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 • Mobile phone subscribers • TV households • PCs • U.K. licenses • German licenses • French licenses • UMTS license fee to date (not ex-haustive)

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

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

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

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

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

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

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

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

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

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

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

Main Components of 802.11 Roaming Medium Access Control Physical Layer

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

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

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)

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

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

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

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

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

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

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

WAP Architecture WAP HTTP/TCP WAP Gateway Internet Web Server

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

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 ?

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)

Ad Hoc Wireless Networks • MAC schemes • Addressing • Routing

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

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

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.

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)

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)

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)

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

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.

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

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

Overview of Wireless Networks