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Overview of Wireless Networks Anuj Puri


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Overview of Wireless Networks Anuj Puri

  1. 1. Overview of Wireless Networks Anuj Puri
  2. 2. Outline <ul><li>Projections of wireless growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>
  3. 3. HUGE EXPECTATIONS AND INVESTMENT IN M-DATA <ul><li>PCs </li></ul><ul><li>TV households </li></ul><ul><li>Mobile phone subscribers </li></ul><ul><li>Millions of subscribers worldwide </li></ul><ul><li>U.K. licenses </li></ul><ul><li>German licenses </li></ul><ul><li>French licenses </li></ul><ul><li>UMTS license fee to date (not ex-haustive) </li></ul><ul><li>European UMTS spectrum auctions </li></ul><ul><li>$ Billions </li></ul>
  4. 4. SUCCESS OF I-MODE IN JAPAN <ul><li>Feb 22, 1999 start </li></ul><ul><li>Aug 8 </li></ul><ul><li>Nov 18 </li></ul><ul><li>Dec 23 </li></ul><ul><li>May 31, </li></ul><ul><li>2000 </li></ul><ul><li>i-Mode has already exceeded 12 million subs </li></ul><ul><li>Number of i-mode subscribers </li></ul><ul><li>Thousands </li></ul>
  5. 5. Outline <ul><li>Projections of wireless growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>
  6. 6. Cellular Networks <ul><li>Mobile phones (internet access) </li></ul><ul><li>Cellular concept </li></ul><ul><ul><li>Frequency reuse </li></ul></ul><ul><ul><li>Handoffs </li></ul></ul>
  7. 7. Organization of Cellular Networks BS – modulation, antenna MSC – switching HLR – information (location) about “home” users VLR – information about visiting users BS (base station) MSC (mobile switching center) HLR (home location register) VLR (visitor location register)
  8. 8. How does a call get to the mobile ? <ul><li>Suppose (510) 643 - 1111 is roaming in the (703) area code </li></ul><ul><li>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 </li></ul><ul><li>A call comes in for (510) 643 – 1111. Then (510) MSC queries its HLR, and directs the call to the (703) MSC </li></ul><ul><li>The (703) MSC forwards the call to the mobile </li></ul>
  9. 9. Handoff MSC HLR VLR <ul><li>Mobile is associated with BS A </li></ul><ul><li>It continuously monitors the signal strength from BS A, </li></ul><ul><li>and BS B </li></ul><ul><li>When the signal strength from BS B becomes stronger, </li></ul><ul><li>it associates with BS B </li></ul>BS B BS A
  10. 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. 11. MULTIPLE MIGRATION PATHS ARE AVAILABLE <ul><li>2G </li></ul>* Footnote Source: Sources <ul><li>2.5G </li></ul><ul><li>3G </li></ul><ul><li>3+G </li></ul><ul><li>4G </li></ul><ul><li>PDC </li></ul><ul><li>GSM </li></ul><ul><li>TDMA </li></ul><ul><li>(IS-136) </li></ul><ul><li>CDMA (IS-95A/B) </li></ul>WCDMA <ul><li>HSPDA </li></ul><ul><li>OFDM </li></ul><ul><li>Software radio </li></ul><ul><li>Array antennas </li></ul><ul><li>GPRS </li></ul><ul><li>EDGE </li></ul><ul><li>CdmaOne </li></ul><ul><li>1XRTT </li></ul><ul><li>1XEVDO/HDR </li></ul><ul><li>1 xtreme </li></ul><ul><li>cdma2000 </li></ul><ul><li>MC-3X </li></ul>
  12. 12. 3G Networks BS B BS A SGSN SGSN GGSN Access Network Physical layer/ MAC IP based Core Network Routing/network handoff
  13. 13. Mobile IP <ul><li>Home Agent (HA) – keeps track of where the mobile is (similar to GGSN) </li></ul><ul><li>Foreign Agent (FA) – delivers packets to the mobile in the foreign network (similar to SGSN) </li></ul><ul><li>All packets for mobile arrive at HA which “tunnels” them to mobile’s FA </li></ul><ul><li>When mobile moves to a new location, it informs its HA of the new FA </li></ul>
  14. 14. Outline <ul><li>Projections of cellular growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>
