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Overview of Wireless Networks

Overview of Wireless Networks. Anuj Puri. Outline. Projections of wireless growth Cellular Networks Wireless LANs and Bluetooth WAP Ad Hoc wireless networks. HUGE EXPECTATIONS AND INVESTMENT IN M-DATA. European UMTS spectrum auctions $ Billions. Millions of subscribers worldwide.

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Overview of Wireless Networks

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  1. Overview of Wireless Networks Anuj Puri

  2. Outline • Projections of wireless growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

  3. HUGE EXPECTATIONS AND INVESTMENT IN M-DATA • European UMTS spectrum auctions • $ Billions • Millions of subscribers worldwide • Mobile phone subscribers • TV households • PCs • U.K. licenses • German licenses • French licenses • UMTS license fee to date (not ex-haustive)

  4. SUCCESS OF I-MODE IN JAPAN • Number of i-mode subscribers • Thousands • i-Mode has already exceeded 12 million subs • Feb 22,1999 start • Aug 8 • Nov 18 • Dec 23 • May 31, • 2000

  5. Outline • Projections of wireless growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

  6. Cellular Networks • Mobile phones (internet access) • Cellular concept • Frequency reuse • Handoffs

  7. HLR (home location register) MSC (mobile switching center) VLR (visitor location register) BS (base station) Organization of Cellular Networks BS – modulation, antenna MSC – switching HLR – information (location) about “home” users VLR – information about visiting users

  8. How does a call get to the mobile ? • Suppose (510) 643 - 1111 is roaming in the (703) area code • Cell phone registers with the (703) MSC, which adds it to (703) VLR and informs the (510) HLR of the location of the cell phone • A call comes in for (510) 643 – 1111. Then (510) MSC queries its HLR, and directs the call to the (703) MSC • The (703) MSC forwards the call to the mobile

  9. BS A BS B Handoff HLR MSC VLR • Mobile is associated with BS A • It continuously monitors the signal strength from BS A, • and BS B • When the signal strength from BS B becomes stronger, • it associates with BS B

  10. Evolution of cellular industry First Generation Analog Voice AMPS Second Generation Digital Voice GSM, IS-95, IS-136, PDC Third Generation Packet data W-CDMA, EDGE, CDMA2000

  11. MULTIPLE MIGRATION PATHS ARE AVAILABLE • 2.5G • 3G • 3+G • 4G • 2G • PDC WCDMA • HSPDA • GSM • GPRS • OFDM • EDGE • Software radio • TDMA • (IS-136) • Array antennas • cdma2000 • MC-3X • CDMA (IS-95A/B) • CdmaOne • 1XRTT • 1XEVDO/HDR • 1 xtreme * Footnote Source: Sources

  12. 3G Networks GGSN SGSN BS A BS B SGSN Access Network Physical layer/ MAC IP based Core Network Routing/network handoff

  13. Mobile IP • Home Agent (HA) – keeps track of where the mobile is (similar to GGSN) • Foreign Agent (FA) – delivers packets to the mobile in the foreign network (similar to SGSN) • All packets for mobile arrive at HA which “tunnels” them to mobile’s FA • When mobile moves to a new location, it informs its HA of the new FA

  14. Outline • Projections of cellular growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

  15. Wireless LANs and Bluetooth • For indoor use or operation over small areas • Operates in ISM (Industrial Scientific and Medical) Band • Spread Spectrum techniques

  16. Main Components of 802.11 Roaming Medium Access Control Physical Layer

  17. Physical Layer • Operate in unlicensed bands • In U.S., 900 MHz, 2.4 GHz, 5.7GHz • Various restrictions on use • Spread Spectrum techniques • Direct Sequence Spread Spectrum • Frequency Hopping Spread Spectrum

  18. Medium Access Layer • Why not use Ethernet protocol ? • Sender cannot detect collision • senders power overwhelms other transmitters • carrier sense does not necessarily mean collision • Receiver has a better idea of whether a collision is happening • Hidden Terminal / Exposed Terminal Problem

  19. Hidden and Exposed Terminals A B C A and B can hear each other B and C can hear each other A and C can not hear each other Both A and C want to transmit to B (Hidden Terminal) B wants to transmit to A when C is transmitting to someone else (Exposed Terminal)

  20. MACA A wants to transmit to B - A sends a RTS to B - B replies with a CTS - A sends data to B RTS: contains the length of data CTS: also contains the length of data Everyone hearing RTS stays quiet for CTS Everyone hearing CTS remains quiet for RTS

  21. 802.11 MAC • CSMA/CA (Carrier Sense / Collision Avoidance) • Carrier Sense (check to see if someone is transmitting) • Collision Avoidance (RTS-CTS-Ack) • Acknowledgments at link level • Fragmentation and Reassembly

