6: Wireless and Mobile Networks6-1Chapter 6Wireless and Mobile NetworksA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWRAll material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights ReservedComputer Networking: A Top Down Approach 4thedition. Jim Kurose, Keith RossAddison-Wesley, July 2007.6: Wireless and Mobile Networks6-2Chapter 6: Wireless and Mobile NetworksBackground: # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access two important (but different) challengeswireless:communication over wireless linkmobility:handling the mobile user who changes point of attachment to network6: Wireless and Mobile Networks6-3Chapter 6 outline6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM)Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-4Elements of a wireless networknetwork infrastructurewireless hosts laptop, PDA, IP phone run applications may be stationary (non-mobile) or mobile wireless does notalways mean mobility6: Wireless and Mobile Networks6-5Elements of a wireless networknetwork infrastructurebase station typically connected to wired network relay - responsible for sending packets between wired network and wireless host(s) in its “area” e.g., cell towers, 802.11 access points6: Wireless and Mobile Networks6-6Elements of a wireless networknetwork infrastructurewireless link typically used to connect mobile(s) to base station also used as backbone link multiple access protocol coordinates link access various data rates, transmission distance6: Wireless and Mobile Networks6-7Characteristics of selected wireless link standardsIndoor10-30mOutdoor50-200mMid-rangeoutdoor200m – 4 KmLong-rangeoutdoor5Km – 20 Km.056.384145-1154IS-95, CDMA, GSM2GUMTS/WCDMA, CDMA20003G802.15802.11b802.11a,gUMTS/WCDMA-HSPDA, CDMA2000-1xEVDO3G cellularenhanced802.16 (WiMAX)802.11a,g point-to-point200802.11nData rate (Mbps)data6: Wireless and Mobile Networks6-8Wireless Network Modes: Infrastructurenetwork infrastructureinfrastructure mode base station connects mobiles into wired network handoff: mobile changes base station providing connection into wired network6: Wireless and Mobile Networks6-9Wireless Network Modes: Ad Hoc Modead hoc mode no base stations nodes can only transmit to other nodes within link coverage nodes organize themselves into a network: route among themselves6: Wireless and Mobile Networks6-10Wireless network taxonomysingle hopmultiple hopsinfrastructure(e.g., APs)noinfrastructurehost connects to base station (WiFi,WiMAX, cellular) which connects to larger Internetno base station, noconnection to larger Internet (Bluetooth, ad hoc nets)host may have torelay through severalwireless nodes to connect to larger Internet: mesh netno base station, noconnection to larger Internet. May have torelay to reach other a given wireless nodeMANET, VANET6: Wireless and Mobile Networks6-11Wireless Link Characteristics (1)Differences from wired link …. decreased signal strength: radio signal attenuates as it propagates through matter (path loss) interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well multipath propagation: radio signal reflects off objects ground, arriving at destination at slightly different times…. make communication across (even a point to point) wireless link much more “difficult”SNR and BER Signal-to-Noise Ratio Larger SNR – easier to extract signal from noise (a “good thing”) Bit Error Rate Probability that a transmitted bit is received in error at the receiver Power vs BER• Increasing transmission power can lower the BER• Problems with increasing the power– Requires more energy– Transmissions are more likely to interfere with other senders6: Wireless and Mobile Networks6-126: Wireless and Mobile Networks6-13Wireless Link Characteristics (2)SNR versus BER tradeoffsgiven physical layer:the higher the SNR the lower the BERgiven SNR:choose physical layer that meets BER requirement, giving highest throughput• SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) 10203040QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)SNR(dB)BER10-110-210-310-510-610-710-46: Wireless and Mobile Networks6-14Wireless network characteristicsMultiple wireless senders and receivers create additional problems (beyond multiple access):ABCHidden terminal problem B, A hear each other B, C hear each other A, C can not hear each othermeans A, C unaware of their interference at BABCA’s signalstrengthspaceC’s signalstrengthSignal attenuation: B, A hear each other B, C hear each other A, C can not hear each other interfering at B6: Wireless and Mobile Networks6-15Code Division Multiple Access (CDMA) used in several wireless broadcast channels (cellular, satellite, etc) standards unique “code” assigned to each user; i.e., code set partitioning all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode dataencoded signal= (original data) X (chipping sequence)decoding:inner-product of encoded signal and chipping sequence allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)6: Wireless and Mobile
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