  15. 15. Wireless LANs and Bluetooth <ul><li>For indoor use or operation over small areas </li></ul><ul><li>Operates in ISM (Industrial Scientific and Medical) Band </li></ul><ul><li>Spread Spectrum techniques </li></ul>
  16. 16. Main Components of 802.11 Roaming Medium Access Control Physical Layer
  17. 17. Physical Layer <ul><li>Operate in unlicensed bands </li></ul><ul><ul><li>In U.S., 900 MHz, 2.4 GHz, 5.7GHz </li></ul></ul><ul><ul><li>Various restrictions on use </li></ul></ul><ul><li>Spread Spectrum techniques </li></ul><ul><ul><li>Direct Sequence Spread Spectrum </li></ul></ul><ul><ul><li>Frequency Hopping Spread Spectrum </li></ul></ul>
  18. 18. Medium Access Layer <ul><li>Why not use Ethernet protocol ? </li></ul><ul><ul><li>Sender cannot detect collision </li></ul></ul><ul><ul><ul><li>senders power overwhelms other transmitters </li></ul></ul></ul><ul><ul><ul><li>carrier sense does not necessarily mean collision </li></ul></ul></ul><ul><ul><li>Receiver has a better idea of whether a collision is happening </li></ul></ul><ul><ul><li>Hidden Terminal / Exposed Terminal Problem </li></ul></ul>
  19. 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. 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. 21. 802.11 MAC <ul><li>CSMA/CA (Carrier Sense / Collision Avoidance) </li></ul><ul><ul><li>Carrier Sense (check to see if someone is transmitting) </li></ul></ul><ul><ul><li>Collision Avoidance (RTS-CTS-Ack) </li></ul></ul><ul><li>Acknowledgments at link level </li></ul><ul><li>Fragmentation and Reassembly </li></ul>
  22. 22. Basic Scheme RTS CTS Data ACK NAV (RTS) NAV (CTS) Defer Access Back-off Window
  23. 23. Some Terminology Access Point Access Point Basic Service Set (BSS) Extended Service Set (ESS) Distribution System
  24. 24. Bluetooth <ul><li>Master-slave architecture </li></ul><ul><li>Frequency hopping system </li></ul><ul><li>System design for cheap production </li></ul>
  25. 25. Outline <ul><li>Projections of cellular growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>
  26. 26. WAP (or the web for small wireless devices) <ul><li>Why not use wired web infrastructure (html, http, tcp) ? </li></ul><ul><ul><li>HTML too feature rich for small devices </li></ul></ul><ul><ul><li>TCP may have too much overhead for low bandwidth wireless links </li></ul></ul><ul><li>WAP (Wireless Application Protocol) </li></ul><ul><ul><li>An optimized stack for wireless applications </li></ul></ul><ul><ul><li>Mobile talks with the WAP gateway </li></ul></ul><ul><ul><li>WAP gateway talks with the web server on the internet </li></ul></ul>
  27. 27. WAP Architecture WAP Gateway Internet Web Server WAP HTTP/TCP
  28. 28. WAP Stack Bearer Services SMS, CSD WDP (Datagram Protocol) WTP (Transaction Protocol) WSP (Session Protocol) WML, etc IP TCP/UDP HTTP HTML
  29. 29. Gateways/Proxies for Wireless Devices ? 2 nd Generation: Low speed data, small displays  WAP 3 rd Generation: Higher speed, IP address for each station  Proxy/ Gateway ? Gateway Internet Web Server
  30. 30. Outline <ul><li>Projections of wireless growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>
  31. 31. Ad Hoc Wireless Networks <ul><li>No base stations or infrastructure required </li></ul><ul><li>Multi-hop wireless networks </li></ul><ul><ul><li>Each node can talk with a neighbor </li></ul></ul><ul><li>Applications </li></ul><ul><ul><li>Sensor networks </li></ul></ul><ul><ul><li>Intelligent control applications (i.e, IVHS) </li></ul></ul>
  32. 32. Ad Hoc Wireless Networks <ul><li>MAC schemes </li></ul><ul><li>Addressing </li></ul><ul><li>Routing </li></ul>
