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