Chapter 6 Wireless and Mobile Networks A 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 Computer Networking A Top Down Approach 5th edition Jim Kurose Keith Ross Addison Wesley April 2009 Thanks and enjoy JFK KWR All material copyright 1996 2009 J F Kurose and K W Ross All Rights Reserved 6 Wireless and Mobile Networks 6 1 Chapter 6 Wireless and Mobile Networks Background 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 challenges wireless communication over wireless link mobility handling the mobile user who changes point of attachment to network 6 Wireless and Mobile Networks 6 2 Chapter 6 outline 6 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 protocols 6 9 Summary 6 Wireless and Mobile Networks 6 3 Elements of a wireless network wireless hosts laptop PDA IP phone run applications may be stationary non mobile or mobile network infrastructure wireless does not always mean mobility 6 Wireless and Mobile Networks 6 4 Elements of a wireless network network infrastructure base 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 points 6 Wireless and Mobile Networks 6 5 Elements of a wireless network network infrastructure wireless 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 distance 6 Wireless and Mobile Networks 6 6 Characteristics of selected wireless link standards Data rate Mbps 200 54 5 11 802 11n 802 11a g 802 11b 4 1 802 11a g point to point data 802 16 WiMAX UMTS WCDMA HSPDA CDMA2000 1xEVDO 3G cellular enhanced 802 15 384 3G UMTS WCDMA CDMA2000 056 2G IS 95 CDMA GSM Indoor Outdoor 10 30m 50 200m Mid range outdoor Long range outdoor 200m 4 Km 5Km 20 Km 6 Wireless and Mobile Networks 6 7 Elements of a wireless network network infrastructure infrastructure mode base station connects mobiles into wired network handoff mobile changes base station providing connection into wired network 6 Wireless and Mobile Networks 6 8 Elements of a wireless network ad hoc mode no base stations nodes can only transmit to other nodes within link coverage nodes organize themselves into a network route among themselves 6 Wireless and Mobile Networks 6 9 Wireless network taxonomy single hop infrastructure e g APs no infrastructure host connects to base station WiFi WiMAX cellular which connects to larger Internet no base station no connection to larger Internet Bluetooth ad hoc nets multiple hops host may have to relay through several wireless nodes to connect to larger Internet mesh net no base station no connection to larger Internet May have to relay to reach other a given wireless node MANET VANET 6 Wireless and Mobile Networks 6 10 Wireless 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 ad destination at slightly different times make communication across even a point to point wireless link much more difficult 6 Wireless and Mobile Networks 6 11 Wireless Link Characteristics 2 SNR signal to noise ratio larger SNR easier to extract signal from noise a good thing SNR versus BER tradeoffs given physical layer increase power increase SNR decrease BER given SNR choose physical layer that meets BER requirement giving highest thruput 10 1 SNR may change with mobility dynamically adapt physical layer modulation technique rate 10 2 BER 10 3 10 4 10 5 10 6 10 7 10 20 30 40 SNR dB QAM256 8 Mbps QAM16 4 Mbps BPSK 1 Mbps 6 Wireless and Mobile Networks 6 12 Wireless network characteristics Multiple wireless senders and receivers create additional problems beyond multiple access B A C C A B Hidden terminal problem B A hear each other B C hear each other A C can not hear each other means A C unaware of their interference at B C s signal strength A s signal strength space Signal attenuation B A hear each other B C hear each other A C can not hear each other interfering at B 6 Wireless and Mobile Networks 6 13 Code 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 data encoded 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 Networks 6 14 CDMA Encode Decode sender data bits code Zi m di cm d0 1 1 1 1 1 1 1 1 1 1 1 1 slot 1 1 slot 1 channel output 1 1 1 1 1 1 1 1 1 d1 1 1 1 1 channel output Zi m 1 1 1 slot 0 1 1 1 1 1 slot 0 channel output M Di Zi m cm m 1 received input code receiver 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 slot 1 M 1 1 1 1 1 1 slot 0 d0 1 d1 1 slot 1 channel output slot 0 channel output 6 Wireless and Mobile Networks 6 15 CDMA two sender interference 6 Wireless and Mobile Networks 6 16 Chapter 6 outline 6 1 Introduction Wireless 6 2 Wireless links characteristics CDMA 6 3 IEEE 802 11 wireless LANs wi fi 6 4 cellular Internet access