Wireless network taxonomy single hop multiple hops host connects to host may have to infrastructure base station (WiFi, relay through several (e.g.APs) WiMAX,cellular) wireless nodes to which connects to connect to larger larger Internet Internet:mesh net no base station,no no base station,no connection to larger no Internet.May have to infrastructure connection to larger Internet(Bluetooth, relay to reach other ad hoc nets) a given wireless node MANET,VANET Wireless and Mobile Networks 7-11
Wireless network taxonomy single hop multiple hops 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) 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 Wireless and Mobile Networks 7-11
Chapter 7 outline 7.I Introduction Mobility Wireless 7.5 Principles:addressing and routing to mobile users 7.2 Wireless links, characteristics 7.6 Mobile IP ·CDMA 7.7 Handling mobility in 7.3 IEEE 802.I I wireless cellular networks LANs(“Wi-Fi") 7.8 Mobility and higher-layer 7.4 Cellular Internet Access protocols ·architecture standards(e.g.,3G,LTE) Wireless and Mobile Networks 7-12
Chapter 7 outline 7.1 Introduction Wireless 7.2 Wireless links, characteristics • CDMA 7.3 IEEE 802.11 wireless LANs (“Wi-Fi”) 7.4 Cellular Internet Access • architecture • standards (e.g., 3G, LTE) Mobility 7.5 Principles: addressing and routing to mobile users 7.6 Mobile IP 7.7 Handling mobility in cellular networks 7.8 Mobility and higher-layer protocols Wireless and Mobile Networks 7-12
Wireless Link Characteristics(1 important 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 Wireless and Mobile Networks 7-13
Wireless Link Characteristics (1) important 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” Wireless and Mobile Networks 7-13
Wireless Link Characteristics(2) SNR:signal-to-noise ratio 10-1 ·larger SNR-easier to 10-2 extract signal from noise(a good thing") 10-3 SNR versus BER tradeoffs 盘10 given physical layer:increase power -increase SNR- 10-5 >decrease BER 106 given SNR:choose physical layer that meets BER requirement, 10-7 giving highest thruput 10 20 30 40 SNR(dB) ·SNR may change with mobility:dynamically adapt 。 QAM256(8 Mbps) physical layer(modulation --·QAM16(4Mbps) technique,rate) —BPSK(1Mbps) Wireless and Mobile Networks 7-14
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 • SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) 10 20 30 40 QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) SNR(dB) BER 10-1 10-2 10-3 10-5 10-6 10-7 10-4 Wireless and Mobile Networks 7-14
Wireless network characteristics Multiple wireless senders and receivers create additional problems(beyond multiple access): A'ssignal C's signal strength strength Hidden terminal problem space ■B,A hear each other Signal attenuation: ■B,C hear each other ■B,A hear each other A,C can not hear each other ■B,C hear each other means A,C unaware of their A,C can not hear each other interference at B interfering at B Wireless and Mobile Networks 7-15
Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C 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 A B C A’s signal strength space C’s signal strength Signal attenuation: ▪ B, A hear each other ▪ B, C hear each other ▪ A, C can not hear each other interfering at B Wireless and Mobile Networks 7-15