  33. 33. Geographical Routing Algorithm <ul><li>Assumptions: </li></ul><ul><li>Each node knows its own position and its neighbors’ position </li></ul><ul><li>Nodes don’t know the global topology </li></ul><ul><li>Destination address is a geographical position to which the packet is to be delivered </li></ul>Geographical network
  34. 34. A Simple Routing Algorithm Routing Decision: Route to the neighbor which is nearest to the packet destination Source Destination
  35. 35. Problem with Simple Routing Source Destination <ul><li>Simple routing doesn’t always work </li></ul><ul><li>The Geographical routing algorithm is an extension of the </li></ul><ul><li>simple routing algorithm. </li></ul>Wall
  36. 36. Routing Tables Routing Table for Station n: (x,y) position Neighbor a (12,4) b Position of n - Position of neighbor a a <ul><li>Routing Algorithm: </li></ul><ul><li>Packet arrives for position p </li></ul><ul><li>at node n </li></ul><ul><li>Node n finds the position to </li></ul><ul><li>which p is closest and forwards </li></ul><ul><li>to the corresponding neighbor </li></ul>Position of neighbor b <ul><li>Routing Tables: </li></ul><ul><li>Routing tables contain some </li></ul><ul><li>additional entries beside neighbors </li></ul>
  37. 37. Route Discovery <ul><li>Packet gets “stuck” when a node does not have a neighbor to which it can forward the packet </li></ul><ul><li>When a packet is stuck, a Route Discovery is started to destination D </li></ul><ul><li>A path p = s(0) s(1)...s(k) is found to D </li></ul><ul><li>Entry [ position(D), s(i+1) ] is added to the routing table of s(i) </li></ul>
  38. 38. Example Pos(A) = (1,1) Pos(B) = (2,2) Pos(C) = (3,1) Links: A ---- B B ---- C A B C Pos(A) --- Pos(B) B Pos(B) --- Pos(A) A Pos(C) C Pos(C) --- Pos(B) B <ul><li>A gets a packet for Pos(C) </li></ul><ul><li>A forwards it to B because pos(B) is closer to pos(C) </li></ul><ul><li>B forwards it to C because pos(C) is closer to pos(C) </li></ul>Pos(C) Pos(C) Pos(C)
  39. 39. Route Discovery 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 C <ul><li>A gets a packet for Pos(D) </li></ul><ul><li>Packet gets stuck at A because Pos(A) is closest to Pos(D) </li></ul><ul><li>Initiate route discovery for D from A </li></ul><ul><li>Update the routing tables and forward the packet </li></ul>Pos(D) Pos(D) A D Pos(A) --- Pos(B) B Pos(D) --- Pos(C) C Pos(B) --- Pos(A) A Pos(C) C Pos(C) --- Pos(B) B Pos(D) D Pos(D) Pos(D) Pos(D) Pos(D) B Pos(D) C
  40. 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. 41. A Geometrical View Routing Table for Station n: (x,y) position Neighbor a (12,4) b Position of n - Position of neighbor a a Position of neighbor b Vornoi View : n a b (12,4) <ul><li>Route discovery is initiated if packet destination falls within </li></ul><ul><li>the cell containing station n </li></ul><ul><li>Each route discovery causes the cell with station n to get split </li></ul>
  42. 42. Routing Table Size <ul><li>How many “splits” before station n is alone in its cell ? </li></ul><ul><ul><li>Each split reduces the cells area ~ 1/2 </li></ul></ul><ul><ul><li>The cell’s area when station n is alone in the cell ~ 1/N </li></ul></ul><ul><ul><li>where N is the number of stations in a unit area </li></ul></ul><ul><ul><li>=> log(N) splits before station n is alone in its cell </li></ul></ul><ul><li>Each split causes a route discovery </li></ul><ul><li>Each route discovery causes L entries to be added to the routing </li></ul><ul><li>tables where L is the average route discovery path length </li></ul><ul><li>=> O( L log(N) ) entries in routing table of each station </li></ul>
  43. 43. Outline <ul><li>Projections of wireless growth </li></ul><ul><li>Cellular Networks </li></ul><ul><li>Wireless LANs and Bluetooth </li></ul><ul><li>WAP </li></ul><ul><li>Ad Hoc wireless networks </li></ul>