz analog → QPSK Modulation → 30 kHz analog signalsignal

FDMA FDMA • 25 MHz band, 30 kHz analog signal25 MHz band, 30 kHz analog signal

Reuse Factor 7Reuse Factor 7

D-AMPS


GSMGSM GSM (Global System for Mobile GSM (Global System for Mobile

Communication)Communication)• Digital mobile telephony system launched in Digital mobile telephony system launched in

Finland in 1991Finland in 1991• Use time division multiplexing (TDMA), Use time division multiplexing (TDMA),

Digitize and compress dataDigitize and compress data• 900 MHz or 1800 MHz frequency band900 MHz or 1800 MHz frequency band• SIM cards (Subscriber Identity Module)SIM cards (Subscriber Identity Module)• Capture 82.4% of all global mobile connectionCapture 82.4% of all global mobile connection• Widely used in Europe and Asia Widely used in Europe and Asia

GSM GSM (continue)(continue)

BandsBands• 2 bands, each band 25 MHz2 bands, each band 25 MHz• 124 Channels of 200 kHz separated by guard bands124 Channels of 200 kHz separated by guard bands

TransmissionTransmission• Voice channel Voice channel → Digitize + Compress → 13-kbps → Digitize + Compress → 13-kbps

digital signaldigital signal• 1 slot = 156.25 bit1 slot = 156.25 bit• 1 Frame (TDMA) = 8 slots; frame duration 120 ms1 Frame (TDMA) = 8 slots; frame duration 120 ms• A Multi-frame = 26 frames (TDMA) = 270.8 kbpsA Multi-frame = 26 frames (TDMA) = 270.8 kbps• 26 frames = 24 traffic frames + 2 control frames26 frames = 24 traffic frames + 2 control frames• 270.8 kbps → GMSK → 200 kHz signal (FDMA)270.8 kbps → GMSK → 200 kHz signal (FDMA)

Reuse Factor 3Reuse Factor 3

GSM


IS-95 CDMA IS-95 CDMA Based on CDMA (Code Division Multiple Access) and Based on CDMA (Code Division Multiple Access) and

DSSS (Direct Sequence Spread Spectrum) DSSS (Direct Sequence Spread Spectrum) Wireless Communications, Chapter Network Concepts Wireless Communications, Chapter Network Concepts

and Standards, IS95 CDMA Cellular Telephony, and Standards, IS95 CDMA Cellular Telephony, Springer, Springer, http://www.springerlink.com/content/g12q456568245556/http://www.springerlink.com/content/g12q456568245556/

Bands and ChannelsBands and Channels• Duplex using two bandsDuplex using two bands• ISM 800-MHz or ISM 900-MHzISM 800-MHz or ISM 900-MHz• 20 Channels of 1.228 MHz, guard bands20 Channels of 1.228 MHz, guard bands• 10 channels for each provider10 channels for each provider• Can be used in parallel with AMPSCan be used in parallel with AMPS• 1 IS-95 Channel = 41 AMPS channels (41 x 30 kHz = 1.23 MHz)1 IS-95 Channel = 41 AMPS channels (41 x 30 kHz = 1.23 MHz)

IS-95 CDMA IS-95 CDMA (cont.)(cont.) Base Channel SynchronizationBase Channel Synchronization

• Base stations use GPS (Global Positioning System)Base stations use GPS (Global Positioning System) Forward Transmission (base to mobile)Forward Transmission (base to mobile)

• 64 Digital Channels (3 kHz each)64 Digital Channels (3 kHz each)• Voice 3 kHz Voice 3 kHz → → 9.6 kbps 9.6 kbps → Error-correcting & repeating bits → → Error-correcting & repeating bits →

19.2 kbps19.2 kbps• Scrambling signal: ESN (Electronic Serial No of mobile station) + Scrambling signal: ESN (Electronic Serial No of mobile station) +

2242 42 pseudo random chip pseudo random chip → Decimator (1 out of 64 bits)→ Decimator (1 out of 64 bits)• 64 channels x 64 Walsh code → CDMA64 channels x 64 Walsh code → CDMA• 1.228 Mcps (Megachips per second) = 19.2 kbps * 64 cps1.228 Mcps (Megachips per second) = 19.2 kbps * 64 cps• QPSK → 1.228 MHzQPSK → 1.228 MHz• 25MHz Band: 20 Channels FDMA25MHz Band: 20 Channels FDMA• Channel 0: Pilot Channel, sends [1, 1, 1, 1, …] for bit syncChannel 0: Pilot Channel, sends [1, 1, 1, 1, …] for bit sync• Ch 1 – 7: paging, send messages to one or more mobile devicesCh 1 – 7: paging, send messages to one or more mobile devices• Ch 8–31 and 33-63: voice traffic channelsCh 8–31 and 33-63: voice traffic channels• Ch 32: give info about the system Ch 32: give info about the system

IS-95 CDMA IS-95 CDMA (cont.)(cont.)

Reverse Transmission (Mobile to Base)Reverse Transmission (Mobile to Base)• 3 kHz Voice 3 kHz Voice → Digitizer → 9.6 kbps → Error → Digitizer → 9.6 kbps → Error

correcting & repetition → 28.8 kbps → 6-symbol correcting & repetition → 28.8 kbps → 6-symbol chuck, 0-64, Symbol Modification → 307.2 kbps = chuck, 0-64, Symbol Modification → 307.2 kbps = (28.8/6) x 64(28.8/6) x 64

• ESN → Long Code Generator 42-bit → 1.228 McpsESN → Long Code Generator 42-bit → 1.228 Mcps• DSSS (Direct Sequence Spread Spectrum)DSSS (Direct Sequence Spread Spectrum)

94 Channels94 Channels 62 Traffic channels 62 Traffic channels 32 Base station access control channels32 Base station access control channels 1.28 Mcps 1.28 Mcps → QPSK → 1.228 MHz→ QPSK → 1.228 MHz

• FDMA 20 channel x 1.228 MHz = 25 MHzFDMA 20 channel x 1.228 MHz = 25 MHz

IS-95 CDMA IS-95 CDMA (cont.)(cont.)

