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Overview of Wireless Networks
Anuj Puri
Outline
Projections of wireless growthCellular NetworksWireless LANs and BluetoothWAPAd Hoc wireless networks
0
200
400
600
800
1,000
1,200
1998 1999 2000 2001 2002 2003
PCs
TV households
Mobile phone subscribers
Millions of subscribers worldwide
HUGE EXPECTATIONS AND INVESTMENT IN M-DATA
46
17
98
35
U.K. licenses
German licenses
French licenses
UMTS license fee to date (not ex-haustive)
European UMTS spectrum auctions
$ Billions
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
SUCCESS OF I-MODE IN JAPAN
Feb 22,1999 start
Aug 8
Nov 18
Dec 23
May 31,2000
i-Mode has already exceeded 12 million subs
Number of i-mode subscribersThousands
Outline
Projections of wireless growthCellular NetworksWireless LANs and BluetoothWAPAd Hoc wireless networks
Cellular Networks
Mobile phones (internet access) Cellular concept Frequency reuse Handoffs
Organization of Cellular Networks
BS(base station)
MSC (mobile switching center)
HLR (home locationregister)
VLR (visitorlocation register)
BS – modulation, antennaMSC – switchingHLR – information (location) about “home” usersVLR – 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 phoneA call comes in for (510) 643 – 1111. Then (510) MSC queries its HLR, and directs the call to the (703) MSCThe (703) MSC forwards the call to the mobile
Handoff
MSC
HLR
VLR
BS B
BS A
• 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
2G
* FootnoteSource: Sources
2.5G 3G 3+G 4G
PDC
GSM
TDMA (IS-136)
CDMA
(IS-95A/B)
WCDMA HSPDA
OFDM
Software radio
Array antennas
GPRS
EDGE
CdmaOne1XRTT
1XEVDO/HDR1 xtreme
cdma2000MC-3X
3G Networks
BS B
BS A
SGSN
SGSN
GGSN
Access NetworkPhysical 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 FAWhen mobile moves to a new location, it informs its HA of the new FA
Outline
Projections of cellular growthCellular NetworksWireless LANs and BluetoothWAPAd Hoc wireless networks
Wireless LANs and Bluetooth
For indoor use or operation over small areasOperates in ISM (Industrial Scientific and Medical) BandSpread Spectrum techniques
Main Components of 802.11
Roaming
Medium AccessControl
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 otherB and C can hear each otherA 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 dataCTS: also contains the length of data
Everyone hearing RTS stays quiet for CTSEveryone 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 levelFragmentation and Reassembly
Basic Scheme
RTS
CTS
Data
ACK
NAV (RTS)NAV (CTS)
Defer Access
Back-off Window
Some Terminology
AccessPoint
AccessPoint
Basic Service Set (BSS)
Extended Service Set (ESS)
DistributionSystem
Bluetooth
Master-slave architectureFrequency hopping systemSystem design for cheap production
Outline
Projections of cellular growthCellular NetworksWireless LANs and BluetoothWAPAd 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 Gateway
Internet
Web Server
WAP HTTP/TCP
WAP Stack
Bearer ServicesSMS, CSD
WDP (DatagramProtocol)
WTP (TransactionProtocol)
WSP (SessionProtocol)
WML, etc
IP
TCP/UDP
HTTP
HTML
Gateways/Proxies for Wireless Devices ?
Gateway Internet
Web Server
2nd Generation: Low speed data, small displays WAP3rd Generation: Higher speed, IP address for each station Proxy/ Gateway ?
Outline
Projections of wireless growthCellular NetworksWireless LANs and BluetoothWAPAd Hoc wireless networks
Ad Hoc Wireless Networks
No base stations or infrastructure requiredMulti-hop wireless networks Each node can talk with a neighbor
Applications Sensor networks Intelligent control applications (i.e, IVHS)
Ad Hoc Wireless Networks
MAC schemesAddressingRouting
Geographical Routing Algorithm
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
Geographicalnetwork
A Simple Routing Algorithm
Routing Decision: Route to the neighbor which is nearest to the packet destination
Source
Destination
Problem with Simple Routing
Source
Destination
• Simple routing doesn’t always work• The Geographical routing algorithm is an extension of the simple routing algorithm.
Wall
Routing Tables
Routing Table for Station n:
(x,y) position Neighbor
a(12,4)
b
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
Routing Tables:• Routing tables contain some additional entries beside neighbors
Route Discovery
Packet gets “stuck” when a node does not have a neighbor to which it can forward the packetWhen a packet is stuck, a Route Discovery is started to destination DA path p = s(0) s(1)...s(k) is found to DEntry [ position(D), s(i+1) ] is added to the routing table of s(i)
ExamplePos(A) = (1,1)Pos(B) = (2,2)Pos(C) = (3,1)
Links:A ---- BB ---- C
A
B
C
Pos(A) ---
Pos(B) B
Pos(B) ---
Pos(A) APos(C) C
Pos(C) ---
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(C)
Pos(C)
Pos(C)
Route Discovery
Pos(A) = (1,1)Pos(B) = (2,2)Pos(C) = (3,1)Pos(D) = (2.5,0)Links:A ---- BB ---- CC ---- D
B
C
• 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
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) B
Pos(D) C
Pos(D)
Pos(D)
Pos(D)
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:
(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)
• 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 routingtables where L is the average route discovery path length=> O( L log(N) ) entries in routing table of each station
Outline
Projections of wireless growthCellular NetworksWireless LANs and BluetoothWAPAd Hoc wireless networks