  22. Basic Scheme RTS Data CTS ACK Defer Access NAV (RTS) Back-off Window NAV (CTS)

  23. Some Terminology Distribution System Access Point Access Point Basic Service Set (BSS) Extended Service Set (ESS)

  24. Bluetooth • Master-slave architecture • Frequency hopping system • System design for cheap production

  25. Outline • Projections of cellular growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

  26. WAP (or the web for small wireless devices) • Why not use wired web infrastructure (html, http, tcp) ? • HTML too feature rich for small devices • TCP may have too much overhead for low bandwidth wireless links • WAP (Wireless Application Protocol) • An optimized stack for wireless applications • Mobile talks with the WAP gateway • WAP gateway talks with the web server on the internet

  27. WAP Architecture WAP HTTP/TCP WAP Gateway Internet Web Server

  28. WAP Stack WML, etc HTML WSP (Session Protocol) HTTP WTP (Transaction Protocol) TCP/UDP WDP (Datagram Protocol) Bearer Services SMS, CSD IP

  29. Gateway Internet Web Server Gateways/Proxies for Wireless Devices ? 2nd Generation: Low speed data, small displays  WAP 3rd Generation: Higher speed, IP address for each station  Proxy/ Gateway ?

  30. Outline • Projections of wireless growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

  31. Ad Hoc Wireless Networks • No base stations or infrastructure required • Multi-hop wireless networks • Each node can talk with a neighbor • Applications • Sensor networks • Intelligent control applications (i.e, IVHS)

  32. Ad Hoc Wireless Networks • MAC schemes • Addressing • Routing

  33. Geographical Routing Algorithm Geographical network • Assumptions: • Each node knows its own position and its neighbors’ position • Nodes don’t know the global topology • Destination address is a geographical position to which the packet is to be delivered

  34. A Simple Routing Algorithm Routing Decision: Route to the neighbor which is nearest to the packet destination Destination Source

  35. Problem with Simple Routing Wall Destination Source • Simple routing doesn’t always work • The Geographical routing algorithm is an extension of the • simple routing algorithm.

  36. Routing Tables Routing Table for Station n: • Routing Tables: • Routing tables contain some • additional entries beside neighbors (x,y) position Neighbor Position of n - Position of neighbor a a • Routing Algorithm: • Packet arrives for position p • at node n • Node n finds the position to • which p is closest and forwards • to the corresponding neighbor Position of neighbor b b a (12,4)

  37. Route Discovery • Packet gets “stuck” when a node does not have a neighbor to which it can forward the packet • When a packet is stuck, a Route Discovery is started to destination D • A path p = s(0) s(1)...s(k)is found to D • Entry [ position(D), s(i+1) ] is added to the routing table of s(i)

  38. Example Pos(A) = (1,1) Pos(B) = (2,2) Pos(C) = (3,1) Links: A ---- B B ---- C B Pos(C) Pos(B) --- Pos(C) Pos(A) A C A Pos(C) Pos(C) C Pos(C) --- Pos(A) --- Pos(B) B Pos(B) B • A gets a packet for Pos(C) • A forwards it to B because pos(B) is closer to pos(C) • B forwards it to C because pos(C) is closer to pos(C)

  39. Pos(D) C B Pos(D) Route Discovery Pos(D) Pos(C) --- Pos(A) = (1,1) Pos(B) = (2,2) Pos(C) = (3,1) Pos(D) = (2.5,0) Links: A ---- B B ---- C C ---- D B B Pos(B) --- Pos(D) Pos(B) Pos(D) Pos(D) D Pos(D) A Pos(A) C A C Pos(C) --- Pos(A) Pos(D) --- B Pos(B) D Pos(C) C Pos(D) • A gets a packet for Pos(D) • Packet gets stuck at A because Pos(A) is closest to Pos(D) • Initiate route discovery for D from A • Update the routing tables and forward the packet

  40. Theorem:There are no cycles in the routing tables. --- Think of the routing entry [ position(D), a] as a path with end point D. Then we are always following a path whose end point is closer to the destination then the end point of the previous path.

  41. A Geometrical View Routing Table for Station n: Vornoi View: (x,y) position Neighbor a Position of n - Position of neighbor a n b a Position of neighbor b b (12,4) a (12,4) • Route discovery is initiated if packet destination falls within • the cell containing station n • Each route discovery causes the cell with station n to get split

  42. Routing Table Size • How many “splits” before station n is alone in its cell ? • Each split reduces the cells area ~ 1/2 • The cell’s area when station n is alone in the cell ~ 1/N • where N is the number of stations in a unit area • => log(N) splits before station n is alone in its cell • Each split causes a route discovery • Each route discovery causes L entries to be added to the routing • tables where L is the average route discovery path length • => O( L log(N) ) entries in routing table of each station

  43. Outline • Projections of wireless growth • Cellular Networks • Wireless LANs and Bluetooth • WAP • Ad Hoc wireless networks

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