Soft HandoffSoft Handoff• A mobile station can communicate with two A mobile station can communicate with two

base stations at the same timebase stations at the same time• A call is rarely dropped during the handoffA call is rarely dropped during the handoff

IS-95 forward transmission


IS-95 reverse transmission


3rd Generation Technologies 3rd Generation Technologies A Combination of TechnologiesA Combination of Technologies

• Audio and VideoAudio and Video• VoIPVoIP• Still & Moving ImagesStill & Moving Images• Digital DataDigital Data• UTMS (Unified Mobile Telephone Service)UTMS (Unified Mobile Telephone Service)

Enhanced multimedia: movie, images, music Enhanced multimedia: movie, images, music Internet SurfingInternet Surfing

Video telephony, Video conferencingVideo telephony, Video conferencing

• Always connected infrastructureAlways connected infrastructure

3rd Generation Technologies 3rd Generation Technologies IMT-2000 (Internet Mobile Communication 2000)IMT-2000 (Internet Mobile Communication 2000)

• Voice quality (public telephone network)Voice quality (public telephone network)• Data rateData rate

144 kbps for access in a moving vehicle144 kbps for access in a moving vehicle 384 kbps for access as the user walks384 kbps for access as the user walks 2 Mbps for stationary user (office or home)2 Mbps for stationary user (office or home)

• Support packet-switched and circuit-switched data Support packet-switched and circuit-switched data servicesservices

• 2 GHz band2 GHz band• 2 MHz Bandwidth2 MHz Bandwidth• Interface to InternetInterface to Internet

3rd Generation Technologies 3rd Generation Technologies WCDMA (wideband CDMA)WCDMA (wideband CDMA)

• Used by most GSM cellular providersUsed by most GSM cellular providers CDMA2000CDMA2000

• Code Division Multiple AccessCode Division Multiple Access• Pioneered by QualcommPioneered by Qualcomm• Used by most CDMA providersUsed by most CDMA providers• Used by Verizon Wireless and SprintUsed by Verizon Wireless and Sprint

Wireless LANsWireless LANs One example: IEEE 802.11 standardOne example: IEEE 802.11 standard CSMA/CA instead of CSMA/CD, as in EthernetCSMA/CA instead of CSMA/CD, as in Ethernet Ethernet: detect collision during transmissionEthernet: detect collision during transmission Wireless: impossible: can only hear own signal Wireless: impossible: can only hear own signal

during transmissionduring transmission Current speeds 1Mb/sec – 54Mb/secCurrent speeds 1Mb/sec – 54Mb/sec Access point / NIC prices have recently dropped Access point / NIC prices have recently dropped

substantiallysubstantially 802.11b: 2-11Mb/sec (we have this) in 2GHz 802.11b: 2-11Mb/sec (we have this) in 2GHz

rangerange 802.11a: 54Mb/sec in 5GHz range (incompatible 802.11a: 54Mb/sec in 5GHz range (incompatible

with 802.11b, very dependent on line of sight)with 802.11b, very dependent on line of sight) 802.11g: ~20Mb/sec, compatible with 802.11b802.11g: ~20Mb/sec, compatible with 802.11b

802.11 Details802.11 Details Medium-range wireless local area network technologyMedium-range wireless local area network technology 2.45GHz Industrial, Scientific, Medical (ISM) Band2.45GHz Industrial, Scientific, Medical (ISM) Band Old: 1Mb/sec , now: 2 - 54Mb/sec transmission speedsOld: 1Mb/sec , now: 2 - 54Mb/sec transmission speeds Older 1Mb/sec spec used Frequency Hopping Spread Older 1Mb/sec spec used Frequency Hopping Spread

Spectrum (FHSS)Spectrum (FHSS)• Units change frequency rapidly according to an agreed Units change frequency rapidly according to an agreed

channel hopping sequencechannel hopping sequence• Helps to reduce interferenceHelps to reduce interference

Higher data rates use Direct Sequence Spread Spectrum Higher data rates use Direct Sequence Spread Spectrum (DSSS) Radio(DSSS) Radio• Units broadcast a broad, redundant signal that is Units broadcast a broad, redundant signal that is

resistant to interferenceresistant to interference US: 11 distinct channels (partially overlapping)US: 11 distinct channels (partially overlapping) Three channels (1, 6, 11) do not overlap at allThree channels (1, 6, 11) do not overlap at all

802.11: Future802.11: Future

Revisions to standards for securityRevisions to standards for security 802.1X / 802.11i (later)802.1X / 802.11i (later) 802.11a: 54Mb/sec, 5GHz 802.11a: 54Mb/sec, 5GHz 802.11g: ~20Mb/sec, compatible w/ 802.11g: ~20Mb/sec, compatible w/

802.11b802.11b 802.11a has more non-overlapping 802.11a has more non-overlapping

channels than 802.11bchannels than 802.11b• 802.11b 3 non-overlapping channels802.11b 3 non-overlapping channels• 802.11a channels do not overlap802.11a channels do not overlap

CPET 565 Mobile Computing Systems Lecture 2 Introduction to Wireless Communication and Networking Hongli Luo Indiana University-Purdue University Fort.

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