Chapter 6 Wireless and Mobile Networks

1 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). Computer They're in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. Networking: A Top They obviously represent a lot of work on our part. In return for use, we only ask the following: Down Approach If you use these slides ( , in a class) that you mention their source (after all, we'd like people to use our book!). 6th edition If you post any slides on a www site, that you note that they are adapted Jim Kurose, Keith Ross from (or perhaps identical to) our slides, and note our copyright of this material.

2 Addison-Wesley March 2012. Thanks and enjoy! JFK/KWR. All material copyright 1996-2012. Kurose and Ross, All Rights Reserved Wireless , Mobile Networks 6-1. Ch. 6: Wireless and Mobile Networks Background: # Wireless ( Mobile ) phone subscribers now exceeds #. wired phone subscribers (5-to-1)! # Wireless Internet-connected devices equals #. wireline Internet-connected devices laptops, Internet-enabled phones 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 Wireless , Mobile Networks 6-2. Chapter 6 outline Introduction Mobility Wireless Principles: addressing and routing to Mobile users Wireless links, characteristics Mobile IP.

3 CDMA Handling mobility in IEEE Wireless cellular Networks LANs ( Wi-Fi ) Mobility and higher-layer Cellular Internet Access protocols architecture standards ( , GSM) Summary Wireless , Mobile Networks 6-3. Elements of a Wireless network network infrastructure Wireless , Mobile Networks 6-4. Elements of a Wireless network Wireless hosts laptop, smartphone run applications may be stationary (non- Mobile ) or Mobile network infrastructure Wireless does not always mean mobility Wireless , Mobile Networks 6-5. Elements of a Wireless network base station typically connected to wired network relay - responsible for sending packets between network wired network and infrastructure Wireless host(s) in its area.

4 , cell towers, access points Wireless , Mobile Networks 6-6. Elements of a Wireless network Wireless link typically used to connect Mobile (s) to base station also used as backbone link network multiple access protocol infrastructure coordinates link access various data rates, transmission distance Wireless , Mobile Networks 6-7. Characteristics of selected Wireless links 200 54 ,g ,g point-to-point Data rate (Mbps). 5-11 4G: LTWE WIMAX. 4 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO. 1 .384 : UMTS/WCDMA, CDMA2000..056 2G: IS-95, CDMA, GSM. Indoor Outdoor Mid-range Long-range 10-30m 50-200m outdoor outdoor 200m 4 Km 5Km 20 Km Wireless , Mobile Networks 6-8. Elements of a Wireless network infrastructure mode base station connects mobiles into wired network handoff: Mobile changes network base station providing infrastructure connection into wired network Wireless , Mobile Networks 6-9.

5 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 Wireless , Mobile Networks 6-10. Wireless network taxonomy single hop multiple hops host connects to host may have to infrastructure base station (WiFi, relay through several WiMAX, cellular) Wireless nodes to ( , APs). which connects to connect to larger larger Internet Internet: mesh net no base station, no connection to larger no no base station, no Internet. May have to infrastructure connection to larger relay to reach other Internet (Bluetooth, a given Wireless node ad hoc nets). MANET,VANET. Wireless , Mobile Networks 6-11.

6 Chapter 6 outline Introduction Mobility Wireless Principles: addressing and routing to Mobile users Wireless links, characteristics Mobile IP. CDMA Handling mobility in IEEE Wireless cellular Networks LANs ( Wi-Fi ) Mobility and higher-layer Cellular Internet Access protocols architecture standards ( , GSM) Summary Wireless , Mobile Networks 6-12. 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 ( , GHz) shared by other devices ( , phone); devices (motors) interfere as well multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times.

7 Make communication across (even a point to point). Wireless link much more difficult . Wireless , Mobile Networks 6-13. Wireless Link Characteristics (2). SNR: signal-to-noise ratio 10-1. larger SNR easier to 10-2. extract signal from noise (a 10-3. good thing ). BER. 10-4. SNR versus BER tradeoffs 10-5. given physical layer: increase power -> increase SNR- 10-6. >decrease BER. 10-7. given SNR: choose physical layer 10 20 30 40. that meets BER requirement, SNR(dB). giving highest thruput QAM256 (8 Mbps). SNR may change with QAM16 (4 Mbps). mobility: dynamically adapt physical layer (modulation BPSK (1 Mbps). technique, rate). Wireless , Mobile Networks 6-14. Wireless network characteristics Multiple Wireless senders and receivers create additional problems (beyond multiple access): A B C.

8 C. A's signal C's signal B strength strength A. 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 , Mobile Networks 6-15. Code Division Multiple Access (CDMA). unique code assigned to each user; , code set partitioning all users share same frequency, but each user has own chipping sequence ( , code) to encode data allows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal ). encoded signal = (original data) X (chipping sequence).

9 Decoding: inner-product of encoded signal and chipping sequence Wireless , Mobile Networks 6-16. CDMA encode/decode channel output Zi,m Zi,m= data d0 = 1. 1 1 1 1 1 1 1 1. d1 = -1. bits -1 -1 -1 -1 -1 -1 -1 -1. sender 1 1 1 1 1 1 1 1 slot 1 slot 0. code channel channel -1 -1 -1 -1 -1 -1 -1 -1. output output slot 1 slot 0. M. Di = S Zi, m=1. M. received 1 1 1 1 1 1 1 1. d0 = 1. -1 -1 -1 -1 -1 -1 -1 -1. input d1 = -1. 1 1 1 1 1 1 1 1 slot 1 slot 0. code channel channel -1 -1 -1 -1 -1 -1 -1 -1. receiver output output slot 1 slot 0. Wireless , Mobile Networks 6-17. CDMA: two-sender interference channel sums together transmissions by sender 1. and 2. Sender 1. Sender 2. using same code as sender 1, receiver recovers sender 1's original data from summed channel data!

10 Wireless , Mobile Networks 6-18. Chapter 6 outline Introduction Mobility Wireless Principles: addressing and routing to Mobile users Wireless links, characteristics Mobile IP. CDMA Handling mobility in IEEE Wireless cellular Networks LANs ( Wi-Fi ) Mobility and higher-layer Cellular Internet Access protocols architecture standards ( , GSM) Summary Wireless , Mobile Networks 6-19. IEEE Wireless LAN. 5-6 GHz range GHz unlicensed spectrum up to 54 Mbps up to 11 Mbps direct sequence spread spectrum GHz range (DSSS) in physical layer up to 54 Mbps all hosts use same chipping : multiple antennae code GHz range up to 200 Mbps all use CSMA/CA for multiple access all have base-station and ad-hoc network versions Wireless , Mobile Networks 6-20.